Ethernet is a family of local area network (LAN) protocols that was first developed in 1976. It uses bus or star topologies and supports data transfer rates of 10/100/1000 Mbps. Fast Ethernet was developed to support higher speeds of 100 Mbps, while Gigabit Ethernet supports 1000 Mbps. Ethernet uses CSMA/CD to handle simultaneous transmission demands in half-duplex mode, while full-duplex mode allows simultaneous transmission in both directions. Token ring is another common LAN protocol that uses a token passing mechanism to control access instead of CSMA/CD.

1. BY
ABHIJEET KUMAR SHAH

2.  The term Ethernet refers to the family of local-
area network (LAN).
 A local-area network (LAN) protocol developed by Xerox
Corporation in cooperation with DEC and Intel in 1976.
 Ethernet uses a bus or star topology and supports data
transfer rates of 10/100/1000 Mbps.
 Ethernet defines the lower two layers of the OSI
Reference Model.

3.  The Ethernet specification served as the basis for the
IEEE 802.3 standard, which specifies the physical and
lower software layers.
 Ethernet uses the CSMA/CD access method to handle
simultaneous demands.
 Ethernet, like other local area networks, falls in a
middle ground between long-distance, low-speed
networks that carry data for hundreds or thousands of
kilometres, and specialized, very high speed
interconnections that are generally limited to tens of
meters.

7. FAST ETHERNET
 Fast Ethernet was designed to compete with LAN
protocols such as FDDI (Fiber Distributed Data
Interface) or Fiber Channel.
 IEEE created Fast Ethernet under the name 802.3u.
 Fast Ethernet is backward-compatible with Standard
Ethernet.
 It can transmit data 10 times faster at a rate of 100
Mbps.

11.  The need for higher data rate resulted in the design of the
Gigabit Ethernet (1000 Mbps).
 The IEEE committee calls the standard 802.3z.
 All configurations of gigabit Ethernet are point to point.
 Point-to-point, between two computers or one computer –
to –switch.
 It supports two different modes of operation: full duplex
mode and half duplex mode.
 Full duplex is used when computers are connected by a
switch.
 No collision is there and so CSMA/CD is not used.

12. (a) point to point between two computers
(b) (b) point to point between switch and computer

13.  Half duplex is used when computers are connected by
a hub.
 Collision in hub is possible and so CSMA/CD is
required.
 The 802.3z committee considered a radius of 25 meters
to be unacceptable and added two new features to
increase the radius-Carrier Extension and Frame
Bursting.
 Carrier Extension tells the hardware to add its own
padding bits after the normal frame to extend the
frame to 512 bytes.
 Frame Bursting allows a sender to transmit a
concatenated sequence of multiple frames in a single
transmission. If the total burst is less than 512
bytes, the hardware pads it again.

15.  The heart of the system is a switch containing a high
speed back-plane and room for typically 4 to 32 plug-
in cards, each containing one to eight connectors.
 When a station wants to transmit a frame, it outputs a
frame to switch.
 The plug-in card checks to see if the frame is for the
other station on the same card. If so, it is copied there
otherwise it is sent over high speed back-plane to
destination station’s card.

16.  All ports on the same card are wired together to form a
local on-card LAN.
 Collisions on this on-card LAN are detected and
handled using CSMA/CD protocol.
 One transmission per card is possible at any instant.
All the cards can transmit in parallel.
 With this design each card forms its own collision
domain.
 In other design, each input port is buffered, so
incoming frames are stored in the card’s on board
RAM.
 It allows all input ports to receive (and transmit) frame
at same time

18.  MAC begins the transmission sequence by transferring the
LLC information into the MAC frame buffer.
 The preamble and start-of-frame delimiter are inserted in
the PRE and SOF fields.
 The destination and source addresses are inserted into the
address fields.
 The LLC data bytes are counted, and the number of bytes is
inserted into the Length/Type field.
 The LLC data bytes are inserted into the Data field. If the
number of LLC data bytes is less than 46, a pad is added to
bring the Data field length up to 46.
 An FCS value is generated over the
DA, SA, Length/Type, and Data fields and is appended to
the end of the Data field.

