1. Chapter 10 Data Link Control Protocols

2. Agenda Definition Functions Attributes Concepts Types Conversion

3. Definition Protocols: set of rules or guidelines for communication between DTEs Data link protocol: rules for operating the circuit and sending message over it

4. Functions Communication startup Character identification and framing Message identification Line control Error control Termination

5. Data Link Protocols Attributes Transparency (DTE – any bit pattern as data) Code independence Efficiency (control codes)

6. Protocol Concepts Line Access –Contention –Polling –Token passing Message format

7. Contention Carrier sense multiple access with collision detection (CSMA/CD) by XEROX For: –Point-to-point circuits –Traffic light for multipoint circuits –Fast speed of circuit –Office application & LAN Not for –Manufacturing due to inconsistent response time

8. Polling Characteristics –One master and slavers –Special polling character Types –Roll call polling (polling list) –Fast select polling (several terminals) –Hub polling (station to station) –Token passing (token) Token (particular sequence of bits, Free or busy)

9. Message Format Start of header (SOH) –Header (Address, sequence, date and time) –Start of text (STX) Text End of text (ETX) or text length Trailer –Block check character (BCC) –Synchronization character (SYN)

10. Asynchronous Data Link Control Protocols - Characteristics Start/stop bits Parity checking Character oriented Less expensive and less complicated equipment For personal computers

11. Asynchronous Data Link Control Protocols - I XMODEM (simple, less reliable error checking) XMODEM-CRC (more reliable) XMODEM-1K (more efficient) YMODEM (reliable, multiple files transfer) YMODEM-G (fast) ZMODEM (fast, good failure recovery) X.PC (pack switching network, multiple sessions on one circuit)

12. Asynchronous Data Link Control Protocols - II KERMIT (reliable, fast file transfer, PC & mainframe) Serial Line Internet Protocol (SLIP) –Full-duplex –IP over asynchronous dial-up or leased lines –No error correction Point-to-point Protocol (PPP) –PC to a TCP/IP network –Full-duplex for synchronous and asynchronous transmission –Authentication, compression, error correction, & packet sequencing

13. Synchronous Data Link Protocols - Classification Character-oriented protocols –Special character for start and end of message –Binary Synchronous Communication Protocol (BSC or BISYNC) Byte-count-oriented protocols –Special character for start of the header, count field, message, block check character (BCC) –DEC’s Digital Data Communication Message Protocol (DDCMP) Bit-oriented protocols –Use flag character for start and end of message –IBM’s Synchronous Data Link Control (SDLC) –ISO’s High-Level Data Link control (HDLC)

14. Binary Synchronous Communications By IBM For 6-bit transcode (SBT), ASCII, EBCDIC SYN at start and middle of transmission Point to point and multipoint (polling) ARQ approach for error checking (ACK1, ACK0, NAK) Pros: –Transparency and non-transparency modes –Efficient, understandable, and widely used –Point-to-point & multipoint operations Cons: –Code dependent –Half-duplex protocol –Cumbersome for transparency mode

15. Digital Data Communications Message Protocol (DDCMP) Usage –Digital Network Architecture (DNA) –High-bandwidth and high-latency (satellite) links Data message and control message Error checking –Use block check character –Unique and increasing sequence number for sending message –ACK indicates the last message received Pro: –Efficient at transparency mode –Variable length of data –Only one control character: SOH –Easy implement for full-duplex and message sequence

16. High-level Data Link Control (HDLC) - I Operating modes –Normal response mode (NRM) for a primary node and one or more secondary modes on a circuit (polling) –Asynchronous balanced mode (ABM) for nodes with peers (most used for efficiency with no polling in full duplex) –Asynchronous response mode (ARM) for primary and secondary nodes with same transmission right (rarely used) Frames –Supervisory or S format: control acknowledge –Unnumbered or U format: (operation mode, start, termination) –Information or I format: (data)

17. High-level Data Link Control (HDLC) - I Flag –01111110 –Bit stuffing 0 after five 1s by hardware –For synchronization Other fields –Address field –Control field: type of frame, sequence number for information frames –Information field: multiple of 8 bits –Frame check sequence (FCS) field: error checking Frame flow –Initialization phase, data transfer phase, and disconnect phase

18. Other Data Link Control Protocols Link access procedure, balanced (LAPB) –Full-duplex, point-to-point mode –For X.25 DTE and packet switching network Link access procedure, D-channel (LAPD) –ISDN network Link access procedure for frame –mode bearer service (LAPF) –High-speed packet switching network on low error rate digital circuits Asynchronous transfer mode –Data transfer on high s-speed, digital, error free network

19. Protocol Conversion Methods –Dedicated hardware protocol converters –Add-in circuit board protocol converters –Software protocol converters –Gateway Functions –Code translation –Control characters, format, and error checking

20. Points to Remember Definition Functions Attributes Concepts Types Conversion

21. Discussion Select proper protocol for the network of a bank state you reasons