Short Notes: LAN Technologies (Ethernet) | Short Notes for Computer Science Engineering - Computer Science Engineering (CSE) PDF Download

 Page 1


Ethernet LANs consist of network nodes and interconnecting media. The network 
nodes fall into two major classes:
• Data terminal equipment (DTE): Devices that are either the source or the 
destination of data frames. DTEs are typically devices such as PCs, 
workstations, file servers, or print servers that,as a group, are all often 
referred to as end stations.
• Data communication equipment (DCE): Intermediate network devices that 
receive and forward frames across the network. DCEs may be either 
standalone devices such as repeaters, network switches, and routers, or 
communications interface units such as interface cards and modems.
Addressing: LAN data transmissions classified into one of three categories: 
Unicast, Multicast, and Broadcast.
• Unicast: Addressing is one-to-one, where one computer sends a frame to 
another computer. Even though many stations can receive the same data, they 
should ignore it since it is not addressed to them. With unicast transmissions, 
a single packet is sent from the source to a destination on a network. The 
source-node addresses the packet by using the network address of the 
destination node. The packet is then forwarded to the destination network and 
the network passes the packet to its final destination.
• Multicast: Addressing is one-to-many, where one computer is sending a frame 
to many other computers. This can be done via a list of addresses, or some 
masking scheme that selects a subset of addresses. With a multicast 
transmission, a single data packet is copied and forwarded to a specific
Page 2


Ethernet LANs consist of network nodes and interconnecting media. The network 
nodes fall into two major classes:
• Data terminal equipment (DTE): Devices that are either the source or the 
destination of data frames. DTEs are typically devices such as PCs, 
workstations, file servers, or print servers that,as a group, are all often 
referred to as end stations.
• Data communication equipment (DCE): Intermediate network devices that 
receive and forward frames across the network. DCEs may be either 
standalone devices such as repeaters, network switches, and routers, or 
communications interface units such as interface cards and modems.
Addressing: LAN data transmissions classified into one of three categories: 
Unicast, Multicast, and Broadcast.
• Unicast: Addressing is one-to-one, where one computer sends a frame to 
another computer. Even though many stations can receive the same data, they 
should ignore it since it is not addressed to them. With unicast transmissions, 
a single packet is sent from the source to a destination on a network. The 
source-node addresses the packet by using the network address of the 
destination node. The packet is then forwarded to the destination network and 
the network passes the packet to its final destination.
• Multicast: Addressing is one-to-many, where one computer is sending a frame 
to many other computers. This can be done via a list of addresses, or some 
masking scheme that selects a subset of addresses. With a multicast 
transmission, a single data packet is copied and forwarded to a specific
subset of nodes on the network. The source node addresses the packet by 
using a multicast address.
• Broadcast: Addressing is one-to-all, where one computer sends data to all 
computers connected to the LAN. Broadcasts are found in LAN environments. 
Broadcasts do not traverse a WAN unless the Layer 3 edge-routing device is 
configured with a helper address (or the like) to direct these broadcasts to a 
specified network address.
LAN Topologies: There are 4 types of LAN topologies are available, (i) Bus, (ii) Ring, 
(iii) Star, and (iv) Mesh. Bus: A bus topology consists of devices connected to a 
common, shared cable.
• Failure of the medium disrupts communication.
• Failure of devices doesn’t effect the communication (passive interface).
• There is a limit on the length of the network (devices don’t amplify/repeat the 
signal).
• The propagation delay isn’t effected by the number of devices.
• The original Ethernet networks were implemented with a coaxial bus 
structure.
• Segment lengths were limited to 500 meters with up to 100 stations 
connected to a single segment.
• Individual segments could be interconnected with repeaters, as long as 
multiple paths did not exist between any two stations on the network and the 
number of DTEs did not exceed 1024.
• Advantages of Bus:
° Use of cable is economical.
° Media is inexpensive and easy to work with.
° System is simple and reliable.
