
PRS28.4G
IBM Packet Routing Switch
prs28.03.fm
August 31, 2000
Architecture
Page 21 of 131
2.1.12.3 Colored Packet
Idle Packets and Data Packets also carry a color, either blue or red. Color packets are used to provide
support for packet lossless switchover.
Some Idle Packets carry a yellow color. The reception of a yellow Idle Packet on a given input is logged into a
register accessible by the local processor. Yellow packets can only be transmitted by the local processor.
Yellow packets are used as link liveness messages.
2.1.12.4 Control Packets
Data Packets for which the bit map field is 0 are detected as control packets and are passed to the local
processor via a dedicated queue. The first bit map byte of an incoming packet is overwritten by the input port
number on which the packet is received.
2.1.12.5 Queue Full
Queue-full information is also provided directly by the island. Sixteen bits carry all logical port full statuses, by
multiplexing the information of all priorities of a given port over one bit. At a given time, all 16 bits carry the full
status for the same priority, for all output queues. All priorities rotate, from the lowest number to the highest,
in a cyclic manner, while the change from one priority to the next only occurs after four byte cycles. An extra
bit indicates when all 16 queue-full bits carry priority 0, and is used to synchronize to this cycle.
2.1.12.6 Queue Empty
Queue-empty information is also provided by a 16-bit bus, for all logical output queues. The information multi-
plexing and timing is identical to the queue-full bits.
2.1.12.7 Look-Up Table
The lookup table is a facility that allows permutation of the bytes of outgoing packets. Only the first 16 bytes
can be permuted among each other or overwritten by one of the 16 bytes. One table is provided for all output
ports.