Technology

WHAT IS TOPOLOGY
The network topology refers to the layout of a network installation (David,  Skandier, 2005). The layout consists of two parts physical and logical network design.

The physical network design refers to the actual arrangement of all the devices that are connected to a particular network and it exists in different layouts bus, mesh, ring, and star topologies (Raza, 2002). It also includes both the network location and cables installed.

On the other hand, logical network design defines how the systems communicate across the physical topologies. Sometimes it is referred to us the network access method or local area network media access method (Siamwalla, Sharma,  Keshav, 2000).  There are two main types of logical topologies shared media and token-based topology.

DIFFERENCES BETWEEN PHYSICAL AND LOGICAL TOPOLOGY
Logical Topology
Shared media - in this system, all the devices have the capability to access the physical layout at any instance. Its main advantage is that the systems have unrestricted access to the physical media. An example of shared media technology is Ethernet. However, its main disadvantage is collisions of data packets within the network. This occurs when two systems send data out in the same traffic simultaneously hence the data packets collide and self-destructs. Shared media networks are normally applicable in the bus and star physical topologies (Scott  Ogletree, 2003).

Token based - It normally works with the use of a token that provides access to the physical media. A token travels around the network whereby when a system needs to send out packets, it grabs the token off of the mediawire then attaches the packets that are sent, and sends it back on the wire. The token is examined by the systems as it travels within the network and if the token arrives at the targeted system, it copies the information off of the wire and the token continues its journey until it gets back to the original sender. When the token sender receives the token back, the system de-touches the token off of the wire and sends out a new empty token so as to be used by the next PC. Such kind of networks rarely experience collisions but the only problem experienced is delay-ness since each PC has to wait until it can use the token. Token-based networks are normally implemented by the ring topology because the token needs to be delivered back to the originating PC for it to release. This kind of network is usually exhibited in ring topology.

Physical topology
The bus topology in most cases is either a physical andor logical design network. It generally utilizes Ethernet cables to connect and it is considered the simplest among the others. A backbone common cable- connects all the devices in a given network and any other device that is being added is connected to the same cable. The backbone connection transmits data through only this particular cable and interruption leads to disconnection of the whole network. To avoid signal reflection in a physical bus topology, it requires termination of each end of the physical bus. The most common implementation of a bus topology is the IEEE 802.3.
Advantages -it is cheap and easy to implement requires less cables than other topologies does not use any specialized network equipment.

Disadvantages - There might be network disruption if computers are added or removed because all systems on the network connect to a single backbone a break in the cable will prevent all systems from accessing the network difficult to troubleshoot.

Note. Scott, M., Ogletree, W. T. (2003). Upgrading and repairing networks. (4th ed.).Que. Part of the upgrading and repairing series.

A mesh topology represents a Wide Area Network whereby there are quite a number of network paths interconnecting various sites (Network Topologies,). In this topology, a router is used in identifying and determining which path is best for data transmission.  For a simple network, for instance two to three sites, it is convenient to create but for quite a number of sites it becomes expensive. Reason being that every network site and subsequent additions of devices needs an independent cable connection. Besides, the amount of work involved while configuring network is cumbersome (Programming Languages Logical and Physical Network Design, 2004). However, its biggest advantage is that failure of one connection does not interfere with the other connections in that same network. Mesh topology normally represents a physical design layout.

Advantages - Provides redundant paths between devices the network can be expanded without disruption to other current users.

Disadvantages - Requires more cables than the other LAN topologies -costly, complicated implementation.
         
Note. Scott, M., Ogletree, W. T. (2003). Upgrading and repairing networks. (4th ed.).Que. Part of the upgrading and repairing series.

The ring topology is a physical design layout whereby each device in the network is connected to its other two neighboring devices. However, in case a new device is being added, the whole connection is disrupted and this involves a lot of work to configure the whole system. Nevertheless, such conflicts in transmitting the data can be mitigated by applying token ring technology but this method is rarely used in setting up a network (Designing a Network Topology, 2004).

Advantages - Cable faults are easily located making troubleshooting easier Ring networks are moderately easy to install.

Disadvantages - Expansion to the network can cause network disruption a single break in the cable can disrupt the entire network.

