by November 1, 2004 0 comments



Structured cabling is to IT infrastructure what foundation is to building-provider of base and stability. Unfortunately, in most cases structured cabling is taken for granted and not implemented properly. This may lead to a lot of problems on your network. So while you may think that the problem is with your network hardware or software, the culprit may actually be the underlying cabling. It’s important, therefore, to know what can go wrong with your structured cabling network and how to analyze it. This story will explain how to analyze your structured cabling and resolve the key issues. 

Before we get into the nitty-gritty of things, remember that one of the biggest headaches for a network administrator is to manage moves, additions and changes on the network, whether for the network devices or the users. If your underlying cabling is not geared to handle these, your network is in for trouble. This can happen if the structured cabling has not been planned out properly during the implementation. However, you must also ensure that you’ve verified everything else before blaming it all on the cabling. For all you know, it could well be a mis-configured network card on a client machine. Having said that, let’s see where can problems lie in your structured cabling, if there are any. 

Cabling problems
What could possibly go wrong in a network cable, you may ask? It’s just a simple copper cable with a few twisted pairs and a connector to plug it into a socket. Believe it or not, there are many things that can go wrong in a cable. For instance, the weakest link in a structured cabling assembly is the humble RJ45 connector, also known as the modular plug. If the twisted pairs are not crimped properly, there may be improper termination, making the cabling susceptible to cross talk. The quality of modular plugs and crimping becomes more important with increasing data transfer rates. For example, this will be a bigger problem for a Gigabit Ethernet cable than a 10BaseT twisted pair cable. 

CAT5

CAT5 (Category 5) cable is a multi-pair (mostly five pairs) cable consisting of twisted pair conductors, used mainly for high performance data transmission. It is tailored for characteristics up to 100 MHz and is typically used for Ethernet networks running at 10 or 100 Mbps. Beyond 100 Mbps networks, you’ll be required to upgrade wholly or partially to CAT5e or higher.

Another problem that can occur is that the pair twists are not maintained in twisted pair cables, especially at the modular plug. Due to the bends or not very careful laying of cables the twists may have opened up or increased in number. Problems can also arise if too much of the jacket is removed from the UTP cable. Ensure that the cable jacket is intact right up to the connector. Cable routing is another common factor contributing to faults. Ensure that it’s not passed next to power or telecom lines. Also ensure that it’s not going through too many bends, as that can affect the number of twists in the UTP cable. Lastly ensure that you have proper documentation of your entire structured cabling layout.

Trouble during implementation
Most of the problems we mentioned above occur during implementation. Therefore, when implementing a structured cabling network, ensure that the manpower you employ is skilled in laying it out. Laying a structured cabling network is not same as laying out telephone or electrical wires. Data cables have specs that must be adhered to while they’re being laid out. For instance, too many bends while laying out UTP cable or doing the wrong mix-n-match of various categories of cables can lead to higher bit errors in data transfers. Additionally, an unmatched or un-tuned channel (both caused by using components from a variety of vendors) will reduce the throughput over the cables. The end result is low overall available bandwidth, resulting in poor network performance. The user will experience problems like increased time for doing file transfers or accessing servers and applications.

Network expansion and upgrades
Network expansion is another juncture where the trouble lies. Is your structured cabling geared to handle expansion, whether in user base, number of network devices or applications? For instance, today you’re running a 10/100 Mbps network, wherein you’re providing 10 Mbps at the desktop and 100 Mbps at the backbone. Tomorrow there’s a need to deploy a new business application such as ERP or VoIP. Would then, this 100 Mbps backbone be sufficient to handle the extra traffic generated by the new application? For this, you need to analyze how heavily is the existing backbone being utilized and how much bandwidth is required by the new business applications. You also need to check whether it can pass through the existing backbone without significantly slowing down the network speed.

CAT5e

Category 5e or Enhanced Category 5 is designed to support full duplex, four-pair Ethernet operation and Gigabit Ethernet. The difference between CAT5 and CAT5e lies in specifications and other performance requirements. It can be used for Gigabit network installation as well as in all newer network installations. The length is 300 meters as against 100 meters in CAT5. Similar to CAT5, CAT5e is a 100 MHz standard, but can handle bandwidth superior to that of CAT5. 

