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ETHERNET
Ethernet
is the most common network, supported by many protocols and its low cost.
Originally developed by Intel, Digital (now Compaq), and Xerox, it is an open
network standard (IEEE
802.3).
The Open Systems
Interconnect (OSI), established in 1984 by
the ISO (International Standards Organization), divides network functions into
seven layers: Physical, Data Link, Network, Transport, Session, Presentation
and Application Protocol.
- Application
- Presentation
- Session
- Transport
- Data Link
- Network
- Physical
TCP/IP
protocol on Ethernet provides all seven
layers of the OSI model.
Ethernet provides these layers of the OSI
(Open Systems
Interconnect)
model.
Figure 1. Ethernet
and the OSI Model.
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The
Application Layer provides the interface between the user's application
and the network through messages. Data is said to move from layer to layer
within the seven layers of the OSI
model.
-
The
Presentation Layer negotiates data exchange formats, also in terms of packets.
-
The
Session Layer allows users to establish connections using intelligently chosen
names in packets.
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The
Transport Layer provides end-to-end, reliable connections, often in terms of
segments.
-
The
Network Layer routes data through a large network.
-
The
Data Link layer determines access to the network media in terms of frames. Its
Media Access Control (MAC) sublayer is responsible for physical addressing.
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The
Physical Layer transforms data into bits that are sent across the physical
media.
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Ethernet and the OSI
Model
With
TCP/IP as its protocol the Ethernet
supports the physical and data link layers and supports all
seven layers of the OSI model. Several types
of Ethernet cables support the physical layer.
The Ethernet use Carrier
Sense Multiple Access/Collision Detection (CSMA/CD) to supports the data
link layer. The CSMA/CD checks the media for other devices
before
transmitting, managing data collisions and reducing the number of data collisions.
TCP/IP and the OSI Model
Ethernet
uses Transmission Control Protocol/Internet Protocol (TCP/IP) to provide layers of
the OSI model. The four layers of the TCP/IP can
loosely fit the seven layers of the OSI. TCP/IP can run on many types of network
connection, including ethernet.
Ethernet supports both the Physical and Data Link
layers of the OSI
model.
The Network layer
of the OSI model corresponds with the
Internet layer of the
TCP/IP model.
Internet Protocol provides this layer, moving data to other devices
on the network.
The Transport
layer corresponds to the Host-to-Host layer of the TCP/IP model.
Almost all
devices on a TCP/IP network are considered hosts, and this layer
communicates data
peer-to-peer (or host-to-host).
The Session,
Presentation and Application layers of the OSI
model correspond
to the
Process/Application layer of the TCP/IP model, providing network services.
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Devices on an Ethernet
network are arranged in either a bus or star topology.
Bus
In a bus
topology, all devices on the network connect to one main cable (trunk cable).
It is easy to
install and configure, and inexpensive. amplification or regeneration do not
require special equipment. If a device want to
send information must first determine if the bus is being used by any other
device. If no other device is attempting to transmit, the device sends the data.
If the trunk cable fails, all devices are affected.
Star
In a star
topology, each device is connected by separate cable to a central device
(hub). If a cable fails it affects only the one device connected
to the failed cable unlike the bus. Star networks are easily expanded, easier to troubleshoot and
support many types of cables. Passive or active
hub is used to connect
more than two devices together
in a star topology. Passive hubs
do not regenerate the signal. Use of active hubs extends network length by
regenerating the signal and sending it across the network.
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Ethernet
supports several types of cables, each
intended for different purposes Below are list of cables from distributed
Systems and Networs by W. Buchaman". :
• 10Base-T
(Twisted-pair Ethernet) – The most widely
used ethernet cabling, it
supports network speeds of 100Mbps. Uses 22- or 26-AWG
UTP cabling to
transmit baseband signals on maximum 100-meter
segments. RJ-45
jacks connect separate cables between device and hub.
Each device must
be at least 2 feet apart and no more than 328 feet
from the hub.
Bridges or routers may be used to accommodate a larger network. There is
no limit on network length. It permits a maximum of 1,024 segments
and 1,024 nodes. See IEEE standard
802.3i.
• 10Base-2
(Thin Ethernet) – Supports network speeds
of 10Mbps. Uses
RG-58 coaxial
cable to transmit baseband signals on 200-meter segments. Total
network length can be 925 meters. Transceivers
reside on the NIC,
simplifying connections. The cable, thinner than 10Base-5, is more flexible
for easier handling. See IEEE standard
802.3a.
• 10Base-5
(Thick Ethernet) – Now rarely used, this
cable was popular for desktop
connections until the introduction of 10BaseT. It supports networks speeds
of up to 10Mbps and uses RG-8 or RG-11 coaxial cable to transmit
baseband signals in 500-meter (1,640 feet) segments.
Total network
length can be 2,500 meters with up to 300 nodes. It requires the use
of transceivers located at least 8 feet
apart and tapped into the cable. A
15-pin AUI, or DIX (Digital, Intel, Xerox) connector is used between
the network cable and the AUI port on the Ethernet
NIC (Network
Interface Card). See IEEE standard
802.3 for details.
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Ethernet
Hub
An
ethernet hub is required if connecting more
than two devices.
1972 - Ethernet used at Xerox PARC
1980 - Consortium of DEC, Intel and Xerox announced the Blue Book
1982 - Version 2 of the Blue Book issued.
1982 - ISOC RFC 826 definition of the address
resolution protocol for Ethernet
1984 - ISOC RFC 894 definition of
IP network using Ethernet links
1985 - IEEE 802.3 (slightly incompatible with v2)
1988 - IEEE published a collection of supplements
1988 - ISOC RFC 1042 definition of IP
networusing IEEE 802.3/LLC
links
1989 - ISO 802.3a Ethernet for thin
coaxial cable (10B2)
1990 - IEEE 802.3i Ethernet over CAT-5
Unshielded Twisted Pair (10BaseT)
1990 - IEEE 802.1D Ethernet Bridging
1993 - 10BT Hubs and Bridges have become a common component in LANs, and
start replacing 10B2/10B5.
1993 - IEEE 802.3j defines Ethernet
over Fibre (10BF)
1993- IEEE 802.1D MAC Layer Bridges
(ISO 10038)
1995 - IEEE 802.3u defines Fast Ethernet (100BTX, 100BT4, 100BFX)
1996 - Fast Ethernet and Fibre links have become common
1998 - 100BT has become a common component in LANs
1998 - IEEE 802.3z defines Gigabit Ethernet over Fibre (later in802.3 ab
over UTP)
2001 - IEEE 802.11 (wireless) and Gigabit Ethernet have become common LAN
comp
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