Local Area Networks

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Local Area Networks

Chapter 6

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Outline

IntroductionEthernetSwitched EthernetWireless Ethernet

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Discussion Questions

What are the components for a small LAN?What is topology?What is CSMA/CD?How to improve the performance of a LAN?Compare and contrast 10Base-2, 10Base-5, 10-Base-T, 100Base-T, 1GbE, 10 GbE and 40 GbE. What is “hidden node” problem in Wireless LAN and how to solve it?

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Networking Experiment

Networking schemes Construct a LAN with a hub Construct a LAN with a router Network two PCs directly

Questions What is the network topology? What parameter do we need to set up the

network? What features does the router provide?

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Dedicated Server LANs

A dedicated server LAN has one or more computers that are permanently assigned to being the network server(s).

In a dedicated server LAN, the server’s usual operating system is replaced by a network operating system.

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Peer-to-Peer NetworksDo not require a dedicated server Have less capability Support a more limited number of

computers Provide less sophisticated software More difficult to manage than

dedicated server LANs.

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LAN Components

There are five basic components to a LANClientServerNetwork Interface CardsNetwork Cables and HubsNetwork Operating Systems

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LAN Components

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Network Interface Cards

Network Interface Card (NIC)Allows the computer to be physically connected to the network cable, which provides the physical layer connection among computers in the network. Most NICs are installed inside the computer.

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Network Cable

Unshielded twisted pair (UTP) wire Shielded twisted pair (STP)Coaxial cableFiber optic cable.

Many LANs use a combination of shielded and unshielded twisted pair.

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Network Cable

Name Type Mbps Dist(m) Used by-------------------------------------------------------------------------Cat 1 UTP 1 90 ModemCat 2 UTP 4 90 Token Ring-4 Cat 3 UTP 10 100 10Base-T EthernetCat 4 STP 16 100 Token Ring-16Cat 5 UTP 100 200 100Base-T EthernetCat 5 STP 100 200 100Base-T EthernetRG-58 Coax 10 185 10Base-2 EthernetRG-8 Coax 10 500 10Base-5 Ethernet

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Network Hubs

Serve two purposes: Provide an easy way to connect network

cables and expand a network. Act as repeaters or amplifiers to prevent

attenuation.

Some hubs are “smart”, because they can detect and respond to network problems.

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Network Operating Systems

Definition: The software that controls the network.

Every NOS provides two sets of software: one that runs the network server(s), and one that runs on the network client(s).

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Network Operating Systems

The server versionEnables the file server, printer server, database server to operate.Usually the computer’s own operating system.Typically replaced the normal operating system on the server Examples: Windows NT Server, NetWare

The client versionProvides the data link and the network layerMust interact with the application layers and the computer’s own operating system.Examples: Windows NT Workstation, Window 98

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LAN Technology in A Layered Model

Application Layer

Transport LayerNetwork Layer

Data Link Layer

Physical Layer Network Interface Card, cabling, hub, etc.

Ethernet, Token Ring, ARCNET,Wireless LAN (IEEE 802.11), AppleTalk

NT network (TCP/IP)Novell NetWare (IPX/SPX)

Applications, such as http. Ftp, email, etc.

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Ethernet (IEEE 802.3)

The Ethernet LAN standard was originally developed by DEC, Xerox, and Intel, but has since become a formalized standard by the Institute of Electrical and Electronics Engineers as IEEE 802.3

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Topology

Topology is the basic geometric layout of the network -- the way in which the computers on the network are interconnected. Two kinds of topologies:

Physical – cable scheme Logical – data flow

Topologies Bus Star Tree Ring

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Ethernet Topology

Ethernet uses a bus topology (a high speed circuit and a limited distance between the computers, such as within one building).

From the outside, an ethernet LAN appears to be a star, because all cables connect to the central hub.

Most ethernet LANs span sufficient distance to require several hubs, but some ethernet LANs are build without the use of hubs (coax bus).