19.  After the frame is assembled, actual frame
transmission will depend on MAC.
 There are two Media Access Control(MAC) protocols
defined for
 Ethernet:
Half-Duplex
Full-Duplex
 Half-Duplex is the traditional form of Ethernet that
uses the CSMA/CD protocol.
 Full-Duplex bypasses the CSMA/CD protocol
 Full-duplex mode allows two stations to
simultaneously exchange data over a point to point
link that provides independent transmit and receive
paths

20.  Refers to the transmission of data in just one direction
at a time.
 Half-Duplex Ethernet is the traditional form of
Ethernet that uses the CSMA/CD.
 The CSMA/CD access rules are summarized by the
protocol's acronym:
carrier sense
multiple access
collision detect
 Half duplex Ethernet assumes that all the "normal"
rules of Ethernet are in effect on the local network.

21.  The network is monitored for presence of a
transmitting station (carrier sense).
 After sending the jam sequence the transmitting
station waits a random period of time (called
“backoff”).
 If an active carrier is not detected then the station
immediately begins transmission of the frame.
 While the transmitting station is sending the frame, it
monitors the medium for a collision.

22.  If a collision is detected, the transmitting station stops
sending the frame data and sends a 32-bit "jam
sequence.
 If repeated collisions occur, then transmission is
repeated
- the random delay is increased with each attempt
 Once a station successfully transmits a frame, it clears
the collision counter it uses to increase the backoff
time after each repeated collision.

24.  Based on the IEEE 802.3x standard, “Full-Duplex”
MAC type bypasses the CSMA/CD protocol
 Full-duplex mode allows two stations to
simultaneously exchange data over a point to point
link
 The aggregate throughput of the link is effectively
doubled
 – A full-Duplex 100 Mb/s station provides 200 Mb/s of
bandwidth

25.  Full-Duplex operation is supported by:
 – 10-Base-T, 10Base-FL, 100Base-TX, 100Base-
FX, 100Base-
 T2, 1000Base-CX, 1000Base-SX, 1000Base-LS, and
1000Base-T.
 Full-Duplex operation is NOT supported by:
 – 10Base5, 10Base2, 10Base-FP, 10Base-FB, and 100Base-
T4.
 Full-Duplex operation is restricted to point to point
links connecting exactly two stations

26. Full Duplex Operation

27.  Full-duplex MACs must have separate frame buffers and
data paths to allow for simultaneous frame transmission
and reception.
 The destination address of the received frame is checked to
determine whether the frame is destined for that station
 If an address match is found
 the frame length is checked and the received FCS is compared to
the FCS that was generated during frame reception.
 If the frame length is okay and there is an FCS match, the frame
type is determined by the contents of the Length/Type field.
 The frame is then parsed and forwarded to the appropriate upper
layer.

28.  ISO data link layer is divided into two IEEE 802 sublayers
Media Access Control (MAC) sublayer
MAC-client sublayer.
 IEEE 802.3 physical layer same as ISO physical layer.
 The MAC-client sublayer may be
 Logical Link Control (LLC)
if the unit is a DTE
 Bridge entity, if the unit is a DCE
 Lan to LAN if
 Ethernet to etnernet
 Ethernet to token ring

29.  The Ethernet MAC Sublayer has two primary
responsibilities:
 Data encapsulation, including frame assembly before
transmission, and frame parsing/error detection during
and after reception
 Media access control, including initiation of frame
transmission and recovery from transmission failure

30.  Token ring local area network (LAN) technology is
a protocol which resides at the data link layer (DLL) of
the OSI model.
 It uses a special three-byte frame called a token that
travels around the ring.
 Token-possession grants the possessor permission to
transmit on the medium.
 Token ring frames travel completely around the loop.
 it was eventually standardized with protocol IEEE
802.5.
 Stations on a token ring LAN are logically organized in
a ring topology .

