Tuesday, January 18, 2011

Ethernet Technology:

Ethernet is a media access method that is specified at the Data Link layer and uses specific Physical layer cabling and signalling techniques. It is important to be able to differentiate between the types of connectors that can be used to connect an Ethernet network together. I'll discuss the different unshielded twisted-pair cabling used today in an Ethernet LAN.
Network Cabling
It's important to understand the difference between the media access speeds Ethernet provides in computer cabling systems. However, it's also important to understand the connector requirements for each implementation before making any decision. The Electronic Industries Association and the newer Telecommunications Industry Association (EIA/TIA) is the standards body that creates the Physical layer specifications for Ethernet. The EIA/TIA specifies that Ethernet use a registered jack connector with a 4 5 wiring sequence on unshielded twisted-pair cabling (RJ-45).
The following points outline the computer network cabling requirements:
• 10Base2 50-ohm coaxial is also called thinnet which is up to 185 meters and supports 30 hosts per segment. Physical and logical bus is used with AUI connectors.
• 10Base5 50-ohm coaxial is also called thicknet which is up to 500 meters and supports 208 users per segment. It uses a physical and logical bus with AUI connectors. It is up to 2500 meters with repeaters and supports 1024 users for all segments.
• 10BaseT EIA/TIA category 3, 4, or 5, using two-pair unshielded twisted-pair (UTP) wiring supports one user per segment; up to 100 meters long.RJ-45 connector is used along with star topology.
• 100BaseTX EIA/TIA category 5, 6, or 7 UTP two-pair wiring supports one user per segment; up to 100 meters long. It uses an RJ-45 MII connector with a physical star topology and a logical bus.
• 100BaseFX Uses fiber cabling 62.5/125-micron multimode fiber supports point-to-point topology; up to 400 meters long. It uses an ST or SC connector, which are duplex media-interface connectors.
• 1000BaseCX Copper shielded twisted-pair that can only run up to 25 meters.
• 1000BaseT Category 5 is a four-pair UTP wiring that can run up to 100 meters.
• 1000BaseSX MMF using 62.5 and 50-micron core; uses a 780-nanometer laser and can go up to 260 meters.
• 1000BaseLX Single-mode fiber that uses a 9-micron core, 1300-nanometer laser and can go from 3 km up to 10 km.
UTP Connections (RJ-45)
The RJ-45 connector is clear so you can see the eight wires mentioned with different colours that connect to the connector's pins. All of theses wires are twisted together into four pairs. Four wires carry the voltage and are considered tip. The other four wires are grounded and are called ring. The RJ-45 connector is crimped onto the end of the wire, and the pin locations of the connector are numbered from the left, 8 to 1.
Twisted wires inside UTP cable eliminate cross talk noise.. Unshielded cable can be used since digital signal protection comes from the twists in the wire. The more twists per inch, the farther the digital signal can supposedly travel without interference. For example, cat 5 cabling such as network cabling cat 5 and category 5 cabling UK have many more twists per inch than category 3 UTP does. Different types of wiring are used for building internetworks. You will need to use either a straight-through or crossover cable.
Straight-Through Cable
In a UTP implementation of a straight-through cable, the wires on both cable ends are in the same order. You can determine that the wiring is a straight-through cable by holding both ends of the UTP cable side by side and seeing that the order of the wires on both ends is identical.
You can use a straight-through cable for the following tasks:• Connecting a router to a hub or switch
• Connecting a server to a hub or switch
• Connecting workstations t a hub or switch
Crossover Cable
In the implementation of a crossover, the wires on each end of the cable are crossed.
It is used to transmit and receive for both rip and ring. Notice that pin 1 on one side connects to pin 3 on the other side, and pin 2 connects to pin 6 on the opposite end.
You can use a crossover cable for the following tasks:
• Connecting uplinks between switches
• Connecting hubs to switches
• Connecting a hub to another hub
• Connecting a router interface to another router interface
• Connecting two PCs together without a hub or switch
When trying to determine the type of cable needed for a port, look at the port and see if it is marked with an "X." by using a straight-through cable when only one port is selected with an "X." and use a crossover when neither port has an "X." or when both ports are designated with an "X"
Rolled Over Cable
In the implementation of a rollover cable, the wires on each end of the cable are opposite. It broadcast to receive and receive to transmit on both side, for both tip and ring. Notice that pin 1 on one side connects to pin 8 on the other side, pin 2 connects to pin 7 on the opposite end, pin 3 connects to pin 6 on the opposite end and pin 4 connects to pin 5 on the opposite end.
You can use a rolled cable for the following tasks:
• For out of band console connection between the console port (RJ45) of the manageable switches and the com port (DB9) of the computer using a RJ45 to DB9 terminal.
• For out of band console connection between the console port (RJ45) of manageable routers and the com port (DB9) of the computer using a RJ45 to DB9 terminal.

