Cisco Systems VC-825 appendix Virtual Interface, Connection Trunk, VC-834

Cisco Hoot and Holler over IP

Hoot and Holler over IP Overview

More information on cRTP may be found in the “Quality of Service Overview” chapter of the Cisco IOS Quality of Service Solutions Configuration Guide at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/qcfintro.htm

In addition to reducing the IP/UDP/RTP headers per packet, the network administrator also has the option of controlling how much voice payload is included in each packet. This is done using the bytes keyword and argument in a VoIP dial peer. The following example shows a dial-peer configuration:

dial-peer voice 1 voip destination-pattern 4085551234 codec g729r8 bytes 40 session protocol multicast

session target ipv4:239.10.108.252:20102

As the number of bytes per packet is modified, so too is the number of packets per second that are sent.

VAD enables the DSPs to dynamically sense when there are pauses in a conversation. When these pauses occur, no VoIP packets are sent into the network. This significantly reduces the amount of bandwidth used per VoIP call, sometimes as much as 40 percent to 50 percent. When voice is present, VoIP packets are again sent. When using Cisco hoot and holler over IP, VAD must be enabled to reduce the amount of processing of idle packets by the DSPs. In basic VoIP, VAD can be enabled or disabled, but since the DSPs also have to do arbitration and mixing, VAD must be disabled to reduce the DSPs’ processing load. In addition to enabling VAD (which is only by default), network administrators should modify the VAD parameters that sense background noise so that idle noise does not consume bandwidth.

This can be configured as in the following E&M port example:

voice class permanent 1

signal timing oos timeout disabled signal keepalive 65535

!

voice-port 1/0/0 voice-class permanent 1 connection trunk 111 music-threshold -30 operation 4-wire

The configuration above is used for a voice port that is in send/receive mode, and only noise above -30Db is considered voice.

Virtual Interface

In all Cisco hoot and holler over IP implementations, the routers are configured with an “interface vif1.” This is a virtual interface that is similar to a loopback interface—a logical IP interface that is always up when the router is active. In addition, it must be configured so the Cisco hoot and holler over IP packets that are locally mixed on the DSPs can be fast-switched along with the other data packets. This interface must reside on its own unique subnet, and that subnet should be included in the routing protocol updates (Routing Information Protocol [RIP], Open Shortest Path First [OSPF], and so on).

Connection Trunk

Cisco hoot and holler over IP provides an “always-on” communications bridge—end users do not need to dial any phone numbers to reach the other members of a hoot group. To simulate this functionality, Cisco IOS provides a feature called “connection trunk.” Connection trunk provides a permanent voice call, without requiring any input from the end user, because all the digits are internally dialed by the router/gateway.

Cisco IOS Voice, Video, and Fax Configuration Guide

VC-834