unk providers offer in-band tones (that is, DTMF carried as audible tones inside the G.711 speech path) and therefore avoid encoding of DTMF in any of the relay mechanisms, the vast majority of providers use RFC-2833 encoding as the DTMF relay method. DTMF Relay Methods H.323 offers three common methods of DTMF relay: H.245 Alphanumeric H.245 Signal RFC-2833 SIP offers four common methods of DTMF relay: SIP NOTIFY RFC-2833 Key Press Markup Language (KPML) (RFC-4730) SIP INFO Both H.323 and SIP additionally enable in-band tones (G.711) for DTMF and the DTMF relay methods listed previously. Although the SIP NOTIFY and SIP INFO methods are specified in the SIP standards (RFC-3265 and RFC-2976, respectively), these are generic methods and not particular to carrying DTMF relay. The RFCs do not specify how to use them for DTMF relay, and therefore any implementation of these methods for DTMF relay should be considered vendor-specific. RFC-2833 is a well-known specification for both SIP and H.323 DTMF relay, and virtual- ly all vendors implement this. The RFC has been superseded by RFC-4733, which is cur- rently not yet commonly implemented. 150 SIP Trunking DTMF Relay Conversion A back-to-back user agent (such as that offered by the CUBE) at the edge of your net- work terminating the external SIP trunk session and reoriginating an internal SIP (or H.323) session can convert these DTMF mechanisms. The same border element can also convert between these mechanisms to provide interworking between different endpoints or applications within your network. Example 8-5 shows the configuration of DTMF relay options available on Cisco IOS dial-peers. Example 8-5 DTMF Relay Configuration Commands dial-peer voice 10 voip description example destination-pattern 408555. session protocol sipv2 session target ipv4:10.10.10.1 dtmf-relay rtp-nte no vad router (config-dial-peer) # dtmf-relay ? h245 alphanumeric DTMF Relay via H245 Alphanumeric IE h245 signal DTMF Relay via H245 Signal IE rtp-nte RTP Named Telephone Event RFC 2833 sip kpml