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Media Access Control

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

Wait until the bus is free and then transmit.If no collision, transmission is completed.If the collision is detected, send a jamming signal.Wait a random amount of time, then re-broadcast.

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Types of Ethernet

10BASE-T (10 Mbps) Uses a twisted-pair cable with maximum distance of 100 meters

100BASE-T (100Mbps) Based on 10Base-T standard, 10 times faster

Three new types of Ethernet. They can use Ethernet traditional half-duplex approach, but most are configured to use full-duplex. Also they can run over fiber-optic cables.

1000Base-T Ethernet, sometimes is called 1 GbE. 10 GbE 40 GbE

Some old Ethernet standards: 10Base-5 (Thicknet), using thick coaxial cable, 500M 10Base-2 (Thinnet/Cheapnet), using RG-58 coaxial able, 185M

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100Base-T Ethernet (IEEE 802.13)

It gives a 100 Mbps data rate using the standard Ethernet bus topology, data link packets and CSMA/CD media access protocol.Three versions of 100Base-X differing only at the physical layer: 100BaseTX uses cat 5 UTP 100BaseFX uses fiber optic cable 100BaseT4 uses 4 sets of cat 3 UTP (inverse

multiplexed)

100Base-T Ethernet can co-exist with 10Base-T Ethernet.

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Wireless LANs (IEEE802.11)

Wireless LANs are growing very rapidly. Wireless LANs transmit data through the air (space) rather than through wire or cable.New terms:

WLAN (Wireless LAN) LAW (Local Area Wireless Network)

IEEE 802.11 standard is likely to be the dominant standard for wireless LANIt is easy to connect wireless LANs to Ethernet. So, it is usually called wireless Ethernet

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Wireless LANs (IEEE802.11)

Topology. The same as traditional Ethernet. It is both a physical star and a logical bus.

A central wireless access point (AP) is a radio transceiver that plays the role of hub. The maximum range is 100-500 feet depending on interference

Wireless LANs use CSMA/CA (Carrier Sense Media Access with Collision Avoidance) similar to CSMA/CD by Ethernet. Two methods are simultaneously used:

Physical carrier sense method. Packets are sent using stop-and-wait ARQ. Receiver waits less time to send ACK than other computers waiting for available time slots.

Virtual carrier sense method. Using AP, hidden node problem must be solved. It is optional.

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Hidden Node Problem

When one computer transmits packets, a computer in another side of AP may not detect the signal and send packets as well. This causes collision at AP. So, AP is the only device that is able to communicate with both computers. To solve the problem, AP uses controlled access method instead of the contention based method. A computer wanting to send packets must send a request (RTS) to AP. If no other computer is using the circuit, AP will respond with a clear to transmit (CTS) specifying the amount of time for the circuit reserved for the computer. All other computers hear the CTS and remain silent for the specified time period.

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Hidden node problem

Access Point

?

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Types of Wireless Ethernet

IEEE 802.11b. Two basic forms:IEEE 802.11a. Expected to run at 5 GHz. Takes more time to be develop. Products became available now (D-Link)IEEE 802.11g. Speed is five times of 11b with the same frequency – 2.4GHz, up to 54Mbps (Linksys WRT54G, D-Link DWL-2000AP)Other type of wireless LANs:

Infrared wireless LAN. Less flexible because most require direct line of sight between transmitters and receivers.

The primary advantage: the reduction of wiring. The primary disadvantage: the low speed (1-4 Mbps).

Bluetooth. Provide seamless networking of devices in a very small area (up to 30 feet)

Small, cheap Called Piconet with no more than 8 devices

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IEEE 802.11b

Two basic forms: Direct-sequence spread-spectrum (DSSS), in 2.4 GHz

band. Transmits signals through a wide spectrum of radio frequencies simultaneously. The signal is divided into many different parts and sent on different frequencies. 1, 2, 5.5, 11 Mbps speeds. 20 Mbps version is in the way out.

Frequency-hopping spread-spectrum (FHSS). Uses the same band, but once each frequency in turn. Sender and receiver synchronize in a frequency. So, minimizes jamming and eavesdropping. 1 Mbps and 2 Mbps.

