XIPLink User Guide XIP OS

XipOSUser Manual

XipOS: User ManualRelease 4.0.2Copyright 2013 XipLink Inc

All rights reserved. Reproduction in whole or in part without permission is prohibited. Information contained herein is subject to change withoutnotice. The specifications and information regarding the products in this document are subject to change without notice. All statements, information,and recommendations in this document are believed to be accurate, but are presented without warranty of any kind, express, or implied. Users musttake full responsibility for their application of any products. Trademarks, brand names and products mentioned in this document are the propertyof their respective owners. All such references are used strictly in an editorial fashion with no intent to convey any affiliation with the name orthe product's rightful owner.

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Table of Contents1. XipLink Optimization Technology Overview ....................................................................... 1

1.1. Introduction ......................................................................................................... 11.2. Background ......................................................................................................... 21.3. The XipLink Advantage ........................................................................................ 2

1.3.1. Protocol Acceleration .................................................................................. 31.3.2. Advanced Compression ............................................................................... 31.3.3. Internet Optimization .................................................................................. 31.3.4. Security .................................................................................................... 41.3.5. Quality of Service ...................................................................................... 41.3.6. XipOS ..................................................................................................... 4

1.4. Supported Capabilities ........................................................................................... 41.4.1. TCP Acceleration Techniques ...................................................................... 41.4.2. UDP Acceleration Techniques ...................................................................... 41.4.3. Compression and Application Acceleration ..................................................... 51.4.4. Tunnelling Options ..................................................................................... 51.4.5. Network Appliance Benefits ........................................................................ 51.4.6. Standards Support and Interoperability ........................................................... 51.4.7. RFC and TCP Enhancements Support ............................................................ 6

1.5. Document Overview ............................................................................................. 61.5.1. Conventions used in this Manual .................................................................. 7

2. Quick Start - XA Series ................................................................................................... 82.1. Unpacking and Box Contents ................................................................................. 82.2. Placing the Optimizer in the Network ...................................................................... 8

2.2.1. Physical Connections .................................................................................. 92.3. Accessing the XipOS Web User Interface ............................................................... 102.4. Login ................................................................................................................ 102.5. XipLink Setup Wizard ......................................................................................... 11

2.5.1. Welcome ................................................................................................ 112.5.2. Select Deployment Options ........................................................................ 122.5.3. Configure Network Interfaces ..................................................................... 132.5.4. Configure DNS ........................................................................................ 152.5.5. Configure Networks .................................................................................. 152.5.6. Set Password ........................................................................................... 172.5.7. Apply Changes To Device Configuration ...................................................... 17

3. Understanding XipLink Optimization ................................................................................ 183.1. Dynamic Transparent Negotiation of Optimization Capabilities ................................... 183.2. SCPS Protocol Acceleration .................................................................................. 193.3. XipLink Transport Control (XTC) Modes ............................................................... 20

3.3.1. XTC - Fixed Rate Control Mode ................................................................. 203.3.2. XTC - Dynamic Rate Control Mode ............................................................ 213.3.3. XTC - Programmable Fixed Rate Control Mode ............................................. 223.3.4. XTC - Enhanced TCP Mode ...................................................................... 22

3.4. Additional TCP Protocol Acceleration Techniques .................................................... 223.4.1. TCP Connection Fast Start ......................................................................... 223.4.2. Acknowledgement Frequency Reduction (AFR) ............................................. 233.4.3. Selective Negative Acknowledgments .......................................................... 233.4.4. Quality of Service .................................................................................... 243.4.5. Streaming Data Compression ...................................................................... 263.4.6. XipOS Tunnelling .................................................................................... 28

3.5. XipLink Hub Optimizations .................................................................................. 283.5.1. XiPix Image Compression ......................................................................... 293.5.2. HTTP Compression .................................................................................. 29

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3.6. XipLink Real-Time (XRT) ................................................................................... 293.7. Byte Caching ..................................................................................................... 313.8. Packet Compression ............................................................................................ 31

3.8.1. Advanced Cellular Compression ................................................................. 313.9. Link Balancing and Bonding ................................................................................ 323.10. Web Cache Communication Protocol .................................................................... 32

3.10.1. WCCP Deployments ............................................................................... 333.10.2. WCCP Configuration Concepts ................................................................. 34

3.11. XipLink Wireless Optimizer Internals ................................................................... 403.11.1. Dynamic Socket Buffers .......................................................................... 403.11.2. Burst Connection Handling ....................................................................... 403.11.3. Installation Flexibility .............................................................................. 413.11.4. Management and Monitoring .................................................................... 41

4. The XipOS Web Interface .............................................................................................. 424.1. Dashboard ......................................................................................................... 42

4.1.1. Device Name ........................................................................................... 424.1.2. Interface Status ........................................................................................ 424.1.3. Service Status .......................................................................................... 424.1.4. Device Status .......................................................................................... 434.1.5. Sampling Rate ......................................................................................... 43

4.2. Main Menu ........................................................................................................ 434.3. Applying Changes .............................................................................................. 444.4. Networking Setup ............................................................................................... 45

4.4.1. Mode ..................................................................................................... 454.4.2. Interfaces ................................................................................................ 474.4.3. DNS ...................................................................................................... 484.4.4. Routes .................................................................................................... 504.4.5. RIP ........................................................................................................ 514.4.6. OSPF ..................................................................................................... 524.4.7. BGP ....................................................................................................... 534.4.8. DHCP .................................................................................................... 544.4.9. SNMP .................................................................................................... 554.4.10. WCCP .................................................................................................. 574.4.11. Redundancy ........................................................................................... 59

4.5. Optimization ...................................................................................................... 624.5.1. Optimization ............................................................................................ 624.5.2. Networks ................................................................................................ 644.5.3. Service Assignment .................................................................................. 704.5.4. Traffic Assignment ................................................................................... 734.5.5. Lightweight Tunnels ................................................................................. 764.5.6. Link Balancing ........................................................................................ 794.5.7. Web Cache ............................................................................................. 80

4.6. System .............................................................................................................. 834.6.1. Support & Docs ....................................................................................... 834.6.2. Logs ...................................................................................................... 834.6.3. Stats ....................................................................................................... 844.6.4. Users ..................................................................................................... 854.6.5. Time ...................................................................................................... 864.6.6. Backup ................................................................................................... 874.6.7. Upgrade .................................................................................................. 884.6.8. Reboot ................................................................................................... 914.6.9. Files ....................................................................................................... 924.6.10. Diagnostics ............................................................................................ 944.6.11. Debugging ............................................................................................. 95

XipOS

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5. Redundancy Deployment Options .................................................................................... 965.1. Router mode Redundancy using CARP .................................................................. 965.2. Bridge mode with STP failover ............................................................................. 965.3. Bridge mode with fail-to-wire ............................................................................... 97

6. Monitoring and Statistics ................................................................................................ 986.1. Optimizer Montoring Tool .................................................................................... 98

6.1.1. Graph Controls ........................................................................................ 996.2. Monitored Data Sets ............................................................................................ 99

7. XipOS Command Line Interface .................................................................................... 1017.1. Introduction ..................................................................................................... 1017.2. Factory Reset ................................................................................................... 102

7.2.1. Accessing the Factory Reset Menu ............................................................. 1027.2.2. Factory Reset Menu ................................................................................ 102

8. Advanced Upgrade Procedures ....................................................................................... 1038.1. Manual Upgrade via CLI .................................................................................... 1038.2. Replacing the Compact Flash Card ....................................................................... 103

8.2.1. Equipment Required ................................................................................ 1048.2.2. Procedure .............................................................................................. 104

9. Troubleshooting and Diagnostic Tools ............................................................................. 1079.1. Netconf Errors .................................................................................................. 1079.2. System Logs .................................................................................................... 108

9.2.1. The System Log File ............................................................................... 1089.2.2. The Netconf Log File .............................................................................. 108

9.3. Diagnostic Tools ............................................................................................... 1099.3.1. netstat ................................................................................................... 1099.3.2. Quality of Service Queue Control .............................................................. 111

