TcpIp Compression in Satellite Environment

8/9/2019 TcpIp Compression in Satellite Environment

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TCP/IP HeaderCompression for

Satellite Environment

Dmitry BatenkovDmitry Batenkov

Vladislav ZolotarovVladislav Zolotarov

Ittay EyalIttay Eyal

Itai RavidItai Ravid

Doris FischerDoris Fischer


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Part I

Satellite Environment

Dmitry BatenkovDmitry Batenkov

Vladislav ZolotarovVladislav Zolotarov


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Compressor

Satellite

Channel

Simulator

Decompressor

Server Client

Topology (5 stations case)


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Server Client

Compressor SATSIM Decompressor

Topology (3 stations case)


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Compression

module

Compression

thread

Receiving

moduleFrom

Server

Sending

moduleTo

SatSim

Compression station


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Sending

module

Receiving

module

Decompression

module

Decompression

thread

SatSim Client

Sending

module

Receiving

moduleForwarding thread

Decompression station


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Decompressor

Server Sending

module

Receiving


Compressor Receiving

module

Sending

module

SATSIM Module

Satellite channel simulator

(5 stations case)


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Server Client

Sending

module

Receiving


Receiving

module

Sending

module

SATSIM Module

Compression

module

Decompression

module

Satellite channel simulator

(3 stations case)


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SendPacket()

NDIS AdapterWinDis

Sending thread

APC callback

Recycling

Sending module


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GetNextPacket()

Receiving thread

NDIS Adapter

APC callback

WinDis

Posting

initial reads

Posting

additional

reads

Access synchronization

Receiving module


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Main thread

Receiving

module

Compression

module BER

Sending

module

Decompression

module

Delay = 0

Second threadTS

TS

TS

TS

TS

TS

Due time

arrived?

SATSIM


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Part IITCP/IP Header Compression

Ittay EyalDoris Fischer

Itai Ravid


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TCP/IP HeaderCompression

Protocol for compressing the TCP/IP header

part of the packet

Based on RFC1144 created by Van Jacobsonin 1990, during his research work at Cisco Ltd.

Compression can get up to 1/8 the size of the

original header (from 40 bytes into 5 bytes)

Originally meant to speed up Low-Speed

Serial Links


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TCP/IP HeaderCompression Cont.

In TCP/IP packet the header size is 40 bytes

Though in low speed connections the

overhead of an error in the header part of the

packet takes a high percentage of the

communication

In some modern technology (like satellite

communication) we find this overhead, crucialbecause of the long delay time while crossing

the atmosphere


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Protocol Main Ideas

High percentage of the packet header stay

constant during a connection

Therefore if we knew what were the fields inthe previous packet header, we can omit fields

that stay constant in the current packet header

We can decrease size of fields that change in a

small amount by passing only the difference in

the fields content (difference relative to the

previous packet header)


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Protocol Details

V. Jacobson suggests we keep an

uncompressed copy of the previous packet

header, on each side of the connection

That way we will update its changed fields eachtime we get a packet

A full packet header will be passed only in the

first packet of a connection (passing also

constant fields of the header) or after an error

Afterwards we will pass only the changed fields

in the packet header


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Protocol

Details

Cont.Since not all the fields change in the same

time, we will pass a bit mask field in each

beginning of a compressed packet

The bit mask field will indicate which fields

have changed from the previous packet

header

The bit mask will have a constant order,

though only the 1s bits will indicate a

changed field


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Protocol Details Cont.

In V. Jacobson suggestion he indicates

the packet compression kind:

TYPE_IP - header content wasn

t touched UNCOMPRESSED_TCP if the connection

number is stamped into the header (in the

IPPROTO_TCP field), but the content of the

other fields didnt change

COMPRESSED_TCP the packet header is

fully compressed


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Protocol

Details

Cont.According to the packet type the

decompressing computer can determine how

it should handle the packet

Decompression is done easily because we

know what was the previous packet header

content

The reversed process is done in order to

decompress the packet headers


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Protocol

Details

Cont.

The changed fields (in which we send the

difference values) are added to the previous

packet header stored in the decompressioncomputer

Checksum is recalculated according to the

updated fields content


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Assurance of the protocolFields content is always recoverable,

because in all times we know what content

was in the previous packet

We can calculate the current full packet

header, in each new packet that arrives

Lost packets (during the communicationprocess) are recovered using the regular

TCP/IP protocol. Regardless to the

compression process


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Benefit of HeaderCompression

Header benefit of compressed packet

(without noise)

0

0.01

0.02

0.03

0.04

13906 44544 489971 6726428 3.5E+07 8.7E+07

File size (Bytes)

Compressionbenefit(%)

Pol .


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Benefit of HeaderCompression

Header benef t ofcompressed packet (wit noise)

-

-- 3

- 2

-

23

3 6 3 6 7

File size (Bytes)

Com

pressionbenefit(%)


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TcpIp Compression in Satellite Environment

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