Long Distance Connection and WAN

Transcription

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 AD/DA Modem Circuit Switch Analogy Network Circuit Switch Digital Network Modem AD/DA Comp LAN Convert Packet Switch Digital Network Convert Comp LAN Modem Other Company CATV/Power Network Modem Modem Satellite Network... Modem

3 Digital Telephone Network and PCM Lecture 6 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 F<2B F=2B T T, sampling interval F=1/T, sampling frequency F>2B

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

5 Digital Telephone Line Standard Lecture 6 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 Koganei T1 T1 T1 Tama

6 High Capacity Digital Lines Lecture 6 - 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 Mbps Synchronous Optical Networking

7 Lecture 6 Local Loop: Analogy Line, ISDN and DSL Subscribers Analogy line ISDN line DSL line Local Central Office ( CO ) Telephone network 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 xdsl Technology Lecture 6 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. Analogy phone 0 Telephone Network Local Central Office (CO) DSL f (KHz) Fa Fb Fc Upstream Downstream 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 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 Phone Computer More and latest at Digital Subscriber Line (DSL): 0 Spectrum of copper pair f (KHz) 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

9 ADSL Lecture 6 DMT (Discrete MultiTone) by ANSI - FDM and QAM modulation - 31 channels (carriers) for upstream channels (carriers) for downstream Analogy phone f (KHz) M Upstream Downstream 0 Spectrum of copper pair f (KHz) ADSL2/2+, VDSL2, etc. - 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 CATV Center M M Solutions: - Alternate upstream path - e.g., dialup - Replaced by bi-directional amplifiers Amplifier M - Cable Modem 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 TV Upstream Downstream (shared by multiple users) TV f (MHz)

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 Leased Line - 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

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 Routing Table and Graph Lecture 6 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 Routing Table Computation Lecture 6 - 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 History of WAN Technologies Lecture 6 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 Mbps 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 Wireless Networks Lecture 6 Wireless LANs Wireless WANs Satellite Networks Cellular Networks Region BS: Base Station BS BS BS TAXI City BS BS BS laptops, PDAs Campus BS BS In-Building F: Carrier Frequency

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

23 Cellular Phone Networks Lecture 6

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 4 Generations of Data Communications Lecture 6

26 Data Transmission Speeds Lecture 6 4G WWAN:

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