° Bus is easy to extend.
• Disadvantages of Bus:
° Network can slow down in heavy traffic.
° Problems are difficult to isolate.
° Cable break can affect many users.
Ring: Connecting computers to a cable that forms a loop is referred to as setting 
up a ring topology.
• Failure of the medium seriously disrupts communication.
• Malfunctioning of the interface can seriously effect communication (devices 
are active).
• There is no limitation on the length of the network (devices repeat/retransmit 
the frame).
• Advantages of Ring:
° System provides equal access for all computers.
° Performance is even despite many users.
• Disadvantages of Ring:
° Failure of one computer can impact the rest of the network.
° Problems are hard to isolate.
° Network reconfiguration disrupts operation.
Page 3


Ethernet LANs consist of network nodes and interconnecting media. The network 
nodes fall into two major classes:
• Data terminal equipment (DTE): Devices that are either the source or the 
destination of data frames. DTEs are typically devices such as PCs, 
workstations, file servers, or print servers that,as a group, are all often 
referred to as end stations.
• Data communication equipment (DCE): Intermediate network devices that 
receive and forward frames across the network. DCEs may be either 
standalone devices such as repeaters, network switches, and routers, or 
communications interface units such as interface cards and modems.
Addressing: LAN data transmissions classified into one of three categories: 
Unicast, Multicast, and Broadcast.
• Unicast: Addressing is one-to-one, where one computer sends a frame to 
another computer. Even though many stations can receive the same data, they 
should ignore it since it is not addressed to them. With unicast transmissions, 
a single packet is sent from the source to a destination on a network. The 
source-node addresses the packet by using the network address of the 
destination node. The packet is then forwarded to the destination network and 
the network passes the packet to its final destination.
• Multicast: Addressing is one-to-many, where one computer is sending a frame 
to many other computers. This can be done via a list of addresses, or some 
masking scheme that selects a subset of addresses. With a multicast 
transmission, a single data packet is copied and forwarded to a specific
subset of nodes on the network. The source node addresses the packet by 
using a multicast address.
• Broadcast: Addressing is one-to-all, where one computer sends data to all 
computers connected to the LAN. Broadcasts are found in LAN environments. 
Broadcasts do not traverse a WAN unless the Layer 3 edge-routing device is 
configured with a helper address (or the like) to direct these broadcasts to a 
specified network address.
LAN Topologies: There are 4 types of LAN topologies are available, (i) Bus, (ii) Ring, 
(iii) Star, and (iv) Mesh. Bus: A bus topology consists of devices connected to a 
common, shared cable.
• Failure of the medium disrupts communication.
• Failure of devices doesn’t effect the communication (passive interface).
• There is a limit on the length of the network (devices don’t amplify/repeat the 
signal).
• The propagation delay isn’t effected by the number of devices.
• The original Ethernet networks were implemented with a coaxial bus 
structure.
• Segment lengths were limited to 500 meters with up to 100 stations 
connected to a single segment.
• Individual segments could be interconnected with repeaters, as long as 
multiple paths did not exist between any two stations on the network and the 
number of DTEs did not exceed 1024.
• Advantages of Bus:
° Use of cable is economical.
° Media is inexpensive and easy to work with.
° System is simple and reliable.
° Bus is easy to extend.
• Disadvantages of Bus:
° Network can slow down in heavy traffic.
° Problems are difficult to isolate.
° Cable break can affect many users.
Ring: Connecting computers to a cable that forms a loop is referred to as setting 
up a ring topology.
• Failure of the medium seriously disrupts communication.
• Malfunctioning of the interface can seriously effect communication (devices 
are active).
• There is no limitation on the length of the network (devices repeat/retransmit 
the frame).
• Advantages of Ring:
° System provides equal access for all computers.
° Performance is even despite many users.
• Disadvantages of Ring:
° Failure of one computer can impact the rest of the network.
° Problems are hard to isolate.
