Other Data Link Protocols: Computer Networks by Prof Kamal K Mehta Associate Professor Dept of Computer Science & Engineering

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1 Other Data Link Protocols:

2 Data Link Protocol ategories A protocol in data communications is the set of rules or specifications used to implement partially a layer or one or more layers of the OSI model. Above protocol is used to implement the data link layer

3 Data Link Protocol ategories Asynchronous protocols - treat each character in a bit stream independently - use start and stop bits to frame the data units - inexpensive - used primarily in modems Synchronous protocols - take the whole bit stream and chop it into characters of equal size - faster than asynchronous transmission

4 Other Data Link Protocols: Examples A: Asynchronous Protocols X-Modem, Y-Modem, Z-Modem, BLAST, KERMIT B: Synchronous Protocols har Oriented Protocols like BS Bit Oriented Protocols like SDL,HDL, LAPs

5 Asynchronous Protocol XMODEM Frame Half-duplex stop-and-wait ARQ protocol SOH Start of Header (1 byte) R - yclic Redundancy heck Signal from receiver side - AK - NAK - AN (cancel)

6 Asynchronous Protocols Example: Find out the maximum possible channel utilization by X Modem Asynchronous Protocol, assuming a text file of 100 characters for transmission.

7 Asynchronous Protocols Example: Text document of 100 characters. Each character is represented 8 bits per character + 1 Bit Start + 1 Bit Stop = 10 bits. So for 100 character = 100x10 = 1000 bits. Ideally we must take 800 bits, but practically we need 1000 bits. Over head bits are =200 bits In terms of character = 200/8=25 character. Hence we can say that on behalf of 100 character we are transmitting (100+25) characters extra. = (100/125) x 100 = 80 % maximum Efficiency will further decrease, if we add transmission overhead, Retransmission etc.

8 YMODEM similar to XMODEM Major differences Data unit = 1024 bytes ANs = 2 Follows ITU-T R-16 format

9 What is R-16 R-12? Example: R-12 = x 12 +x 11 +x 3 +x 2 +x+1 R-16 = x 16 +x 15 +x 2 +1 R-ITT = x 16 +x 12 +x 5 +1 R-16 and R-ITT catch all Single and double errors Odd number of bit errors Bursts of length 16 or less % of 17-bit error bursts % of 18-bit and longer error bursts ITT :(onsultative ommittee for International Telephony and Telegraphy) R-16 calculation link

10 BLAST (BLocked ASynchronous Transmission), like XMODEM, it is a communications protocol for file transfer over asynchronous communication ports and dial-up modems by ANSI. Features of Blast: bit-oriented data encoding R (cyclic redundancy check) error detection a sliding window transmission scheme selective retransmission of corrupted blocks simultaneous bi-directional data transfer

11 Kermit: It is ftp by olumbia university It is a computer file transfer/management protocol. It provides a consistent approach to file transfer, terminal emulation, and character set conversion across many different computer hardware and OS platforms. Emulation: Hardware and Software that enables one computer to behave like another computer. Terminal emulation: omposed of LI: ommand line interface TUI : Text User Interface

12 Z Modem: Telenet funded a project Application file transfer protocol. Throughput problems of XMODEM and KERMIT resolved Reliability over packet switched networks while preserving XMODEM's simplicity.

13 Summary for Asynchronous: 1. Transmission of two extra bits (2 per byte) reduce data throughput. 2. Synchronization is achieved for each character only. 3. When the sender has no data to transmit (idle line) then the sender and receiver are NOT synchronized. 4. Asynchronous protocols are suited for low speed data communications. Asynchronous transmission, we relied on the start bit to start the motor and thus begin the preparation to decode the incoming character.

