Ch. 1

The packets used to transmit voice on the Internet are similar to the packets that are used to send email. What are some of the advantages of this approach?

An advantage of using a common packet format is that a single device such as a computer, laptop or PC, is able to run any network communication application. This is possible because one packet format, IP, can serve all these applications and can be transferred across all networks. As long as the device can process IP packets, it can support any networked application.

12.Why is Internet traffic considered "bursty" compared to voice traffic?

Bursty traffic is traffic that occurs in distinct spurts, interspersed by periods of silence. Internet traffic is considered bursty compared to voice traffic because people generally speak in long sentences and the periods of silence are few and far between. By contrast, on the Internet, users typically ask for information that is delivered almost instantaneously by the network generating a burst of traffic. This burst is followed by a relatively long period of silence as the user processes the downloaded information before seeking additional information. Therefore on the Internet, the traffic flow generated by an individual user is quite bursty.

What is business data communications?

Business data communications is the movement of information from one computer application on one computer to another application on another computer by means of electrical or optical transmission systems.

Provide a high-level overview of the structure of a typical data packet. What are the kinds of information you are likely to find in the header of a typical packet?

Each packet has 2 parts - the body and the header. The body of the packet is the segment from the original data carried by the packet. The header is the information added to the body during packetization. The header information aids in the delivery of the packet to the correct destination without errors. The header also enables the body of the packet to be correctly reassembled with the bodies delivered by other packets. The kinds of information in a typical packet header include the address of the data source, the destination, and error detecting information.

1. Use traceroute to trace the route from your home or work computer to your university's website. Show the traceroute output. What networks were encountered along the way? What information about the geographic locations of the routers can you infer from the trace? What was the longest mean delay on any 1 hop along the way?

For my computer, this is shown in figure 17 in chapter 1. The figure is included here for reference as Figure 2. The networks encountered include USF, Florida lambda rail (flrnet), and national lambda rail (nlr). The flrnet routers seem to be located in Tampa (tpa), Tallahassee (tlh), Houston (hous), and Chicago (chic-hous). The longest mean delay is 107 seconds at the 74.114.96.113 router. (Pic. Figure 2: Traceroute output)

13. What is layering?

Layering is the practice of arranging functionality of components in a system in a hierarchical manner such that lower layers provide functions and services that support the functions and services of higher layers. The end user in a layered system interacts only with the top-most layer. The lowest layer typically interacts with physical world to perform the task requested by the end user.

15.Why is layering useful in computer networking?

Layering is useful in computer networking because it provides an effective way to organize all the functionality required for data communication. Each layer is responsible for a specific function in data communication and developers of each layer of the software can focus on improving how that specific functionality is delivered. A side benefit of layering is that it enables up gradation of each layer independently of other layers. For example, you can upgrade a version of your web browser or switch to a different web browser without changing any other network software. You can also easily move between wired and wireless computer networks without changing browsers or email clients. Again, this is possible because the network access functionality is defined in a layer independent of the application layer.

What are some of the factors that make packet switching more complex technologically than traditional phone circuits (circuit switching)?

Packet switching is more complex than circuit switching because it requires data to be segmented into packets at the sending end, and reassembled from packets at the receiving end. The packets need to be delivered reliably to the destination. However, the rewards of the complexity are efficiency. Experiments suggest that packet switching can send up to 100 times more data using the same network resources as circuit switching.

7.What is packetization?

Packetization is the process of breaking down user data into small segments and packaging each of these segments appropriately so that they can be delivered and reassembled across the network. Data segments produced by packetization are generally called packets, although the terms frames and datagrams are also used. Packetization is therefore the idea of sending information as small blocks of information.

Why is packetization useful in business data communication?

Packetization is useful in business data communication because it makes for easy transport of data. Packet networks can serve as a common infrastructure for all forms of information transfer, including phone, video and data.

16.What are the five layers of the TCP/ IP model?

