Installation guide

46 Planning and Installation Guide ShoreTel 14.2
Network Requirements and Preparation Bandwidth Requirements
3
In general, to ensure voice quality on the LAN, the ShoreTel system must be used in a switched
Ethernet network. To ensure voice quality on the WAN, the ShoreTel system requires that you do the
following:
 Get a service-level agreement (SLA) from your WAN service provider that guarantees prioritization
of voice traffic.
 Prioritize your voice traffic ahead of your data traffic on network routers.
 Set the ShoreTel admission control feature to ensure that the voice traffic does not flood the WAN
links.
With these items taken into consideration, you can simply and easily achieve toll-quality voice using
the ShoreTel system.
The ShoreTel system is designed to work in multi-vendor network environments and, therefore,
leverages Quality of Services (QoS) standards to ensure voice prioritization including:
 Layer 2 IP Precedence (802.1p and 802.1q) (this only applies on the LAN)
 Layer 3 Differentiated Services Code Point (DiffServ/ToS)
Impact of Long Network Outages
The ShoreTel system is a completely distributed system in which each ShoreTel voice switch provides
all call control functionality for inbound and outbound calls, as well as features such as transfer,
conference, pickup, and trunk selection. When there is a long network outage, the switches detect the
problem and run isolated from the switches that can no longer be reached. In the ShoreTel system,
switches communicate every 30 seconds and disconnect when there is no response after 60 seconds.
TCP and UDP Port Usage in the ShoreTel System
For information about the ports ShoreTel devices and applications use to communicate with other
ShoreTel devices and applications, see the Port Usage appendix in the ShoreTel Maintenance Guide.
Bandwidth Requirements
The amount of bandwidth required for voice calls depends on these details:
 Number of simultaneous calls
 Voice encoding scheme in use
 Amount of signaling overhead
Within a site, G.722 wideband encoding is recommended because bandwidth in the LAN is
inexpensive and readily available. Between sites, G.729a is recommended because it uses the least
amount of bandwidth. Linear codecs provide slightly higher voice quality than G.711, but they should
not be used if there are any bandwidth concerns.
If you select linear broadband or linear encoding, end points that do not support either codec negotiate
for the highest quality codec for both end points, and G.711 is the only high-quality codec shared by all
end points. Table 12 provides bandwidth information for different codecs.