Ip Networking Over Satelite Course Sampler

Copyright by Burt H. Liebowitz 2004

IP NETWORKING OVERSATELLITE

Burt H. LiebowitzMay 2004

Global Internet

Throughput vs. Round Trip Delay with Window Size as a Parameter

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For Government, Military and Commercial Enterprises


Seminar Outline1- Introduction and Purpose2- Fundamentals of Data Networking3- The Internet and Its Protocols4- Quality of Service Issues in IP Networks5- Satellite Data Networking Architecture6- System Design and Economic Issues for Satellite-

Based IP Networks7- TDMA/DAMA Design Example8- Predicting Performance in Mission-Critical Networks9- Conclusions and a View of the FutureBibliography and Table of Acronyms


Part 2 - Fundamentalsof Data Networking

Sender

Receiver

Network cloud

Application

Link

Application

Application

Host

Satellite node

HostNode

Node

Node

Node

Node

SourceHost

Host Host Destination

Host

Destination

Host

Satellite node

Application

Application

Host

• Overview

• Issues

• Protocol Layers

• Link Layer Protocols– Frame Relay

– ATM

– Aloha

– DVB

– Ethernet

• The Physical Layer


ATM Switching

NetworkHeader

2 bit Payload Typereserved

1 bit priority

8 4 4 8 4 2 1 1 8Header error

control - detects2 bit error; corrects 1

bit error

VPI VPI VCI VCI VCI

EndPoint

EndPoint

These VCs are switched under onevirtual path identifier


Digital Video Broadcast(DVB)

• A world-wide standardfor one-way transmissionof digital TV via satellite(S), cable (C) orterrestrial (T).

• Utilizes MPEG-2compression and packetstandard – fixed size188-byte cells

• Supports data as well asvideo transmissions.

• Supports multipleprogram streams, each ofwhich can be encrypted

• Will discuss in detaillater in the seminar

Satellite dish

Hub LAN

There is areturn linkstandardcalledDVB/RCS

Corporate and ContentProvider Hosts

DVB Hub

Virtual Circuit,Defined by aProgramIdentifier)


pop

Internet Structure

IP Network

IP Network

IP Network

Router

pop poppop

rasras

dasdas

NAP

pop

rasras

AS - Autonomous System

DNS - Domain Name Server

POP - Point of Presence

DAS - Direct Access System

RAS - Remote Access System

NAP - Network Access Point

HostY

(partof X)

Web Client

DNS

Client terminal contains browser toconnect to world-wide-web

Internet ServiceProvider (ISP)

AS 1

AS 3

AS 2

Network X

RouteAdvertisement:Network X ispart of AS1


Impact of TCP Window Size andRTT on Throughput

Throughput vs. Round Trip Delay with Window Size as a Parameter

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0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Round Trip Delay in Seconds

Effect

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Kbps

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8192

16384

32768

65536

window sizein bytes

Effective Throughput in a Non-Congested, Error-Free Link with Channel Speed of2048 Kbps – assuming very long file transfer

Throughput vs. RTT With Window Size as a Parameter

RTT in seconds


Impact of Bit Errors on TCP/IPThroughput

File Size is I MB

RTT is 540 ms

Figure showsimpact of WindowSize (in Kbytes)

It should be notedthat impact of biterrors willdiminish as filesize decreases

Measurements provided courtesyof Mentat Corporation

• Unfortunately TCP cannot tell the difference between a packet loss due to bit errors or congestion -therefore TCP overreacts to bit errors by reducing throughput

• The moral of this story is that it is essential to have a link with a low bit error rate!

-8 -7 -6 -5

Bit Error Rate (10-n)

Effect of Bit Errors on Throughput

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VOIP Integration with IP Networks• Many of the quality issues can be resolved if

VOIP is confined to private networks– steps can be taken to insure that adequate

bandwidth is available to minimize delay, jitter andlost packets.