Besides the backbone, think about different segments on your network. How much traffic are they generating? Is it that though the traffic is evenly spread out across all segments, users in some segments are still experiencing slow performance?

Considering that the hardware and software is similar across all segments, the fault can be with the cabling in that segment. 
Smart network administrators always keep some headroom for the addition of some users to the network. If this exercise is done properly, then the network bottlenecks in the organization can be reduced multifold. But you will still need to examine the network to find out how this increase in the number of users has affected network performance. 

Uneven expansion
Some organizations grow organically and others haphazardly. This uneven growth can also take a toll on the network, making it vulnerable to crashes. The network administrator should always keep an eye on the network when network expansion is in progress. They should make sure that the cables of the same kind as well of the same speed are being used while upgradation. If that has not happened then analyzing the network becomes imperative. 

Analysis
There are several things to be analyzed in a cable, and there are different types of cable-testing tools available for the purpose. You’ll find everything from simple LED display testers to indicate an open or a short in a UTP cable to high-end testers that can measure NEXT (Near End Cross Talk) and impedance. Before moving ahead with the tools, it’s important to have a basic understanding of what to analyze in your structured cabling. 

CAT6

The major improvement in Cat6 over Cat5e is an increase in bandwidth from 100 MHz to up to 250 MHz allowing it to run more bandwidth consuming applications. CAT6 has higher signal-to-noise-ratio thus reducing the number of errors and increasing reliability, making it a better choice for Gigabit Ethernet networks. Apart from higher specifications, it has backward compatibility with 5, 5e and 3 cables, and jack interoperability for modular RJ-45 connectors. It supports double the bandwidth of CAT5e with Power Sum Attenuation to Cross Talk Ratio (PSACR) up to 200 MHz.
The quality of the data transmission depends upon the performance of the components of the channel. To transmit in accordance with the CAT6 specifications, jacks, patch cables, patch panels, cross-connects, and cabling must all meet CAT6 standards. If different category components are used with CAT6 components, then the channel will achieve the transmission performance of the lower category. For instance, if CAT6 cable is used with CAT5e jacks, the channel will perform at a CAT5e level.

The basic test to be carried out in a structured cabling layout is a wiremap test. This is done to identify errors in wiring installation. It tests and verifies end-to-end, pin-to-pin connectivity for a UTP cable. It can detect any kind of miswires, breaks, opens, shorts, crossovers or splits in cabling. Any structured cabling vendor can do it and give you a complete report of the it. 

While the wiremap gives you an idea of the accuracy of your cabling, it doesn’t tell you anything about its performance. This becomes extremely important when laying out Cat 5e or Cat 6 cabling for gigabit or 100 Mbps Ethernet. Improper cabling can drastically affect the performance of a Gigabit Ethernet network. 

The most important aspect to measure in judging cabling performance is NEXT. This occurs when signals from one pair in a UTP cable are picked up by another pair in the vicinity. It can increase with frequency, and can only be minimized by using tightly twisted pairs using proper insulation that conform to EIA/TIA cabling specifications. There are other attributes to measure in a cable like attenuation and cable length accuracy. Some of the tools required to measure these are so expensive that an organization may not want to purchase them. Instead, you may just get a structured cabling expert to use them on your infrastructure and give you useful insights about it. We discuss some of these tools here.

Cabling testers and analyzers 
These are hardware equipment used to analyze the cabling on a network. They can also be used to test network performance using IP across the network backbone. Some of the things that a LAN analyzer can determine are cable length, open connections, crossed wires, unused network connections, collisions, errors and broadcasts.

Fluke Networks manufactures many of these hardware handheld analyzers. For example, Etherscope Network Assistant is the latest solution that can help a network administrator in diagnosing Gigabit network problems. It has a full color touch-screen display and allows users to clearly monitor key devices and identify vital network statistics including protocol mix, top senders, top broadcasters and error sources. Its specific network monitoring capabilities include identifying length,
shorts, opens, cross-over cables, miswires and split pairs. 

