4 telephony gateway capacity, Telephony gateway capacity – Polycom H340 User Manual
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Deploying SpectraLink e340, h340 and i640 Wireless Telephones
BEST PRACTICES GUIDE
October 2010
Note that traffic analysis is based on the aggregate traffic for all users, so users with higher or lower usage are
included in these averages.
The traffic engineering decisions are a tradeoff between additional call resources and an increased probability of call
blocking. Call blocking is the failure of calls due to an insufficient number of call resources being available. Typical
systems are designed to a blocking level (or grade of service) of 0.5 percent to two percent at the busiest times.
Traffic model equations use the aggregate traffic load, number of users and number of call resources to determine
the blocking probability. The blocking probability can also be used along with the aggregate traffic load to determine
the number of call resources required. Traffic model equations and calculators are available at www.erlang.com.
Consider a system with APs that can support six active telephone calls. If a blocking probability of one percent or
less is desired, each AP can support approximately 13 moderate wireless telephones users. If the AP coverage
supports 12 simultaneous calls per AP, each AP can then support approximately 39 moderate users. This allows
some users to be in-call and others in standby.
The Table 2 shows maximum users per AP based on the AP’s ability to handle simultaneous calls:
Table 2 - Users Supported per Access Point
Areas where heavier wireless telephone usage is expected, such as cafeterias, staff lounges, and auditoriums, can
obtain higher call capacity and handle more users by installing additional APs. For most enterprise applications
however, the table above should be sufficient in demonstrating the number of wireless handsets supported within
each AP’s coverage area.
2.3.4 Telephony Gateway Capacity
Telephone system administrators should consider the user distribution on SpectraLink 8000 Telephony Gateways
much in the same way as they do PBX line cards. Telephony Gateways incorporate a physical connection to a PBX
line card. The phone system administrator should spread departments or functional areas across multiple PBX line
cards and across multiple Telephony Gateways so that a failure of either component does not cause a complete
wireless handset outage in one department or area. In addition, system administrators must consider that one
Telephony Gateway can support a maximum of eight handsets in an active call state. While the Telephony Gateway
User Calling Intensity
Light
Moderate
Heavy
Erlangs per User
0.10
0.15
0.20
Max Active Calls per
AP
Users Supported per AP
(1% Blocking Probability)
1
1
1
1
2
2
2
2
3
4
3
3
4
8
6
4
5
13
9
7
6
19
13
10
7
25
17
13
8
31
21
16
9
37
25
19
10
44
30
22
11
51
34
26
12
58
39
29