Presentation on theme: "1 LAN / WAN / Extranet and Network Topology. 2 Motivation n Local Area Networks (LAN) were motivated by: –Decreasing computer size –Decreasing computer."— Presentation transcript:
1 LAN / WAN / Extranet and Network Topology
2 Motivation n Local Area Networks (LAN) were motivated by: –Decreasing computer size –Decreasing computer cost –Realizing computers could help with many tasks
3 Interchangeable Media n The first data transfers: –Used: Magnetic tapes Disks n Data transferred between computers in a method similar to using floppy disks.
4 LAN Generations n First –CSMA/CD and token ring –Terminal to host and client server –Moderate data rates n Second –FDDI –Backbone –High performance workstations n Third –ATM –Aggregate throughput and real time support for multimedia applications
5 Third Generation LANs n Support for multiple guaranteed classes of service –Live video may need 2Mbps –File transfer can use background class n Scalable throughput –Both aggregate and per host n Facilitate LAN/WAN internetworking
6 LAN technologies n MAC protocols used in LANs, to control access to the channel n Token Rings: IEEE (IBM token ring), for computer room, or Department connectivity, up to 16Mbps; FDDI (Fiber Distributed Data Interface), for Campus and Metro connectivity, up to 200 stations, at 100Mbps. n Ethernets: employ the CSMA/CD protocol; 10Mbps (IEEE 802.3), Fast E-net (100Mbps), Giga E-net (1,000 Mbps); by far the most popular LAN technology
7 A Computer Consists Of Circuit Boards n Inside a computer are electronic components on circuit boards. –Containing electronic components –Containing wires n Computers having different circuit boards for external devices.
8 Circuit Boards Plug Into A Computer n Computers are built so it contains a set of sockets. –Using wires to connect sockets together –Using wires to carry power and data –Plugging circuit boards into sockets to control external devices
9 Illustrations of the components visible in a computer when the cover has been removed. A circuit board can plug into each socket; wires connect the sockets to other components.
10 Connecting Computers In Early Systems n Transferring data between two computers consisted of two circuit boards connected by a cable. Figure 7.2 Illustration of an early computer communication system formed using two circuit boards plugged into sockets in two computers.
11 Early Systems n The computers use cables to transfer data electronically. –Operating like an I/O device –Writing data to circuit board Figure 7.3 Two pairs of interface boards connecting three computers. Each new computer added to the set requires a new pair of interface boards and an additional cable.
12 Early Systems n Advantage of early LANs were speed. n Disadvantages of early LANs were inconvenience and cost. Requiring effort to: –Add a new computer –Connect incompatible hardware
13 Connecting A Computer to A LAN n A computer needs additional hardware to connect it to a LAN. n The speed of the LAN does not depend on the speed of the computer attached to it. –Communication by heterogeneous computers
14 Computers connected to a LAN. Each computer attaches to the hub with a cable; the computers can then communicate directly. In many LAN systems, a cable connects each computer to a hub.
15 NIC n A computer needs network interface hardware and a cable that connects to the LAN. n A computer uses the network interface to send and receive data.
16 The Importance Of LAN Technology n LANs changed the way people used computer networks. –Sharing resources –Connecting machines within a building
17 Relationship To The Internet n Xerox gave universities a prototype of a new LAN technology. –Beginning of Ethernet –Developing the idea of inexpensive and widely available LANs
18 Many Independent Networks n By late 1970s, many organizations began installing Local Area Networks because they: – Were inexpensive. – Were easy to install – Could operate them independently of a central administration.
19 The Proliferation of LANs n Advantages – An organization can: budget funds decide who has access devise policies for use n Disadvantages – Independent groups can: Encourage proliferation of different LAN technologies
20 n Engineers have devised many LAN technologies n LAN performance determines cost. n LAN technology may only work with specific computers. Facts About LANs
21 LANs Are Incompatible n Various LAN technologies are completely incompatible. –Connecting multiple LANs is not possible Engineered to operate over limited distance May be electrically incompatible Encoding information may not make sense to another LAN n Various LAN technologies are completely incompatible. –Connecting multiple LANs is not possible Engineered to operate over limited distance May be electrically incompatible Encoding information may not make sense to another LAN
22 IEEE802.3 Medium Access Control n Random Access – Stations access medium randomly n Contention –Stations content for time on medium
23 IEEE Frame Format
24 10Mbps Specification (Ethernet) n 10Base510Base210Base-T10Base-FP n 10Base510Base210Base-T10Base-FP n Medium n MediumCoaxialCoaxialUTP850nm fiber n Signaling n SignalingBasebandBasebandBasebandManchester n ManchesterManchesterManchesterOn/Off n Topology n TopologyBusBusStarStar n Nodes n Nodes
25 100Mbps (Fast Ethernet) n 100Base-TX100Base-FX100Base-T4 n 2 pair, STP2 pair, Cat 5UTP2 optical fiber4 pair, cat 3,4,5 n MLT-3MLT-34B5B,NRZI8B6T,NRZ
26 Gigabit Ethernet Configuration
27 Gigabit Ethernet - Differences n Carrier extension n At least 4096 bit-times long (512 for 10/100) n Frame bursting
28 Gigabit Ethernet - Physical n 1000Base-SX –Short wavelength, multimode fiber n 1000Base-LX –Long wavelength, Multi or single mode fiber n 1000Base-CX –Copper jumpers <25m, shielded twisted pair n 1000Base-T –4 pairs, cat 5 UTP n Signaling - 8B/10B
29 Wide Area Technologies Exist n WAN technology includes an additional special-purpose computer at each site that: –Connects to the transmission lines –Keeps communication independent of the computer
30 Few WANs, Many WANs n WANs cost much more than LANs. –Require more planning –Require more hardware n Only a few companies build their own WAN.
