Nortel BCM50 2.0, Руководство по установке

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46 Chapter 6 IP telephone overview
NN40020-309 NN40020-309
IP network
In the network shown in Figure 10 , several LANs and a WAN are shown. When planning your
network, be sure to consider all requirements for a data network. Your network administrator
should be able to advise you about the network setup and how the BCM50 2.0 fits into the
network.
WAN
A Wide Area Network (WAN) is a communications network that covers a wide geographic area,
such as state or country. For BCM50 2.0, a WAN is any IP network connected to a WAN card on
the BCM50 2.0 system. This may also be a direct connection to another BCM50 2.0 system.
If you want to deploy IP telephones that will be connected to a LAN outside of the LAN that the
BCM50 2.0 is installed on, you must ensure the BCM50 2.0 is able to communicate across the
WAN interface at that location.
LAN
A Local Area Network (LAN) is a communications network that serves users within a confined
geographical area. For BCM50 2.0, a LAN is any IP network connected to the integrated interface
(a LAN card) on the BCM50 2.0 system. Often, the LAN can include a router that forms a
connection to the Internet. A BCM50 2.0 can have up to two LAN connections.
Public Switched Telephone Network
The Public Switched Telephone Network (PSTN) can play an important role in IP telephony
communications. In many installations, the PSTN forms a fallback route. If a call across a VoIP
trunk does not have adequate voice quality, the call can be routed across PSTN lines instead, either
on public lines or on a dedicated ISDN connection between the two systems (private network).
The BCM50 2.0 also serves as a gateway to the PSTN for all voice traffic on the system.
Key IP telephony concepts
In traditional telephony, the voice path between two telephones is circuit switched. This means
that the analog or digital connection between the two telephones is dedicated to the call. The voice
quality is usually excellent, since there is no other signal to interfere.
In IP telephony, each IP telephone encodes the speech at the handset microphone into small data
packets called frames. The system sends the frames across the IP network to the other telephone,
where the frames are decoded and played at the handset receiver. If some of the frames get lost
while in transit, or are delayed too long, the receiving telephone experiences poor voice quality.
On a properly-configured network, voice quality should be consistent for all IP calls.