
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
94
When a group is already started, IMA supports the addition of links to the group.
As illustrated by Figure 15, adding a link with a transport delay that is within the
range of the existing links does not present any problems. The DCB for the new
link must be aligned with the existing links and added to the round-robin for
playout.
Adding a link with a smaller transport delay increases the differential delay of the
group. This requires that the depth of the DCB buffer be larger than any of the
existing links. As long as the differential delay is within acceptable bounds, the
new link can be accepted. The DCB for the new link is aligned with the existing
links and added to the round-robin for playout.
Figure 16
transport delay
- Snapshot of DCB Buffers after addition of Link with smaller
1
9
13
17
21
25
5
DCB
Link 0
2
10
14
6
3
7
DCB
Link 1
DCB
Link 2
Write
Pointer 0
Write
Pointer 1
Write
Pointer 2
Group
Read
Pointer
4
12
16
20
24
28
32
8
36
DCB
Link3
Write
Pointer 3
Adding a link with a larger transport delay requires the DCB buffer depth to be
smaller than the DCB for the link with the largest delay. If the desired DCB depth
for the new link is less than 0, this means that the data for the other links has
been played out prior to the arrival of data for the new link. This is shown in
Figure 17. For the new link to be accepted, delay must be added to all other links
in the group. When delay is added to the other links in the group, the playout of
ATM cells is halted until enough delay is built up. This causes CDV for the group.