10. Support .................................................................................................................... 11310.1. Support Resources ........................................................................................... 11310.2. Return Procedures ........................................................................................... 11410.3. Frequently asked Questions ............................................................................... 115

11. Appendixes .............................................................................................................. 11811.1. XipLink Product Matrix .................................................................................... 118

Glossary of Terms ........................................................................................................... 120

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List of Figures1.1. XipLink Interoperability between devices ......................................................................... 11.2. XipOS ........................................................................................................................ 22.1. Placement of the Optimizer ............................................................................................ 82.2. XA-500 ...................................................................................................................... 92.3. XA-2000 ..................................................................................................................... 92.4. XA-4000 | XA-10K ..................................................................................................... 92.5. XA-30K ...................................................................................................................... 93.1. Dynamically negotiated optimization .............................................................................. 183.2. Unoptimized connections using standard TCP .................................................................. 193.3. XTC Fixed Rate Control ........................................................................................... 203.4. XTC - Dynamic Rate Control Mode .............................................................................. 213.5. XTC - Programmable Fixed Rate Control Mode ............................................................... 223.6. TCP Connection Fast Start ........................................................................................... 233.7. AFR and Selective Negative Acknowledgments ............................................................... 243.8. QoS Re-Prioritizes Traffic ............................................................................................ 253.9. Streaming Data Compression ........................................................................................ 273.10. Compression Samples ................................................................................................ 283.11. XRT Packet Coalescing .............................................................................................. 303.12. Basic Single Interface Mode WCCP Deployment ............................................................ 333.13. Basic Router Mode WCCP Deployment ........................................................................ 333.14. WCCP Hub Deployment ............................................................................................ 343.15. WCCP Service Groups ............................................................................................... 353.16. Bridge at remote - Router at hub ................................................................................. 414.1. Router Mode Redundancy Setup ................................................................................... 605.1. Router Mode Redundancy Setup ................................................................................... 965.2. Bridge Mode Redundancy Setup ................................................................................... 975.3. Fail-to-wire Diagram ................................................................................................... 97

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List of Tables1.1. SCPS-TP Capabilities .................................................................................................... 51.2. HTTP RFC's ................................................................................................................ 52.1. Factory default IP addresses ......................................................................................... 103.1. XRT: Benefit of Coalescing Multiple Streams .................................................................. 303.2. XRT: Effect of Different Capture Window Sizes .............................................................. 304.1. Differences Between Router, Bridge and Single Interface Modes ......................................... 464.2. XipOS SNMP Traps .................................................................................................... 5611.1. XipLink XA Product Matrix ...................................................................................... 118

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List of Examples4.1. Multi-Link / Multi-Site Network Example ....................................................................... 669.1. netstat Active Connections .......................................................................................... 1109.2. netstat -e DSB Output ................................................................................................ 1109.3. Sample netstat -s -p scps Output .................................................................................. 1119.4. Using pfctl to View QoS Queue Status ......................................................................... 111

1Chapter 1. XipLink OptimizationTechnology Overview1.1. Introduction

XipLink delivers wireless optimization technology in many flexible ways:

The XE-Series provide portable optimization software for any BSD, Linux or Windows based devices. The XE-104 is a preloaded single board computer optimizer. The XA-Series are scalable appliances that deliver optimization from 2 to 155 Mbps.

Wireless optimization functions described in this overview operate transparently between userscommunicating across any two wireless IP networks that have optimization installed. For example, userson an aircraft with XE-Series software embedded in the airborne satellite modem will have their traffictransparently optimized when the connection request encounters an XA-Series appliance installed at theservice provider's hub site. Embedded XipLink software interoperates with any other XipOS enableddevice.

Figure 1.1. XipLink Interoperability between devices

The challenges of wireless optimization for satellite and terrestrial communication links are significantlydifferent from traditional WAN optimization controllers or application accelerators:

Wireless is a medium that experiences much higher latency and loss. The price per bit on wireless links, especially over satellites, is much higher. The ROI on improved use of the capacity is short, often measured in months.

XipLink OptimizationTechnology Overview

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1.2. BackgroundXipLink Optimization Software algorithms originate with aerospace research originally intended toincrease the communications throughput between spacecraft and the Earth. It was quickly recognized thatthese same techniques work equally well when optimizing the complete end-to-end wireless link fromground station to ground station. Researchers were also pleasantly surprised by the fact that the techniqueshad virtually no negative effects on traditional TCP-based applications.

This pioneering work resulted in standards from NASA and other space agencies collectivelycalled the Space Communications Protocol Specification (SCPS) and, subsequently a standard namedInteroperable Performance Enhancing Proxy (I-PEP). The SCPS (pronounced skips) specificationcombines recommendations for the use of several standard IETF TCP enhancements as well as methodsfor the dynamic and transparent negotiation of options like special TCP acknowledgement schemesand data compression. The I-PEP standard, which builds on SCPS, is designed specifically for satellitecommunication profiles but also enables the negotiation of innovative vendor proprietary algorithms. Thiswas a primary intention of the standard, and remains a key to its continued use and recent compliancemandates by the U.S. Department of Defense.

While the IETF has introduced some standards for TCP improvement over the years, the SCPS basedprotocol, along with specialized wireless optimization algorithms originally designed by vendors forspace communications, continue to deliver the most advanced wireless optimization capabilities availabletoday. These same algorithms continue to find greater and greater use in commercial and military VSATapplications and function equally well over space segments and terrestrial wireless links.

XipLink Mission StatementOur Mission is to leverage XipLink's proven software in our partner`s network solutions,enabling operators and users to optimize available wireless bandwidth for maximumdata throughput at the lowest capital cost.

1.3. The XipLink AdvantageAt the heart of the XipLink optimizers is our proprietary optimization system, the XipOS. This systemencapsulates various components, each component playing a vital role in ensuring that you can achieveoptimal data performance through your current wireless infrastructure, thereby ensuring a reduction inoperational costs and an increase in end-user satisfaction. That's the XipLink Advantage!

Figure 1.2. XipOS

Protocol Accelerat ionAdvanced Com pressionInternet Opt im izat ionSecurityQuality of Service (QoS)XipOS


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1.3.1. Protocol AccelerationThe goal of protocol acceleration is to fill the available upstream and downstream bandwidth pipe. StandardTCP was not originally intended to operate over wireless connections. The following factors severelyundermine the performance of standard TCP.

Long propagation Delay. Long-delay channels require larger windows than what standard TCPoffers, and a more accurate Round Trip Time (RTT) evaluation. In addition, cumulative ACKs anddelayed ACKs are not well suited for long-delay environments. Finally, Slow Start and CongestionAvoidance prove to be rather inefficient in the presence of long propagation delays.

Connection Asymmetry. Wireless communications are very often used to provide asymmetricbandwidth services that are intended for large-scale information consumption. Typical internetapplications (e.g. FTP, WEB) require relatively low bandwidth from the user to the information provider(e.g. FTP or HTTP server) and relatively high bandwidth towards the user. This effectively means thedownstream throughput (towards the user) is controlled by the rate of upstream ACK's (toward theserver). Upstream congestion affects downstream throughput, even though there is plenty of downstreamcapacity available.

High Error Rate. Wireless communications can be influenced by various external factors such asradio interference and weather. Standard TCP interprets packet loss as loss due to congestion and thusreduces the transmission rate, degrading throughput even further.

SCPS standards were implemented to add an advanced layer of transmission control for TCPcommunication thereby addressing the inherent problem with standard TCP flow control to ensuremaximum throughput

XipOS provides further optimization through XipLink's proprietary transmission control extensions(XTC), while still conforming to the SCPS standards.

More information on XTC can be found in the chapter on XipOS Functionality.

