T-1 Telephony Has Important Variations
Learn how T1 lines can support your PBX telephone system or IP PBX for VoIP at lower costs than multiple analog phone lines
By: John Shepler
T1 telephony was originally invented to transfer hundreds and thousands of phone calls between telephone company central offices. It’s grown far beyond that initial vision to become the digital phone line of choice for thousands upon thousands of businesses. You may already have or be thinking about installing a T1 phone trunk for your business. But are you aware that you have many options to consider?
Relationship Between DS0, DS1 and T1
T1 is a digital line standard that can be used for voice, data, video or all of these. In its original form, it transports 24 separate phone calls on individual channels called DS0. The combination of these is the T1 line or DS1. Each of the DS0 channels is responsible for transmitting digitized voice, plus call control and signaling.
ISDN PRI for PBX
Today’s T1 voice circuit of choice is called a T1 PRI or ISDN PRI. It’s is still organized as 24 channels on a single digital phone trunk, but one of the channels is used exclusively for call control and signaling, leaving the other 23 channels as the equivalent of 23 separate phone lines. The signaling channel is also used to support data services such as Caller ID.
T1 PRI is popular with businesses that have their own PBX telephone systems and with telephone intensive operations, such as customer contact centers and call centers. Nearly all PBX equipment supports this line format. If more than 23 outside lines are needed, then additional T1 PRI lines can be installed.
Dynamic T1 Lines
There’s a T1 telephony solution designed especially for smaller companies that can’t fathom needing 23 phone lines. Integrated T1 lets you have up to a dozen outside phone lines and uses the rest of the T1 line capacity for broadband Internet service. If you get what’s called a dynamic T1, it will automatically assign any bandwidth not currently being used for phone calls into the broadband pool. This is a very efficient use of resources and can be less expensive than having a dozen separate phone lines plus an independent broadband service.
T1 and VoIP
VoIP has become a popular form of telephone service. An Internet connected T1 line can provide the bandwidth and reliability to support VoIP phone services for a dozen or more simultaneous calls.
T1 PRI lines will also interface with IP PBX systems, the VoIP equivalent of the PBX telephone system. T1 PRI is known for its high voice quality, reliability and support of telephony features such as Direct Inward Dialing.
There is also a new form of T1 telephony called SIP trunking. SIP is the signaling standard used in VoIP phone systems. A SIP trunk is often implemented on a T1 data line, but it is not connected to the Internet. It is a direct point to point connection between your business location and your service provider. This avoids the vagaries of Internet performance and helps the service provider ensure high voice quality and service reliability.
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