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Long Distance Connection and WAN

Lecture 6. Long Distance Connection and WAN. Digital Telephone, PCM and Nyquist Sampling Theorem DSU/CSU, T Line Series and OC line Series Local Loop DSL Technologies - ADSL, HDSL, SDSL, VDSL Cable Modem WAN and Packet Switch Switch Addressing and Routing Typical WANs

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Long Distance Connection and WAN

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  1. Lecture 6 Long Distance Connection and WAN • Digital Telephone, PCM and Nyquist Sampling Theorem • DSU/CSU, T Line Series and OC line Series • Local Loop • DSL Technologies - ADSL, HDSL, SDSL, VDSL • Cable Modem • WAN and Packet Switch • Switch Addressing and Routing • Typical WANs - ARPANET, X.25, Frame Rely, SMDS, ATM • Wireless WANs, Cellular Networks

  2. Lecture 6 Long Distance Telephone Network and Others • A single LAN can’t handle an arbitrary number of computers • A LAN is usually owned by a company, organization, university, …, which can’t build their own long distance links to connect computers in arbitrary sites • Telephone and other companies offer long distance connections which can be leased to build large computer networks covered many distance sites Telephone Company Circuit Switch Analogy Network Modem Modem AD/DA AD/DA Circuit Switch Digital Network Convert Convert Comp LAN Packet Switch Digital Network Comp LAN Other Company Modem CATV/Power Network Modem Modem Satellite Network Modem . . .

  3. Lecture 6 Digital Telephone Network and PCM Analogy telephone network: transfers analogy voice signal in the frequency range [0, 3.5KHz] Digital telephone network: transfers digital voice signal PCM(Pulse Code Modulation): a standard of conversion from analogy voice to digital voice - Analogy signal is first sampled in sampling interval T or with sampling frequency F=1/T - Nyquist sampling theorem: Original analogy signal can be reconstructed from a sequence of sampled values if F>2B where B is the maximum signal frequency - Sampling frequency of digital voice = 8 KHz - Each sampled value is quantized to an integer in [-127, 127] - Encoding the integer to an 8-bit binary value, PCM hardware is a analogy-to-digital (AD) device - Bit rate of one digital voice channel: 8KHz x 8 bits = 64 Kbps Nyquist Rate 00000111 F<2B 00000110 00000101 00000100 F=2B 00000011 00000010 00000001 F>2B 00000000 T T, sampling interval F=1/T, sampling frequency

  4. Lecture 6 DSU/CSU - Computer industry and telephone industry use own standards in different encoding - DSU/CSU perform the conversion between two standards - DSU (Data Service Unit): Translations between two encoding • CSU (Channel Service Unit): management of line termination and diagnose DSU/CSU  Gateway http://en.wikipedia.org/wiki/Gateway_(telecommunications)

  5. Lecture 6 Digital Telephone Line Standard Japan Japan Japan - Specified by the telephone industry in each country, different from the world • Fractional T1= 64, 9.6 or 4.8Kbps, use multiple fractional T1 with multiplxier • Can be leased in two points • Three campus networks in Hosei University are connected by T1 (before 2001) To outside Ichigaya T2 T1 T1 T1 Koganei Tama

  6. Lecture 6 High Capacity Digital Lines - Use both electrical signal and optical signal • Electrical standard called Synchronous Transport Signal (STS) • Optical standard called Optical Carrier (OC) • Engineers usually use OC- terminology for everything • OC-3 is popular • OC-3: three OC-1 lines, OC-3C: a single line operating at 155.520 Mbps Synchronous Optical Networking

  7. Lecture 6 Local Loop: Analogy Line, ISDN and DSL Analogy line Local Central Office ( CO ) Telephone network ISDN line DSL line Subscribers Local Loop Analogy line: - Analogy signal (300~3300Hz), modem needed, low speed (34/56Kbps) ISDN (Integrated Services Digital Network): - BRI (Basic Rate Interface) = 2B+D, B=64Kbps for data, D=16Kbps for control - PRI (Primary Rate Interface)=23B+64D=1.544Mbps=T1 - called Narrowband ISDN (N-ISDN), relatively slow - B-ISDN (Broadband ISDN), 155 or 622 Mbps to each subscriber xDSL (Digital Subscriber Line) - use existing telephone line to provide high speed transmission, current technology