1.3.2. Advanced CompressionXipOS uses streaming data compression to effectively compress the TCP payload. This has a two-foldadvantage over per-packet compression. Primarily there are more compressible patterns available, creatinga higher compression ratio. Secondly it efficiently uses the TCP window and thus reduces the number ofpackets transmitted. Please see the section on Streaming Data Compression for an in-depth discussion

1.3.3. Internet OptimizationThere are three methods by which internet web traffic is optimized

Domain Name Caching. Internet traffic is based on IP addresses, however most web page URL's usedomain names instead of IP addresses. Internet applications like web browsers need to resolve domainnames into IP addresses in order to communicate with servers. On high latency links the time requiredto resolve domain names causes further delays. The XipOS domain name cache saves the results ofdomain name resolutions, so that subsequent requests for a cached name can be spared a round-trip time.

Web Proxy (optional). The web proxy option is currently only available on the XipLink XA-4000Cand XA-500C series optimizers. These models transparently cache all internet web data for a period oftime. Subsequent requests for the same data are served directly out of the cache.

XHO (XipLink Hub Optimization). This is a Hub Side only deployment which supportshttp compression and image transcoding through lossy compression. There is no requirement for


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additional remote units although deploying a SCPS enable remote will provide further acceleration andoptimization benefits.

1.3.4. SecurityXipOS includes a basic firewall to protect your network from possible attacks, allowing you to specifyport and/or address ranges that you want to allow or block. The network behind a XipOS device can alsobe protected via NAT.

1.3.5. Quality of ServiceQuality of Service (QoS) delivers the ability to prioritise certain traffic types, such as VoIP and streamingmedia, above others like FTP transfers. Different locations can use dedicated and unique QoS queuesto ensure that each location receives a guaranteed minimum committed throughput while also takingadvantage of any available unused throughput.

XipLink's QoS implementation uses Hierarchical Fair Service Curves to prioritize, guarantee and controltraffic based on user-defined policies.

1.3.6. XipOSXipOS encapsulates all the above components and offers multiple forms of management and monitoringthrough a secure web interface, SSH and SNMP.1

XipOS is the foundation of all XipLink products, ensuring transparency and interoperability betweenXipLink devices or with any other SCPS-compliant I-PEP device.

1.4. Supported Capabilities1.4.1. TCP Acceleration Techniques

XTC Bandwidth Rate Control Bandwidth Rate Control / Non Use of Congestion Control. Rate can be modified in real time and can

account for non-TCP traffic in the path Quality of Service via Fair Weight Queuing Algorithm SACK support Selective Negative Acknowledgments (SNACK) Fast Start (T/TCP) Acknowledgement Frequency Reduction Maximize throughput and fairness while minimizing latency Packet overhead configuration (for IP-in-IP protocols) Firewalling and NAT capabilities Inflight data volume control for TDMA Networks DSCP reading/marking Black Hole Detection Automatic traffic bypass

1.4.2. UDP Acceleration Techniques XRT (XipLink RealTime): UDP Packet Coalescing; Robust Header Compression (RoHC)

1 Cryptographic security features are only available on "Crypto" product models.


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1.4.3. Compression and Application Acceleration TCP streaming data compression (only with bracketed deployments) XiPix HTTP image transcoding (Optional) HTTP compression (Optional)

1.4.4. Tunnelling Options Lightweight IP Tunnelling (no licence requirements) Advanced Cellular Compression (ACC) (optional licence required)

1.4.5. Network Appliance Benefits Fail-to-wire support with certain hardware platforms Bridge Mode redundancy via STP Router Mode redundancy via CARP Configuration download/upload Graphical redundancy configuration SNMP support with a defined MIB and trap generation Support for routing protocols such as RIP, OSPF and BGP Support for load-balancing using WCCP hash assignment, with L2 or GRE forwarding Easy to use web interface

1.4.6. Standards Support and InteroperabilitySCPS-TP is internationally recognized as ISO recommendation 15893:2000 and Consultative Committeeon Space Data Systems CCSDS 714.0-B-2 and MIL-STD-2045-44000 among others. It has beenrecommended as the standard technique for performance enhancement by the U.S. Department of Defencefor MILSATCOM IP communications.

XipLink has been demonstrated to be Interoperable with the SCPS-TP standard.

Table 1.1. SCPS-TP CapabilitiesSCPS-TP Capabilities Enhanced TCP (with latest recommendations) Rate Control / Non Use of Congestion Control. Rate can be modified in real time and can account for

non-TCP traffic in the path. Quality of Service also supported via Weight Fair Queuing Algorithm. Selective Negative Acknowledgments Short SNACK (long SNACK not recommended) RFC 1644: T/TCP (also known as Fast Start) Acknowledgement Frequency Reduction Default Source of Data Loss (DSDL). However rarely supported by link layer.

Essentially all SCPS-TP features are supported except for Best Effort Transport Service (BETS) whichrequires specialized applications. An API is also provided to control all of these capabilities, either througha system or socket interface. Use of enhancement can be selective.

Table 1.2. HTTP RFC'sRFC TitleRFC 1945 Hypertext Transfer Protocol -- HTTP/1.0


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RFC TitleRFC 2616 Hypertext Transfer Protocol -- HTTP/1.1

XipLinks HTTP Acceleration and data compression are proprietary algorithms. Refer to the WhitepaperInternet Over Satellite Optimization with XipLink for further information.

1.4.7. RFC and TCP Enhancements SupportRFC TitleRFC 793 Transmission Control ProtocolRFC 1122 Requirements for Internet Hosts - Communication LayersRFC 1191 Path MTU Discovery RFCRFC 1323 TCP Extensions for High PerformanceRFC 1644 TCP Extensions for Transactions Functional SpecificationRFC 2018 TCP Selective Acknowledgment OptionsRFC 2338 Virtual Router Redundancy ProtocolRFC 2488 Enhancing TCP Over Satellite Channels using Standard MechanismsRFC 2581 TCP Congestion ControlRFC 2582 The New Reno Modification to TCP's Fast Recovery AlgorithmRFC 2988 Computing TCP's Retransmission TimerRFC 3135 Increasing TCP's Initial WindowRFC 3390 Performance Enhancing Proxies Intended to Mitigate Link-Related DegradationsRFC 3782 The New Reno Modification to TCP's Fast Recovery Algorithm

1.5. Document OverviewThis rest of this manual is divided into the following chapters:

Chapter 2 Quick Start. Provides instructions on how to quickly set up and configure your XipLinkdevice.

Chapter 3 Understanding XipLink Optimization. Explains the concepts underlying XipLink'soptimization capabilities, giving you the information you need to make the most of your XipLink device.

Chapter 4 The XipOS Web Interface. Contains detailed instructions on how to configure all aspectsof your XipLink device through its web user interface.

Chapter 5 Statistics. Describes how to view statistical graphs of your XipLink device's performance.

Chapter 7 Advanced Upgrade Procedures. Explains how to perform certain unusual upgrades thatare not handled by the web UI's upgrade process.

Chapter 8 Troubleshooting and Diagnostic Tools. Contains information about how to work withweb UI errors and the device's logs.

Chapter 9 Support. Explains how to contact XipLink's support department, or return a defectivedevice. Also contains a list of frequently asked questions.


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1.5.1. Conventions used in this ManualThe following icons appear throughout this manual.

A note contains important information you need to know in order to properly use your XipLinkdevice.

A tip provides insight into a particular way of using your XipLink device.

An important note contains critical information that must be followed in order for your XipLinkdevice to function.

Failure to heed a warning could result in a severe disruption in your network.

8Chapter 2. Quick Start - XA SeriesThis section of the manual will enable you to quickly get up and running. It is assumed that youhave some knowledge on Network Topologies and Wireless setups. It is recommended that youread through the other chapters to get an overall insight on how this unit needs to be configuredfor your particular network topology.

2.1. Unpacking and Box ContentsPlease verify that you have received the following within your package contents:

1. XA Unit2. Power Cable3. Network Cable (Cat 5 Ethernet cable)4. Console serial cable (RS232 DB9 null modem cable) or USB to RS232 Cable5. QuickStart leaflet to provide basic startup information.

When unpacking and handling the contents of the box please take all precautions againstelectrostatic discharge as this may cause permanent damage the equipment. Please note:any damage due to electrostatic discharge will void the product warranty.

2.2. Placing the Optimizer in the NetworkIn a typical installation the optimizer is placed in-line into the segment between the LAN network andthe Wireless Modem.

