Information Technology Reference
In-Depth Information
PoS interfaces. Packets in PoS interfaces can be marked by setting IP Precedence bits. IP
Precedence bits enable mechanisms such as CAR, RED, and WRED on the network.
Compression
Cisco internetworking devices use the Stacker and Predictor data compression algorithms.
Stacker is based on the Lempel-Ziv (LZS) compression algorithm. LZS is available in Cisco's
Link Access Procedure, Balanced (LAPB), high-level data link control (HDLC), X.25, and
Frame Relay data compression solutions. FRF.9 and IP Payload Compression (IPComp)
protocol use the LZS compression algorithm.
The Predictor compression algorithm tries to predict the next sequence of characters in the data
stream by using an index to look up a sequence in the compression dictionary.
The Predictor data compression algorithm makes more efficient use of CPU cycles but requires
more memory. You can use both LZS and Predictor data compression algorithms with Point-to-
Point Protocol (PPP) or LAPB encapsulated interfaces.
HDLC Interface Compression
Under HDLC interfaces, the Stacker compression is the only method available for compression.
The configuration is shown in Example 11-15.
Example 11-15
Stacker Compression Configuration
R5(config)#interface serial 1
R5(config-if)#compress ?
stac stac compression algorithm
R5(config-if)#compress stac
TCP Header Compression
Another compression method is TCP header compression, which is described in RFC 1144,
“Compressing TCP/IP Headers for Low-Speed Serial Links.” Because of the processing over-
head, you generally use TCP header compression on links with speeds of 64 kbps or less. You
must use only this form of compression to gain advantage for interactive traffic with small pay-
loads, such as Telnet. Header compression can produce varying throughput improvements
across low-speed lines depending on line rate. Header compression is enabled on an interface
as follows:
R5(config-if)#ip tcp header-compression
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