© 2006 Cisco Systems, Inc. All rights reserved.ONT v Implement the DiffServ QoS Model Understanding WAN Link Efficiency Mechanisms

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Link Efficiency Mechanisms Overview

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Compression Data compression works by the identification of patterns in a stream of data. Basic elements of compression: –Remove redundancy as much as possible. –There is a theoretical limit, known as Shannon's limit. Many compression algorithms exist, for different purposes: –MPEG compression for video –Huffmann compression for text and software –LZ compression, used in Stacker compression Two methods of compression are used: –Hardware compression –Software compression

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Compression (Cont.) Payload compression reduces the size of the payload. Header compression reduces the header overhead. Compression increases throughput and decreases latency.

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Link Efficiency Mechanisms Link efficiency mechanisms are often deployed on WAN links to increase the throughput and to decrease delay and jitter. Cisco IOS link efficiency mechanisms include: –Layer 2 payload compression (Stacker, Predictor, MPPC) –Header compression (TCP, RTP, class-based TCP, and class-based RTP) –LFI (MLP, FRF.12, and FRF.11.C)

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Layer 2 Payload Compression

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Layer 2 Payload Compression Layer 2 payload compression reduces the size of the frame payload. Entire IP packet is compressed. Software compression can add delay because of its complexity. Hardware compression reduces the compression delay. Serialization delay is reduced; overall latency might be reduced.

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Layer 2 Payload Compression Results Compression increases throughput and decreases delay. Use hardware compression when possible. Examples are Stacker, Predictor, and MPPC.

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Header Compression

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Header Compression

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Header Compression Results Header compression increases compression delay and reduces serialization delay.

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Large Packets Freeze Out Voice on Slow WAN Links

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Large Packets Freeze Out Voice on Slow WAN Links Problems: Excessive delay due to slow link and MTU-sized (large) packets Jitter (variable delay) due to variable link utilization

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Large Packets Freeze Out Voice on Slow WAN Links Problems: Excessive delay due to slow link and MTU-sized (large) packets Jitter (variable delay) due to variable link utilization

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Large Packets Freeze Out Voice on Slow WAN Links Problems: Excessive delay due to slow link and MTU-sized (large) packets Jitter (variable delay) due to variable link utilization

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Large Packets Freeze Out Voice on Slow WAN Links Problems: Excessive delay due to slow link and MTU-sized (large) packets Jitter (variable delay) due to variable link utilization

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Link Fragmentation and Interleaving

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Link Fragmentation and Interleaving LFI reduces the delay and jitter of small packets (such as VoIP).

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Applying Link Efficiency Mechanisms

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Applying Link Efficiency Mechanisms Identify bottlenecks in the network. Calculate Layer 2 and Layer 3 overhead. Decide which type of compression to use, such as TCP header compression. Enable compression on WAN interfaces.

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Example

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Summary Data compression effectively increases bandwidth. Link efficiency mechanisms (including Layer 2 payload compression, header compression, and LFI) deployed on WAN links can increase throughput and decrease delay and jitter. Payload compression uses a compression algorithm to compress the payload of Layer 2 frames. Header compression reduces overhead by compressing the IP and upper-layer headers. A VoIP packet may be sent to the hardware TxQ, where large FTP packets may still be waiting for transmission. The VoIP packet must wait until the large packets are transmitted, producing an unacceptable delay in the voice path.

© 2006 Cisco Systems, Inc. All rights reserved.ONT v Summary (Cont.) LFI reduces delay and jitter for small packets (for example, VoIP) by fragmenting large packets to allow a VoIP packet to wait no more than a predefined amount of time. Header compression and LFI are typically configured at the WAN edge for WAN links below T1 or E1 speeds, to optimize the use of the WAN link and to prevent long serialization delay. Layer 2 payload compression is less commonly being deployed on WAN links.

© 2006 Cisco Systems, Inc. All rights reserved.ONT v