1. CSE 8344 Introduction A quick look at network fundamentals

2. CSE 8344 Introduction Transmission Fundamentals Factors that determine the best way to connect – Cost of connection – Speed – Immunity to interference – Security – Logistics

3. CSE 8344 Digital vs. Analog

4. CSE 8344 Digital Less susceptible to distortion and interference Digital signals can be regenerated to extend the length of the cable Extremely low error rate Cheaper Digital multiplexing much simpler than FDM

5. CSE 8344 Data Encoding Techniques Digital Data, Analog Signals Amplitude shift keying (ASK) Frequency shift keying (FSK) Phase shift keying

6. CSE 8344 Digital Data, Digital Signals Non-return-to-Zero Level (NRZ-L) NRZ - I Manchester Encoding Differential Manchester encoding Disadvantages of NRZ Synchronization is difficult DC component

7. CSE 8344 Digital Data, Digital Signal (cont’d) Advantages of Differential encoding – Easy detection – Can keep track of the polarity Advantages of bi-phase encoding – Synchronization – No dc component – Error detection

8. CSE 8344 Analog Data, Digital Signal Based on the sampling theorem Pulse code modulation Delta modulation

9. CSE 8344 Parallel vs. Serial Transmission Parallel – Dedicated functions to the wires – Higher speed for short distance interconnections – Not feasible for long distances (more than 100m ) – Reduction in performance – Cross talk in long cables – Cost

10. CSE 8344 Parallel vs. Serial Serial – Serialize the data – Add control characters – Format the data into frames – Use appropriate communication protocol

11. CSE 8344 Direction of Transmission Simplex –Transmission in one direction only Half-Duplex –Transmission in one direction at a time Full-Duplex –Transmission in both directions

12. CSE 8344 Synchronous vs. Asynchronous Asynchronous – One character at a time – One start bit – One or more stop bits – The receiver resynchronizes after each stop code – Cheap but inefficient

13. CSE 8344 Synchronous Arrival time of each bit is predictable To prevent timing drift the receiver and transmitter clock should be synchronized Preamble and Postamble SYNC characters Character Oriented Bit Oriented Bit stuffing

14. CSE 8344 Transmission Media Guided Media – Twisted Pair of Cables – Coaxial Cables – Optical Fibers Unguided Media – Radio – Microwave – Satellite

15. CSE 8344 Multiplexing For cost-effective transmission, multiplexing will let the medium carry multiple signals simultaneously Commonly used techniques: – FDM - Frequency Division Mux – TDM - Time Division Mux – WDM - Wavelength Division Mux – CDM - Code Division Mux (frequency hopping and spread spectrum techniques)

16. CSE 8344 Statistical MUX Scan the buffer and create a variable-size frame Also called Concentrator T-1 carrier

17. CSE 8344 Communication Switching Techniques Spectrum of Switching Techniques – Circuit switching – Multi-rate circuit switching – Cell relay – Frame relay – Packet switching

18. CSE 8344 Circuit Switching Dedicated communication path between two stations Three Phases – Circuit establishment Check also whether the destination is ready to accept the request –Data transfer Could be either digital or analog signaling Generally full duplex – Circuit disconnect

19. CSE 8344 Packet Switching Greater line efficiency Data rate conversion Connection request is always accepted irrespective of the traffic Dynamic routing and priority assignment possible

20. CSE 8344 Packet Switching - Approaches Datagram – Each packet is treated independently – The packets may be received out of sequence – Some packets may be lost in the event of some node crashes Virtual Circuit – A preplanned route is established before the data is sent – At any time, each station can have more than one VC to any other station and can have VCs to more than one station

21. CSE 8344 – Provides sequencing, error control, and flow control – If an intermediate node fails, all virtual circuits going through that node may be lost - less reliable when compared to datagrams Multi-rate Switching – Combines circuit switching and multiplexing

22. CSE 8344 Frame relay Too much overhead built into packet switching Frame relays take advantage of the low error rates of networking facilities Cell Relay – ATM – Fixed length packets

23. CSE 8344 OSI Layers Application –provides electronic mail, file transfers etc. Presentation –Translates data format, encrypts and decrypts data Session –Synchronizes communicating users, recovers from errors Transport –Determines network, may assemble and reassemble packets

24. CSE 8344 OSI Layers (cont’d) Network –Determines routes, manages billing information Data Link – Detects or correct errors, defines frames Physical –Transmits physical data

25. CSE 8344 Protocol Concepts What if the transmitted message is too long? How do we react to damaged transmission What if the transmitter and receiver run different speeds? What if both the parties want to transmit and receive at the same time ?

26. CSE 8344 Basic Functions of Protocols Error Control –Automatic Repeat Request Flow Control –Ranging from Stop-and-Wait to Unrestricted

27. CSE 8344 Sliding Window Protocols Compromise between stop-and-wait and unrestricted Define a window containing I frames numbered starting at w Every frame numbered less than w has been sent and acknowledged No frame numbered > w+I has been sent There could be Outstanding frames within the window

28. CSE 8344 Frame Format Source Address –Address of the station sending the frame Destination address –address where the frame should be sent to Frame number –sequence number Ack –Number of the frame being acknowledged, Piggy backing

29. CSE 8344 Frame Format (cont’d) Type of frame –data, ack, nak etc. Data, and CRC

30. CSE 8344 Go-Back-N Protocol Frame numbers 0 through 2^K - 1 Receiver expects frames in order If a frame arrives damaged, a nak will be sent If a sending station receives an acknowledgment for frame j and then k, it assumes that all the frames in between have been received correctly When frame timer expires sender resends all frames

31. CSE 8344 Selective Repeat Protocol Receiver buffers the incoming frame; will deliver it only after all its predecessors have arrived Whenever an out of order frame arrives, a nak is sent When the frame timer expires only the timed-out frame is resent

32. CSE 8344 Protocol Representations State Transition Diagrams (STDs) 1110 01 00 (Ack,Data)