VoIP over IPsec

Mon Feb 17 18:37:58 UTC 2003

Using hardware encryption with the qos pre-classify feature, I imagine that jitter will no longer be an issue - (that is, the jitter you mention previously is introduced by the lack of prioritization into the encryption queue).  Or am I missing something?

C.

-----Original Message-----
From: Stephen Sprunk [mailto:stephen at sprunk.org]
Sent: Monday, February 17, 2003 2:24 AM
To: Charles Youse
Cc: nanog at merit.edu
Subject: Re: VoIP over IPsec

Thus spake "Charles Youse" <cyouse at register.com>
> In order to cut costs in our telecom budget I'm toying with the idea
> of replacing a lot of our inter-office leased lines with VPN
> connections over the public Internet.  [...]
> Assume for the moment that latency and bandwidth are not an issue;
> e.g., any two points that will be exchanging voice data will both have
> transit from the same provider with an aggressive SLA.

Latency, bandwidth, and packet loss are moot.  Jitter is VoIP's enemy.

> Does anyone have any experience running VoIP over such tunnels?
> Is there a technical reason why this solution is not feasible?  Are
> Cisco routers not happy doing VoIP/IPsec/GRE in concert?

IPsec itself will not cause you problems; there's no theoretical conflict.

Unfortunately, IOS can introduce jitter when encrypting packets.  To
mitigate this, you can apply QOS, with a strict priotiy queue for the VoIP
packets and the "qos pre-classify" feature.  Your mileage will vary
depending on the CPU power of the router, the traffic levels, and whether
you're using hardware encryption.

S

Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking