Cisco Systems 78-13983-04 manual Redundancy Support, RTP Header Compression

Chapter 1 Overview of the MWR 1900

Software Features

Figure 1-2 RTP Header Compression

Before RTP header compression:

20 bytes	8 bytes 12 bytes
IP	UDP	RTP	Payload
Header			20 to 160 bytes

After RTP header compression:

2 to 4 bytes

Payload

IP/UDP/RTP header 20 to 160 bytes

12076

RFCs 2508 and 2509 describe a method for compressing not only the RTP header, but also the associated UDP and IP headers. Using this method, the 40 bytes of header information is compressed into approximately 2 to 4 bytes, as shown in Figure 1-2. Because the frames are compressed on a link-by-link basis, the delay and loss rate are lower, resulting in improved performance.

The MWR 1900 network processor offloads both the compression and decompression of RTP frames from the Cisco IOS software.

Note The MWR 1900 router can be configured to perform only IP/UDP compression, in which case the header is reduced from 28 bytes to 2 to 4 bytes.

Redundancy Support

To ensure availability, the backhaul links to an MWR 1900 router are redundantly cabled to the VWIC-2MFT-T1-DIR/ VWIC-2MFT-E1-DIR cards. This card, designed specifically for the MWR 1900 router, is a modified 2-port T1/E1 Multiflex VWIC with Drop and Insert.The modifications include the addition of relays to activate the T1/E1 ports. The relays allow “Y” cabling for router redundancy where the T1/E1 link is not redundant and default to open. The relays are controlled by HSRP/redundancy protocol between the two routers connected to the same T1/E1.

Note If you choose to use the MWR 1900 router in a non-redundant configuration, you must close the relays on the card using the standalone subcommand. Also, redundancy parameters are processed when the router is booted up. These parameters cannot be changed “on the fly.”

Cisco MWR 1900 Mobile Wireless Edge Router Software Configuration Guide

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