° Network reconfiguration disrupts operation.
Star: Connecting computers to cable segments that branch out from a single point[ 
or hub, is referred to as setting up a star topology.
• Failure of the medium does not seriously disrupt communication.
• Malfunctioning of the station doesn’t seriously effect the communication.
• The network can use guided or unguided media.
• Failure of the hub disrupts the communication.
• The network can use any medium, like twisted pair, coax, or fiber
• The central network unit is either a multiport repeater (also known as a hub) 
or a network switch.
• All connections in a star network are point-to-point links implemented with 
either twisted-pair or optical fiber cable.
• Advantages of Star:
° Modifying system and adding new computers is easy.
° Centralized monitoring and management are possible.
• Disadvantages of Star:
° Failure of one computer does not affect the rest of the network.
° If the centralized point fails, the network fails.
Mesh: A mesh topology connects all computers in a network to each other with 
separate cables.
• Advantages of Mesh: System provides increased redundancy and reliability as 
well as ease of troubleshooting.
• Disadvantages of Mesh: System is expensive to install because it uses a lot 
of cabling.
LAN Technologies
• LAN Protocols function at the lowest two layers of the OSI reference model 
between the physical layer and the data link layer.
• The IEEE 802.3 standard defines Ethernet protocols for (Open Systems 
Interconnect) OSI's Media Access Control (MAC) sublayer and physical layer 
network characteristics.
• The IEEE 802.2 standard defines protocols for the Logical Link Control (LLC) 
sublayer.
• Media contention occurs when more than one network device has data to 
send at the same time. The following two methods are used to access the 
network media where multiple devices cannot talk on the network 
simultaneously.
° CSMA/CD : This network uses Ethernet technology.
° Token Passing : It uses Token Ring technology.
Carrier Sense Multiple Access with Collision Detect (CSMA/CD):
• The CSMA/CD method is internationally standardized in IEEE 802.3 and ISO 
8802.3
• CSMA/CD is a type of contention protocol.
• Standard Ethernet networks use CSMA/CD to physically monitor the traffic on 
the line at participating stations.
Page 4


Ethernet LANs consist of network nodes and interconnecting media. The network 
nodes fall into two major classes:
• Data terminal equipment (DTE): Devices that are either the source or the 
destination of data frames. DTEs are typically devices such as PCs, 
workstations, file servers, or print servers that,as a group, are all often 
referred to as end stations.
• Data communication equipment (DCE): Intermediate network devices that 
receive and forward frames across the network. DCEs may be either 
standalone devices such as repeaters, network switches, and routers, or 
communications interface units such as interface cards and modems.
Addressing: LAN data transmissions classified into one of three categories: 
Unicast, Multicast, and Broadcast.
• Unicast: Addressing is one-to-one, where one computer sends a frame to 
another computer. Even though many stations can receive the same data, they 
should ignore it since it is not addressed to them. With unicast transmissions, 
a single packet is sent from the source to a destination on a network. The 
source-node addresses the packet by using the network address of the 
destination node. The packet is then forwarded to the destination network and 
the network passes the packet to its final destination.
• Multicast: Addressing is one-to-many, where one computer is sending a frame 
to many other computers. This can be done via a list of addresses, or some 
masking scheme that selects a subset of addresses. With a multicast 
transmission, a single data packet is copied and forwarded to a specific
subset of nodes on the network. The source node addresses the packet by 
using a multicast address.
• Broadcast: Addressing is one-to-all, where one computer sends data to all 
computers connected to the LAN. Broadcasts are found in LAN environments. 
Broadcasts do not traverse a WAN unless the Layer 3 edge-routing device is 
configured with a helper address (or the like) to direct these broadcasts to a 
specified network address.
LAN Topologies: There are 4 types of LAN topologies are available, (i) Bus, (ii) Ring, 
(iii) Star, and (iv) Mesh. Bus: A bus topology consists of devices connected to a 
common, shared cable.
