RTP header compression over IPSec VPN WAN link?

[chinenyeonyerionwu]

Hello,

My company has a WAN link that uses IPSec VPN. Now we are introducing IP  Voice over this link. Can I use compressed RTP (RTP header compression)  over an IPSec VPN link.

Thanks

Chinenye

[acampbell]

Chininye

From link:-
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/V3PN_SRND/v3p_comp.html#wp1035253

Looks like CRTP can not be used over IPSEC

cRTP Not Compatible with IPSec
Network managers implement cRTP as a link efficiency mechanism to decrease the overhead of voice traffic on low-speed (less than E1) links. cRTP compresses the IP/UDP/RTP header in an RTP data packet from 40 bytes to approximately 2-to-5 bytes. However, cRTP and IPSec are inherently incompatible standards. The original IP/UDP/RTP header is encrypted by IPSec by the time the RTP compressor is called upon to perform the compression. Therefore cRTP cannot associate the encrypted IP/UDP/RTP packet with a known media stream, compression does not occur, and bandwidth savings are not realized. The encrypted IP/UDP/RTP packet simply by-passes the compression process and continues.

HTH

Alex

[chinenyeonyerionwu]

Hello Alex,

Thanks a lot for that very informative response, and also the link. Seems that's the logical answer to that question. I will explore other options to the situation: maybe migrating the link to MPLS VPN. Do you think MPLS offers much less header bytes than IPSec?

[acampbell · Accepted solution]

Chineye,

Most info I can see seems to infer that we should really only use cRTP over point to point links.

Looks like other protocols like MPLS etc do not wantus tinkering with the IP headers.

HTH

Alex

[chinenyeonyerionwu]

Alex,

Thank you for your insights which have helped me resolve this issue. I will simply implement the IP telephony with the resources my client have on ground, while advising them to subscibe for more bandwidth. Then in the future, as they introduce technologies like Video conferencing, I will advise for MPLS, combined with application acceleration network modules over WAN.

Thank you.

Chinenye