Bit Oriented Data Link Protocols Examples: ! High-level Data Link ...

Bit Oriented Data Link Protocols 

Examples: 

! High-level Data Link Control (HDLC) - ISO 

! Advanced Data Communications Control Procedures 

(ADCCP) - ANSI 

! Synchronous Data Link Control (SDLC) - IBM 

! Link Access Procedure, Balanced (LAPB) - ITU-T (for 

X.25) 

! Link Access Procedure, D-Channel (LAPD) - ITU-T (for 

ISDN) 

! Link Access Procedure for Frame-Mode Bearer Services 

(LAPF) 

! Logical Link Control (LLC) - IEEE 802.2 

Copyright © December 21, 2004 by Chaim Ziegler, Ph.D. 

DataLink2-1

HDLC 

! Type of Stations: 

1. Primary (issues commands) 

2. Secondary (issues responses) 

3. Combined 

! Link Configurations: 

1. Unbalanced: 

Consists of one primary and one or more 

secondaries. 

2. Balanced: 

Consists of two combined stations only. 



HDLC Data Transfer Modes: 

! Normal Response Mode (NRM): 

This is an unbalanced configuration. The primary 

uses polling and selection. 

! Asynchronous Response Mode (ARM): 

This is an unbalanced configuration. The secondary 

may send response frames without explicit 

permission from the primary. 

! Asynchronous Balanced Mode (ABM): 

This is a balanced configuration. Either combined 

station may initiate transmission. 



HDLC Frame Structure 

! All transmissions use frames w ith follow ing fields: 

- Flag: 8 bits (01111110) with bit stuffing 

- Address: One or more octets (for multipoint lines) 

- Control: 8 or 16 bits 

- Information: variable length 

- Frame Check Sequence (FCS): 16 or 32 bits 

- Flag: 8 bits 

! Types of Frames: 

- Information Frames (I Frames) 

- Supervisory Frames (S Frames) 

- Unnumbered Frames (U Frames) (IBM - NS) 

! HDLC uses synchronous transmission 



HDLC Command/Response Repertoire 

Format Commands Responses C-Field Format 

8 7 6 5 4 3 2 1 

Information 

Transfer 

I 

(Information) 

I 

(Information) 

N(R) 

P 

F 

N(S) 0 

RR 

(Receive Ready) 

RR 


N(R) 

P 

F 

0 0 0 1 

Supervisory 

RNR 

(Receive Not 

Ready) 

REJ 

(Reject) 

RNR 

(Receive Not 

Ready) 

REJ 

(Reject) 

N(R) 

N(R) 

P 

F 

P 

F 

0 1 0 1 

1 0 0 1 

SREJ 

(Selective Reject) 

SREJ 


N(R) 

P 

F 

1 1 0 1 

SNRM 

(Set Normal 

Response Mode) 

1 0 0 P 1 1 1 1 

SARM 

Set Asynch. 


DM 

(Disconnect Mode) 

0 0 0 P 

F 

1 1 1 1 

Unnumbered 

SABM 

(Set Asynch. 

Balanced Mode) 

SNRME 

(Set Normal 


SARME 

Set Asynch. 


SABME 

(Set Asynch. 

Balanced Mode) 

0 0 1 P 1 1 1 1 

1 1 0 P 1 1 1 1 

0 1 0 P 1 1 1 1 

0 1 1 P 1 1 1 1 

DISC 

(Disconnect) 

RD 

(Request Disc.) 

0 1 0 P 

F 

0 0 1 1 

UA 

(Unnumbered Ack) 

0 1 1 F 0 0 1 1 

SIM 

(Set 

Initialization Mode) 

RIM 

(Request 

Initialization Mode) 

0 0 0 P 

F 

0 1 1 1 

FRMR 

(Frame Reject) 

1 0 0 F 0 1 1 1 

RSET 

(Reset) 

UP 

(Unnumbered Poll) 

1 0 0 P 1 1 1 1 

0 0 1 P 0 0 1 1 

UI 

(Unnumbered Info) 

UI 

(Unnumbered Info) 

0 0 0 P 

F 

0 0 1 1 

XID 

(Exchange ID) 

XID 

(Exchange ID) 

1 0 1 P 

F 

1 1 1 1 

TEST 

(Test) 

TEST 

(Test) 

1 1 1 P 

F 

0 0 1 1 



HDLC I Frame & S Frame Extended Numbering Formats 

Format Commands Responses C-Field Format 

8 7 6 5 4 3 2 1 

Information 

Transfer 

I 

(Information) 

I 

(Information) 

N(S) 0 

N(R) 

P 

F 

RR 


RR 


0 0 0 0 0 0 0 1 

N(R) 

P 

F 

Supervisory 

RNR 

(Receive Not 

Ready) 

RNR 

(Receive Not 

Ready) 

0 0 0 0 0 1 0 1 

N(R) 

P 

F 

REJ 

(Reject) 

REJ 

(Reject) 

0 0 0 0 1 0 0 1 

N(R) 

P 

F 

SREJ 


SREJ 


0 0 0 0 1 1 0 1 

N(R) 

P 

F 



HDLC Operation 

1. I-Frames: 

! Contains user data 

! Contains the sequence number of the transmitted 

frame 

! Contains a piggybacked acknowledgement for 

received I-frames (N(r) = Next frame expected) 

! Maximum window size is 7 or 127 

! I-frame contains a poll/final (P/F) bit. 

- In NRM the primary sets the P-bit to issue a 

POLL. The secondary sets the F-bit in last 

I-frame of a response. 

- In ARM and ABM, the P/F bit is used to force 

a response. 



2. S-Frames: 

Used for both flow control and error control 

a) Receive Ready (RR) 

! Used as positive acknowledgement (thru 

N(r)-1) when no I-frame is available for 

piggybacking. 

