user manual

Cisco Hoot and Holler over IP
Hoot and Holler over IP Overview
VC-834
Cisco IOS Voice, Video, and Fax Configuration Guide
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.