ECE537/8 #1Spring 2009© 2000-2009, Richard A. Stanley

ECE537 Advanced and High Performance Networks

8: Frame Relay, ATM, and Other High-Speed Networks

Professor Richard A. Stanley, P.E.

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Overview of Tonight’s Class

• Student presentations/discussions on TEMPEST

• Review of last time

• Overview of frame relay, ATM, and other networking protocols of interest

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Last time

• While TEMPEST is a uniquely government program, the issue of compromising emanations is not; it affects all systems

• Sensitive information is not limited to government systems

• Networks exacerbate the compromising emanations problem, and they must be considered in network design

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Packet-Switching Networks

• Basic technology the same as in the 1970s• One of the few effective technologies for long

distance data communications• Frame relay and ATM are variants of packet-

switching• Advantages:

– flexibility, resource sharing, robust, responsive• Disadvantages:

– Time delays in distributed network, overhead penalties– Need for routing and congestion control

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Circuit-Switching

• Long-haul telecom network designed for voice

• Network resources dedicated to one call

• Shortcomings when used for data:– Inefficient (high idle time)– Constant data rate

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Packet-Switching

• Data transmitted in short blocks, or packets

• Packet length < 1000 octets

• Each packet contains user data plus control info (routing)

• Store and forward

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Figure 4.1 The Use of Packets

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Figure 4.2 Packet Switching:

Datagram Approach

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Advantages over Circuit-Switching

• Greater line efficiency (many packets can go over shared link)

• Data rate conversions

• Non-blocking under heavy traffic (but increased delays)

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Disadvantages relative to Circuit-Switching

• Packets incur additional delay with every node they pass through

• Jitter: variation in packet delay

• Data overhead in every packet for routing information, etc

• Processing overhead for every packet at every node traversed

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Figure 4.3 Simple Switching Network

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Switching Technique

• Large messages broken up into smaller packets• Datagram

– Each packet sent independently of the others– No call setup– More reliable (can route around failed nodes or

congestion)• Virtual circuit

– Fixed route established before any packets sent– No need for routing decision for each packet at each

node

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Figure 4.4 Packet Switching: Virtual-Circuit Approach

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Routing

• Adaptive routing

• Node/trunk failure

• Congestion

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X.25

• 3 levels

• Physical level (X.21)

• Link level (LAPB, a subset of HDLC)

• Packet level (provides virtual circuit service)

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Figure 4.5 The Use of Virtual Circuits

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Figure 4.6 User Data and X.25 Protocol Control Information

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Frame Relay Networks

• Designed to eliminate much of the overhead in X.25

• Call control signaling on separate logical connection from user data

• Multiplexing/switching of logical connections at layer 2 (not layer 3)

• No hop-by-hop flow control and error control• Throughput an order of magnitude higher than X.25

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Figure 4.7 Comparison of X.25 and Frame Relay Protocol Stacks

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Figure 4.8 Virtual Circuits and Frame Relay Virtual Connections

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Frame Relay Architecture

• X.25 has 3 layers: physical, link, network

• Frame Relay has 2 layers: physical and data link (or LAPF)

• LAPF core: minimal data link control– Preservation of order for frames– Small probability of frame loss

• LAPF control: additional data link or network layer end-to-end functions

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LAPF Core

• Frame delimiting, alignment and transparency

• Frame multiplexing/demultiplexing

• Inspection of frame for length constraints

• Detection of transmission errors

• Congestion control

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LAPF-core Formats

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User Data Transfer

• No control field, which is normally used for:– Identify frame type (data or control)– Sequence numbers

• Implication:– Connection setup/teardown carried on separate

channel– Cannot do flow and error control

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Frame Relay Call Control

• Frame Relay Call Control

• Data transfer involves:– Establish logical connection and DLCI– Exchange data frames– Release logical connection

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Frame Relay Call Control

4 message types needed

• SETUP

• CONNECT

• RELEASE

• RELEASE COMPLETE

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ATM Protocol Architecture

• Fixed-size packets called cells

• Streamlined: minimal error and flow control

• 2 protocol layers relate to ATM functions:– Common layer providing packet transfers– Service dependent ATM adaptation layer

(AAL)

