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31Taking as many defaults as possible, list the configuration commands needed to configure precedence-based FRED on interface S1/1.
interface serial 1/1
random-detect flow-based
By using the random-detect flow-based command, Cisco IOS Software adds the random-detect command automatically.
32Taking as many defaults as possible, list the configuration commands needed to configure DSCP-based FRED on interface S1/1.
interface serial 1/1
random-detect dscp-based
random-detect flow-based
If you had just used the random-detect flow-based command, and not the randomdetect dscp-based command, Cisco IOS Software would have added the randomdetect command automatically, which enables precedence-based WRED.
Chapter 7
“Do I Know This Already?” Quiz
Compression
1Describe what is compressed, and what is not compressed, when using payload compression. Be as specific as possible regarding headers and data.
Payload compression does not compress the data-link header and trailer, but it does compress all the headers and data between the two. Specifically, the IP, TCP, UDP, RTP headers as appropriate, and the user data, are compressed.
2Describe what is compressed, and what is not compressed, when using TCP header compression. Be as specific as possible regarding headers and data.
IP packets that also have TCP headers are compressed. The compression algorithm does not compress the data-link header or trailer. It does compress both the IP and TCP headers. It does not compress any user data that follows the TCP header.
808 Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Sections
3Describe what is compressed, and what is not compressed, when using RTP header compression. Be as specific as possible regarding headers and data.
IP packets that also have RTP headers are compressed. The compression algorithm does not compress the data-link header or trailer. It does compress the IP, UDP, and RTP headers. It does not compress any user data that follows the RTP header.
4List the three point-to-point payload compression options available in IOS.
Stacker, Microsoft Point-to-Point Compression (MPPC), and Predictor.
5When TCP header compression is used, what is the range of sizes of the part of the frame that can be compressed, and what is the range of sizes for this field of the frame after compression?
TCP header compression compresses the 20-byte IP header and 20-byte TCP header, with the combined field size of 40 bytes. The compressed field will be between 3 and 5 bytes.
6When RTP header compression is used, what is the range of sizes of the part of the frame that can be compressed, and what is the range of sizes for this field of the frame after compression?
RTP header compression compresses the 20-byte IP header, 8-byte UDP header, and 12-byte RTP header, with the combined field size of 40 bytes. The compressed field will be between 2 and 4 bytes.
Link Fragmentation and Interleave
7List the words represented by the abbreviation LFI.
Link fragmentation and interleaving.
8To achieve a 20-ms serialization delay on a 128-kbps link, how long can the fragments be?
The formula is max-delay * bandwidth, which is .02 * 128,000 = 2560 bits, or 320 bytes.
9What queuing tools can you enable directly on a serial interface when using multilink Point-to-Point Protocol with link fragmentation and interleaving (MLP LFI), as compared to when you are just using PPP?
All the queuing tools available for use with PPP are also available with MLP LFI. There are no restrictions.
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10What command can you use to determine the fragment size used for MLP LFI? What is the only parameter of the command?
The ppp multilink fragment-delay command sets the maximum serialization delay in milliseconds. IOS calculates the fragment size using the formula max-delay * bandwidth.
11What command enables FRF and sets the fragment size?
The frame-relay fragment fragment_size command.
12What other QoS feature for Frame Relay must you enable when you configure FRF.12 as well?
Frame Relay traffic shaping (FRTS).
Q&A
Compression Tools
1Describe what is compressed, and what is not compressed, when using payload compression. Be as specific as possible regarding headers and data.
Payload compression does not compress the data-link header and trailer, but it does compress all the headers and data between the two. Specifically, the IP, TCP, UDP, RTP headers as appropriate, and the user data, are compressed.
2Describe what is compressed, and what is not compressed, when using TCP header compression. Be as specific as possible regarding headers and data.
IP packets that also have TCP headers are compressed. The compression algorithm does not compress the data link header or trailer. It does compress both the IP and TCP headers. It does not compress any user data that follows the TCP header.
3Describe what is compressed, and what is not compressed, when using RTP header compression. Be as specific as possible regarding headers and data.
IP packets that also have RTP headers are compressed. The compression algorithm does not compress the data-link header or trailer. It does compress the IP, UDP, and RTP headers. It does not compress any user data that follows the RTP header.
4List the three point-to-point payload compression options available in IOS.
Stacker, Microsoft Point-to-Point Compression (MPPC), and Predictor.