  8. Lecture 6 xDSL Technology xDSL is a family of technologies to use existing analogy telephone line (copper pair) for delivery of high-speed data between a subscriber and telephone central office. Telephone Network xDSL family ADSL: Asymmetric Digital Subscriber Line HDSL: High-rate Digital Subscriber Line SDSL: Symmetric Digital Subscriber Line VDSL: Very high bite rate Digital Subscriber Line Local Central Office (CO) DSL Analogy phone xDSL ADSL HDSL SDSL VDSL Bit rate 32K~3M Up 1.5M 1.5M 1.5~2.3M Up 32K~40M Down 1.5M 1.5M 13~52M Down Mode Asymmetric Symmetric Symm Asym wire 1 pair 2 pairs 1 pair 1 pair Length 3.7~5.5km 3.7km 3.0km 1.4km f (KHz) 0 20 25 Fa Fb Fc Upstream Downstream More and latest at Digital Subscriber Line (DSL): http://en.wikipedia.org/wiki/Digital_subscriber_line Phone Computer FDM – Frequency Division Multiplexing Frequency range (<20KHz) for analogy phone Frequency range (>25Kz) for data transmission Local line quality Low frequency is better than high frequency Characteristic of each line is different from others Spectrum of copper pair 0 f (KHz)

  9. Lecture 6 ADSL DMT (Discrete MultiTone) by ANSI - FDM and QAM modulation - 31 channels (carriers) for upstream - 255 channels (carriers) for downstream Analogy phone f (KHz) … … … 0 20 25 200 250 1M Upstream Downstream Spectrum of copper pair ADSL2/2+, VDSL2, etc. http://en.wikipedia.org/wiki/Asymmetric_Digital_Subscriber_Line_2 0 f (KHz) - Concurrent and independent uses of analogy phone and data transmission - Upstream ~few Mbps, Downstream ~tenths M, suited for accessing Internet

  10. Lecture 6 Cable Modem Technology … Cable TV already brings high bandwidth coax into houses Conventional Cable TV is one direction - Signal broadcast at central location - Amplifiers boost signal through network - Amplifiers are unidirectional Solutions: - Alternate upstream path - e.g., dialup - Replaced by bi-directional amplifiers Cable modems encode and decode data from cable TV coax - One in cable TV center connects to network - One in home connects to computer Users share the cable - Each subscriber is assigned an address - TDM is used like multiple computers in LAN M M CATV Center Amplifier M - Cable Modem TV TV … f (MHz) Upstream Downstream (shared by multiple users)

  11. Lecture 6 Cable Modem Connections Hybrid Fibre-Coaxial (HFC)

  12. Lecture 6 Cable Modem Connections

  13. Lecture 6 FTTX - Fiber To The X Fiber to the x

  14. Lecture 6 WAN and Switch WAN – Wide Area Network: A network that can span a large geographic area, e.g., multiple cities, countries or continents. WAN building blocks: (1) Long-distance connection (e.g., T1/T3 lines, OC1/OC3 lines, etc.) (2) Packet switch -A hardware device connected to other switches and computers - Has CPU, memory, I/O interface, etc. - Handles packet WAN, Wiki Packet Header Frame Data or Payload Trailer Dest Addr Sour Addr

  15. Lecture 6 Illustration of A WAN Animation • Place one or more switches at each site • Interconnect switches: LAN technology for local connections Leased digital lines for long distance connections • Interconnections depend on traffic amount and reliability requirement • Packet is sent from source, travels switch-to-switch, and delivered to destination • Switch stores packet in memory, examines address, and forwards it toward destination Leased Line

  16. Lecture 6 Addressing in WAN • Each computer has a unique address • It is a two-part hierarchical address including 2 integers: [Integer1, Integer2] Integer1 for switch number Integer2 for computer number

