Ethernet is a local area network protocol used in both bus and star topologies. It was developed in 1972 and standardized by IEEE as 802.3. Ethernet uses CSMA/CD access method and has evolved from 10 Mbps speeds using coaxial cable to today's Gigabit speeds using twisted pair or fiber optic cabling. The Ethernet frame contains destination and source addresses, data, and a frame check sequence for error detection.

1. ETHERNET
802.3

2. WHAT IS ETHERNET ?
Ethernet is a certain type of a
local area network (LAN) which
was developed in 1972 in the
renowned PARC-research facility
of Xerox in Palo Alto by Robert
Metcalfe. In the meantime the
companies Intel, DEC and Xerox
have specified a common
standard that has been
established in the IEEE-standard
802.3.
Ethernet: It is a LAN protocol that
is used in Bus and Star topologies
and implements CSMA/CD as the

3. HISTORY
1969 student Robert Metcalfe (founder of 3Com in
1979) develops a Host Interface Controller for
DARPA (Defense Advanced Research Projects
Agency) in the company DEC.
1970 the ALOHA-Net (multiple access protocol) is
developed and tested at the university of Hawaii
1972 the idea is picked up by the XEROX Palo Alto
Research Center (Metcalfe works there by then).
The project goal is: experimental Ethernet

4. HISTORY
1976 the results of the project are published. The
companies DEC, Intel and Xerox join in the
company DIX and complete Ethernet to the market entry
stage.
1980 Ethernet version 1.0 is passed.
1981 IEEE starts standardization efforts. The Ethernet
specification is accepted without major
modifications.
1982 Publication of Ethernet version 2.0
1985 worldwide recognition of the Ethernet standard as
ISO/DIS 8802/3

5. HISTORY
1986 Publication of the 10Base2- and
10BroadT standards
1987 Standardization of the 10BaseT
spezification
1991 Publication of the 10BaseF standard
1994 more than 10.000 suppliers support the
Ethernet globally
1995 Standardization of the 100 Mbit/s Ethernet
1997 Standardization efforts for the Gigabit
Ethernet and presentation of first
products prior to the completion of the
standard

6. ETHERNET TCP/IP
Ethernet-
Header
Ethernet-DATA FCS
IP-
Header
IP-DATA
IP-
frame
TCP-
Header
TCP-DATA
TCP-
frame
Ethernet-
frame
LAYER 7
Modbus etc.

7. ACCESS METHOD:
CSMA/CD
Station is ready to
send
check
“Ether”
Sending of data and
checking the “Ether”
Waiting according
to back-off
algorithm
Medium
occupied
Discovered
collision
medium
available
send
jam signal
No collision
New attempt

8. BACK-OFF ALGORITHM
If a collision has occurred, the stations try to send
again after a certain period of time.
After the first collision there a two different back-off
times available, from which one is chosen at random.
Transmission probability is 50%
After the second consecutive collision there are four
different back-off times available, from which one is
chosen at random.
The transmission probability now is 75%

9. DELAY DEPENDING ON THE
NETWORK LOAD
delay
20 % 40 %
30 %
10 % 50 % 60 % 70 % 80 %
Network load
low
high High
throughput
Beginning
problems
Overload

10. ETHERNET ADDRESS
Also called "MAC address"
Globally unique ID for each device
Burnt into ROM, cannot be modified
Six Bytes in which manufacturer, device model and serial
number are coded
Readable with many auxiliary tools e.g. WINIPCFG

11. ETHERNET FRAME
Preamb
le
SF
D
DA SA LE
N
FC
S
Pad
Data
7 1 6 6 2 >=46
4
Preamble DA SA Type FCS
Pad
Data
8 6 6 2 >=46
4
Ethernet II DIX Frame:
IEEE 802.3 Frame:
Frame formats.
(a) DIX Ethernet
(b) IEEE 802.3.

12. 802.3 MAC Frame

13. ETHERNET FRAME
Preamble
Trailer consisting of the bit sequence “0101010101...” serving the bit synchronization
of the receiver.
SFD (Start Frame Delimiter)
Start character consisting of the bit pattern “10101011” showing the recipient that the
actual information will follow now.
DA (Destination Address)
Evaluated by the recipient‘s address filter; only data frames destined for this recipient
will be passed on to the communication software.
SA (Source Address)
Sender‘s address
LEN (Length)
Indicates the length of the subsequent data field in Bytes according to IEEE 802.3.