• This is accomplished by providing ample bandwidthand admissions control (H.323, SIP)

• Integration with PSTN and admissions control viaVOIP Gateways (for both public and private IPNetworks)– digitize, compress, admission control, signaling

– could be part of router

VOIPGate-way

VOIPGate-way

Router

Internet

The PSTN

Local PBX

Local PBX

PrivateIPNetwork

VOIPGate-way

VOIPGate-way

Router


Performance Enhancement - AKA“Session Splitting”

Session Splitter

SessionSplitter ClientThe Net

Terrestrial RTTmoderate size windowStandard TCP protocol

between server and session splitter acting as client

Satellite RTTlarge window

tailored protocol

Terrestrial or LAN RTTmoderate size windowStandard TCP protocol

between client and session splitter acting as server

Without SessionSplitting, throughput

would be determined bytotal RTT and smallest

window size

With session splitting,transfer can take place at

speed determined bydelay of terrestrialInternet and Server

window size

Looks likeclient to real

server

Looks like server toreal client ClientServer

This approach violates theend to end integrity ofTCP- but could be usedwhere the satellite link isthe termination of thesession

Mentat, Flash, Fourelle provide Performance EnhancingSoftware; SkipWare provides PEP based on SCPS


IPsec Modes of Service• Transport (Tactical*)

– Original IP header in the clear, rest of packet is encryptedand authenticated

• Encryption provided at host location– Encryption negotiated between hosts

• Tunnel (Strategic*)– Original IP packet is encrypted including header

• Encryption and new header is provided at tunnel end point (router)– tunnel negotiated between end points associated with networks

*”Tactical” and“Strategic” are terms

used in HAIPE

router router

Routers create tunneland perform encryption

IP NetworkClear Clear

EncryptedEncrypted


Space Segment Overview• Low Earth Orbit (LEO) - 400 to 1000

mile orbit• Medium Earth Orbit (MEO) - 6,250 to

12,500 mile orbit• Geosynchronous Earth Orbit (GEO) -

22,500 mile orbit• We will focus on GEOs*

– most satellite data links are run over GEOs• GEOs can use stationary antennas• GEOs have wide coverage area

– On the other hand• ~250 ms one way delay• distance attenuates signals

*Will discuss LEOs and advanced satellites later in this seminar


Representative Transponder Capacities

Results aregiven inmegabits persecond relativeto a transpondercapacity in MHz;

Note that thesebandwidths areobtainable only ifthe proper linkbudget is used

There is nosuch thing as afree lunch; thehigher bit ratesneed morepower and/orlarger antennas

reed-solomon factor= 0.92 separation factor = 1.2

coding rate > r(1/2) r(3/4) r(5/6) r(7/8)bps/Hztransponder capacity= 36 MHz

QPSK 2 27.6 41.5 46.1 48.48PSK 3 41.5 62.2 69.1 72.616QAM 4 55.3 82.9 92.2 96.8

transponder capacity= 54 MHzQPSK 2 41.5 62.2 69.1 72.68PSK 3 62.2 93.3 103.7 108.916QAM 4 82.9 124.4 138.2 145.1

transponder capacity= 72 MHzQPSK 2 55.3 82.9 92.2 96.88PSK 3 82.9 124.4 138.2 145.116QAM 4 110.6 165.9 184.3 193.5

There is an advantage to saturating a transponder - that is, to putup a single carrier and eliminate backoff. Can get more effectivepower and could reduce separation factor


A Shared Carrier Point to MultipointNetwork

Router

This is also a one to three network;however the carrier uplinked from the hubsite is seen by all the remote sites. Thecarrier is multiplexed. Each packet on thecarrier is identified with a destinationaddress. The appropriate destination (s)select the packet; the others discard thepacket

Shared Carrier Downlink

These are actuallythe same carrier,seen identically by allreceiving stations

Hub site

M

MM Router

MM Router

MM Router

DD

MM

DD

IPNetworks


TDMA/DAMA Return LinksEach site

transmits a burston the same

carrier at specifiedtimes - there canbe no collisions

Combineddownlink to hub

Time Division Multiple Access (TDMA)

Demand Assigned Multiple Access DAMA)


RequestingBandwidth - continued

• Timing Considerations

Tf Tf

Tsd Tsd

Tf

t1 - the time atwhich need for

more bandwidtharises

t2 - the time atwhich theterminal

acquires thenew bandwidth

Taq

Tf Time duration of frame

Tsd One way satellite delay

Taq Time to acquire newbandwidth

Tc - time tocollect requestsat master site

TfTaq ~ 2*Tsd + 3/2* +Tc

Assumption: requests are madeusing low utilization aloha signalingchannel - probability of collision isvery low.


