Chapter 9: Network Requirements and Preparation Planning and Installation Guide
ShoreTel 11.1 117
9.4.5.1 Summary of the Network Requirements
Table 9-7 summarizes the network requirements for bandwidth, latency, jitter, and packet
loss.
9.4.5.2 Impact of Long Network Outages
The ShoreTel system is a completely distributed system in which each ShoreGear 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 will 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.
9.4.6 Bandwidth Management
In addition to the network requirements discussed above, bandwidth management
techniques need to be deployed to ensure that real-time voice data is not affected by bursts
or high amounts of data traffic.
9.4.6.1 Local Area Network
To manage bandwidth in the local area network (intra-site) and meet the requirements for
toll-quality voice, use Ethernet switching. Ethernet switching is cost effective and simple to
provision. Your LAN configuration requirements will vary depending on your
infrastructure and whether your network includes IP phones.
IP phones sample the user’s voice and convert the voice signal to IP packets using the Real
Time Protocol (RTP). These packets must be tagged for higher prioritization in the
network. ShoreTel IP phones have embedded Ethernet switches and will automatically
prioritize voice traffic ahead of any data traffic coming from daisy-chained personal
computers (for example, large files transfers and email).
On the local area network, there are several methods to prioritize voice packets, including:
IP Precedence = 5 (configurable, recommendation is 5)
Parameter Requirement
Bandwidth (WAN) With ADPCM and no RTP Header Compression: 52 Kbps per call
With G.729a and no RTP Header Compression: 26 Kbps per call
With G.711 and no RTP Header Compression: 82 Kbps per call
If your network uses VPN, bandwidth use is affected.
Latency and jitter for toll
quality
< 100 msecs total
100 msecs less 42 msecs allocated for the ShoreTel system yields a
58 msec budget for the network.
When G.729a encoding is used, 100 msecs less 62 msecs allocation for the
ShoreTel system yields a 38 msec budget for the network.
Latency and jitter for acceptable
quality
< 150 msecs total
150 msecs less 42 msecs allocated for the ShoreTel system yields a
108 msec budget for the network.
When G.729a encoding is used, 150 msecs less 62 msecs allocated for the
ShoreTel system yields an 88 msec budget for the network.
Packet loss < 1% for voice calls, and no packet loss for fax and modem calls
Table 9-7 Network Requirements
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