Network Physical Topologies Are Categorized Computer Science Essay

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There are different network topologies that can be implemented for the creation of the in house network (LAN). These network topologies are into two main groups, which are Physical Topology and Logical Topology.

Physical Topology means the physical design or arrangement of a network including the devices, location and cable installation, while Logical Topology refers to how the data or signals are transferred along the cables as the as illustrated to its design.

Topology can be considered as a virtual shape or structure of a network. This shape actually does not correspond to the actual physical design of the devices on the computer network necessarily mean that it presents a ring topology

Network (Physical) topologies are categorized into the following three basic types:

Bus topology

Star topology

Ring topology

Tree topology

Mesh topology

Bus network topology:

A Bus Topology is a network architecture in which a group of clients or computers are connected through a single cables (backbone), called a bus. Bus networks are the simplest way to connect multiple clients, but may have problems when two clients want to transmit at the same time on the same bus. Thus systems which use bus topology normally have some scheme of collision handling or collision avoidance for communication on the bus, quite often using Carrier Sense Multiple Access or the presence of a bus master which controls access to the shared bus resource.

The Bus Topology is usually terminated at the end of each cable where there is no computer attachment; this process is known as termination. The following are some of advantages and disadvantages of Bus Topology.

Advantages:

• Easy to implement and extend

• Well suited for temporary or small networks not requiring high speeds (quick setup)

• Easy to connect a computer or peripheral to a linear bus.

• Requires less cable length than a star topology.

• Cheaper than other topologies.

• Cost effective as only a single cable is used

Disadvantages:

• If there is a problem with the cable, the entire network goes down.

• Maintenance costs may be higher in the long run.

• Entire network shuts down if there is a break in the main cable.

• Terminators are required at both ends of the backbone cable.

• Difficult to identify the problem if the entire network shuts down.

• Not meant to be used as a stand-alone solution in a large building

• Performance degrades as additional computers are added or on heavy traffic.

• Proper termination is required (loop must be in closed path).

• Significant Capacitive Load (each bus transaction must be able to stretch to most distant link).

• It works best with limited number of nodes.

• It is slower than the other topologies.

Fig. 1. Bus topology

Star Network Topology:

In local area networks with a star topology, each network host is connected to a central hub. In contrast to the bus topology, the star topology connects each node to the hub with a point-to-point connection. All traffic that transverses the network passes through the central hub. The hub acts as a signal booster or repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.

Fig. Star topology

Ring Network Topology:

In local area networks where the ring topology is used, each computer is connected to the network in a closed loop or ring. Each machine or computer has a unique address that is used for identification purposes. The signal passes through each machine or computer connected to the ring in one direction. Ring topologies typically utilize a token passing scheme, used to control access to the network. By utilizing this scheme, only one machine can transmit on the network at a time. The machines or computers connected to the ring act as signal boosters or repeaters which strengthen the signals that transverse the network. The primary disadvantage of ring topology is the failure of one machine will cause the entire network to fail.

Fig. 1. Ring topology

Tree Network Topology:

The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node that has no other node above it in the hierarchy (The hierarchy of the tree is symmetrical.) Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy, the number, being referred to as the 'branching factor' of the hierarchical tree. This tree has individual peripheral nodes.

Fig. 1. Tree topology

Mesh Network Topology:

The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that communicating groups of any two endpoints, up to and including all the endpoints, is approximated by Reed's Law.

Fig. 1. Mesh topology

Summary Chart:

Physical Topology

Common Cable

Common Protocol

Bus

Twisted Pair

Coaxial

Fiber

Ethernet

Star

Twisted Pair

Fiber

Ethernet

Tree

Twisted Pair

Coaxial

Fiber

Ethernet

Mesh

Ethernet

NETWORK MEDIA:

Media is the medium through which information usually moves from one network device to another. There are several types of media which are commonly used with LANs. In some cases, a network will utilize only one type of media, other networks will use a variety of media types. The type of media chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of media and how they relate to other aspects of a network is necessary for the development of a successful network.

Network Cabling:

Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.

The following sections discuss the types of cables used in networks and other related topics:

Unshielded Twisted Pair (UTP) Cable

Shielded Twisted Pair (STP) Cable

Coaxial Cable

Fiber Optic Cable

Cable Installation Guides

Wireless LANs

Unshielded Twisted Pair (UTP) Cable:

Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks (See fig. 1.1).

Fig.1.1. Unshielded twisted pair

The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated six categories of wire (additional categories are emerging).

Categories of Unshielded Twisted Pair:

Category

Speed

Use

1.

1 Mbps

Voice Only (Telephone Wire)

2.

4 Mbps

Local Talk & Telephone (Rarely used)

3.

16 Mbps

10BaseT Ethernet

4.

20 Mbps

Token Ring (Rarely used)

5.

100 Mbps (2 pair)

1000 Mbps (4 pair)

100BaseT Ethernet

Gigabit Ethernet

5e.

1,000 Mbps

Gigabit Ethernet

6.

10,000 Mbps

Gigabit Ethernet.

Unshielded Twisted Pair Connector:

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 1.2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

Fig. 1.2. RJ-45 connector

Shielded Twisted Pair (STP) Cable:

Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution. Shielded cables can also help to extend the maximum distance of the cables.

Shielded twisted pair cable is available in three different configurations:

Each pair of wires is individually shielded with foil.

