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1. Local Area Network Basics

2. 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

3. 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
Standard
Protocols
Ethernet Token Ring ARCnet

4. 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

5. LAN Architecture - II
• 802.4
– Defines a standard for Token Bus architecture
– Token bus is similar to token ring, but it uses
coaxial cables

6. 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

7. 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

8. 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

9. 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

10. 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.

11. Elements of Ethernet System
Elements of Ethernet
System
Set of Medium Access
Medium Ethernet frame
Control Rules

12. 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

13. 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

14. 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

15. 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

16. Working of CSMA/CD

17. 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.

18. Types of Ethernet
Cabling Standards
10Base5 10Base2 10Base-T 10Base-F

19. 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

20. 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

21. 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

22. 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

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

24. 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