Mitel MiVOICE BUSINESS, Инструкция по инженерии

Страница: 220 / 381

Engineering Guidelines
206
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.
The IP phones are in constant communication with the 3300 ICP. All signalling traffic, as well
as traffic to and from the PSTN, goes through the 3300 ICP. The controller should be placed
higher up the physical network, at some central switch point (for example, where all the access
Layer 2 switches connect, or where there is a router or Layer 3 device to other subnets).
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.