Network Cables Online Blog    

Q. The company I work for is interested in installing network cabling for residential homes in the construction phase (as the home
is being built) well I am supposed to make some brochure about this and I have no idea where to even start. Some of the things I now I need (text information) are: why is it going to benefit the consumer and builder, what are the perks of having network cable, and why is it easier and a more efficient way to connect to the internet. I am not asking you for the answers but I would like to know if you can suggest any web sites that I may find information about the questions I asked above.
Thank you for your time

A. This is a big question!

First of all, we are in the ‘Information Age’ and more and more households are using the internet and have more than one computer. Because of this, home networking is becoming commonplace and it is a more efficient method of connecting two or three computers to the internet over one phone line or DSL (Digital Subscriber Line).

The main benefits of installing the cabling during construction are the cost and ease of implementation. Cable is fairly inexpensive and installing it during the building work is far easier than trying to do it once the property is finished and decorated. I get a lot of email from people all over the world who are cabling their houses to connect PC’s together, and hiding cables in wall cavities or chasing out and re-plastering is not an easy task for them, unlike most office environments where this is not such an issue.

Another point worth raising is that residential cabling is not just for connecting PC’s together. ‘Smart Houses’ also use intelligent devices such as alarm systems, refrigerators and heating/air conditioning systems all of which can be networked to a controlling PC or accessed via the Internet when you are away from home. OK, you may be asking why would we need to? but it is starting to happen. And, of course, the cabling system can also be used for telephones, which makes adding an extension phone as simple as plugging it in at the nearest cabling outlet and patching it through at the panel.

Although most all network are a mesh it is good to know the basics.

Q. what are some advantages and disadvantages about star, ring, and bus topologies?

A. In answer to your question regarding Network Topologies I hope the following helps.

Bus Topology
Advantages – Simple to implement, all machines are ‘daisy chained’ which makes wiring as easy as stringing coax cable from one computer to the next and so on.
Disadvantages – Not very versatile when machines have to be moved, as rewiring part of the network is necessary. Not very fault tolerant, on some systems (10Base2) if one part of the bus is disconnected the whole segment of the network goes down. Not suitable for voice.

Ring Topology
Advantages – Fairly simple to wire. Quite fault tolerant, with a Token Ring network if the main ring is disconnected anywhere, the ring uses a loop back system to maintain ring integrity.
Disadvantages – It is only really used with Token Ring networks these days and it uses Type 1 cable, this is very bulky and is not really suitable for running voice. Again, moves and additions mean rewiring and re-routing cables.

Star Topology
Advantages – These days most buildings are cabled using a star topology with Cat 5e or Cat 6 cable. This gives the network a centralized wiring point which makes connecting and disconnecting machines as simple as plugging and unplugging an RJ45 connector in to a hub or switch (Ethernet, Token Ring and any other type of network or service that is required). It can also be used for voice, data, video and any low voltage application.

Disadvantages – Requires a centralized wiring point, which can be just a cabinet on the wall for small installations, or a dedicated air conditioned room with racks and cabinets in large office accommodation. On large installations the sheer bulk of cable coming back to the wiring closet can be difficult to control and keep tidy.

How can I tell if a cable is a crossover or straight through?
Q. I currently have 2 PCs, one running windows xp and one running windows 98 which I would like to network together using the XP machine as the host. I have 2 rj45 ethernet cards and a 10 metre cat 5e twisted pair cable.
Is there any way to tell if I have the right cable as my computers aren’t communicating and I have tried every other troubleshooting resource, and the only conclusion I can come to is that my cable is not a crossover type.
Any advice would be GREATLY appreciated!

A. If you hold both of the RJ45 connectors side by side and look at them from the bottom (ie. the clip is away from you) you can make out which colour is connected to which pin. The pins you are interested in are (from left to right) 1 & 2 and 3 & 6. If they are the same either end then it is a straight through cable, if pin 1 (usually orange/white, but not necessarily) is connected to pin 3 at the other end and 2 is connected to pin 6 (and vice versa) then you have a crossover cable. If you look at the testing page of the Network Cabling Help website, about half way down there are some pictures of the pin outs for RJ45 connectors. The ‘crossed pair’ image is actually the correct wiring for a crossover cable and above it is the correct wiring for a straight through cable. If you have a straight through cable then it won’t work without a hub, if pins 1 & 2 and 3 & 6 are crossed over then the problem lies with the way the network is setup.

Cat 5 crossover cable?
Q. I have been looking at your site and it was very helpful.
I’m trying to connect two computers with a cat 5 crossover cable. The cable that I received in the mail was crossed correctly, but it was also crossed at 4 &5. My question is will this cable work by just joining PC to PC without any hubs or anything else. I bought the cable from an individual.

A. If you are using it for 10BaseT or 100BaseT Ethernet then the wiring should be 1 to 3, & 2 to 6
Pins 4 & 5 aren’t used on 10/100BaseT Ethernet systems so it should be OK. If you are planning to use Gigabit Ethernet or Token Ring then it won’t work.

Cable length limits?
Q. I know that cables have restrictions on distance, but I really would like to know why those limits are for each cable. E.g. Why is Cat X cable limited to 100m, and thinnet 185M etc. I have just accepted these values but have been asked why and I do not know a technical enough answer as I have never been a cabler. I could not find this on your site and was hoping it might be added or if you could email me back with why. Thanks.

