ETHERNET

 In 1985, the computer society of IEEE started a project

called project 802. to set standards to enable
intercommunication among equipment from variety of
manufactures.
 IEEE has subdivided the data link layer into 2 sub
layer
Logical Link control(LLC)

 Media Access control(MAC)
• Logical Link Control(LLC):
In project IEEE 802, flow control, error control and part of framing duties are
collected in to one sub layer called LLC.
Media Access Control(MAC): It define specific access method for each
LAN.
GENERATION OF ETHERNET(TYPES)
 Ethernet gone through 4 generation:
 Standard Ethernet(10Mbps)
 Fast Ethernet(100Mbps)
 Gigabit Ethernet(1Gbps)
 Ten gigabit Ethernet(10Gbps)

Standard Ethernet Frame Format:

 Preamble- Alert Receiver.
 SFD(start frame Delimiter) :used for synchronize the
data transmission and receiver. Used to signal as
beginning of frame.
 CRC- Error Detection.

1.Ethernet implementation:
1.10Base 5- the name derived from size of cable. It is also
known as thick net or thick Ethernet. A segment of the
original 10Base5 cable can be up to 500m long.
2.10Base 2- It also known as thin-net, cheapnet, cheapernet,
thinwire Ethernet or thin Ethernet. In this “10” means the
network operates at 10 Mbps, “Base” refers to the fact that the
cable is used in a base band system and the “2” means that a
given segment can be no longer than 200m
3.10 Base T- It is also known as twisted pair Ethernet.
The “T” stands for twisted pair. A 10BaseT
segment is usually limited to less than 100m in
length.
4.10 Base F- It uses star topology to connect station to
a hub. The stations are connected to hub by fiber
optic cables.
2.Fast Ethernet(100Mbps):
The fast Ethernet was designed to compute with Lan
protocol such as FDDI or fiber channel.
 Auto Negotiation: It is a new feature added to fast Ethernet.
It allow stations or a hub to negotiate the mode or data rate
of operation.
 To allow station to check hub’s capability.
 It is implemented as – 100Base Tx, 100 Base Fx
3.Giga bit Ethernet(1Gbps): the need for an even
higher data rate resulted in the design of gigabit
Ethernet protocol(1000Mbps).
Goals: Upgraded data rate, Make compatible with
Standard and fast Ethernet, use same frame format,
Auto negotiation.
Implementation:
1000Base Sx- 1000Mbps speed with Short wire
1000Base Lx- 1000Mbps speed with Long wire
1000Base Cx- 1000Mbps speed with thick copper
1000Base T- 1000Mbps speed with twisted pair
cable
4.Ten Gigabit Ethernet(10Gbps): in metro Politian
area(MAN), to extend technology,
with the goal of- upgrade data rate to 10Gbps.
Make compatible with standard, fast, gigabit.
Use same frame format.
RINGS(IEEE 802.5)
 Ring network is like Ethernet a shared media networks.
Like Ethernet, IBM’s Token Ring has a nearly identical
IEEE standard, known as 802.5.
 As the name suggests, a ring network consists
of a set of nodes connected in a ring .
 Data always flows in a particular direction around the
ring, with each node receiving frames from its upstream
neighbor and then forwarding them to its downstream
neighbor.
A ring is viewed as a single shared medium.
Node D

Cabling
Node C Node A

Node B
 The most common early forms of ring network were all
token rings. The word “token” comes from the way
access to the shared ring is managed.
 The idea is that a token, which is really just a special
sequence of bits, circulates around the ring; each node
receives and then forwards the token.

