Administrators must have solid knowledge of the logical standards and the physical media used on today’s networks.
Logical standards define the characteristics such as the configuration of the network, the speed at which they operate and how devices access the network.
Physical media refers to the cabling and connectors used to create the network.
The above two define and dictate the maximum distance between devices, the capability of media to withstand outside interference and even how much space is required in wiring closets and equipment cabinets. Choosing the correct media is very important because they form the foundation for the entire network.
When working with any media, you must be aware of the factors that influence its suitability for a given network implementation.
Interference, transmission speed, media length and installation and repair are some of the most common factors that affect media.
Media Interference (EMI) – common sources of EMI (electromagnetic Interference) are:
- Computer Monitors.
- Fluorescent light fixtures.
- Basically anything that creates an electromagnetic field.
Some types of media are more affected by EMI than others, like for example copper-based media are more affected by EMI and thus they’re coated with layers of shielding to reduce the interference, while fiber-optic cables are not affected by EMI. Another form of interference is something that’s called crosstalk, which occurs when signals from two cables or wires in close proximity to one another interfere with each other. As a result, the signals on both cables get corrupted. EMI and crosstalk are sometimes the cause of intermittent network problems. Intermittent is a term given to describe a problem that occurs on electronic equipment every so often at short intervals, thus they’re difficult to recreate by the engineer. So when something like this happens it’s worth checking the cabling for EMI or crosstalk.
Data Transmission Rate – another important factor is the transmission rate or speed. Different media types are rated to support different maximum speeds. Whether they’re used to their maximum speed or not depend on the networking standards used and the network device connected. These rates or speeds are measured in bits per seconds a 100 Mbits/s or 100Mbps means 100 million bits that can traverse the media in one second.
Media Length – each media type has a certain max length that it can be used to reliably transmit or receive data, going over this maximum length can cause problems that can be as bad as failure to transmit or receive data because as the signal traverses the wire it gets weaker until it drops. This weakening is called attenuation. The shielding some media such as copper cables have protects it from interference and thus as a result of that the distance the signal can travel increases. Another way that can be used to increase the distance a signal can travel is to use a switch, router, repeater or a hub, which will reproduce the signal; in another words it will amplify the signal to its original strength. Fiber-optic cables do not suffer from attenuation; however they do suffer from something called chromatic dispersion. This is however different from attenuation; the end result is still the same because the longer the distance the light travels the weaker it gets to the extent that it becomes unusable.
1.1 Secure Transmission and Physical Media
When it comes to security physical media (wired) provide some level of security because for someone to tap into the line they need to have physical access to the media to tap into the cable. Fiber-optic is more secure than copper-based media because of the light transmissions and glass or plastic construction make it particularly hard to tap into. Wireless security is another topic of its own and produced another challenge for administrators.
1.1.1 Installation and Repair
Some network media are easier to manage and install than others. This might seem like a minor consideration, but in real-world applications, it can be important. For example, fiber-optic cable is far more complex to install and troubleshoot than twisted-pair. It’s so complicated that special tools and training are often needed to install a fiber-optic-based network. It is important to be aware of what you are in for when it’s time to implement or repair the network media.
1.1.2 Simplex, Half-Duplex and Full-Duplex
Simplex enables only one-way communication over the media such as a car radio. There is only one transmitting device and all other devices are receiving devices.
Half-Duplex enables each device to both send and receive, but only one of these processes can occur at one time.
Full-Duplex is the most preferred method to use on networks, it enables devices to send and receive simultaneously. This method can also increase the transmission rate of network media. Like for example if we have a 100Mbps network interface car (NIC) connected at full-duplex, its rate can be doubled to 200Mbps.
1.1.3 Cable Media
Network media is divided into two distinct categories: cable and wireless. Cable media come in three common types: twisted-pair, coaxial and fiber-optic.
The materials used to construct cable media include:
- Metal (normally copper) – Copper-based cable is widely used to connect LANs and wide area networks (WANs).
- Glass or plastic – Optical cable, which uses glass or plastic, is mainly used for large-scale network implementations or over long distances.
Twisted-Pair Cable – inexpensive, easy to work with and is well suited for modern networks. It comes in two types unshielded twisted-pair (UTP) and shielded twisted-pair (STP). UTP is far the most commonly used for both telephone and computer networks. STP has extra shielding, which makes it cope against interference better than UTP and the signal can travel for longer. Although it is better than UTP it’s also more expensive. The Electric Industries Association/Telecommunications Industries Association (EIA/TIA) specified certain categories for these cables.
The following lists the different categories of twisted-pair cables:
- Category 1 – Voice-grade UTP telephone cable. Because of its susceptibility to interference and attenuation and its low bandwidth capability, Category 1 UTP is not practical for network applications.
- Category 2 – Data-grade cable capable of transmitting data up to 4Mbps. Category 2 cable is too slow for networks. It is unlikely that you will encounter Category 2 used on any network today.
- Category 3 – Data-grade cable capable of transmitting data up to 10Mbps with a possible bandwidth of 16MHz. Years ago, Category 3 was the cable of choice for twisted-pair networks. As network speeds pushed the 100Mbps speed limit, Category 3 became ineffective.
- Category 4 – Data-grade cable that has potential data throughput of 16Mbps. Category 4 cable was often implemented in the IBM Token Ring networks. Category 4 cable is no longer used.
- Category 5 – Data-grade was typically used with Fast Ethernet operating at 100Mbps with a transmission range of 100 meters. Although Category 5 was a popular media type, the cable is an outdated standard with newer implementations using the 5e standard. Category 5, despite being used primarily for 10/100 Ethernet networking, can go faster. The IEEE 802.11ae standard specifies 1000Mbps over Category 5 cable. More on IEEE standards can be found in Chapter 6, “Ethernet Networking Standards.”
- Category 5e – Data-grade cable used on networks that run at 10/100 Mbps and even theoretically specifies 1000Mbps depending on the implementation. However, actual speeds would likely be a lot less. Category 5e cabling can be used up to 100 meters, depending on the network and standard used. Category 5e cable provides a minimum of 100MHz of bandwidth.
- Category 6 – High-performance UTP cable capable of transmitting data up to 10Gbps. Category 6 has a minimum of 250MHz of bandwidth and specifies cable distances up to 100 meter cable length with 10/100/1000Mbps transfer, along with 10Gbps over shorter distances. Category 6 cable is typically made up of four twisted-pairs of copper wire, but its capabilities far exceed those of other cable types. Category 6 twisted-pair use a longitudinal separator, which separates each of the four pairs of wires from each other. This extra construction significantly reduces the amount of cross talk in the cable and enables for the faster transfer rates.
- Category 6a – Category 6a (augmented 6) offers improvements over Category 6 by offering a minimum of 500MHz of bandwidth. It specifies transmission distances up to 100 meters and is used with 10Gbps networking standards such as 10Gbase-T.
A note to be made here, when we talk about the data rate of a cable, that doesn’t mean they have speed. It basically means the cable can support that speed.