Cabling lan
From Mycomputer Notes
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Ethernet performs three functions: | Ethernet performs three functions: | ||
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#Decoding data packets and checking them for valid addresses before passing them to the upper layers of the OSI model | #Decoding data packets and checking them for valid addresses before passing them to the upper layers of the OSI model | ||
#Detecting errors within data packets or on the network | #Detecting errors within data packets or on the network | ||
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=LAN Devices= | =LAN Devices= | ||
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| width="50%" | <ul><li>Minimizes collisions </li><li>Filters traffic based on MAC address </li><li>Maintains address tables</li><li>Manages access to the physical medium </li><li>Transparent to upper layers </li><li>Best used in low traffic areas</li></ul><p> </p> | | width="50%" | <ul><li>Minimizes collisions </li><li>Filters traffic based on MAC address </li><li>Maintains address tables</li><li>Manages access to the physical medium </li><li>Transparent to upper layers </li><li>Best used in low traffic areas</li></ul><p> </p> | ||
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| - | | width="50%" | <ul><li>Can cause bottlenecks </li><li>Broadcasts </li><li>Messages sent to all devices </li><li>Destination MAC address unknown </li><li>Can cause Broadcast Storm </li><li>Network time outs, traffic slowdowns, unacceptable performance</li> <li>Bridges increase the latency (delay) in a network by 10-30% | + | | width="50%" | <ul><li>Can cause bottlenecks </li><li>Broadcasts </li><li>Messages sent to all devices </li><li>Destination MAC address unknown </li><li>Can cause Broadcast Storm </li><li>Network time outs, traffic slowdowns, unacceptable performance</li><li>Bridges increase the latency (delay) in a network by 10-30%</li></ul> |
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Revision as of 21:48, 2 March 2006
We know that each LAN is unique but many designs aspects are common to all of them. Most of them fallow the same communication standanrd and shared the same components. This chapter presents information on elements of Ethernet LANs and common LAN devices.
Physical Layer Implementation
Ethernet was first implemented by the Digital, Intel, and Xerox group (DIX). DIX created and implemented the first Ethernet LAN specification, which was used as the basis for the Institute of Electrical and Electronics Engineers (IEEE) 802.3 specification, released in 1980 Together Ethernet and IEEE 802.3 currently maintain the greatest market share of any LAN protocol.
Today, the term Ethernet is often used to refer to all carrier sense multiple access/collision detection (CSMA/CD) LAN’s that generally conform to Ethernet specifications, including IEEE 802.3. IEEE 802.3 and Ethernet v2.0
Ethernet performs three functions:
- Transmitting and receiving data packets
- Decoding data packets and checking them for valid addresses before passing them to the upper layers of the OSI model
- Detecting errors within data packets or on the network
LAN Devices
Many types of devices, other then a workstation, make-up the LAN. This divices include repeaters, hubs, bridges and switches.
- Repeater
- The purpose of the Repeater is to regenerate and retime network signals at the bit level to allow them to travel longer distance on the media. The 4 repeater rule for 10Mbps bus based Ethernet known as "5-4-3" is used as standard when extending the LAN.
- Hubs
- Are multiport repeaters and it generally has 4 to 24 ports and it is most commonly used in Ethernet 10BASET & 100BASET. Using a Hub changes the network topology from linear, each device plugs directly to the wire, to a Start Topology. The hub electronically repeats data arriving from the cable out of all ports connected to the same network signal. Hubs comes in 3 flaveours:
- Active --> must be plug to an electrical outlet.
- Intelligent --> same functionality as an acitve hub but they include a microprocessor chip and some diagnostic capabilities.
- Passive --> They only function is to be a physical connetion point. They do not boost or clean the signal.
All the devices connected to the hub can hear all the trafic therefore Hubs maintained a single Collision Domain.
- Bridges
- When times comes and we need to break up a LAN into smaller easily managed segments it is time to introduce a Bridge. Segmenting a single LAN into smaller segments can extend the capabilities of the LAN because it decreases the trafic through the entire LAN. Other devices used to connect netwokr segments together are (bridges, swithes, routers and gateways). A bridge makes intelligent decisionsabout whether or not to pass signals onto the next segment of a newtork, thus reducing traffic. It cab be used to connect dissimilar Layer 2 Protocols (i.e Ethernet, Token Ring, FDDI)
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Disadvantages |
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- Switching
- A switch is a sort of a multiport bridge, but much faster, and the number of port depends on how many networks segments are to be linked. The switch chooses the port to which the destination device or workstaion is connected. It alleviates congestion in Ethernet LAN by reducing trafic and increasing bandwith.
| Advantages |
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- Broadcast Domains
- All hosts connected to the same switch are still in the same broadcast domain. A broadcast from one node will be seen by all other nodes connected through the LAN switch
- Segmentation
- Two primary reasons for segmenting a LAN:
- Isolate traffic between segments
- Achieve more bandwidth per user by creating smaller collision domains
- Know when to segment
- It is important to note that even though 100% of the bandwidth may be available, Ethernet networks perform best when kept under 30-40% of full capacity. Bandwidth usage that exceeds the recommended limitation results in increased collisions.
- Routers
- The Router is a layer 3 (Network) device, but operates at layers 1-3. Routers create the highest level of segmentation because of their ability to make exact determinations of where to send the data packet.
Because routers perform more functions than bridges, they operate with a higher rate of latency.
NIC
In the CSMA/CD access method, networking devices with data to transmit over the networking media work in a listen-before-transmit mode. NICs
- Provides ports for network connection
- Communicate with network via serial connection
- Communication with computer through parallel connection
Resources required: IRQ, I/O address, upper memory addresses, DMA
Selection Factors for NICs
- Type of network (Ethernet, Token Ring, FDDI)
- Type of media (Twisted pair, coax, fiber)
- Type of system bus (PCI, ISA)
- NIC Operations
- Layer 1 & Layer 2 device
- Communicates with upper layers in the computer
- Logical Link Control (LLC)
- Has MAC address burned in
- Encapsulates data into frames
- access to the media
- Also Layer 1
- Creates signals and interfaces with the media On-board transceiver
