DCN386 Introduction To SDLC

SDLC Intro-Continue
P=Primary Unit
S=Secondary Unit

-SDLC is a primary Systems Network Architechture (SNA) link layer protocol for WAN links

-Used with PPP & multipoint links bounded & unbounded media, half & full duplex transmission, transmission facilities, and circuit switched and packet switched networks.

- Network nodes: primary and secondary

Primary - control the operation of other station called, secondaries.

P & S connected by four basic configs-

Point-to-Point - two nodes 1P & 1S
Multipoint - 1P 2xS
Loop - topology P = First & Last S (connected to first and last S)
Hub go-ahead - In bound/outbound channel
P-outb-S S-inb-P
In bound daisy-chained back to the P through each S
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Derivative Protocols
- IEE 802.2 LLC is a modification of HDLC for LAN enviroments

-HDLC is a compatible super set of SDLC

-Qualified logical link control is a link layer protocol defined by IBM that allows SNA to be transported across X.25 networks.

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High-Level Data Link Control (HDLC)
-HDLC supports sync, full-duplex operation

-HDLC 32-bit checksum, does not support the loop or hub go-ahead configs

SDLC 1 transfer mode
HDLC Supports THREE:

Normal Response Mode (NRM) - Used by SDLC. S cannot communicate with a P until P gives permission

Asynchronous Response Mode (ARM) - S to intiate comm w/ a P unitil P have given permission

Asynchronous balanced Mode (ABM) - Combined mode ABM - act as a P or S depending on the situation - Occurs through multiple combined nodes - No permission required-

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Link Access Procedure Balance
- in X.25 protocol stack
- shares same frame types, and field functions as SDLC & HDLC
- Restricted to ABM
- Can be established through DTE & DCE
- Intiate call P responding S
- LAPB use of the P/F bit is different from that of other protocols
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IEEE 802.2
Three types of service
T1- procides unack connectionless service
-TCP/IP componsate for this
-commonly used

T2 -connection oriented
-ack data upon receipt
-used in IBM communication

T3 -ACK service
-Factory automated enviroments
-where eroor detection is important

Upper-layer proccess use IEEE 802.2 services through service access points.

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802.2 header DSAP - Destination service acc point
- identifies the receiving upper-layer proccesses
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