Local Area Networks

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Local Area Networks:

Y. C. Chen Department of Computer Science and Information Engineering Spring 2005 Local Area Networks

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Spring 2005 Local Area Networks 2 Overview Data Link Layer Medium Access Control of LANs Physical Layer Metropolitan Area Networks Personal Area Networks Quality of Services Security Applications

Overview:

Spring 2005 Local Area Networks 3 Overview Traditionally, communications networks can be viewed in 3 categories: Wide Area Networks (WANs), which span a very large geographical area, such as from city to city or across countries and oceans. WANs are usually operated by transmission service providers. Metropolitan Area Networks (MANs), which span a large area such as a city, or company sites in different locations within the same city. MANs are usually operated by organizations. Local Area Networks (LANs), which span a limited area such as a company complex, a building, a campus, or even a small office. LANs are usually operated by a single organization. In recent years, the so-called Personal Area Networks (PANs) become more and more popular. This is due to the advance in home broadband access so that multiple stations and peripherals form a small network in a single residential home. Topics regarding LANs, MANs and PANs will be discussed in the class.

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Spring 2005 Local Area Networks 4 LAN characteristics are determined by Local Area Networks (LANs) Topologies MAC (Medium Access Control) Transmission media Size of coverage Local Area Networks are privately-owned networks within a small area, usually a single building or campus of up to a few kilometers. Since it is restricted in size, that means their data transmission time can be known in advance, and the network management would be easier.

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Spring 2005 Local Area Networks 5 Cost reductions through sharing of information and databases, resources and network services. Increased information exchange between different departments in an organization, or between individuals. The trend to automate communication and manufacturing process. Improve the community security. Increasing number and variety of intelligent data terminals, PCs and workstations. Motivations for Local Area Networking Local area networks are usually privately owned with limited coverage, this means that the underlying network technologies and network services may be freely selected. This leads to network architectures markedly different from those of Wide Area Networks. The growing demand for local area networks is due to technical, economic and organizational factors:

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Spring 2005 Local Area Networks 6 A local area network is a small group of interconnected workstations and associated devices that share the resources within a small geographic area. Usually, a local area network may serve as few as several users or many more. The nowadays main local area network technologies are: Ethernet (Fast Ethernet, Gigabit Ethernet, 10G Ethernet) Fiber Channel Hipper LAN Token ring ATM LAN FDDI (Fiber Distributed Data Interface) Wireless LAN …….. There are also some other technologies such as 100VG, token bus, ARCnet, but those are almost obsolete. Various Local Area Networks

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Spring 2005 Local Area Networks 7 There are two methods of networking computers together, Peer-to-Peer, and Client-Server. The proper method to use depends on the requirements. Peer-to-Peer Networking It offers a quick way to tie all your resources and people together. Users can access information from and share it directly with others in the network. Users can easily share files and directories in a peer-to-peer network. Client/Server Networking Clients are connected to a centralized server. The server provides centralized security, backup, and recover capability and controls access to sensitive files and expensive peripherals. A dedicated server improves data integrity, because the most current version of a document will be saved in one location. This type of network requires a network operating system. LAN Approaches

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Spring 2005 Local Area Networks 8 LAN Topologies Bus (Including Tree) – All the stations are attached to a common medium, so there may be collision if two or more stations try to transmit at the same time. Traditional Ethernet uses bus topology. Ring – All the stations are attached to the same medium which forms a ring structure, however, data from multiple stations may be transmitted upon receiving a token (FDDI, Token Ring, RPR). Ring networks suffer the complexity of token manipulation. Star – A switched Ethernet basically uses a star topology. It becomes popular due to the fast growing bandwidth demand, and both bus and ring topologies are hard to be scaled up in bandwidth. Mesh – it connects stations in an arbitrary manner. Mesh topology encounters some routing problems which are hard to be accommodated.

