Mitel 5560 IPT none Specifications download pdf (Page 221)

Network Configuration Concepts

207

Bandwidth management and call admission control can be used to ensure that voice quality is

maintained in parts of the network where there may be bandwidth constraints. For details, refer

to “Bandwidth, Bandwidth Management, Codecs and Compression” on page 167.

Refer to the 3300 ICP Resiliency guide for detailed calculations and breakdown of signalling

messages for different connections.

Serialization Delay

Serialization delay happens because data is queued in a particular device, but cannot be sent

because another packet is currently being sent. In a fast link, such as in the LAN, the delay is

fairly small (a few milliseconds) and is easily resolved with the end-device jitter buffer.

However, in a WAN access connection, the data rate is not as high as within the LAN. In this

case, the waiting delay increases as the data rate reduces. If a particularly large packet (for

example, 1500 bytes) is being sent, then other devices must wait until it has gone before they

can gain access.

The IP phone and gateway devices are capable of handling delay variations (jitter) up to high

limits. However, in order to maintain the best voice quality performance, this variation should

be kept below 30 ms, with an ideal limit of 20 ms. The following figure shows waiting delay

against link speed, as well as against maximum transmission units (MTU). The value for MTU

can be programmed in routers so that packets with a payload greater than this number can be

reduced in size. The graph shows that when a packet of 1500 bytes is sent, a data-rate of about

700 kbps is needed on the WAN link in order to meet the ideal 20 ms limit.

Figure 29: Serialization delay Frame Relay

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Mitel 5560 IPT none Specifications Page 221