1. What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

2. The Network Core mesh of interconnected routers the fundamental question: how is data transferred through net? –circuit switching: dedicated circuit per call: telephone net –packet-switching: data sent thru net in discrete “chunks”

3. Network Core: Circuit Switching End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required

4. Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” –frequency division –time division

5. Network Core: Packet Switching each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed, resource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use store and forward: packets move one hop at a time –transmit over link –wait turn at next link Bandwidth division into “pieces” Dedicated allocation Resource reservation

6. Network Core: Circuit Switching End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required

7. Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” –frequency division –time division

8. Network Core: Packet Switching each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed, resource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use store and forward: packets move one hop at a time –transmit over link –wait turn at next link Bandwidth division into “pieces” Dedicated allocation Resource reservation

9. Network Core: Packet Switching Packet-switching versus circuit switching: human restaurant analogy other human analogies? A B C 10 Mbs Ethernet 1.5 Mbs 45 Mbs D E statistical multiplexing queue of packets waiting for output link

10. Network Core: Packet Switching Packet-switching: store and forward behavior

11. Packet switching versus circuit switching 1 Mbit link each user: –100Kbps when “active” –active 10% of time circuit-switching: –10 users packet switching: –with 35 users, probability > 10 active less that.004 Packet switching allows more users to use network! N users 1 Mbps link

12. Packet switching versus circuit switching Great for bursty data –resource sharing –no call setup Excessive congestion: packet delay and loss –protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? –bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 6) Is packet switching a “slam dunk winner?”

13. Basic Network Concepts Circuit switching - {basic TELCO service. Guaranteed response because resources are guaranteed. Inefficient for some applications} Virtual-circuit packet-switching - {divide the info into packets to multiplex} Datagram packet-switching - {like the US Mail....} Connectionless vs Connection-oriented {At the Link layer, do we do acknowledgements? At the network layer,do all the packets have to follow the same route?} Multiplexing - {single media, multiple independent 'circuits'} {putting multiple 'sessions' on a single media}

14. Packet-switched networks: routing Goal: move packets among routers from source to destination –we’ll study several path selection algorithms (chapter 4) datagram network: –destination address determines next hop –routes may change during session –analogy: driving, asking directions virtual circuit network: –each packet carries tag (virtual circuit ID), tag determines next hop –fixed path determined at call setup time, remains fixed thru call –routers maintain per-call state

15. Physical Media physical link: transmitted data bit propagates across link guided media: –signals propagate in solid media: copper, fiber unguided media: –signals propagate freelye.g., radio Twisted Pair (TP) two insulated copper wires –Category 3: traditional phone wires, 10 Mbps ethernet –Category 5 TP: 100Mbps ethernet

16. Physical Media: coax, fiber Coaxial cable: wire (signal carrier) within a wire (shield) –baseband: single channel on cable –broadband: multiple channel on cable bidirectional common use in 10Mbs Ethernet Fiber optic cable: glass fiber carrying light pulses high-speed operation: –100Mbps Ethernet –high-speed point-to- point transmission (e.g., 5 Gps) low error rate

17. Physical media: radio signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: –reflection –obstruction by objects –Interference Radio link types: microwave –e.g. up to 45 Mbps channels LAN (e.g., waveLAN) –2Mbps, 11Mbps wide-area (e.g., cellular) –e.g. CDPD, 10’s Kbps satellite –up to 50Mbps channel (or multiple smaller channels) –270 Msec end-end delay –geosynchronous versus LEOS

18. Physical Layer Issues Theoretical Underpinning –or, Bandwidth 101 Media Characteristics –Optical Fiber –Coax –Copper Wire (Twisted Pair) –Wireless Other Useful Ideas

19. Signals Propagation - {how fast does the signal travel in that media, esp. compared to light?} Frequency - {number of oscillations per second of the electromagnetic field of the signal} Bandwidth - {the width/size, in Hz, of the signal -- usually defined by where most of the energy is} Data Rate - {the number of bits per second. Distinct from, but related to, frequency and bandwidth} Baud - {Changes per second in the signal. Limited by bandwidth.}

20. Freq/BW/DR Power Frequency BW FREQ {see Fig 2-1}

21. 1 0 01100010 TTime

22. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Harmonic number 0.50 0.25 rms amplitude

23. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Harmonic number 0.50 0.25 rms amplitude 1 harmonic

24. 1 0

25. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Harmonic number 0.50 0.25 rms amplitude 2 harmonics

26. 1 0

27. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Harmonic number 0.50 0.25 rms amplitude 4 harmonics

28. 1 0

29. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Harmonic number 0.50 0.25 rms amplitude 8 harmonics

