1. CMPE 80N - Introduction to Networks and the Internet 1 CMPE 80N Winter 2004 Lecture 5 Introduction to Networks and the Internet

2. CMPE 80N - Introduction to Networks and the Internet 2 Announcements First quiz on Friday, 01.16. –Covers material up to and including 01.14. –Closed books, notes, etc.

3. CMPE 80N - Introduction to Networks and the Internet 3 Data Transmission Analog and digital transmission. Historically, communication infrastructure for analog transmission. –Digital data needed to be converted: modems (modulator-demodulator).

4. CMPE 80N - Introduction to Networks and the Internet 4 Modems MODEM = Modulator/Demodulator –Converts digital to analog before transmitting over analog channel (e.g., telephone networks). To transmit data: DAC (digital-to-analog converter) To receive data: ADC (analog-to-digital converter) 2-way communication: needs two modems. –Each modem contains circuitry to encode outgoing data and decode incoming data.

5. CMPE 80N - Introduction to Networks and the Internet 5 Types of Communication Half-duplex communication: –Only one party can talk at a time. E.g., walkie-talkie. Full-duplex communication: –Both parties can talk at the same time. E.g., telephone Modems use full-duplex communication.

6. CMPE 80N - Introduction to Networks and the Internet 6 Modems (cont’d) Modems contain complex circuitry to: –Modulate/demodulate the analog signal. Allows for the transmission of moderately high bit-rate over the telephone line. –Compress the data. Reduces the amount of bits to be transmitted –Detect bit errors due to transmission. Achievable bit rates. –E.g., 14.4 - 56 Kb/s

7. CMPE 80N - Introduction to Networks and the Internet 7 Input/Output Connections

8. CMPE 80N - Introduction to Networks and the Internet 8 I/O Connections How to connect peripheral devices to a computer. Serial and parallel connections. –Serial: bits are sent one at a time. –Sequence of bits sent in parallel using parallel wires.

9. CMPE 80N - Introduction to Networks and the Internet 9 I/O Connections: Standards Standard: defines the details of a particular technology. RS-232 is a standard for serial communication between digital devices. –It’s full duplex. –20-30 Kb/s. –Can only connect one device at a time. So if you want to connect a PC to many devices, you need as many cables coming out of your PC.

10. CMPE 80N - Introduction to Networks and the Internet 10 USB and FireWire USB (Universal Serial Bus). –Can connect many devices through a USB hub. –Bitrates: 12 Mb/s (USB 1.1) to 480 Mb/s (USB 2.0). –Provides power to small devices (e.g., mouse). Firewire (IEEE 1394). –Can connect many devices through a FireWire hub. –Bitrates: up to 400 Mb/s. –Very popular for video cameras and storage systems, also to connect two devices (without a PC). –Can provide power to small devices (e.g., video cameras).

11. CMPE 80N - Introduction to Networks and the Internet 11 Some Considerations RS-232, USB, Firewire, all have constraints on the maximum length of the wire. We already know a solution: modem. –Uses the telephone network. However, modems provide insufficient bitrate. –Also, when using the modem, you cannot use the telephone for voice communication!

12. CMPE 80N - Introduction to Networks and the Internet 12 Solution: Broadband Coonections

13. CMPE 80N - Introduction to Networks and the Internet 13 Broadband Connection Types –Integrated Services Digital Network (ISDN). –Asymmetric Digital Subscriber Line (ADSL). –Cable Modem. –Wireless. –Satellite Links.

14. CMPE 80N - Introduction to Networks and the Internet 14 ISDN ISDN provides for communication of digitized voice and data to subscribers over the conventional “local loop” (i.e., using the same wiring as for analog telephone). In the Basic Rate Interface (BRI), ISDN offers three separate digital channels (2B+D). All on the same wire! (Multiplexing) Primary Rate Interface (23B+D). –Requires higher capacity lines than local loop!

15. CMPE 80N - Introduction to Networks and the Internet 15 ISDN (cont’d) The two B channels are intended to carry digital voice, data, or digital streams –Bitrate of each B-channel: 64 kb/s (overall, 128 kb/s) The D channel is used as a control channel –E.g., to request services which are then supplied over the B channels, to carry caller ID information, etc. –Bitrate of D channel: 16 kb/s.

