Mitel 5560 IPT none Specifications download pdf (Page 220)

Engineering Guidelines

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Network Measurement Criteria

Assuming that jitter and packet loss are not an issue, the one parameter left that affects the

voice and conversation quality is end-to-end delay. From ITU-T recommendations (and practical

experience), the end-to-end delay for a voice call should not exceed 150 ms. The characteristics

of the end devices such as the gateway (Ethernet and TDM bridge in the 3300 ICP) and the

IP phones are known.

In assessing a network, consider the network limits shown in the following table.

“Ping” delay is the value obtained using a PC ping utility. The ping utility sends a message from

one PC to a second PC. When the second PC receives the message, it sends a message back

to the first PC. The first PC determines the propagation delay encountered on the network

between the two PCs. Typically the send and receive paths have equal delays. Estimate jitter

by using ping over a short and longer-term period. Estimate packet loss by using ping over a

longer period (24 hours or more). Networks that are used for both voice and data can have

variations in the amount of network delay. For instance, if computer backup utilities run on a

regularly scheduled basis, network delay can increase. Perform longer-period delay

measurements over a time period that represents the customer's core operational hours.

Other tools, such as network analyzers, can also be used to determine packet loss. Many

analyzers look for VoIP and RTP packets, and can identify when a packet is missing as well

as average jitter.

Although ping can be used as a quick check or as a backup method, it is recommended that

networks be fully evaluated before installation. Mitel Consultants and Integrators, can provide

Professional Services to perform a full VoIP network pre-installation evaluation.

Bandwidth Requirements

Consider the following when calculating bandwidth requirements:

• Level of call traffic (more phone calls means more bandwidth)

• Bandwidth required for speech connections (that is, codec to be used)

• Bandwidth required for signalling.

In general, the level of call traffic defines the number of Erlangs (busy channels) and hence,

the number of “channels.” As a simple rule of thumb, add 10% to the voice bandwidth to ensure

adequate signalling bandwidth. In practice, the signalling is needed only to set up a call and

clear it down. The signalling messages are also sent via TCP and acknowledged. Some delay

is tolerated in this case, unlike the voice case.

Table 63: Network limits

Packet loss Jitter End-to-end delay Ping delay

Go! <0.5% <20 ms <50 ms <100 ms

Caution <2% <60 ms <80 ms <160 ms

Stop! >2% >60 ms >80 ms >160 ms

1 2 ... 215 216 217 218 219 220 221 222 223 224 225 ... 380 381

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Mitel 5560 IPT none Specifications Page 220