14. ETHERNET FRAME
Data and Pad
The data field may contain 46 to 1500 user data bytes. Are there less than
46 bytes the Ethernet controller independently adds padding bytes, until
the total amount (data + pad) is 46. This miminum length is crucial for the
CSMA/CD procedure to work faultlessly. The data field can be used at will,
it only has to contain complete bytes.
FCS (Frame Check Sequence)
A check character. It is obtained by taking the rest of the division operation
from the formula representing the wide-spread cyclic- redundancy-check
procedure. This formula is applied to the bit sequence including the
address field through to the padding field. In case of en error the whole
frame is ignored, i.e. not passed on to the application program.

15. ETHERNET ADDRESS
WIN-NT: ipconfig /all

16. ETHERNET MEDIA

17. NAMING OF THE CABLE TYPES
Example: 10base5
 10 Transmission rate in Mbytes/s
 baseBase or Broadband (data is sent as digital signals through the media as a
single channel that uses the entire bandwidth)
 5 Segment length in 100 meters
UTP unshielded twisted pair
STP shielded twisted pair
S/STP screened shielded twisted pair

18. Ethernet evolution through four generations

19. •<data rate><Signaling method><Max segment length or cable type>

20. 10Base5 Implementation

21. Connection of stations to the medium using 10Base2

22. 10BaseT
• Uses twisted pair Cat3 cable
 Star-wire topology
• A hub functions as a repeater with additional functions
• Fewer cable problems, easier to troubleshoot than coax
• Cable length at most 100 meters

23. Figure: 10Base-T implementation

24. Figure: 10Base-F implementation

25. 13.4 FAST ETHERNET
100 Mbps transmission rate
same frame format, media access, and collision
detection rules as 10 Mbps Ethernet
can combine 10 Mbps Ethernet and Fast Ethernet
on same network using a switch
media: twisted pair (CAT 5) or fiber optic cable (no
coax)
Star-wire topology
 Similar to 10BASE-T
CAT 3
CAT 5

26. Figure 13.19 Fast Ethernet topology

27. Figure Full-duplex switched Ethernet

28. Figure Switched Ethernet

29. GIGABIT ETHERNET
 Speed 1Gpbs
 Minimum frame length is 512 bytes
 Operates in full/half duplex modes
mostly full duplex

30. IEEE 802.3 CABLE TYPES
Name Cable Max. Max Cable
Segment
Length
Nodes
/segment
10Base5 thick coax 500 meters 100
10Base2 thin coax 185 meters 30
10BaseT twisted pair 100 meters 1
10BaseF Fiber Optic 2Km 1
Toplogy
Bus
Bus
Star
Star

31. IEEE Standard for LANs

32. Ethernet address
 Six bytes = 48 bits
 Flat address not hierarchical
 Burned into the NIC ROM
 First three bytes from left specify the vendor. Cisco 00-00-0C, 3Com 02-60-8C and the
last 24 bit should be created uniquely by the company
 Destination Address can be:
 Unicast: second digit from left is even (one recipient)
 Multicast: Second digit from left is odd (group of stations to receive the frame –
conferencing applications)
 Broadcast (ALL ones) (all stations receive the frame)
 Source address is always Unicast

34. The least significant bit of the first byte
defines the type of address.
If the bit is 0, the address is unicast;
otherwise, it is multicast.
Note

35. The broadcast destination address is a
special case of the multicast address in
which all bits are 1s.
Note

36. Unicast and Multicast Address

37. Frame length:
Minimum: 64 bytes (512 bits)
Maximum: 1518 bytes (12,144 bits)
Note

38. ETHERNET TOPOLOGIES

39. Figure: Topologies of Gigabit Ethernet

40. REPEATER / HUB
Repeater
Hub

41. BRIDGE
Bridge
A
B
C
D
E F

42. SWITCH = MULTIPORT BRIDGE
Bridge
Switch

43. CHARACTERISTICS OF THE
SWITCHES
Cut-Trough Switch
 noc cheking of the data frames
Store-and-Forward
 checking of the data frames
Frames with same destination
 kept in internal short term memory thus queueing them
 discard them or create collision
Broadcast messages
 go to all stations anyway (z.B. ARP) so switches are of no advantage
here
 there are specific approaches of different switch manufacturers to
reduce broadcast data traffic

44. TYPICAL OFFICE WIRING
Hub/Switch
Hub/Switch
Patch
field
Patch
field Network socket
Patch cable
„normal“ Cat 5 cable
RJ 45