Figure 2.1. Placement of the Optimizer

Unaccelerated passing through the optimizer from the LAN is proxied, compressed and accelerated thenforwarded over Wireless interface. Any accelerated traffic arriving on the Wireless side is decompressedand then passed back to the LAN. It is important to ensure that the LAN side is always connected to eitherthe Router or Bridge interfaces, and that the wireless equipment is connected to the Wireless interface,otherwise network throughput will be degraded or disrupted.

Other deployment options, including out-of-path configurations, are possible. See the section on WebCache Communication Protocol for scenarios that rely on certain Cisco routers, or contact XipLink forother possibilities.

Quick Start - XA Series

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2.2.1. Physical ConnectionsAll ports on the XA's are clearly marked for identification. Each unit contains a Serial Console port towhich you can gain direct access to the unit's console using the included serial cable, See the section onManagement through the CLI for more information.

Some units include a USB port, but these are currently not used.

2.2.1.1. Product Labels

Figure 2.2. XA-500

Figure 2.3. XA-2000

Figure 2.4. XA-4000 | XA-10K

Figure 2.5. XA-30K


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2.3. Accessing the XipOS Web User InterfaceTo access the unit via the Web interface, you will need to make the device available on your PC's network,or you can connect the device directly to your PC's LAN port using the supplied Ethernet cable.

The factory default configuration of the device is as follows:

Table 2.1. Factory default IP addresses

Interface IP NetmaskManagement 172.16.1.200 255.255.255.0Wireless 10.0.0.200 255.255.255.0Bridged Not ConfiguredRouter 192.168.1.200 255.255.255.0

It is recommended that you initially connect to the device through the Management interface. This willallow you to configure the device's main network settings without having to reset your PC's IP address. Toallow for minimum downtime, you may configure the device prior to installing it in-line on your network.

Steps to take

Connect your PC to the management interface, either via a network or direct LAN cable. Reconfigure your PC/Laptop to any IP address on the 172.16.1.0/24 subnet (except 172.16.1.200, which

is the device's default IP address). For example, use IP address 172.16.1.1 and netmask 255.255.255.0.Please refer to your PC operating system's instructions on how to configure your PC's IP address.

Open your web browser and point it to http://172.16.1.200/

For Crypto versions you will need to connect via a secure https connection on usinghttps://172.16.1.200.

2.4. LoginUse the factory default user name and password to log in.

User Name: admin

Password: xiplink

If the login is successful you will be presented with the Quick Config Wizard welcome screen.


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2.5. XipLink Setup WizardConfiguration of your XipOS device is done through a secure web interface.

Please note that your web browser requires JavaScript support. It is recommended that yourdisplay supports a minimum resolution of 1024x768.

The web interface allows you to configure your device and view live statistics. When you first accessthe web UI you will be presented with the Quick Config Wizard that will guide you step-by-step throughthe basic configuration options. The unit will be operational once the Quick Config Wizard is complete.Further configuration refinements can then be made within the Networking Setup and Optimization areasof the main UI.

2.5.1. WelcomeWelcome and thank you for purchasing our XipLink product. Here you will be able to view and acceptthe license agreement. Please complete the required registration information before accepting the licenseagreement.

End User Licence AgreementThe use of this device and the installed software is subject to agreeing to the XipLink EULA. Before youcan continue with the configuration of the device, you must read the agreement, complete the licenseedetails (see below), and accept the agreement's terms.

Agreement accepted bySupply the name of the user who has accepted this license.

From organizationSupply the name of the organization to which this license is granted.


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Serial numberThis is the software serial number of your XipOS installation. It is different than the hardware serial numberof the device.

License agreement acceptedOnce you have agreed to the software license and completed the above details, you can click on thischeckbox to accept the license.

On-Line RegistrationOnly Visible once agreement is accepted

Please register this unit as on-line registration assists us in supporting your device and enables us to sendyou notification of any future software updates.

Should you not have Internet access when first configuring the device, you may register the device anytime by returning to this page and selecting On-Line Registration.

Open User GuideIf the PC you are using to configure the device also has Internet access, you can register the device on-line. On-line registration assists us in supporting your device and enables us to send you notification ofany future software updates.

Should you not have Internet access when first configuring the device, you may register the device anytime by returning to this page and selecting On-Line Registration.

2.5.2. Select Deployment Options

The deployment options specify the network topology in which this device is going to be used. To completethis section, you will need to know where and how this device will form part of your network: whichIP addresses to use and preferably some form of network diagram. Please see the section InstallationFlexibility for detailed information on this topic.


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Router, Bridge or Single InterfaceDesignate this device as a router, bridge or running in Single Interface mode. Which to choose dependson your network topology and where the unit is physically located.

In Bridge mode the unit is transparent to the network and will pass traffic though without the source anddestination being aware that the device is in their path.

In Router mode, the unit is assigned two IP addresses and traffic needs to be explicitly routed through theseaddresses. In Router mode you can also enable Network Address Translation (NAT). If you do, you needto specify which interface will do the NAT translation. For most NAT installations, this is the Wirelessinterface with a public IP address.

Single Interface mode allows you to connect only the Wireless interface through to the network and thenvia tunnelling you would route clients via this PEP. For detailed information refer to the Networking Modesection.

Management InterfaceThe Management interface on the device can be configured to act either as a management interface or asa hybrid RX/TX interface. The selection here depends on your particular deployment requirements:

Select the "Use as additional (management) interface" option when the Management interface will be usedto manage the device. Typically this is used for out-of-band management, to ensure that managementtraffic is separate from routed traffic for security reasons. SNMP monitoring and traps are often sent viathis interface to a central Network Monitoring System.

Select the "Hybrid" option when you have two separate wireless channels, one for transmitting (TX) andonce for receiving (RX). This is typically used for a remote deployment where you will have a dedicatedSCPC transmission channel and a broadband shared downlink DVB channel. Terminating both channelsin a single XipOS device does away with any requirement for an additional upstream router.

Hub or RemoteIs the unit deployed at a hub site that communicates with many remote XipLink devices, or is it deployedat a remote end point and only communicates with one other XipLink device? If XipLink devices aredeployed on both sides of this device, you need to select Hub/Mesh.

Device nameFor ease of reference and administration, you should configure a unique name for this device. This nameis displayed in the web UI, allowing visual confirmation of the device being configured.

The name of the device must consist solely of alphanumeric characters without spaces or punctuation.

2.5.3. Configure Network InterfacesThis section allows you to configure the physical interfaces of the XipLink unit. You can enable or disableany interface, and also set various options for each.


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Wireless interface. This interface always faces your wireless equipment. Accelerated/compressedtraffic arrives on this interface to be de-compressed and forwarded to its final destination on the Routedinterface.

Routed interface. Unaccelerated traffic is sent to this interface to be optimized before leaving theWireless interface.

Management interface. This interface is primarily used for out-of-band management of the device.It allows you to reconfigure the primary interfaces without having to concern yourself with losing yourconnection to the device. Should you use a separate management network, you can reconfigure thisinterface to use a specific IP address on the management subnet. This allows you to manage and monitor thedevice through this interface without interfering with the core routed traffic. Firewall configurations canalso prevent any management traffic through the main Wireless or Routed interfaces, thereby providingan additional level of security to the device.

Address TypeStatic. Assign a fixed IP address to this interface. You also need to supply the netmask.

DHCP. Obtain an IP address from a DHCP server on this interface's network.

None. Assign no IP address to this interface. This is only useful when the device is in Bridge mode.

Maximum Transmission Unit (MTU)The MTU setting defines the maximum size of a IP packet that can be transmitted without fragmentation.Values can range from 576 to 1500.

MediaDefines the type of media that is connected to the Ethernet interface. The default is autoselect, whichshould work in most environments. If you connect the device to any network equipment that is manuallyconfigured, the auto-detection may not always work. It is then best to manually configure the media typeto avoid conflicts.

VLANThis setting allows you to bind this interface to a particular VLAN


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Default gatewayThe default gateway is the exit and entry point in a particular network subnet. All traffic that is destinedfor another network will be routed via this Gateway IP address.