31.  In token ring , Data being transmitted sequentially
from one ring station to the next with a control token
circulating around the ring controlling access.
 Token passing mechanism is shared
by ARCNET, token bus, and FDDI ,and has theoretical
advantages over the stochastic CSMA/CD of Ethernet.
 A token ring network is wired as a star, with 'hubs' and
arms out to each station and the loop going out-and-
back through each.
 Cabling is generally "Type-1" shielded twisted
pair, with unique hermaphroditic
connectors, commonly referred to as IBM data
connectors in formal writing or colloquially as Boy
George connectors

32.  In 1985, token ring ran at 4 Mbit/s.
 In 1989 IBM introduced the first 16 Mbit/s token ring
products and the 802.5 standard was extended to
support this.
 In 1981, Apollo Computer introduced their proprietary
12 Mbit/s Apollo token ring (ATR).
 Proteon introduced their 10 Mbit/s ProNet-10 token
ring network in 1984.

33.  A data token ring frame is used by stations to
transmit media access control(MAC) management
frames or data frames from upper layer protocols and
applications.
 Token Ring support two basic frame types: tokens and
data/command frames.
 Tokens are 3 bytes in length and consist of a start
delimiter, an access control byte, and an end delimiter.
 Data/command frames vary in size, depending on the
size of the Information field

34. PDU from
SD AC SD AC FC DA SA LLC (IEEE CRC ED FS
802.2)
up to
8 8 8 8 8 48 48 32 8
18200x8 8 bits
bits bits bits bits bits bits bits bits bits
bits

35.  Starting Delimiter(SD) consists of a special bit pattern
denoting the beginning of the frame. The bits from
most significant to least significant are J,K,0,J,K,0,0,0. J
and K are code violations.
 Access Control(AC) this byte field consists of the
following bits from most significant to least significant
bit order: P,P,P,T,M,R,R,R. The P bits are priority bits, T
is the token bit which when set specifies that this is a
token frame, M is the monitor bit which is set by the
Active Monitor (AM) station when it sees this
frame, and R bits are reserved bits.

36.  Frame Control(FC) a one byte field that contains bits
describing the data portion of the frame contents
which indicates whether the frame contains data or
control information. In control frames, this byte
specifies the type of control information.
+ Bits 0–1 Bits 2–7
0 Frame type Control Bits
Frame type – 01 indicates LLC frame IEEE 802.2 (data)
and ignore control bits; 00 indicates MAC frame and
control bits indicate the type of MAC control frame

37.  Destination address (DA) a six byte field used to
specify the destination(s) physical address .
 Source address(SA) Contains physical address of
sending station . It is six byte field that is either the
local assigned address (LAA) or universally assigned
address (UAA) of the sending station adapter.
 Data a variable length field of 0 or more bytes, the
maximum allowable size depending on ring speed
containing MAC management data or upper layer
information.Maximum length of 4500 bytes.
 Frame Check Sequence a four byte field used to store
the calculation of a CRC for frame integrity verification
by the receiver.

38.  Ending Delimiter(ED) The counterpart to the starting
delimiter, this field marks the end of the frame and
consists of the following bits from most significant to
least significant: J,K,1,J,K,1,I,E. I is the intermediate
frame bit and E is the error bit.
 Frame Status(FS)a one byte field used as a primitive
acknowledgement scheme on whether the frame was
recognized and copied by its intended receiver.
A C 0 0 A C 0 0
1 bit 1 bit 1 bit 1 bit 1 bit 1 bit 1 bit 1 bit
A = 1, Address recognized C = 1, Frame copied

39.  TOKEN FRAME
Start Delimiter Access Control End Delimiter
8 bits 8 bits 8 bits
 Abort Frame
SD ED
8 bits 8 bits
Used to abort transmission by the sending station

40.  Empty information frames are continuously circulated
on the ring.
 When a computer has a message to send, it inserts a
token in an empty frame (this may consist of simply
changing a 0 to a 1 in the token bit part of the frame)
and inserts a message and a destination identifier in
the frame.
 The frame is then examined by each successive
workstation. The workstation that identifies itself to
be the destination for the message copies it from the
frame and changes the token back to 0.

41.  When the frame gets back to the originator, it sees that
the token has been changed to 0 and that the message
has been copied and received. It removes the message
from the frame.
 The frame continues to circulate as an "empty"
frame, ready to be taken by a workstation when it has a
message to send.

42. Thank
You