• Failure of the medium disrupts communication.
• Failure of devices doesn’t effect the communication (passive interface).
• There is a limit on the length of the network (devices don’t amplify/repeat the 
signal).
• The propagation delay isn’t effected by the number of devices.
• The original Ethernet networks were implemented with a coaxial bus 
structure.
• Segment lengths were limited to 500 meters with up to 100 stations 
connected to a single segment.
• Individual segments could be interconnected with repeaters, as long as 
multiple paths did not exist between any two stations on the network and the 
number of DTEs did not exceed 1024.
• Advantages of Bus:
° Use of cable is economical.
° Media is inexpensive and easy to work with.
° System is simple and reliable.
° Bus is easy to extend.
• Disadvantages of Bus:
° Network can slow down in heavy traffic.
° Problems are difficult to isolate.
° Cable break can affect many users.
Ring: Connecting computers to a cable that forms a loop is referred to as setting 
up a ring topology.
• Failure of the medium seriously disrupts communication.
• Malfunctioning of the interface can seriously effect communication (devices 
are active).
• There is no limitation on the length of the network (devices repeat/retransmit 
the frame).
• Advantages of Ring:
° System provides equal access for all computers.
° Performance is even despite many users.
• Disadvantages of Ring:
° Failure of one computer can impact the rest of the network.
° Problems are hard to isolate.
° Network reconfiguration disrupts operation.
Star: Connecting computers to cable segments that branch out from a single point[ 
or hub, is referred to as setting up a star topology.
• Failure of the medium does not seriously disrupt communication.
• Malfunctioning of the station doesn’t seriously effect the communication.
• The network can use guided or unguided media.
• Failure of the hub disrupts the communication.
• The network can use any medium, like twisted pair, coax, or fiber
• The central network unit is either a multiport repeater (also known as a hub) 
or a network switch.
• All connections in a star network are point-to-point links implemented with 
either twisted-pair or optical fiber cable.
• Advantages of Star:
° Modifying system and adding new computers is easy.
° Centralized monitoring and management are possible.
• Disadvantages of Star:
° Failure of one computer does not affect the rest of the network.
° If the centralized point fails, the network fails.
Mesh: A mesh topology connects all computers in a network to each other with 
separate cables.
• Advantages of Mesh: System provides increased redundancy and reliability as 
well as ease of troubleshooting.
• Disadvantages of Mesh: System is expensive to install because it uses a lot 
of cabling.
LAN Technologies
• LAN Protocols function at the lowest two layers of the OSI reference model 
between the physical layer and the data link layer.
• The IEEE 802.3 standard defines Ethernet protocols for (Open Systems 
Interconnect) OSI's Media Access Control (MAC) sublayer and physical layer 
network characteristics.
• The IEEE 802.2 standard defines protocols for the Logical Link Control (LLC) 
sublayer.
• Media contention occurs when more than one network device has data to 
send at the same time. The following two methods are used to access the 
network media where multiple devices cannot talk on the network 
simultaneously.
° CSMA/CD : This network uses Ethernet technology.
° Token Passing : It uses Token Ring technology.
Carrier Sense Multiple Access with Collision Detect (CSMA/CD):
• The CSMA/CD method is internationally standardized in IEEE 802.3 and ISO 
8802.3
• CSMA/CD is a type of contention protocol.
• Standard Ethernet networks use CSMA/CD to physically monitor the traffic on 
the line at participating stations.
• It is a set of rules determining how network devices respond when two 
devices attempt to use a data channel simultaneously (called a collision).
• If no transmission is taking place at the time, the particular station can 
transmit.
• If two stations attempt to transmit simultaneously, this causes a collision, 
which is detected by all participating stations.
° The stations that collided attempt to transmit again after a random time 
interval.
° If another collision occurs, the time intervals from which the random 
waiting time is selected are increased step by step. This is known as 
Binary exponential back off.
IEEE Standards
• IEEE 802.1: Standards related to network management.
