CCM 4300 Lecture 2 Computer Networks: Wireless and Mobile Communication Systems. Dr Shahedur Rahman School of Science and Technology

Transcription

1 CCM 4300 Lecture 2 Computer Networks: Wireless and Mobile Communication Systems Dr Shahedur Rahman School of Science and Technology 1

2 Recap of Last Session defined a computer network and identified some of the basic components. explored the history of computers and computer networks and how they have evolved. identified some of the advantages and disadvantages of using computer networks. 2

3 Session Content Classification of computer networks Switched circuit switching packet switching broadcast networks scale Network standards 3

4 Lesson objectives To introduce a taxonomy of computer network : identify basic transmission technologies Classify different networks based on their scale. Understand the importance of standards 4

5 Classification of computer networks There is no generally accepted taxonomy into which all computer networks fit, but two dimensions stand out as important: Transmission technology Switched network Broadcast network Scale LANs, MANs, WANs, HANs, PANs, CANs, WLANs 5

6 Transmission Technology Switched networks data are transferred from source to destination though a series of intermediate nodes. The nodes provide the switching facility that will move data to their destination circuit-switched network a dedicated, physical circuit is first established between the source and destination nodes before the data transmission takes place packet-switched network messages are first partitioned into smaller units called packets, which are that sent to the destination node one at a time via intermediate switches 6

7 Circuit Switching End-end resources reserved for call call setup required dedicated resources: no sharing Release of resources 7

8 Circuit Switching network resources (e.g., bandwidth) divided into pieces and pieces allocated to calls For instance we can divide link bandwidth using frequency division time division One of the main advantages of circuit switching is that some QoS can be guaranteed Example of Circuit switching is the PSTN (the telephone network). Here each user has 64Kbs guaranteed during the call What are the disadvantages of Circuit switching? 8

9 Why packet switching? Computer data transmission is normally bursty in nature Burstytraffic refers to an uneven pattern of data transmission: sometime very high data transmission rate while other time it might be very low. In this case circuit network is wasteful of network bandwidth since must have sufficient channel bandwidth to handle burst level of traffic which is then used most of the time The solution is packet switching which allows sharing 9

10 Packet Switching A 10 Mbs Ethernet When the link is free the packet is sent C B Packets are buffered waiting for a free output link 1.5 Mbs 45 Mbs D This schema of data transfer is often called store-and-forward E Packet-switching is like sending a standard letter through the post other analogies? 10

11 Packet Switching each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed resource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use Bandwidth division into pieces Dedicated allocation Resource reservation 11

12 Packet Switching What if messages were sent as single units? Very long packets can increase the delay incurredateachswitchuntilthelinkisfree Short packets can reduce the delay and fixed packets can allow hardware optimisation 12

13 Packet switching versus circuit switching Packet switching allows more users to use network! E.g., 1 Mbit link each user: 100Kbps when active active 10% of time circuit-switching: 10 users packet switching: N users 1 10 i=0 35 p i 1 p i ( ) 35 i 1 Mbps link with 35 users, probability > 10 active less than.0004 (probability that out of 35, ten or less more transmitting at the same time is ) 13

14 Packet switching vs circuit switching Why should I choose circuit switching? A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth. Extra mechanisms are required for flow control, congestion control, and QoS. A circuit-switched network is suitable for application with long sessions with predictable smooth bandwidth requirements. 14

15 Packet switching vs circuit switching Why should I choose packet switching? When connections are short-lived the setup delay may represent a large part of the total connection time, thus reducing the network's capacity. Reserved resources cannot be used by any other users even if the circuit is inactive, which may further reduce link utilisation. 15

16 Transmission Technology Broadcast networks there are no intermediate switching nodes. The network share a single communication medium or channel one packet radio and satellite networks stations transmit and receive via antenna and share the same channel or radio frequency Local Area Networks (LANs) transmission by any station propagates the length of the medium 16

17 Scale Local Area Networks (LANs) LANs interconnects computing resources within a moderately (IEEE usually relates this to 10 km or about 6 miles or less in radius) sized geographical area This can include a room, several rooms within a building, or several buildings of a campus (e.g. Hendon campus) Various topologies are possible for LANs such as bus, star, ring, mesh 17

18 Metropolitan Area Network (MAN) MANs interconnects computing resources that span a metropolitan area The main reason for ever distinguishing MANs as special category is that a standard had been adopted for them (called Distributed Queue Dual Bus (DQDB, IEEE 802.6) MANs generally refer to networks that span a larger geographical area than LANs but a smaller geographical area than WANs 18

19 Metropolitan Area Network (MAN). A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of local networks. For instances this include Companies with buildings located throughout a local county or city A large campus 19

20 Internet Structure Sprint London backbone network 20

21 Wide Area Networks (WANs) WANs Interconnects computing resources that are widely separated geographically (usually over 100 Km ). This includes towns, cities, states and countries (e.g. The Internet) A WAN can be thought as consisting of a collection of LANs Most WANs consists of two distinct components: transmission lines, which moves data between nodes switching elements (router), which uses specialised computers to connect two or more transmission lines. 21

