The following is a quick ref of the basic configuration options for T1s and what these configurations actually mean. It's here because it's hard to find something similar in any one particular reference. They all get way to complicated way to quickly or only give you the buzzwords.
and a the string 10111001 would look something like this:
T1 signaling requires that in every 15 bits there be at least one pulse (1) in order to maintain framing. This is referred to as the one's density requirement. This leads to the following (more common) implementations of AMI.
With Zero Code Suppression 8 zeros (would never be transmitted but) would be converted to look something like:
This frame happens 8000 times a second leading to the formula:
which is the speed of a DS1/T1. In actuality, the framing/info bit is not usable, so the formula for 'data/voice-usable bits' becomes:
DS0s (one channel of a T1) are basically one byte position in each frame or:
Remember, when you use (Bit 7) Zero Code Suppression you lose one bit per 8, so the above formula (for B7ZS) becomes
There are two types of framing typically used today.
The framing/signaling bit is used purely for frame alignment. The odd frames 'frame/signaling bit' is the F bit or Frame alignment signal (101010). The even frames 'frame/signaling bit' is the M bit or Multiframe alignment signal (001110).
Additionally, each byte in the 6th and 12th frame have their Least Significant Bit used (stolen) for signaling (6th frame-A bits, 12 frame-B bits). An example of signaling via these bits is:
|AB = 00||on -hook (inactive)|
|AB = 11||off-hook (active)|
When working with voice, the 6th and 12th frame signal bits are not crucial. The human ear 'glosses over' the lack of the bit. With data, however your channels (would) lose 1 bit out of every 6 bytes. You can assume that the channel is always off-hook, so use a clear channel instead.
The framing/signaling bit is used as follows:
|ESF Frame Number||F-Bit Assignment|
FDL can be used to report framing bit errors, CRC errors, out-of-frame (OOF) events, line code (bipolar) violations, and controlled slip events. Performance summaries can be reported including errored seconds (at least one CRC event), Bursty seconds (2-319 errored seconds), severely errored seconds (> 319 errored seconds, or OOF), and failed seconds state (10 consecutive severely errored seconds).
Each byte in the 6th, 12th, 18th, and 24th frame has it's Least Significant bit used (stolen) for signaling (6th frame-A bits, 12th frame-B bits, 18th frame-C bits, 24th frame-D bits).
An example of signaling via these bits is:
|ABCD = 0000||on -hook (inactive)|
|ABCD = 1111||off-hook (active)|
Out-of-frame condition on incoming DS1 signal for 2 to 3 seconds.
Also referred to as "loss of signal" alarm.
An SF yellow alarm is when bit 2 is set to zero in all channels. An ESF yellow alarm is a data link (FDL) message of 0000000011111111.
Indicates that the signal was lost upstream. The all 1s are sent to indicate local network continuity.