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Chapter 12: AI2524 X.25 Configuration Steps
August 1997 Page 12-49
2524UM
2. In interface configuration mode, select an encapsulation and pro-
tocol if using a single protocol or select the multiple protocol op-
eration by performing one or more of these tasks:
z
Enable encapsulation of a single protocol on the line using DCE
operation.
encapsulation lapb dce [
protocol
]
z
Enable encapsulation of a single protocol on the line using DTE
operation.
encapsulation lapb [dte] [
protocol
]
z
Enable use of multiple protocols on the line using DCE opera
tion.
encapsulation lapb dce multi
z
Enable use of multiple protocols on the line using DTE opera-
tion.
encapsulation lapb [dte] multi
Single protocol LAPB defaults to IP encapsulation. Multiprotocol
LAPB does not support source-route bridging or TCP/IP header com-
pression, but does support transparent bridging. Only protocols sup-
ported by a single protocol encapsulation are supported by
multiprotocol LAPB encapsulation.
Example: Typical LAPB Configuration
In this example, the frame size (N1), window size (k), and maximum
retransmission (N2) parameters retain their default values. The
en-
capsulation
interface configuration command sets DCE opera-
tion to carry a single protocol, IP by default. The
lapb t1
interfac
configuration command sets the retransmission timer to 4,000 milli-
seconds (4 seconds) for a link with a long delay or slow connecting
DTE device.
interface serial 3
encapsulation lapb dce
lapb t1 4000
Modify LAPB Protocol Parameters
X.25 Level 2 or LAPB operates at the data link layer of the OSI refer-
ence model. LAPB specifies methods for exchanging data (in units
called frames), detecting out-of-sequence or missing frames, retrans
mitting frames, and acknowledging frames. Several protocol parame-