Exploring the functions of a network
What is a network:
a bunch of connected devices and end systems, such as computers and servers, that can communicate with each other. Networks can be presented in different environments which can be categorized by the place where users exist, there are 4 major categories to where networks are implemented:
- Main office: is a site where everyone is connected via a network and where the bulk of corporate information is located. It can have hundreds or even thousands of people who depend on network access to do their job. A main office may use several connected networks, which can span many floors in an office building or cover a campus that contains several buildings.
- Remote locations:
- Branch offices: smaller groups of people work and communicate with each other via a network. Although some corporate information may be stored at a branch office, it’s more likely that branch offices have local networks resources such as printers, but must access information directly from the main office.
- Home offices: When individuals work from home, the location is called a home office. Home office workers often require on-demand connections to the main or branch offices to access information or use network resources such as file servers (where you store corporate or branch offices information and data, not like personal FTP servers).
- Mobile users: mobile users connect to the main office network while at the main office, at the branch office, or traveling. The network access needs of mobile users is based on where the mobile users are located.
Common physical components of a network:
There are 4 major categories of physical components in a computer network:
- Interconnections: they consist of components that provide means for data to travel from one point to another point in the network, this category includes components such as the following:
- NICs: (Network Interface Cards), translates the data produced by the computer into a format that can be transmitted over the local network (digital to analog).
- Network media: such as cables or wireless media, that provide the means by which the signals are transmitted from one network device to another.
- Connectors: provide the connection points for the media, i.e RJ-45
- Switches: devices that provide network attachments to the end systems and intelligent switching of the data within the local network.
- Routers: interconnects networks and chooses the best path between networks for data to go through.
Interpreting a network diagram:
When working with networks, you will most likely be presented by iconic representation of network devices and media that are most common in networks world, the following are some of the most common devices that I might mention during this topic:
Resource-sharing and benefits:
Networks allow end users to share both information and hardware resources. The major resources that are shared in a computer network include the following:
- Data and applications: where users can share files and even software application programs.
- Resources: resources that can be shared include both input devices such as cameras and output devices such as printers.
- Network storage: there are several ways today in which the network makes storage available to users. DAS (Direct attached storage), NAS (Network attached storage) that makes storage available through a special network appliance, SANs (Storage area networks) that provides a network of storage devices.
- Backup devices: a network can also include backup devices, such as tape drivers, that provide a central means to save files from multiple computers. Network storage (NAS) is also used to provide archive capability, business continuance and disaster recovery.
The overall benefit to users who are connected by a network is an efficiency of operation through commonly available components that are used in everyday tasks–sharing files, printing and storing data. This efficiency results in reduced expenditures and increased productivity.
Network user applications and their impacts on the network:
There are many applications available for users in a network environment, but some applications are common to nearly all users.
- E-mail: is a very valuable application for most network users. Users can communicate information electronically in a timely manner, to not only other users in the same network but also other users outside the network.
- Web browsers: allows access to the Internet through a common interface.
- Instant messaging: provides considerable benefit in the corporate world.
- Collaboration: working together as individuals or groups is greatly facilitated when the collaborations are on a network. Individuals creating separate parts of an annual report or a business plan, can either transmit their data files to a central resource for compilation or use a workgroup software application to create and modify the entire document, without any exchange of paper. i.e Lotus Notes
- Databases: allows users on a network to store information in central locations so that others on the network can easily receive selected information in the formats that are most useful to them.
However, applications can affect network performance and network performance can affect applications.
When considering the interaction between the network and applications that ran on the network, bandwidth was historically the main concern. In nowadays applications can be categorized in 3 aspects:
- Batch applications: like FTP, TFTP, inventory updates.. no direct human interaction, you run it, then you forget about it, everything is controlled by the application.
- Interactive applications: like inventory inquiries, database updates, internet browsing.. human-to-machine, bandwidth became more important as users became impatient with slow responses. However since the response time was more dependent on the server than on the network, bandwidth was still not critical. In most cases QoS features could overcome bandwidth limitations by giving interactive applications preference over batch applications.
- Real-time applications: like VoIP and video conferences.. human-to-human, because of the amount of information that is transmitted, bandwidth has become critical. In addition, because there applications are time-critical, latency has become critical too. Even variations in the amount of latency can affect the network. Not only the bandwidth mandatory, QoS is mandatory. VoIP and video applications must be given the highest priority.
Characterstics of a network:
Try to say characterstics 10 times without misspelling..
oh wait you seriously tried that!
Networks can be described and compared according to network performance and structure, as follows:
- Speed: how fast data is transmitted over the network, aka data rate.
- Cost: indicates the general cost of components, installation and maintanance of the network.
- Security: indicates how secure the network is, including the data that is transmitted over the network.
- Availability: is a measure of the probability that the network will be available for use when it’s required. Availability is calculated by dividing the time a network is actually available by the total time in a year and then multiplying by 100 to get a percentage, for example, if a network is unavailable for 15 minutes a year because of network outages, its availability is calculated as follows:
- [Number of minutes in a year – downtime] / [Number of minutes in a year] * 100 = (525600 – 15) / 525600 * 100 = 99.9971%
- Scalability: indicates how well the network can accommodate more users and data transmission requirements. If a network is designed and optimized for just the current requirements it can be very expensive and difficult to meet new needs when the network grows.
- Reliability: indicates the dependability of the components that make up the network. This is often measured as a probability of failure or mean time betweek failures (MTBF).
- Topology: in networks, there are two types of topologies, the physical topology which is the arrangment of the cables, network devices, and end systems, and the logical topology which is the path that the data signals take through physical topology.
Physical topology vs. Logical topology:
The physical topology of a network refers to the physical layout of the devices and cabling. You must match the appropriate physical topology to the type of cabling (twisted pair, coaxial, fiber and so on) that will be installed.
Therefore, understanding the type of cabling used is important in understanding each type of physical topology.
I list three primary categories of physical topologies:
- Bus: in early bus topologies, computers and other network devices were cabled together in a line using coaxial cable. Modern bus topologies establish the bus in a hardware device (HUB) and connect the host devices to the bus using twisted pair wiring.
- Ring: computers and other network devices are cabled together, with the last device connected to the first to form a circle, or ring. The physical connection can be made using either coaxial or fiber cables.
- Star: a central cabling device connects the computers and other network devices. The physical connection is commonly made using twisted pair wiring.
The logical topology of a network refers to the logical paths that the signals use to travel from one point on the network to another; that is, the way in which data accesses the network media and transmits packets across it. Physical and logical topologies of the network can be the same, for example, in a network physically shaped as a linear bus, the data travels along the length of the cable. Therefore, the network has both a physical bus topology and a logical bus topology. However that is the least common case.
Star topology is by far the most common implementation of LANs today. Ethernet uses a logical bus topology in either a physical bus or a physical star. An Ethernet hub is an example of a physical star topology with a logical bus topology.
That would be all for today, next — types of physical topologies.
* edit: this topic continues here: https://xacker.wordpress.com/2008/11/09/physical-topologies/