3.Transmission Media and Networking Topologies
Transmission medium
• Computer transmission media includes cable and wireless technologies that allow networked devices to contact one another.
• Transmission media cannot guarantee that other network devices will understand a message.
• It can, however, guarantee a message delivery path.
• Factors to be considered while choosing Transmission Medium
- Transmission Rate
- Cost and Ease of Installation
- Resistance to Environmental Conditions
- Distances
Types of transmissions
There are two types of transmission media:
1 . Guided or Wired Transmission media which can be seen physically and has a proper bounded channel to flow the signal.
Types of Wired transmission media:
1 . Twisted Pair Cable
2. Coaxial Cable
3. Optical Fiber Cable
1 . Twisted Pair Cable
2. Coaxial Cable
3. Optical Fiber Cable
2. Unguided or Wireless
Wireless transmission media is the one in which data signals gets transmitted through the air.
They are not guided or bound to a channel to follow.
Types of Wireless transmission media:
1 . Radio Transmission
2. Microwave Transmission
Types of Wireless transmission media:
1 . Radio Transmission
2. Microwave Transmission
Twisted pair cable
Twisted pair (TP) cable uses copper wire as telecommunication cable. Because copper is such a good conductor of electrons, copper wires do not constrain electromagnetic signals well. Twisting the copper wires reduces crosstalk and signal emissions. Each intertwined strand conducts a current whose emitted waves are cancelled out by the other wire’s emissions.
There are two type of Twisted Pair Cables
1. Shielded Twisted Pair (STP)
2.Unshielded Twisted Pair (UTP)
Shielded Twisted Pair (STP) Cable Twisted pair cables are often shielded in an attempt to prevent
electromagnetic interference.
• Because the shielding is made of metal, it may also serve as a ground.
• Usually a shielded or a screened twisted pair cable has a special grounding wire added called a drain wire which is electrically connected to the shield or screen. The drain wire simplifies connection to ground at the connectors.
There are two type of Twisted Pair Cables
1. Shielded Twisted Pair (STP)
2.Unshielded Twisted Pair (UTP)
Shielded Twisted Pair (STP) Cable Twisted pair cables are often shielded in an attempt to prevent
electromagnetic interference.
• Because the shielding is made of metal, it may also serve as a ground.
• Usually a shielded or a screened twisted pair cable has a special grounding wire added called a drain wire which is electrically connected to the shield or screen. The drain wire simplifies connection to ground at the connectors.
STP cable Functionality
The following summarizes the functionality of STP cable:
- Speed and throughput is 10 to 100 Mbps
- Average cost per node is Moderately expensive
- Media and connector size is Medium to large
- Maximum cable length is 100 meters
Unshielded Twisted Pair (UTP) Cable
UTP is commonly used in telephone systems. It is widely available and has been largely standardized.
The Electrical Industries Association (EIA) popularized a category labelling scheme for five different qualities of twisted pair cable:
Category 1 and 2: Voice and low-speed data (less than or equal to 4 Mbps)
Category 3: Data (typically 10-16 Mbps, although 100 Mbps is possible)
Category 4: Data (less than or equal to 20 Mbps)
Category 5: High-speed data (less than or equal to 100 Mbps) used for 100Base-TX
Category 5e (enhanced): High-speed data (less than or equal to 100 Mbps) used for 1000Base-T
Category 6: High-speed data (less than or equal to 250 Mbps) used for 1000Base
The Electrical Industries Association (EIA) popularized a category labelling scheme for five different qualities of twisted pair cable:
Category 1 and 2: Voice and low-speed data (less than or equal to 4 Mbps)
Category 3: Data (typically 10-16 Mbps, although 100 Mbps is possible)
Category 4: Data (less than or equal to 20 Mbps)
Category 5: High-speed data (less than or equal to 100 Mbps) used for 100Base-TX
Category 5e (enhanced): High-speed data (less than or equal to 100 Mbps) used for 1000Base-T
Category 6: High-speed data (less than or equal to 250 Mbps) used for 1000Base
UTP Connectors
The connector used for UTP cable is RJ-11 for telephone line that has four wires and RJ-45 for computer networking which has four pair, 8 wires.
• RJ 45 connector is most of the time connected to the UTP cable.
• The job of connecting a RJ 45 connector to UTP cable is called crimping.
