
PM73487 QRT
PMC-Sierra, Inc.
PMC-980618
Issue 3
622 Mbps ATMTraffic Management Device
Released
Datasheet
38
lar to the SC1 and SC2 classes (Q
2
, Q
10
, Q
3
, Q
41
, Q
11
, ..., Q
7
, Q
15
, Q
2
, ...).
The transmit queue controller scheduler provides the following benefits:
QoS - the strict priority scheme among SC1, SC2, and GP SCs, and the weighted round-
robin algorithms allows satisfaction of QoS guarantees.
CDV minimization - the treatment of the strict priority SCs ensure that cells within these
SCs get timely service.
MCR guarantee - the timeslot table ensures all SCs will receive a minimum amount of
servicing (clearly, the aggregate bandwidth given to the SC1 and SC2 VCs affects the
remaining bandwidth to be divided between the GP SCs).
Fairness maximization - the weights of the SCs (1, 4, 16, or 64) allow different SCs to
support different bandwidth requirements (for example, high bandwidth SCs are assigned
64 and are serviced 64 times as often as low bandwidth SCs, which are assigned 1).
Output isolation - the cells of channels destined for different VOs are kept in separate data
structures. This helps isolate the effects of congestion on one VO from causing congestion
on another VO.
Figure 42. Transmit Service Class (SC) Map (Per VO)
Unicast Traffic
Multicast Traffic
Strict Priority SC1
Strict Priority SC2
Timeslot-Based Priority
General Purpose
Weighted Round-
Robin SCs
Q
0
Q
1
Q
2
S
0
S
1
Q
3
Q
4
Q
5
Q
6
Q
7
S
125
S
126
VC
Cells are FIFO-Queued
within an SC
Q
8
Q
9
Q
10
Q
11
Q
12
Q
13
Q
14
Q
15