T1 Lines to
Support Enterprise VoIP
How T1 lines support both enterprise
VoIP systems and data networks vs traditional circuit switched
PBX.
T1 lines are often associated with their
original use of aggregating multiple telephone calls on a single
digital trunk by using TDM or Time Division Multiplexing. But
T1 lines are also good conduits for voice over IP telephony between
company locations or to remote gateways that interface with the
PSTN (Public Switched Telephone Network).
T1 Heritage in Circuit Switched Telephony
The original T1 framing was designed to accommodate 24 toll quality
telephone calls digitally on a dual copper pair. Each call is
digitized and assigned to one of 24 eight bit time slots rigidly
synchronized to atomic clocks. Interfaces called channel banks
provide the multiplexing and demultiplexing. At each end of the
T1 line, you have basically 24 independent telephone lines. A
T1 PRI line works similarly, but reserves one channels for signaling
and data including Caller ID.
T1 and T1 PRI lines are still attractive
options for standard switched circuit PBX business telephone
systems. The interface characteristics remain the same, but line
prices have dropped dramatically over the past few years. Most
PBX and larger Key systems have interface boards available that
connect directly to the T1 / PRI line.
New Requirements to Support VoIP Telephony
VoIP works somewhat differently from circuit switched telephony.
Voice is still converted from analog to digital format, sometimes
using the same CODEC (Coder / Decoder). But instead of transmitting
the voice bits in a rigid round-robin time sequence, several
samples of digital voice are formatted into a voice packet. The
packet follows the same IP or Internet Protocol as data packets
so that voice and data can be mingled on a single digital network.
The packets are transmitted from source to destination as fast
as the network will accommodate.
For VoIP applications, you want to use
the entire 1.5 Mbps capacity of the T1 line as a WAN or Wide
Area Network. A T1 line set up this way is called "unchannelized."
Think of it as a big data pipe, similar to a local area network
but going from point to point. The two ends of the T1 line can
both be company sites, or one end can be connected to the Internet.
Bandwidth and Quality Management
One important difference between TDM based T1 phone lines and
VoIP is that your network takes over the job of managing bandwidth
for a VoIP system. The routers or IP PBX system you are using
need to ensure quality of service by prioritizing voice packets
over less time sensitive data packets. You also need to make
sure you have enough network bandwidth to accommodate the maximum
amount of voice traffic needed. If you outgrow a single T1 line,
you can easily bond additional lines to get 2x, 3x, 4x, or more
bandwidth as your business grows.
The Integrated T1 Approach to Network
Convergence
I mentioned that unchannelized T1 data lines can accommodate
both voice and data traffic, since the packets both use the IP
format and will go through switches and routers similarly. This
principle is often used to provide what's called integrated T1
line service which is both telephone and Internet access on the
same T1 line. A device called an IAD converts phone conversations
to VoIP format, intermingles voice and Internet data packets
over the T1 line, and then send the voice packets to the phone
network and the data packets to the Internet at the terminating
end.
Convergence with IP Telephony
Enterprise VoIP users have the opportunity to use T1 lines for
both voice and data connections between office and plant sites.
An IP PBX or IP Phones convert the telephone conversations to
voice packets so a separate IAD is not required. A voice gateway
may be needed to provide interface to the telephone company for
calls that leave the organization.
Ethernet WAN Connections
You should also know that some WAN connections are now available
in native Ethernet protocol. By ordering Ethernet, Fast Ethernet
or Gigabit Ethernet WAN connections, the enterprise network can
be interconnected efficiently regardless of how far-flung remote
locations happen to be.
Interested in the Most Cost Effective
WAN Connections?
You are invited to discuss your needs with our consultants at
no cost and get competitive quotes for the bandwidth you need.
Simply use our inquiry form below. A member of our technical
support team will be in touch quickly. There is no cost or obligation
for this service.
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