A crimping tool for RJ 11 and RJ 45 connection
• RJ 45 connector is most of the time connected to the UTP cable.
• The job of connecting a RJ 45 connector to UTP cable is called crimping.
A crimping tool for RJ 11 and RJ 45 connection
Wiring Standards
• Wiring standards are used to set Ethernet cables according to the connection of it between similar or dissimilar devices. There are different types of Ethernet available:
1. Straight-through cable
2. Crossover cable
3. Rolled cable cables
1. Straight-through cable
2. Crossover cable
3. Rolled cable cables
• T-568A and T-568B are the two wiring standards for RJ-45 connector data
cable specified by TIA/EIA-568-A wiring standards document.
• The two wiring standards are used to create a crossover cable where T-568A
is used on one end and T-568B on the other end.
• In straight-through cable where on both ends you can use T-568A or T568Bwiring standards.
cable specified by TIA/EIA-568-A wiring standards document.
• The two wiring standards are used to create a crossover cable where T-568A
is used on one end and T-568B on the other end.
• In straight-through cable where on both ends you can use T-568A or T568Bwiring standards.
Straight-Through Cables
Straight-through cable is a type of twisted pair copper wire cable for local area network, where the RJ-45 connectors at each end have the same pinout i.e., arrangement of conductors. Straight-through cable is also commonly referred to as patch cable. However, this might be confusing in some situations because patch cable also has a broader definition that emphasizes the fact that there is a
connector on each end rather than the equality of the pinouts. Straight-through cable is used to connect computers and other end-user devices e.g., printers to networking devices such as hubs and switches. It can also be used to directly connect like devices e.g., two hubs or two switches if the cable is plugged into an uplink port on one but not both of the devices.
connector on each end rather than the equality of the pinouts. Straight-through cable is used to connect computers and other end-user devices e.g., printers to networking devices such as hubs and switches. It can also be used to directly connect like devices e.g., two hubs or two switches if the cable is plugged into an uplink port on one but not both of the devices.
Crossover Cables
A crossover cable is a type of twisted pair copper wire cable for local area network in which the wires on the cable are crossed over so that the receive signal pins on the RJ-45 connector on one end are connected to the transmit signal pins on the RJ-45 connector on the other end. This is the opposite of the usual straight-through LAN cable, in which the receiver and transmission signal pins on one connector are connected to the corresponding pins on the other connector. Its purpose is to allow the
direct connection of two LAN devices, such as two hubs, two switches or a hub and a switch. It can also be used to create a direct connection between two computers. An alternative to using a crossover cable is to use a hub or switch that has an uplink port. An uplink port is a jack i.e., a socket for an RJ-45 connector that reverses the transmission and receiver circuits. Some uplink ports have a switch that allows the user to select the mode of operation.
The physical appearance of crossover cable is generally identical to that of straight-through cable.
direct connection of two LAN devices, such as two hubs, two switches or a hub and a switch. It can also be used to create a direct connection between two computers. An alternative to using a crossover cable is to use a hub or switch that has an uplink port. An uplink port is a jack i.e., a socket for an RJ-45 connector that reverses the transmission and receiver circuits. Some uplink ports have a switch that allows the user to select the mode of operation.
The physical appearance of crossover cable is generally identical to that of straight-through cable.
