Cisco Hdlc; Table 14: Chdlc I-Frame; Table 15: Chdlc Protocol Fields - Alcatel-Lucent 7750 Configuration Manual

Port Features

Cisco HDLC

Cisco HDLC (cHDLC) is an encapsulation protocol for information transfer. It is a bit-oriented
synchronous data-link layer protocol that specifies a data encapsulation method on synchronous
serial links using frame characters and checksums.
cHDLC monitors line status on a serial interface by exchanging keepalive request messages with
peer network devices. It also allows routers to discover IP addresses of neighbors by exchanging
Serial Link Address Resolution Protocol (SLARP) (see
address-response messages with peer network devices.
The basic frame structure of a cHDLC frame is shown in
to PPP in an HDLC-link frame (RFC 1662, PPP in HDLC-like Framing). The differences to PPP
in and HDLC-like frames are in the values used in the address, control, and protocol fields.

Table 14: cHDLC I-Frame

Flag
0x7E
•
•
•

Table 15: cHDLC Protocol Fields

IP
Cisco SLARP
ISO CLNP/ISO ES-IS DSAP/SSAP1
•
•
Page 68
Address
0x0F/0x8F
Address field — The values of the address field include: 0x0F (unicast), 0x8F (broadcast).
Control field — The control field is a
Protocol field — The following values are supported for the protocol field:
Protocol
Information field — The length of the information field is in the range of 0 to 9Kbytes.
FCS field — The FCS field can assume a 16-bit or 32-bit value. The default is 16-bits for
ports with a speed equal to or lower than OC-3, and 32-bits for all other ports. The FCS for
cHDLC is calculated in the same manner and same polynomial as PPP.
SLARP on page
Control Protocol
0x00 —
ways set to value 0x00.
l
Field Value
0x0800
0x8035
0xFEFE
7750 SR Interface Configuration Guide
69) address-request and
Table 14. This frame structure is similar
Information
Field
—
FCS
16/32 bits