The cables used for computer networks fall into three main categories: Coaxial, Twisted Pair, and Fiber Optic. Each of the cable types has its own merits and demerits in terms of their cost, installation, maintenance, and susceptibility to interferences. Coaxial cables are rarely used these days because of the vast popularity gained by twisted pair cables. The following sections discuss each of the cable types.
(i) Coaxial cable
A coaxial cable consist of a stiff copper wire as core surrounded by an insulating material. The insulator is encased by a cylindrical conductor. The outer conductor is covered by a protective plastic sheath. The signal is transmitted by the inner copper wire and is eclectically shielded by the outer metal sleeve. It can be used both analog and digital transmission. It is expensive as compare to fiber optic cable and easy to handle.
(i) Coaxial cable
A coaxial cable consist of a stiff copper wire as core surrounded by an insulating material. The insulator is encased by a cylindrical conductor. The outer conductor is covered by a protective plastic sheath. The signal is transmitted by the inner copper wire and is eclectically shielded by the outer metal sleeve. It can be used both analog and digital transmission. It is expensive as compare to fiber optic cable and easy to handle.
Coaxial cables are mainly used for carrying television signals (for example, CATV), but some older computer networks based on the 10Base2 standard also utilized these cables for connecting workstations and other network devices. Usually the coaxial cables used for different purposes have different characteristics; cables for one purpose cannot be used for another. For example, the cable used for CATV cannot be used for computer networks. Figure shows a piece of coaxial cable.
Coaxial cable networks are easy to install and low in cost. The downside is that they are prone to degradation of signals as they travel long distances. This degradation is called attenuation. They can also break easily and cause network downtime. Coaxial cables fall mainly into the following two categories:
Thin coaxial cable
Also known as Thin net. The type of thin coaxial cable used for computer networks is RG-58, which has 50-Ohm resistance. Network segments using this cable are used with 50-Ohm terminators and devices are connected using 50-Ohm BNC-T connectors. The RG-6 type coaxial has 75-Ohm resistance and is used for CATV and cable modem.
Thick coaxial cable
Also known as Thick net. The type of thick coaxial cable used for computer networks is RG-8. As the name suggests, this cable is about twice as thick in diameter as thin coaxial cable. These cables use vampire taps, which cut through the cable to provide connectivity to network devices. Vampire Taps use transceivers with a 15-pin AUI connector. Thick coaxial cables also use 50-Ohm terminators on both ends of the network segment.
Two kinds of coaxial cable are widely used.
(i) 50-Ohm ( Base band coaxial cable)
(ii) 75-Ohm ( Broadband coaxial cable)
(i) 50-Ohm ( Base band coaxial cable)
50-Ohm cable is commonly used for digital transmission. For 1 km cables, a data rate of 1 to 2 Gbps is feasible. Longer cables cab also be used, but only at lower data rates or with periodic amplifiers. Baseband networks are the network where the entire bandwidth of the cable is utilized for a single channel.
(ii) 75-Ohm (Broadband coaxial cable)
75-Ohm cable is commonly used for analog transmission in cable TV transmission. Broadband situation, where the coaxial cable’s bandwidth is separated into sub channels of either equal or varying frequency ranges that can be treated as separate communication media.
Thin coaxial cable
Also known as Thin net. The type of thin coaxial cable used for computer networks is RG-58, which has 50-Ohm resistance. Network segments using this cable are used with 50-Ohm terminators and devices are connected using 50-Ohm BNC-T connectors. The RG-6 type coaxial has 75-Ohm resistance and is used for CATV and cable modem.
Thick coaxial cable
Also known as Thick net. The type of thick coaxial cable used for computer networks is RG-8. As the name suggests, this cable is about twice as thick in diameter as thin coaxial cable. These cables use vampire taps, which cut through the cable to provide connectivity to network devices. Vampire Taps use transceivers with a 15-pin AUI connector. Thick coaxial cables also use 50-Ohm terminators on both ends of the network segment.
Two kinds of coaxial cable are widely used.
(i) 50-Ohm ( Base band coaxial cable)
(ii) 75-Ohm ( Broadband coaxial cable)
(i) 50-Ohm ( Base band coaxial cable)
50-Ohm cable is commonly used for digital transmission. For 1 km cables, a data rate of 1 to 2 Gbps is feasible. Longer cables cab also be used, but only at lower data rates or with periodic amplifiers. Baseband networks are the network where the entire bandwidth of the cable is utilized for a single channel.
(ii) 75-Ohm (Broadband coaxial cable)
75-Ohm cable is commonly used for analog transmission in cable TV transmission. Broadband situation, where the coaxial cable’s bandwidth is separated into sub channels of either equal or varying frequency ranges that can be treated as separate communication media.
Since, broadband networks use standard cable television technology, the cables can be used up to 300 MHz and can run for nearly 100 km due to the analog signaling, which is much less critical than digital signaling.
