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Chapter 10 Homework

Chapter 10 Homework. 10 - 2, 11, 33, 41, 62. Chapter 10 Data Link Control. Flow Control Error Control High-Level Data Link Control (HDLC) Other Data Link Control Protocols. Terminology. What is a Frame? A group of bits representing a block of data.

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Chapter 10 Homework

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  1. Chapter 10 Homework • 10 - 2, 11, 33, 41, 62

  2. Chapter 10Data Link Control • Flow Control • Error Control • High-Level Data Link Control (HDLC) • Other Data Link Control Protocols

  3. Terminology • What is a Frame? • A group of bits representing a • block of data.

  4. Some Reasons for Sending Data in Frames • Limitation on the receiving device buffer size • Transmission of large blocks of data means higher probability for errors • Fair access of medium

  5. Data Link Layer

  6. Data Link Error Control Line Management Flow Control How much data May be sent? How can errors be corrected? Who should send now?

  7. Some Requirements for Effective Data Transmission Systems • Frame Synchronization • Flow Control • Error Control • Addressing • Handling control info and data ( preferred on the same link) • Link Management • Connection initiation • Connection maintenance • Connection termination

  8. Flow Control: Regulates the flow of data from a transmitting device so that the receiver’s buffers do not overflow • Bit errors by transmission system should be detected and corrected.

  9. Flow Control Methods • Stop-and Wait Flow Control • Sliding-Window Flow Control

  10. Stop-and Wait Flow Control • Send a Frame. • Wait until an acknowledgement • is received. • Send next frame

  11. ENQ/ACK

  12. ENQ(enquiry)/ACK

  13. Efficiency of Stop-and-Wait Flow Control Define: • Transmission time • Processing time • Propagation time

  14. Efficiency(utilization) of Stop-and-Wait Flow Control U= d=distance L=frame length R=data rate This represents the ratio of the length of the medium in bits(bit length) to frame length.

  15. Sliding-Window Flow ControlProcess Two Stations A & B connected by full duplex link. • B allocates buffer space for W frames. • Acan send W frames without waiting for acknowledgement. • B acknowledges a frame that includes the sequence number of the next expected frame. • (for 3-bit field sequence number rages from 0-7)

  16. Error Detection(Checksum) • Sender performs one’s complement of the sum of all the 16-bit words in the segment.(all the 1’s convertred to 0 and all 0’s converted to 1) • This is placed in the checksum field of the packet. • At the receiver, all 16-bit words including the checksum are added. • If no errors occurred, the sum will be: • 1111111111111111 (16 ones) • Presence of any zero indicates an error.

  17. Error Detection (Checksum Example) • Assume we have the following 16-bit words: • 0110011001100110 • 0101010101010101 • The sum is (using modulo 2 arithmetic equivalent to XOR operation) • 1011101110111011 • 0100010001000100 (one’s complement of the sum) • 1111111111111111 (sum of the one’s complement and all 16-bit words at the receiver)

  18. Error DetectionCyclic Redundancy Check (CRC)

  19. Error Control Methods • Stop-and-wait ARQ (automatic repeat request) • Go-back-N ARQ • Selective-reject ARQ

  20. Error Control Methods • Stop-and-wait ARQ • Is based on stop-and-wait flow control

  21. Error Control Methods • Go-back-N ARQ • Is based on sliding-window flow control

  22. Error Control Methods • Selective-reject ARQ • Frames are retransmitted only if negative acknowledgement is received.

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