• AAL maps other protocols to ATM

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Protocol Model has 3 planes

• User

• Control

• management

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ATM Protocol Architecture

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Logical Connections

• VCC (Virtual Channel Connection): a logical connection analogous to virtual circuit in X.25

• VPC (Virtual Path Connection): a bundle of VCCs with same endpoints

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ATM Connection Relationships

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Advantages of Virtual Paths

• Simplified network architecture

• Increased network performance and reliability

• Reduced processing and short connection setup time

• Enhanced network services

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Table 5.1

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VCC Uses

• Between end users

• Between an end user and a network entity

• Between 2 network entities

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Figure 5.3

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VPC/VCC Characteristics

• Quality of Service (QoS)• Switched and semi-permanent virtual channel

connections• Cell sequence integrity• Traffic parameter negotiation and usage

monitoring• (VPC only) virtual channel identifier

restriction within a VPC

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Control Signaling

• A mechanism to establish and release VPCs and VCCs

• 4 methods for VCCs:– Semi-permanent VCCs– Meta-signaling channel– User-to-network signaling virtual channel– User-to-user signaling virtual channel

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Control Signaling

• 3 methods for VPCs– Semi-permanent– Customer controlled– Network controlled

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ATM Cells

• Fixed size

• 5-octet header

• 48-octet information field

• Small cells reduce delay for high-priority cells

• Fixed size facilitate switching in hardware

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Header Format

• Generic flow control

• Virtual path identifier (VPI)

• Virtual channel identifier (VCI)

• Payload type

• Cell loss priority

• Header error control

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Figure 5.4

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Generic Flow Control

• Control traffic flow at user-network interface (UNI) to alleviate short-term overload conditions

• When GFC enabled at UNI, 2 procedures used:– Uncontrolled transmission– Controlled transmission

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Table 5.3

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Header Error Control

• 8-bit field calculated based on remaining 32 bits of header

• error detection

• in some cases, error correction of single-bit errors in header

• 2 modes: – error detection– Error correction

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Figure 5.5

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Figure 5.6

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Figure 5.7

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Service Categories

• Real-time service– Constant bit rate (CBR)– Real-time variable bit rate (rt-VBR)

• Non-real-time service– Non-real-time variable bit rate (nrt-VBR)– Available bit rate (ABR)– Unspecified bit rate (UBR)– Guaranteed frame rate (GFR)

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Figure 5.8

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ATM Adaptation Layer (AAL)

• Support non-ATM protocols– e.g., PCM voice, LAPF

• AAL Services– Handle transmission errors– Segmentation/reassembly (SAR)– Handle lost and misinserted cell conditions– Flow control and timing control

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Applications of AAL and ATM

• Circuit emulation (e.g., T-1 synchronous TDM circuits)

• VBR voice and video• General data services• IP over ATM• Multiprotocol encapsulation over ATM (MPOA)• LAN emulation (LANE)

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AAL Protocols

• AAL layer has 2 sublayers:– Convergence Sublayer (CS)

• Supports specific applications using AAL

– Segmentation and Reassembly Layer (SAR)• Packages data from CS into cells and unpacks at

other end

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Figure 5.9

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Figure 5.10

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AAL Type 1

• Constant-bit-rate source

• SAR simply packs bits into cells and unpacks them at destination

• One-octet header contains 3-bit SC field to provide an 8-cell frame structure

• No CS PDU since CS sublayer primarily for clocking and synchronization

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AAL Type 2

• Variable bitrate, connection-oriented, low latency (delay) service– Takes advantage of existing SDH/PDH transport

bandwidth by multiplexing small (voice and control) packets into standard ATM cells which would otherwise be largely unfilled

• Basic component is the CPS packet – Unanchored unit of data that can cross ATM cells, and

starts from any location within the payload of the ATM cell, other than the STF

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AAL Type 3/4

• May be connectionless or connection oriented

• May be message mode or streaming mode

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Figure 5.11

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AAL Type 5

• Streamlined transport for connection oriented protocols– Reduce protocol processing overhead– Reduce transmission overhead– Ensure adaptability to existing transport

protocols

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Figure 5.13

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Emergence of High-Speed LANs

• 2 Significant trends– Computing power of PCs continues to grow

rapidly– Network computing

• Examples of requirements– Centralized server farms– Power workgroups– High-speed local backbone

