Cisco SPA509G Administration Guide - Page 318

Cisco SPA IP Phone Field Reference Ext Tab B Parameter DTMF Tx Volume for AVT Packet Use Remote Pref Codec Codec Negotiation Description Allows you to manually configure the AVT Tx volume. The value of this parameter is inserted into the volume field of the payload in the AVT packet. Values are based on the AVT specification as described in RFC 2833, RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals. According to RFC 2833, the volume field is represented by 6 bits, and describes the power level of the tone, expressed in dBm0 after dropping the sign. Valid range for this parameter is 0 to 63. If the provisioned value is negative, it will be negated first. Thereafter, if the value is beyond the high limit of 63, it will be clipped to 63. The default value is 0, and is the recommended setting. However, some gateways do not accept this volume setting. If the gateway does not accept the value of 0, the DTMF tone is not relayed to the remote end. As a workaround for the phone to interoperate with those gateways, you can change the value to a value greater than 0. If set to yes, the phone communicates using the remote phone's preferred codec. If set to no, the Cisco IP phone communicates using its own preferred codec (as indicated in the Preferred Codec field and in the SDP by order of preferences). The default vale is no. When set to Default, the Cisco IP phone responds to an Invite with a 200 OK response advertising the preferred codec only. When set to List All, the Cisco IP phone responds listing all the codecs that the phone supports. The default value is Default, or to respond with the preferred codec only. A codec resource is considered allocated if it has been included in the SDP codec list of an active call, even though it eventually might not be chosen for the connection. If the G.729a codec is enabled and included in the codec list, that resource is tied up until the end of the call whether or not the call actually uses G.729a. If the G729a resource is already allocated (and since only one G.729a resource is allowed per phone), no other low-bit-rate codec can be allocated for subsequent calls. The only choices are G711a and G711u. Since two G.723.1/G.726 resources are available per IP phone, you should disable the use of G.729a to guarantee support for two simultaneous G.723/G.726 codecs. Cisco Small Business SPA300 Series, SPA500 Series, and WIP310 IP Phone Administration Guide 317