31 WANs And LANs Are Incompatible n Many Wide Area Networks and Local Area Networks exist. –Cannot connect a WAN to a LAN –Cannot interconnect the wires from two different networks
32 WANs for Voice n Requires very small and nonvariable delays for natural conversation--difficult to provide this with packet-switching n As a result, the preferred method for voice transmission is circuit-switching n Most businesses use public telephone networks, but a few organizations have implemented private voice networks
33 WANs for Data n Public packet-switched networks (X.25) n Private packet-switched networks n Leased lines between sites (non-switched) n Public circuit-switched networks n Private circuit-switched networks (interconnected digital PBXs) n ISDN (integrated X.25 and traditional circuit- switching)
34 WAN Considerations n Nature of traffic –stream generally works best with dedicated circuits –bursty better suited to packet-switching n Strategic and growth control--limited with public networks n Reliability--greater with packet-switching n Security--greater with private networks
35 Wireless LANs n IEEE n Basic service set (cell) –Set of stations using same MAC protocol –Competing to access shared medium –May be isolated –May connect to backbone via access point (bridge) n Extended service set –Two or more BSS connected by distributed system –Appears as single logic LAN to LLC level
36 n Wireless LAN —links clients within the vicinity of each other. n A network adapter card that is connected to a transmitter, called an access point, via a cable. n The transmitter located on a wall gives the signal an uninterrupted path to a wall-mounted receiver on the far side of the room. n Data packets are transmitted over the airwaves to the receiver, which is also connected to network clients by a cable. n Wireless Extended LAN —connections to clients a couple of miles away. n Similar connectivity is an Extended LAN. n Transmitter and receiver are typically located outside the buildings. n Forms an electronic data communication bridge called a wireless bridge. n Data packets up to 25 miles away from the transmitter use spread spectrum radio technology.
37 Wireless LAN - Physical n Infrared –1Mbps and 2Mbps –Wavelength nm n Direct sequence spread spectrum –2.4GHz ISM band –Up to 7 channels –Each 1Mbps or 2Mbps n Frequency hopping spread spectrum –2.4GHz ISM band –1Mbps or 2Mbps n Others under development
38 Wireless LANs n Mobility n Flexibility n Hard to wire areas n Reduced cost of wireless systems n Improved performance of wireless systems
39 LAN Extension n Buildings with large open areas –Manufacturing plants –Warehouses n Historical buildings n Small offices n May be mixed with fixed wiring system
40 Single Cell Wireless LAN
41 Multi Cell Wireless LAN
42 Client/Server Architecture n Combines advantages of distributed and centralized computing n Cost-effective, achieves economies of scale n Flexible, scalable approach
43 Intranets n Uses Internet-based standards & TCP/IP n Content is accessible only to internal users n A specialized form of client/server architecture
44 Extranets n Similar to intranet, but provides access to controlled number of outside users –Vendors/suppliers –Customers
45 There are six topologies used in the design of a computer network: Bus Star Ring Token Passing Hubs Hybrid Every computer network has the same basic components: Cables or wireless connection Network adapter cards that transmit and receive information Client software that makes all these components work together Topology: The way in which components are assembled.
46 Topologies n Tree n Bus –Special case of tree One trunk, no branches n Ring n Star
47 LAN Topologies
48 A bus topology requires: Clients are connected to the same cable known as a trunk, segment, or backbone. All data packets are received by every client regardless of whether the data packet is addressed. Data packets not addressed to the client are ignored. Data packets addressed to the client are accepted and processed by the client. Data packets travel the complete length of the cable, then bounce back. This is called signal bounce and continues until the signal loses energy and dissipates. The network operating system has the responsibility to keep the transmission moving along the cable. A client can malfunction and the network continues to operate, which is called a passive topology. A passive topology is easy to construct, highly reliable, and susceptible to slow performance during heavy network traffic. A break in the cable is commonly caused by an improper network connection. Breaks are hard to track down because every client and device on the network could be suspect. A network outage does not shut down a client's operation. Clients work as a stand-alone.
