1. Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Network Layer Electrical and/or Optical Signals Application A Application B Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer Communication Network Figure 2.6 Review of seven layers
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3. Data Link Layer WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998
6. 1 2 Physical layer entity Data link layer entity 3 Network layer entity Physical Layer Data link Layer Physical Layer Data link Layer A B A B Packets Packets Frames (a) (b) Peer-to-peer protocol across a single hop 1. take packets 2. form frame 3. transfer through Physical layer 5. deliver to network layer Several pairs of data link & physical entities Only one network layer entity, a router may connect several different networks 4. Pass up 3 2 1 1 2 2 1 3 2 1 1 2 2 1 2 1 Medium
7. Physical Layer Data link Layer Physical Layer Data link Layer End system Network Layer Network Layer Physical Layer Data link Layer Network Layer Physical Layer Data link Layer Network Layer Transport Layer Transport Layer Messages Messages Segments End system Network Peer-to-peer protocol operating end-to-end across network
8. Medium A B 3 C 3 4 3 4 End System End System Network 1 2 Physical layer entity Data link layer entity Network layer entity Network layer entity Transport layer entity Figure 5.4 Peer-to-peer protocol operating end-to-end across network 1. Layer 4 not in middle 2.Data go up and down in router 3. Different paths 4. Out of order, delay, duplicate, lost 3 2 1 1 2 2 1 3 2 1 1 2 2 1 2 1 2 1 1 2 2 1 2 1 2 1 2 1 1 2 3 3 4
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10. 1 2 3 4 5 Data Data Data Data ACK/NAK ACK/NAK ACK/NAK ACK/NAK End-to-end Hop-by-hop Figure 5.7 Adaptation functions may be implemented end-to-end or hop-by-hop Data are ACK or NAK by the other end Data are ACK or NAK by each hop 1 2 3 4 5 Data Data Data ACK/NAK Data
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17. (a) Frame 1 lost or badly garbled A B One frame Another frame ACK The frame ACK time Time-out Another frame (b) ACK lost A B One frame Another frame ACK the frame ACK time Time-out Another frame ACK Figure 5.9 Using timer to retransmit the frame when a frame or acknowledgement lost Any problem? Frame was received twice when ACK lost. How to solve it? Introduce sequence number (SN) into frame and discard duplicate frame
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