Local Area Networks: Elements, Servers, and Layers

What are the elements of a network?

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There are usually three basic elements of a computer network: software, hardware, and protocols. A combination of these three elements forms a network. When we assume that a computer network is like a rail or road where vehicles pass through, then the “traffic rules” are the protocols in a computer network. These protocols are rules or set out procedures on how two or more machines can communicate. The main uses of this rule are to control traffic and prevent congestion in the network. They are also used to show how application programs communicate with each other and how they exchange the rules. The ISO has a seven-layered architecture which is used to describe how the protocols are applied in each layer. These layers perform certain specific functions in the transportation of the data between them (Drew, 2000, pp. 126).

Computer network software is the information or programming which is used to make it possible for various computers to communicate or be able to connect to each other. Hence, it is used to allow the computers in a network to share diverse information. It usually puts information into packets and these packets contain the header and trailer. The trailer and the header enclose information regarding the destination of the packet and the code of the packet. There is various software that this possible depending on the nature of such things as security. (Jason, 2003, pp. 270).

Computer network hardware usually refers to various equipment that facilitates various equipment to be connected to form a computer network. These various equipment include switches, routers, network interface cards, and other hardware. This also includes the connection materials i.e. cables. Information is usually transferred using an electrical signal hence the frequent use of copper-based Ethernet adapters. Other equipments that are associated with computer networks are the data center equipment, network services, and content delivery.

Difference between router and switches

These two devices allow the capability of computers or a computer to connect to other computers, certain network devices, or other networks. They have ports that are used to connect other network devices. But, the difference comes around during their operations and functionality.

A switcher usually pays a lot of attention to certain traffic that passes through it and is able to know the particular addresses of the same traffic. An example is when it sees information from a machine X and comes through port 2, it then knows that the machine X is connected to port 2 and any traffic that is to be submitted to machine X should go through that port and not any other port (Meyn, 2007, pp. 90).

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On, the other hand a router is usually complicated and smarter compared to a switch. A router is a device that can be programmed to understand, manipulate and direct the data to a certain specific destination. Certain routers support the use of firewalls for their discrete use and security. They are also configured to treat different traffic differently. They are mostly used in the connection of the private network to various networks such as WANs (Schoun, 2006, pp. 50).

Difference between a Wide Area Network and a Local Area Network

A local area network (LAN) is a computer network that covers a small geographical area such as an office, home, or a group of buildings but is an area associated. They are usually suitable in those scenarios where the objective is oriented; serves a specific object or the aim of the organization.

A wide area network (WAN) is a type of computer network that covers a broader area. This means that they use routers and public communication links. An example is an internet. They are usually used to connect LANs with various networks such as MANs and PANs. This will enable computers in a certain location to communicate with other computers in different regions. Most WANs are specific to a specific organization. They use network protocols such as TCOP / IP. The functions of a WAN are many and different compared to LAN. WAN can be accessed by many people through such things as HTTP and websites (Roderick, 2002).

What is the difference between an Intranet and an Extranet?

An Intranet is usually an information portal that is designed specifically for internal communications of medium, large, small institutions of varying size and complexity. They are usually custom-designed to meet the specific needs of a certain institution no matter where they are situated, whereas the extranet is specifically designed for external use alone. These are usually limited to access and require specific communications protocols (Rashi, 2002, pp. 114).

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Intranet can be used in schools, institutions, and companies while the extranet is used by banks, specific agents to a certain organization.

SMTP in detail

The communication of e-mail requires various different protocols and elements. Hence, the duties for delivering emails are undertaken by Simple Mail Transfer Protocol (SMTP). It is usually associated with TCP / IP.

It usually consists of simple text-based protocols and the destination of the text is specified. The information is then moved from one position to the next with various protocols that are associated. The outgoing mail STMP is usually known by the email client and with the help of the MX (Mail eXchange), the information can be sent. It also contains the domain name of the recipients. Usually, the SMTP initiates a connection with the TCP through port 25 which is standard. Hence, it is usually a push protocol and supports various mail clients such as POP3, IMAP, or an ETRN (Radal, 2002, pp. 143).

When there is an outgoing message the email client requires just the IP address of the SMTP. The server will then deliver the message on behalf of the sender. It usually supports various policies and network designs. It has no restrictions to the type of topology, the location of the client, or the e-mail provider. The original SMTP had not supported the authentication of the senders. They later developed and designed the SMTP-AUTH. But, it didn’t support spamming problems that are associated with e-mails.

