Skip to main content

CSMA/CD



CSMA/CD
In order to manage collisions Ethernet uses a protocol called Carrier Sense Multiple Access/Collision Detection (CSMA/CD). CSMA/CD is a type of contention protocol that defines how to respond when a collision is detected, or when two devices attempt to transmit packages simultaneously. Ethernet allows each device to send messages at any time without having to wait for network permission; thus, there is a high possibility that devices may try to send messages at the same time.
After detecting a collision, each device that was transmitting a packet delays a random amount of time before re-transmitting the packet. If another collision occurs, the device waits twice as long before trying to re-transmit.
Ethernet Products
The standards and technology just discussed will help define the specific products that network managers use to build Ethernet networks. The following presents the key products needed to build an Ethernet LAN.
Transceivers
Transceivers are also referred to as Medium Access Units (MAUs). They are used to connect nodes to the various Ethernet media. Most computers and network interface cards contain a built-in 10BASE-T or 10BASE2 transceiver which allows them to be connected directly to Ethernet without the need for an external transceiver.
Many Ethernet devices provide an attachment unit interface (AUI) connector to allow the user to connect to any type of medium via an external transceiver. The AUI connector consists of a 15-pin D-shell type connector, female on the computer side, male on the transceiver side.
For Fast Ethernet networks, a new interface called the MII (Media Independent Interface) was developed to offer a flexible way to support 100 Mbps connections. The MII is a popular way to connect 100BASE-FX links to copper-based Fast Ethernet devices.
Network Interface Cards
Network Interface Cards, commonly referred to as NICs, are used to connect a PC to a network. The NIC provides a physical connection between the networking cable and the computer’s internal bus. Different computers have different bus architectures. PCI bus slots are most commonly found on 486/Pentium PCs and ISA expansion slots are commonly found on 386 and older PCs. NICs come in three basic varieties: 8-bit, 16-bit, and 32-bit. The larger the number of bits that can be transferred to the NIC, the faster the NIC can transfer data to the network cable. Most NICs are designed for a particular type of network, protocol, and medium, though some can serve multiple networks.
Many NIC adapters comply with plug-and-play specifications. On these systems, NICs are automatically configured without user intervention, while on non-plug-and-play systems, configuration is done manually through a set-up program and/or DIP switches.
Cards are available to support almost all networking standards. Fast Ethernet NICs are often 10/100 capable, and will automatically set to the appropriate speed. Gigabit Ethernet NICs are 10/100/1000 capable with auto negotiation depending on the user’s Ethernet speed. Full duplex networking is another option where a dedicated connection to a switch allows a NIC to operate at twice the speed.
Hubs/Repeaters
Hubs/repeaters are used to connect together two or more Ethernet segments of any type of medium. In larger designs, signal quality begins to deteriorate as segments exceed their maximum length. Hubs provide the signal amplification required to allow a segment to be extended a greater distance. A hub repeats any incoming signal to all ports.
Ethernet hubs are necessary in star topologies such as 10BASE-T. A multi-port twisted pair hub allows several point-to-point segments to be joined into one network. One end of the point-to-point link is attached to the hub and the other is attached to the computer. If the hub is attached to a backbone, then all computers at the end of the twisted pair segments can communicate with all the hosts on the backbone. The number and type of hubs in any one-collision domain is limited by the Ethernet rules. These repeater rules are discussed in more detail later.
A very important fact to note about hubs is that they only allow users to share Ethernet. A network of hubs/repeaters is termed a “shared Ethernet,” meaning that all members of the network are contending for transmission of data onto a single network (collision domain). A hub/repeater propagates all electrical signals including the invalid ones. Therefore, if a collision or electrical interference occurs on one segment, repeaters make it appear on all others as well. This means that individual members of a shared network will only get a percentage of the available network bandwidth.
Basically, the number and type of hubs in any one collision domain for 10Mbps Ethernet is limited by the following rules:
Network Type
Max Nodes Per Segment
Max Distance Per Segment
10BASE-T
2
100m
10BASE-FL
2
2000m

Comments

Post a Comment

Popular posts from this blog

Education of India Part 2

History [ edit ] Main article:  History of education in South Asia The remnants of the library of  Nalanda , built in the 5th century BCE by  Gupta kings . It was rebuilt twice after invasion, first after an invasion from the  Huns  in the 5th century BCE and then after an invasion from the  Gaudas  in the 7th century CE but abandoned after the third invasion by  Turkic invaders  in the 12th century. Takshasila  (in modern-day Pakistan) was the earliest recorded centre of higher learning in India from possibly 8th century BCE, and it is debatable whether it could be regarded a university or not in modern sense, since teachers living there may not have had official membership of particular colleges, and there did not seem to have existed purpose-built lecture halls and residential quarters in Taxila, in contrast to the later Nalanda university in eastern India.  Nalanda  was the oldest university-system of education in the world in the modern sense of university. There al
Post a Comment
Read more

Save a Workbook in another File Format

  Save a Workbook in another File Format When you save an Excel 2013 Workbook, by default it saves in the  .xlsx  format. Excel 2013 supports saving in other formats, but whenever you save a workbook in another file format, some of its formatting, data, and features might not be saved. File Formats (File Types) that are supported in Excel 2013 − Excel File Formats Text File Formats Other File Formats Excel File Formats Format Extension Description Excel Workbook .xlsx The default XML-based file format for Excel 2007-2013. Cannot store Microsoft Visual Basic for Applications (VBA) macro code or Microsoft Office Excel 4.0 macro sheets (.xlm). Strict Open XML Spreadsheet .xlsx An ISO strict version of the Excel Workbook file format (.xlsx). Excel Workbook (code) .xlsm The XML-based and macro-enabled file format for Excel 2007-2013. Stores VBA macro code or Excel 4.0 macro sheets (.xlm) Excel Binary Workbook .xlsb The binary file format (BIFF12) for Excel 2007-2013. Template .xltx The defa
Post a Comment
Read more

Change in Charts Group

  Change in Charts Group The Charts Group on the Ribbon in MS Excel 2013 looks as follows − You can observe that − The subgroups are clubbed together. A new option  ‘Recommended Charts’  is added. Let us create a chart. Follow the steps given below. Step 1  − Select the data for which you want to create a chart. Step 2  − Click on the  Insert Column Chart  icon as shown below. When you click on the  Insert Column chart , types of  2-D Column Charts , and  3-D Column Charts  are displayed. You can also see the option of More  Column Charts . Step 3  − If you are sure of which chart you have to use, you can choose a Chart and proceed. If you find that the one you pick is not working well for your data, the new  Recommended Charts  command on the  Insert  tab helps you to create a chart quickly that is just right for your data. Chart Recommendations Let us see the options available under this heading. (use another word for heading) Step 1  − Select the Data from the worksheet. Step 2  − C
Post a Comment
Read more