Mitel 5560 IPT none Specifications download pdf (Page 216)

Engineering Guidelines

202

Wideband audio is not supported over the analogue PSTN. The G.722.1 CODEC is also not

easily supported over the digital PSTN (BRI, PRI) and could nominally be used only for point

to point connections. For these reasons the G.722.1 CODEC is only supported on IP end

devices.

The G.722.1 wideband codec is also supported by some 3rd party SIP products, so allowing

for interoperability of this feature between different vendor end devices.

Hub network versus switched network

The best network configuration is one that is entirely switched. Switched networks allow full

network bandwidth to be made available to the end user and greatly reduce collisions with a

resulting decrease in network usage. This in turn makes more bandwidth available for another

application, such as voice. It is strongly advised that VoIP installations use switches within the

network architecture.

A hub works by sharing bandwidth among a number of devices. The devices use CSMA/CD

to control access, but effectively “fight” each other for access. The devices that fail to get access

wait for an available slot. Hubs do not have QoS control. If data needs to be sent in a timely

manner, there is a high probability of introducing unnecessary jitter with potential packet loss

and degradation in voice quality.

In a switched environment, all ports can pass data to a LAN switch with minimal delay. Data is

passed to queues, and priority can be given to types of data, such as those marked by IEEE

802.1p/Q tags. If two devices share a common LAN switch, they can effectively pass data to

each other at high speed (as though they were the only devices on the network) while other

devices could be doing the same. Using a switch is like having multiple networks. Network

efficiency and management are greatly improved.

Since connections in a switched network are typically point to point, there is also the possibility

of configuring the connection to be full duplex. This virtually doubles the bandwidth, since data

can be sent and received at the same time. In a half-duplex environment, data can be sent or

received only sequentially. Equipment configured with auto-negotiation always determines the

highest possible data rate and makes it available connection by connection. Simple hubs are

generally fixed at 10BaseT half-duplex.

Using a switched network ensures that maximum bandwidth is available to the end devices

with minimal delay and best voice quality of service.

LAN architecture

Networks usually consist of different layers. Two main parts are the core network and the access

network. Larger networks can include additional layers such as a distribution layer. Ideally, the

3300 ICP should have a connection higher up in the network, located more towards the core

than at an access point. The optimum connection point is in the distribution layer. Phones should

connect to the access layer.

CAUTION: E911 services can only be provided to IP phones that are connected

to an L2 switch within the Enterprise private address space. Ethernet hubs will

not provide accurate location information that can be used by E911 services,

and must not be used when this function is a system requirement.

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