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
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.
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.
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
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
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
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
33.
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
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