A. The length limits are not for the particular cables as such, they are for the type of data signal that they carry.

Let me try and explain!

Thinnet (RG58 coax) was used for 10Base2 Ethernet, at 10Mbps on RG58 coax Ethernet can reliably operate upto a distance of 185m. The native cabling environment of the AS400 is Twinax and the standard operating speed is only 1Mbps. At this speed it has a maximum distance of 1800m, however, if Cat 5 forms part or all of the link the distance can drop to between 36m and 364m.

So for a proprietary network such as Thinnet, the distance is set at the maximum length that the signal will work reliably at a given speed over a given type of cable. So far so good!

Now, when we talk about Cat 5, 5e, 6 etc. these are cabling ‘Standards’ which define a method of connecting all types of networking protocols, over a cabling system that uses a common media, common connectors and a common topology. So the length limit was arbitrarily set for the worst case scenario. 10BaseT may well work on Cat 5 for 150m but ATM, AS400, Token Ring etc. may not, and because a structured cabling system has to work for all networking methods, a limit had to be set.

I don’t think I have explained this very well but I hope you get idea. Incidentally, I have heard talk of the length limit being dropped from the standards as it is the overall Attenuation to Crosstalk Ratio which determines a cables ability to transmit a signal successfully, and not the length of the cable. If anyone can elaborate on this point please let me know.

Cat 5 and Cat 5E
The basic Cat 5 system used to be the only real choice, but developments in Ethernet technology led to the introduction of ‘Enhanced Category 5′ or Cat 5E. Both systems are capable of transmission rates up to 100MHz, but the test parameters for Cat 5 assumed that data signals would only use two of the four pairs (one pair for transmitting and one pair for receiving) and crosstalk measurements were only taken between each pair combination. With Gigabit Ethernet however, all four pairs can be used to transmit simultaneously, and so the cross talk on each pair has to be measured for the combined effects of the other three pairs.

Cat 6
At last! the standard for Cat 6 has been approved for publication by the EIA (TIA/EIA-568-B.2-1). Category 6 is capable of transmission frequencies up to 250Mhz and has a positive power sum attenuation to crosstalk ratio upto 200MHz using improved cables and RJ45 connectors. The problem that manufacturers have, is that to meet the Cat 6 specification, requires the use of cables and connectors which are designed to work together as a ‘tuned’ system. This means that if you install a Cat 6 system the manufacturer will only guarantee performance if all of the components including the patch leads are from their Cat 6 product range. In fact, by mixing Cat 6 components from different manufacturers you could end up with a system with worse performance characteristics than a conventional Cat 5e system. That said, it is worth noting that Cat 6 systems are backwards compatible with Cat 5/5e cabling and when mixed with these lower bandwidth systems the performance criteria of the lower specification will still be met.

Testing Cat 6 cables can be a frustrating process, apart from taking longer because the tester has to scan frequency steps up to 200MHz instead of 100MHz, the fine line between pass and fail is accentuated it seems by the slightest kink and twist. The most significant factor when testing a Cat 6 system can be return loss failures due to the test leads themselves. All connectors have a life cycle and with the average RJ45 connector this is around one or two thousand insertions, so test leads should be replaced after every 1000 tests or so. OK, not a problem but at around $200 per set this cost will have to be considered when pricing jobs.

Fluke seem to have a solution to this problem with their DSP-LIA101S Permanent Link Adapters. The connector at the end of the leads are interchangeable and replaceable with connectors from different manufacturers to ensure compatibility with the system under test. Although a good idea, the adapters are over $500 and a new pair of “Personality Modules” cost over $100. Surely the test plugs should now be considered as ‘consumables’ and the price lowered to reflect this.

Cat 7
This is proposed to be a 600MHz system using a shielded cable with individually screened pairs and a new type of connector. The cable and connectors are slightly bigger than Cat 5e and installation time can be increased because of the complexity of the termination. There are two main draw backs with installing this type of cabling, the first is the additional cost involved, and the second is that almost all networking hardware uses RJ45 jacks. To connect to the cabling system, you have to use Cat 7 to Cat 5e patch leads, and because any system is only as good as its weakest link, your speed is back down to 100MHz. Ratification of the Cat 7 standard could be two years away by which time fibre might be a cheaper alternative.

Shielded or Unshielded
This is a subject that has been debated and argued over for a long time, and as yet, there are still no definite answers. Most countries in Europe, and in particular Germany, argue that apart from protecting data signals against high frequency noise from outside sources, shielded cable also protects the humans against the possibility of having their brains fried due to the effects of high frequency emissions from the cable itself. Other countries, such as the UK, US and Canada, aren’t particularly bothered by this because nothing has been proved, and after all, millions of people wander around with mobile phones pressed against the side of their heads with no apparent side effects, er… yet. My advice would be to install unshielded cable unless the customer insists on a shielded system.

Shielded cables and components are more expensive and are more time consuming to terminate, you should also bear in mind that a shielded cable that isn’t properly grounded has worse performance characteristics than an unshielded cable. If a shielded cable isn’t grounded at all, the screen can act like an antenna and induce all manner of noise on to the data signal.

Low Smoke Zero Halogen
In public buildings, such as airports, shops and hospitals, then the cable should be Low Smoke Zero Halogen (LS0H or LSZH).