Chapter 9: Network Requirements and Preparation Understanding the Requirements for Toll-Quality Voice
ShoreTel 8 Planning and Installation Guide 109
9.4.7 Distributed Call Control Signaling
Voice switches maintain communication with each other. A single voice switch maintaining
basic connectivity with 59 other voice switches consumes less than
1.5 Kbps of bandwidth.
9.4.8 Admission Control in the Wide Area Network
To ensure that your voice traffic does not overwhelm the wide area network and degrade
voice quality, the ShoreTel 8 system has an Admission Control feature. From ShoreWare
Director, you can limit the amount of WAN bandwidth used for telephone calls on a per-
site basis. For a telephone call to be established between sites, admission control must be
met at both sites. If the admission control limit is reached at a site, additional calls cannot
be placed to or from the site, thus ensuring the voice quality of calls already in progress. If
the user is making an outbound call, the call is automatically routed out of a trunk at the
site. When making an extension-to-extension call, the user is informed that there is
insufficient network bandwidth to complete the call. The user can try again later or dial the
external number of the other user.
If PSTN failover is enabled for a user extension, the user’s extension-to-extension calls are
automatically routed to the public switched telephone network (PSTN) when there is
insufficient bandwidth for an IP connection to phone.
9.4.9 Spanning Tree Protocol
Spanning Tree Protocol (STP) is used by Ethernet switches and routers to determine if
there are multiple paths on the network between any two endpoints. You must disable STP
on any network port that has a ShoreGear switch or ShoreWare server connected.
9.4.10 Traffic Shaping to Reduce Bottlenecks
Given that more applications are requiring WAN bandwidth, the need to optimize is
increasingly important. This is particularly true for enterprises that want to deploy voice
over virtual networks where quality of service and traffic shaping are required. With traffic
shaping, it is possible to set policies that determine who or what gets top priority. For
example, by prioritizing the various flows of traffic, an administrator can make sure that
UDP (voice) traffic gets a higher priority than FTP (file download) traffic.
Call Manager Bandwidth Use
Personal .2 Kbps
Advanced .2 Kbps
.2 Kbps + 1.5 Kbps
1.5 Kbps per monitored extension
6.5 Kbps per queued call
6.5 Kbps per queued call
1.5 Kbps per agent
Table 9-8 Typical Call Manager Bandwidth Use