49 Frame Transmission - Bus LAN
50 Bus and Tree n Multipoint medium n Transmission propagates throughout medium n Heard by all stations –Need to identify target station Each station has unique address n Full duplex connection between station and tap –Allows for transmission and reception n Need to regulate transmission –To avoid collisions –To avoid hogging Data in small blocks - frames n Terminator absorbs frames at end of medium
51 Clients connect to a central device called a concentrator or hub. Clients transmit and receive data packets to and from the concentrator. It is the job of the concentrator to redirect data packets to the appropriate client. Clients only receive data packets addressed to them. Star topology reduces the network traffic clients must handle. The concentrator detects if a client is not connected to the network and returns data packets to the sender. Failure of one client does not disable the entire network. Network services become unavailable if the concentrator malfunctions. Clients use 10BaseT network adapter cards that automatically detect trouble with the concentrator. The client then stops any transmission of data packets and operates as a stand-alone computer until the concentrator becomes operational.
52 Ring Topology n Repeaters joined by point to point links in closed loop –Receive data on one link and retransmit on another –Links unidirectional –Stations attach to repeaters n Data in frames –Circulate past all stations –Destination recognizes address and copies frame –Frame circulates back to source where it is removed n Media access control determines when station can insert frame
53 Frame Transmission Ring LAN
54 Each client is connected consecutively to the single cable. There are no ends to the ring network that must be sealed with a terminator. Data packets pass clockwise from one client to the next. If the data packet isn't addressed to the client, the client resends the data packet to the next client. The client strengthens the signal, allowing the data packet to travel a further distance. Clients connect to a hub. Within the hub is the ring. If one client is not working properly, there is a good chance the entire network will fail. This depends on the network operating system. IBM token ring automatically ignores inactive clients.
55 A token ring is a ring-like topology. Clients are connected together to form a ring. Each data packet is transmitted to each client on the network. A special packet, called a token, is used to control transmissions on the network. The token packet is delivered to a client clockwise along the network. The client can accept the token and transmit a data packet. Addresses, data, and other necessary information are added to the token packet. The modified token packet becomes the new data packet and is sent to the hub for delivery to the destination. The destination client acknowledges the data packet. The client that sent the data packet creates a new token packet and passes it to the next client. The client can ignore the token packet, which is then passed along to the next client on the ring. This is called token passing. Token packets can travel more than 10,000 times around the network per second.
56 Star Topology n Each station connected directly to central node –Usually via two point to point links n Central node can broadcast –Physical star, logical bus –Only one station can transmit at a time n Central node can act as frame switch
57 Hubs A hub is a central processing device on a network. A hub is used with the star and ring topologies as a concentrator for network traffic. Hub topology is used to divide large network requirements into smaller, serviceable LANs called segments. A hub enables a network administrator to monitor and manage network traffic. A hub is used to link segments together; cabling used by various clients can be mixed and matched. Types of Hubs Networks use one of two kinds of hubs: Passive hubs Active hubs Passive Hubs A passive hub acts as a connector box known as a wiring panel. A passive hub connects cables from all clients. A passive hub only provides connectivity among network clients. It does not interrupt transmissions on the network. Active Hubs An active hub ID known as a multi-port repeater. An active hub joins together clients. An active hub boosts the signal along the network like a repeater. An active hub can, in some cases, redirect data packets to the appropriate client.
58 Hybrid Topology The disadvantage of each topology is reduced by combining topologies. The combined topology is called a hybrid network. There are two common hybrid networks: star bus and star ring topology. Star Bus Topology The star bus topology combines the star topology and the bus topology. Clients of the smaller networks use the star topology to connect to its network concentrator. Network concentrators are linked together in a bus topology. The star bus topology controls traffic flow on the network. Traffic between concentrators is less demanding than traffic among clients. The bus topology is a more direct and efficient design for connecting concentrators. The star topology avoids transmission conflicts among clients. The star bus topology enables network expansion. If network response time is slow because of an increase in traffic, clients can be transferred to a different segment with its own concentrator.
59 The star ring topology combines the best of the star and ring topologies. The star ring topology is referred to as the star wired ring topology. The star ring topology divides the network into smaller networks each having a concentrator or hub used to connect clients. Concentrators are joined together using a master concentrator (sometimes called the main hub) in the form of a ring. The advantage is that network traffic is handled by a topology that best suits the volume of traffic. The network is scalable. A hybrid network reduces the chance that a complete network failure will occur. Only clients directly linked to a concentrator will lose access to network services if the concentrator malfunctions.