14 Synchronous Protocols haracter-oriented protocols (or byte-oriented protocols) - the frame or packet is interpreted as a series of characters Bit-oriented protocols - the frame or packet is interpreted as a series of bits

15 haracter Oriented Protocol: BS (Binary Synchronous Protocols) Bit Oriented Protocol: SDL (Synchronous Data Link ontroll) HDL (High Data Link ontroll) LAPs (Link Access Procedure Balance)

16 Features of Synchronous Protocols: 1. Efficiency is achieved by grouping characters together called BLOKS 2. No start and stop bits for each character. 3. Send more characters between the start and end sequences. 4. HEDER: start type sequence, prefixes each block of characters. 5. TAIL: A stop type sequence, suffixes each block of characters. 6. An extra ending sequence is added to perform error checking. 7. The tail is expanded to include a check code 8. Group multiple characters into BLOKS. 9. Developed for High Speed Networks. No start bit, hence the transmitter sends a special code when it has nothing to send. To keep the receiver in a state of readiness.

17 haracter-oriented Protocols

18 Binary Synchronous ommunication (BS) - the best-known character-oriented protocol Supports half-duplex transmission Uses stop-and-wait ARQ flow control and error correction

19 BS Half duplex, can be used with ASII, EBDI, and Six Bit Transcode ontrol information is in the form of code words taken from the character set(example..?) ontrol information is carried in separate frames as well as within data frames Line control, flow control, error control

20 BS Data Frames: S Y N S Y N S O H Header S T X Data E T X B B SYN: Synchronization haracters, used to alert receiver for initialization of timing/counter w.r.t the sender. SOH: Indication of beginning of header. Header: Includes Address of sender and the Receiver along with ID of frame number i.e. 0 or 1.

21 BS Data Frames: S Y N S Y N S O H Header S T X Data E T X B B STX: Indicated that the control information is ending and the data is starting. ETX: Indicates end of text and start of control character. B: Block heck ount is same as LR(1 char), or R(2 har)

22 Previous Lecture we have seen following topic: Asynchronous Protocols: X-Modem Y-Modem Z-Modem, BLAST, KERMIT Synchronous Protocol: haracter Oriented BS Bit Oriented : SDL HDL LAP-B Question 1: While using haracter Based Protocol, and using ETX, EOT ontrol haracters, do we generate 3 bytes or it is single byte..? Question 2: How a multi frame transmission is handled in BS protocol?

23 BS Multiblock frame: S Y N S Y N S O H Header S T X Block Data I T B B B S T X Block Data E T X B B Multi Block: One frame may have multi blocks(data Field) inside. ITB: Intermediate Text Block: Used to separate data fields. ETX: Is on behalf of all blocks of a frame.

24 BS Multi-frame transmission: One block may have multiple data field Each frame is ended with ETB For every ETB we get AK When the last frame is transmitted then we send ETX AK is generated on behalf of ETB as well as ETX S Y N S Y N S O H S T X I T B B B Header Data S T X E T B B B Data B B A 1 K S Y N S Y N S Y N S Y N S O H S T X I T B B B Header Data S T X E T X B B Data B B A 0 K S Y N S Y N End of 4 th data segment, end of second Block, end of first frame

25 BS Role of ontrol Frames: Frames used only for signaling SYN SYN {ontrol haracters} B onnection establishment onnection termination (end of transmission) Flow and error control (AK0, AK1, NAK)

26 Data Transparency BS When sending binary data, certain information may be identical to control characters Solution: Define transparent blocks and use character stuffing Start transparent text block with DLE STX End transparent text block with DLE ETX, DLE ITB, DLE ETB To send DLE character, send DLE DLE

27 Bit Oriented Protocol SDL HDL LAP B Synchronous Data link ontrol High Data Link ontrol Link Access Protocol (Balanced); ISO 3309 ISO 4335

29 HDL (High Data Link Protocol) What is the role of HDL? General Features: Provides Frame Format (Standard) lassifies Systems Deals with Link configuration(how link is used..?) Defines mode of transmission (Who will initiate..?) Flow / Error control Synchronous Transmission Bit oriented system Developed by ISO, examples are ISO 3309 & ISO 4335.