The protocols that are associated with SMTP are the MUA which is usually from the sender, the MSA which is the mail server. From the MSA the message is delivered to MTA and runs from the same machine. The MTA then looks for the address destination from the MXs records and pushes the information via TCP port number 25 and through the SMTP. It’s then received by the MTA and delivered by the mail delivery agent (MDA) to a local mail delivery server. The MDA either stores the information or forwards it with the help of SMTP or its branch LMTP. It’s then ready for its retrieval by the authenticated mail clients (MUAs) (Rolf, 2003, pp. 143).

SMTP has various disadvantages and advantages. One advantage of SMTP is that it’s very popular and frequently used by many applications. It is also supported by many types of platforms and by many vendors. Hence, the machines that are used don’t have to be configured. The initial cost of its implementation is low and the associated administration costs are also low. Hence, it makes a lot of savings in terms of running the business using it. The addressing style and scheme are simple and can be checked easily if there is any kind of problem.

Like all equipment and software that has an advantage, it has to have a disadvantage. One problem which is associated with SMTP is that it lacks various types of functions, these functions are the poor type of security. Also, the simplicity of its functionality reduces or limits its usefulness.


This is the inclusion of data from different protocols regions. It is mainly between the upper layer protocol and the lower protocol. This then allows information and various functionality to be added. An example is the internet protocol where most applications use User Datagram (UDP) or the Transmission Control Protocol (TCP). Information in user data is then encapsulated in a certain UDP datagram which is later encapsulated through an IP packet then it’s sent to the data link layer. Decapsulation is the removal of the added information in a packet.


When the information enters the data link layer it checks for cyclic redundancy check (CRC) on the frame. This is done so that it checks whether there are errors, if it finds out that there are no errors it starts working on it. It will remove the added layer which was added previously. The information is then passed to the upper layer (Network Layer). When the packet reaches the Network layer the IP address is stripped and passed to the transport layer. The packet name changes to a segment. It rebuilds the segment and confirms with the sending machine if it was the complete message. This process of communication uses the TCP because it’s sending back an ACK message. It then sends the data stream to the application layer (Shapiro, 2003, pp. 20).

What is a DHCP server?

Its main duties are to assign the IP addresses default gateway, subnet mask, and other IP associated parameters. When a peripheral is added to a network the DHCP client sends a signal or a query from the DHCP server. Usually, the DHCP server manages details that constitute other peripherals and their configurations. When the server receives the signal it will assign the computer with IP address, Time period, and other TCP/IP configurations. This information is usually initiated when the machines are booting up.This is a device that is used to assign unique Internet Protocol (IP) to computers that are on a network. This is due to the fact that there is no more than one computer in the network share the IP address to prevent conflicts. When a computer is added to a network the DHCP servers assign a specific IP address such as if it is available. This assignment of the IP address usually lasts for a small specified period. But, two network cards can use the same address if they are grouped to work in a single network. The importance of this is to improve redundancy or capacity (William, 2003, pp. 37).

There are three ways that the DHCP allocates the addresses: dynamic, automatic, and manual. Dynamic usually uses the principle of lease time, the lease period can fluctuate from one hour to several months depending on the type of application. This IP address can be maintained for a long period and supports renewal before the lease expires. Automatic also called DHCP Reservation usually allows the permanent allocation of the IP address. Manual is when the client physically locates the address and with the help of DHCP protocol messages shows that the addresses are located. This then prevents the DHCP protocol from assigning the same IP address to another machine.

The DHCP has various advantages that include easier administration management since the IP addresses are automatically configured by the DHCP server. Also even if the machine has been moved to a different subnet, after rebooting the machine will still be able to use the network.

Domain Name System

This is a method in which all addresses associated with the computer network are created. It helps to make the internet to be user-friendly by using simple English to identify varied information concerning the internet. The internet usually contains four elements: a domain name, server prefix, extension, and the county code but it is optional. An example is when it changes human-readable hostnames to IP addresses e.g. www.computers.com to 312.32.454.656. It can also be able to store certain information and addresses such as a list of mail exchange servers.

How do these two relate to each security?

Due to the frequent use of DHCP protocol before the introduction of internet security, there arise potential risks such as unauthorized DHCP servers and Unauthorized DHCP clients. Certain new security measures have been introduced like rejecting information from sources that are not valid and with the help of IPsec within the DHCP server. They should be linked to a secure type of DNS server which allows for troubleshooting.