Understanding Ethernet Networking
Ethernet refers to the family of Local Area Network implementation that was jointly developed by Digital Equipment Corporation, Intel Corporation and Xerox Corporation. It consists of certain specifications and standards as well as hardware devices and components.
Ethernet Connection
The Ethernet protocol provides for a verity of cabling options, one of which is a specification referred to as 10Base5.
Connecting cable is known as AUI (Attachment Unit Interface) and network attachment device is known as Media Attachment Unit (MAU) rather than transceiver.

Ethernet is a baseband LAN specification invented by Xerox corporation operates at 10 Mbps using CSMA/CD (Carrier Sense Multiple Access Collision Detection).
As a contention-based environment Ethernet allows any station on the network to transmit when ever the Ethernet network is quite. Collisions could be found whenever stations listen for traffic and hear nothing and transmit regularly. In this situation both types of transmissions are damaged and device should transmit later. Back-off algorithm is used whenever colliding stations should retransmit data.
Ethernet Network Design
Ethernet was designed to serve in network with sporadic, occasionally heavy traffic requirements. A network using Ethernet is usually considered as a low cost LAN.
Layer 1 and Layer 2 of OSI model related services are provided by Ethernet.
For creating an Ethernet network, you have usually implemented a network interface card on a primary circuit board. Cabling conventions of Ethernet describe use of transceiver for attaching cable to physical medium. Transceiver may perform some physical layer functions such as collision and detection. The transceiver cable connects end stations to a transceiver.

How to Set Ethernet Full and Half Duplex
Full Duplex Ethernet
Full duplex provides the means of transmitting and receiving simultaneously on a single wire. Full duplex Ethernet is used between two endpoint like for between switches and servers, between switches and routers etc. Full duplex also permit bandwidth on Ethernet and Fast Ethernet networks very easy and cost effective and also fast.. By using features such as Fast EtherChannel, "bundles" of Fast Ethernet connections can be grouped together to increase bandwidth to increase bandwidth up to 4000%.
Full duplex broadcasting is used in Gigabit Ethernet to increase collective bandwidth ranging from 2 Gbps to 2 Gbps for point to point links and also used to increase distances of for specific type of media. Further more Gigabits Ethernet Channel allows creating 8 Gbps connections between switches. Full duplex Ethernet minimize chances of collisions so that CSMS/CD does not need to be used for flow control.
. However, a full duplex flow control method has been put forward in the standards committee with flow control as on option clause. This standard is referred to as IEEE 802.3x; it formalizes full duplex technology and it's expected to be supported in future Gigabit Ethernet products. Because of the volume of full duplex 100 mbps network interfaces cards (NICs), it is likely that this standard will realistically apply to Fast Ethernet.
Half Duplex 10g Ethernet
For half duplex transmission, CSMA/CD will be utilized to ensure that stations can communicate over a single wire and that collision recovery can take place. CSMS/CD implementation should be same as for Ethernet and Fast Ethernet and also it allows creation of shared Gigabit Ethernet using hub of half duplex via point to point connections.
Because the CSMA/CD protocol is delay sensitive, a bit budget per collision domains must be created. When CSMS/CD is used delay sensitivity is always there however full duplex operation has no delay sensitivity and collision domains are defined as time passes fo maximum length frame transmission.
This transmission, in turn, governs the maximum separation between two end stations on a shared segment. When network speed grows, frame transmission speed decreases and collision domains diameters is maximum. Budget of collision domain is used as maximum signal delay time for different networking components like repeaters, MAC layer and medium also.
Increase in speed of Ethernet speed depends upon some terms that how you are implementing CSMS/CD. Speed which is more than 100 Mbps packet sizes are shorter than length of slot time in bits. (Slot-time is defined as the unit of the time for Ethernet MAC to handle collisions). Handling slot time problem you may find carrier extensions in Ethernet specifications. Carrier extensions are used to add bits to frames until frames meets the minimum requirements which slot time is needed. Following this method, smaller packet sizes can cover with minimum slot time required and it permit seamless operation with current Ethernet CSMS/CD.
More change to the Ethernet requirement is the adding up of frame bursting. Frame bursting is an optional feature in which, in a CSMA/CD environment, and an end station can transmit a burst of frames over the wire without having to relinquish control.
Other devices are put back to stop transmission when there is no idle time on wire.
.The transmitting station that is bursting onto the wire fills the inter-frame interval with extension bits such that the wire never appears free to any other end station.