30 3:Supports Three station type Primary Secondary ombine HDL 1:Transmission Details Half Duplex and Full Duplex transmission. Switched and non Switched hannels. Point to Point and Multipoint Lines. 5: Supports Three Modes of transmission NRM (Normal Response Mode) ARM (Asynchronous Response Mode) ABM (Asynchronous Balance Mode) 2: Supports three frame types I frame: Information frame Six fields S frame: Supervisory frame Five fields U frame:unnumbered frame Six fields 4: HDL Link onfigurations Balance Unbalance Symmetric

31 Supports Three station type Primary Station: ontrols operation of link Frames issued are called commands Maintains separate logical link to each secondary station. Secondary Station: Under control of primary station Frames issued called responses ombine Station: May issue commands and responses

32 HDL Link onfiguration One primary and one or more secondary stations Supports full duplex and half duplex Two combined stations Supports full duplex and half duplex

33 HDL Link onfiguration

34 Mode of Transmission (1)Normal Response Mode Normal Response Mode (NRM) Unbalanced configuration Primary initiates transfer to secondary Secondary may only transmit data in response to command from primary Used on multi-drop lines Host computer as primary Terminals as secondary

35 Mode of Transmission (2)Asynchronous Balance Mode Asynchronous Balanced Mode (ABM) Balanced configuration Either station may initiate transmission without receiving permission Most widely used

36 Mode of Transmission (3) Asynchronous Response Mode (ARM) Unbalanced configuration Secondary may initiate transmission without permission from primary Primary responsible for line Rarely used

37 I frame: Information frame Six fields S frame: Supervisory frame Five fields U frame: Unnumbered frame Six fields. HDL Frame Types

38 Details of HDL Fields

Details of HDL Fields HDL Flag Field Delimit frame at both ends 01111110 May close one frame and open another Receiver hunts for flag sequence to synchronize Bit stuffing used to avoid

39 Details of HDL Fields HDL Flag Field Delimit frame at both ends May close one frame and open another Receiver hunts for flag sequence to synchronize Bit stuffing used to avoid confusion with data containing inserted after every sequence of five 1s If receiver detects five 1s it checks next bit If 0, it is deleted If 1 and seventh bit is 0, accept as flag

40 Flag field is also used for following purpose Breaks a long single frame into multiple frames. Bit stuffing is used to avoid confusion.

41 Bit stuffing and removal process

HDL Address Field Identifies secondary stations that sent or will receive frame Addressing is done irrespective of, who is sending (Primary or Secondary)

42 HDL Address Field Identifies secondary stations that sent or will receive frame Addressing is done irrespective of, who is sending (Primary or Secondary) Usually 8 bits long May be extended to multiples of 7 bits LSB of each octet indicates that it is the last octet (1) or not (0) All ones ( ) is broadcast

43 HDL Address Field Bit streams are; It is difficult to identify end of last byte of address frame Address bits

44 HDL ontrol Field (Used to identify Frame Type) First one or two bits of control filed identify frame type P/F Poll / Final bit POLL : To prompt receiver to know what is happening N(S) Sequence no of frame sent N(R) Sequence no of frame expecting ODE ode for supervisory or unnumbered frame

45 Poll/Final Poll Final Application depends on the context ommand frame (P bit is set) Response frame (F bit is set)

46 HDL Information Field Only in I frame and some U frames Variable length

47 HDL FS Field Error detection 16 bit R Optional 32 bit R

48 I-frame control field in HDL Explanation of N(S) and N(R) I 0,0 I 1,0 I 0,2 I 2,1

49 S-frame control field in HDL Explanation of ODE field of S-frame I 1,0 REJ, 1 I 1,0 RR, 2

50 11.21 U-frame control field in HDL

51 Table 11.1 U-frame control command and response ommand/response Meaning SNRM Set normal response mode SNRME Set normal response mode (extended) SABM Set asynchronous balanced mode SABME Set asynchronous balanced mode (extended) UP Unnumbered poll UI Unnumbered information UA Unnumbered acknowledgment RD Request disconnect DIS Disconnect DM Disconnect mode RIM Request information mode SIM Set initialization mode RSET Reset XID Exchange ID FRMR Frame reject