 The problem of node failure may be addressed by

connecting each station into using electromechanical
Relays
 MSAU( multiple station Access point) it uses packet of
switch in single box. It look like star topology.
TOKEN RING ACCESS CONTROL:
 The network adaptor for a token ring contains a
receiver and a transmitter.
 Most of the time, when a node is neither the source nor
the destination of the data on the ring, its adaptor is
simply retransmitting the data that its receiver
receives.
 Token ring holding Time(THT): It is the time how
long a given node is allowed to hold the token.
Token Ring Maintenance:
 Each IEEE 802.5 token ring has one station designated
as a monitor. The monitor’s job is to ensure the health of
the ring by, for example, making sure that the token is
not lost.
 One responsibility of the monitor is to make sure that
there is always a token some where in the ring, either
circulating or currently held by a station.
 To detect missing token, the monitor watch passing
token and maintain a timer equal to maximum possible
token time.
Interval Delay= NumStations ×THT+ Ring Latency
Where,
Ring Latency- It is total propagation delay of ring
Token Ring Frame Format:
FDDI(FIBER DISTRIBUTED DATA INTERFACE)
 Although FDDI is similar to IEEE 802.5 in many
respects, there are significant differences.
 For one, FDDI runs on fiber, not copper (although a
later standard, CDDI, was defined to allow copper links
to be used).
Working:
FDDI network consists of a dual ring—two independent
rings that transmit data in opposite directions. The
second ring is not used during normal operation but
instead comes into play only if the primary ring fails.
 Each node maintains an estimate of the token
rotation time (TRT)—the expected maximum time for
the token to make one complete trip around the ring.
FDDI RING
FDDI OPERATION
 FDDI operates exactly like token ring, with one
difference. Token ring employs a single wire through
all the hosts in the network.
 In FDDI if a problem occurs on the primary ring, the
secondary can be activated to form a complete data
circuit and maintain service.
 SWITCHED NETWORKS
 A network is a set of connected devices, when we have
multiple devices we have problem in connection. One
solution is to make point to point connection by using
topology.
 Eg- Our cell phone is not directly connected to every
person. But instead it connected to an exchange that
connect switches, which create connection.
 A switch is a multipoint, multi output devices that
transfer packets.
 Switches are hardware and / or software
devices capable of creating temporary
connections between two or more devices
linked to the switch but not to each other.
 There are three methods in switching are,

1. circuit switching
2. packet switching
3. message switching
CIRCUIT SWITCHING(DATAGRAM
NETWORK)
 A circuit Switch consist of switches connected by
physical links in which each link is divided into n-
channels.
 There are three phases in circuit switching:
 Establish
 Transfer
 Disconnect

 The telephone message is sent in one go, it is not

broken up. The message arrives in the same order
that it was originally sent.
Node A circuit
with B

Node B End
system
 PACKET SWITCHING
 In packet-based Switching networks, the message
gets broken into small data packets.
 These packets are sent out from the computer and
they travel around the network seeking out the
most efficient route to travel as circuits become
available.
 This does not necessarily mean that they seek out
the shortest route.
• Used in the Internet
• Data is sent in Packets (header contains
control information e.g., source and
destination addresses)

Header Data
 In the datagram approach to packet switching, each
packet is treated independently from all there. Even
when one packet represents just a piece of a multi
packet transmission, the networks treats it as though
it existed alone. Packets in this technology are
referred to datagram.
 The datagram approach can be used to deliver four
packets from station A to station X. In this example,
all four packets belong to same message but may go by
different paths to reach their destination.
VIRTUAL CIRCUIT NETWORK
 A virtual Circuit network is a cross between a
circuit and datagram(packet) switch.
 Two stages of process
 Connection setup
 Data transfer.
VIRTUAL
CIRCUIT
DIAGRAM

21
MESSAGE SWITCHING
 Message switching is best known by the
descriptive term store and forward. In this
mechanism, a node receives a message,
stores it until the appropriate route is free,
then sends it along.
 Store & forward is considered a switching
technique because there is no direct link between
the sender and receiver of a transmission. A
message is delivered to the node along one path
then rerouted along another to its destination.
 In message switching, the messages are stored &
relayed from secondary storage (disk), while in
packet switching the packets are stored and
forwarded from primary storage (RAM).
 CONNECTING DEVICES:
 To connect LAN we use connecting devices. Connecting
devices can operate in different layer of internet model.
 Connecting device are classified into 5 categories based
on layer they operate.

HUB
 HUB
 A hub is a device that operates only in physical layer.
 It connect the wires which comes from different
branches. Eg- In star topology Ethernet LAN.
 HUB is actually a multi port REPEATER.

REPEATERS:
 A repeater is a device that operate only in physical
layer. It connect segment of LAN.
 BRIDGES
 Itoperate in both physical and data link
layer.
 In physical layer device regenerate signal it
receives.
 In Data link layer act as switch and check
source and designation addresses in the
frames.
TYPES OF BRIDGES:
1.Transparent Bridge.
2.Source Routing Bridges.
TRANSPARENT BRIDGES
 Bridge in which station are completely un aware of the
bridges existence. If bridge is added or deleted from
system reconfiguration of station is unnecessary.
 Transparent Bridge must meet 3 criteria.

 Frames must forward from one station to another.

(forwarding)
 The forwarding table is automatically made learning
frame movement in network.(learning)
 Loops in the system must prevented.

