2. 2
Ethernet is a family of computer networking
technologies commonly used in local area networks,
metropolitan area networks and wide area networks. It
was commercially introduced in 1980 and first
standardized in 1983 as IEEE 802.3, and has since been
refined to support higher bit rates and longer link
distances.
4. 4
Specified in the family of standards known as IEEE 802.3,
Ethernet was originally developed by Xerox in the 1970s.
Ethernet was initially designed to run over coaxial cables, but a
typical Ethernet LAN now uses special grades of twisted
pair cables, or fiber optical cabling. Wi-Fi standards (IEEE
802.11a, b, g, n and now ac) define the equivalent of Ethernet
for Wireless LANs.) Ethernet standards are steadily evolving to
embrace new media, higher transmission speeds and changes in
frame content (e.g., 802.3ac to accommodate VLAN and priority
tagging) and functional requirements (e.g., 802.3af,
defining Power Over Ethernet [POE]crucial to most Wi-Fi and IP
telephony deployments)
5. 5
The data link layer is used for the encoding, decoding and
logical organization of data bits. Data packets are framed
and addressed by this layer, which has two sublayers.
The data link layer's first sublayer is the media access
control (MAC) layer. It is used for source and destination
addresses. The MAC layer allows the data link layer to
provide the best data transmission vehicle and manage
data flow control.
The data link layer's second sublayer is the logical link
control. It manages error checking and data flow over a
network
7. 7
The Logical Link Control (LLC) layer is one of two sublayers
of the Data-Link layer in the Open Systems Interconnection
(OSI) model of communication. The LLC layer is concerned
with managing traffic (flow and error control) over the
physical medium. The LLC layer also identifies a line
protocol, such as SDLC, NetBIOS, or NetWare, and may also
assign sequence numbers to frames and track
acknowledgements.
The other Data-Link sublayer is the Media Access Control
layer
8. 8
MAC, Media Access Control, address is a globally unique identifier
assigned to network devices, and therefore it is often referred to as
hardware or physical address. MAC addresses are 6-byte (48-bits) in
length, and are written in MM:MM:MM:SS:SS:SS format. The first 3-bytes
are ID number of the manufacturer, which is assigned by an Internet
standards body. The second 3-bytes are serial number assigned by the
manufacturer.
MAC layer represents layer 2 of the TCP/IP (adopted from OSI Reference
Model), where IP represents layer 3. MAC address can be thought of as
supporting hardware implementation whereas IP address supports
software implementation.
11. START FRAME DELIMITER(SFD):The second field (1byte:10101011)signals the
beginning of the frame . The SFD warns the station that this is the last chance for
synchronization . The last 2 bits is11 and alerts the receive that the next field is the
destination address.
DESTINATION ADDRESS(DA):The DA field is 6bytes and contain the physical
address
of the destination station to receive the packet
SOURCE ADDRESS: The SA field is also 6 bytes and contains the physical address
of
the sender of the packet.
LENGTH/TYPE : This field is defined as a type field or length field.Theoriginal
Ethernet
used this field as the type field to define the upper –layer protocol using the MAC
frame.
DATA : This field carries data encapsulated from the upper –layer protocols.It is a
minimum of 46 and a maximum of 1500 bytes.
CRC : The last filed contains error detection information,in this case a CRC-32.
12. 12
The physical layer is the first layer of the Open System Interconnection
Model (OSI Model). The physical layer deals with bit-level transmission
between different devices and supports electrical or mechanical interfaces
connecting to the physical medium for synchronized communication.
This layer plays with most of the network’s physical connections - wireless
transmission, cabling, cabling standards and types, connectors and types,
network interface cards, and more
The physical layer is aimed at consolidating the hardware requirements of
a network to enable the successful transmission of data
Network engineers can define different bit-transmission mechanisms for
the physical layer level, including the shapes and types of connectors,
cables, and frequencies for each physical medium.
15. 15
802 Standards. IEEE 802.2, 802.3, 802.5,
802.11
The Institute of Electrical and Electronics Engineers is a standards setting body. Each
of their standards is numbered and a subset of the number is the actual standard.
The 802 family of standards is ones developed for computer networking.
In this section, you will learn:
- What the 802.2, 802.3, 802.5, 802.11 standards encompass;
- Features, topology, and network cabling for each of these standars.
First, let's discuss 802. IEEE, or Institute of Electrical and Electronics Engineers, is a
standards setting body. They create standards for things like networking so products
can be compatible with one another. You may have heard of IEEE 802.11b - this is the
standard that IEEE has set (in this example, wireless-b networking).
