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New Member

CCME-VPN-QOS-CRTP compression not working

The network topology for our configuration is :

One router 2821 with ccme installed and from atm (dsl) interfaces we have VPN tunnels to two remote offices

Each office has a c870 router and 7912 cisco ip phones

We want to activate the crtp compression for network bandwith savings

The configuration for qos in 2821 router is :

class-map match-any voice-signaling

match dscp af31

match protocol sip

class-map match-any voice-udp

description Class Mapping for VoIP RTP

match dscp ef

match protocol rtp

!

!

policy-map voice-qos

description VoIP QoS

class voice-udp

priority percent 50

compress header ip rtp

class voice-signaling

bandwidth 8

class class-default

fair-queue

compress header ip tcp

the policy-map is bound to dialers interfaces

The configuration for qos in each c870 router is the same as above

The output of the ?sh ip rtp header-compression? command for the 2821 router is :

RTP/UDP/IP header compression statistics:

We're compressing using MQC profiles, use the

MQC commands to see the stats for each class.

Interface Virtual-Access2 (compression off, IPHC, NON TCP)

Rcvd: 0 total, 0 compressed, 0 errors, 0 status msgs

0 dropped, 0 buffer copies, 0 buffer failures

Sent: 0 total, 0 compressed, 0 status msgs, 0 not predicted

0 bytes saved, 0 bytes sent

Connect: 16 rx slots, 16 tx slots,

0 misses, 0 collisions, 0 negative cache hits, 16 free contexts

We're compressing using MQC profiles, use the

MQC commands to see the stats for each class.

Interface Dialer1 (compression off, IPHC, RTP)

Rcvd: 0 total, 0 compressed, 0 errors, 0 status msgs

0 dropped, 0 buffer copies, 0 buffer failures

Sent: 0 total, 0 compressed, 0 status msgs, 0 not predicted

0 bytes saved, 0 bytes sent

Connect: 16 rx slots, 16 tx slots,

0 misses, 0 collisions, 0 negative cache hits, 16 free contexts

Note : in each crypto map in all routers the command (qos pre-classify) is active

As I understand from this output no compression is active

Can you please tell me why this is happening ?

1 REPLY
New Member

Re: CCME-VPN-QOS-CRTP compression not working

IPSEC and Compressed RTP (cRTP) are incompatible standards. The RTP header is already encrypted when the packet reaches the compression engine and therefore cannot be compressed.

See this SRND on Voice and Video Enabled IPSec VPN Solutions:

http://www.cisco.com/application/pdf/en/us/guest/netsol/ns171/c649/ccmigration_09186a008074f2d8.pdf

Hope that helps.

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