Categorize standard media types and associated properties. This chapter describes fiber and copper media type characteristics, including media converters, distance and speed limitations, and related technologies. Learn more in our CompTIA Network+ video course.
Fiber Media Network Cabling
When using fiber connectivity within a network infrastructure, the digital signals sent by network devices are converted into light beams, sent across the fiber link, and converted back into digital signals on the other side. One of the major advantages of using this approach instead of other technologies (e.g., RF signals) is that nobody can easily tap into that connection without being noticed. However, if this does happen, the intruder can be easily identified by monitoring systems because the signal will drop significantly. The major advantages of using fiber cabling include the following:
- It offers high transfer rates (more than 10Gbps)
- It operates over long distances (up to 100 km)
- It is immune to radio interference
Fiber signals experience very slow degradation, so fiber connections can be used over very long distances, unlike copper connectivity. Fiber cabling is also immune to radio interference that can come from microwaves, wireless networks, mobile phones, or other devices (because light signals do not interfere with radio signals). For these reasons, fiber cabling is recommended in industrial environments that are electrically noisy.
Fiber connections can operate based on two technologies:
- Multi-mode fiber
- Single-mode fiber
| Note: There is a direct compatibility requirement between the type of fiber used and the type of device interface/transceiver in which you plug the fiber. You cannot use single-mode fibers with multi-mode transceivers or multi-mode fibers with single-mode transceivers. |
Multi-mode fiber technology involves the light beam travelling across multiple paths inside the fiber, bouncing off the fiber walls, as presented in Figure 14.1 below. This technology is called multi-mode because the light beam can travel in “multiple modes” across the cable.
Figure 14.1 – Multi-Mode Fiber
Multi-mode fiber is often used for communication over short distances, either inside a building or outside if the distance is less than 2 km. If you try to use it on longer distances, you will experience signal degradation because of the light beams that bounce off the fiber walls. Because the light does not have to travel over very long distances, multi-mode fiber connections can use inexpensive light sources based on LED technologies, unlike the case with single-mode fibers. Using inexpensive components allows you to keep the cost down for multi-mode fiber infrastructures.
While multi-mode fiber allows the light to travel on multiple paths, the main characteristic of single-mode fiber is that it offers a single light path across the fiber, as shown in Figure 14.2 below:
Figure 14.2 – Single-Mode Fiber
When using a single-mode fiber, the light follows a direct path (a “single mode”) to the destination, without the light beam bouncing off the cable walls like in the case with multi-mode fiber. Single-mode fiber is generally used for communications over very long distances (up to 100 km). Communication can even exceed 100 km, but in that case you would have to use special devices to regenerate the signal.
The light source in single-mode fiber is more expensive than in the case of multi-mode fiber because laser beams are used instead of LED sources. Laser beams offer a very strong light that can reach the other side of the cable, even over long distances, without major attenuation. Because of this, equipment using single-mode fiber will be a lot more expensive than equipment using multi-mode fiber. In addition, the actual single-mode fiber cables are more expensive than multi-mode fiber cables because the core of the fiber must be manufactured with different technologies in order to be very thin. For this reason, single-mode fiber is generally used only in special cases and not over short distances.
Copper Media Network Cabling
Cabling is a critical part of the network infrastructure, so you have to make sure that you are using exactly the right types of cable based on your requirements. When building a new infrastructure, you should be 100% sure that you are using the correct type of cable because choosing the wrong cable would be very costly (i.e., you would have to completely re-cable the infrastructure).
Network cabling is used to connect backbone devices, even in the case of wireless infrastructures. At some point every network needs some kind of cabling installation.
There are a variety of copper cable types that can be used in network infrastructures:
- Coaxial
- Twisted-pair (UTP and STP)
Coaxial Cable
Coaxial cables use a single thick copper conductor running through the middle of the cable, as shown in Figure 14.3 below:
Figure 14.3 – Coaxial Cable
Coaxial cables were used for a long time in these older Ethernet network types:
- 10Base5 (Thicknet: RG-8/U)
- 10Base2 (Thinnet: RG-58)
These days coaxial cable is still used on cable television systems but rarely in network environments. Some providers are also able to send broadband Internet signals over the coaxial cable along with the TV signals. This technology is still used in some parts of the world for home-user Internet connections.
