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Communication Networksnetworks EE3414EE3414 MultimediaMultimedia CommunicationCommunication SystemsSystems II CommunicationCommunication NetworksNetworks GuestGuest Instructor:Instructor: YihanYihan LiLi ECEECE Dept.,Dept., PolytechnicPolytechnic UniversityUniversity Communication Networks and Services z Communication networks: a set of equipment and facilities that provides a service to transfer information between users located at various geographical points z Services z Radio and television z Telephone service z Cellular telephone service z Electronic mail z World Wide Web (WWW) z Video on demand 2 Broadcast Network z Broadcast Communication Network do not have intermediate switching nodes z Each station has a transmitter/receiver that communicates over a medium shared by other stations z Transmission from any station is received by all other stations z Example: radio and television broadcasting z Related high audio and video quality is expected z A significant amount of delay can be tolerated 3 Telephone Service z Real-time service z Connection-oriented: a connection has to be set up z Users expect the network to be capable all the time z Security and privacy 4 Cellular Telephone Service z Extends the normal telephone service to mobile users z Hand off, when users move from one cell to another 5 Electronic Mail (e-mail) z User provides a text message and a name/address to a mail application z A local mail server transmits the message to a destination server across a computer network z Requires reliability, delivers without errors to the correct destination z No need to set up connection z Can tolerate large delays 6 World Wide Web z One computer can access documents located in other computers connected to the Internet z A browser is used to display the documents z Uniform resource locator (URL) specifies the name of the machine and the name and location of the document z e.g., http://www.poly.edu/ z Delay requirement 7 Communication Network Design z Network z a set of equipment and facilities z transfers information between a source and a destination z Note: Network nodes do not generate information z classified based on the way in which the nodes exchange information Communication Networks Switched Broadcast Communication Networks Communication Networks 8 Broadcast Communication Networks z Broadcast Communication Network do not have intermediate switching nodes: Each station has a transmitter/receiver that com-municates over a medium shared by other stations Transmission from any station is received by all other stations e.g., TV networks z More like utility networks (power, water, etc.) Packet Radio Satellite Bus Local Network Network Network 9 Switched Communication Networks z Consists of an interconnected collection of nodes z Data are transmitted from source to destination by being routed through the nodes z The switching method describes how data are processed and routed in the network Switched Communication Networks Circuit-Switched Packet-Switched Networks Networks Datagram Network Virtual Circuit Network 10 Network Design Requirements z Cost-effective z Easy to manage z Resilient z High-speed z Scalable z Protocol: a set of rules that governs how two communicating parties are to interact 11 Simple Solution Connect each pair of devices by a dedicated point-to-point link Sufficient if the number of devices is small. 12 Simple Solution With a large number of devices it is not practical to connect each pair of devices 13 General Communication Network A communication network provides a general solution to the problem of connecting many devices: z Connect each device to a network node z Network nodes exchange information and carry the information from a source device to a destination device host Network Communication Node Network 14 General Architecture z Intermediate nodes: signal relay z End-to-End: multi-hop transportation 3 2 4 1 5 Star Ring Mesh 15 Role of Switches z A switch interconnects many links allowing for data to be switched from one link to another. 