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Classical Ethernet

• Bus topology LAN

• 10 Mbps

• CSMA/CD medium access control protocol

• 2 problems:– A transmission from any station can be received

by all stations– How to regulate transmission

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Solution to First Problem

• Data transmitted in blocks called frames:– User data– Frame header containing unique address of

destination station

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Figure 6.1

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CSMA/CD

Carrier Sense Multiple Access/ Carrier Detection

1. If the medium is idle, transmit.2. If the medium is busy, continue to listen until the

channel is idle, then transmit immediately.3. If a collision is detected during transmission,

immediately cease transmitting.4. After a collision, wait a random amount of time,

then attempt to transmit again (repeat from step 1).

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Figure 6.2

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Figure 6.3

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Medium Options at 10Mbps

• <data rate> <signaling method> <max length>• 10Base5

– 10 Mbps

– 50-ohm coaxial cable bus

– Maximum segment length 500 meters

• 10Base-T– Twisted pair, maximum length 100 meters

– Star topology (hub or multipoint repeater at central point)

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Figure 6.4

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Hubs and Switches

Hub• Transmission from a station received by central

hub and retransmitted on all outgoing lines• Only one transmission at a time

Layer 2 Switch• Incoming frame switched to one outgoing line• Many transmissions at same time

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Figure 6.5

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Bridge• Frame handling done

in software• Analyze and forward

one frame at a time• Store-and-forward

Layer 2 Switch• Frame handling done

in hardware• Multiple data paths

and can handle multiple frames at a time

• Can do cut-through

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Layer 2 Switches

• Flat address space• Broadcast storm• Only one path between any 2 devices

• Solution 1: subnetworks connected by routers• Solution 2: layer 3 switching, packet-forwarding

logic in hardware

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Figure 6.6

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Figure 6.7

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Figure 6.8

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Figure 6.9

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Figure 6.10

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Figure 6.11

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10 Gbps Ethernet Benefits over ATM

• No expensive, bandwidth consuming conversion between Ethernet packets and ATM cells

• Network is Ethernet, end to end• IP plus Ethernet offers QoS and traffic policing

capabilities approach that of ATM• Wide variety of standard optical interfaces for 10

Gbps Ethernet

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Fibre Channel

• 2 methods of communication with processor:– I/O channel– Network communications

• Fibre channel combines both– Simplicity and speed of channel

communications– Flexibility and interconnectivity of network

communications

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Figure 6.12

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I/O channel• Hardware based, high-speed, short distance• Direct point-to-point or multipoint

communications link• Data type qualifiers for routing payload• Link-level constructs for individual I/O

operations• Protocol specific specifications to support

e.g. SCSI

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Fibre Channel Network-Oriented Facilities

• Full multiplexing between multiple destinations

• Peer-to-peer connectivity between any pair of ports

• Internetworking with other connection technologies

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Fibre Channel Requirements

• Full duplex links with 2 fibres/link

• 100 Mbps – 800 Mbps

• Distances up to 10 km

• Small connectors

• High-capacity

• Greater connectivity than existing multidrop channels

• Broad availability

• Support for multiple cost/performance levels

• Support for multiple existing interface command sets

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Figure 6.13

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Fibre Channel Protocol Architecture

• FC-0 Physical Media

• FC-1 Transmission Protocol

• FC-2 Framing Protocol

• FC-3 Common Services

• FC-4 Mapping

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Summary

• There are many networking protocols other than IP, and each is suited to one or more particular needs

• Because of the proliferation of IP at the desktop, viable networking protocols must support encapsulation of virtually any sort of end protocol

• Efficiency is important

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Homework• You must interconnect two tactical networks, separated by

from 15 to 100 kM. IP is used for services at the user desktop, and is 100Base-T extended by a combination of WiFi and WiMAX links, but IP is not deemed suitable for backbone use. What protocol would you select for backbone trunking? Why? Would you argue for IP backbone despite the first direction not to use it? Why? What problems do you anticipate? Why?

• Be prepared to discuss your findings with the class for 5-10 minutes next week. You may use slides if you desire.

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Disclaimer

• Parts of the lecture slides contain original work of William Stallings and Prentice-Hall, and remain copyrighted materials by the original owner(s). The slides are intended for the sole purpose of instruction in computer networks at Worcester Polytechnic Institute.