1. IEEE 802.X Standards
• The Institute of Electrical and Electronics Engineers
(IEEE) has developed a series of networking standards
to ensure that networking technologies developed by
manufacturers are compatible.
• These standards describe the cabling, physical
topology, electrical topology and access schemes of
network products.
• These standards describe the protocols used in the
lower two layers of the OSI model:
1. Physical layer
2. Data link layer.
They don’t go above those layers.
2. • The committee structure of the IEEE is
numbered like the decimal system.
• The general committee working on these
standards is 802.
• Various subcommittees, designed by decimal
numbers, have worked on different version of
the standards.
3. IEEE 802.5
• The IEEE 802.5 standard specifies the
characteristics for Token Ring networks.
• Token Ring was introduced by IBM in the mid-
1980s.
4. What is token ring LAN?
• Token ring LAN technology is a local area network
protocol which resides at the data link layer (DLL) of
the OSI model.
• Stations on a token ring LAN are logically organized in a
ring topology with data being transmitted sequentially
from one ring station to the next with a token travelling
around the ring.
• This standard describes a token passing protocol which
means that a machine can only use the network when
it has control of the “token”
• This ensures that there are no collisions because only
one machine can use the network at any given time.
5. • Token ring protocol uses a special three-byte
frame called a token that travels around the
ring.
• Token ring frames travel completely around
the loop.
• Stations that have data frames to transmit
must first acquire the token before they can
transmit data frames.
6. • When no station is transmitting a data frame, a
token frame circles the loop.
• This token frame is repeated from station to
station until arriving at a station that needs to
transmit data.
• When a station needs to transmit data, it first has
to capture the free Token and replace the data
with its own message.
• Once the sending station receives its data frame,
it converts the frame back into a token.
• On 4 Mbit/s Token Ring, only one token may
circulate; on 16 Mbit/s Token Ring, there may be
multiple tokens.
7. Operation of Token Ring
• At the start, a free Token is circulating on the
ring.
• If machine 1 wants to send some data to
machine 4, so it first has to capture the free
Token.
• It then writes its data and the recipient's
address onto the Token (represented by the
yellow flashing screen).
8. • The packet of data is then sent to machine 2 who
reads the address, realizes it is not its own, so
passes it on to machine 3.
• Machine 3 does the same and passes the Token
on to machine 4.
• This time it is the correct address and so number
4 reads the message (represented by the yellow
flashing screen).
• Machine 4 cannot, however, release a free Token
on to the ring, it must first send the message back
to number 1 with an acknowledgement to say
that it has received the data (represented by the
purple flashing screen).
9. • The receipt is then sent to machine 5 who
checks the address, realizes that it is not its
own and so forwards it on to the next
machine in the ring, number 6.
• Machine 6 does the same and forwards the
data to number 1, who sent the original
message.
• Machine 1 recognizes the address, reads the
acknowledgement from number 4
(represented by the purple flashing screen)
and then releases the free Token back on to
the ring ready for the next machine to use.
10. • That's the basics of Token Ring and it shows
how data is sent, received and acknowledged.
11. • The following is a list of the specific characteristics
specified in the 802.5 standard:
• Speed: The 802.5 Token Ring specifies network speeds
of 4 and 16Mbps.
• Topology: Token Ring networks use a logical ring
topology and most often a physical star.
• Media: Token Ring networks use unshielded twisted
pair cabling or shielded twisted pair.
• Access method: 802.5 specify an access method
known as token passing.. The token travels around the
network looking for computers with data to send. The
computer's data is passed along with the token until it
gets to the destination computer at which point, the
data is removed from the token and the empty token
placed back on the ring.
12. 802.3 IEEE Standard
• The IEEE 802.3 standard defines the characteristics for
Ethernet networks.
• The Ethernet specification served as the basis for the
IEEE 802.3 standard
• What is an Ethernet?
• A LAN architecture or telecommunications networking
protocol introduced by Xerox Corp. in 1979.
• It was developed as an inexpensive way of sending
information quickly between offices machines
connected together in a single room or building.
• The original data rate of 10 megabits per second has
been increased to 100 megabits per second for a new
standard known as fast Ethernet.
13. • Ethernet uses a bus or star topology and
supports data transfer rates of 10 Mbps.
14. The features for 802.3 are listed here:
• Speed: The original IEEE 802.3 standard specified
a network transfer rate of 10Mbps.
• There have been modifications to the standard,
the result being Fast Ethernet (802.3u), which can
transmit network data up to 100Mbps and higher,
as well as Gigabit Ethernet (802.3z), which can
transmit at speeds up to 1000Mbps.
• 802.3ae is a very fast 803.3 standard. Known as
10-Gigabit Ethernet.
15. Topology:
• The original Ethernet networks used a bus or
star topology because the original 802.3
standard included specifications for both
twisted pair and coaxial cabling.
16. Media
• The media refers to the physical cabling used
to transmit the signal around the network.
• The original 802.3 specifications identified
coaxial and twisted pair cabling to be used.
• The more modern standards specify twisted
pair and fiber-optic cable.
• 802.3ae currently only supports fiber media.
17. Access method
• The access method refers to the way that the
network media is accessed.
• Ethernet networks use a system called Carrier
Sense Multiple Access with Collision
Detection (CSMA/CD).
• The CSMA/CD method is internationally
standardized in IEEE 802.3
• CSMA/CD works by monitoring the computers
that are sending data on the network.
18. • If two computers transmit data at the same
time, a data collision will occur.
• To prevent collisions, the systems sending the
data will be required to wait a period of time
and then retransmit the data to avoid the
collision.
19. • Carrier Sense Multiple Access / Collision
Detection, a set of rules determining how
network devices respond when two devices
attempt to use a data channel simultaneously
(called a collision).
• CSMA/CD is a type of contention protocol i.e.
how to handle competition of resources.
• The term contention is used especially in
networks to describe the situation where two
or more nodes attempt to transmit a message
across the same wire at the same time.
