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 7-19 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.)

Figure 7-19 Payload and Header Compression

Payload Compression

Payload Compression

DL

IP

TCP

Data

DL

TCP Header Compression RTP Header Compression

( N

DL

IP

UDP

RTP

Data

DL

Table 7-16 outlines the main points of comparison for the three payload compression tools.

Table 7-16 Point-to-Point Payload Compression tools—Feature Comparison

Table 7-16 outlines the main points of comparison for the three payload compression tools.

Table 7-16 Point-to-Point Payload Compression tools—Feature Comparison

Feature

Stacker

MPPC

Predictor

Uses Lempel-Ziv (LZ) compression algorithm

Yes

Yes

No

Uses Predictor public domain compression algorithm

No

No

Yes

Supported on High-Level Data Link Control (HDLC)

Yes

No

No

Supported on X.25

Yes

No

No

Supported on Link Access Procedure, Balanced (LAPB)

Yes

No

Yes

Supported on Frame Relay

Yes

No

No

Supported on Point-to-Point Protocol (PPP)

Yes

Yes

Yes

Supported on ATM (using multilink PPP)

Yes

Yes

Yes

Table 7-17 list the various configuration and show commands used with payload compression.

Table 7-17 Configuration Command Reference for Payload Compression

Table 7-17 list the various configuration and show commands used with payload compression.

Table 7-17 Configuration Command Reference for Payload Compression

Command

Mode and Function

compress predictor

Interface configuration mode; enables Predictor compression on one end of the link.

compress stac

Interface configuration mode; enables Stacker compression on one end of the link.

compress mppc [ignore-pfc]

Interface configuration mode; enables MPPC compression on one end of the link.

compress stac [distributed | software]

Interface configuration mode; on 7500s with VIPs, allows specification of whether the compression algorithm is executed in software on the VIP.

compress {predictor | stac [csa slot | software]}

Interface configuration mode; On 7200s, allows specification of Predictor or Stacker compression on a compression service adapter (CSA).

compress stac caim element-number

Interface configuration mode; enables Stacker compression using the specified compression AIM.

frame-relay payload-compress {packet-by-packet | frf9 stac

[hardware-options] | data-stream stac [hardware-options]}

Interface configuration mode; enables FRF.9 or data-stream style compression on one end of a Frame Relay link. Hardware-options field includes the following options: software, distributed (for use w/VIPs), and CSA (7200s only).

The TCP and RTP header compression configuration process, as mentioned, is very simple. Tables 7-18 and 7-19, respectively, list the configuration and show commands.

Table 7-18 Configuration Command Reference for TCP and RTP Header Compression

Command

Mode and Function

ip tcp header-compression [passive]

Interface configuration mode; enables TCP header compression on point-to-point links.

ip rtp header-compression [passive]

Interface configuration mode; enables RTP header compression on point-to-point links.

frame-relay ip tcp headercompression [passive]

Interface/subinterface configuration mode; enables TCP header compression on point-to-point links.

frame-relay ip rtp header-compression [passive]

Interface or subinterface configuration mode; enables RTP header compression on point-to-point links.

Table 7-18 Configuration Command Reference for TCP and RTP Header Compression (Continued)

Command

Mode and Function

frame-relay map ip ip-address dlci [broadcast] tcp header-compression [active | passive] [connections number]

Interface or subinterface configuration mode; enables TCP header compression on the specific VC identified in the map command.

frame-relay map ip ip-address dlci [broadcast] rtp header-compression [active | passive] [connections number]

Interface or subinterface configuration mode; enables RTP header compression on the specific VC identified in the map command.

Table 7-19 Exec Command Reference for TCP and RTP Header Compression

Command

Function

show frame-relay ip rtp headercompression [interface type number]

Lists statistical information about RTP header compression over Frame Relay; can list information per interface

show frame-relay ip tcp headercompression

Lists statistical information about TCP header compression over Frame Relay

show ip rtp header-compression

[type number] [detail]

Lists statistical information about RTP header compression over point-to-point links; can list information per interface

show ip tcp header-compression

Lists statistical information about TCP header compression over point-to-point links

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 7-20 outlines the basic process.