22 WAN vs LAN 1. Two computers communicating through a WAN 2. Two computers communicating through a LAN Which computers are exchanging data faster? LAN usually operates at much higher rates compared to WAN. This is mainly due to the proximity of the computers and the lack of congestion. It is common to experience up to 90 mbps in a LAN while achieving 10 to 20mbps is already a great achievement for WAN. 22

23 WAN vs LAN Is a LAN more secure than a WAN? Conceptually LAN could be more secure due to the fact that all the computers are within a specific area and are physically easier to secure. The data on a wide area network could pass insecure networks in order to reach its intended destination. 23

24 PAN Personal Area Network A personal area network (PAN) is a computer network used for communication among computer devices, including telephones and personal digital assistants, in proximity to an individual's body. The devices may or may not belong to the person in question. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink). A PAN covers the few meters that surround the user s workspace It provides the ability to synchronise computers, access local peripherals such a printers and pocket devices It can be made possible using IrDA, Bluetooth, ZigBee, USB 24

25 HAN Home Area Network A home area network (HAN) is a residential local area network It is used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a cable tv or Digital Subscriber Line (DSL) provider. Additionally, a home server may be added for increased functionality. Intended to provide the home with an infrastructure to interconnect a variety of homes appliances Enable them to be accessed through the Internet through a central home gateway. Therefore, a home computer network, will in the future allow multiple computers as well as multiple devices to connect with a network protocol. 25

26 CAN Company Area Network provides access up to a range of few hundred meters, e.g. an office block b A single access point, wired at a fixed location, supports a number of wireless users within a specified range without the need of cumbersome Ethernet cabling to form a star topology. CANs have also emerged as hotspots in various locations such as coffee shops and airports providing users with Internet access 26

27 CAN Controller Area Network Is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer CAN uses message based protocols, designed specifically for automotive applications but now also used in other areas such as industrial automation and medical equipment. A modern automobile may have as many as 70 electronic control unit (engine control unit, airbags, cruise control). A CAN can be used to connect them together. 27

28 Network standards Many network vendors exist each with its own ideas about how things should be done. Without coordination there would be a complete chaos. The only way out is to agree on some network standards. Andrew S. Tanenbaum Computer network 2003 A standard is a stated norm or requirements about technical systems. It is usually a document that establishes uniform criteria, methods, processes and practises. Not only standards allow different computers to communicate, but they also increase the market for the products that comply with the standard 28

29 Network standards Network standards fall into two categories: De facto (Latin for from the fact ): they have not been approved by any organised body but they have been adopted as a standard because of their widespread use. For instance Unix, MP3, PDF, DOC, IBM PC format Dejurestandards (Latin for by Law ): they are formal, legal standards adopted by some authorised standardisation body. 29

30 Network Standards - cont Recognised body can be classified into four major categories: (1) National, (2) Regional, (3) International, (4) Industry, Trade, and Professional. National Standards Organisations generally responsible for standards within a nation - British Standards Institute (BSI) - American National Standards Institute (ANSI) 30

31 Network Standards - cont Regional Standards Organisation restrict their activity to a specific geographical region but generally influences standards outside their regions - European Telecommunications Standards Institute (ETSI) Previously CEPT - European Committee for Standardization (CEN) - European Computer Manufactures Association (ECMA) 31

32 Network Standards International Standards Organization promotes standards for worldwide use - International Standards Organisation (ISO) - International Telecommunications Union (ITU) formally known as the CCITT - Comité Consultatif Internationale Télégraphique et Téléphonique. 32

33 Network Standards ITU major divisions: Consists of ITU -T, which is responsible for communications, interfaces, and other standards relating to telecommunications I series - Integrated Services Digital Network (ISDN) X series - Data communication networks (e.g. X.25) ITU R, which is responsible for allocation of frequency band in the electromagnetic spectrum for telecommunications, and for making recommendation relating to radio communications. 33

34 Network Standards - cont Industry, Trade and Professional Standards Organizations restrict their activity to member interest areas but generally influence other areas - Electronic Industry Association (EIA) - The Institute of Electrical and Electronics Engineers - Institute of Electrical Engineers (IEE) - Internet Engineering Task Force (IETF) Standards organizations are composed of delegates, from the government, academia and vendors who will be developing products based on the proposed protocols. The formal standards process, which is designed to ensure that a consensus is reached, is often lengthy and sometimes can take years for approval. 34

35 Network standards Why do we need to bother with networking standards? - enables interoperability - independence from vendor proprietary approaches - enables open procurement -Standards should be international in scope Important to track emerging standards - know when it is safe to use them - need to know where they come from 35

36 Summary! Classification of computer networks Switched scale Network standards Are there any questions? 36