DTMF中继在思科路由器

双音多频(DTMF)信令用于传统模拟普通老式电话业务(PoTS)电话，将数字发送到交换中心，用于呼叫路由或其他一些专门功能。DTMF数字也用于专用功能，如语音邮件登录、自动服务员(AA)和交互式语音响应(IVR)系统。DTMF数字是允许在PSTN上进行音频拨号的频率组合。脉冲拨号历来与旋转式电话一起使用。IP语音系统有许多方法来利用DTMF数字，具体取决于所使用的信令机制。思科路由器上所有传统的时分多路复用(TDM)接口都默认支持传递DTMF数字。思科VoIP(话音IP)拨号对等在默认情况下不支持DTMF数字。根据所使用的信令协议，可以在VoIP拨号对等机上配置多个dtmf中继功能。然后，VoIP拨号对等点将在频带内(IB)或频带外(OOB)传递DTMF数字。在波段中，DTMF- relay将在语音媒体流的RTP报头中使用一个特殊的有效载荷类型标识符(PTI)，以区别数字与DTMF pad和实际的语音通信。 An out of band mechanism will pass DTMF digits in the signaling protocol (SCCP, SIP, MGCP, or H.323) instead of using the RTP media stream. There are four DTMF relay mechanisms that are supported on VoIP dial-peers: • H245-alphanumeric • H245-signal • SIP-Notify • Rtp-nte H.245 mechanisms are only available on H.323 dial-peers. H.245 is part of the H.323 protocol suite. is the default protocol used on VoIP dial-peers. SIP Notify is only used in the SIP signaling protocol. RTP NTE stands for Real-Time Protocol (RTP) Named Telephone Events (NTE). NTE are mechanisms used in the IETF (Internet Engineering Task Force) RFC (request for comments) 2833. RFC2833 is the de facto standard used in the industry standard for multi-vendor interoperability in SIP environments. The next blog entry will focus on the method in which DTMF digits are passed from Cisco phones.