• IEEE 802.2: Standard for the data link layer in the OSI Reference Model
• IEEE 802.3: Standard for the MAC layer for bus networks that use CSMA/CD. 
(Ethernet standard)
• IEEE 802.4: Standard for the MAC layer for bus networks that use a token­
passing mechanism (token bus networks).
• IEEE 802.5: Standard for the MAC layer for token-ring networks.
• IEEE 802.6: Standard for Metropolitan Area Networks (MANs).
Ethernet (IEEE 802.3):
• The term Ethernet refers to the family of local-area network (LAN) products 
covered by the IEEE 802.3 standard that defines what is commonly known as 
the CSMA/CD protocol.
• A standard for a 1-persistent CSMA/CD LAN.
• It operates at 10 Mbps using carrier sense multiple access collision detect 
(CSMA/CD) to run over coaxial cable.
• It covers the physical layer and MAC sublayer protocol.
• 3 Ethernet uses Manchester Phase Encoding (MPE) for coding the data bits 
on the outgoing signal.
• In Ethernet, both the data link and the physical layers are involved in the 
creation and transmission of frames.
• The physical layer is related to the type of LAN cabling and how the bits are 
transmitted and received on the cable.
• The hardware address, or MAC address is transmitted and stored in Ethernet 
network devices in Canonical format i.e. Least significant Bit (LSB) first called 
as little endian.
• The data link layer is divided into sublayers, the Logical Link Control (LLC) and 
the Media Access Control layers (MAC).
• The frames created by these layers contain several fields that are processed 
by Network Interface Cards (NICs) in the sending and receiving devices.
Three data rates are currently defined for operation over optical fiber and twisted­
pair cables:
• 10 Mbps -1 0Base-T Ethernet
• 100 Mbps - Fast Ethernet
Page 5


Ethernet LANs consist of network nodes and interconnecting media. The network 
nodes fall into two major classes:
• Data terminal equipment (DTE): Devices that are either the source or the 
destination of data frames. DTEs are typically devices such as PCs, 
workstations, file servers, or print servers that,as a group, are all often 
referred to as end stations.
• Data communication equipment (DCE): Intermediate network devices that 
receive and forward frames across the network. DCEs may be either 
standalone devices such as repeaters, network switches, and routers, or 
communications interface units such as interface cards and modems.
Addressing: LAN data transmissions classified into one of three categories: 
Unicast, Multicast, and Broadcast.
• Unicast: Addressing is one-to-one, where one computer sends a frame to 
another computer. Even though many stations can receive the same data, they 
should ignore it since it is not addressed to them. With unicast transmissions, 
a single packet is sent from the source to a destination on a network. The 
source-node addresses the packet by using the network address of the 
destination node. The packet is then forwarded to the destination network and 
the network passes the packet to its final destination.
• Multicast: Addressing is one-to-many, where one computer is sending a frame 
to many other computers. This can be done via a list of addresses, or some 
masking scheme that selects a subset of addresses. With a multicast 
transmission, a single data packet is copied and forwarded to a specific
subset of nodes on the network. The source node addresses the packet by 
using a multicast address.
• Broadcast: Addressing is one-to-all, where one computer sends data to all 
computers connected to the LAN. Broadcasts are found in LAN environments. 
Broadcasts do not traverse a WAN unless the Layer 3 edge-routing device is 
configured with a helper address (or the like) to direct these broadcasts to a 
specified network address.
LAN Topologies: There are 4 types of LAN topologies are available, (i) Bus, (ii) Ring, 
(iii) Star, and (iv) Mesh. Bus: A bus topology consists of devices connected to a 
common, shared cable.
• Failure of the medium disrupts communication.
• Failure of devices doesn’t effect the communication (passive interface).
• There is a limit on the length of the network (devices don’t amplify/repeat the 
signal).
• The propagation delay isn’t effected by the number of devices.