52 HDL Operation Exchange of Information frame Supervisory frames and Unnumbered frames Three phase Initialization Data transfer Disconnect Timing diagram Link setup & disc Two way data Exchange Busy ondition Reject Recovery Time out recovery

53 Timing Diagram to Explain 1. Link Set up & Disconnect 2. Two Way Exchange of Data 3. Busy ondition 4. Reject Recovery 5. Time out Recovery

54 A Examples of Operation 1: Link Setup and Disconnect SABM B T SABM UA Identify the frame type All are U frames DIS UA

55 A I 0,0 Examples of Operation 2:Two way Data Exchange B I 0,1 I 1,1 I 2,1 Identify the frame type I 1,3 I 3,2 All are I frames except RR4(S Frame) I 2,4 I 3,4 RR 4

56 Examples of Operation 3:Busy ondition (M/c A is not sending next frame and not receiving further frames from B A I 3,0 B Busy RNR 4 ( Busy) RR 0,P(ommand) RNR 4,F(Response) Identify the frame type I frame as well as S Frame RR 0,P ( ommand) RR 4,F ( Response) I4,0

57 Examples of Operation A 4: Reject Recovery I 3,0 I 4,0 I 5,0 REJ 4 B I 4,0 I 5,0

58 Examples of Operation 5:Time out Recovery with P/F bits A I 2,0 B T I 3,0 RR 3 RR 0,P RR 3,F I 3,0 RR 4

59 IEEE Protocols omputer Networks by Prof Kamal K Mehta Associate Professor Department of omputer Science & Engineering SSET Bhilai (.G.)

60 IEEE Network Protocols omputer Networks by Prof Kamal K Mehta Associate Professor Department of omputer Science & Engineering SSET Bhilai (.G.)

61 Number Topic Overview & Architecture of LAN s Logical Link ontrol Ethernet Token Bus Token Ring ( IBM entry into LAN world) Dual queue dual bus( Early metropolitan area Network) Technical advise on broadband tech Technical advise on fiber optic technology Isochroous LAN Virtual LAN s and security Wireless LAN s Demand Priority ( Hewlett-Packard s LAN) Unlucky no, No body wanted it able modems Personal Area Net ( BLUE TOOTH) Broad band networks Resilience Packet Ring.

62 Introduction to the following MA (Media Access ontrol) Technique SMA /D: arrier Sense Multiple Access/ollision Detect As soon as collision is detected, then protocol will send JAM signal to all other station. Token Bus: Token Ring: DQDB(Dual Queue Dual Bus):

63 Two Unwanted situations: ollision ongestion

64 Function of Media Access ontrol Sub Layer 1. Provides Access to Shared Media 2. Allow Multiple device to uniquely identify each other in DLL 3. ontrol of Access to media 4. Detection of Error

65 Goal of Media Access ontrol Sub Layer 1. Initialization: When power on, it will enable all station of enter into state of readiness. 2. Fairness: Treat each station equally, as per the specification 3. Priority: To assign priority as per the application need. 4. Limitation to one station: Must allow only station at one time 5. Receipt: Ensure reception of packet in only one copy to correct destination, in correct order.

66 Goal of Media Access ontrol Sub Layer 6. Error Limitation: Protocol must be able to implement suitable Error handling mechanism 7. Recovery: If 2 packets collides, then it must be able to recover (able to halt the transmission and select one station to retransmit). 8. Re configurability: Must support addition/deletion of nodes 9. ompatibility: Must support the devices supplied by all vendors. 10. Reliability: Must ensure network operation in spite of failure of one or more stations.

(Sicherungsschicht) Chapter 5 (part 2) [Wa0001] HDLC - 1.

Data Link Layer (cont.) (Sicherungsschicht) Chapter 5 (part 2) [Wa0001] HDLC - 1 LOGICAL LINK CONTROL MEDIUM ACCESS CONTROL PHYSICAL SIGNALING DATA LINK LAYER PHYSICAL LAYER ACCESS UNIT INTERFACE PHYSICAL