Class Based TCP Header Compression Example Cont

20 20

ppp

IP

TCP

Telnet

V J

PPP

cTCP

Telnet

v 1

^ y

Overhead = 46 / (46 + 5) Overhead = 90% Delay = (46 + 5) / 64 kbps Delay = 6 ms

10 5

Overhead = 10/(10+ 5) Overhead = 67% Delay = (10 + 5) / 64kbps * 8 Delay = 2 ms

Pay load

Overhead

Delay on

Overhead

Delay on

size

No comp.

64 kbps

Comp.

64 kbps

10

82%

7 ms

50%

2 ms

50

48%

12 ms

17%

7 ms

100

32%

18 ms

9%

13 ms

500

8%

67 ms

2%

62 ms

1500

3%

189 ms

1%

184 ms

Systems, Inc. All rights reserved

Systems, Inc. All rights reserved

The figure shows the packet size before and after TCP header compression. After TCP header compression, the IP and TCP headers are reduced to 4 bytes, resulting in 10 bytes of overall headers. The overhead is reduced from 90 percent to 67 percent when small packets are used. Because of the packet size reduction, the serialization delay decreases from 6 ms to 2 ms on the same 64-kbps link.

The table in the figure shows how TCP header compression impacts performance when different packet sizes are used. TCP header compression is most effective on small packets, and is often used on slow links.

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