16. CMPE 80N - Introduction to Networks and the Internet 16 ISDN (cont’d) To connect computer to ISDN, user needs a special network termination device (NT1). –NT1 device a.k.a. ISDN modem. A modem converts a digital signal to an analog signal; ISDN is inherently digital, so no such conversion is necessary. Need to dial a number to start a connection

17. CMPE 80N - Introduction to Networks and the Internet 17 ISDN (cont’d) ISDN was initiated in 1984, and was available in the USA in the early 90s. It was an attempt to replace the analog phone system with a digital voice+data system. –It never really succeeded… Currently, ISDN is obsolete, because it offers limited bitrate at a fairly high price. Still a possibility for Internet connection where other forms of broadband are not available.

18. CMPE 80N - Introduction to Networks and the Internet 18 ADSL ADSL allows transmission of high bit-rates over local loop. –It does not require any changes in the wiring. In addition, it does not preempt the local loop. –A user can use the telephone for analog voice communication and at the same time transmit data or stream video. It requires a splitter and a ADSL modem –The splitter separates voice/fax signals from data stream. –PC to ADSL modem: typically USB.

19. CMPE 80N - Introduction to Networks and the Internet 19 ADSL scheme

20. CMPE 80N - Introduction to Networks and the Internet 20 ADSL (cont’d) To achieve high bitrate transmission, ADSL must use sophisticated technology –It is “adaptive”: ADSL modems at the two ends probe the line between them to find its characteristics, and then agree to communicate using techniques that are optimal for that line. Depending on the characteristics of the wiring, different bit-rates can be achieved –If a house is too far form the “End office” (switching center), ADSL is not available.

21. CMPE 80N - Introduction to Networks and the Internet 21 ADSL (cont’d) ADSL is asymmetric: it provides a higher bit- rate downstream than upstream. –Downstream: 32 kb/s to 6.4 Mb/s (more typically, 1.5 Mb/s) –Upstream: 32 to 640 kb/s (more typically, 256 kb/s) Asymmetry is OK when high bitrate data is transmitted to the user. –E.g.: Video-On-Demand, Internet radio… In some cases, symmetric communication is preferable. –E.g.: Videoconferences

22. CMPE 80N - Introduction to Networks and the Internet 22 Cable Modems CATV (Community Antenna TV, or cable TV) uses coax cable (less susceptible to interference) –1-Km coax cable can accommodate bitrates of 1-2 Gb/s! Only one cable is used for a neighborhood –Different TV channels are multiplexed on it. Cable systems are designed to carry many more television signals than currently available. –There is unused capacity that can be used for data communication! –>80% of US homes are already reached by CATV

23. CMPE 80N - Introduction to Networks and the Internet 23 Cable Modems (cont’d) User can connect using a cable modem –A splitter separates the TV and the data signals. Problem: all users in the neighborhood share the same available capacity in the same cable! –If all users in the neighborhood transmit data at the same time, the available bitrate is reduced. E.g., if there are 50 Mb/s available, and 100 users in the neighborhood use it simultaneously, each user has only 0.5 Mb/s

24. CMPE 80N - Introduction to Networks and the Internet 24 Cable Modems (cont’d) Coax cables from several neighborhoods connect to a concentrator –The concentrator uses high capacity fiber optics cables to connect to the head end, which is connected to the Internet. Communication is asymmetric –Originally, CATV was designed only for downstream communication! Available bitrates: –Downstream: 1.5 to 2 Mb/s –Upstream: 128 kb/s

25. CMPE 80N - Introduction to Networks and the Internet 25 Satellite Systems Digital communication satellites were deployed by telecommunication companies as an alternative to terrestrial lines. –They can now be used as “local loop” technology (e.g., DirectPC). Advantages: –Can reach arbitrary geographic locations. –Does not require wiring. –Has high bandwidth. –Perfect for broadcasting (can reach many users at once).

26. CMPE 80N - Introduction to Networks and the Internet 26 Satellite Systems (cont’d) Disadvantages: –It’s a shared medium (the bitrate depends on the number of simultaneous users). –Delay (latency) can be relatively high (<1s) Not ideal for playing interactive app’s (e.g., games). –You have to put a dish on your roof! Initially, uplink was not provided. –Needed to use a separate phone line to uplink information. Nowadays it is a two-way system.

27. CMPE 80N - Introduction to Networks and the Internet 27 Physical Layer: Summary Different types of signal: –Analog and digital. Analog communication infrastructure: –Need to convert digital to analog before transmitting: ADC. –DAC before entering computer. Digitization: –Sampling. –Sampling period and frequency (samples/sec or Hertz). –Sample representation (quantization). –Bit rate.

