Chapter 21 Appendix A: Operation Commands
144
lmi_type polling is only needed if the protocol parameter is set to frame_relay.
ansi – ANSI DS1.616 Annex D
q933 – ITU Q.933 Annex A
n391 full status polling counter, 1 ~ 255 (optional for frame_relay and no need for
other protocol)
n392 error threshold before declaring link down., 1 ~ 10
(optional for frame_relay and no need for other protocols)
n393 monitored event count, 1 ~ 10
(optional for frame_relay and no need for other protocols)
t391 link integrity polling interval, 5 ~ 30
(optional for frame_relay and no need for other protocols)
HDLC Protocol Overview
HDLC (High-level Data Link Control) specifies a packetization standard for serial links. It is documented in
ISO 3309. HDLC supports several modes of operation. One such mode is a simple sliding window mode
which provides reliable delivery. Another mode, Unnumbered Information, is unreliable. Unfortunately,
because the Internet retransmits information at higher levels (ie. TCP), most Internet applications use this
unreliable mode.
The beginning and end of each HDLC frame is marked by the binary code flag characters 01111110 ( zero,
six ones, zero). Flag characters cannot appear in the intervening data. To make this work, data sometimes
needs to be modified in a transparent manner. On bit-synchronous links, a method called bit stuffing is used.
In bit stuffing a binary 0 is inserted after every sequence of five 1s. Thus, the longest sequence of 1s that
may appear in the data is 0111110, a sequence that only has five 1s. The receiver, upon seeing the five 1s,
examines the next bit. If it is 0, the bit is discarded and the frame continues. If it is 1, then the receiver
knows that this must be the flag sequence at the end of the frame.
Data integrity is checked at the end of the frame by a Frame Check Sequence (FCS). The Frame Check
Sequence is a Cyclic Redundancy Check (CRC) calculated using the polynomial x^16 + x^12 + x^5 + 1.
Between HDLC frames, the link is in what we refer to as an idle state. Most synchronous links constantly
transmit data when in the idle state. The links can transmit all 1s, which is called mark idle; or they can
transmit all flag characters which is called flag idle.
Command: >set wan1 pvc dlci
Syntax: set wan1 pvc dlci pvc_no dlci [CIR] [Bc] [Be]
Explanation: To create/delete a Frame Relay PVC or set the DLCI number when the WAN1 is running
Frame Relay.
Parameters: pvc_no the pvc number, value from 1 ~ 10
dlci DLCI of the WAN1, 16 ~ 991
CIR Committed Information Rate (kbps)
Bc Committed Burst Size (kbits)
Be Excess Burst Size (kbits)
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