Rollover Cables
A rollover cable is a network cable that connects a computer terminal to a network router’s console port. It is also referred to as a Cisco console cable and is normally flat and light blue so as to distinguish it from other network cable types. The pinouts on one end of the cable are reversed from the opposite end, which is how the cable derived its name. Rollover cables are also known as
Yost cables or Yost Serial Device Wiring Standard connectors. Rollover cables primarily connect a device to a switch or router’s console port. This permits an engineer or programmer to connect to the network device and manipulate the programming as required. Although many network programming tasks can now be centrally completed, there remains the need for technicians to use rollover cables
for network hardware upgrades, maintenance, and troubleshooting
Yost cables or Yost Serial Device Wiring Standard connectors. Rollover cables primarily connect a device to a switch or router’s console port. This permits an engineer or programmer to connect to the network device and manipulate the programming as required. Although many network programming tasks can now be centrally completed, there remains the need for technicians to use rollover cables
for network hardware upgrades, maintenance, and troubleshooting
Coaxial Cable
Coaxial cable or coax is a type of network cable that has an inner conductor surrounded by a tubular insulating layer which is again surrounded by a tubular conducting shield. Many a time coaxial cables also have an insulating outer jacket or sheath. The word coaxial is derived from the structure of the cable i.e. the inner conductor and the outer shield sharing a geometric axis. In year 1880, Oliver Heaviside - English engineer and mathematician patented the design of Coaxial cable. When Ethernet based LANs make using of thick coaxial cable for interconnection is referred as Thicknet. Ethernet Networks where thinner coaxial cables are used it is referred as Thinnet. Thicknet is also referred as 10Base5 systems, where 10 mean 10Mbps speed for data transmission and receiving and Base means baseband and 5 indicate the maximum distance between hosts that carries the data i.e. 500 meter. RG-8/U cable is used as thick cable in thicknet based LAN network. Thinnet is also referred as 10Base2, where 2 indicate 200 meter of maximum distance between two hosts. RG-58/U is used as thin cable in thinnet based LAN network. For attaching coaxial cable to the device we have to use BNC connector which has to be crimped by a plier. A thinnet coaxial cable
Fiber-Optic Cable
Fiber-Optic cable is a cable that has one or more optical fibers that are used to carry data in the form of light. Fiber-Optic cable consists of a core and a cladding layer with a different refraction index that reflects the light back into the core. The jacketed fiber is generally enclosed, with a bundle of flexible fibrous polymer strength members like aramid i.e. Twaron or Kevlar, in a lightweight plastic cover to form a simple cable, which is then sheathed in PVC or plenum. As fiber-optic cable transmits digital signals using light impulses not similar to other cable that uses electricity, due to light impulses the data is immune to Electro Magnetic Interference (EMI) and Radio Frequency Interference (RFI).
The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.
The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.
Type of Fiber-Optic Cable
Different types of cable are used for different applications, for example long distance telecommunication, or providing a high-speed data connection between different parts of a building. The cable itself comes in either
1. Single-mode fiber (SMF)
2. Multimode fiber (MMF)
The difference between single-mode fiber (SMF) and multimode fiber (MMF) is in the number of light rays i.e. the number of signals the fiberoptic cable can carry. Multimode fiber is most often used for shorter distance applications and single-mode fiber for spanning long distance applications.
1. Single-mode fiber (SMF)
2. Multimode fiber (MMF)
The difference between single-mode fiber (SMF) and multimode fiber (MMF) is in the number of light rays i.e. the number of signals the fiberoptic cable can carry. Multimode fiber is most often used for shorter distance applications and single-mode fiber for spanning long distance applications.
Advantages of Fiber-Optic cable
1. No Electro Magnetic Interference (EMI) and Radio Frequency Interference (RFI).
2. The data can be carried up to 40 kilometers i.e. about 25 miles.
3. Since the fiber is a dielectric, it does not present a spark hazard
4. Fiber-Optic cable provides bandwidth up to 10 Gbps
2. The data can be carried up to 40 kilometers i.e. about 25 miles.
3. Since the fiber is a dielectric, it does not present a spark hazard
4. Fiber-Optic cable provides bandwidth up to 10 Gbps
Disadvantages of Fiber-Optic cable
1. Installation is not so easy.
2. Cost is also high as compared to other cables.
3. Fibers can be broken or have transmission loses when wrapped around curves of only a few centimeters radius.
4. Troubleshooting is difficult.
5. For troubleshooting such cable the equipment used are also more expensive.
2. Cost is also high as compared to other cables.
3. Fibers can be broken or have transmission loses when wrapped around curves of only a few centimeters radius.
4. Troubleshooting is difficult.
5. For troubleshooting such cable the equipment used are also more expensive.
Radio Transmission
Radio waves are the basic unit of wireless communication. By varying the characteristics of a radio wave frequency, amplitude, or phase, these waves can be made to communicate information of many types, including audio, video, and data. Radio waves that carry information are called radio signals, and the process of encoding intelligence onto a radio wave so that it can be transmitted over the air is
called modulation. The radio waves can travel through walls or through an entire building. Depending upon the frequency, they can travel long distances or short distances. Satellite relay is the one example of long distance communication. In radio transmission, a transmitter is needed to send the broadcast signal and a receiver is needed to accept that signal. While some networks use a transceiver, which act as sender as well as receiver for signals from wireless devices. Radio waves are Omni-directional, that means they transmit signal in all directions from the transmitter Wireless networks using broadcast radio often use one of the 802.11 specifications.