 Hence This bridge is called as LEARNING BRIDGE

 Whenever bridge receive a frame on port1 that is
addressed to host A. It should not forward the
frame out to Port2.
 Anytime a frame addressed to host A was
received on port 2, the bridge would forward the
frame out on port 1.

Forwarding table
maintained by a bridge
SOURCE ROUTING BRIDGES
 Another way to prevent loops in a system with
redundant bridges is to use source routing bridges.
 In source routing bridge a sending station defines the
bridge that the frame must visit. The address of these
bridge are included in the frame.

 To solve looping problem IEEE specification reuires that

bridges use spanning tree algorithm to create loopless
topology.
SPANNING TREE ALGORITHM
 The bridges have to exchange configuration messages
with each other and then decide whether or not they are
the root or a designated bridge based on this message.
The configuration contains three pieces of information.
1. The ID for the bridge that is sending the message
2. The ID for what the sending bridge believes to be
the root bridge
3. The distance, measured in hops, from the sending
bridge to the root bridge.
The algorithm selects as follows. Each bridge has
a unique identifier. In the above example they
are labeled as B1, B2, B3 … the algorithm first
elects the bridge with smallest ID as the root of
the spanning tree.
 The root bridge always forwards frames out over all of
its ports. Then each bridge computes the shortest path
to root and notes which of its ports is on this path.
 This port is also elected as the bridge's preferred path
to the root. Finally, all the bridges connected to a given
LAN elect a single designated bridge that will be
responsible for forwarding frames toward the root
bridge.
WIRELESS LAN
 Wireless communication is one of the fastest growing
technology.
 IEEE has defined a specification for wireless LAN
called IEEE 802.11
Some most used wireless network are,
1.Wireless LAN(IEEE 802.11)
2.Bluetooth (IEEE 802.15)
3.Wifi( IEEE 802.11)
4.WiMax(IEEE 802.16)
WIRELESS LAN(IEEE 802.11)
 IEEE has defined the specification for a wireless LAN called
802.11 which cover the physical and data link layers. It
sometimes called as wireless ETHERNET.
ARCHITECTURE:
The standard define two kind of services.
1)BSS(Basic Service Set)
2)ESS(Extended Service Set)
1)BSS(Basic Service Set):
IEEE defines BSS as the building block of wireless LAN.
A BSS is made up of stationary or mobile wireless station and
an optional central base station known as Access point(AP).
BSS without AP is stand alone network and called as AdHoc
network
BSS with AP is called Infrastructure BSS
2)ESS(Extended Service Set):
It is made up of 2 or more BSS with AP. In this case BSS
connected to Distributed system which is a wired LAN

Complication in wireless LAN:

The complication in wireless LAN is referred as Collusion
Avoidance, which is referred as 1.Hidden Station problem
2. Exposed Station problem.
HIDDEN STATION PROBLEM
 Consider the situation where A and C are both within range of B but
not each other.
 Suppose both A and C want to communicate with B and so they each
send it a frame. A and C are unaware of each other since their signals
do not carry that far.
 These two frames collide with each other at B, but unlike an
Ethernet, neither A or C is aware of this collision. A and C are said to
be hidden nodes with respect to each other.

 By using RTS, CTS handshaking signals the hidden station problem

is avoided. sender transmits a Request to send (RTS) frame to the
receiver; the RTS frame includes a field that indicates how long the
sender wants to hold the medium. The receiver then replies with a
clear to send (CTS) frame.
2. EXPOSED STATION PROBLEM
 Station A is transmitting to Station B. Also C has
some data to D. which can be send with out
interfering the transmission A to B.
 C is exposed to Transmission A to B.

This can be avoided using handshaking signals. In

following time diagram.
2.BLUETOOTH (IEEE 802.15)
 Blue tooth is wireless LAN technology designed to
connect devices of different function as telephone,
notebook, computer etc.
 A Bluetooth is AdHoc network i.e., network formed
spontaneously. The device called gadgets find other and
make a network called PICONET.
 IEEE 802.15 standard defined protocol for blue tooth
called PAN(personal area network) operate in small
area.
Architecture:
1.PICONET
2.SCATTERNET.
PICONET
 A Bluetooth network is called as piconet or small
net. It has up to 8 station, one of which is primary
and rest is secondary.
 all the secondary are synchronize with primary.
(similar to master and slave)
SCATTERNET
 Piconet combine to form Scatternet.
 A secondary station is one piconet can be primary to
another piconet.
 This station can receive in first piconet(as a secondary)
and deliver them to secondary in second piconet.