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Communication Networks  Data Communications  Network Architectures  Internet  Standards Chapter 1 Introduction Services and Application of Communication Networks Data Communications Network Architectures Internet Standards Wireless System Lab, NCNU 1 Chapter 1 Introduction Services and Applications of Communication Networks Wireless System Lab, NCNU 2 Communication Services & Applications Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service. E-mail E-mail server Exchange of text messages via servers Wireless System Lab, NCNU 3 Communication Services & Applications Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service. Web Browsing Web server Retrieval of multimedia (text, images, audio, and video) information from web servers Wireless System Lab, NCNU 4 Communication Services & Applications Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service. Instant Messaging (MSN, Skype) Direct exchange of text messages Wireless System Lab, NCNU 5 Communication Services & Applications Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service. Telephone Real-time bidirectional voice exchange Wireless System Lab, NCNU 6 Communication Services & Applications Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service. Cell phone Real-time voice exchange with mobile users Wireless System Lab, NCNU 7 Communication Services & Applications Communication service can enable the exchange of information between users at different locations. The ultimate goal: anytime, anywhere, and any- service. Short Message Service Fast delivery of short text messages Wireless System Lab, NCNU 8 Many Other Examples! Peer-to-peer applications BT, Emule, Foxy file exchange Audio & video streaming Network games On-line commerce Text messaging by PDAs, cell phones (SMS) Voice-over-Internet (VoIP) …… All these build on the Communication Networks. Communication Networks 與我們的生活息息相關! 9 Wireless System Lab, NCNU 9 Some Important Concepts What is communication services? applications? Services (服務): basic information transfer capability Internet transfer of individual information Internet reliable transfer of a stream of bytes Real-time transfer of a voice signal Applications (應用): build on communication service E-mail & WEB build on reliable network service FAX and modems build on basic telephone service Emerging applications build on multiple network services SMS builds on reliable Internet service and cellular telephone text messaging Wireless System Lab, NCNU 10 What is Communication Network? Communication What a wonderful Network cloud! Includes equipments (hardware & software) and facilities to provide the basic communication service Virtually invisible to the user; Usually represented by a cloud Equipments (設備) Facilities (設施) Routers, servers, Copper wires, coaxial switches, multiplexers, cables, optical fiber hubs, modems, … How are communication networks designed and operated? Wireless System Lab, NCNU 11 Communication Network Architecture Network architecture: a plan that specifies how the network is built and operated Architecture is driven by the network services Overall communication process is complex Network architecture conceptually partitions all communication processes into separate functional areas called layers Evolution of communication network architecture: telegraph, telephone, and computer networks Wireless System Lab, NCNU 12 Information Exchange Evolution 百億倍(1011)於 1850 1.0E+14 1.0E+12 ? 1.0E+10 1.0E+08 1.0E+06 per second per 1.0E+04 Information transfer 1.0E+02 1.0E+00 1850 1875 1900 1925 1950 1975 2000 Next Telegraph Telephone Internet, Optical Generation networks networks & Wireless networks Internet Wireless System Lab, NCNU 13 Network Architecture Evolution Telegraph Networks Message switching & digital transmission Telephone Networks Circuit Switching Analog transmission → digital transmission Fixed → mobile communications Internet Packet switching & computer applications Next-Generation Internet Multiservice packet switching network Wireless System Lab, NCNU 14 Chapter 1 Introduction Data Communications and Networks Wireless System Lab, NCNU 15 1-1 Data Communications Telecommunication: communication at a distance, including telephone, telegraph, and TV. Tele is Greek for "far“. Data: information presented in whatever form is agreed upon by the parties creating and using the data Data communications: the exchange of data between two devices via some form of transmission medium such as a wire cable, wireless … Wireless System Lab, NCNU 16 Performance of Data Communications Data delivery: send data to the correct destination (throughput (Mb/s)) Accuracy: receive data correctly (BER, PER). Timeliness: send data in a timely manner. Delay: voice needs real-time transmissions (150 ms~300 ms). Jitter: delay variation. Some packets arrive with 30-ms delay and others with 40- ms delay. Video stream (eg, IPTV) needs small-jitter transmissions. Wireless System Lab, NCNU 17 Five Components of Data Communications 1. Sender. 