Configuring hdlc, Overview, Hdlc frame format and frame type – H3C Technologies H3C SR8800 User Manual
Page 50: Enabling hdlc encapsulation on an interface
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Configuring HDLC
Overview
High-level Data Link Control (HDLC) is a bit-oriented link layer protocol. Its most prominent feature is that
it can transmit any types of bit stream transparently.
•
HDLC supports point-to-point link only and does not support point-to-multipoint link.
•
HDLC supports neither IP address negotiation nor authentication. It uses keepalive messages to
check link status.
•
HDLC works only on synchronous interfaces or synchronous/asynchronous interfaces in
synchronous mode. The router supports HDLC encapsulation only on POS interfaces.
HDLC frame format and frame type
HDLC frames fall into the following types: information frame (I frame), supervision frame (S frame) and
unnumbered frame (U frame).
•
Information frame transmits useful data or information.
•
Supervision frame is responsible for error control and flow control.
•
Unnumbered frame is responsible for the link establishment, teardown, and so on.
An HDLC frame is composed of flag field, address field, control field, information field and checksum
field:
•
The flag field, 0111110, marks the beginning and end of an HDLC frame. Each frame begins with a
7E and ends with a 7E. The 7E between two neighboring frames functions both as the end of the
frame in the front and as the beginning of the following frame.
•
The address field is eight bits and identifies the source or destination where the frame is sent or
received.
•
The control field is eight bits and identifies the control type and defines the frame type (control or
data).
•
The information field can be an arbitrary binary bit set. The minimum length can be zero and the
maximum length is decided by the frame check sequence (FCS) field or the buffer size of the
communicating node. Usually, the maximum length is between 1000 and 2000 bits.
•
The checksum field can use a 16-bit CRC to check the content of a frame.
Enabling HDLC encapsulation on an interface
To enable HDLC encapsulation on an interface:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter interface view.
interface interface-type
interface-number
N/A
- H3C SR6600-X H3C SR6600 H3C MSR 5600 H3C MSR 50 H3C MSR 3600 H3C MSR 30 H3C MSR 2600 H3C MSR 20-2X[40] H3C MSR 20-1X H3C MSR 930 H3C MSR 900 H3C WX6000 Series Access Controllers H3C WX5000 Series Access Controllers H3C WX3000 Series Unified Switches H3C LSWM1WCM10 Access Controller Module H3C LSWM1WCM20 Access Controller Module H3C LSQM1WCMB0 Access Controller Module H3C LSRM1WCM2A1 Access Controller Module H3C LSBM1WCM2A0 Access Controller Module