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
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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
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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
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 packets packets ] Path stays fixed for ] Route of each packet ] Path stays fixed for entire connection is independent entire connection ] No setup delay ] Call setup delay ] Call setup delay ] Transmission delay ] Transmission delay ] Negligible for each packet for each packet transmission delay ] Queueing delays at ] Queueing delays at ] No queueing delay switches switches ] Busy signal ] Delays increase in ] Delays increase in overloaded network overloaded networks overloaded networks ] Fixed bandwidth for ] Bandwidth is shared ] Bandwidth is shared each circuit by all packets by all packets ] No overhead after ] Overhead in each ] Overhead in each call setup packet packet 38 QoS Requirements of Real- Time Applications z Constraints on delay and jitter z For telephony traffic, one-way delay requirement is 25ms if there are no echo cancellers on the path, 150ms with an echo canceller for excellent quality voice, and 400ms with an echo canceller for acceptable quality voice. z Delay in transmitting a voice packet on a packet-switched network consists of packetization delay (time to fill the packet), emission delay on the links (packet size divided by transmission rate), propagation delay on the links (length of the link divided by the speed of light in the link medium), queueing delays, and playout delays at the receiver. z Voice codec rates vary; PCM codecs generate data at 64kbps, Good speech codecs at 16 kbps or below.
39 Matching of applications needs/traffic to networking modes z Bursty traffic: best served by packet-switched networks z Continuous traffic: best served by circuit-switched networks z Delay-sensitive traffic: best served by connection- oriented networks z Short delay-insensitive transfers: best served by connectionless networks z Conclusions: z Interactive, streaming and recording applications best served by packet-switched connection-oriented networks; z Short non-real-time transfers: best served by (packet- switched) connectionless networks z Large non-real-time transfers: best served by circuit- switched networks 40 Key Factors in Communication Network Evolution z Success new telecommunication service z Technology must be available to implement z Government regulations much permit the service to be offered z Market for the service exist z Standards, to move away from single providers
41 Standards z Standards are agreements, with industrywide, national and possibly international scope, that allow equipment manufactured by different vendors to be interoperable z Standards on interfaces, allow interconnecting equipment z Standards on data communications, allow computers ‘talking to one another’ z Result from a consultative process (on a national and possibly international basis z e.g., International Telecommunications Union (ITU) z Enable smaller companies to enter large markets z Allows network operators to choose equipment from multiple suppliers 42 References z A. Leon-Garcia and I. Widjaja, Communication networks, Chapter 1
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