The components of a coaxial cable are as follows (starting inside, from the inside layer):
- The wire conductor: placed in the middle of the cable
- The insulator shield around the conductor: prevents the conductor from being affected by interference
- The metal shield around the insulator: offers protection from damage, as coaxial cables are often used in industrial environments
- The plastic jacket around the metal shield: also for protective purposes, as coaxial cables can be used outside in open environments
Twisted-Pair Cable
Twisted-pair cable is a type of copper cable commonly used in modern network cabling systems. It contains four pairs of twisted wires (each pair consists of a full colored wire and an intermittent white wire) encased inside a plastic shield, as shown in Figure 14.4 below:
Figure 14.4 – Twisted-Pair Cable (UTP)
This type of cable uses a balanced pair operation, meaning each wire from a pair carries an equal and opposite set of signals. These pairs can be Transmit+/Transmit- or Receive+/Receive-. The main advantage of using this internal cable design is that the twisted-pairs that carry the opposite signals help cancel signal interference. When the signal reaches the other end, the receiver compares what it sees over both wires in a pair and extracts a “clean” signal.
Even within the same cable, each pair has a different twist rate, as can be seen in Figure 14.4 above (the brown pair has the lowest twist rate). This assures minimal interference between wire pairs within the same cable.
There are two different types of twisted-pair cables:
- Unshielded Twisted-Pair (UTP)
- Shielded Twisted-Pair (STP)
The UTP cable is a common cable type that offers no additional shielding. It is the least expensive twisted-pair type of cable and it is used in regular network infrastructures that do not need to be protected from external interference.
The STP cable comes with an additional interference protection layer in the form of a metal shielding that wraps around each one of the four cable pairs. The metal shielding has to be grounded at both sides of the cable to be effective. An example of an STP cable is shown in Figure 14.5 below:
Figure 14.5 – STP Cable
STP cables are generally used in industrial environments where other signals can interfere with the transmission. This type of cable is generally more expensive than UTP cables.
Cable Categories
As networking became more popular and companies began to build their own data centers, it became apparent that network cabling standardization was required. The standardization process consists of a wiring setup that allows different amounts of traffic to be carried, ranging from 10Mbps to 10Gbps and more. Each of these bandwidths can be achieved using a certain type of cable that fulfills some specific criteria.
One of the organizations involved in creating such standards is the Electronic Industries Alliance (EIA), which is an alliance of trade associations that develops standards for the computing industry. Another organization that is involved with cabling standards is the Telecommunications Industry Association (TIA). TIA handles standards but they also do market analysis, trade shows, and other events. An important cabling standard used in enterprise networks is ANSI/TIA/EIA-568, the Commercial Building Telecommunications Cabling Standard.
Standardized copper cabling involves the existence of different cabling categories. Each one of these has a certain standard associated with it:
- Category 3 (10Mbps Ethernet)
- Category 5 (100Mbps Ethernet)
- Category 5e (1Gbps Ethernet)
- Category 6 (10Gbps Ethernet over 55 m)
- Category 6a (10Gbps Ethernet over 100 m)
Category 3 was one of the first standardized categories and was designed to support 10Mbps Ethernet and 4Mbps Token Ring. Even though this was used on a large scale, enterprises needed more bandwidth after a short time and this led to the development of Category 5, which supported 100Mbps Ethernet connectivity. This upgrade happened at the same time FastEthernet connections were extended to desktops, with the evolution of network interface cards.
As networks got faster and there was a need for Gigabit Ethernet, Category 5e (Category 5 Enhanced) was standardized, which offered 1Gbps Ethernet connectivity. In order to achieve such a high transmission rate, Category 5e involved tighter specifications for both the cable and the connectors.
Category 6 allows 10Gbps Ethernet connectivity over copper on distances up to 55 meters. There is an even more advanced standard that allows 10Gbps Ethernet connectivity on distances over 100 meters if strict cable and connector conditions are met.
UTP Cable Connectivity Types
There are two cable types that can connect a UTP cable to the two connectors:
- Straight-through cables
- Crossover cables
For each of these cable types, there are two standards:
- TIA/EIA-568A
- TIA/EIA-568B
The UTP cable types are shown in Figure 14.6 below:
Figure 14.6 – UTP Cable Types
| Note: The difference between the TIA/EIA-568A and the TIA/EIA-568B standards is the 1/2 and 3/6 pair colors, which are inversed (first pair is green for TIA/EIA-568A and orange for TIA/EIA-568B). Based on the country you are in, you might have to use one of these two standards. 1/2 are green on TIA/EIA-568A whereas they are yellow on TIA/EIA-568B. |
Straight-through cables are often referred to as patch cables and they are the most common Ethernet cable type used in Ethernet environments. They are used to connect workstations (laptops or desktops) directly to Ethernet sockets, patch panels, or network devices (switches). If you look at Figure 14.6 above, you can see that the straight-through cable wires match the connector pins at both ends (i.e., the wire connected on one side of a pin connects to the other side of the same pin).
