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| What is a digital telephone line? |
 A
digital telephone line or digital trunk is a type of telephone line that
carries voice and/or data by using digital sampling.
By converting analog signals to digital, these types of trunks allow for
more information to be transferred over a single connection. For instance
the maximum speed of an analog modem is 56 Kilobits per second (Kbps) while
the maximum speed of a digital T1 line is 1.544 Megabits per second (Mbps) –
almost 30 times more. |
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| How does a digital telephone line
work? |
 Digital
telephone lines use Time Division Multiplexing (TDM), a method of
transmitting multiple digital signals over one communication media, to
accommodate up to 24 voice conversations over one circuit. The most
common digital telephone lines are T1 and Primary Rate Interface (PRI). They
are the typical method in which larger offices with considerable call
volumes receive telecommunication services. |
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| T1 vs. PRI |
| PRI is also known as ISDN PRI.
ISDN stands for Integrated Services Digital Network. There are two speeds of
service offered: BRI or Basic Rate Interface and PRI or Primary Rate
Interface. BRI is a low capacity service intended for residential and small
business applications. PRI is the high capacity service carried on T1 trunk
lines between telco central offices and your location.
PRI divides a T1 digital signal into 24
channels of 64 Kbps capacity per channel. 23 of these channels can be
assigned as one telephone call each, the equivalent of having 23 separate
telephone lines. The 24th channel is used for signaling information and
special features such as caller ID. It is a popular service for call centers
which need the ANI automatic number identification or caller ID data.
T1 service can be provided as channelized or
unchannelized. In the channelized T1 version, there are 24 channels. Each
channel can be a telephone call. T1 gives you 24 phone lines in place of the
23 that can be accommodated with PRI. However, since there is no separate
signaling channel, the signaling information that tells when a phone is on
hook or off hook is carried within each channel by using or "robbing" the
least significant bit. Unfortunately, channelized T1 doesn't provide any
capability for ANI or caller ID data. You need PRI service for that. |
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| Networking your companies phone
systems |
 T1
circuits can also be used to network remote phone systems within the same
company. For instance an office in Michigan can be networked using a T1 tie
trunk to another office in California. A user in Michigan can then connect
to a user in California simply by dialing their extension number. This
bypasses tolls and allows employees in the business to communicate
seamlessly. Routing tables can also be set up to find the most cost
effective ways to distribute calls through the Michigan and California
offices. |
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| Can my phone system handle a T1? |
| PBXs that service the SMB and
enterprise class markets can accommodate both analog and digital telephone
lines. This allows business to grow from a few incoming lines and
handful of extensions to multiple T1/PRI lines and a hundreds of extensions.
Most SMB PBXs allow up to 3 T1/PRI circuits while enterprise class systems
can add many more. To make sure that your PBX is compatible with
T1/PRI reference your system manuals, consult with your installation
professional, or contact the manufacturer. |
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| When should I consider ordering
T1/PRI? |
| Analog telephone lines should
be considered for small and medium sized businesses that require up to 15
incoming lines. When more than 15 are required, a T1/PRI is usually a better choice in terms of both cost and features. |
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Questions? Give us a
call! 800-929-8061
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equipment. Metroline
Inc. does not represent Avaya Communication, Lucent Technologies, Nortel
Networks, Cisco, Toshiba, Mitel, NEC, Dell, ShoreTel or their affiliates in any way. Merlin, Merlin Legend, Merlin Magix, Partner, Partner Plus, Partner II, Partner ACS, Spirit, Definity, IP Office, and Avaya Communication Manager are registered trademarks of Avaya
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