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Spring 2005 Local Area Networks 9 Bus Topology Bus Extender Example: Traditional Ethernet LAN Topologies

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Spring 2005 Local Area Networks 10 Hub/Tree (also the bus) Topology Example: 100VG-AnyLAN LAN Topologies

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Spring 2005 Local Area Networks 11 : Examples: FDDI, Token ring Each station attaches to the network via a repeater Data are transmitted in packets which contains source address and destination address The station will copy the data destined to itself, and the source is responsible for removing the data from the ring Media can be twisted pair, coaxial cable, or optical fiber Repeater Station Ring Topology LAN Topologies : : :

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Spring 2005 Local Area Networks 12 Digital Switch Digital PBX ( P rivate B ranch e X change) Switched Ethernet Star Coupler - Passive - Optical fiber, baseband coaxial - Active - Twisted pair Example: ATM LAN Star Topology : : : : : : LAN Topologies

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Spring 2005 Local Area Networks 13 LAN Topologies Mesh Topology

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Spring 2005 Local Area Networks 14 Wireless LAN Topologies PAU PAU Infrastructure Portable-to-fixed Network Fixed-wire replacement Server Ad hoc 50-100 m 10-20 m LAN Topologies

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Spring 2005 Local Area Networks 15 LAN Interconnection Traditional LAN interconnection devices Repeater – it operates at OSI layer 1 and transmits data bits over a physical medium. Bridge – it operates at OSI layer 2 and is commonly used to connect similar LAN segments. Switch – it operates at OSI layer 2 or layer 3 and is used to interconnect multiple similar or dissimilar LANs. Router – it operates at OSI layer 3. A router is used to interconnect individual networks whose sizes vary from very small to very large. Routers may be categorized into backbone router (or core router), border router and access router depending on their role in the network.

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Spring 2005 Local Area Networks 16 Example: Switched Ethernet Switched Ethernet provides high performance, high bandwidth, and flexibility required for today's LAN. Switches allow different nodes of a network to communicate directly with each other in a smooth and efficient manner, and provide a separate connection for each node in a organization's internal network. Basically, a LAN switch creates a series of instant networks that contain only the two devices communicating with each other at that particular moment. Layer 2 switching provides the dedicated bandwidth and network segmentation critical for directly connecting users to the network, while Layer 3 provides for switching and routing, maximizing speed, bandwidth, and flexibility in the network core or aggregation points. There are three main techniques for Ethernet switching: Store and Forward: Switch receives the full frame to it's memory and then decides what to do with it. Cut Through: Switch makes the decision on re-transmission when it has received the destination MAC address. Fragment Free (Modified Cut Through): Switch makes the decision on re-transmission after it has received the first 64 bytes of the frame. Switched LAN

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Spring 2005 Local Area Networks 17 LAN Access Methods Broadcasting – In a broadcast LAN, transmitted information will be received by all stations simultaneously. The medium access schemes are random access such as CSMA/CD which may cause contention, and controlled access such as token-passing, in which no contention will occur. Switching – In a switched architecture, a switch forward data packets to their destinations that may be a single user station or another LAN segment.

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Spring 2005 Local Area Networks 18 LAN Selections - Wired Wired LAN Medium access control Fixed slots Control token CSMA/CD Transmission media RF modem Headend Broadband CATV Thick-wire Thin-wire Baseband Carrier band Coaxial cable Twisted pair Fiber optic Topologies Star Ring Bus Hub/tree Application domains Universities/hospitals Office automation Factory automation Standards bodies Closed systems ISO IEEE NBS EIA ECMA EIA: Electrical Industries Association (USA) ECMA: European Computer Manufacturers Association NBS: National Bureau of Standards

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Spring 2005 Local Area Networks 19 LAN Selections - Wireless Wireless LAN Medium access control FDMA CSMA/CA CDMA Transmission media Infrared Radio Topologies Ad hoc Infrastructure Applications Standards IEEE ETSI (Hipper LAN) CDMA: Code Division Multiple Access ETSI: European Telecom. Standards Institute CSMA/CD: CSMA with Collision Detection FDMA: Frequency Division Multiple Access CSMA/CA: CSMA with Collision Avoidance TDMA: Time Division Multiple Access CSMA/CD TDMA Pulse-position modulation Direct modulation Multi-subcarrier modulation Single-carrier modulation Transmission schemes Carrier modulation Spread spectrum On-off keying Direct Sequence Frequency hopping Airports Warehouses Retail stores Old buildings Hospitals

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Spring 2005 Local Area Networks 20 IEEE LAN Standards 802.1 Higher Layer LAN Protocols 802.3 MAC CSMA/ CD 802.4 MAC Token Bus 802.5 MAC Token Ring 802.6 MAC DQDB 802 Executive Committee 802.10 LAN Security Data Link Phy- sical 802.9 MAC Isoc. LAN 802.11 MAC WLAN 802.12 MAC 100VG 802.15 MAC PAN 802.16 MAC Broad- band Wireless Access 802.17 MAC RPR 802.2 Logical Link Control

