Applied Innovation AISwitch AI2524, User Manual, Page: 310 / 418

AI2524 Router Card User’s Manual
Page 12-52 August 1997
2524UM
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LAPB T4. The LAPB standards define a timer to detect unsig-
naled link failures (T4). The T4 timer is reset every time a frame
is received from the partner on the link. If the T4 timer expires,
Receiver Ready frame with the Poll bit set is sent to the partner,
which is required to respond. If the partner does not respond, the
standard polling mechanism is used to determine whether the link
is down. The period of T4 must be greater than the period of T1.
Another LAPB timer function allows brief hardware failures
while the protocol is up, without requiring a protocol reset. When
a brief hardware outage occurs, the link will continue uninterrupt-
ed if the outage is corrected before the specified hardware outage
period expires.
Configure LAPB Priority and Custom Queuing
AI2524 priority queuing and custom queuing are available for LAPB
to allow you to improve link responsiveness to a given type of traffic
by specifying the priority of that type of traffic for transmission on the
link.
Priority queuing is a mechanism that classifies packets based on cer-
tain criteria and then assigns the packets to 1of 4 output queues, with
high, medium, normal, or low priority. Custom queuing similarly clas-
sifies packets, assigns them to 1 of 10 output queues, and controls the
percentage of an interface's available bandwidth that is used for a
queue.
For example, you can use priority queuing to ensure that all Telnet
traffic is processed promptly and that Simple Mail Transfer Protocol
(SMTP) traffic is sent only when there is no other traffic to send. Pri
ority queuing in this example can starve the non-Telnet traffic; custom
queuing can be used instead to ensure that some traffic of all categories
is sent.
Both priority queuing and custom queuing can be defined, but only
one method can be assigned to a given interface.
To configure priority and custom queuing for LAPB, perform thes
tasks:
1. Perform the standard priority and custom queuing tasks except the
task of assigning a priority or custom group to the interface.
2. Perform the standard LAPB encapsulation tasks, as specified in
the
Configure a LAPB Datagram Transport section of this chapter.
3. Assign either a priority group or a custom queue to the interface.