Ethernet is the most common LAN (Local Area Network) technology in use today.
Ethernet was developed by Xerox in the 1970s, and became popular after Digital Equipment Corporation and Intel joined Xerox in developing the Ethernet standard in 1980.
Ethernet was officially accepted as IEEE standard 802.3 in 1985.
The original Xerox Ethernet operated at 3Mbps. Ethernet networks up to 10Gbps now exist.
Ethernet Cabling
The first Ethernet standard, 10Base-5, ran over thick coaxial cable. A later standard, Ethernet 10Base-2, ran over a much thinner coaxial cable. These two versions of Ethernet were colloquially known as thicknet and thinnet.
Modern Ethernet standards run on UTP (Unshielded Twisted Pair) or fiber-optic cabling.
Ethernet Standard Cable Specification
10Base-T Category 3 UTP
100Base-TX Category 5 UTP
1000Base-T Cat 5e UTP
1000Base-SX Optical Fiber
Ethernet Topologies
Ethernet 10Base-5 and 10Base-2 used a bus topology. Bus topologies were difficult to maintain and troubleshoot.
Modern Ethernet networks use a star topology with an Ethernet hub, switch, or router at the center of the star.
It is still possible to create a two-node Ethernet network in a bus topology using a null-Ethernet cable between the two devices.
Ethernet DTE and DCE
All nodes on an Ethernet network are either DTE (Data Terminal Equipment) or DCE (Data Communications Equipment).
Ethernet DTE are devices such as computers and printers which are trying to communicate on the Ethernet network.
Ethernet DCE are devices such as switches and routers which are trying to help other devices communicate on the Ethernet network.
Ethernet CSMA/CD
Like any network, Ethernet must have an algorithm for determining when each network node is allowed to communicate.
In Ethernet, this algorithm is known as CSMA/CD (Carrier Sense Multiple Access / Collision Detection).
CSMA/CD has proven to be a very capable, if highly anarchistic, algorithm.

Ethernet at the Physical Layer
Ethernet is the most popular Local Area Network architecture that was jointly developed by Digital Equipment Corporation, Intel Corporation and Xerox Corporation. It consists of certain specifications and standards as well as hardware devices and components. Ethernet provides services corresponding to physical layer and data link layer of the OSI reference model. Each Ethernet physical layer protocol has a three part name that summarizes its characteristics. The components specified in the naming convention correspond to LAN speed, signalling method, and physical media type.
The following table summarizes the differences between the various physical-layer specifications of Ethernet:

Ethernet Value
Data rate (mbps) 10 10 10 10 10 10
Signalling method Baseband Baseband Baseband Baseband Baseband Baseband
Maximum segment length 500 500 500 500 500 500
Media 50-ohm coaxial 50-ohm coaxial 50-ohm coaxial UTP cable Fiber-optic UTP cable

