T1 PRI Phone Lines For Call
PRI or Primary Rate Interface
T1 lines offer cost savings and advanced features to improve
call center performance.
By: John Shepler
If you own a call center or are thinking
about it, you'll likely be interested in digital telephone service.
Individual analog phone lines are only a good solution if you
have a handful of seats and don't need to integrate your phone
service with a computer system containing customer records. Once
you reach a dozen lines, moving from analog to T1 digital carrier
service is almost certainly a cost savings. If you elect to go
with a VoIP telephone system, you'll need reliable broadband
service for even fewer lines.
T1 Lines For Call Centers
First let's consider call centers with traditional PBX phone
systems and, say, 10 to 12 lines. Your PBX equipment has or can
get a digital interface that brings all your phone lines in on
a single T1 carrier. Now, you have a choice of how you want your
T1 line configured. The original legacy configuration is called
channelized T1 and offers 24 independent phone lines per T1 line.
These lines can be set up for local and/or long distance service
and as incoming only, outgoing only or both. What you don't get
are any of the advanced features such as Caller ID or ANI (Automatic
Number Identification). That's because the 24 channels of the
T1 line are completely consumed in carrying the voice conversations.
How PRI Works
A more sophisticated T1 line configuration is called T1 PRI or
Primary Rate Interface. This term comes from ISDN or Integrated
Services Digital Network) technology. A PRI line is also channelized
into individual telephone lines, but carries 23 simultaneous
calls rather than 24. What happened to the other channel? It's
been assigned to be a data channel to serve the 23 bearer or
voice channels. All the dialing information is passed through
the data channel rather than as touch-tones over the voice channels.
That helps make call set up and tear down faster. You'll experience
that as phone calls going through faster. On the receiving end,
the data channel accepts Caller ID or ANI information. This can
be fed to display units to show who's calling, or fed to a CTI
(Computer Telephone Integration) system so that customer information
will pop up on an agent's screen based on the number of the incoming
You are not limited to a single T1 or PRI
line. Many larger systems can double, triple, quadruple and so
on the capacity of the phone system. A single PRI data channel
can service two PRI lines, freeing up one extra channel for voice.
In practice, if you are going to have multiple PRI lines, you'll
probably want at least two data channels for redundancy.
T1 Lines for VoIP
What about VoIP and softswitches? VoIP or Voice over IP networks
actually convert phone conversations to digital data within the
telephone instruments. Your phone wiring then becomes a standard
Ethernet LAN which can serve both telephones and computers. They
all look the same to the network. For transmission of data beyond
your facility you'll use an unchannelized T1 line. That's a T1
that is configured to look line one big data pipe with 1.5 Mbps
bandwidth. It's also called a data T1 line because the information
is carried as IP data packets. Data T1 lines can be combined
in a process called bonding to multiply the bandwidth of the
network from 2 to 6 times or more. SIP trunks are now the standard for VoIP trunking and are available with both copper and fiber optic provisioning.
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