16 Communication Network Architecture z Access network is used to provide end users access to services and connectivity to other end users z Backbone network interconnects access networks z LAN (Local Area Network), typically deployed in offices/campus buildings z WAN (Wide Area Networks), interconnects offices, buildings, homes, regions 17 Network Configuration 18 Example: vBNS Network 19 Source: National Science Foundation Network Functions z Addressing z Identify which network input is to be connected to which network output z Traffic control z To ensure the smooth flow of information through the network z Reroute or prevent information traffic during congestion z Network management z Monitor the network performance z Detect and recover from faults z Configure the network resources z Multiplexing z connect multiple information flows into shared connection lines z Routing z determine the path across the network z Switching approach 20 Multiplexing of Signals z Multiplexers are used to multiplex data bits from different communication sessions on to one link. z Time Division Multiplexing (TDM) z Frequency Division Multiplexing (FDM) z Wavelength Division Multiplexing (WDM). (a) (b) A A A Trunk A group B B B MUX MUX B C C C C 21 Figure 4.1 Time Division Multiplexing (a) Each signal transmits 1 unit every 3T seconds A A 1 2 t 0T 3T 6T B B 1 2 t 0T 3T 6T C C 1 2 t 0T 3T 6T (b) Combined signal transmits 1 unit every T seconds A B C A B C 1 1 1 2 2 2 t 0T 1T 2T 3T 4T 5T 6T 22 Figure 4.3 Frequency Division Multiplexing (a) Individual signals occupy W Hz A f 0 W B f 0 W C f 0 W (b) Combined signal fits into channel bandwidth B A C 23 f Figure 4.2 Wavelength Division Multiplexing Optical Optical MUX deMUX λ1 λ1 λ2 λ λ 1 λ2. λm 2 Optical fiber λm λm 24 Figure 4.18 Switching Approaches z Circuit-switched (e.g., Telephone network) z Packet-switched connectionless z Connectionless z packet headers carry destination addresses and routing through the network is based on the destination address z e.g., Internet - IP protocol based z Connection-oriented z a "connection" is set up (i.e., a route is selected) prior to data transfer and released after data transfer. z e.g., ATM: Asynchronous Transfer Mode Switched Communication Networks Circuit-Switched Networks Packet-Switched Networks 25 Datagram Networks Virtual Circuit Networks Circuit Switching In a circuit-switched network, a dedicated communication path is established between two stations through the nodes of the network The dedicated path is called a circuit-switched connection or circuit A circuit occupies a fixed capacity of each link for the entire lifetime of the connection. Capacity unused by the circuit cannot be used by other circuits Data is not delayed at the switches 26 Circuit Switching Circuit-switched communication involves three phases: 1. Circuit Establishment 2. Data Transfer 3. Circuit Termination “Busy Signal” if capacity for a circuit not available. Most important circuit-switching networks z Telephone networks z ISDN (Integrated Services Digital Networks) 27 Telephone Network Source Signal Go Signal Ahead Message Release Signal Destination Telephone call setup 28 Making a Phone Call 29 Circuit Switching A node in a circuit-switching network: Configured according to request 30 Circuit Switching circuit 2 circuit 1 31 Packet Switching Example: Internet Operates much like the postal system, where an envelope is sent in the mail with a destination address Each intermediate post office determines the next hop post office based on this address Intermediate post offices are comparable to IP routers Data are sent as formatted bit-sequences, so-called packets Header and Trailer carry control information Each packet is passed through the network from node to node along some path (Routing) At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks) No capacity is allocated for packets Header Data Trailer 32 Packet Switching 3 2 3 1 33 Datagram Packet Switching Packets are called datagrams The network nodes process each packet independently If Host A sends two packets back-to-back to Host B over a datagram packet network, the network cannot tell that the packets belong together. In fact, the two packets can take different routes. Implications of processing packets independently z A sequence of packets can be received in a different order than it was sent z Each packet header must contain the full address of the destination 34 Datagram Packet Switching A.1 C.2 C.1 A.2 C.1 C.2 A.3 C.1 C.2 A.1 A.3 C.2 A.2 A.1 A.3 A.2 A.2 A.1 A.2 A.2 A.3 35 Virtual-Circuit Packet Switching Virtual-circuit packet switching is a hybrid of circuit switching and packet switching All data is transmitted as packets All packets from one packet stream are sent along a pre- established path (virtual circuit) Guarantees in-sequence delivery of packets However, packets from different virtual circuits may be interleaved Examples z X.25, since the 1970s, used in many public packet switching networks z ATM (Asynchronous Transfer Mode), developed in the 1980s, for transmission of voice, video, and data in a single network 36 Virtual-Circuit Packet Switching C.2 C.1 A.1 VC 2 C.1 A.2 C.2 A.3 C.2 C.1 A.1 C.1 A.2 C.2 A.3 A.2 A.1 A.3 A.1 VC 1 A.2 A.3 37 Comparison Datagram Packet VC Packet Circuit Switching Switching Switching ] Dedicated ] No dedicated ] No dedicated transmission path transmission path transmission path ] Continuous ] Transmission of ] Transmission of transmission
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