In this section, we will look at several networking technologies: 802.2, 802.3, 802.5,
802.11, and FDDI. Each of these is just a standard set of technologies, each with its
own characteristics.
16. 16
802.2 Logical Link Control
The technical definition for 802.2 is "the standard for the
upper Data Link Layer sublayer also known as the Logical Link
Control layer. It is used with the 802.3, 802.4, and 802.5
standards (lower DL sublayers)."
802.2 "specifies the general interface between the network
layer (IP, IPX, etc) and the data link layer (Ethernet, Token
Ring, etc).
Commonly referred to as the LLC or Logical Link Control
specification. The LLC is the top sub-layer in the data-link
layer, OSI Layer 2. Interfaces withthe network Layer
17. 17
802.3 Ethernet
"Grandaddy" of the 802 specifications. Provides
asynchronous networking using "carrier sense, multiple
access with collision detect" (CSMA/CD) over coax,
twisted-pair copper, and fiber media. Current speeds
range from 10 Mbps to 10 Gbps.
18. 18
The original token-passing
standard for twisted-pair, shielded
copper cables. Supports copper
and fiber cabling from 4 Mbps to
100 Mbps. Often called "IBM
Token-Ring."
19. 19
Wireless LAN Media Access Control and Physical
Layer specification. 802.11a,b,g,etc. are amendments to
the original 802.11 standard. Products that implement
802.11 standards must pass tests and are referred to as
"Wi-Fi certified."
21. 21
The second implementation is called
10Base2,thin Ethernet , cheaper net .
The cable is thinner and more flexible.
The transceiver is a part of NIC , which is
installed inside the station.
The implementation is most cost effective than
10Base5as thin coaxial cable is less expensive
than thick coaxial cable and the tee connection
are much cheaper than taps.
22. 22
The name 10BASE5 is derived from several
characteristics of the physical medium. The
10 refers to its transmission speed of 10
Mbit/s. The BASE is short for baseband
signaling as opposed to broadband, and
the 5 stands for the maximum segment
length of 500 meters (1,600 ft.).
It was the first Ethernet specification to
use a bus topology with a external
transceiver connected via a tap to a thick
coaxial cable.
10Base5:Thick
Internet
23. 23
The third implementation is called 10Base-
T or Twisted Pair Ethernet.
It uses star topology and the station are
connected via two pairs of twisted
cable(one fro sending and one for
receiving)between the station and the hub.
The maximum length of the twisted cable
here is defined as 100m,to minimize the
effect of attenuation in the twisted cable.
26. 26
Although there are several types
of optical fiber 10Mbps Ethernet
, the most common is called
10Base-F.
10Base-F uses a star topology to
connect stations to a hub.
The stations are connected to a
hub using two-optic cables.
30. 30
The first step in the Ethernet evolution was the division of a
LAN by bridge. Bridges have two effects on an Ethernet LAN
1) Raising Bandwidth
2) Collision of domains
1)Raising Bandwidth
Unbridged Ethernet network, the total capacity (10Mbps)
is shared among all station with a frame to send; the stations
share the bandwidth of the network. If only one station has
frames to send, it benefits for the total capacity (10Mbps). But if
more than one station needs to use the network, the capacity is
shared.
33. 33
Separating collision domains
A collision domain is a network segment connected by
a shared medium or through repeaters where data packets
may collide with one another while being sent. ... A network
collision occurs when more than one device attempts to send a
packet on a network segment at the same time.
34. 34
An Ethernet LAN that uses switches to connect individual
hosts or segments.
In the case of individual hosts, the switch replaces the repeater
and effectively gives the device full 10 Mbps bandwidth to the
rest of the network. In the case of segments, the hub is
replaced with a switching hub.
In traditional Ethernets, in which all hosts compete for the
same bandwidth, are called shared Ethernets.
35. 35
Switched Ethernets are becoming very popular because they
are an effective and convenient way to extend the bandwidth
of existing Ethernets.
The figure of switch Ethernet is as below.
36. 36
One of the limitations of 10Base5 and 10Base2 is that
communicati9on is half-duplex(10Base-T is always full-duplex).
A station can either send or receive, but may not do both.
Full-duplex switched Ethernet mode increase the capacity of
each domain from 10 to 20 Mbps
Instead of using one link between the station and the switch ,
the configuration user two links: one to transmit and to receive.
Switch Ethernet in full duplex mode
38. 38
Each station or switch can send and receive independently
without worrying about collision.
Each link is a point to point dedicated path between the
station and the switch.
There is no longer a need for carrier sensing and no need
for collision detection.
The job of the MAC layer becomes much easier.
39. 39
MAC Control Layer
Stander Ethernet was designed as a connectionless
protocol at the MAC sublayer.
