RFC 2833 DTMF Relay

The last blog entry covered DTMF relay. This blog entry will focus on Cisco IP Phone and Cisco SIP Trunk DTMF relay support. Cisco’s first generation of IP phones do not support RFC2833 DTMF-Relay. All digits are sent out of band in either SCCP or SIP signaling packets depending on the phone load. Cisco first generation phones are referred to as Type A phones in the Cisco Unified Communications Manager 6.x SRND (Solution Reference Network Design) guide available at www.cisco.com/go/srnd. Type A phones include the following phones: • 7902 • 7905 • 7910 • 7912 • 7940 • 7960 Cisco’s second generation phones support RFC2833 DTMF Relay when registered with Cisco Unified Call Manager versions 5.0 and later. These phones include the following: • 7906 • 7911 • 7941 • 7942 • 7945 • 7961 • 7962 • 7965 • 7970 • 7971 • 7975 SIP trunks in Cisco Call Manager 4.x did not support RFC2833 DTMF-Relay, but support of this protocol was introduced in Cisco Unified Call Manager 5.0. RFC2833 supports is very important for multi-vendor interoperability since this is the preferred way of exchanging DTMF digits between vendors. Call Manager 4.x used MTP (Media Termination Point) media resources to convert out of band SIP Notify DTMF messages into RFC2833 in-band (RTP) messages. Java Telephony Application Protocol Interface (JTAPI) connections used for CTI (Computer Telephony Integration) ports in CUCM only support out of band DTMF messages. JTAPI connections are used to connect CUCM servers to other servers in the unified communications architecture. JTAPI integrations are used to connect CUCM to Cisco Emergency Responder (CER) and or UCCX (Unified Contact Center Express). UCCX is commonly referred to as CRS (customer response server) or IPCC (IP Contact Center). Have you run into any problems related to DTMF Relay or SIP interoperability? What would like to see covered in the next blog post? Feel free to comment on anything in this blog or anything you would like to see covered in future blog entries.