Ethernet Networking

Ethernet Cable - Color Coding

The information listed here is to assist Network Administrators in the color coding of Ethernet cables. Please be aware that modifying Ethernet cables improperly may cause loss of network connectivity. Use this information at your own risk, and insure all connectors and cables are modified in accordance with standards. The Internet Centre and its affiliates cannot be held liable for the use of this information in whole or in part.

T-568A Straight-Through Ethernet Cable

The TIA/EIA 568-A standard which was ratified in 1995, was replaced by the TIA/EIA 568-B standard in 2002 and has been updated since. Both standards define the T-568A and T-568B pin-outs for using Unshielded Twisted Pair cable and RJ-45 connectors for Ethernet connectivity. The standards and pin-out specification appear to be related and interchangeable, but are not the same and should not be used interchangeably.

T-568B Straight-Through Ethernet Cable

Both the T-568A and the T-568B standard Straight-Through cables are used most often as patch cords for your Ethernet connections. If you require a cable to connect two Ethernet devices directly together without a hub or when you connect two hubs together, you will need to use a Crossover cable instead.

RJ-45 Crossover Ethernet Cable

A good way of remembering how to wire a Crossover Ethernet cable is to wire one end using the T-568A standard and the other end using the T-568B standard. Another way of remembering the color coding is to simply switch the Green set of wires in place with the Orange set of wires. Specifically, switch the solid Green (G) with the solid Orange, and switch the green/white with the orange/white.

Ethernet Cable Instructions:

1. Pull the cable off the reel to the desired length and cut. If you are pulling cables through holes, its easier to attach the RJ-45 plugs after the cable is pulled. The total length of wire segments between a PC and a hub or between two PC's cannot exceed 100 Meters (328 feet) for 100BASE-TX and 300 Meters for 10BASE-T.
2. Start on one end and strip the cable jacket off (about 1") using a stripper or a knife. Be extra careful not to nick the wires, otherwise you will need to start over.
3. Spread, untwist the pairs, and arrange the wires in the order of the desired cable end. Flatten the end between your thumb and forefinger. Trim the ends of the wires so they are even with one another, leaving only 1/2" in wire length. If it is longer than 1/2" it will be out-of-spec and susceptible to crosstalk. Flatten and insure there are no spaces between wires.
4. Hold the RJ-45 plug with the clip facing down or away from you. Push the wires firmly into the plug. Inspect each wire is flat even at the front of the plug. Check the order of the wires. Double check again. Check that the jacket is fitted right against the stop of the plug. Carefully hold the wire and firmly crimp the RJ-45 with the crimper.
5. Check the color orientation, check that the crimped connection is not about to come apart, and check to see if the wires are flat against the front of the plug. If even one of these are incorrect, you will have to start over. Test the Ethernet cable.

Ethernet Cable Tips:

• A straight-thru cable has identical ends.
• A crossover cable has different ends.
• A straight-thru is used as a patch cord in Ethernet connections.
• A crossover is used to connect two Ethernet devices without a hub or for connecting two hubs.
• A crossover has one end with the Orange set of wires switched with the Green set.
• Odd numbered pins are always striped, even numbered pins are always solid colored.
• Looking at the RJ-45 with the clip facing away from you, Brown is always on the right, and pin 1 is on the left.
• No more than 1/2" of the Ethernet cable should be untwisted otherwise it will be susceptible to crosstalk.
• Do not deform, do not bend, do not stretch, do not staple, do not run parallel with power cables, and do not run Ethernet cables near noise inducing components.