2.5.4. Configure DNS

The Domain Name System (DNS) translates domain names meaningful to humans into IP addresses thatcan be routed across the network. It is an IP address directory, similar to a telephone directory, that holdsall the domain name to IP address translations.

DNS ServersHere you need to configure the primary and secondary DNS server IP's that are reachable from thisparticular device.

DomainYou can also supply a default domain name. The device will use this domain to resolve "unqualified" hostnames (i.e. names without a '.' in them). This setting is optional and rarely needed.

2.5.5. Configure Networks


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This section allows you to configure the device with the basic characteristics of the Wireless interface'slink. Please see the section on the Networks tab to fine tune the configuration for your environment.

Link PropertiesClick the Edit Link Properties button to configure your wireless link's properties. You can also edit theproperties of the "Unassigned" link, which is a catch-all for traffic that the optimizer does not accelerate.Normally the "Unassigned" link has the same properties as the wireless link.

The Maximum Transmit Bandwidth is the maximum speed at which the device will transmit data overthe link, while the Maximum Receive Bandwidth is the expected maximum speed that the device willreceive data from the link.

Bandwidth and rate values must be specified with a unit:

Mb = 1,000,000 bits per second Kb = 1,000 bits per second b = 1 bit per second

These values can only be integer numbers (without commas); decimal points are ignored.

The Link Round Trip Time is the total amount of time (in milliseconds) it takes for a packet to travelover the link in both directions. This critical value is used by the Rate Control algorithms and also ensuresthat sufficient buffer space is allocated to manage inflight data.

Network PropertiesSelect Standalone hub deployment if your optimizer is to be deployed as a pure XHO hub (i.e. without aremote XipOS device). Selecting this option disables SCPS acceleration and TCP-level compression. Theoptimizer still proxies all TCP connections, but only applies XHO optimizations to HTTP connections.

If you have a hub where some sites have a remote XipOS device and others do not, you can override thissetting on a per-site basis using a QoS queue for each site and configuring specific TCP optimizations onthe Service Assignment tab.

If your optimizer is a pure XHO hub, only select Adjust settings for an external Optimizer/PEP ifyou have an upstream Performance Enhancing Proxy (PEP) installed between this optimizer's Wirelessinterface and the wireless transmission equipment. This is required for any PEP that creates spoofedconnections, such as a web cache.

The 'Wireless' ethernet max speed setting controls the maximum speed of traffic on the Wirelessinterface. This is typically the speed at which the interface syncs to its switch. For example, set this to1000Mb for 1000BaseTX Ethernet media.


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2.5.6. Set Password

Please choose a password to access the device.

Supply the current password (the factory default password is xiplink) and provide a new password andconfirmation.

The password score indicates the new password's strength. The higher the value the more difficult thepassword is to break. Use a password with numbers, a mix of upper- and lowercase letters and punctuationcharacters to get a high score. A score of at least 50 is recommended.

2.5.7. Apply Changes To Device ConfigurationPlease review all of your settings before applying the changes. Should the Apply Changes option not beavailable, you will first need to accept the license agreement before you can proceed.

The XipOS software distinguishes between the active "running" configuration and the permanent "startup"configuration that is loaded when the device reboots. This distinction lets you experiment with differentconfiguration settings, and allows you to undo your changes by rebooting or power-cycling the device.

When you apply your changes, by default they are saved to both the running and startup configurations.You can prevent the changes from being written to the startup configuration by de-selecting the "Alsoapply to 'startup' configuration" checkbox, which will mean that the changes will only be in effect untilthe device is rebooted.

The system saves your changes by first applying them to the running configuration. If this succeeds (and the"Also apply to 'startup' configuration" checkbox is selected) then the changes are saved to the permanentstartup configuration. Should any failure occur while modifying the running configuration, the system willattempt to roll back the changes to the previous state, all UI changes will be kept intact so that you canedit the changes and reapply the configuration. To retrieve the original settings as was previously applied,you will need simply refresh the web browser to reload these settings.

When changing the IP address of the device, you will receive a popup to notify you to now connect tothe newly configured IP address. This is particularly true when changing the IP of the interface throughwhich you are currently connected.

The feedback window indicates the progress and success or failure of the configuration updates.

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Chapter 3. Understanding XipLinkOptimization

This chapter describes the techniques and features of XipLink's optimization technology. Understandingthese concepts will help you get the most out of your XipLink product.

Unlike application accelerators or cache machines, which usually reside very close to the enterpriseLAN and which communicate across many intermediate links, wireless optimizers are installed to closelybracket the wireless link.

XipLink is committed to standards compliance wherever possible, but in the interest of delivering themaximum wireless capacity XipLink also uses industry leading proprietary algorithms as explained below.The SCPS standard allows such vendor-specific extensions, and XipLink leverages this fundamentalcapability to rapidly deliver improved algorithms while remaining completely interoperable andtransparent.

3.1. Dynamic Transparent Negotiation ofOptimization Capabilities

The XipLink optimizer transparently proxies every TCP connection. Following the SCPS standard,extended TCP options are exchanged between SCPS-enabled proxies during TCP connectionestablishment. These options, which are transparent to non-SCPS applications, allow for the negotiationof standard SCPS optimization capabilities on each connection.

In addition to standard SCPS capabilities, other enhancements such as selective negative acknowledgments(SNACK) and the use of XipLink high ratio data compression are also negotiated during TCP connectionestablishment, using standard SCPS extensions for vendor-specific options.

Figure 3.1. Dynamically negotiated optimization

The SCPS TCP options underlying optimization negotiation can be routed over any Layer 3 IP network.This is a key underlying principle in the XipLink system architecture, and allows XipLink to deliveroptimization to users across any network topology without the need for awkward network configurationsuch as tunnels:

TDMA satellite networks Point-to-point and point to multi-point networks Hub and Spoke networks Mesh networks

Understanding XipLink Optimization

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Networks that may be only partially installed

Once a hub site has an optimizer appliance installed, remote users that are XipLink-enabled, either bysoftware embedded in their wireless device or by connecting through an optimizer on their LAN, getfully maximized throughput. Other users who are not XipLink-enabled continue to use standard TCP, butwithout optimization benefits.

Figure 3.2. Unoptimized connections using standard TCP

3.2. SCPS Protocol AccelerationXipOS optimizes the transport layer for communications across a wireless link in several ways.The conceptual algorithms for protocol operations over the wireless air interface are based on theSCPS standard. XipLinks implementation of TCP protocol acceleration also uses additional advancedalgorithms that are the result of years of engineering and exacting simulation to ensure maximum use ofthe available bandwidth.

XipOS addresses the loss and latency of wireless communications by applying specialized wirelessalgorithms and other optimization techniques to fully and fairly utilize the available capacity. StandardTCP encounter several problems when used across a wireless link:

Slow connection setup due to long delay (latency) Slow discovery of the available wireless bandwidth Erratic use of the available bandwidth Slow response to packet loss that occurs in the network Overreaction to packet loss at high bandwidths, dramatically reducing the output rate Hard-coded parameters, such as window sizes, limit throughput Poor response to simultaneous packet loss in many data streams (holes) Protocol header overhead inefficiently consumes available bandwidth Considerable bandwidth required for acknowledgements

XipLink protocol acceleration algorithms mitigate these issues with a combination of approaches that workcollectively to achieve the highest performance for each wireless environment.

Features of the XipLink TCP protocol acceleration module:

Selective Negative Acknowledgment (SNACK). A loss recovery scheme that is highly efficientover wireless links and works with different congestion control algorithms to adapt to packet loss.

Acknowledgement frequency reduction. (AFR) A technique that lowers protocol overhead by 33%or more and is especially effective over high-speed, asymmetric links.


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Dynamic window scaling. Algorithms that scale TCP windows with network load, removing anyartificial limits on communication capacity.

Large windows. Uses buffers that are larger than those of other devices in the network, ensuring thatadditional latency is not introduced.