The 802.11b specification provides transfer rates up to 11 Mbps.
The 802.11a specification provides transfer rates up to 54 Mbps.
Microwave Transmission
Microwave transmission is the transmission of information or energy by electromagnetic waves whose wavelengths are measured in small numbers of centimeter; which are called microwaves. Microwaves are widely used for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly to the receiving antenna. This allows nearby microwave equipment to use the same frequencies without
interfering with each other. Another advantage is that the high frequency of microwaves gives the
microwave band a very large information-carrying capacity. The microwave band has a bandwidth 30 times that of all the rest of the radio spectrum below it. Disadvantage of microwaves is that they are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency
radio waves can.
interfering with each other. Another advantage is that the high frequency of microwaves gives the
microwave band a very large information-carrying capacity. The microwave band has a bandwidth 30 times that of all the rest of the radio spectrum below it. Disadvantage of microwaves is that they are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency
radio waves can.
Network Topology
The term Network Topology defines the geographic arrangement of computers or networking devices. The term Topology refers to the way in which the various nodes or computers of a network are linked together. It describes the actual layout of the computer network hardware. Two or more devices connect to a link; two or more links form a topology. The study of network topology recognizes six basic topologies:
1. Bus
2. Ring
3. Star
4. Mesh
5. Hybrid
1. Bus
2. Ring
3. Star
4. Mesh
5. Hybrid
Bus Topology
The Bus Topology consists of one continuous length of cable (trunk) that is shared by all the nodes in the network and a terminating resistor (terminator) at each end that absorbs the signal when it reaches the end of line. Without a terminator the electrical signal would reach the end of copper wire and bounce back, causing errors on the network. Data communication message travels along the bus in both directions until it is picked up by a workstation or server NIC. If the message is missed or not recognized, it reaches the end of the cabling and dissipates at the terminator. Bus Network Topology requires a multipoint connection. All nodes on the bus topology have equal access to the trunk. This is accomplished using short drop cables or direct T-connectors. The number of devices and the length of the trunk can be easily expanded.
Advantages of Bus Topology
It uses established standards and it is relatively easy to install and use for small networks.
It requires less media other topologies.
Failure of one node does not affect the network functioning.
Cheaper
Expansion is easier.
New node can be easily added by using a connector.
It requires less media other topologies.
Failure of one node does not affect the network functioning.
Cheaper
Expansion is easier.
New node can be easily added by using a connector.
Disadvantages of Bus Topology
If the main central line fails the entire network collapses.
The bus networks are difficult to reconfigure, especially when the acceptable number of connections or maximum distances have been reached.
They are also difficult to troubleshoot because everything happens on a single media segment.
This can have dangerous consequences because any break in the cabling brings the network to its knee.
Sharing a single communication channel results in slower access time.
In this topology, higher network traffic slows down the bus speed. Only one device transmits at a time, other devices wait for their turn. As a result there is no coordination between the devices for reservation of transmission time slots, so data collisions are frequent.
The bus networks are difficult to reconfigure, especially when the acceptable number of connections or maximum distances have been reached.
They are also difficult to troubleshoot because everything happens on a single media segment.
This can have dangerous consequences because any break in the cabling brings the network to its knee.
Sharing a single communication channel results in slower access time.
In this topology, higher network traffic slows down the bus speed. Only one device transmits at a time, other devices wait for their turn. As a result there is no coordination between the devices for reservation of transmission time slots, so data collisions are frequent.
Ring Topology
The ring topology is a circular loop of point-to-point links. Each device connects directly to the ring or indirectly through an interface device or drop cable. Message travel around the ring from node to node in a very organized manner. Each workstation checks the message for a matching destination address. If the address doesn't match the node simply regenerates the message and sends it on its way.
If the address matches, the node accepts the message and sends a reply to the originating sender.
If the address matches, the node accepts the message and sends a reply to the originating sender.
Advantages of Ring Topology
They are very easy to troubleshoot because each device incorporates a repeater.
A special internal feature called be aconing allows troubled workstations to identify themselves quickly.
There is no master computer on controller. Every computer has equal chance to place the data and access the token.
There are no collisions.
Data packets travel at greater speeds.
It is easier to locate the problems with device and cable i.e. fault isolation
is simplified. If one device does not receive a signal within a specified time, it can issue an alarm. This alarm alerts the network operator to the problem and its location.
