Local Area Network Basics

1
Local Area Network Basics

• Chapter 4

2
Chapter Objectives

• Describe Ethernet standard
• Explain Ethernet
• Understand the concept of CSMA/CD and CSMA/CA
  protocols
• Explain different types of Ethernet
• Understand about repeaters, bridges and hubs used
  to extend computer networks

3
Recall

• Types of copper wire cables are
• Coaxial cables (Also known as Coax)
• Twisted pair Cables (TP)
• Shielded Twisted pair (STP)
• Unshielded Twisted pair (UTP)
• Wireless transmission media are
• Radio Waves
• Microwave
• Infrared

4
IEEE Standards

• An association that promotes engineering and
  electronic improvement
• IEEE 802 was started in February 1980
• IEEE 802 committee defines frames, speed,
  distances and types of cabling to use for
  networking

5
Protocols and Procedures

• Protocols are set of rules which are used by the
  nodes on a network to communicate with each other
• Protocols are developed by committees, different
  companies developed products confirming to those
  protocols

6
LAN Architecture - I

• 802.3
• Defines a standard for physical layer and data
  link layer of the Ethernet architecture that uses
  wired connection
• Ethernet is an architecture that mainly uses bus
  topology
• Defines various cabling used for different types
  of topologies

7
LAN Architecture - II

• 802.4
• Defines a standard for Token Bus architecture
• Token bus is similar to token ring, but it uses
  coaxial cables

8
LAN Architecture - III

• 802.5
• Defines a standard for Token ring architecture
• Uses the 10 Base T cabling standard
• Uses twisted pair cabling to connect devices
  instead of coaxial cable
• Passes data from one computer to another like in
  a token bus network

9
IEEE 802.3 Logical relationship with OSI
Reference Model

• IEEE 802.3 physical layer corresponds to the OSI
  physical layer
• OSI data link layer is divided into two IEEE 802
  sublayers
• The Media Access Control (MAC) sublayer
• The Logical Link Control (LLC) sublayer

10
Ethernet

• Defined by IEEE as the 802.3 standard
• Most widely adapted LAN technology
• Supports data transfer rates of 10 Mbps, 100 Mbps
  and 1 Gbps

11
Introduction to Ethernet

• Nodes on an Ethernet network are either DTE
  (computer, printer) or DCE (switch, router)
• Three data rates currently defined for the
  operation over optical fiber and twisted-pair
  cables
• 10 Mbps 10Base-T Ethernet
• 100 Mbps - Fast Ethernet
• 1000 Mbps - Gigabit Ethernet

12
Working of Ethernet

• Ethernet frame is used to transfer data over a
  network
• Each device in an Ethernet network is uniquely
  identified by a 48 bit (6 bytes) address called
  Ethernet address
• Ethernet addresses are represented as six pairs
  of hexadecimal digits separated by a colon.

13
Elements of Ethernet System
14
Ethernet Medium

• Transmits information over the network
• Computer D transmits information for Printer C
• Computer B and A also receives the information
• All devices inspect the destination address
• If the received frame is not meant for them, they
  will reject the frame

15

• Next Data Transmission continue through CBT up to
  types of Ethernet

16
Data Transmission

• When a computer wants to transmit, it listens to
  the cable (transmission medium)
• If two or more devices simultaneously transmit
  data on an idle cable, collision may occur

17
Example of Collision

• Each device decides to broadcast an Ethernet
  frame to other device
• Devices listens to the Ethernet medium and
  detects that no carrier is present
• Devices transmit simultaneously, causing a
  collision

18
Carrier Sense Multiple Access/ Collision
Detection (CSMA/CD)

• Permits one device to access to the network media
  at a time to avoid collision
• Networks using CSMA/CD technology such as
  Ethernet, network devices compete for the network
  media

19
Working of CSMA/CD
20
Carrier Sensing Multiple Access / Collision
Avoidance (CSMA/CA)

• Set of rules that can avoid collisions, unlike
  CSMA/CD that handles network transmissions once
  collisions are detected
• In CSMA/CA, all devices are forced to wait for a
  random number of time slots and sense the medium
  again
• If the medium is sensed to be busy, the device
  stops the timer until it becomes free again.

21
Types of Ethernet
22
10Base-5

• Thick coaxial cable is also referred to as
  thicknet
• 10Base5 refers to specifications of thick coaxial
  cable carrying Ethernet signals
• The 5 refers to the maximum segment length i.e.
  500 meters
• RG-8 coaxial cable is used
• A 15-pin female DB connector called AUI connector
  is used to connect the device

23
10Base-2

• 10Base-2 (thin coaxial cable) is also referred to
  as thinnet
• In 10Base-2, 2 refers to approximate maximum
  segment length of the cable which is 185 meters
• 10Base2 uses RG-58 coaxial cable with BNC
  connectors
• Cheaper and easier to install as compared to 10
  Base 5 and 10 Base F

24
10Base-T

• Allows stations to be attached via twisted pair
  cable
• 10 refers to the transmission speed of 10 Mbps
• T refers to twisted pair cable
• In a 10BaseT network, each computer (node) is
  connected to a hub

25
10 Base-F

• Uses fiber optic cable
• Possesses excellent noise immunity and is the
  method of choice when running between buildings
  or widely separated hubs
• 10 Base-F is expensive as the connectors and
  terminators used in 10 Base-F are costly

26
Comparing Ethernet Types
Ethernet types 10Base5 10Base2 10BaseT 10BaseF
Media Type Thick coaxial (RG8) Thin coaxial (RG58) UTP Fiber-optic
Max.segment length (meters) 500 185 100 1000
Frequency(MHZ) 10 10 10 10
Max Nodes/Segment 100 30 1024 1024k
27
Extending the network

• A computer network can be extended using
  repeaters, hubs and bridges
• In computer networks, a bridge is an
  Internetworking device
• Repeater regenerates signal
• Repeaters remove the unwanted noise in an
  incoming signal
• A hub is a multi port repeater which provides a
  common point for the connection of network
  devices

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Summary - I

• Ethernet is a local-area network (LAN) structural
  design developed by DEC, Intel and Xerox
  Corporation.
• Ethernet is a very common and widely used method
  of networking computers in a LAN environment.
• All nodes on an Ethernet network are either Data
  Terminal Equipment (DTE) or Data Communications
  Equipment (DCE).

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Summary - II

• Protocols are set of rules that the nodes on a
  network use to communicate with each other
• Carrier Sense Multiple Access/Collision Detection
  (CSMA/CD) is a network control protocol which
  uses a carrier sensing system
• Carrier Sense Multiple Access/Collision Avoidance
  (CSMA/CA) is a set of rules used to avoid
  collisions.
• 10 Base-2, 10 Base-5, 10 Base-T, and 10 Base-F
  are different types of cabling for Ethernet

30
Summary - III

• A repeater is a device that is used on a link to
  regenerate the signal to extend the physical
  length of a network.
• Bridges are usually used to divide a busy network
  into separate segments and to connect multiple
  LANs.
• Hub is a Repeater with multiple ports and
  operates at the physical layer.