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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Command Reference, Cisco IOS Release 15.1(3)MR
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Chapter Cisco MWR 2941 Router Command Reference, Release 15.1(3)MR
ip rtp header-compression
Usage Guidelines You can compress IP/User Datagram Protocol (UDP)/RTP headers to reduce the size of your packets.
Compressing headers is especially useful for RTP because RTP payload size can be as small as 20 bytes,
and the uncompressed header is 40 bytes.
ietf-format Keyword
The ietf-format keyword indicates that the IETF format of header compression will be used. For HDLC
interfaces, the ietf-format keyword compresses only UDP packets. For PPP interfaces, when the
ietf-format keyword is specified, TCP header compression is also enabled. For this reason, the ip tcp
header-compression command appears in the output of the show running-config command. Because
both RTP header compression and TCP header compression are enabled, both UDP packets and TCP
packets are compressed.
Note The Cisco MWR 2941 supports UDP header-compression in IEFT format only.
With the ietf-format keyword, any even destination port number higher than 1024 can be used. Valid
RTP packets that meet the criteria (that is, the port number is even and is higher than 1024) are
compressed using the compressed RTP packet format. Otherwise, packets are compressed using the
less-efficient compressed non-TCP packet format.
Note The header compression format (in this case, IETF) must be the same at both ends of the network. That
is, if you specify the ietf-format keyword on the local router, you must also specify the ietf-format
keyword on the remote router.
Support for Distributed IPHC on Multilink Interfaces
You can use the configure distributed IPHC (dIPHC) on a multilink interface for improved Multilink
Point-to-Point Protocol (MLPPP) performance.
Distributed IP Header Compression (dIPHC) allows the Cisco MWR 2941 to compress IP packet headers
for more efficient use of bandwidth. Release 3.5 improves dIPHC performance by shifting processing
from the main CPU to the network processor.
When using the ip rtp header-compression ietf-format command for dIPHC on a multilink interface,
note the following:
• The Cisco MWR 2941 supports for UDP traffic only.
• The Cisco MWR 2941 supports up to 300 dIPHC sessions over 3 multilinks.
• The Cisco MWR 2941 supports only the IEFT format of IPHC.
• The Cisco MWR 2941 supports dIPHC only for UDP traffic.
• After enabling dIPHC on an interface, ensure that you “flap” the interface by using the shutdown
and no shutdown commands in interface configuration mode for the configuration to take effect.
• If a QoS policy is attached to the multilink interface on which IPHC has been enable, ensure that
you configure the platform header-compression match access-group command in interface
configuration mode to apply an extended named Access Control List (ACL) of static flows (source
IP address, destination IP address, and destination port) to compress using IPHC.
You must configure the matching ACL as an extended named access-list and add the static flow
configuration to a Multilink interface that is in an UP state and on which the ip rtp
header-compression command is configured.
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