Network devices usually have one of the following two network interface types:
- Media Dependent Interface (MDI): usually used on workstation NICs
- Media Dependent Interface Crossover (MDIX): usually used on network switches
Straight-trough cables are generally used between MDI and MDIX; in other words, between workstations and switches. With a straight-through cable, the Transmit interface pins on one side connect to the Receive interface pins on the other side, and vice versa, as illustrated in Figure 14.6 above (MDI on the left side and MDIX on the right side of each picture). The connections are as follows:
- Transmit+ connects to Receive +
- Transmit- connects to Receive –
- Receive+ connects to Transmit+
- Receive- connects to Transmit-
On an MDI device the Transmit pins are 1 and 2 and the Receive pins are 3 and 6. On an MDIX device this is the other way around: the Transmit pins are 3 and 6 and the Receive pins are 1 and 2. This follows the normal communication principle that states a device is receiving what the other device is transmitting. You must use a straight-through cable when you have an MDI device connected to an MDIX device.
| Note: In a straight-through cable, pins 4, 5, 7, and 8 are not used so they might or might not be connected to the corresponding wires. |
When connecting a workstation to a workstation (MDI to MDI) or a network device/switch to another network device/switch (MDIX to MDIX), you must use a crossover cable because the transmit pins are 1 and 2 on both sides, and you cannot use a direct connection between them (i.e., a straight-through cable). A visual representation of a crossover cable connection can be seen in Figure 14.6 above. Basically, a crossover cable is a straight-through cable that inverses the 1/2 pair with the 3/6 pair (pin 1 connects to pin 3 and pin 2 connects to pin 6).
Modern network devices don’t necessarily require a crossover cable because they are smart enough to detect a cable misconfiguration and inverse their network interface Transmit and Receive pins (i.e., it performs the crossover function within the network interface card). This feature is called Auto-MDIX and it allows network devices to be connected with either a straight-through or crossover cable.
T1 is another type of connection that uses crossover cables. When connecting a T1 Channel Service Unit/Data Service Unit (CSU/DSU) to a router or other device, you can use a straight-through cable, but when connecting a T1 CSU/DSU to another T1 CSU/DSU, you should use a crossover cable. T1 uses different pairs to communicate, so with a T1 crossover cable you must connect pins 1/2 on one end (Transmit) to pins 4/5 on the other end (Receive), meaning pin 1 on one side must be connected to pin 4 on the other side and pin 2 on one side must be connected to pin 5 on the other side.
Plenum versus Non-Plenum Network Cabling
Office buildings usually have fake ceilings that connect every working space in the campus. This fake ceiling offers space for a variety of uses:
- Air conditioning system
- Different types of pipes
- Network cabling channels
The area above the fake ceiling is called a plenum if it offers air flow through it. On the other hand, a non-plenum area is one that contains air-supply-dedicated pipes that connect to the working space below so the air does not flow freely above the fake ceiling (i.e., it’s a non-circulating air space).
| Note: A special situation is having dedicated pipes for air going into the working space but using free air flow for air coming in from the working space, thus creating a plenum. |
The plenum area becomes very important in the case of a fire because it can make the fire worse by feeding it oxygen in the open space above the fake ceiling. In those environments you have to be very careful about the type of network cabling you use on top of the fake ceiling, as the cables may be affected by a fire and can even act as a facilitator for fire to reach other building areas. To avoid such potential disasters, you need to use a special type of cable in plenum areas. A plenum-rated cable looks just like a standard UTP cable but it has some differences:
- The outer protection jacket, which is usually made of special materials like PVC or FEP, is more resistant to fire
- It is not as flexible as regular cables because of the outer jacket material
Media Convertors
Depending on network specifics, you might need to connect a fiber cable to a copper interface or a copper cable to a fiber interface. An example of this would be an ISP connection offered over an optical fiber that needs to be plugged in to a copper-based router. There are generally three options to solve these situations:
- Change the network device to one that is compatible with the interface
- Change the cable to one that is compatible with the connector type
- Use a media convertor
The preferred method is using a media convertor because the first two options presented above are generally very expensive and time consuming. Media conversion happens at Layer 1 by taking the signals specific to a certain technology (copper or fiber optics) and translating them to signals specific to the other category using special electronic circuits.
A common use of this might be the need to extend a copper cable that can only go up to 100 meters. In order to send the signal over longer distances, you can convert the signal to fiber and then re-convert it to copper at the other end. This is completely transparent for the devices on both ends because the conversion is being done at Layer 1.
Figure 14.7 – Media Converter
A standard media converter is depicted in Figure 14.7 above; it has a single fiber port and a single copper port for translating purposes. Media converters exist in many sizes and can even be found in rack-mountable form, which is able to translate a large number of connections.