! Primary can issue a POLL by setting P-bit. 

! Secondary response w ith F-bit set if it has no 

data to send. 

b) Receive Not Ready (RNR) 

! Used as positive acknowledgement (thru 

N(r)-1) and a request that no more I-frames 

be sent until a subsequent RR is used. 

! Primary or Combined station can set P-bit to 

solicit the receive status of a 

secondary/combined station. 

! Secondary/Combined station response to Poll 

w ith F-bit set if the station is busy. 

c) Reject (REJ) 

! Go-Back-N technique (Retransmit from N(r)) 

d) Selective Reject (SREJ) 

! Selective Repeat technique (Repeat N(r)) 



3. U-Frames: 

Categories: 

! Mode Setting 

SNRM, SNRME, SARM, SARME, SABM, SABME 

UA, DM 

RIM, SIM 

RD, DISC 

! Information Transfer 

UP 

UI 

! Recovery 

FRMR, RSET 

! Miscellaneous 

XID 

TEST 

- Invalid Control Field 

- Data Field Too Long 

- Data Field Not Allow ed With Received 

Frame Type 

- Invalid Receive Count 



HDLC Command/Response Repertoire Options 

Basic Repertoire: 

Commands: 

I, RR, RNR, (SNRM or SARM or SABM), DISC 

Responses: 

I, RR, RNR, UA, DM, FRMR 

Functional Extensions (Options): 

1. For Switched Circuits 

Commands: ADD - XID; Responses: ADD - XID, RD 

2. For 2-way Simultaneous 

Commands & Responses: ADD - REJ 

3. For Single Frame Retransmission 

Commands & Responses: ADD - SREJ 

4. For Information 

Commands & Responses: ADD - UI 

5. For Initialization 

Commands: ADD - SIM; Responses: ADD - RIM 

6. For Group Polling 

Commands: ADD - UP 

7. Extended Addressing 

8. Delete Response I Frames 

9. Delete Command I Frames 

10. Extended Numbering 

11. For Mode Reset (ABM only) 

Commands: ADD - RSET 

12. Data Link Test 

Commands & Responses: ADD - TEST 

13. Request Disconnect 

Responses: ADD - RD 

14. 32-bit FCS 



Examples of HDLC Operation 

Link Establishment and Termination - NRM 



Data Transfer - NRM 



Link Establishment and Termination - ABM 



Data Transfer - Balanced Mode 



Busy Condition 



Reject Recovery 



Selective Reject Recovery 



Timeout Recovery 



LAPB State Diagram 

! LAPB Addresses: 



LAPB Commands and Responses 



Various Data Link Control Frame Formats 



The Point-to-Point Protocol (PPP) 

! Used on the Internet for router-to-router and home 

user-to-ISP data links. 

! PPP provides three features: 

- A framing method that delineates frames. the frame 

format also handles error detection. 

- A Link Control Protocol (LCP) for bringing lines up, 

testing them, negotiating options, and bring 

them down gracefully. This protocol supports 

both synchronous and asynchronous circuits and 

both byte-oriented and bit-oriented encodings. 

- A w ay to negotiate netw ork layer options in a w ay 

that is independent of the network layer protocol 

used. A different Network Control Protocol 

(NCP) is used for each network layer supported. 



PPP State Diagram for Line Activation 

! Dead (or IDLE): 

No active carrier or connection exists. 

! Establish: 

LCP option negotiation begins. 

! Authenticate (optional): 

The two end points authenticate each other. 

! Network: 

The appropriate NCP protocol is invoked. 

! Open: 

Data transport takes place. 

! Terminate: 

The connection is closed. 



PPP Frame Format 

! The PPP frame format is similar to HDLC. 

! The address and control fields are always constant. 

! The Protocol field indicates what kind of packet is in 

the Payload field (e.g., LCP, NCP, IP, IPX, AppleTalk, 

etc.) 

! The Payload field has a variable length and its 

maximum is negotiated. The default maximum is 

1500 bytes. 



The Link Control Protocol (LCP) 

! LCP Packet Encapsulated in a PPP Frame: 

- Code: Defines the type of LCP packet. 

- ID: Value used to match a request w ith a response. 

! LCP Packets (Protocol field = C021 

16): 

Options: packet size, authentication, compression. etc. 



The Password Authentication Protocol (PAP) 

! Authentication means validating a user w ho needs to 

access a set of resources. 

! PPP has two protocols for authentication: Password 

Authentication Protocol (PAP) and Challenge 

Handshake Authentication Protocol (CHAP). 

! PAP: 

! PAP Packets (Protocol field = C023 

16): 



Challenge Handshake Authentication Protocol (CHAP) 

! CHAP - 3-w ay handshake (passw ord is never sent): 

! CHAP Packets (Protocol field = C223 

16): 



The Network Control Protocol (NCP) 

! NCP is a set of control protocols to allow the 

encapsulation of data from various netw ork layer 

protocols; such as, IP, IPX, AppleTalk, etc.. 



The Internetwork Protocol Control Protocol (IPCP) 

! IPCP is the protocol used to establish a netw ork layer 

connection for carrying IP data. 

! IPCP Packet Encapsulation in a PPP Frame: 

! IPCP Packets: (protocol field = 802116): 

- Configure-request 

- Configure-ack 

- Configure-nak 

- Configure-reject 

- Terminate-request 

- Terminate-ack 

- Code-reject 

! Note: 

After configuration, the link is ready to carry IP data 

in the payload field of a PPP frame. The protocol field 

value is set to 002116 

to indicate IP data is being 

carried. 



Example PPP Session

Bit Oriented Data Link Protocols Examples: ! High-level Data Link ...

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