Local Area Networks

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Local Area Networks

• Chapter 6

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Outline

• Introduction
• Ethernet
• Switched Ethernet
• Wireless 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 servers usual
  operating system is replaced by a network
  operating system.

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Peer-to-Peer Networks

• Do 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 LAN
• Client
• Server
• Network Interface Cards
• Network Cables and Hubs
• Network 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 cable
• Fiber 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 Modem
• Cat 2 UTP 4 90 Token Ring-4
• Cat 3 UTP 10 100 10Base-T Ethernet
• Cat 4 STP 16 100 Token Ring-16
• Cat 5 UTP 100 200 100Base-T Ethernet
• Cat 5 STP 100 200 100Base-T Ethernet
• RG-58 Coax 10 185 10Base-2 Ethernet
• RG-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 version
• Enables the file server, printer server, database
  server to operate.
• Usually the computers own operating system.
• Typically replaced the normal operating system on
  the server
• Examples Windows NT Server, NetWare
• The client version
• Provides the data link and the network layer
• Must interact with the application layers and the
  computers own operating system.
• Examples Windows NT Workstation, Window 98

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LAN Technology in A Layered Model
Applications, such as http. Ftp, email, etc.
Application Layer
Transport Layer Network Layer
NT network (TCP/IP) Novell NetWare (IPX/SPX)
Ethernet, Token Ring, ARCNET, Wireless LAN (IEEE
802.11), AppleTalk
Data Link Layer
Physical Layer
Network Interface Card, cabling, hub, 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 LAN
• It 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 layer
• IEEE 802.3 Ethernet
• IEEE 802.4 Token bus, an old protocol
• IEEE 802.5 Token ring
• IEEE 802.6 Distributed queue dual bus (DQDB)
  protocol, similar to FDDI
• IEEE 802.9 Integrated voice and data networking,
  including ISDN, Iso-ethernet
• IEEE 802.12 100Base-VG
• IEEE 802.13 100Base-X
• IEEE 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 Performance
• Solution 2 - Increase Circuit Capacity
• Solution 3 - Reduce Network Demand

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Tiered LANs

• Cost of attachment to a LAN tends to increase
  with data rate
• Alternative to connecting all devices is to have
  multiple tiers
• Multiple 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
  NetBIOS
• When 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
Internet Model
Windows Network Model
Layer 7
I/O Named Pipes Mail Server
Application layer FTP, TELNET, HTTP, etc.
Environment Subsystem
Layer 6
Provider Interface
Layer 5
NetBIOS (Redirector)
Transport layer TCP, UDP
Layer 4
TDI WINSOCK
NetBEUI
TCP/IP
Layer 3
Network layer IP
NDIS 3.0 NDIS Environment and Drivers
Layer 2 Layer 1
Data link layer
Physical layer
802.2 802.3 802.4 802.5
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/IP

• NetBIOS 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.