Local Area Network Dr. Farid Farahmand Revised on: 10/6/12Data Network Areas o WAN (Wide Area Networks) o MAN (Metropolitan Area Networks) o LAN (Local Area Networks) n Sharing resources in small but geographically dispersed networkLAN Applications o personal computer LANs n low cost n limited data rate n share resources o printers, hard drives, etc. n Potential issues for a single LAN o reliability o capacity o cost o High-speed office networks n used particularly for desktop image processing o a single page with 200 pictures elements (black and white) is about 3 Mbits! n high capacity local storage o backend networks n interconnecting large systems (mainframes and large storage devices) o high data rate o high speed interface o distributed access o limited distance o limited number of devices o backbone LANs n interconnect low-speed LANs n Resolve typical drawbacks to LANs LAN LAN BackboneLAN Applications o storage area networks (SANs) n separate network to handle storage needs o à shared storage n detaches storage tasks from specific servers n shared storage facility o eg. hard disks, tape libraries, CD arrays n accessed using a high-speed network o eg. Fibre Channel n improved client-server storage access n direct storage-to-storage communication for backup Project: Build a SAN!Storage Area NetworksLAN Topologies o Mesh Topology n Devices are connected with many redundant interconnections between network nodes. n In a full mesh topology every node has a connection to every other node in the network. o Star Topology n All devices are connected to a central switch/hub/repeater. Nodes communicate across the network by passing data through the switch/hub n Typically has unidirectional links o Bus Topology n All devices are connected to a central cable, called the bus or backbone. n The bus is often terminated on both ends if not connected to any devices. n The bus is typically duplex. o Ring Topology n All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. n Closed loop with unidirectional links (links are point-to-point) o Tree Topology n A hybrid topology. Groups of star-configured networks are connected to a linear bus backbone. http://www.webopedia.com/quick_ref/topologies.asp Tree MeshFrame Transmission Frame is absorbed Frame is removed when it returns to Its sourceEthernet – General o Most common LAN technology allowing multiple devices to connect to each other and share resources o Developed by Xerox in 1970 o Also known as IEEE 802.3 n IEEE 802.3 Energy Efficient Ethernet Study Group o Each standards organization focuses on particular layers of the protocol stack n Institute for Electrical and Electronic Engineers (IEEE) n World Wide Web Consortium (W3C) n Internet Engineering Task Force (IETF)Various Standard Emphasis - Institute for Electrical and Electronic Engineers (IEEE) - World Wide Web Consortium (W3C) - Internet Engineering Task Force (IETF)Other Standardization Bodies o Institute of Electrical and Electronics Engineers (IEEE) o The European Computer Manufacturers Association (ECMA) o The International Electrotechnical Commission (IEC) o The International Organization for Standardization (ISO).IEEE 802 Model and Standards o IEEE divides Layer 2 of the protocol stack into two conceptual sub-layers n The Logical Link Control (LLC) o sublayer specifies addressing and the use of addresses for demultiplexing as described later in the chapter n The Media Access Control (MAC) o sublayer specifies how multiple computers share underlying mediumIEEE 802 Model and Standards o IEEE assigns a multi-part identifier of the form XXX.YYY.ZZZ n XXX denotes the category of the standard n YYY denotes a subcategory n If a subcategory is large enough, a third level can be addedEthernet Protocol Architecture EEE 802.2 is the IEEE 802 standard defining Logical Link Control (LLC) EEE 802.3 is a collection of IEEE standards defining the Physical Layer and Data Link Layer's media access control (MAC) sublayer of wired Ethernet. 802.2 802.3Ethernet Protocol Stack Interface Interface EEE 802.2 is the IEEE 802 standard defining Logical Link Control (LLC) EEE 802.3 is a collection of IEEE standards defining the Physical Layer and Data Link Layer's media access control (MAC) sublayer of wired Ethernet.Ethernet Protocol Architecture IEEE 802 Layers o Physical n encoding/decoding of signals n preamble generation/removal n bit transmission/reception n transmission medium and topologyIEEE MAC SUB-LAYER Chapter 14Multi-Access Protocols & Channel Allocations o LAN technologies allow multiple computers to share medium n any computer on the LAN can communicate with any other n in order to share the medium we have to get access o We use the term multi-access to describe the way medium access is achieved o Thus, LAN is considered to be a multi-access networkChannel (medium) Access Control Protocols o How are multiple computers coordinated to control (share) a single medium? o In other words: n What are the multi-access protocols in multi-access networks? Permission is required Just send it! Take turnChannelized Access Protocols o Channelization refers to a mapping between a given communication and a channel in the underlying system n There should be a mapping between entities and a channel is referred to as 1-to-1 and static o Static channel allocation works well for situations where the set of communicating entities is known in advance and does not change n A dynamic channel allocation scheme can be established when a new station appears, and the mapping can be removed when the station disappears Three main types of channelization Also referred as multiplexing techniquesControlled Access Protocols o Controlled access protocols provide a distributed version of statistical multiplexing nControlled Access Protocols- Polling o Polling uses a centralized controller cycling through stations on the network and gives each an opportunity to transmit a packet o