Install guide

22 Release Note
Rapier Switch Software Release 2.1.0
C613-10200-01 Rev A
senders of traffic on ports which have too many packets in the input queue can
be informed of the situation and made to restrict the flow of packets.
Flow control for Ethernet ports consists of two mechanisms. The mechanism
for a given port is dependent on the duplex mode of the port. For full duplex
ports, flow control is achieved by sending a special PAUSE MAC frame out the
port, which tells the sending device not to send any more frames for a random
period of time. This mechanism is defined in IEEE Standard 802.3. For half
duplex ports, flow control is achieved by asserting the jamming signal on the
port, a mechanism known as back pressure. The jamming signal causes
collisions on the link, so that the sending device waits for a random period of
time before sending any more frames.
The maximum size of the ingress queue depends on the model. For any given
port on the switch, there will be a command to control whether either of the
mechanisms for flow control will be employed. The following table illustrates
this. This shows the action taken on a port of given duplex mode with the
various combinations of flow control enabled, when the flow control state is
entered.
Both kinds of flow control are enabled by default on every Ethernet port, and
they can be enabled and disabled using the command:
ENABLE SWITCH PORT=port-list
FLOW={JAMMING|PAUSE}[,{PAUSE|JAMMING}]
DISABLE SWITCH PORT=port-list
FLOW={JAMMING|PAUSE}[,{PAUSE|JAMMING}]
The FLOW parameter specifies the types of flow control to be enabled for the
port. One or both types may be enabled with this command. If JAMMING is
specified, flow control for half duplex ports by asserting the jamming signal
will be enabled. If PAUSE is specified, flow control for full duplex ports by
sending PAUSE frames will be enabled. Both these forms of flow control are
enabled by default.
Table 7shows the effect of flow control parameter settings on the behaviour of
ports when maximum ingress queues are exceeded.
For the Rapier switch, jamming on all half duplex ports is set by a single
parameter. The Rapier switch will not reach the jamming threshold, but will
discard packets before reaching this limit.
Port trunking
Port trunking, also known as port bundling or link aggregation, allows a
number of ports to be configured to join together to make a single logical
connection of higher bandwidth. This can be used where a higher performance
link is required, and makes links even more reliable.
Table 7: Effect of flow control parameters on ports
Flow control parameter settings Half duplex Full duplex
PAUSE disabled and jamming disabled packets discarded packets discarded
PAUSE disabled and jamming enabled assert jamming packets discarded
PAUSE enabled and jamming disabled packets discarded send PAUSE
PAUSE enabled and jamming enabled assert jamming send PAUSE