30. 1 0

31. Maximum Data Rates Nyquist: –DataRate <= 2*BandWidth * log 2 V where ‘V’ is the number of values which are encoded into the signal. In the On/Off, 0/1 world, V = 2. Your highspeed modem has V = 16. Shannon: –The real world is noisy, so Nyquist was an optimist. Marti: –Complexity costs money and adds fragility. So be choosy. DR ~ 2 * BW {Max by Theory} DR ~ 1/2 * BW {Practical} <- In an On/Off world (V = 2)

32. Physical Effects Bandwidth Limits - {Signals consist of many (infinite) different sine waves, not all of which can be carried by the media} Dispersion - {Particularly for multimode fiber, different parts of the signal may move at different speeds, thus changing the shape of the signal at the receiver} Jitter - {Imperfect clock synchronization along the transmission path} Noise - {Unwanted, external energy that may corrupt the signal}

33. Media Optical Fiber Multimode Single Mode Coax Broadband Baseband Twisted Pair Shielded Unshielded

34. Cost and Performance Media Types: UTP Coax Baseband Broadband Fiber Multimode Single Mode Increasing Bandwidth Increasing Cost But remember, cost includes --material --LABOR --electronics Biggest part of installation cost

35. Distances Media Types: UTP Coax Baseband Broadband Fiber Multimode Single Mode Typically 100m +/- 200m-500m up to 40km depends on power budget; can be 100s of km* * Most LANs use 2km between devices

36. Fiber Facts Core Cladding Protective Coating Core Cladding 50 125 Multimode (microns) 62.5 125 " " 8 to 10 n/a Singlemode

37. Fiber Facts, cont. "photons" Modes == Different paths thru core Since the photons travel at the same speed, but for different distances, the energy is spread out, or dispersed, at the receiver Fiber is specified as XX Mhz-km. So a specification of 800Mhz-km means you could have a bandwidth of 400Mhz over a 2km distance or 1.6Ghz over a 0.5km distance. Dispersion has two components: modal and material

38. Traditional Baseband Coax Terminator Transceiver Transceiver Cable Host

39. CATV Systems Headend Amplifier Splitter Network Interface Unit Translator "Forward" Signal "Return" Signal

40. Twisted Pair Just copper wire where each two wires (“pairs”) have been twisted around each other in the cable. {Phone wire} Rejects common mode noise Minimizes antenna characteristics Shielded or Unshielded refers to a ground sheath around the whole cable. Cat 3 vs Cat 4 vs Cat 5

41. Design

42. Modulation ASK - Amplitude Shift Keying {varying signal strength} FSK - Frequency Shift Keying {varying signal frequency} PSK - Phase Shift Keying {don't ask!} {NB the above three methods are usually applied to signal carriers} PCM/PWM - Pulse Code Modulation/ Pulse Width Modulation {good for fiber} Others "Modification of a transmitted signal to encode information (bits)"

43. Switching Circuit Switching –Guaranteed resource –No size limit on information sent Packet Switching - Divides the information into packets; restricts sizes; also sharing of resources –Virtual Circuit // Connect-oriented –Datagram // Connection-less

44. Multiplexing TDM - {time division multiplexing} {low overhead, inefficient} FDM - {frequency division multiplexing} STDM - { statistical time division multiplexing} {some overhead, more efficient, may FAIL}

45. Multiplexing Examples TDM STDM A B C D BADCBADCBADCBAD 2400 9600 4800 A B C D BACACBDCBDBABBD

46. Multiplexing w/ Packets Like STDM, except NO "ROUND ROBIN"

47. Framing & Synchronization Synchronous - Sender and receiver somehow share a common clock. good for longer runs of data; more efficient but requires the clock signal somehow be sent along with the data Asynchronous - Sender and receiver use different clocks so data runs have to be shorter. Doesn't require the extra clock signal Synchronous vs Asynchronous - Framing & clocks Isochronous vs Aperiodic - Characteristics of traffic {beware of confusion as each writer may mix terms} {Here synchronization refers to the sender's and receiver's clocks} {Frames are packets added signal needed to transmit them on Physical Layer}

48. Specific Framing Bit Stuffing - Used to ensure special framing and/or control characters are not sent in the data. A problem because the 'clock' is usually continuous but data may not be there, so we have to know when the line is idle and when a frame starts {frame delimiter} Manchester Encoding - Example of combining clock with data to form a single signal -- no separate line is required. It does require twice the bandwidth of the original signal

49. Manchester Encoding Ensures for each bit there is a clock transition. Data values (0 or 1) are encoded by positive or negative clock transitions in the middle of the bit time. Transitions are made at bit edges if needed so that the correct transition can be made in the middle of the bit.

50. TELCO Architecture Users Trunks CO

51. TELCO Trunking Older, Analog World: Frequency Multiplexing Current World: Digitizing & Time Multiplexing