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Spring 2005 Local Area Networks 21 IEEE LAN Standards 802.1 Higher LAN Protocols 802.2 Logical link control (LLC) (No Activity) 802.3 CSMA/CD (Ethernet) 802.4 Token Bus (No Activity) 802.5 Token Ring (No Activity) 802.6 Metropolitan area network (No Activity) 802.7 Broadband technical advisory (No Activity) 802.8 Fiber optic technical advisory (Obsolete) 802.9 Integrated services LAN (No Activity) 802.10 Interoperable LAN Security (No Activity) 802.11 Wireless LAN 802.12 100 VG-AnyLAN (No Activity) 802.14 Cable-TV based broadband (Obsolete) 802.15 Wireless Personal Area Network 802.16 Broadband Wireless Access (WiMAX) 802.17 Resilient Packet Ring (RPR)

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Spring 2005 Local Area Networks 22 LAN LAYERS OSI LAYERS Logical link control (LLC) Medium access control (MAC) Physical (PHY) Higher layers Application Presentation Session Transport Network Data link Physical Layers of LAN and OSI Model

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Spring 2005 Local Area Networks 23 Outline Structure of a LAN Station Logical Link Control CSMA/CD Token Reserved Physical signaling P’ P’ AUI Broadband Baseband Fiber Physical Medium Attachment LLC MAC PLS DTE MAU PMA MDI AUI: Attachment Unit Interface LLC: Logical Link Control MAC: Medium Access Control MAU: Medium Access Unit PLS: Physical Signaling PMA: Physical Medium Attachment

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Spring 2005 Local Area Networks 24 Layered Architecture Regardless the mode of operation of the underlying MAC sublayer - CSMA/CD, token ring, wireless - a standard set of user services is defined for use by the LLC sublayer to transfer LLC PDUs to a correspondent layer. These user service primitives are: MA_UNITDATA.request MA_UNITDATA.indication MA_UNITDATA.confirm LLC layer MA_UNITDATA.request MA_UNITDATA.confirm MA_UNITDATA.request MA_UNITDATA.confirm MAC layer Peer LLC layer MA_UNITDATA.indication MA_UNITDATA.indication For a CSMA/CD LAN, the confirm primitive indicates that the request has been successfully (or not) transmitted , while for a token LAN it means that the request has been successfully (or not) delivered .

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Spring 2005 Local Area Networks 25 Layered Architecture Each service primitive has its associated parameters. Those parameters in the MA_UNIDATA.request primitive are - the required destination address (individual, group or broadcast address) - a service data unit (LLC PDU), - and the required class (i.e. priority) of service associated with the PDU. The MA_UNIDATA.confirm primitive includes a parameter that specifies the success or failure of the associated MA_UNIDATA.request primitive. The confirm primitive is not generated as a result of a response from the remote LLC sublayer, but rather by local MAC entity. If the parameter indicates success, this simply shows that the MAC protocol entity was successful in transmitting the service data unit into the network medium. If unsuccessful, the parameter indicates why the transmission attempts failed. For example, ‘excessive collision’ is a typical failure parameter if it is a CSMA/CD network.

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Spring 2005 Local Area Networks 26 Layered Architecture Network L_DATA.req (NPDI) L_DATA.ind (NPDI) MAC layer Network L_DATA.ind (NPDU) L_DATA.req (NPDU) MA_UNITDATA.req (UI) MAC layer MA_UNITDATA.ind (UI) MA_UNITDATA.req (UI) LLC LLC MA_UNITDATA.req (UI) Physicalmedium Source DTE Destination DTE LLC/MAC sublayer interactions LLC protocol is based on the high-level link control (HDLC) protocol, thus it supports two types of user service: connectionless and connection-oriented. Almost all LAN installations use connectionless protocol, therefore the only primitive used is L_DATA.request, and all data is transferred using the unnumbered information (UI) frame. Parameters used for this primitive are source/destination address and user data ( network-layer protocol data unit;NPDU ).

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Spring 2005 Local Area Networks 27 Layered Architecture Interlayer primitives and parameters Network protocol entity NPDU L_DATA.request DSAP+DA SSAP+SA Service class Length indicator User data(NPDU) LLC protocol entity DSAP SSAP (NPDU) LLC PDU MA_UNIDATA.req DA SA Service class Length indicator User data(LLC PDU) MAC protocol entity Preamble SFD DA SA LLC PDU FCS LLC MAC Link Network LLC service primitive MAC service primitive physical layer

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