Shared Link Systems Product Offerings

Reference: http://satellitetoday.com/viaonline/issue/0501cover.htm

PRODUCT Outbound/Downstream(from hub)

Inbound/Upstream

(from remote)

Comments

AlohaNet SAMA DVB CDMA/DAMA Aloha upstreamEMS DVB TDMA/DAMA DVB/RCS upstream

Gilat Skyblaster DVB TDMA/DAMAHNS PES Prop. TDM TDMA/DAMA Enterprise

HNS Direcway DVB TDMA/DAMA Consumer and enterpriseRecently introduced as IPOS standard (TIA)

iDIRECT Prop. TDM TDMA/DAMA Supports turbo code on up and down streamNera DVB TDMA/DAMA DVB/RCS upstream

Newtec 2Way-Sat DVB TDMA/DAMA DVB/RCS upstreamRaytheon SMDS 2100 DVB TDMA/DAMA DVB/RCS upstream

Shiron Intersky DVB SCPC/DAMA Can vary carrier size dynamicallySTM Olante DVB TDMA/DAMA DVB/RCS upstream

ViaSat ArcLight DVB CDMA/TDMA/DAMA

overlaps inbound and outbound bandwidth

ViaSat LinkStar DVB TDMA/DAMA Will soon have a DVB/RCS optionViaSat Surfbeam TDM –

DOCSISTDMA-DOCSIS Uses cable modem standard – not yet available:

designed for consumer market


TDMA DAMA Full MeshedNetworks

Similar to TDMA return link except that all remotesites look at the same down link; in that way eachremote site can transmit directly to each other remotesite without having to go thru a hub site

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One site isdesignated as acontrol site; itprocessesbandwidthrequests andcreates theburst plan

12 3

4 6

Remote bursts are combined insatellite and transmitted on acommon downlink frequency


Satellite Adaptation for ReliableMulticast

• Use UDP for downstream

• Receiver sends periodic acks to indicate that some large number of blockshave been successfully received

• When bad block is received– Receiver picks random number to determine when it can send nack

• this is done to prevent all receivers from nacking a block sent in error from the hub

– While waiting to nack, receiver will process new blocks from the sender• during this time, if receiver sees retransmit of bad block, it updates its file and aborts the

nack

• if timer runs out before receiver sees a retransmit, the receiver transmits its nack

12345

Site 1 nacks firstSite 2 aborts nackSite 3 nacks Site 4 aborts nackSite 5 aborts nack

Second nack is ignored

4th block has error on uplink First nack causes sender to retransmit block 4

Hub

There are some scalabilityissues with this approach


A TDMA/DAMA Design Example

• We wish to design a 25-node, hub-based network

• We know the downstream and upstream data and voicerequirements

• We have three architectural alternatives– SCPC – MF/SCPC

– DVB – DVB/RCS

– TDM – MF/TDMA/DAMA (proprietary)

• Our task is to find the most cost-effective solution,considering– Capital costs

• amortized over five years

– Satellite bandwidth costs• based on a monthly lease over a five year period


NETWORK MODEL

Satellite dish

PRIVATENETWORK

R

HUB

INTERNET

25 Sites

• Major Applications– Access to Enterprise Data Base– Specialized Transactions– Email– Web Access– Voice

• 1 Theater

• 25 Sites per Theater ofOperation

• 1 hub per Theater

E

C: call managerE: encryptorF: firewallM: satellite TDM or TDMA modemR: routerV: voice over IP Gateway

V

E M

C

M E R

V C

F

EE


Impact of Number of Busy Sites

Satellite Bandwidth as a Function of Busy Sites

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DVB-RCS

Proprietary

Parameters• 25 sites total• Basic VOIP

– No compression, VAD orencryption

Total Cost Based on Number of Busy Sites

$-

$1,000

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Proprietary


Part 8 – Predicting Performance inMission-Critical Networks

• Overview and Definitions

• A Reference Problem

• Introduction to Queuing Theory– single server

– priority queues

• Application of Queuing Theory to Reference Problem

• Use of Simulation


A Closer Look at the System

• A call center with an operational outpost in an underservedregion of the world (“the remote site”)

• The nominal number of Operators is 192

• Operators answer calls– access a data base at the hub or at company locations (via an intranet)

• Average time between calls per operator is 120 seconds

• Response time is critical, as is voice quality

• We need to know if proposed satellite link can support operatorneeds– If so, can we support even more operators on the link?


R esp o n se an d D elay T im es

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average delay for c rit ic al trans ac tionbw for non-c rit ic al trans ac tionsaverage delay for voic eperc entile for priority voic eperc entile for non-priority voic e

RESPONSE TIME CURVES: We would like to know the average response time for eachof the transactions, based on the number of call takers serviced on the 1.8 Mbps line. In this

way we can see the impact of traffic on response time, and determine if we can indeedhandle the 192 call takers envisioned for this service.