  17. Lecture 6 Next-Hop Forwarding and Routing Table Routing table of switch 2 • Packet switch must choose outgoing connection for forwarding If destination is local computer, packet switch delivers computer port If destination is attached another switch, this packet switch forwards to next hop through connection to another switch • Packet switch doesn't keep complete information about all possible destination • A routing table just keeps next hop • For each packet, packet switch looks up destination in its routing table and forwards through connection to next hop • Next hop to destination does not depend on source of packet • Called source independence

  18. Lecture 6 Routing Table and Graph Graph: Node models switch Edge models connection Routing tables without default routes Routing tables with default routes • Each switch or node has a routing table: Left entry right entry destination switch edge number pair - Default route can remove duplicate routes, reduce memory and improve performance

  19. Lecture 6 Routing Table Computation • Static routing table: fixed in switch booting and does not change • Dynamic routing table: initialized in booting and alters as conditions in the network change Shortest path computation: - Label on edge represents “distance” - Possible distance metric: geographic distance, economic cost, capacity, etc - “Shortest” means the minimum sum of distances in all paths between two nodes - Darkened path is minimum from node 4 to node 5 Algorithms for computing shortest paths - Dijkstra’s algorithm - Distance Vector (DV) algorithm Dijkstra's algorithm Distance Vector Routing

  20. Lecture 6 History of WAN Technologies ARPANET - The first WAN, began in 1960s, low speed: 56Kbps - Funded by Advanced Research Projects Agency, an organization of US Defense Department - Incubator for many of current ideas, algorithms and internet technologies X.25 - Early standard for connection-oriented networking from ITU, which was originally CCITT - Early commercial service, more popular in Europe - Predates computer connections, used for terminal/timesharing connection Frame Relay - Telco service for delivering blocks of data - Connection-based service; - Typically 56Kbps or 1.5Mbps; can run to 100Mbps • SMDS - Switched Multi-megabit Data Service - Connectionless service; any SMDS station can send a frame to any other station - Typically 1.5-100Mbps ATM - Asynchronous Transfer Mode - Designed as single technology for voice, video, data, ... - Low jitter (variance in delivery time) and high capacity - Uses fixed size, small cells - 48 bytes data, 5 bytes header - Can connect multiple ATM switches into a network - Potential in future B-ISDN - Can be worked as a LAN

  21. Lecture 6 Region TAXI City laptops, PDAs Campus In-Building Wireless Networks • Wireless LANs • Wireless WANs • Satellite Networks • Cellular Networks BS: Base Station BS BS BS BS BS BS BS BS F: Carrier Frequency

  22. Lecture 6 Cellular Wireless Networks • Geographic region divided into cells • Frequencies/timeslots/codes reused at spatially-separated locations. • Co-channel interference between same color cells. Cllular Network: http://en.wikipedia.org/wiki/Cellular_network

  23. Lecture 6 Cellular Phone Networks

  24. Lecture 6 Handoff in Cellular Networks • Base stations/main stations coordinate handoff and control functions • Shrinking cell size increases capacity, as well as networking burden

  25. Lecture 6 4 Generations of Data Communications

  26. Lecture 6 Data Transmission Speeds 4G WWAN: http://en.wikipedia.org/wiki/4G

  27. Exercise 6 1. For an analogy TV signal, its frequency range is in [0, 6MHz]. To transmit the TV signal across a digital network, it is necessary to convert the analogy signal to a digital TV signal. What is the minimum sampling frequency in such conversion? Suppose that every sample will be encoded into 16 bits binary value (this is called TV PCM coding). Calculate bit rate of the digital TV signal after PCM coding. 2. Summarize the features and performance of typical long-distance connection technologies including T and OC series services, conventional modem, ISDN, xDSL and Cable modem. 3. Explain why bit rates of the upstream and the downstream in ADSL are not fixed? 4. In a packet switch network, the address of each computer consists two parts: one identifies a switch and other identifies a computer attached to that switch. Why? 5. Suppose that a packet switch network with a five nodes is given below. Give a routing table for each of the five nodes. 2 3 5 1 4

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