IBM PowerPRS Q-64G
Preliminary
Packet Routing Switch
3. Functional Description
This section describes basic PowerPRS Q-64G functionality, including information about:
• Packet type
• Physical interface and packet processing
• Packet format according to packet type
• Ingress, egress, and subport flow control
• Packet reception and transmission
• Side communication channel
• Switchover support
3.1 Packet Types
There are four types of packets:
• Data packets
• Control packets
• Service packets
• Idle packets
All the packet types can be carried on either the high channel or the low channel. These two channels simul-
taneously carry one packet apiece, and the packets can be different types.
Note: The grants used for ingress, egress, and subport flow control are carried in the header and payload of
ingress and egress packets. See Section 3.3 Packet Format According to Packet Type on page 28 for more
information.
3.1.1 Data Packets
Data packets contain user data to be switched from an input to one or more outputs. Data packets have a
priority of 0, 1, 2, or 3, with 0 being the highest priority. In the basic configuration, the PowerPRS Q-64G
output queue scheduler prioritizes packet transmission for each output port in the following order:
1. Service packets
2. Control packets
3. Priority 0 data packets
4. Priority 1 data packets
5. Priority 2 data packets
6. Priority 3 data packets
Besides the packet priority, data packets also carry routing information (destination bitmap), filtering informa-
tion used for switchover support (color coding), and a “best-effort discard” flag.
prsq-64g.01.fm
December 20, 2001
Functional Description
Page 25 of 199
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