DTX-1800 is another cable-testing and certification tool. It is capable of testing Wiremap, Length, Propagation Delay, Delay Skew, DC Loop Resistance, Insertion Loss (Attenuation), Return Loss (RL), NEXT, Attenuation-to-cross talk Ratio (ACR) and ELFEXT. But all this power of analyzing comes at a cost, with a suggested price of about $ 8500.

CAT7

Though some vendors are marketing variants of the proposed Cat7 wires, the standard is still in nascent stage. The major difference between Cat7 and the previous versions (Cat 5, 5E, 6) is that in Cat7 cables all four pairs are individually shielded plus there’s an overall shielding around all four pairs. As per the standards, the CAT7 will do away with the RJ-45 connector and use a brand new connector instead. Also Cat7 cables would have enhanced performance with speeds up to 10 Gbps.

You can get in touch with NETPLACE, Mumbai (Tel: 23893931. E-mail: netplace@vsnl.com) for other products available
from Fluke Networks that can help you in analyzing your structured cabling infrastructure.

OTDR (Optical Time Domain Reflectometer)
Similar to LAN analyzers, OTDRs are hardware instruments used to determine the light loss in an optical fiber network. It throws a sharp beam into the network and measures its reflection as well as backscatter, which helps locate the fault while troubleshooting a fiber optic network. 

Cable Comparison

Parameter/Types CAT5 CAT5e CAT6 CAT7
Frequency
(MHz)
1-100 1-100 1-250 1-600
Attenuation
(dB)
24 24 21.7 20.8
NEXT
(dB)
27.1 30.1 39.9 62.1
Power-sum
NEXT (dB)
NA 27.1 37.1 59.1
ACR
(dB)
3.1 6.1 18.2 41.3
ELFEXT
(dB)
17 17.4 23.2 NA
Power-sum
ELFEXT (dB)
NA 20.8 24.8 NA
Propagation
delay (ns)
548 548 548 504
Delay
skew (ns)
50 50 50 20
Characteristic
Impedence (ohms)
100 100 100 NA
Return
Loss (dB)
16 20.1 20.1 NA

SNMP software
This is a cable-testing software. Many structured cabling vendors use SNMP-based software to suit their equipment. It provides useful insights about structured cabling through a Web browser. 

Whichever may be the software, in this case, it all boils down to the knowledge of your network administrator and his ability to manage the network and keep it error free.

With inputs from Vikas Pinjarkar, D-Link India, Venkatesh Babu, Systimax, and
Ankit Kawatra and Sudarshana Mishra, CyberMedia Labs

Q&A




When to shift from CAT5 to CAT6?
It is better to install the best cabling available so that it will last at least for the next 7 to 8 years and will be able to support all the upgrades in terms of increase in the number of machines supported by the network and the increasing bandwidth demand of various applications. Since category 6 link and channel requirements are backward compatible with category 5e makes, it very easy to choose CAT6 over CAT5e. Applications that worked over category 5e also work over category 6. Because of its improved transmission performance and superior immunity from external noise, systems operating over CAT6 cabling encounter fewer errors when compared with CAT5e. This means fewer re-transmissions of lost or corrupted data packets that gives higher reliability for CAT6 networks compared to CAT5e networks. Remember however that installing Cat 6 cabling is a more delicate process than for Cat 5e. Plus, the cost of cabling and the installation could also be much higher. 

Can I make my own patch cords?
It is preferable to have factory assembled patch cords rather than field-assembled ones. Patch cords are precision products, just like the cables and the connectors. They are best manufactured and tested in a controlled environment to ensure consistent, reliable performance. This is necessary to ensure interoperability and backward compatibility.

Can I skip CAT 6 and go straight for optical fiber?
Fiber optic cables are still very expensive. These days optical fiber together with optical transceivers cost about twice as much as an equivalent system built using category 6 and associated copper electronics. Moreover the installation of copper cabling such as CAT6 is simpler as compared to fiber.

Can I mix brands of cabling equipment? 
There are set standards in some areas of network equipment manufacturing such as performance requirements and jack configuration, but there are many aspects of network device design that are not yet standardized. So it is recommended that you don’t mix and match different manufacturers’ hardware. Installers generally prefer to use network products that are easy to install and reliable.

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