Chapter 3: Planning and System Design Planning and Installation Guide
ShoreTel 11.1 53
3.3.6 Trunk Requirements
Trunks provide connectivity between users on the ShoreTel system and the public switched
telephone network (PSTN). In this next task in the system design process, you determine
the number of trunks required.
The number of trunks required on your system varies, depending on the number of users
and your specific application needs. It is important to size your trunking correctly because
not having enough trunks can lead to blocked calls when all trunks are busy, and too many
trunks can lead to wasted money on monthly access charges.
See Chapter 5, starting on page 67, for more information about trunk features, ordering,
You have several options for determining the number of trunks your site requires:
Review the number of trunks on your current system. In general, this is one of the
best methods to gauge the number of trunks you need.
You can also request a traffic analysis from your service provider, interconnect, or
telecom manager to understand your current trunk utilization. This method will
help you understand your current usage and allow you to maintain the current
Visit a web site, such as www.erlang.com, to use a traffic calculator for determining
your trunk requirements.
Fill in the Trunks section of the spreadsheet shown in Figure 3-1 to determine the
number of trunks you need. The spreadsheet automatically calculates the trunking
Consider Table 3-2 and the following:
Larger locations can typically use lower-density trunking (15%).
Smaller locations need higher-density trunking (50%).
Some applications, such as call centers, can demand higher-density trunking
When planning trunks, consider the call volume for your workgroups or ACD groups.
Since there is generally a queuing solution in place for ACD calls, the number of trunks
required should be based on the full utilization of the expected number of agents and
sufficient trunks for the expected number of waiting callers.
3.4 Determine Number of ShoreGear Voice Switches
The ShoreTel system is a software solution that runs on standard platforms across the
network equipment in your enterprise. The ShoreGear hardware portfolio offers a broad
family of voice switches to meet the needs of our different customers. Each ShoreGear
voice switch connects to your IP network using a 10/100M auto-sensing Ethernet port.
Refer to Appendix G, starting on page 303 for a description of all ShoreGear switches.
Trunk Density Trunks/Users %
Table 3-2 Trunk Density