T-8110L AGERE [Agere Systems], T-8110L Datasheet - Page 139

• Manufacturer Part Number: T-8110L
• Manufacturer: AGERE [Agere Systems]

February 2004
Agere Systems Inc.
Appendix A. Constant and Minimum Delay Connections
A.1 Connection Definitions
A forward connection is defined as one in which the output to time slot has a greater value than the input from time
slot, or, put another way, the delta between them is positive.
A reverse connection is defined as one in which the output to time slot has a lesser value than the input from time
slot, and the delta between them is negative.
For example, going from TS(1) to TS(38) is a forward connection, and the TS is +37, but going from TS(38) to
TS(1) is a reverse connection, with a TS of –37:
Similarly, a delta can be introduced for streams which will have a bearing in certain exceptions (discussed later):
There is only one combination which forms a TS of +127 or –127:
but there are two combinations which form TS s of +126 or –126:
there are three combinations which yield +125 or –125, and so on.
The user can utilize the TS to control the latency of the resulting connection. In some cases, the latency must be
minimized. In other cases, such as a block of connections which must maintain some relative integrity while cross-
ing a frame boundary, the required latency of some of the connections may exceed a one frame (>128 time slots)
to maintain the integrity of this virtual frame.
The device uses a control bit at each connection memory location, VFC, for controlling latency, allowing each con-
nection to select one of two alternating data buffers.
A.2 Delay Type Definitions
Constant Delay—This is a well-defined, predictable, and linear region of latency in which the to time slot is at
least 128 time slots after the from time slot, but no more than 256 time slots after the from time slot.
Mathematically, constant delay latency is described as follows*, with L denoting latency, and VFC set to the value
indicated:
Example:
Simple summary:
* Since TS = TS( to ) –TS( from ), the user can modify the equations to solve for either TS( to ) or TS( from ).
Switching from TS(37) to TS(1) as a constant delay, the delta is –36, so FME is set to 0 and the result-
ing latency is 256 – 36 = 220 time slots. Thus, the connection will be made from TS(37) of frame(n) to
TS(1) of frame(n + 2).
where TS = TS(to) – TS(from).
STR = STR(to) – STR(from).
TS = TS(127) – TS(0) = +127, and
TS = TS(0) – TS(127) = –127,
TS = TS(127) – TS(1) = TS(126) – TS(0) = +126, and
TS = TS(1) – TS(127) = TS(0) – TS(126) = –126,
Forward connections, VFC = 1: L = 128 + TS (0
Reverse connections, VFC = 0: L = 256 + TS (–127
Use constant delay for latencies of 128 to 256 time slots,
set VFC = 1 for forward connections,
set VFC = 0 for reverse connections.
Ambassador T8110L H.100/H.110 Switch
TS
TS
127)
–1)
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