A special internal feature called be aconing allows troubled workstations to identify themselves quickly.
There is no master computer on controller. Every computer has equal chance to place the data and access the token.
There are no collisions.
Data packets travel at greater speeds.
It is easier to locate the problems with device and cable i.e. fault isolation
is simplified. If one device does not receive a signal within a specified time, it can issue an alarm. This alarm alerts the network operator to the problem and its location.
Disadvantages of Ring Topology
A ring network requires more physical media than a bus network.
A break in cable ring brings down the entire network.
Adding or removing the node disturbs the network activity.
In ring network, communication delay is directly proportional to the number of nodes in the network. Hence addition of new nodes in the network also increases communication delay.
It is considerably difficult to install and reconfigure ring topology
Media failure on unidirectional or single loop causes complete network failure.
A break in cable ring brings down the entire network.
Adding or removing the node disturbs the network activity.
In ring network, communication delay is directly proportional to the number of nodes in the network. Hence addition of new nodes in the network also increases communication delay.
It is considerably difficult to install and reconfigure ring topology
Media failure on unidirectional or single loop causes complete network failure.
Star Topology
The star Topology uses a central controlling hub connecting all computers with the help of a twisted pair cable. Each network device has a dedicated point-to-point link to the central hub. There is no direct link between these computers and the computers can communicate via central controller only. This strategy prevents troublesome collisions and keeps the lines of communications open and free of traffic. The routing function is performed by the central controller which centrally controls communication between any two computers by establishing a logical path between them. It means that if one computer A wants to send data to another computer B, Computer A sends the data to the controller & this controller then sends the data to computer B. This Topology, obviously, require a great deal of cabling. This design provides an excellent platform for reconfiguration and trouble-shooting. Changes to the network are as simple as plugging another segment into the hub and a break in the LAN is easy to isolate and doesn't affect the rest of the network.
Advantages of Star Topology
Presently start topology is used.
It is easier to add new node or modify any existing node without disturbing network i.e. expansion is easier.
Addition of new node does not increase communication delay.
If any local computer or link fails, the entire system does not collapse. Only that link or computer is affected.
It is easy to find device and cable problems i.e. fault identification and isolation is easier.
Media faults are automatically isolated to the failed segment.
It is easier to add new node or modify any existing node without disturbing network i.e. expansion is easier.
Addition of new node does not increase communication delay.
If any local computer or link fails, the entire system does not collapse. Only that link or computer is affected.
It is easy to find device and cable problems i.e. fault identification and isolation is easier.
Media faults are automatically isolated to the failed segment.
Disadvantages of Star Topology
If the central controller or hub fails, entire system collapses.
Cabling cost is more as each node is connected individually to the hub.
Requires more cable than most topologies.
Moderately difficult to install.
Mesh Topology
In mesh topology, each node is connected to every other node in the network i.e. each node has a dedicated point to point link to every other node. Dedicated means that the link carries the traffic only between two devices it connects. In this way there exist multiple paths between two nodes of the
network. In case of failure of one path, the other one can be used.
network. In case of failure of one path, the other one can be used.
Advantages of Mesh Topology
It is robust as the failure of one node does not collapse the entire system.
If one link fails, the entire system continues to work.
There is no traffic congestion problem as dedicated links are being used.
Dedicated links ensure faster transmission without any delay.
Dedicated links also ensure data privacy and security.
Point to point links makes fault identification and isolation easier.
If one link fails, the entire system continues to work.
There is no traffic congestion problem as dedicated links are being used.
Dedicated links ensure faster transmission without any delay.
Dedicated links also ensure data privacy and security.
Point to point links makes fault identification and isolation easier.
Disadvantages of Mesh Topology
Connecting each device to every other device in the network makes installation and reconfiguration difficult.
It has high cabling cost as n (n-l)/2 links are required to connect n nodes.
It has high cabling cost as n (n-l)/2 links are required to connect n nodes.
Hybrid Topology
The hybrid Topology is a type of Topology that is composed of one or more interconnections of two or more networks that are based upon different physical topologies. When two hubs of different topologies are joined so that the devices attached to them can communicate, it is called a Star-Bus network. When two or more star topologies are linked together using a specialized hub called a MAU (Multi-utilization Access Unit), it is known as Star-Ring topology.
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