[VoiceOps] VoIP over 3G/4G Data Connection

Jay Hennigan jay at west.net
Sun Jul 27 15:43:08 EDT 2014

On 7/27/14 11:14 AM, Colton Conor wrote:

> I assume we are going to be dealing with alot of packet loss whether its
> going to 3G or 4G. We are also going to be dealing with high latency on
> 3G. Since we have no control over both of these issues, what other
> recommendations do you have? I have heard changing the ptime can help,
> and certain codes have different ptime settings. I have also read about
> trying to keep the MTU size down, and using SIP header compression
> helps. I don't know much about this. 

MTU won't matter for the RTP as those are relatively small packets.
Yes, keep the RTP over UDP, I don't even think TCP is an option for it.
 With your SIP over TCP, fragmentation won't be a problem so I'd not
worry about the MTU there either.

I'd try the standard 20 ms. ptime and see if you have any issues.
Nonstandard ptime values can cause trouble if the other side can't
negotiate.  You'll likely have some latency due to jitter buffers
growing as well as the inherent cellular latency.  Echo suppression
should be enabled.

Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV

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