Information About Configuring Serial Interfaces; Cisco Hdlc Encapsulation; Ppp Encapsulation - Cisco 800M Series Configuration Manual

Chapter 4 Configuring the Serial Interface
Table 4-2
LED Name
CONN
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Information About Configuring Serial Interfaces

To configure serial interfaces, you should understand the following concept:
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Cisco HDLC Encapsulation

Cisco High-Level Data Link Controller (HDLC) is the Cisco proprietary protocol for sending data over
synchronous serial links. Cisco HDLC also provides a simple control protocol called Serial Line Address
Resolution Protocol (SLARP) to maintain serial link keepalives. Cisco HDLC is the default for data
encapsulation at Layer 2 (data link) of the Open System Interconnection (OSI) stack for efficient packet
delineation and error control.
Note Cisco HDLC is the default encapsulation type for the serial interfaces.
When the encapsulation on a serial interface is changed from HDLC to any other encapsulation type, the
configured serial subinterfaces on the main interface inherit the newly changed encapsulation and they
do not get deleted.
Cisco HDLC uses keepalives to monitor the link state, as described in the
page

PPP Encapsulation

PPP is a standard protocol used to send data over synchronous serial links. PPP also provides a Link
Control Protocol (LCP) for negotiating properties of the link. LCP uses echo requests and responses to
monitor the continuing availability of the link.
LEDs on the Serial WAN Module
Cisco HDLC Encapsulation, page 41
PPP Encapsulation, page 41
Keepalive Timer, page 43
Frame Relay Encapsulation, page 44
4-43.
Cisco 800M Series Integrated Services Routers Software Configuration Guide
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Information About Configuring Serial Interfaces
Description
Indicates the interface status
and shows that line protocol is
up.
Shows that the line protocol is
down.
Indicates that the hardware
loopback status is configured
on the serial interface.
Indicates that loopback is not
configured.
"Keepalive Timer" section on
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