2. Receiver. 3. Message: text, digitals, images, audio, and video. 4. Transmission media: the physical path by which a message travels from sender to receiver. 5. Protocol: a set of rules govern data communications. (開車靠左邊、靠右邊。紅燈右轉。) Which one is your major study area? Wireless System Lab, NCNU 18 Data Flow Types Simplex Half-duplex Full-duplex Wireless System Lab, NCNU 19 Simplex Unidirectional, as on a one-way street. Only one device uses the entire capacity to send data in one direction. Examples? Examples: broadcast, TV, input, output, keyboards and monitors. Wireless System Lab, NCNU 20 Half-Duplex Bidirectional, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive. Examples? Examples: walkie-talkies, ham radio. Wireless System Lab, NCNU 21 Full-Duplex Bidirectional, both stations can transmit and receive simultaneously (like a two-way street with both direction traffic). Transmissions in two directions share the whole channel capacity. The full-duplex mode is used when two devices want to send and receive all the time. Examples? Examples: telephone, video conferencing. Wireless System Lab, NCNU 22 Chapter 1 Introduction Network Architectures Wireless System Lab, NCNU 23 1-2 Networks Network: a set of devices (often referred to as nodes) connected by communication links Node: can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes Most networks are distributed processing Network criteria Performance: throughput, delay Reliability (可靠度) Security (安全性) Wireless System Lab, NCNU 24 Physical Structures of Networks Types of Connections: Point-to-Point (點對點) Multipoint/Multidrop (點對多點) • Microwave or satellite links • TV remote control • ADSL. • Medium is shared by multiple nodes. • Ethernet connected by coaxial cables. • Cable modem. Wireless System Lab, NCNU 25 Physical Topology (拓墣) Wireless System Lab, NCNU 26 A Fully Connected Mesh Topology Fully-connected: Each nodes is connected to each other. Better reliability, security and privacy. However, each node needs (n-1) ports. n(n - 1)/2 duplex physical links are needed for fully connection. Expensive. Backbone connections between regional networks. Wireless System Lab, NCNU 27 A Star Topology Each device has a link only to a central controller (hub). The controller acts as an exchange. Less expensive, one port and one connection for a node. Robustness issue: One link failure only affects one node. However, if the hub goes down, the whole system is dead. Wireless System Lab, NCNU 28 A Bus Topology Only one backbone is needed to connect all the nodes. Less expensive. A fault or break in the bus cable stops all transmission, even between devices on the same side. The damaged area reflects signals back in the direction of origin, thereby creating noise. (Cable end is needed.) Difficult recovery and fault isolation. (需要查線) Wireless System Lab, NCNU 29 A Ring Topology Only one backbone is needed to connect all the nodes. Repeater can amplify the signal along the ring. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. Fault recovery is easy. Unidirectional traffic can be a disadvantage. A break in the ring disables the entire network. Dual ring can overcome this issue. Wireless System Lab, NCNU 30 A Hybrid Topology Star + bus Wireless System Lab, NCNU 31 Categories of Networks Local area network (LAN): Less than 2 miles. Metropolitian area network (MAN): Metropolitan wide, tens of miles. Wide area network (WAN): Worldwide. Router WAN Switch Switch Router WAN Router Gateway Router Ethernet LAN Switch Hub Hub Switch MAN Hub BS Switch Ring LAN Wireless LAN Wireless System Lab, NCNU 32 An Isolated LAN Connecting Computers to a Hub The most common LAN topologies are bus, ring, and star. Mesh topology is too expensive. Examples: Labs, offices, department. Wireless System Lab, NCNU 33 Wide Area Networks (WANs) Long-distance transmission over large geographic areas (a country, a continent,
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