topology Bus Bus Bus Star Point-to-Point Bus
Ethernet Topology
Ethernet topology is based on following three categories:
• Ethernet 10 Mbps: A single LAN specification that operate at 10 Mbps over coaxial Ethernet 10base2 or 10base5 cable.
• 100-Mbps Ethernet: A single LAN specification, also known as Fast Ethernet that operates at 100 Mbps over UTP Ethernet cable.
• 1000-Mbps Ethernet: A single LAN specification, also known as Gigabit Ethernet that operates at 1 Gbps (1000 Mbps) over fiber optics and twisted pair Ethernet cables.
100BaseT Overview
100BaseT uses the existing IEEE 802.3 CSMA/CD specification. As a result, 100BaseT retains the IEEE 802.3 frame format, size and error-detection mechanism. In addition, it supports all applications and networking software currently running on 802.3 networks. 100BaseT maintains dual speeds of 10 and 100 Mbps using 100BaseT Fast Link Pulses (FLPs). 100BaseT hubs must detect dual speeds much like Token Ring 4/16 hubs, but adapter cards can support 10Mbps, 100 Mbps, or both.
100BaseT Signalling
100BaseT supports two signalling types:
• 100BaseX
• 4T+
Both signalling types are interoperable at the station and hub levels. MII ( Media Independent Interface) which same like AUI interface provides interoperability at base level. The hub provides interoperability at the hub level.
The 100BaseX signalling scheme has a convergence sublayer that adapts the full duplex continuous signalling mechanism of the FDDI Physical Medium Dependent (PMD) layer to the half duplex, start-stop signalling of the Ethernet MAC sublayer. 100BaseTX's use of the existing FDDI specification has allowed quick delivery of products to market. 100BaseX is the signalling scheme used in the 100BaseTX and the 100BaseFX media types.
The 4T+ signalling scheme uses one pair of wires for collision detection and the other three pairs to transmit data. It also permits 100BaseT to work with existing Category 3 cabling while all four pairs are installed on desktop. 4T+ is the signalling scheme used in the 100BaseT4 media type, and it supports half duplex operation only.
100BaseT Hardware
Components used for a 100BaseT physical connection include the following:
Physical medium: This device caries signals between computers and can be one of three 100BaseT media types:
• 100BaseTX
• 100BaseFX
• 100BaseT4
Medium Dependent Interface (MDI): The MDI is a mechanical and electrical interface between the transmission medium and the physical layer device.
Physical Layer Device (PHY): the PHY provides either 10 or 100 Mbps operation and can be a set of integrated circuits (or a daughter board) on a Ethernet port, or an external device supplied with an MII cable that plugs into an MII port on a 100BaseT device (similar to a 10 Mbps Ethernet transceiver).
Media Independent Interface (MII): It is used with a 100 Mbps external transceiver to attach a 100 Mbps Ethernet device to several of these three media types. The MII has a 40 pin plug and cable that stretches up to 0.5 meters.
Cables and Connectors
What is AUI?
Ethernet is usually implemented a network interface card on a primary circuit board. Ethernet cabling standards indicates that how to utilize a transceiver to connect a cable to the physical network medium. The transceiver performs a lot of of the physical layer functions, as well as collusion discovery. Transceiver cable is connected end stations to a transceiver.
Ethernet provides for a verity of cabling options such as 10Base2, 10base5 and 10baseT. The 10base2 Ethernet connection is very rare nowadays because the 10base2 drivers are not so longer available while the 10base5 cable is referred as an AUI (Attachment Unit Interface) and the network attachment device is called a MAU (Media Attachment Unit), instead of a transceiver.
AUI Cable
The AUI connector is connecting with AUI to AUI cable. The AUI to AUI interface cable can be connected with the switch AUI port with the help of AUI and transceiver.

Gigabit Ethernet Physical Layer Implementation
The Gigabit Ethernet specification addresses three forms of transmission media: long-wave (LW) laser over single-mode and multimode fiber (to be known as1000Base LX), sort-wave (SW) laser over multimode fiber (to be known as 1000BaseSX), and the 1000BaseCX medium, which allows for transmission over balanced shielded 150 ohm copper cable. The IEEE 802.3ab committee is examining the use of UTP cable for Gigabit Ethernet transmission (1000BaseT); that standard is expected sometime in 1999.
1000BaseT draft specification would be used to enable Gigabit Ethernet to extend distances up to 100 meters for category 5 UTP cable which is widely used for cabling in buildings.
The Fibre Channel PMD specification currently allows for 1.062 gigabit signalling in full duplex, Gigabit Ethernet will increase this signalling rate to 1.25 Gbps. The 8B/10B encoding allows a data transmission rate of 1000 Mbps.Existing type of connector for Fibre Channel and for Gigabit Ethernet is SC connector for both single and multimode fibre. The Gigabit Ethernet specification calls for media support for multimode fiber-optic cable, single-mode fiber-optic cable, and a special balanced shielded 150 0hm copper cable.

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