There is a foil or braid shield inside the jacket covering all wires (as a group).

There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).

Coaxial Cable:

Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield (See fig. 1.3). The metal shield helps to block any outside interference from

Fig. 1.3. Coaxial cable

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial

Thin coaxial cable is also referred to as thinner. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable has been popular in

Thick coaxial cable is also referred to as thick net. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does.

Coaxial Cable Connectors

The most common type of connector used with coaxial cables is the Bayonne-Neill-Councilman (BNC) connector (See fig. 1.4). Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather.

Fig. 1.4. BNC connector

Fiber Optic Cable:

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials (See fig. 5). It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between

Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is

The center core of fiber cables is made from glass or plastic fibers (see fig 1.5). A plastic coating then cushions the fiber center, and Kevlar fibers help to strengthen the cables and prevent breakage. The outer insulating jacket made of Teflon or PVC.

Fig. 1.5. Fiber optic cable

There are two common types of fiber cables -- single mode and multimode. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. Single mode can provide more distance, but it is more expensive.

Ethernet Cable Summary:

Specification

Cable Type

10BaseT

Unshielded Twisted Pair

10Base2

Thin Coaxial

10Base5

Thick Coaxial

100BaseT

Unshielded Twisted Pair

100BaseFX

Fiber Optic

100BaseBX

Single mode Fiber

100BaseSX

Multimode Fiber

1000BaseT

Unshielded Twisted Pair

1000BaseFX

Fiber Optic

1000BaseBX

Single mode Fiber

1000BaseSX

Multimode Fiber

Installing Cable - Some Guidelines:

When running cable, it is best to follow a few simple rules:

Always use more cable than you need. Leave plenty of slack.

Test every part of a network as you install it. Even if it is brand new, it may have problems that will be difficult to isolate later.

Stay at least 3 feet away from fluorescent light boxes and other sources of electrical interference.

If it is necessary to run cable across the floor, cover the cable with cable protectors.

Label both ends of each cable.

Use cable ties (not tape) to keep cables in the same location together.

Wireless LANs:

Fig. 1.6. Wireless lan

More and more networks are operating without cables, in the wireless mode. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations and the file server or hubs. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission, or by satellite.

Wireless networks are great for allowing laptop computers or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables.

The two most common types of infrared communications used in schools are line-of-sight and scattered broadcast. Line-of-sight communication means that there must be an unblocked direct line between the workstation and the transceiver. If a person walks within the line-of-sight while there is a transmission, the information would need to be sent again. This kind of obstruction can slow down the wireless network. Scattered infrared communication is a broadcast of infrared transmissions sent out in multiple directions that bounces off walls and ceilings until it eventually hits the receiver. Networking communications with laser are virtually the same as line-of-sight infrared networks.

Wireless standards and speeds:

The Wi-Fi Alliance is a global, non-profit organization that helps to ensure standards and interoperability for wireless networks, and wireless networks are often referred to as Wi-Fi (Wireless Fidelity). The original Wi-Fi standard (IEEE 802.11) was adopted in 1997. Since then many variations have emerged (and will continue to emerge). Wi-Fi networks use the Ethernet protocol.

Standard

Max Speed

Typical Range

802.11a

54 Mbps

150 feet

802.11b

11 Mbps

300 feet

802.11g

54 Mbps

300 feet

Advantages of wireless networks:

Mobility - With a laptop computer or mobile device, access can be available throughout a school, at the mall, on an airplane, etc. More and more businesses are also offering free Wi-Fi access.

Fast setup - If your computer has a wireless adapter, locating a wireless network can be as simple as clicking "Connect to a Network" -- in some cases, you will connect automatically to networks within range.

Cost - Setting up a wireless network can be much more cost effective than buying and installing cables.

Expandability - Adding new computers to a wireless network is as easy as turning the computer on (as long as you do not exceed the maximum number of devices).

Disadvantages of wireless networks:

Security - Wireless networks are much more susceptible to unauthorized use. If you set up a wireless network, be sure to include maximum security. You should always enable WEP (Wired Equivalent Privacy) or WPA (Wi-Fi Protected Access), which will improve security and help to prevent virtual intruders and freeloaders.

Interference - Because wireless networks use radio signals and similar techniques for transmission, they are susceptible to interference from lights and electronic devices.

Inconsistent connections - How many times have you hears "Wait a minute, I just lost my connection?" Because of the interference caused by electrical devices and/or items blocking the path of transmission, wireless connections are not nearly as stable as those through a dedicated cable.

Power consumption - The wireless transmitter in a laptop requires a significant amount of power; therefore, the battery life of laptops can be adversely impacted. If you are planning a laptop project in your classroom, be sure to have power plugs and/or additional batteries available.

Speed - The transmission speed of wireless networks is improving; however, faster options (such as gigabit Ethernet) are available via cables. In addition, if set up a wireless network at home, and you are connecting to the Internet via a DSL modem (at perhaps 3 Mbps), your wireless access to the Internet will have a maximum of 3 Mbps connection speed.

A Provide recommendation for with topology and medium to use including reasons for this recommendation:

Tree Network Topology:

A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable (See fig. 3). Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Fig. 1.2.1. Tree topology

Unshielded Twisted Pair Connector:

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector (See fig. 1.2.2). A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector.

Fig. 1.2.2. RJ-45 connector

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