AI2524 Router Card User’s Manual
Page 12-48 August 1997
2524UM
Configure LAPB You can use only LAPB as a serial encapsulation method if you hav
a private serial line. You must use one of the X.25 packet-level encap-
sulations when attaching to an X.25 network.
The LAPB standards distinguish between two types of hosts: Data
Terminal Equipment (DTE), and Data Circuit-terminating Equipment
(DCE). At Level 2, or the data link layer in the OSI model, LAPB al-
lows for orderly and reliable exchange of data between a DTE and a
DCE. A router using LAPB encapsulation can act as a DTE or DCE
device at the protocol level, which is distinct from the hardware DTE
or DCE identity.
Using LAPB under noisy conditions can result in greater throughput
than HDLC encapsulation. When LAPB detects a missing frame, th
router retransmits the frame instead of waiting for the h igher layers to
recover the lost in formation. This behavior is good on ly if the host tim-
ers are relatively slow. In the case of quickly expiring host timers,
however, you will discover that LAPB is spending much of its tim
transmitting host retransmissions. If the line is not noisy, the lower
overhead of HDLC encapsulation is more efficient than L A PB. When
you are using long-delay satellite links, for example, the lock-step be-
havior of LAPB makes HDLC encapsulation the better choice.
To configure LAPB, complete these tasks. The tasks in the first section
are required; the remaining are optional.
zConfigure a LAPB Datagram Transport
zModify LAPB Protocol Param eters
zConfigure LAPB Priority and Cus tom Queuing
zConfigure Transparent Bridging over Multiprotocol LAPB
zMonitor and Maintain LAPB and X.25
Configure a LAPB Datagram Transport
Set the appropriate LAPB encapsulation to run da tagrams o ver a serial
interface. One end of the link must be DTE, the other must be DCE.
1. Specify a serial interface.
interface serial
number