Coaxial cable is difficult to connect to network devices and generally requires more planning than does twisted-pair system. Many coaxial cable systems require the connectors on the main cable to be attached directly to the adapter on the PCs.
Installation
Coaxial cable is difficult to installed in tow configuration: daisy-chain(from device-to-device—Ethernet) and star(ARCnet).
Advantages of Coaxial Cable:
(i) It has better shielded against electromagnetic interference than twisted-pair cable, so it can span longer distance at higher data bps.
(ii) It can be used for both analog and digital data transmissions.
(iii) Coaxial cable has higher bandwidth and excellent noise immunity.
(iv) It is inexpensive as compared to fiber optic cable and easy to handle.
Installation
Coaxial cable is difficult to installed in tow configuration: daisy-chain(from device-to-device—Ethernet) and star(ARCnet).
Advantages of Coaxial Cable:
(i) It has better shielded against electromagnetic interference than twisted-pair cable, so it can span longer distance at higher data bps.
(ii) It can be used for both analog and digital data transmissions.
(iii) Coaxial cable has higher bandwidth and excellent noise immunity.
(iv) It is inexpensive as compared to fiber optic cable and easy to handle.
(ii) Twisted pair cables
Twisted pair cables have replaced coaxial cables in most computer networks. These cables use twisted pairs of insulated cables bundled inside a plastic sheath. The twists in cables are used to prevent electromagnetic interference, which results in crosstalk, among cables. Twisted pair cables are easy to install, lower in cost than coaxial and fiber optic cables, and can achieve greater data transmission speeds than coaxial cables. These cables are usually identified by their category numbers. The category number indicates the number of cable pairs and the purpose for which they can be used. These category numbers are denoted as CAT-1, CAT-2, CAT-3, CAT-5, etc. Figure shows a piece of twisted pair cable.
Twisted pair cables have replaced coaxial cables in most computer networks. These cables use twisted pairs of insulated cables bundled inside a plastic sheath. The twists in cables are used to prevent electromagnetic interference, which results in crosstalk, among cables. Twisted pair cables are easy to install, lower in cost than coaxial and fiber optic cables, and can achieve greater data transmission speeds than coaxial cables. These cables are usually identified by their category numbers. The category number indicates the number of cable pairs and the purpose for which they can be used. These category numbers are denoted as CAT-1, CAT-2, CAT-3, CAT-5, etc. Figure shows a piece of twisted pair cable.
Unshielded Twisted Pair (UTP) cables.
UTP cables are the most commonly used of the two types of twisted pair cable categories. UTP cables are inexpensive and easy to install and maintain. These cables are vulnerable to electromagnetic interferences (EMI) and radio frequencies interferences (RFI) and hence cannot carry data signals to longer distances. Electric or electronic equipment and high-voltage electric cables in the vicinity of these cables can cause significant disturbances.
Shielded Twisted Pair (STP) cables.
STP cable comes with a layer of shielding material between the cables and the sheath. STP cables provide some degree of protection from EMI and RF disturbances and can carry signals to greater distances. But this advantage comes with the extra cost of installation.
UTP cables are the most commonly used of the two types of twisted pair cable categories. UTP cables are inexpensive and easy to install and maintain. These cables are vulnerable to electromagnetic interferences (EMI) and radio frequencies interferences (RFI) and hence cannot carry data signals to longer distances. Electric or electronic equipment and high-voltage electric cables in the vicinity of these cables can cause significant disturbances.
Shielded Twisted Pair (STP) cables.
STP cable comes with a layer of shielding material between the cables and the sheath. STP cables provide some degree of protection from EMI and RF disturbances and can carry signals to greater distances. But this advantage comes with the extra cost of installation.
(iii) Fiber optic cables
Fiber optic (also called Optical Fiber) cable is made up of very thin glass or plastic stretched out and put inside a sheath. The transmission in fiber optic cables is based on the transport of light signals. An optical transmitter is located at one side of the cable and a receiver is at the other side. Fiber optic cables are immune to EMI and RF disturbances because they depend on optical signals unlike electrical signals in UTP/STP cables. They can also carry data signals longer distances than do UTP or STP cables due to minimal attenuation. It is also considered the most secure of all cable types.
Fiber optic cables are very expensive in terms of the cost involved in installation and maintenance. It needs expensive hardware, skilled technicians, and special tools for installation. This is the reason that fiber optic cable is used only in data centers for providing high-end connections to critical servers and other network devices where high-speed data transfers are required. Figure 11 shows a piece of fiber optic cable.
The two main types of fiber optic cables are single mode and multimode.
Single mode fiber optic cable.
The single mode fiber optic cable is made up of a core glass or plastic fiber surrounded by a cladding. It uses a single beam of light and can thus travel to greater distances than a multimode fiber optic cable. Single mode fiber optic cable uses an 8 to 10 micron core and 125 micron cladding. Figure shows a typical single mode fiber optic cable.