Basic Theory:

By looking at a T-568A UTP Ethernet straight-thru cable and an Ethernet crossover cable with a T-568B end, we see that the TX (transmitter) pins are connected to the corresponding RX (receiver) pins, plus to plus and minus to minus. You can also see that both the blue and brown wire pairs on pins 4, 5, 7, and 8 are not used in either standard. What you may not realize is that, these same pins 4, 5, 7, and 8 are not used or required in 100BASE-TX as well. So why bother using these wires, well for one thing its simply easier to make a connection with all the wires grouped together. Otherwise you'll be spending time trying to fit those tiny little wires into each of the corresponding holes in the RJ-45 connector.

computer memory

Firstly we will discus computer memory

There are many types of computer memory modules available. In this day and age, computers (laptops, PCs, etc.) generally do not use a single type of memory; rather, a combination of memory chips and modules are normally found in today's computers, depending on requirements and applications. The following is an overview of the types of computer memory:

SIMM (Single In-Line Memory Module) Dating back to the days of 286, 386, and 486 PCs, SIMMs are generally plug-in memory modules that are inserted into the CPU motherboard (or an extender memory board). A SIMM can be comprised of BEDO (Burst Extended Data Out Dynamic Random Access Memory), DRAM (Dynamic Random Access Memory) or EDO (Extended Data Out Dynamic Random Access Memory), with the memory chips (one or more) soldered on a PCB (printed circuit board). As mentioned above, it is the SIMM that is plugged into the CPU motherboard or memory extend card to expand the memory capability of the computer. Generally, when one is adding memory to a computer, it is in the form of a SIMM. Early SIMMs handled 8 data bits at a time in a 30-pin configuration; later, when CPUs were processing 32-bits, newer generation SIMMs were constructed in a 72-pin configuration.

DIMM (Dual In-Line Memory Module) DIMMs have two rows of DRAM, BEDO, or EDO memory chips. DIMMS allow for double the memory on the same size printed circuit board. A typical DIMM would be constructed in a 168-pin configuration and handle 64 data bits at a time.

SODIMM (Small Outline Dual In-Line Memory Module) SODIMMs are generally found in notebook computers and are smaller than standard DIMMs. In general, there are 2 types of SODIMMs – the first handling 32 data bits at a time with a 72-pin configuration, and the second handling 64 data bits with a 144-pin configuration. RIMM (Rambus In-Line Memory Module) Rambus Inc. in coordination with Intel developed a new memory technology called Direct RDRAM, with the in-line modules known as RIMMs. RIMMs have a 184-pin configuration and deliver a peak transfer rate of 1.6 Gigabytes per second (in 16 data bit segments). SORIMM (Small Outline Rambus In-Line Memory Module) SORIMMs have a similar outline as a SODIMM, but use the Rambus memory technology. Different Types of Memory Chips:

DRAM (Dynamic Random Access Memory) The most common type of computer memory. DRAMs hold data for a relatively brief period of time and need to be refreshed at regular intervals. DRAMs are measured by access time (in nanoseconds, or ns) and storage capacity (in megabytes, or MB). EDO (Extended Data Out) Memory Higher-performing memory than DRAM, with a gain in performance of roughly 10-15% over DRAM. BEDO (Burst Extended Data Out) Memory Higher-performing memory than EDO, with a gain in performance of roughly 13% over EDO. SDRAM (Static Dynamic Random Access Memory) A memory chip that retains memory and does not need refreshing. Another advantage of SDRAM is that it synchronizes with the CPU timing. Although faster than DRAM, it is also more expensive; available in speeds from 66 to 266 MHz. DDR SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory) A memory integrated circuit that permits transactions on the rising as well as the falling edges of the clock cycle, with a bus clock speed of 100 MHz with a data transfer rate of 200 MHz.

OTHER MEMORY TYPES VRAM (Video Random Access Memory) VRAM is a video version of fast page mode memory and is found primarily in video accelerator cards.

Flash Memory A memory chip that is non-volatile, re-writable that functions like a combination random access memory and a hard disk drive. In the case of power being lost, data is retained in memory. Advantages of flash memory include low voltage, durability and high speed; for this reason, flash memory is used in printers, pagers, digital cameras, audio recorders and cell phones.

Shadow RAM (Random Access Memory) During the booting up of a computer, a minimal set of instructions to start the computer and video are stored in ROM (read only memory), known as BIOS (basic input output system). Since ROM normally executes slowly, Shadow RAM allows for the transfer of selected segments of the BIOS code from ROM to RAM memory (which is faster).