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Configuring a Cisco SPA504g for use with IP-Phone-C

IP-Phone-C is a VOIP service provided by AsahiNet. It is a rebranding of NTT's Hikari VOIP service, so these notes may be applicable to similar services from other resellers.

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.

Subscriber Information

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>

Audio Configuration

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

NAT Configuration

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