Fiber optic (also called Optical Fiber) cable is made up of very thin glass or plastic stretched out and put inside a sheath. The transmission in fiber optic cables is based on the transport of light signals. An optical transmitter is located at one side of the cable and a receiver is at the other side. Fiber optic cables are immune to EMI and RF disturbances because they depend on optical signals unlike electrical signals in UTP/STP cables. They can also carry data signals longer distances than do UTP or STP cables due to minimal attenuation. It is also considered the most secure of all cable types.
Fiber optic cables are very expensive in terms of the cost involved in installation and maintenance. It needs expensive hardware, skilled technicians, and special tools for installation. This is the reason that fiber optic cable is used only in data centers for providing high-end connections to critical servers and other network devices where high-speed data transfers are required. Figure 11 shows a piece of fiber optic cable.
The two main types of fiber optic cables are single mode and multimode.
Single mode fiber optic cable.
The single mode fiber optic cable is made up of a core glass or plastic fiber surrounded by a cladding. It uses a single beam of light and can thus travel to greater distances than a multimode fiber optic cable. Single mode fiber optic cable uses an 8 to 10 micron core and 125 micron cladding. Figure shows a typical single mode fiber optic cable.
Note: The core and cladding for fiber optic cables is measured in terms of microns. One micron is equal to one millionth of a meter or one thousandth of a millimeter.
Multimode fiber optic cable.
The multimode fiber optic cable is made up of a 50 micron or a 62.5 micron core and 125 micron cladding. In this cable, multiple beams of light travel through the core and are reflected by the cladding. Some of the beams even get refracted into the cladding, causing loss of signal. This reduces the distance that data signals can travel in a multimode fiber optic cable.
The following are the common types of fiber-optic cable:
(a) 8.3-micron core/12.5-micron cladding, single mode.
(b) 62.5-micron core/125-micron cladding, multi mode
(c) 50-micron core/125-micron cladding, multi mode
(d) 100-micron core/140-micron cladding, multi mode
Characteristics of Fiber-optic cable
Fiber-optic cable has the following characteristics:
Cost
Fiber-optic cable is slightly more expensive than copper cable, but costs are falling. Associated equipment costs can be much higher than for copper cable, making fiber-optic networks much more expensive. Single mode fiber-optic devices are more expensive and more difficult to install than multimode devices.
Installation
Fiber-optic cable is difficult to install than copper cable. Every fiber connection and splice must be carefully made to avoid obstructing the light path. Also the cables have a maximum bend radius, which makes cabling more difficult.
Node Capacity
In the case of Ethernet network, fiber-optic cables have the useful upper limit of around 75 nodes on a single collision domain.
Attenuation
Fiber-optic cable has much lower attenuation as compared to copper cable, mainly because the light is not radiated out in the way electricity is radiated from copper wire.
Mode of transmission
Fiber-optic channels are half-duplex, which means that light signals can only move in one direction at a time.
Uses of Fiber-optic
Fiber-optic media can support high bandwidth applications including video conference with the desktop, digital voice/image/graphics networking in the LAN environment. Fiber-optic cable can be used for LAN as well as for long distance transmission although tapping onto it is more complex than connecting to an Ethernet.
Multimode fiber optic cable.
The multimode fiber optic cable is made up of a 50 micron or a 62.5 micron core and 125 micron cladding. In this cable, multiple beams of light travel through the core and are reflected by the cladding. Some of the beams even get refracted into the cladding, causing loss of signal. This reduces the distance that data signals can travel in a multimode fiber optic cable.
The following are the common types of fiber-optic cable:
(a) 8.3-micron core/12.5-micron cladding, single mode.
(b) 62.5-micron core/125-micron cladding, multi mode
(c) 50-micron core/125-micron cladding, multi mode
(d) 100-micron core/140-micron cladding, multi mode
Characteristics of Fiber-optic cable
Fiber-optic cable has the following characteristics:
Cost
Fiber-optic cable is slightly more expensive than copper cable, but costs are falling. Associated equipment costs can be much higher than for copper cable, making fiber-optic networks much more expensive. Single mode fiber-optic devices are more expensive and more difficult to install than multimode devices.
Installation
Fiber-optic cable is difficult to install than copper cable. Every fiber connection and splice must be carefully made to avoid obstructing the light path. Also the cables have a maximum bend radius, which makes cabling more difficult.
Node Capacity
In the case of Ethernet network, fiber-optic cables have the useful upper limit of around 75 nodes on a single collision domain.
Attenuation
Fiber-optic cable has much lower attenuation as compared to copper cable, mainly because the light is not radiated out in the way electricity is radiated from copper wire.
Mode of transmission
Fiber-optic channels are half-duplex, which means that light signals can only move in one direction at a time.
Uses of Fiber-optic
Fiber-optic media can support high bandwidth applications including video conference with the desktop, digital voice/image/graphics networking in the LAN environment. Fiber-optic cable can be used for LAN as well as for long distance transmission although tapping onto it is more complex than connecting to an Ethernet.
No comments:
Post a Comment