They are shared media implementation. As the number of devices increases the speed will be reduced.

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*IEEE LAN Standards

IEEE 802.2: Logic link control (LLC) layer of data link layerIEEE 802.3: Ethernet IEEE 802.4: Token bus, an old protocolIEEE 802.5: Token ringIEEE 802.6: Distributed queue dual bus (DQDB) protocol, similar to FDDIIEEE 802.9: Integrated voice and data networking, including ISDN, Iso-ethernetIEEE 802.12: 100Base-VGIEEE 802.13: 100Base-XIEEE 802.16

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Improving LAN Performance

Why: When most computers in an organization are on LANs, performance can be a problem.

How: In order to improve performance, you must locate the bottleneck, the part of the network that is restricting the data flow.

Generally speaking, this bottleneck is in one of two places: The network server The network circuit

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Improving LAN Performance

Step one: Identify Where the bottleneck lies

If in the server -The server utilization during periods of poor performance is high (60-100%).

If in the network circuit -The server utilization during periods of poor performance is low (10-40%).

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Improving LAN Performance

Step two: Applying the following solutions:

Solution 1 - Increase Server PerformanceSolution 2 - Increase Circuit CapacitySolution 3 - Reduce Network Demand

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Tiered LANs

Cost of attachment to a LAN tends to increase with data rateAlternative to connecting all devices is to have multiple tiersMultiple advantages Higher reliability Greater capacity (less saturation) Better distribution of costs based on

need

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Tiered LAN Diagram

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*NetBIOS vs. NetBEUI

NetBIOS has 18 commands for PC connections.NetBEUI adds 8 more and is used as a transport protocol. It is faster and more efficient than NetBIOSWhen NetBEUI is in use, NETBIOS becomes API that invokes NetBeui.They can support a LAN with less than 200 PCs.

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*Windows Network Model

Layer 7

Layer 6

Layer 5

Layer 4

Layer 3

Layer 2Layer 1

Physical layer

Data link layer

Network layer: IP

Transport layer:TCP, UDP

Application layer:

FTP, TELNET, HTTP, etc.

Internet Model Windows Network Model

I/O Named Pipes Mail Server

Environment Subsystem

NetBIOS (Redirector)

TDI WINSOCK

802.2 802.3 802.4 802.5

NDIS 3.0NDIS Environment

and Drivers

NetBEUI TCP/IP

Provider Interface

NDIS: Network Driver Interface Specification

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*NDIS

NDIS (Network Driver Interface Specification) is a Windows specification for how communication protocol programs (such as TCP/IP) and network device drivers should communicate with each other.

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*NetBIOS

NetBIOS (Network Basic Input/Output System)Created by IBM for its early PC Network, was adopted by Microsoft, and has since become a de facto industry standard. A program that allows applications on different computers to communicate within a local area network (LAN). Used in Ethernet, token ring, and Windows NT networks.

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*NetBEUI

NetBEUI (NetBIOS Extended User Interface) Developed by IBM for its LAN Manager product and has been adopted by Microsoft for its Windows NT, LAN Manager, and Windows for Workgroups products. A new, extended version of NetBIOS, the program that lets computers communicate within a local area network.Formalizes the frame format (or arrangement of information in a data transmission) that was not specified as part of NetBIOS.

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*NetBIOS over TCP/IPNetBIOS over TCP/IP runs over the TCP/IP, so that you can share drives and printers over the Internet.In the "Network" configuration window in Windows 95, there is no option for NetBIOS over TCP/IP, but a "NetBEUI" entry, with which Microsoft actually means NetBIOS over NetBEUI. With the installation of TCP/IP protocol, Windows automatically installs the "NetBIOS over TCP/IP”. If you do want the TCP/IP protocol, but not "NetBIOS over TCP/IP" (because of security problem), you should uncheck "Files and Printer Sharing" in the Bindings tab of the TCP/IP entry in Network Configuration.