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Configuring the Data Link Layer Protocol for E1, T1, and Serial Interfaces
Configuring the Logical Interface
Configuring HDLC as the Data Link Layer Protocol
One of the oldest Data Link Layer protocols for a WAN, HDLC actually
predates the PC. Although it was developed for a mainframe environment,
which includes primary and secondary devices, HDLC has been updated for
use in the PC environment. However, some functionality and terminology have
survived from its early use, as evidenced by its modes of operation.
HDLC has three modes of operation:
Normal Response Mode (NRM). A secondary device can transmit only
when the primary device specifically instructs it to do so.
Asynchronous Response Mode (ARM). A secondary device can initiate a
transmission; however, the primary device controls the establishment and
termination of the link.
Asynchronous Balanced Mode (ABM). Devices at both ends of a connec-
tion are configured to be both primary and secondary devices and can establish
a link, transmit data without permission, and terminate a link.
When you configure the ProCurve Secure Router to use HDLC for an E1 or T1
connection, it operate in ABM.
HDLC uses three different types of frames:
■ Unnumbered frames establish a link.
■ Supervisory frames carry error and flow control information.
■ Information frames carry the Network Layer packets across the WAN link.
Create the HDLC Interface
To begin configuring HDLC as the Data Link Layer protocol for an E1, T1, or
serial interface, you must create a logical interface. From the global configura-
tion mode context, enter:
Syntax: interface <interface> <number>
Replace <interface> with HDLC and replace <number> with any number
between 1 and 1024. Each HDLC interface you configure on the router must
have a unique number.
For example, if you are configuring the first HDLC interface on the router, you
could enter:
ProCurve(config)# interface hdlc 1
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