The 5 layers of the TCP/IP stack are: Application layer Transport layer Network layer Data-link layer Physical layer

21.How has the OSI model been useful in the development of computer networks?

The OSI model helped the development of computer networking because technology developers were able to define their technologies in terms of the layers served by their technology. In the end, all proprietary technologies were seen as operating at the data link layer. IP and TCP were used for network and transport layer functionality.

20.What is the OSI model? What was the motivation for the development of the OSI model?

The OSI model is the Open Standards Interconnect model. It is a model, not a real technology solution for networking. The motivation for the development of the OSI model was that in the early days of networking, many firms developed their own proprietary technologies for computer networking. Each of these technologies was a complete networking solution, and the technologies were usually not properly layered. Unfortunately, IT managers had a hard time getting these technologies to interoperate with each other. The result was that if a firm adopted the networking technology of one company, it was forced to buy all computer equipment from the same company. The result was that the choice of a networking technology often made organizations captive customers of the technology vendor, which could charge steep prices for subsequent sales. The challenge therefore was to ensure interoperability between these competing technologies. To overcome this challenge, the ISO came up with the OSI model. The primary contribution of the OSI model in modern networking is that it specified the concept of layers in computer networking and defined the services to be offered at each layer. This improved interoperability between networking technologies.

19.What devices does a packet typically encounter in its journey from source to destination?

The most common devices encountered by a packet while traveling from source to destination are switches and routers. In addition, packets may also encounter network management devices such as proxy servers and firewalls.

17.What are the primary functions of each layer in the TCP/ IP stack?

The primary functions of the 5 layers of the TCP/IP stack are: 5. Application layer: commands to support common end user network needs 4. Transport layer: reliable end-to-end data delivery 3. Network layer: routing and network addressing 2. Data-link layer: error-free transmission over 1 link 1. Physical layer: converts data to signals for transmission over physical media

23.What are the primary functions of each of the seven layers of the OSI model?

The primary functions of the seven layers of the OSI model are: 7. Application layer: request-reply mechanism for remote operations across a network 6. Presentation layer: syntax conversion from host-specific syntax to syntax for network transfer 5. Session layer: create and terminate connection; establish synchronization points for recovery in case of failure 4. Transport layer: segmentation, reassembly of packets in one connection, multiplexing connections on one machine 3. Network layer: routing and network addressing 2. Data link layer: error-free data transmission over a single link 1. Physical layer: convert data to signals for transmission over physical media

TCP is often considered the most important layer of the TCP/ IP model. What are the primary responsibilities of TCP?

The primary responsibility of TCP is segmentation and reassembly of packets. TCP provides highly reliable host-to-host data delivery over packet switched networks of arbitrary levels of complexity and unreliability.

22.What are the seven layers of the OSI model?

The seven layers of the OSI model are: 7. Application layer 6. Presentation layer 5. Session layer 4. Transport layer 3. Network layer 2. Data link layer 1. Physical layer

1. Use traceroute to trace the route from your home or work computer to the website of a university or company on another continent. Show the traceroute output. What networks were encountered along the way? What information about the geographic locations of the routers can you infer from the trace? What was the longest mean delay on any 1 hop along the way? What factors do you think caused this delay?

This is shown in figure 18 in chapter 1 and is included here as Figure 3 for reference. The networks encountered include flrnet, nlr, and pacificwave. In addition to the routers above, one of the routers seems to be located in Tokyo. The longest hop takes about 115 msecs (transpac). This delay is due to the length of the cable that crosses the Pacific Ocean. (Pic. Ocean.)

Briefly describe what traceroute does and how it is useful (you may find articles on traceroute on sources such as Wikipedia useful).

Traceroute is a computer network tool used to show the route taken by packets across an Internet Protocol (IP) network. Traceroute is often used for network troubleshooting. By showing a list of routers traversed, it allows the user to identify the path taken to reach a particular destination on the network. This can help identify routing problems or firewalls that may be blocking network traffic. (Wikipedia.com)