recommend low-bandwidth VoIP provider compatible with Obi?
sfzcadmin:
We are trying to set up VoIP service over a very limited bandwidth satellite connection and would like to find a VoIP provider who will allow the lowest-bandwidth overhead codec possible to set up on an Obi box. (Maybe one that offer the g.723.1 codec). Can anyone make any recommendations?
pc44:
Hi sfzcadmin,
I'm not familiar with the G.723.1 codec. It looks like it transmits "at 5.3 and 6.3 kbit/s."
If so, would G.729 "8 kbit/s" suffice in your environment? You would know better than I would, but if it would work for you, then you might consider Vitelity.net as one possible VoIP provider.
pc44 :)
sfzcadmin:
The problem with 729 is that it seems to carry about 30kpbs of overhead. I was wondering if the other codecs did as well.
Stewart:
Voxbeam claims to support G.723.1 (6.3 kbps) on all their routes. However, OBi devices don't implement that codec, so transcoding software would be needed at your end. I'm a satisfied Voxbeam customer, though I've never used or even tried their compression codecs.
Note that if you are using SIP (or H.323, MGCP or XMPP for that matter), the audio is encapsulated in RTP. In addition to the payload, each packet has 12 bytes of RTP overhead, 8 bytes UDP overhead, 20 bytes IP overhead, plus additional overhead dependent on the satellite technology employed.
With G.723.1, frames are fixed at 30 ms, containing 24 bytes payload + 40 bytes RTP/UDP/IP + ?? bytes for the link and physical layers. (17067 + ?? kbps)
With G.729, 20 ms packetization is most common, but if you chose 30 ms, the packet is only 6 bytes longer than for G.723.1. (18667 + ?? kbps)
IMO, it's likely that your problem is not caused by exceeding the bandwidth capability of the link, but by severe jitter, greater than what the jitter buffers can handle. At your end, your device may have some adjustments, or a software jitter buffer can be used. The OBi is very tolerant in this regard. Of course, such buffering is at the expense of already awful latency. In the upstream direction, you have a tougher problem, because you have no control over the jitter buffer at the provider. If you have intractable outbound choppy voice issues, you may need to set up an intermediate server. This may be in the cloud, at your headquarters, or anywhere that you have a solid, low-latency connection to the Internet.
sfzcadmin:
Hi Stewart - your answer was incredibly enlightening - thank you.
So if we set the frames at 30ms frames on a g.729 connection, that will be the best "bang" for our bandwdith buck on an Obi?
The satellite provider wants to sell us 20kpbs CIR (for constant quality of service) on the phone lines for $130 a month, but we've been testing it out and it doesn't seem to help all that much. (I'd rather pay for more total bandwidth with that money). We are getting 3MB down, 256kpbs up right now, but if we upgrade the equipment, we'll get 1MB up, which could deal with that jitter problem, no?
What is a software jitter buffer? Is that something the router would handle? Would using an Obi202 AS our router help with this issue, since that voice traffic would get prioritized? And can I set the frame rate on the Obi codec setting or is this something the provider does generally?
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