Note: This graph is for traffic flowing from the hub -there will be less traffic in the other direction

192 CallTakers


Part 9 - A View of the Future

• Satellite Enhancements– More power and large antennas

– Spot beams and frequency reuse

– On board processing

– Inter-satellite links

– Ka and higher band satellites

• Advanced Satellites– Commercial

– Military

• The “Ideal” Earth Station


Frequency Reuse can ExpandCapacity of Satellite

• In this example we dividefrequency spectrum into 7segments– Frequency reuse factor is 7

• Assume– 100 beams

– 500 MHz spectrum

• Available frequency =

2*100*500/7

= 14.3 GHz

This factor of 2 comes from antenna polarization

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Baseband Switching

Issues• Complexity

• Takes up weight and power

• Counter productive if too muchmulticast

• Layer 2 or Layer 3 switching?

Switch/Router

demod

demod

receiver

receiver

mod

mod

trans

trans

Benefits• Connectivity for spot beams

– Point to point

– Multicast

• 3 dB gain in link budget– Separation of up and down links

Optional PEP

Optional DAMA


MILITARY DATA NETWORKING SATELLITES- FUTURE

SYSTEM CAPACITY ON BOARD PROCESSING

INTER-SATELLITE LINKS

FREQUENCY BANDS

Wideband Gapfiller Satellite (WGS) First satellite to be launched in 2004

39, 125 Mhz channels preliminary estimate of 2.4 Gbps capacity per satellite

Yes – Channelizer divides capacity into 1872, 2.6 MHz subchannels. Channels can be switched based on network management commands

No X and Ka band (cross-banded)

References: www.losangeles.af.mil/smc/mc/wgs.htm; “Future US Military Satellite Communications Systems"” Glen Elfers and Stephen B. Miller, The Aerospace Corporation www.aero.org/publications/crosslink/winter2002/08.html Advanced EHF Under contract

Gigabits per second capacity Up to 8 Mbps per individual terminal. More than 12 times capacity of Milstar in some scenarios

RF switching Yes, will employ RF cross links

EHF bands because of limited availability of X and Ka for military use

References: “Future US Military Satellite Communications Systems"” Glen Elfers and Stephen B. Miller, The Aerospace Corporation www.aero.org/publications/crosslink/winter2002/08.html

Transformational Satellite (TSAT): EHF communications (44Ghz up; 20Ghz down), Space-based IProuter, .8 to 3.1 Gbps per satellite; Laser Cross Links, Ka and X-band payloads – “Implementing theGlobal Information Grid (GIG), Dr. Michael S. Frankel, DASD


Desirable Attributes for FutureMilitary Terminal

• MF/TDMA/DAMA– Bandwidth on demand with priorities– Can support either star or full mesh– Bandwidth efficient burst allocation

• 100s of terminals per network• Multi-beam support• Efficient bw utilization

– Turbocode or better– Dynamic coding and modulation

(DCM)

• Wide range of coding and modulation– BPSK, QPSK, 8PSK, 16QAM/PSK– Rate ½-8/9

• Multi frequency band– C,Ku,X,Ka

• Uplink power control

• MF/TDMA/DAMA– Bandwidth on demand with priorities– Can support either star or full mesh– Bandwidth efficient burst allocation

• 100s of terminals per network• Multi-beam support• Efficient bw utilization

– Turbocode or better– Dynamic coding and modulation

(DCM)

• Wide range of coding and modulation– BPSK, QPSK, 8PSK, 16QAM/PSK– Rate ½-8/9

• Multi frequency band– C,Ku,X,Ka

• Uplink power control

• L-band IF interface• Remote site can support up to 2 Mbps• Wide range of terrestrial interfaces• Network Management channel• Router functionality

– Basic routing functions– High degree of QoS including

• MLPP (Multilevel Precedence andPreemption)

– Header Compression

• Built in TCP performanceenhancement

• High level of Security– Large keys, AES and 3DES– Authentication

• L-band IF interface• Remote site can support up to 2 Mbps• Wide range of terrestrial interfaces• Network Management channel• Router functionality

– Basic routing functions– High degree of QoS including

• MLPP (Multilevel Precedence andPreemption)

– Header Compression

• Built in TCP performanceenhancement

• High level of Security– Large keys, AES and 3DES– Authentication

REFERENCE: “IP Modem Functional Capabilities Description” (FCD) Version 1.5April 15, 2004, Defense Information Systems Agency (DISA)

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Ip Networking Over Satelite Course Sampler

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