Bandwidth requirements for IP Communicator

[malberttoo]

Gurus,

I have a user who has been using IP Com in the States (we have a CME), and recently Estonia on a WiFi connection, and had excellent results.

He is now in Malawi, and his computer gets Internet connectivity by means of a cellular dongle of some sort. He uses the Cisco VPN client to get connectivity back to the office.

He says that the dongle is reporting speeds of between 220 and 250 Mbps, but IP Com is unusable. What I can hear of him is choppy and broken, and what he can hear of me is even less.

However, seconds later he can fire up Skype and the conversation is nearly perfect.

So not having much experience thus far with IP Com, I was wondering if anyone knows what the bandwidth requirements are for it, or has any experience using it in a lower-bandwidth environment.

Thanks,

-Michael

[Jonathan Schulenberg]

This is a simple matter of CODEC selection. IP Communicator and Skype use two very different sets of CODECs.

• IP Communicator 7.0 is capable of using G.722, G.711, G.729, or iLBC. All of these transmit a packet every 20ms by default.
  • iLBC is 15.2kbps plus overhead by default. This is your best bet but is relatively new to Cisco. You'll need to adjust configuration in CUCM and run a relatively new IOS version or TNP firmware version to get a call to negotiate this CODEC.
  • G.722/G.711 are 64kbps plus overhead. These are the second-best route in my experience. While they do consume higher bandwidth, the lack of CS-ACELP makes them degrade better than G.729 does.
  • G.729 is 8kbps plus overhead. This codec has the lowest bandwidth requirement which may be useful in a cellular data connection; however, it uses a predictive algorithm called CS-ACELP that makes it very susceptible to jitter and loss. This will degrade the worst/fastest because packets are inter-dependent.

Also worth noting, there is another option called iSAC; however, CIPC does not support this. This is even newer than iLBC to Cisco and, while promising, is only possible with CSF or 8900/9900 series phones at present.

• Skype on the other hand uses SILK for audio between current client versions (calls with older clients would use older CODECs instead). Skype submitted this to the IETF apparently. So far, Cisco has not adopted this codec into their end points.

For now, your best bet will be to get iLBC working if you want to use the Cisco client. Also, changing your VPN client to UDP instead of TCP would help. TCP-based IPsec tunnels spend time/bandwidth retransmitting packets that won't be useful.