LAN / WAN / Extranet and Network Topology

1. LAN / WAN / Extranet andNetwork Topology

2. Motivation • Local Area Networks (LAN) were motivated by: • Decreasing computer size • Decreasing computer cost • Realizing computers could help with many tasks

3. Interchangeable Media • The first data transfers: • Used: • Magnetic tapes • Disks • Data transferred between computers in a method similar to using floppy disks.

4. LAN Generations • First • CSMA/CD and token ring • Terminal to host and client server • Moderate data rates • Second • FDDI • Backbone • High performance workstations • Third • ATM • Aggregate throughput and real time support for multimedia applications

5. Third Generation LANs • Support for multiple guaranteed classes of service • Live video may need 2Mbps • File transfer can use background class • Scalable throughput • Both aggregate and per host • Facilitate LAN/WAN internetworking

6. LAN technologies • MAC protocols used in LANs, to control access to the channel • Token Rings: IEEE 802.5 (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. • 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 • Inside a computer are electronic components on circuit boards. • Containing electronic components • Containing wires • Computers having different circuit boards for external devices.

8. Circuit Boards Plug Into A Computer • 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 • 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 • 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 • Advantage of early LANs were speed. • 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 • A computer needs additional hardware to connect it to a LAN. • The speed of the LAN does not depend on the speed of the computer attached to it. • Communication by heterogeneous computers

14. In many LAN systems, a cable connects each computer to a hub. Computers connected to a LAN. Each computer attaches to the hub with a cable; the computers can then communicate directly.

15. NIC • A computer needs network interface hardware and a cable that connects to the LAN. • A computer uses the network interface to send and receive data.

16. The Importance Of LAN Technology • LANs changed the way people used computer networks. • Sharing resources • Connecting machines within a building

17. Relationship To The Internet • 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 • 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. Advantages An organization can: budget funds decide who has access devise policies for use Disadvantages Independent groups can: Encourage proliferation of different LAN technologies The Proliferation of LANs

20. Facts About LANs • Engineers have devised many LAN technologies • LAN performance determines cost. • LAN technology may only work with specific computers.

21. LANs Are Incompatible • 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 • Random Access • Stations access medium randomly • Contention • Stations content for time on medium

23. IEEE 802.3 Frame Format

24. 10Mbps Specification (Ethernet) • <data rate><Signaling method><Max segment length> • 10Base5 10Base2 10Base-T 10Base-FP • Medium Coaxial Coaxial UTP 850nm fiber • Signaling Baseband Baseband Baseband Manchester • Manchester Manchester Manchester On/Off • Topology Bus Bus Star Star • Nodes 100 30 - 33

25. 100Mbps (Fast Ethernet) • 100Base-TX 100Base-FX 100Base-T4 • 2 pair, STP 2 pair, Cat 5UTP 2 optical fiber 4 pair, cat 3,4,5 • MLT-3 MLT-3 4B5B,NRZI 8B6T,NRZ

26. Gigabit Ethernet Configuration

27. Gigabit Ethernet - Differences • Carrier extension • At least 4096 bit-times long (512 for 10/100) • Frame bursting

28. Gigabit Ethernet - Physical • 1000Base-SX • Short wavelength, multimode fiber • 1000Base-LX • Long wavelength, Multi or single mode fiber • 1000Base-CX • Copper jumpers <25m, shielded twisted pair • 1000Base-T • 4 pairs, cat 5 UTP • Signaling - 8B/10B

29. Wide Area Technologies Exist • 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 • WANs cost much more than LANs. • Require more planning • Require more hardware • Only a few companies build their own WAN.

31. WANs And LANs Are Incompatible • 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 • Requires very small and nonvariable delays for natural conversation--difficult to provide this with packet-switching • As a result, the preferred method for voice transmission is circuit-switching • Most businesses use public telephone networks, but a few organizations have implemented private voice networks

33. WANs for Data • Public packet-switched networks (X.25) • Private packet-switched networks • Leased lines between sites (non-switched) • Public circuit-switched networks • Private circuit-switched networks (interconnected digital PBXs) • ISDN (integrated X.25 and traditional circuit-switching)

34. WAN Considerations • Nature of traffic • stream generally works best with dedicated circuits • bursty better suited to packet-switching • Strategic and growth control--limited with public networks • Reliability--greater with packet-switching • Security--greater with private networks

35. Wireless LANs • IEEE 802.11 • 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) • Extended service set • Two or more BSS connected by distributed system • Appears as single logic LAN to LLC level

36. Wireless LAN—links clients within the vicinity of each other. • A network adapter card that is connected to a transmitter, called an access point, via a cable. • The transmitter located on a wall gives the signal an uninterrupted path to a wall-mounted receiver on the far side of the room. • Data packets are transmitted over the airwaves to the receiver, which is also connected to network clients by a cable. • Wireless Extended LAN—connections to clients a couple of miles away. • Similar connectivity is an Extended LAN. • Transmitter and receiver are typically located outside the buildings. • Forms an electronic data communication bridge called a wireless bridge. • Data packets up to 25 miles away from the transmitter use spread spectrum radio technology.

37. Wireless LAN - Physical • Infrared • 1Mbps and 2Mbps • Wavelength 850-950nm • Direct sequence spread spectrum • 2.4GHz ISM band • Up to 7 channels • Each 1Mbps or 2Mbps • Frequency hopping spread spectrum • 2.4GHz ISM band • 1Mbps or 2Mbps • Others under development

38. Wireless LANs • Mobility • Flexibility • Hard to wire areas • Reduced cost of wireless systems • Improved performance of wireless systems

39. LAN Extension • Buildings with large open areas • Manufacturing plants • Warehouses • Historical buildings • Small offices • May be mixed with fixed wiring system

40. Single Cell Wireless LAN

41. Multi Cell Wireless LAN

42. Client/Server Architecture • Combines advantages of distributed and centralized computing • Cost-effective, achieves economies of scale • Flexible, scalable approach

43. Intranets • Uses Internet-based standards & TCP/IP • Content is accessible only to internal users • A specialized form of client/server architecture

44. Extranets • Similar to intranet, but provides access to controlled number of outside users • Vendors/suppliers • Customers

45. 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. • There are six topologies used in the design of a computer network: • Bus • Star • Ring • Token Passing • Hubs • Hybrid

46. Topologies • Tree • Bus • Special case of tree • One trunk, no branches • Ring • 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 • Multipoint medium • Transmission propagates throughout medium • Heard by all stations • Need to identify target station • Each station has unique address • Full duplex connection between station and tap • Allows for transmission and reception • Need to regulate transmission • To avoid collisions • To avoid hogging • Data in small blocks - frames • Terminator absorbs frames at end of medium