from a streaming source. This source makes music available to any possible on-net or off-net device
placed on hold. On-net devices include station devices and applications placed on hold, consult hold, or
park hold by an interactive voice response (IVR) or call distributor. Off-net users include those
connected through Media Gateway Control Protocol (MGCP) and H.323 gateways. The MoH feature is
also available for plain old telephone service (POTS) phones connected to the Cisco IP network through
Foreign Exchange Station (FXS) ports. The integrated MoH feature includes media server, database
administration, call control, media resource manager, and media control functional areas. The MoH
server provides the music resources and streams.
device or feature places a call on hold, Cisco CallManager connects the held device to an MoH media
resource. Essentially, Cisco CallManager instructs the end device to establish a connection to the MoH
server. When the held device is retrieved, it disconnects from the MoH resource and resumes normal
activity.
audio stream. A unicast MoH stream is a point-to-point one-way audio Real-Time Transport Protocol
(RTP) stream between the server and the endpoint device. Unicast music on hold uses a separate source
stream for each user or connection. As more endpoint devices go on hold via a user or network event,
the number of MoH streams increases. Thus, if twenty devices are on hold, then twenty streams of RTP
traffic are generated over the network between the server and these endpoint devices. These additional
MoH streams can potentially have a negative effect on network throughput and bandwidth. However,
unicast MoH can be extremely useful in those networks where multicast is not enabled or where devices
are not capable of multicast, thereby still allowing an administrator to take advantage of the MoH
feature.
endpoints requesting an MoH audio stream can join as needed. A multicast MoH stream is a
point-to-multipoint one-way audio RTP stream between the MoH server and the multicast group IP
address. Multicast music on hold conserves system resources and bandwidth because it enables multiple
users to use the same audio source stream to provide music on hold. Thus, if twenty devices are on hold,
then potentially only a single stream of RTP traffic is generated over the network. For this reason,
multicast is an extremely attractive technology for the deployment of a service such as MoH because it
greatly reduces the CPU impact on the source device and also greatly reduces the bandwidth
consumption for delivery over common paths. However, multicast MoH can be problematic in situations
where a network is not enabled for multicast or where the endpoint devices are not capable of handling
multicast.
Multicast Design document, available online at
modules with MGCP and Cisco CallManager Release 3.3(3) or later; Cisco 2600, 3600, and 3700 Series
Routers with MGCP or H.323 and Cisco IOS Release 12.2(8)T or later.