Note. Scott, M., Ogletree, W. T. (2003). Upgrading and repairing networks. (4th ed.).Que. Part of the upgrading and repairing series.

The star topology is usually either a physical andor logical design layout whereby network devices have got one central location referred to as a hub or switch (Scott  Ogletree, 2003). This topology is the most advantageous because if one of the devices fails, the others are not affected. Configuring the network is simple as any one cable can easily be connected to the hub or switch. It is usually applied in Ethernet networks.

Advantages - Star networks are easily expanded without disruption of the network Cable failure affects only a single user easy to troubleshoot and isolate problem (Designing a Network Topology, 2004)

Disadvantages - Requires more cable than most of the other topologies a central connecting device allows for a single point of failure it is a bit more difficult to implement.

Note. Scott, M., Ogletree, W. T. (2003). Upgrading and repairing networks. (4th ed.).Que. Part of the upgrading and repairing series.

Wireless topology is implemented using either infrastructure (managed) or ad-hoc (unmanaged) topologies.

Infrastructure wireless topology is commonly used to extend a wired LAN to include more wireless devices. Wireless devices communicate with the wired LAN through Access Point (AP) or Wireless Access Point (WAP) -the AP or WAP is the base station. Infrastructure wireless networks have many access points which acts as a provider of wireless coverage for a large area or a single access point for a small area.

Ad-hoc wireless topology Devices normally communicate directly between themselves without using an access point. This is commonly used to offer connection to a small number of wireless devices.

Advantages - high mobility, fast setup, cost effective and expandable.

Disadvantages - less secure, disturbance, inconsistent, and power consuming.

FACTORS TO CONSIDER WHEN DESIGNING A NETWORK
Craft (2006) emphasizes that once a decision has been made on the network protocols and services to be offered in the network, potential bottlenecks should be identified and evaluated depending on your network needs, and then one can redesign the physical aspects of the network. Thomas (2008) states that the potential clientele its expertise- should be considered before designing any network. The work pattern for various departments needs to be assessed so that one can appropriately place devices such as servers, high bandwidth links, and such in the appropriate physical location of the network. For example if one expects most traffic to come from the finance department, you will need to provide that finance department with a large data pipe to sufficient accommodation.

Another vital consideration is the persons allowed to access the network. Will you need to allow an internet connection for just your internal network users, or will there be a need to allow outside vendors to access your network Users tolerance to a little downtime network problem should be considered. Can they tolerate Will one need to implement clustered servers to provide for a high degree of uptime, or do your users applications not suffer from a temporary loss for the use of a server. To provide for a maximum uptime, one can afford to come up with a redundancy into the network and hence prevent a single point of failure from making the network resources unavailable .
 
A decision must be made on whether to keep the current protocols or upgrade them. If an upgrade is to be done the transition is supposed to be very smooth whereas if the network is to be created from the scratch, factors that should affect the network have to be considered keenly. According to Scott  Ogletree (2003), Ethernet is one of the most popular LAN protocol in the world while TCPIP is the popular protocol suite that runs on Ethernet but there are cases in which other technologies have their nichesshortcomings. Therefore, support cost implications can be considered to maintain the older proprietary protocols.

Servers and redundant devices are also important considerations in where to fix them. Besides, the physical security is also another paramount consideration if for instance, the security of the equipments and data has to be achieved. Any data stolen can be used by the competitors of a particular company to sabotage its activities. Mueller  Ogletree (2003) in their work notes that training in documentation is necessary to be offered for both the system administrators and the highly skilled end userspower users of the new technology. There should be a document that stipulates the physical and logical layout of the network which is being implemented or upgraded (Network Tutorial, 2010). Such documentation is useful especially when anything goes amiss as it facilitates in troubleshooting the network.

Administrators and users should be provided with the required technology training as far as the new system is concerned. For instance, technical users who will be responsible for managing the network are supposed to be trained in the procedures for which they will be responsible in. Finally, the overall budget cost of the new design layout inclusive of labor- needs to be within the organizations financial obligations.

Conclusion
Designing a network entails having the necessary expertise in network design or being in a position to hire such services. In addition, considerations of the different types of network designs are necessary to be done in terms of cost, reliability, scalability and extensibility. This goes a long way in establishing the most suitable network design layout for a certain enterprise and mitigates financial losses which may arise as a result of inefficient network.