Figure 7-20 Basic Concept Behind LFI Tools

Interface Output Queue, no LFI

Figure 7-20 Basic Concept Behind LFI Tools

Interface Output Queue, no LFI

Interface Output Queue, with LFI, 300 Byte Fragments

300 Byte Fragment #5 of Original

300 Byte

300 Byte

Fragment

Fragment

#4 of

#3 of

Original

Original

300 Byte Fragment #2 of Original

Delay Sensitive 60 Byte Packet

300 Byte

Fragment

#1 of

Original

Figure 7-21 depicts how MLP LFI works with a queuing tool on an interface.

Figure 7-21 MLP LFI Interaction with Queuing

1500 Byte Packet Arrives, Followed by One 60 Byte Packet

1500 Byte Packet Arrives, Followed by One 60 Byte Packet

For perspective, Table 7-20 summarizes the calculated fragment sizes based on the bandwidth and maximum delay.

Table 7-20 Fragment Sizes Based on Bandwidth and Serialization Delay

For perspective, Table 7-20 summarizes the calculated fragment sizes based on the bandwidth and maximum delay.

Table 7-20 Fragment Sizes Based on Bandwidth and Serialization Delay

Bandwidth/Link Speed

10-ms Delay

20-ms Delay

30-ms Delay

40-ms Dela

y

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

1600*

3200*

4800*

6400*

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.

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 7-22 outlines the main concept.

Figure 7-22 Classification Between FRTS LLQ Shaping Queues and Interface Dual FIFO Queues with FRF.12

Shaping Queues Created by LLQ Configuration

Shaping Queues Created by LLQ Configuration

Table 7-21 summarizes the queuing tools and identifies when you can use them with FRTS and FRF.12:

Table 7-21 Queuing Tool Support with FRTS and FRF.12 (IOS 12.2 Mainline)

Desired Features

Queuing Tools Supported on Each VC (Shaping Queues)

FRTS only

FIFO, PQ, Custom Queuing (CQ), Weighted Fair Queuing (WFQ), Class Based Weighted Fair Queuing (cBWFQ), LLQ, IP RTP Priority

FRTS with FRF.12 enabled

WFQ, CBWFQ, LLQ, IP RTP Priority

FRTS, FRF. 12, with actual interleaving of packets

LLQ, IP RTP Priority

Table 7-22 summarizes the core functions of MLP LFI versus FRF. 12, particularly how they each interact with the available queuing tools.

Table 7-22 Comparisons Between MLP LFI and FRF.12

Table 7-22 summarizes the core functions of MLP LFI versus FRF. 12, particularly how they each interact with the available queuing tools.

Table 7-22 Comparisons Between MLP LFI and FRF.12

Step in the Process

MLP LFI

FRF.12

Configures maximum delay, or actual fragment size

Maximum delay

Fragment size

Classification into the interface output queues

Based on the queuing tool enabled on the interface

All packets coming from LLQ or RTP Priority shaping queues placed in higher-priority queue

Table 7-22 Comparisons Between MLP LFI and FRF.12 (Continued)

Step in the Process

MLP LFI

FRF.12

Number of interface output queues

Based on the queuing tool enabled on the interface

2 queues, called Dual FIFO

How queue service algorithm causes interleaving to occur

Based on queuing tool's inherent queue service algorithm; PQ, LLQ, and RTP Priority most aggressively interleave packets

PQ-like algorithm, always servicing High queue over Normal queue

* The popular theory disagrees with this table. The popular theory states that all unfragmented packets end up in the high-priority queue, and all fragments end up in the Normal queue.

* The popular theory disagrees with this table. The popular theory states that all unfragmented packets end up in the high-priority queue, and all fragments end up in the Normal queue.

MLP, by its very nature, fragments packets. Figure 7-23 shows what really happens.

Figure 7-23 MLP Bundle with 3 Active Links—What Does Happen

---, f

500 (Frag 1)

----

->•

500 (Frag 2)

> *

100 1500

->

R2 1 100 1500

500 (Frag 3)

1

Tables 7-23 and 7-24 list the pertinent configuration and show commands for MLP interleaving, respectively.

