PM7341 datasheet(91/413 Pages) PMC

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PRELIMINARY

INVERSE MULTIPLEXING OVER ATM

PM7341 S/UNI-IMA-84

DATASHEET

PMC-2000223

ISSUE 4

INVERSE MULTIPLEXING OVER ATM

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

10.2.4.5

Delay Compensation Buffers

Since IMA must re-create the original cell stream in the proper order, delay

compensation buffers (DCBs) are used to remove the differential delay between

the links in a group. As cells arrive from each link, they are placed in that link’s

DCB. Links with the least transport delay will have the largest amount of data in

the DCB, while links with the largest amount of transport delay will have the least

amount of data in the DCB.

At group start-up, all the links are compared to determine the link with the largest

transport delay and the link with the least transport delay. The difference between

these is the differential delay. Data is queued for all links until the corresponding

data arrives for the link with the largest transport delay. Figure 15, shows a group

with 3 links with a differential delay of 5 cells. Link 0 has the shortest transport

delay and link 2 has the longest transport delay. Once the data has arrived for all

of the links, it is played out to the ATM layer at the IDCC rate, thus keeping the

depths of each DCB at a nominally constant level. (Depths are instantaneously

effected by the presence of stuff cells and ICP cells, but these effects are

transitory).

Figure 15

- Snapshot of DCB Buffers

DCB

Link 0

DCB

Link 1

DCB

Link 2

Write

Pointer 0

Write

Pointer 1

Write

Pointer 2

Group

Read

Pointer

PM7341 Datasheet(PDF) 91 Page - PMC-Sierra, Inc

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