During the creation of DNS, there were no internet security issues, hence poor security. An example is DNS cache poisoning which confuses the DNS. A DNSSEC is added to DNS to support cryptographically signed responses. Even if there is enough encryption there is usually the effect of a virus. This is due to the TTL effect. There can also be the difference between similar addresses, for example, PayPal.com and paypa1.com that a computer cannot differentiate, for instance, 1 and I. It’s a big issue for those domains which support internationalized domain names and is exploited during phishing. But with the help of Forward Confirmed reverse DNS can help check the DNS results (Meyn, 2007, pp. 90).

Application Layer standards

There are various layers that information can pass in a network. The policy of the ISO model and the TCP / IP model has the same characteristics, but the difference is the number of layers that information can successfully pass. In an ISO model, the layers are seven in total and it is mostly referred to as the original layer. They include the application layer, presentation layer, session layer, transport layer, network layer, data link layer, and physical layer. On the other hand, the TCP / IP model is five-layered.

The application, internet, and data link layers are:

  1. Application layer.
  2. Network Layer
  3. Transport Layer
  4. Data Link Layer.
  5. Physical Layer

Application Layer

This is the highest layer in an OSI architecture and it servers as an intermediary to applications so that they can perform their duties in an open environment. It is the fifth layer in the TCP IP layer model and the seventh in the OSI model. The programs that assist the application layer are called the application processes. It usually operates using various protocols on different layers mostly the layer that is below it. It also supports the application which provides specific elements which are called modules that are used to support various commonly available application-related services. It directs the presentation layers on certain duties and provides semantic conversation between certain processes. Some common applications that it uses are virtual terminals, job transfer, and virtual files (Randal, 2002, pp.144).

Transport Layer

It bridges between the application layer and the network layer. This is the second-highest level in a TCP IP model. It’s the fourth layer in the seven-layer ISO model and it mediates between the session layer and network layer. It usually contains two protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). The TCP is frequently used. It is usually controlled by the Computer OS and advances the basic Network layer duties to a more powerful type. It usually takes the available packet and adds other information such as the address of the destination IP address. They (TCP) provide the end-to-end reliable means for good communication. The flow control is managed by the ARQ protocol.

Network Layer

This is the third layer to both the OSI and TCP/IP models. It is also called the Internet layer by the TCP/IP model. It lies between the transport layer and the data link layer. Duties are the transfer of information from the client to the server and vice versa. It does this by providing certain means of transferring data from one point to the other through many networks and maintains the quality of the service and provides functions for error control.

Data Link layer

This is the second layer in both the OSI and TCP /IP models. It lies between the network layer and the physical layer. It’s the layer that moves data between nodes that are adjacent, for example, WAN network or LAN. They provide the producers and conditions that give it the power to mediate between different networks and also can detect and correct any errors that may have occurred in the physical layer. The protocols that it usually uses are the Ethernet for LAN and PPP, ADCCP, and HDLC.

Physical layer

This is the lowest layer in both the seven-layer model and the five-layer model. It solves any requests that are requested by the data link layer. It is the most basic layer and usually provides the raw bits. Nothing is usually added to the data by this layer. It usually provides a mechanical, electrical, or procedural capability for transmission of the medium. Here the communication uses various types of cables to enable it to transfer the information. Examples of these cables are coaxial and copper wires.


Drew, H. (2000). Windows 2000 Network Services, New York, Sam Publishers, pp. 126 -145.

Jason, G. (2003). Computers: The definitive Guide, New York, McGraw-Hill Osborne Media, pp. 270.

Meyn, P. (2007). Control Techniques for Complex Networks, London, Cambridge University Press, pp. 82 – 120.

Michael, H. (2003). Writing Secure Code, New York, Microsoft Press, pp. 210.

Randal, K. (2002). AIX 5L Administration, California, Peachpit Press, pp. 133 – 150.

Rashi, G. (2002). Microsoft Windows 2000 security, London, Premier Press, pp. 97 – 127.

Roderick, W. (2002). Advanced Linux Networking, Briston, Addison Wesley, pp.16-112.

Schoun, R. (2006). MAC OS X System Administration Reference, Apple Training Series, pp. 43 – 89.

Shapiro, E. (2003). Computer Network Protocols, New York, Macmillan Company, pp. 12 – 67.

William, B. (2003). Introduction to World Wide Web, New York, New Riders, pp. 35 – 39.

Rolf, O. (2003).Security Technology for the World Wide Web, Norwood, Artech House Publishers, pp. 32 – 56.

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