28. CMPE 80N - Introduction to Networks and the Internet 28 Physical Layer: Summary (Cont’d) Modems. Input/output connections. –RS 232. –USB. –Firewire. Broadband. –ISDN. –ADSL. –Cable modem. –Satellite.

29. CMPE 80N - Introduction to Networks and the Internet 29 Other Wireless Networks

30. CMPE 80N - Introduction to Networks and the Internet 30 Cellular Networks Cellular phones:voice. Cellular networks: shift from voice to data. New wireless devices: pagers, PDAs. New services: Web access, e-mail, instant messaging, etc.

31. CMPE 80N - Introduction to Networks and the Internet 31 Cellular Concept: Motivation Early mobile radio systems: –Large coverage with single, high-powered transmitter. –But, no frequency re-use due to interference. Since finite spectrum allocation, need: high capacity (number of users) with limited spectrum and wide coverage.

32. CMPE 80N - Introduction to Networks and the Internet 32 Some Cellular Terminology Mobile. Base station. Mobile Switching Center (MSC). Handoff. Cell.

33. CMPE 80N - Introduction to Networks and the Internet 33 Cellular Architecture cell BS mobile

34. CMPE 80N - Introduction to Networks and the Internet 34 Cellular Fundamentals System-level idea, no major technological changes. –Many low-power transmitters instead of single, high power on (large cell). –Service area divided into small cells covered by each low power transmitter. –Each transmitter (or base station) allocated a portion of the spectrum. –Nearby BSs assigned different channel group to minimize interference. –Scalability: as more users subscribe, more BSs can be added using lower transmission power).

35. CMPE 80N - Introduction to Networks and the Internet 35 Frequency Reuse A B C D E F G G E F

36. CMPE 80N - Introduction to Networks and the Internet 36 Handoff/Handover Mobile hosts can change cells while communicating. Hand-off occurs when a mobile host starts communicating via a new base station. Handoff decision made based on signal strength.

37. CMPE 80N - Introduction to Networks and the Internet 37 Cellular Networks: Evolution Evidence of the wireless success! –Since 1996, number of new mobile phone subscribers exceeded number of new fixed phone subscribers! 1 st. Generation (1G): analog technology. –FDMA. –Analog FM.

38. CMPE 80N - Introduction to Networks and the Internet 38 Second Generation (2G) Most of today’s cellular networks use 2G standards. Early 90s. Digital technology. –Lighter, smaller devices with longer battery life. –Better reception and channel utilization.

39. CMPE 80N - Introduction to Networks and the Internet 39 3G Wireless Networks Multi-megabit Internet access, VoIP, ubiquitous “always-on” access. Single mobile device for everything (integrated service approach). New, world-wide standard. –International Mobile Telephone 2000 (IMT 2000)

40. CMPE 80N - Introduction to Networks and the Internet 40 Wireless Local Area Networks Local area network connectivity using wireless communication. IEEE 802.11 WLAN standard. Example: WaveLan, Aironet Wireless LAN may be used for –Last hop to a wireless host. –Wireless connectivity between hosts on the LAN.

41. CMPE 80N - Introduction to Networks and the Internet 41 Other WLAN Standards HomeRF –Proponents of 802.11 frequency hoping- spread spectrum (FH-SS). –HomeRF 2.0 –10 Mbps FH-SS. HIPERLAN –Europe, mid 1990s. –Similar capability to IEEE 802.11b.

42. CMPE 80N - Introduction to Networks and the Internet 42 MANETs Mobile, (wireless), multi-hop ad-hoc networks. Formed by wireless hosts which may be mobile. Without (necessarily) using a pre-existing infrastructure. Routes between nodes may potentially contain multiple hops. Mobilitty cause routes to change.

43. CMPE 80N - Introduction to Networks and the Internet 43 Multi-hop May need to traverse multiple hops to reach destination.

44. CMPE 80N - Introduction to Networks and the Internet 44 Why MANETs ? Ease of deployment. Speed of deployment. Decreased dependence on infrastructure.

45. CMPE 80N - Introduction to Networks and the Internet 45 Many Applications Personal area networking. –Cell phone, laptop, ear phone, wrist watch. Military environments. –Soldiers, tanks, planes. Civilian environments. –“Smart” environments. Emergency operations –Search-and-rescue –Policing and fire fighting –Monitoring and surveillance.