• The original Ethernet networks were implemented with a coaxial bus 
structure.
• Segment lengths were limited to 500 meters with up to 100 stations 
connected to a single segment.
• Individual segments could be interconnected with repeaters, as long as 
multiple paths did not exist between any two stations on the network and the 
number of DTEs did not exceed 1024.
• Advantages of Bus:
° Use of cable is economical.
° Media is inexpensive and easy to work with.
° System is simple and reliable.
° Bus is easy to extend.
• Disadvantages of Bus:
° Network can slow down in heavy traffic.
° Problems are difficult to isolate.
° Cable break can affect many users.
Ring: Connecting computers to a cable that forms a loop is referred to as setting 
up a ring topology.
• Failure of the medium seriously disrupts communication.
• Malfunctioning of the interface can seriously effect communication (devices 
are active).
• There is no limitation on the length of the network (devices repeat/retransmit 
the frame).
• Advantages of Ring:
° System provides equal access for all computers.
° Performance is even despite many users.
• Disadvantages of Ring:
° Failure of one computer can impact the rest of the network.
° Problems are hard to isolate.
° Network reconfiguration disrupts operation.
Star: Connecting computers to cable segments that branch out from a single point[ 
or hub, is referred to as setting up a star topology.
• Failure of the medium does not seriously disrupt communication.
• Malfunctioning of the station doesn’t seriously effect the communication.
• The network can use guided or unguided media.
• Failure of the hub disrupts the communication.
• The network can use any medium, like twisted pair, coax, or fiber
• The central network unit is either a multiport repeater (also known as a hub) 
or a network switch.
• All connections in a star network are point-to-point links implemented with 
either twisted-pair or optical fiber cable.
• Advantages of Star:
° Modifying system and adding new computers is easy.
° Centralized monitoring and management are possible.
• Disadvantages of Star:
° Failure of one computer does not affect the rest of the network.
° If the centralized point fails, the network fails.
Mesh: A mesh topology connects all computers in a network to each other with 
separate cables.
• Advantages of Mesh: System provides increased redundancy and reliability as 
well as ease of troubleshooting.
• Disadvantages of Mesh: System is expensive to install because it uses a lot 
of cabling.
LAN Technologies
• LAN Protocols function at the lowest two layers of the OSI reference model 
between the physical layer and the data link layer.
• The IEEE 802.3 standard defines Ethernet protocols for (Open Systems 
Interconnect) OSI's Media Access Control (MAC) sublayer and physical layer 
network characteristics.
• The IEEE 802.2 standard defines protocols for the Logical Link Control (LLC) 
sublayer.
• Media contention occurs when more than one network device has data to 
send at the same time. The following two methods are used to access the 
network media where multiple devices cannot talk on the network 
simultaneously.
° CSMA/CD : This network uses Ethernet technology.
° Token Passing : It uses Token Ring technology.
Carrier Sense Multiple Access with Collision Detect (CSMA/CD):
• The CSMA/CD method is internationally standardized in IEEE 802.3 and ISO 
8802.3
• CSMA/CD is a type of contention protocol.
• Standard Ethernet networks use CSMA/CD to physically monitor the traffic on 
the line at participating stations.
• It is a set of rules determining how network devices respond when two 
devices attempt to use a data channel simultaneously (called a collision).
• If no transmission is taking place at the time, the particular station can 
transmit.
• If two stations attempt to transmit simultaneously, this causes a collision, 
which is detected by all participating stations.
° The stations that collided attempt to transmit again after a random time 
interval.
° If another collision occurs, the time intervals from which the random 
waiting time is selected are increased step by step. This is known as 
Binary exponential back off.
IEEE Standards
• IEEE 802.1: Standards related to network management.
• IEEE 802.2: Standard for the data link layer in the OSI Reference Model
• IEEE 802.3: Standard for the MAC layer for bus networks that use CSMA/CD. 
(Ethernet standard)
• IEEE 802.4: Standard for the MAC layer for bus networks that use a token­
passing mechanism (token bus networks).