3.3. XipLink Transport Control (XTC) ModesXipLink offers the largest selection of highly tuned congestion control algorithms. These deliver theabsolute maximum capacity over a wireless link when properly matched and configured for the networkwhere the optimizer is installed.

XipLink Transport Control (XTC) modes are rate-control and congestion-control algorithms that maximizecapacity on a wireless link, beyond the single congestion control mechanism offered in the SCPS standard.As a result, XipOS can deliver significantly more throughput when the rate control algorithm is properlymatched to the wireless network where the optimizer or software is installed.

A very important concept when discussing rate control algorithms in wireless networks is to understandthat the XTC mode may be different for a hub site versus a remote site even though they are operatingon the same network.

For example, in a hub-and-spoke TDMA network, the high-powered hub site may be capable oftransmitting at a fixed rate and so would be set to Fixed Rate Control mode, while the remote sites mayexperience general RF contention and lower RF power budgets and would therefore be configured inProgrammable Fixed Rate Control mode or Dynamic Rate Control mode. Congestion control is alwaysviewed from the perspective of the sending device and it is not uncommon to find the modes configureddifferently on either end of a wireless link in order to deliver the maximum capacity.

The following sections describe the XipLink Transport Control (XTC) modes and briefly explain wheneach is typically used.

3.3.1. XTC - Fixed Rate Control ModeFixed Rate Control mode allows the network operator to configure the outbound traffic rate to a fixed,maximum rate. Whether there is one connection or hundreds, the XipLink optimizer will shape the TCPoutput traffic to sustain this fixed output rate and hold it very close to that maximum.

One specific goal of this mode is to ensure that performance does not decrease as the round trip time(RTT) climbs.

Figure 3.3. XTC Fixed Rate Control

Fixed Rate Control mode is perfectly suited to both ends of a dedicated link like Single Channel Per Carrier(SCPC) space segments, but can also be used on both ends of stable TDMA or even DVB-RCS networks.


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In licensed or unlicensed terrestrial networks this algorithm is always recommended at the hub site andcan often be used at remote sites in stable point-to-point networks such as those served by a CPE deviceand good antenna.

Fixed Rate Control mode is infrequently used in mobile devices due to the constantly changing signal-to-noise ratio (SNR) these devices encounter as they roam. Even when operating in a licensed spectrum, thevery nature of a roaming mobile device and their limited RF power budgets make the bandwidth appeardynamic.

3.3.2. XTC - Dynamic Rate Control ModeDynamic Rate Control mode is the default congestion control mechanism for a SCPS connection. Thismode is useful in several situations, such as:

When the wireless traffic may be passing through one or more unknown service provider networks. If there is limited buffering capability within the network. If an intermediate controller is policing the traffic. When I-PEP interoperability is important.

Dynamic Rate Control mode uses proprietary techniques that dynamically discover the availablebandwidth and then anticipate and reduce the output rate before congestive loss occurs.

XipLink Dynamic Rate Control mode is based on years of research and uses algorithms that are designedto operate best on wireless networks. Wireless optimizers configured to use this mode rapidly determinethe available bandwidth and respond very quickly by either increasing or decreasing the TCP output whenthe available bandwidth varies. This rapid convergence is accomplished by calculating the buffering thatoccurs within the network using volume-based algorithms. The optimizer then rapidly controls the outputTCP flow rate to ensure the smallest buffers are not overrun, which would cause packet loss.

Figure 3.4. XTC - Dynamic Rate Control Mode

Dynamic Rate Control mode is recommended when the available bandwidth is unknown or varies widely,often on dynamic TDMA or DVB-RCS networks, particularly at the remote sites. While not as effectiveat completely filling a stable link, in many wireless devices it is more important to constantly and quicklyadjust the transmission rate for maximum capacity.Dynamic Rate Control mode is also an alternative for links where a traffic shaper may exist in the pathbetween two XipLink optimizers. The traffic shaper's policing would work against Fixed Rate Controlmode, dropping optimized traffic that may appear on the network as an aggressive TCP sender holdinga very high data rate.


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3.3.3. XTC - Programmable Fixed Rate Control ModeThis XTC mode, Programmable Fixed Rate Control, allows the available bandwidth setting of a fixedrate link to be varied multiple times per second using the XipLink API. When a wireless modem or otherexternal device is capable of determining when the bandwidth changes and can generate a message toXipOS, this mode permits co-ordination of the TCP output to match the available bandwidth across varyingdegrees of capacity. This function is becoming more and more important in policy enforcement around adevice's spectrum usage as well as to keep up with Adaptive Coding Modulation (ACM) dynamics.Using Programmable Fixed Rate Control mode, an external device can vary the available bandwidthwhen it detects a change in the size or depth of its outbound link buffers or a change in the link's speedor modulation characteristics. The external device sets the new available bandwidth using the XipLinkAPI. The optimizer software can throttle the TCP output up or down, maximizing the capacity across thelink without driving the link to a loss condition due to buffer overflow or upstream network congestion.

Figure 3.5. XTC - Programmable Fixed Rate Control Mode

Full performance on dynamic bandwidth links can be achieved using this mode, but Programmable FixedRate Control mode requires software integration within an embedded system or external integration usingthe XipLink API. As such, this mode is only available with specific devices that support this capability.Programmable Fixed Rate Control mode can operate both at coarse intervals, as when a ship changessatellites as it moves across an ocean, and also very rapidly (sub-second) when tightly coupled with adevice that aggressively monitors the available bandwidth.

3.3.4. XTC - Enhanced TCP ModeThis is a simple rate control algorithm that follows the basic TCP Reno recommendations for congestioncontrol. It uses improved TCP slow start to react to packet loss. It is useful on stable links when FixedRate Control cannot be used due to an upstream QoS traffic shaper, similar to Dynamic Rate Control.

3.4. Additional TCP Protocol AccelerationTechniques3.4.1. TCP Connection Fast Start

Using TCP fast start technology, data can be included in the initial connection handshake. This combinesin a single round trip both connection establishment and the first few bytes of data in the TCP connection.


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Without TCP fast start, an application has to wait for setup request and acknowledgement to traverse theslow wireless link before sending any data.

A typical Internet user with a standard web browser may open several connections to many servers foreach web page viewed. TCP fast start can significantly decrease the time needed for a page to load, andwill also greatly reduce the amount of contention on the wireless network by decreasing the number ofpackets sent and reducing the overall bandwidth consumed.

Figure 3.6. TCP Connection Fast Start

XipLinks fast start is based on our efficient implementation of IETF RFC 1644. Traditional TCP usesa 3-way handshake before data transmission can begin. If we consider a minimum second delay ineach direction, just establishing a TCP connection to a server could require over a second, even beforerequesting the first bits of data. The benefits of TCP fast start are most apparent when multiple connectionsare used together in sequence, such as with HTTP and other client-server applications.

3.4.2. Acknowledgement Frequency Reduction (AFR)On asymmetric links, enabling AFR will reduce the number of acknowledgments the receiver will sendback as data is received. When AFR is active, the XipLink optimizer will use a calculated delayedacknowledgement time based on the configured bandwidth and delay along with a proprietary XipLinkalgorithm. Standard TCP's every-second-packet acknowledgment framework was originally devised tosustain high speed LAN throughput. In contrast, with AFR the XipLink optimizer acknowledges a muchlarge volume of data with a single packet.

When enabled, this feature can reduce packet overhead by 33% or more while sustaining maximumthroughput across the wireless link. As the link speed increases, or when a communication link is highlyasymmetric, protocol reduction benefits continue to increase while sustaining the maximum bandwidthcapacity.

3.4.3. Selective Negative AcknowledgmentsThe Selective Negative Acknowledgements (SNACK) technique works in combination withAcknowledgment Frequency Reduction and allows for rapid response to packet loss. It is much moreresponsive than traditional TCP's packet acknowledgment scheme which has proven ineffective whenapplied to wireless links.

Using SNACK to communicate only those packets lost in transmission allows communications to continueeven at very high error rates. This makes XipLink wireless optimization algorithms very resilient torain fade and other RF related conditions while scaling to very high throughputs. SNACK is more bit-


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efficient than Selective Acknowledgement (SACK) and is more effective against the multiple losses thatare common with wireless interference.

