Configuring a Cisco SPA504g for use with IP-Phone-C
This note describes how to configure a SPA504g VOIP handset with the IP-Phone-C service. This information should be applicable to other VOIP handsets, although their configuration details will vary.
Configure an extension on the handset as follows:
EXT > Display Name = <Your 050 Phone Number> EXT > User Id = <Your 050 Phone Number> EXT > Password = <Your Password> EXT > Use Auth Id = Yes EXT > Auth Id = <Your User Id>
The IP-Phone-C SIP server only supports the G711u codec. Other codecs, or too many proposed codecs, may trigger a "488 Not Acceptable Here" response. Therefore configuration with just G711u is recommended.
EXT > Preferred Codec = G711u EXT > Use Pref Codec Only = Yes
If you are using NAT, enable keepalives:
EXT > NAT Keep Alive Enable = Yes
RTP Packet Size
The IP-Phone-C SIP server only accepts a SDP attribute a=ptime with the value 20. Any other value will result in a "488 Not Acceptable Here" response, incorporating a "307 Session description parameter not understood" warning. This is an extremely difficult issue to debug without a priori knowledge, and the engineer involved should be ashamed of themselves for not providing a more meaningful error response.
The SPA504g emits the correct value with the following configuration:
SIP > RTP Packet Size = 0.02