Cisco iOS拨号对等体：VoIP拨号对等配置

在最后一个博客中，创建了两个VoIP拨号对等体，指向两个不同的CUCM服务器对群集执行呼叫处理。我们将开始讨论以下拨号对等体100的拨号对等选项：拨号对等体型100 VoIP目的地 - 模式11 ... IP QoS DSCP CS3信令DTMF-Relay H245-Alphanumeric NO VAD Codec G711U1AW首选项1会话目标IPv4：10.1.1.1 VoIP拨号对等体默认转发所有数字。此行为与Pots Dial对等体的默认数字剥离规则非常不同。POTS拨号对等数字剥离规则默认情况下只转发通配符数字。由于配置的目​​的是将5位数字转发到CUCM，因此在拨号对等器100中没有使用数字操作命令（无数条带，前向数字，前缀等）。CUCM版本4.0将AF31的默认QoS信令标记更改为CS3。虽然思科IP电话的ASIC负责标记IP电话中所有信令和媒体报文的DSCP值，但可以更改CUCM的企业参数配置以创建不同的标记。QoS SRND一直在暗示使用CS3对于现在多年的信令，而且大多数IP电话部署使用CS3进行信令。Cisco iOS VoIP拨号对等体默认使用较旧的AF31 QoS标记，但这可以改变，如拨号对等100中的“IP QoS DSCP CS3信令”命令所示。双音多频（DTMF）继电器允许数字按下在对话期间，通过IP语音发送。 There are many ways to send DTMF digits and multiple methods can be configured in a prioritized list in a single dial peer. H245 is the media negotiation layer of H.323 that is responsible for negotiating codecs and opening logical channel connections. The “dtmf-relay h245-alphanumeric: command specifies that the dial-peer should send DTMF digits in the signaling path (h245) and not the media path (RTP). In the following example, both h245-alphanumeric and h245-signal are configured, but h245-alphanumeric is preferred because it appears as the first option: Dtmf-relay h245-alphanumeric h245-signal Dial-peers use the H.323 protocol by default. In future blogs, we will discuss converting VoIP dial-peers to session initiation protocol (SIP) and investigate the in band (RTP) RFC2833 dtmf-relay mechanism (dtmf-relay rtp-nte). All VoIP dial-peers run voice activity detection (VAD)/silence suppression by default. Although the “no vad” command is used to turn off this mechanism, the “show dial-peer voice” command displays VAD as silence suppression. VAD is a mechanism that turns off the transmission of packets when there is silence in a conversation (without ending the call). VAD can save bandwidth in a conversation, but has the disadvantage of clipping out the beginning and ending syllables of speech. VAD is turned on by default in VoIP dial-peers, but is off by default on Cisco IP phones controlled by both CUCM and CUCME. The bandwidth savings of VAD is normally not worth the quality issues associated with using the technology. VAD parameters can be tuned on an individual dial peer basis, but it is normally best to turn off the mechanism. VAD can be turned on in CUCM (if desired) by changing the Call Manager service parameters for Silence Suppression. It is recommended to leave VAD turned off in CUCM unless it is absolutely necessary. Cisco IOS VoIP dial-peers use the compressed G.729 codec by default. In our example, we are using dial-peer 100 to route inbound PSTN calls from the ISDN PRI circuit to CUCM. Most environments are connecting their voice gateway routers to the network via Fast Ethernet (100Mbps) or Gigabit Ethernet (1000Mbps) technology where there is little to no need for the bandwidth savings of G.729. The codec default was change to G.711ulaw, but a voice codec configuration could have been used to allow H.245 to negotiate between both G.711ulaw and G.729. The global configuration below would be used to set up the voice-class codec: Voice class codec 1 Codec preference 1 g711ulaw Codec preference 2 g729r8 Each VoIP dial-peer can now leverage the global codec voice class as shown below: Dial-peer voice 100 voip Voice-class codec 1 The session target command is used in VoIP dial-peers to point the dial-peer to an IP address, while POTS dial-peers used the port command to steer calls to a TDM interface on the router. The next blog will discuss the preference command used with dial-peer hunting and continue our conversation of VoIP dial-peers. REFERENCES Global Knowledge Cisco Unified Communications classes www.globalknowledge.com/go/cisco Cisco Press Books – CVOICE / GWGK / TUC http://www.ciscopress.com/markets/detail.asp?st=44706 Voice Activity Detection / Silence Suppression http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a00800a9982.shtml