[VoiceOps] RTP Proxy TTL Behavior

Jeff Anderson ciscoplumber at gmail.com
Mon Feb 11 10:15:24 EST 2019

I am seeing 64 on our endpoints like polycoms vvx and adtrans TA908, etc.
On our carrier switches I am seeing 256.

It's very specific call flows that will exhibit this behavior, more corner
case stuff but we are observing it nonetheless.

On Mon, Feb 11, 2019 at 9:11 AM Glen Gerhard <glen at cognexus.net> wrote:

> Hi Jeff,
> The B2BUA is a signaling function, not necessarily an IP layer function.
> Yes, some SBCs may give you the ability to modify the TTL but I'd look more
> at the Gateway/IP Phone configuration.
> What is the TTL being sent out by the end device? Some of those are
> defaulted to absurdly low TTL, I've seen as low as 16. In general that is
> where they configuration should be changed.
> ~Glen
> On 2/11/2019 7:04, Jeff Anderson wrote:
> We are occasionally running into a situation where our IP Header TTL
> expires in transit for RTP streams. It has been our observation that our
> SBC B2BUA that anchors media is not resetting the TTL on RTP packets but is
> on SIP packets.
> Is there a standard expected behavior for how SBC B2BUA with media
> anchoring might handle RTP packets? I would have thought if it resets the
> SIP packet TTL it would also reset the RTP packet TTL.
> Thoughts?
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> --
> Glen Gerhardglen at cognexus.net
> 858.324.4536
> Cognexus, LLC
> 7891 Avenida Kirjah
> San Diego, CA 92037
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