Chapter 2 Section 3 (2.3) Flashcards
Why is layered architecture so advantageous to OSI and TCP/IP models?
: Each layer is assigned a specific set of functionalities and responsibilities. This means that one layer does not have to do the work of all the other layers or understand what the other layers are doing. Instead, each layer is responsible only for its assigned duties, no more, no less.
What are the three key services provided at the application layer of the OSI model?
(1) synchronizing the services between a user application and the protocol(s) it may use, (2) ensuring that necessary resources required by an application service are available, and (3) making sure that the correct communication protocol or service is available to the application.
Why do open models lend themselves to duplication?
The designers of technologies that use these models do not have to take on the cost and labor of creating new ones. Models, because they are conceptual, can be modified to fit varying conditions. Technologies based on established models provide known advantages and disadvantages. Software and hardware vendors who create products based on accepted models can produce products that have a wider consumer appeal.
What do the Open Systems Interconnection (OSI) and the Transmission Control Protocol/Internet Protocol (TCP/IP) models have in common?
First, they are both open architecture models. This means that anyone, anywhere, at any time, can freely design or create technologies based on these models, which is a real advantage. Second, both models are based on a layered architecture. This means that each model can be broken into several distinct components, called layers. Each layer within the model has its own particular and specific responsibilities and functionalities. A major topic discussed throughout this text is what these layers do, how they do it, and why. And finally, each model is well established and accepted by the data and telecommunications industries as models that provide clear guidelines as to how to build a data communications network that works. But remember, models are conceptual guidelines; how they are physically implemented can vary.
What are the responsibilities of the data link layer in the OSI model?
This layer takes unpackaged bit stream data arriving from the physical layer and packages the bits into units called frames. The data link layer attaches a physical address to each frame. This layer is responsible for getting each frame from one node to another on its way from sender to receiver. This layer also provides for flow control, error control, and access control. So, whereas the network layer provides for logical addressing, the data link layer provides for physical addressing.
What are some questions a networking technologist might ask before implementing a physical data communications network?
What is the purpose of the network? What services will this network be expected to provide? What types of connectivity, 10 people or 100,000, are required? What are the physical dimensions the network? Is the network limited to the size of a room or the expanse of a country? What type of business and user applications will this network have to support? Are the applications online real-time, 24/7 as they say, or are they batched? Based on business requirements, what bandwidth and transmission issues need to be addressed? Will there be a need for remote accessibility? What size budget is available? Will there be a qualified staff to support the network? Does management understand the types of resources the network might require, and is management willing to support those needs? Do any regulatory issues–city, state, county, national, and/or international–need to be addressed?
What is a MAN, a LAN, and a WAN? For what purpose is each used?
A metropolitan area network (MAN) is a network that generally spans a city or a county. An organization can use a MAN to cover greater distances at higher data rates than those offered by a LAN (local area network). A MAN can be used to connect BNs and LANs. An organization may find, if justified by transmission-volume needs, that having a private MAN may be less expensive than leasing these services from a local telecommunications company. A MAN is between a LAN and a WAN (wide area network) in terms of its geographic scope. However, MANs, unlike LANs, are usually subject to federal and state regulations.
Explain the two categories (“end-to-end layers” and “chained layers”) of the OSI model’s seven layers.
With the OSI model, the seven layers can be divided into two categories: end-to-end layers and chained layers. The top four layers are the end-to-end layers: application, presentation, session, and transport. These four layers are “end-to-end” because the layers on the sender’s “end” and receiver’s “end” directly communicate with each other. The four top layers on each “end” establish a communication. This communication provides an “end-to-end” connectivity. The remaining three lower layers–network, data link, and physical–are the chained layers. These three layers are “chained” in that they are used to link, or chain, one physical device to another in a communication path. The number of devices that need to be linked, or chained, depends on the number of intermediary devices or networks between the sender and receiver of a communication. In a network or enterprise, there may be many intermediary devices or networks between a sender and receiver. The lower three layers provide the chain of links that permits the sender and receiver to have a communication.
Describe a backbone network.
An organization’s enterprise network may consist of dozens, hundreds, or thousands of individual networks. The networks of the enterprise are typically connected through a backbone network (BN). A BN is usually a high-speed circuit that connects all of the networks within the enterprise, allowing them to communicate with each other.
What is the role of common carriers in a WAN?
Business data communication needs may require that data be transported over great geographic distances, such as across a state, several states, a country, or even around the world. A network on this scale is called a wide area network (WAN). A WAN will very commonly use circuits provided by common carriers. In our discussion, a common carrier is a business or company that provides communication services of varying types to the general public. Common carriers include such organizations as Sprint, MCI, and AT&T, among others. A WAN can connect BNs and MANs. The infrastructures that create and support a WAN are heavily regulated. Figure 2.6 illustrates a WAN that spans a continent.