The copper-to-fiber and fiber-to-copper conversions need to be performed electronically, which means that the media converter must be plugged into a power source in order to operate. This information is useful during a connectivity issue troubleshooting process, as you might need to verify that the media converter is up and running.
| Note: A special case of a media converter that does not need to be connected to a power source is one that converts multi-mode fiber to single-mode fiber, or vice versa. In this case the converter uses a passive mirror-based technology to switch between the two media types. |
Depending on the type of fiber used, you need a compatible media converter. The most common situations that would require a media converter include the following:
- Multi-mode fiber to copper
- Single-mode fiber to copper
- Copper to multi-mode fiber
- Copper to single-mode fiber
- Single-mode fiber to multi-mode fiber
- Multi-mode fiber to single-mode fiber
- Fiber to coaxial
Distance and Speed Limitations
When working with networking media, one of the things you have to keep in mind is that the copper and the fiber you are using can only be used over a certain distance, depending on associated speeds and frequencies, as shown in Table 14.1 below. Even though coaxial cable is not really used in modern networks, you should be aware of its limitations because you might find some coaxial cables in legacy network environments.
Table 14.1 – Coaxial Cable Characteristics
| Type | Standard | Speed | Distance |
| Thicknet | 10Base5 | 10Mbps | 500 m |
| Thinnet | 10Base2 | 10Mbps | 185 m |
You can see that coaxial cables can function over large distances because they offer a lot of protection against interference.
With twisted-pair cabling there are a number of categories that offer different speeds and distances, as shown in Table 14.2 below:
Table 14.2 – Twisted-Pair Cable Characteristics
| Category | Standard | Speed | Distance |
| Category 3 | 10BaseT | 10Mbps | 100 m |
| Category 5 | 100BaseTX | 100Mbps | 100 m |
| Category 5e | 1000BaseT | 1Gbps | 100 m |
| Category 6 (1Gbps) | 100BaseT | 1Gbps | 100 m |
| Category 6 (10Gbps) | 10GBaseT | 10Gbps | 55 m |
| Category 6a | 10GBaseT | 10Gbps | 100 m |
The standards for fiber types differ based on the type of signal used, as shown in Table 14.3 below:
Table 14.3 – Fiber Characteristics
| Fiber Type | Standard | Speed | Distance |
| Multi-mode | 100BaseFX | 100Mbps | 2 km |
| Multi-mode | 1000BaseSX | 1Gbps | 200 to550 m |
| Multi-mode | 10GBaseSR | 10Gbps | 300 m |
| Single-mode | 1000BaseLX | 1Gbps | 2 km |
| Single-mode | 10GBaseLR | 10Gbps | 10 km |
Broadband over Powerline
Broadband over Powerline (BPL) is a relatively new standard that aims to take advantage of the fact that every building is connected to a power system. BPL uses power cables to transmit radio signals that can be interpreted by network devices. The IEEE standard for BPL is IEEE 1901 and it is based on a standard called Homeplug AV.
This technology can be used in remote locations that don’t have other kinds of infrastructures to provide Internet connectivity. Another use for BPL is home automation, where it can control electronic devices in the house (e.g., lights, temperature, alarm system, etc.) from a remote location.
An important thing to consider is that BPL uses radio signals, so depending on the frequencies used, BPL communication might be susceptible to interference.
BPL can run at the following speeds:
- Low speed with a narrow bandwidth (15 to 500 kHz); usually used by utility providers that need to read home meters from outside
- Medium speed with a bandwidth up to 576Kbps ( 9 to 500 kHz)
Summary
When using fiber connectivity within the network infrastructure, the digital signals sent by network devices are converted into light beams, sent across the fiber link, and converted back into digital signals on the other side. The major advantages of using fiber cabling include the following:
- It offers high transfer rates (more than 10Gbps)
- It operates over long distances (up to 100 km)
- It is immune to radio interference
There are a variety of copper cable types that can be used in network infrastructures:
- Coaxial
- Twisted-pair (UTP and STP)
Standardized copper cabling involves the existence of different cabling categories. Each one of these has a certain standard associated with it:
- Category 3 (10Mbps Ethernet)
- Category 5 (100Mbps Ethernet)
- Category 5e (1Gbps Ethernet)
- Category 6 (10Gbps Ethernet over 55 m)
- Category 6a (10Gbps Ethernet over 100 m)
There are two cable types that can connect a UTP cable to the two connectors:
- Straight-through cables
- Crossover cables
For each of these cable types, there are two standards:
- TIA/EIA-568A
- TIA/EIA-568B
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