Frame Slip - Nortel Meridian 1 Option 11C Manual

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Frame slip

553-3011-310 Standard 13.00
Digital signals must have accurate clock synchronization for data to be
interleaved into or extracted from the appropriate timeslot during
multiplexing and de-multiplexing operations. A frame slip is defined as the
repetition of, or deletion of, the 193 data bits of a DS-1 frame due to a
sufficiently large discrepancy in the read and write rates at the buffer (clocks
aren't operating at exactly the same speed).
When data bits are written into (added to) a buffer at a slightly higher rate than
that at which they are being read (emptied), sooner or later the buffer
overflows. This is a slip-frame deletion.
In the opposite situation, when data bits are written (added) into a buffer at
slightly lower rate than that at which they are being read (emptied), eventually
the buffer runs dry or underflows. This is also a slip-frame repetition.
Either occurrence is called a slip (or a controlled slip). The Option 11C
contains a buffer large enough to hold about 2 full DS-1 frames (193 * 2 =
386). It is normally kept half full (1 frame). Slippage has impact on the data
being transferred, as is shown in the table below, and all of the degradations
shown in the table can be controlled or avoided with proper clock (network)
synchronization.
Table 18
Impact of slip on service types
Service
Encrypted Text
Video
Digital Data
Facsimile
Voice Band Data
Voice
January 2002
Potential Impact
Encryption key must be resent.
Freeze frame for several seconds. Loud pop
on audio.
Deletion or repetition of Data. Possible
Misframe.
Deletion of 4-8 scan lines. Drop Call.
Transmission Errors for 0.01 to 2 s. Drop Call.
Possible Click