Table 7-23 Configuration Command Reference for MLP Interleaving

Command

Mode and Function

ppp multilink [bap]

Interface configuration mode; enables multilink PPP on the interface, dialer group, or virtual template

ppp multilink interleave

Interface configuration mode; enables interleaving of unfragmented frames with fragments of larger frames

ppp multilink fragment delay time

Interface configuration mode; enables MLP fragmentation, and defines fragment size, with formula bandwidth/time

ppp multilink fragment disable

Interface configuration mode; disables MLP fragmentation

ppp multilink group group-number

Interface configuration mode; links a physical interface to a dialer group or virtual template

Table 7-24 Exec Command Reference for MLP Interleaving

Command

Function

show ppp multilink

Lists information about the active links currently in the same MLP bundle

show interfaces

Lists statistics and status about each interface, including multilink virtual interfaces

show queueing [interface atm-subinterface [vc [[vpi/] vci]]]

Lists configuration and statistical information about the queuing tool on an interface

Tables 7-25 and 7-26 list the configuration and show commands for Frame Relay fragmentation, respectively.

Table 7-25 Command Reference for Frame Relay Fragmentation

Command

Mode and Function

frame-relay traffic-shaping

Interface subcommand; enables FRTS on the interface.

class name

Interface DLCI subcommand; enables a specific FRTS map-class for the DLCI.

frame-relay class name

Interface or subinterface command; enables a specific FRTS map-class for the interface or subinterface.

map-class frame-relay map-class-name

Global Configuration mode; Names a map-class, and places user in map-class configuration mode

frame-relay fragment fragment size

Map-class configuration mode; enables FRF.12 for VCs using this class

Table 7-26 Exec Command Reference for Frame Relay Fragmentation

Command

Function

show frame-relay fragment [interface interface] [dlci]

Shows fragmentation statistics

show frame-relay pvc [interface-type interface-number] [dlci]

Shows statistics about overall performance of a VC

show queueing [interface atm-subinterface [vc [[vpi/] V«]]]

Lists configuration and statistical information about the queuing tool on an interface

Figure 7-24 shows the framing when FRF.3 and FRF. 11 are used, both for IP telephony traffic and for local voice gateway traffic.

Figure 7-24 Framing of Voice Traffic with FRF.3 and FRF. 11 VCs

With Data VC

With VoFR VC

IP Telephone Traffic

FRF.3 Header

IP

UDP

RTP

G.729 Voice

FRF.3 Trailer

Voice Gateway Traffic

FRF.3 Header

IP

UDP

RTP

G.729 Voice

IP Telephone Traffic

FRF.3

FRF.11

G.729

FRF.3

Header

Header

IP

UDP

RIP

Voice 1

Trailer |

Voice Gateway Traffic

FRF.3

FRF.11

G.729

FRF.3

Header

Header

Voice

Table 7-27 summarizes some of the key comparison points about FRF. 12 and FRF. 11-C.

Table 7-27 FRF.11-C and FRF.12 Comparison

Table 7-27 summarizes some of the key comparison points about FRF. 12 and FRF. 11-C.

Table 7-27 FRF.11-C and FRF.12 Comparison

Function

FRF.12 Behavior

FRF.11-C Behavior

Queuing option on the interface output queues

Dual FIFO

Dual FIFO

Classification into the interface output queues

Based on queuing tool used for shaping, with LLQ and IP RTP Priority putting packets into the high-priority queue

Voice frames placed in High queue, all others in Normal queue, regardless of shaping queue configuration

Fragmentation based on size, or type of packet

Based only on size; must be careful not to fragment voice packets

Nonvoice frames fragmented, and voice frames are not, regardless of size

Frame Relay network can be aware of voice vs. nonvoice frames, and acts accordingly

No

Yes

Underlying type of VC, and general public availability

FRF.3, available from most if not all public Frame Relay services

FRF.11, not generally available from public Frame Relay services

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