TO: ALL WOOD COUNTY EMERGENCY COMMUNICATIONS AMATEURS
ALL NON-WOOD COUNTY EMERGENCY COMMUNICATIONS AMATERUS
FROM: KEN HARRIS WA8LLM
WOOD COUNTY EMERGENCY COMMUNICATIONS INCORPORATED
WOOD COUNTY BULLETIN NR 12.33 DATE: August 12, 2012
SUBJECT: WHAT IS A T1?
If you have ever heard someone say they are using a T1, or the information is being passed over a T1, have you ever gave it any thought of what they are talking about?
A T1 is just the name given to a protocol such as WiFi, Ethernet, Wireless, Packet, etc. A T1 is a digital system that operates at the speed of 1.544 Megabits Per Second. The "T" stands for Timing. It can handle up to 24 individual channels, each with 56 Kilobit of bandwidth.
Each channel can pass analog or digital information. As a timing type system, each channel is scanned 8000 times a second, in sequence, 1, 2, 3, 4, etc. Since each channel is scanned 8000 time a second, each channel has a bandwidth of 4000 Hz, one half the scanning rate, but due to filtering and preventing cross channel interference, the analog bandwidth is restricted to about 3200 Hz. Each channel is broken down into eight binary bits, of 128. At the beginning of each scan a framing bit is added to keep the receiving and transmitting end of the system in sync.
The information on each channel is measured for its frequency, and it's level, and given a binary number between Zero and 127, Zero to 63 is negative and 64 to 127 is positive. The binary number is then placed in it's channel slot, in series with the rest of the channels.
At the receiving end of the T1, each channel is separated into the 24 channels, and the binary number is converted back into an analog or a digital signal, and then passed onto the terminal equipment.
Ken Harris WA8LLM
WCEC
Wood County WV