Figure 3.7. AFR and Selective Negative Acknowledgments

SNACK is an important component of TCP protocol optimization in satellite and terrestrial wirelessnetworks because the higher error rates experienced over wireless links magnify the effects of high latencyon retransmissions.

3.4.4. Quality of ServiceThe XipLink wireless optimizer provides several Quality of Service (QoS) capabilities that work with bothinternal optimization functions as well as with network-wide QoS services.

All traffic, including traffic not slated for acceleration, still passes through a fast path in the XipOS kernel.Constantly monitoring all traffic passing through the optimizer ensures that it will not saturate the linkwith accelerated data, which might cause packet loss in unaccelerated protocols.

QoS connections that meet an operator's defined Differentiated Services criteria are given preferred accessto the available bandwidth, ensuring that mission-critical or performance-sensitive applications receivethe bandwidth they need.

Any XipLink wireless optimizer can also tag, mark or re-mark specific traffic as it leaves the device. Thisenables the network operator to deliver an end-to-end integrated QoS system using differentiated userclasses or queues. This capability can be used to prioritize some traffic or limit the bandwidth used byothers.

3.4.4.1. QoS OverviewQuality of Service allows you to classify packets that pass through the device and assign different prioritiesto different kinds of traffic. Without QoS, traffic passes through the device on a first-in first-out (FIFO)basis. This can degrade performance when the link becomes congested, and it also allows bandwidth-


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hungry applications such as P2P or bulk file downloads to overwhelm the link and prevent the timelydelivery of streaming or interactive protocols. These problems are compounded on links with high round-trip times.

Figure 3.8. QoS Re-Prioritizes Traffic

QoS also helps a hub site deal fairly with multiple remote "spoke" sites when each remote site can have itsown downlink rate that differs from the hub site's uplink rate. With QoS you can configure the hub witha fixed maximum transmission rate for each remote site. This in turn allows each remote site to apply itsrespective downlink rate without causing congestion and limiting bandwidth to other remote sites.

QoS only applies priorities and shaping to traffic transmitted over the wireless link from theXipLink optimizer. The device has no way to control the rates at which it receives data (asidefrom standard TCP congestion control mechanisms, which do not differentiate types of traffic).QoS is therefore normally applied on both devices on either side of the wireless link to controlhow each device transmits data.

3.4.4.2. QoS QueuesXipOS uses the concept of QoS queues to define traffic priorities. Each queue has a parent and zero or morechild queues. A special top-level (parentless) queue named root defines the total amount of bandwidththat can be transmitted from a device. (The root queue's limitations are set by the maximum bandwidthof the Wireless link.)

The root queue is a conceptual entity and is not exposed in the XipOS GUI.

The parent-child relationships between queues define how bandwidth is allocated among the queues. Aqueue cannot reserve more bandwidth that what has been reserved by its parent.

Each childless (or "leaf") QoS queue is associated with a firewall rule that defines what kind of trafficthe queue controls.

The order of firewall rules is critical to successfully applying QoS.

One of the childless queues must be designated as the default queue. The default queue shapes all trafficthat does not match any other queue. The default queue is the only leaf queue not explicitly associatedwith a firewall rule.


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The Unassigned QueueAll XipLink optimizers have an "Unassigned" queue that acts as a catch-all for unclassified traffic that doesnot match any of the other queues. To lower the priority of unclassified traffic, configure the Unassignedqueue with lower bandwidth properties than the other top-level queues.

In Single Interface mode, traffic sent to the LAN network is classified in the Unassigned queue.

3.4.4.3. QoS AlgorithmThe XipOS queueing algorithm is based on Hierarchical Fair Service Curves (HFSC), with severaladaptations for wireless and satellite links. HFSC allows proportional bandwidth distribution (supportingequal or unequal bandwidth sharing) as well as control and allocation of latency. Each QoS queue can beconfigured with three main bandwidth transmission parameters:

Maximum transmission rate Guaranteed transmission rate Priority transmission rate

All queues in the hierarchy can have a maximum and a guaranteed rate. Leaf queues, since they are theonly queues that actually hold packets, can also have a priority rate.

The maximum rate is simply an upper limit on the queue's sending rate. Whenever a queue reaches itsmaximum rate, no further packets can be sent by that queue until the rate subsides.

The guaranteed rate controls the queue's relationship with its siblings at the same level in the QoS queuehierarchy. This is the bandwidth guaranteed to a queue when the link is saturated, ensuring that trafficis distributed properly among the sibling queues. Separating the guaranteed and priority rates allows thesystem to meet priority delay times under all circumstances. It also means that a queue can send a packetto meet its priority rate even if doing so temporarily violates the guaranteed rate of one of its ancestorqueues in the hierarchy.

The guaranteed rate of a given queue must be equal to or greater than the sum of the guaranteedrates of the queue's children. This ensures that all queues can achieve their configuredguaranteed rates.

For example, if a queue has two children with guaranteed rates of 2Mbps and 3Mbps, then thatqueue must have a guaranteed rate of at least 5Mbps.

A queue's guaranteed rate can be specified either as an absolute value or as a percentage of its parent'sguaranteed rate. A queue with multiple children can have some of its children specify their guaranteedrates as percentages and others as absolute rates.

The priority rate is filled first across all queues. In other words, if there is traffic available in severalqueues the system will first service the queues that have not yet reached their priority rates. Priority ratesshould not be oversubscribed. They are often used for real time protocols like VoIP, gaming and otherlatency-sensitive applications. XipOS queues also have a delay parameter that limits the amount of timea packet can spend in the queue. This allows fine control over jitter and the quality of streaming protocolssuch as voice calls.

3.4.5. Streaming Data CompressionIn addition to optimizing the TCP protocol for transport over wireless links, XipOS also applies high-ratio data compression to the TCP payload. To achieve a high compression ratio the software performs


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continuous compression on the entire stream of data for each on-going connection, taking advantage ofthe streaming nature of TCP.

Stream-based compression is superior to other payload compression strategies that compress data withinindividual IP packets. These older per-packet compression algorithms yield lower compression ratios anddo not reduce the overall number of packets needed to send the compressed information.

Figure 3.9. Streaming Data Compression

XipOS stream compression algorithms are tuned to ensure that additional latency is not introducedthrough the buffering required for optimal data compression, which might lead to lower overall bandwidthutilization. Data compression is most effective when performed on larger data sets, because more patternsinside the data can be found and removed. However, if only a few hundred bytes of data are transmittedat a time, the data is briefly buffered before automatically being forwarded out the wireless port withoutwaiting for more data - maintaining very low latency. The timers that ensure this balance between waitingtime and data volume are based on years of real-world deployment and simulation experience.

A XipLink wireless optimizer will compress only the TCP payload, leaving the TCP headers in theclear. This allows TCP acceleration algorithms to operate on, and XTC rate controls to be applied to, thecompressed data stream. This enables the wireless optimizer to transmit at the maximum output rate, asprescribed by the rate control settings, even as the compression ratio varies from packet to packet.

Other compression strategies that can yield higher compression ratios but typically operate by putting alltraffic into a common compressed tunnel. Such systems require end-to-end or tunnel based configurations,and are not well suited to wireless links because they limit network scalability and add packet overhead,all detrimental to maximizing capacity at low capital cost.

The compression ratio of a particular data stream is completely dependent on the nature of the data itself.Text - as found in web pages, email, etc. - is highly compressible while random data is not compressibleat all. Internet video streams are generally very compressible while video from modern video surveillancesystems is so well encoded by the camera there is not much left that can be compressed. It never hurts torun these streams through the compression module, but user expectations for compression ratios must berealistic based on the type of traffic being transmitted.


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Figure 3.10. Compression Samples

Most XipLink customers see between a 40% and 300% compression ratio depending on the data itself andthe usage patterns. In general, compression ratios average about 2:1, but this is an area of rapid technologyinnovation and improvements which will continue to yield higher and higher ratios on traffic that is notalready pre-compressed.

