This will be a closed book test. You may bring copies of the commkit code (commkit.c and srcalls.c), and any higher level code, and corresponding header files.

This exam will cover material from chapters 6, 10, 11, 12, and 13. You will also be responsible for the commkit software from chapters 6, 10, and 11.

1. Synchronous Communications.
   1. Longitudinal Redundancy Check (LRC)
   2. Cyclic Redundancy Check (CRC)
   3. Backward Error Recovery
      1. Stop-and-Wait (also efficiency).
      2. Go-Back-N
      3. Selective Retransmission
   4. Forward Error Recovery (Hamming Codes)
   5. Synchronous Protocols.
      1. Byte-oriented (Bisync)
      2. Bit-oriented (Synchronous Data Link Control, SDLC).
   6. Synchronous hardware.
   7. Commkit Stop-and-Wait software.
   8. Questions.
      1. Generate a simple (e.g., 8 bit) CRC number and verify its correctness.
      2. Check numbers for LRC correctness.
      3. Create and/or verify Hamming encoded bytes.
      4. . Describe the differences in efficiency between the 3 backward error recovery protocols.
      5. . Give an example, with diagrams, of a sliding window error recovery. Assume that the window size is 4.
      6. . Using the state machine descriptions for the stop-and-wait protocol from commkit, show how the protocol recovers from a corrupted frame error (bad CRC).
      7. Explain what changes would be necessary in the function {\bf Xmit_protocol} if the go-back-n protocol (with window size 4) were to be implemented in Commkit.
2. Wide Area Nets.
   1. Addresses:
      1. Hierarchial
      2. Global
   2. Routing
      1. Flooding (with hop count)
      2. Routing table
   3. Creating Routing tables
      1. Static Allocation.
      2. Dynamic or Adaptive routing.
      3. Backward learning.
   4. Packet Transmission.
      1. Datagram Service.
      2. Messaging.
      3. Virtual Circuits.
   5. Virtual Circuits.
      1. Call Establishment.
      2. Data Transfer.
      3. Call Clearing.
   6. Software Layering.
      1. Physical Layer
      2. Data Link Layer
      3. Network layer.
      4. Communication Services provided by each layer.
      5. Peer-entity communication
   7. X.25 Network layer protocol.
   8. Commkit WAN (only network layer software).
   9. Efficiency of protocols (from handouts).
   10. Questions.
       1. What is the difference between Hierarchial and Global addressing? What are the advantages and disadvantages of each?
       2. What are the advantages of flooding vs routing tables and vice versa?
       3. Give an example network with 5 or more nodes using backward learning to create routing tables.
       4. Contrast datagram service with virtual circuits. What are the relative merits of each?
       5. Give an example of the creation of a virtual circuit between 5 nodes. Describe what happens in each nodeÕs virtual circuit table.
       6. Give an example of a communication from one DTE through 2 other DTEs to a destination DTE in terms of the layers of protocols.
       7. Describe what functions in wanex.c receives the call request packet and how they create the correct entry in the virtual circuit table.
       8. Assume that you are going to put in a transmission line between two stations. You have 100 kbps transmitters and your protocol will be ABP with 100 bit ACKs and 1000 bit packets. You want the efficiency to be at least 90% and anticipate an error probability of 1%. If you use coaxial cable, what is the maximum distance between stations?
3. Bus LANs.
   1. Centralized LAN control.
   2. Collision Detection (CD).
   3. Collision resolution algorithms.
      1. Non-persistent.
      2. 1-persistent.
      3. p-persistent.
   4. Carrier Sense Multiple Access (CSMA) networks.
      1. passive bus.
      2. Distributed control.
   5. Ethernet.
      1. Physical organization.
      2. Relationship of physical organization with maximum transmission speed.
      3. Ethernet packet organization.
      4. Types of addressing.
      5. Truncated Exponential backoff algorithm.
      6. Ethernet hardware.
   6. IEEE 802.3
      1. Differences with Ethernet.
      2. Different protocols.
   7. Commkit Lan Software.
   8. Questions
      1. Describe and give the relative advantages/disadvantages of the three different collision resolution algorithms.
      2. Describe electically how collision detection is performed by ethernet transceivers.
      3. Why is centralized control not used in LAN buses?
      4. Assume that you wanted to increase the maximum length of an Ethernet segment to 4Km. Assuming that all other aspects of Ethernet connections and frames remain the same, what would the minimum size of the user data field of an Ethernet packet be?
      5. What is the speed and maximum distance of a 10Base5 802.3 implementation?
      6. Describe how the Commkit LAN software detects a collision. Does Commkit really implement a CSMA/CD mechanism?
      7. Assume that I have given you figure 11.12 (state machine for a bus network transmission). Show on the diagram what happens if a collision is detected when the second byte of the CRC is being sent.
4. Ring LANs.
   1. IEEE 802.4 Token Bus.
      1. Frame format.
      2. Message Priority.
      3. Network maintenance.
   2. Ring networks.
      1. Physical Topology.
      2. Mechanism for passing tokens.
      3. Single frame operation and single token operation
   3. Ring net errors.
   4. Monitors.
   5. Physical connections.
   6. Examples.
      1. IBM Token Ring.
      2. IEEE 802.5 Token Ring
      3. FDDI
   7. . Questions.
      1. Give advantages/disadvantages of the Token bus LAN vs the Token ring LAN.