Chapter 9: Network Requirements and Preparation WAN Technology Choices
ShoreTel 8 Planning and Installation Guide 111
9.5 WAN Technology Choices
9.5.1 Minimum Bandwidth Requirements
The minimum WAN bandwidth required to deploy a voice switch at a site depends on the
number of calls expected. With ADPCM, a single call consumes 52 Kbps, and if this call
becomes a conference call, another 52 Kbps is needed, yielding a total of 104 Kbps. From a
broadband perspective, the first available technology is 128 Kbps (ISDN), which leaves
only 24 Kbps for other IP traffic. For teleworking applications, where only a single call is
needed, 128 Kbps can be used. For other sites on the voice network, the minimum
bandwidth recommended is 384 Kbps.
Various technologies are available from different service providers to provide IP
connectivity between locations, as shown in Table 9-11.
9.5.2 Leased T1
Leased T1 facilities are the most robust WAN technology available. Leased T1s are point-to-
point links that inherently meet the network requirements for toll-quality voice since no
ISP is involved. Dedicated T1s are priced on a per unit distance basis, making this a very
cost-effective option over short distances.
Codec Data Rate (Kbps) MOS Interactive
Linear 128 Not tested Not tested
G.711 64 4.46–4.87 4.66
ADPCM 32 3.96–4.05 4.33
G.729a 8 Not tested Not tested
Table 9-10 ShoreTel MOS and Interactive Test Results
Technology Upstream Bandwidth Kbps Downstream Bandwidth Kbps Calls with ADPCMa
a. Your bandwidth will vary, based on the WAN overhead for your particular system.
T1 1544 1544 26
Frame Relay Varies Varies Varies
SDSL 1544 1544 26
SDSL 1024 1024 17
SDSL 768 768 13
SDSL 512 512 8
SDSL 384 384 6
IDSL 144 144 1 call only
ADSL 128 1,000 (varies) 1 call only
Cable 128 (varies) 1,000 (varies) 1 call only
ISDN BRI 128 128 Not supported
Dial-up modem 28.8–56 28.8–56 Not supported
Table 9-11 IP Connectivity Chart
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