3.4.6. XipOS TunnellingIn today's dynamic networks, customers typically have minimal control of content proxying and filteringon their service providers' networks. When the XipOS is deployed in an environment where the optimizeris not placed in a hub or teleport, or when the intercommunication between the two XA's connect over thepublic internet, it is possible that TCP packets may be stripped of the SCPS or acceleration options addedto the TCP headers. This effectively means that the acceleration options will not be negotiated betweenthe various instances of XipOS.

To address these situations, XipOS provides a UDP tunnelling feature to protect acceleration options beingstripped from the TCP headers. All traffic is optimized prior to being transmitted within this tunnel, sothat the maximum capacity of the link can be obtained.

Tunnelling also enables remote installations of XipOS optimizers to operate behind a NAT firewall, orwithin a private network segment, or where the service provider only provides private IP addresses.

Finally, tunnelling is required for XipLink Real-Time (XRT) optimization.

3.5. XipLink Hub OptimizationsSome XipLink optimizer models support hub-only optimizations (XHOs) that improve performancewithout the need to deploy a second optimizer on the other side of the wireless link. Hub optimizationsprovide benefits when they are enabled on the "upstream" or "Internet" side of a wireless link.

The XHO capabilities are:


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XiPix web image compression. HTTP compression for browser-compatible decompression.

3.5.1. XiPix Image CompressionXiPix technology automatically reduces the resolution of web images on the fly, dramatically reducingimage file sizes with only a minor impact on the user experience. XiPix compression is transparent to theend user, and is compatible with all other XipLink optimization technologies.

An operator can configure XiPix's level of compression, allowing you to specify the tradeoff betweenimage size and quality.

XiPix technology only applies to JPEG images transmitted over HTTP. Most Internet web sites use JPEG-format images.

XiPix is a separately licensed capability, and can only be enabled with a valid activation code.Please contact XipLink to obtain an activation code.

3.5.2. HTTP CompressionXipLink's HTTP compression takes advantage of the standard compression capabilities defined in theHTTP protocol. All modern browsers support HTTP compression standards, but few web servers takeadvantage of it.

With XHO HTTP compression, a XipLink optimizer can automatically and transparently compress HTTPtraffic that is not already compressed by the web server. The user's web browser will decompress thetraffic, so there is no need to deploy a second optimizer on the user's side of the wireless link.

3.6. XipLink Real-Time (XRT)XipLink Real Time optimizations compress and coalesce multiple small UDP packets to significantlyenhance UDP bandwidth efficiency. Wireless products have inherent limitations to the number of packetsper second they can process. XRT reduces the number of packets required to carry a given volume of real-time traffic.

How can UDP traffic benefit from XRT?

Most VoIP traffic consists of headers - approximately 40%. Most headers do not change much from packet to packet. Multiple streams each have their own overhead and many common headers. Inefficiencies apply to most UDP-based protocols, from standard VoIP and Skype to other small-packet

applications such as Citrix. XRT does not alter the data payload in any way, so it does not rely on any particular VoIP codec or

UDP application.

XRT is an extension of XipOS lightweight tunnelling. You must enable tunnelling in order touse XRT.

Packet CoalescingPacket coalescing is a technique that combines the payloads of many small network packets into a singlelarge packet that can be transmitted and processed more efficiently. The following figure illustrates howXRT packet coalescing reduces the effective packet-per-second rate of real-time traffic.


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Figure 3.11. XRT Packet Coalescing

Packet coalescing is not merely applied on each connection between a client and server, but on multipledata streams between various hosts offering a greater benefit. The benefit is proportional to the numberof data streams available for coalescing.

The table below illustrates the benefit of coalescing multiple VoIP streams.

Table 3.1. XRT: Benefit of Coalescing Multiple Streams

Codec & Bit Rate Capture Window # of calls BandwidthSavings

PPS Benefit Ratio

G.729 (8 Kbps) 20 ms 1 8% 1G.729 (8 Kbps) 20 ms 2 33% 2G.729 (8 Kbps) 20 ms 5 47% 5G.729 (8 Kbps) 20 ms 10 52% 10G.729 (8 Kbps) 20 ms 20 54% 20G.729 (8 Kbps) 20 ms 50 56% 50G.729 (8 Kbps) 20 ms 100 57% 70G.729 (8 Kbps) 20 ms 200 57% 70

These results were obtained under laboratory conditions. Actual results will vary based on theindividual packet sizes in the data stream, the capture window size, and the maximum coalescedpacket size.

Note the convergence towards a 57% bandwidth savings as more streams are coalesced.

The next table shows the impact of the capture window size on packet coalescing. Increasing the capturewindow size would increase the benefit, although it may also increase jitter if not enough UDP traffic ispresent.

Table 3.2. XRT: Effect of Different Capture Window Sizes

Codec & Bit Rate Capture Window # of calls BandwidthSavings

PPS Benefit Ratio

G.729 (8 Kbps) 5 ms 10 37% 3G.729 (8 Kbps) 10 ms 10 47% 5G.729 (8 Kbps) 15 ms 10 50% 8G.729 (8 Kbps) 20 ms 10 52% 10


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The bandwidth savings and packet-per-second benefit both increase as the capture window increases,although the effect flattens out with larger window sizes.

Header CompressionXRT can also apply standard Robust Header Compression (RoHC) to UDP streams, where uncompressedheaders can account for as much as 60% of the network traffic.

Header compression applies to IP and UDP headers, and can also apply to Real-time Transport Protocol(RTP) headers. Since many RTP-based protocols use non-standard UDP port numbers, it is necessary toexplicitly tell the optimizer which traffic should be considered for RTP header compression.

3.7. Byte CachingByte caching, also known as data deduplication, is a compression technique which reduces duplicatedblocks of data that may be very large and/or separated by a large amount of intervening data.

XipLink's byte caching can achieve significant reduction of large data sets, with compression ratiostypically reaching 80%. These savings are also achievable on data that is already compressed by standardcompression algorithms, such as ZIP files and video streams.

XipLink's byte caching is implemented at the IP level. This enables it to detect and reduce duplicate dataamong all data streams passing through the device. For example, XipLink's byte caching can leveragethe data it sees in any protocol to compress that same data when it re-appears in any other protocol. Soa file downloaded by one client application will "prime the pump" and if that file is downloaded againby a different client, perhaps using a different protocol, XipLink's byte caching will be able to provideimmediate and significant savings on the second transmission.

XipLink's IP-level byte caching also provides benefits even when the application-layer traffic isencapsulated in one or more layers of tunnelling. It is fully compatible with any kind of IP-within-IPlayering.

Finally, XipLink's byte caching works around small changes in duplicated data. So a few changed, added,or missing bytes in the data stream won't invalidate the cache for the rest of the data.

Byte caching is an extension of XipOS lightweight tunnelling. You must enable tunnelling inorder to use byte caching.

Byte caching is only available on disk-equipped XA models. This includes the "C" models, aswell as the XA-10K and XA-30K.

3.8. Packet CompressionXipLink's packet compression reduces the size of individual IP packets. Compressing at the IP layer allowsthis technique to provide benefits to any kind of IP traffic, but it is especially beneficial for UDP-basedprotocols such as VoIP.

Packet compression is an extension of XipOS lightweight tunnelling. You must enabletunnelling in order to use packet compression.

3.8.1. Advanced Cellular CompressionAdvanced Cellular Compression (ACC) is a modified form of packet compression that provides benefitsin networks that make extensive use of tunnelled protocols. In these environments, which are common


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among cellular service providers, the main payload is nested inside multiple layers of encapsulation. Thesemultiple embedded protocol headers overwhelm individual packet compression.

ACC leverages the data from one packet to help compress those that follow. This allows it to efficientlycompress the embedded headers, resulting in significant savings over simple single-packet compression.

ACC is a separately licensed capability, and can only be enabled with a valid activation code.Please contact XipLink to obtain an activation code.

3.9. Link Balancing and BondingLink balancing spreads multiple TCP sessions over two physical links, enabling more efficient use ofoverall network capacity. The links are continuously monitored, and their usage is intelligently managedby instantaneously moving sessions between links, withou

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