• IEEE 802.5: Standard for the MAC layer for token-ring networks.
• IEEE 802.6: Standard for Metropolitan Area Networks (MANs).
Ethernet (IEEE 802.3):
• The term Ethernet refers to the family of local-area network (LAN) products 
covered by the IEEE 802.3 standard that defines what is commonly known as 
the CSMA/CD protocol.
• A standard for a 1-persistent CSMA/CD LAN.
• It operates at 10 Mbps using carrier sense multiple access collision detect 
(CSMA/CD) to run over coaxial cable.
• It covers the physical layer and MAC sublayer protocol.
• 3 Ethernet uses Manchester Phase Encoding (MPE) for coding the data bits 
on the outgoing signal.
• In Ethernet, both the data link and the physical layers are involved in the 
creation and transmission of frames.
• The physical layer is related to the type of LAN cabling and how the bits are 
transmitted and received on the cable.
• The hardware address, or MAC address is transmitted and stored in Ethernet 
network devices in Canonical format i.e. Least significant Bit (LSB) first called 
as little endian.
• The data link layer is divided into sublayers, the Logical Link Control (LLC) and 
the Media Access Control layers (MAC).
• The frames created by these layers contain several fields that are processed 
by Network Interface Cards (NICs) in the sending and receiving devices.
Three data rates are currently defined for operation over optical fiber and twisted­
pair cables:
• 10 Mbps -1 0Base-T Ethernet
• 100 Mbps - Fast Ethernet
1000 Mbps - Gigabit Ethernet
Ethernet Specifications:
Characteristic Ethernet
Value
IEEE S02.3 Values
10Base5 10Base2 lOBaseT lOBaseF 10 Base -TX 100BaseT4
D ata rate (M bps) 10 10 10 10 10 100 100
Signaling m ethod B aseband B aseband B aseband B aseband B aseband B aseband B aseband
M axim um segm ent 
length (m )
500 500 185 100 2.000 100 100
M edia 50-ohm coax 
(thick)
50-ohm coax 
(thick)
50-ohm coax 
(thill)
U nshielded 
tw isted-pair cable
Fiber-optic Cat 5 UTP U nshielded 
tw isted-pair cable
N odes/segm ent 100 100 30 1024 1024
Topology Bus B us B us Star Point-to-
po int
B us B us
Advantages of Ethernet over other technologies:
• It is easy to understand, implement, manage, and maintain.
• It allows low-cost network implementations.
• It provides extensive topological flexibility for network installation.
• It guarantees successful interconnection and operation of standards- 
compliant products, regardless of manufacturer.
IEEE 802.3 Frame Format: Maximum 802.3 frame size is 1518 bytes and the 
minimum size is 64 bytes.
bytes 7 1 6 6 2
46 - 1500 4
Preamble Destination Source Length LLC Data Unit
Pad FCS
IEEE 802.3 Frame
• Preamble field: Establishes bit synchronization and transceiver conditions so 
that the PLS circuitry synchs in with the received frame timing.
• Start Frame Delimiter: Sequence 10101011 in a separate field..
• Destination address: Hardware address (MAC address) of the destination 
station (usually 48 bits i.e. 6 bytes).
• Source address: Hardware address of the source station (must be of the 
same length as the destination address, the 802.3 standard allows for 2 or 6 
byte addresses).
• Length: Specifies the length of the data segment, actually the number of LLC 
data bytes.
• Pad: Zeros added to the data field to 'Pad out' a short data field to 46 bytes.
• Data: Actual data which is allowed anywhere between 46 to 1500 bytes within 
one frame.
• FCS: Frame Check Sequence to detect errors that occur during transmission.
Propagation Delay: Time taken for a signal to travel from the transmitter to the 
receiver
• Speed of light is the fastest a signal will propagate 
o 3 x io8 m/sec through space 
° 2 x io8 m/sec through copper