Mitel Inter-Tel 5000 Installation And Maintenance Manual page 116

Chapter 4: Specifications
Performance Criteria
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Inter-Tel also recommends the following PSTN performance characteristics:
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All of the preceding PSTN requirements are consistent with the EIA/TIA-464B specifications.
Use Ethernet switching mechanisms rather than Ethernet hubs. Switches offer inherent
Ethernet advantages over hub (shared) technology. Switches provide advantages such as
segmentation, full-duplex operations, Layer 2 prioritization, etc.
IMPORTANT
For any router that will have VoIP traffic passing through it, program the router to prioritize the
packets sent by the IP devices. In addition, program the external router to fragment large data
packets into smaller packets. This reduces the possibility that voice packets will have to wait for
a large data packet at the router.
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Network Jitter: Variance in delay. For near toll quality service, average jitter should not
exceed 20 ms and maximum jitter should not exceed 40 ms. For business communication
quality service, average jitter should not exceed 40 ms and maximum jitter should not
exceed 80 ms.
Hops: The number of router points a data packet must pass through during transmission.
Hops should not exceed 15 in order to minimize the number of potential problem points.
Committed Information Rate (CIR) and Burst Rate (BR): 512 Kbps/each. This criterion
means that 512 Kbps will always be available, and the link may achieve a BR of up to
1024 Kbps for short periods if the bandwidth is available from the WAN provider. Typically,
there is no guarantee of BR availability. Voice traffic should stay below the CIR value.
When voice traffic exceeds the CIR value, packets may begin to queue within the Frame
Relay network and become subject to delay. These packets could eventually be tagged as
Discard Eligible (DE). Packets marked as DE could be discarded before reaching their
destination. The potential queuing delay and packet loss can adversely affect voice quality.
Loop Current: 18–20 mA
Line Voltage: 42.5–56.5 V
Ring Voltage: 55–130 Vrms (Class A)
db Level: Must pass at least +3dBm without distortion into a 600-ohm load
Using background music and paging on a hard IP endpoint, such as the IP
PhonePlus, consumes as much bandwidth as a telephone call to the device.
If the site has limited bandwidth, make sure IP endpoint users do not enable
background music and that they limit using the paging feature.
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Inter-Tel 5000 Installation Manual – Issue 2.4, May 2008