的Cisco IOS拨号对等：网络电话拨号对等配置

在最近的博客，两个VoIP拨号点创建为指向集群进行呼叫处理两个不同的CUCM服务器。我们将开始讨论拨号对等体100下方的拨号对等体选项：拨号端声音100 VOIP目标模式11 ...的IP QoS DSCP CS3信令DTMF中继H245字母数字没有VAD编解码器g711ulaw偏好1会话目标的IPv4：10.1.1.1的VoIP拨号对等体默认转发所有数字。此行为是不是默认的数字剥离的POTS拨号点的规则有很大不同。POTS拨号对等数字剥离规则强制，只有通配符数字默认转发。由于意图的结构是转发5位到CUCM，无位操作命令已在拨号对等体100中使用（无位条，前向数字，前缀等）。CUCM 4.0版更改了默认的QoS信令标志着从AF31到CS3。虽然思科IP电话的ASIC负责标志着IP电话的所有信令和媒体数据包的DSCP值，CUCM的企业参数配置可以更改为创建不同的标记。服务质量SRND已经表明使用的CS3现在多年信令和大多数的IP电话部署使用CS3信令。的Cisco IOS的​​VoIP拨号对等体使用较早AF31 QoS标记默认，但是这可以由“的IP QoS DSCP CS3信令”命令，在拨号对等体100所描绘的双音多频（DTMF）中继允许数字按压来改变在通话过程在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