One of the key differences between different network types is their geographical scope. A local area network, or LAN, is made up of a smaller group of computers linked together and located in the same small area such as a room, a floor or a building. A backbone network, or BN, is a larger network which connects multiple LANs, WANs, MANs or other BNs together and can range from a few hundred feet to miles in size. Metropolitan area networks, or MANs, normally range in size from a few miles up to thirty miles and LANs and BNs from different areas to each other as well as to WANs. Wide area networks, or WANs, can be hundreds or thousands of miles in size and connect MANs and BNs across these distances.
Question 14: Explain how a message is transmitted from one computer to another using layers.
The message is first created at the application layer using a software application. This software translates the message based on the protocol being used to transfer the message and places the necessary information along with the message into a Protocol Data Unit (PDU) which is also known as a ‘packet’. This packet is then passed on to the Transport Layer. The transport layer, using its own Transmission Control Protocol, or TCP, takes the packet from the application layer and places it in a TCP packet along with whatever additional data the TCP segment requires, and passes it along to the Network Layer.
The Network Layer, as with the previous layers, has its own protocols. In this case we’ll use the Internet Protocol, or IP. IP determines the next destination as the message is routed through the network, places the TCP packet inside an IP packet along with any additional required data and passes in on to the Data Link Layer. The Data Link Layer will again have its own protocols and rules for transmitting the message and will format the message with the necessary start and stop markers, add error checking data, place the IP packet within a new packet based on the Data Link Layer protocol being used and pass it on to the Physical Layer.
The Physical Layer is whatever physical hardware is being used to transmit the message to the other computer. The hardware then converts the data passed to it into a series of electrical pulses and sends them across the network to their destination. The electrical pulses are then captured by the receiving hardware, which then passes the Data Link Layer packet to be unpacked by the Data Link Layer. From there the Network Layer’s packet is passed on to the Network Layer to be unpacked. The Transport Layers packet is passed on to the Transport Layer which finally passes the Application Layer’s packet on to be processed by the Application Layer.
Question 17: Describe two important data communications standards-making bodies. How do they differ?
One major data communications standards making body is the Telecommunications Group, or International Telecommunications Union. The Telecommunications Group is standards setting group based out of Geneva with members from approximately 200 countries and focuses on setting technical standards.
Another is the Internet Engineering Task Force, or IETF, is an organization which sets the standards which govern how much of the internet operates.
While both of the organizations are similar in that they are standard making bodies focused on data communications, they differ in the scope of their focus as well as the structure of membership. The ITU’s membership is made up of representatives from different countries around the world and focuses on technical standards for international telecommunications. The IETF’s membership completely different, the IETF membership is open to anyone and anyone may attend their meetings and receive their mailings. They also have a much narrower focus and solely set standards regarding the operation of the internet.
FitzGerald, J., & Dennis, A. (2009). Business data communications and networking. Hoboken, NJ: John Wiley.