There is no explicit flow control or error control to
inform the sender that the frame has arrived at the
destination without error.
When the receiver receives the frame it does not send
any positive or negative acknowledgement.
40. 40
Fast Ethernet was designed to compete with LAN protocols
such as FDDI or fiber Channel.
IEEE created Fast Ethernet under the name 802.3u.
Fast Ethernet is backward-compatible with Sander Ethernet,
but it can transmit data 10 time faster at a rate of 100 Mbps.
The goal of the fast Ethernet as below
:- Upgrade the data rate at the 100 Mbps.
:- Make it compatible with standard Ethernet.
:- Keep the same frame format.
41. 41
MAC sublayer
A main Consideration in the evolution of Ethernet from 10 to
100 Mbps was to keep the MAC sublayer untouched.
A decision was made to drop the bus topology and keep only
the star topology.
For the star topology there are two choices, as we say before:
Half duplex and Full duplex approach, the connection is
made via a switch without buffers at each port.
42. 42
A new feature added to fast Ethernet is called
Autonegotiation. It allows a station or hub a range of
capabilities.
To allow incompatible devices to connect to one another. For
example a device with a maximum capacity of 10 Mbps can
communicate with a device a 100 Mbps capacity (but can
work at a lower rete).
To allow one device to have multiple capabilities.
To allow a station to check a hub’s capabilities.
43. 43
Physical Layer
The Physical layer In Fast Ethernet is more complicated than
the one in Standard Ethernet.
Topology:-
Fast Ethernet is designed to connect two or more stations
together. If there are only two stations, they can be
connected point to point.
If there are there or more stations need to be connected in a
star topology with a hub or a switch at the center
44. 44
The figure of two station which are connected to point to point.
In the star topology the station are more then two are
connected with switch
45. 45
Implementation
Fast Ethernet implementation at the physical layer can be
categorized as either two-wire or four-wire.
The two-wire implementation can either category 5
UTP(100base-TX) or fiber-optic cable (100Base-FX).
The four-wire implementation is designed only for category 3
UTP (100base-T4).
Let’s understand with figure which is as below.
46. 46
100Base-TX uses two pairs of twisted-pair cable(either
category 5 UTC or STP).
100Base-FX uses two pairs of fiber cables. Optical fiber can
easily handle high bandwidth requirement by using simple
encoding schemes.
A 100Base-TX network can provide a data rate of 100 Mbps,
but it requires the use of category 5 UTP or STP cable.
47. 47
The need for an even higher data rate resulted in the design of
the Gigabit Ethernet protocol (100Mbps).
The IEEE committee calls the Standard 802.3z. The goal of the
Gigabit Ethernet design can be summarized as below.
1 Upgrade the data rate to 1Gbps.
2 Make it compatible with Standard of Fast Ethernet.
3 Use the same frame format.
4 Keep the same minimum and maximum frame lengths.
48. 48
MAC sublayer
A main consideration in the evolution of Ethernet was to
keep the MAC sublayer untouched.
However to achieve data rate 1Gbps this was longer
possible.
Gigabit Ethernet has two distinctive approaches for
medium access: half duplex and full duplex.
49. 49
Full Duplex Mode
In full duplex mode there is a central switch connected to
all computers or other switches.
In this mode each switch has buffers for each input port in
which data are stored until they are transmitted.
There is no collision implies that the maximum length of
the cable is determined by the signal attenuation in the
cable not by the collision detection process.
50. 50
Half Duplex mode
Gigabit Ethernet can also be used in half-duplex mode,
although it is rare.
In this case a switch can be replaced by a hub, which acts
as the common cable in which a collision might occur
51. 51
Physical Layer
The physical layer in Gigabit Ethernet is more complicated
than that in standard or fast Ethernet.
Topology Gigabit Ethernet is designed to connect two or
more stations. If there are only two stations, they can be
connected point to point.
There are three or more stations need to be connected in a
star topology with a hub or a switch at the center.
54. 54
The IEEE committee created Ten-Gigabit Ethernet and
called it Standard 802.3ae. The goal of Ten Gigabit Ethernet
design can be summarized as follow.
1 Upgrade the date rate to 10Gbps.
2 Make it compatible with Standard, fast.
4 Use the same frame format.
5 Keep the same minimum and maximum frame lengths.
55. 55
MAC Sublayer
Ten-Gigabit Ethernet operates only in full duplex mode.
Physical Layer
The physical layer in Ten-Gigabit Ethernet is designed for
using fiber-optic cable over long distances.
Three implementations are the most common: 10GBase-s,
10GBase-L and 10GBase-E.
