Foundation Summary

The "Foundation Summary" is a collection of tables and figures that provide a convenient review of many key concepts in this chapter. For those of you already comfortable with the topics in this chapter, this summary could help you recall a few details. For those of you who just read this chapter, this review should help solidify some key facts. For any of you doing your final prep before the exam, these tables and figures are a convenient way to review the day before the exam.

Figure 8-17 shows the fields compressed by payload compression, and by both types of header compression. (The abbreviation "DL" stands for data link, representing the data-link header and trailer.)

LFI tools attack the serialization delay problem by breaking the large packets into smaller pieces (fragmentation), and then sending the smaller frames ahead of most of the new fragments of the original large frame (interleaving). Figure 8-18 outlines the basic process.

Figure 8-19 depicts how MLP LFI works with a queuing tool on an interface.

Figure 8-19. MLP LFI Interaction with Queuing

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For perspective, Table 8-12 summarizes the calculated fragment sizes based on the bandwidth and maximum delay.

Table 8-12. Fragment Sizes Based on Bandwidth and Serialization Delay

Bandwidth/Link Speed	10-ms Delay	20-ms Delay	30-ms Delay	40-ms Delay
56 kbps	70	140	210	280
64 kbps	80	160	240	320
128 kbps	160	320	480	560
256 kbps	320	640	960	1280
512 kbps	640	1280	1920[*]	2560[*]
768 kbps	1000	2000[*]	3000[*]	4000[*]
1536 kbps	2000[*]	4000[*]	6000[*]	8000[*]

^[*] Values over 1500 exceed the typical maximum transmit unit (MTU) size of an interface. Fragmentation of sizes larger than MTU does not result in any fragmentation.

Two of these queuing tools, if enabled on the shaping queue of a VC, cause packets to be placed in the High Dual FIFO queue on the physical interface. Figure 8-20 outlines the main concept.

MLP, by its very nature, fragments packets. Figure 8-21 shows what really happens.

To help you focus on the commands used specifically for LFI, Table 8-13 summarizes the commands and related information.

Table 8-13. MLP LFI and FRF.12 Configuration: The Essentials

Function	MLP LFI Behavior	FRF.12 Behavior
Config command	ppp multilink fragment-delay delay ppp multilink interleave	frame-relay fragment size
Config mode	The config mode reached by using the interface multilink y command	The config mode reached by using the map-class frame-relay command
Other required features	MLP	FRTS
How to configure Queuing to cause Interleaving	Enable a queuing tool with PQ, like LLQ, under the multilink interface	Enable a queuing tool with PQ, like LLQ, under the map-class frame-relay command
Important show commands	show interface multilink	show frame-relay fragment show queueing interface x/y
Info in those show commands	Statistics on numbers of fragments and interleaves	Statistics on numbers of fragments, plus stats on Dual-FIFO queue interleaving, respectively