Session Layer Questions 1. Define the purpose of the session layer within the OS

Question

Session Layer Questions

1. Define the purpose of the session layer within the OSI model.

2. Give a brief overview of an RPC and define its main goal.

3. List the four primary actions of the session layer and give a description of each.

4. What are 5 examples of session later protocols?

5. Define Network Address Translation.

6. What is dialog control?

7. What are the three basic transmission modes and give a brief definition for each.

8. What are the four services the session layer provides and give a brief definition of each.

9. Give a brief description of SQL and its purpose?

10. Describe token management.

Explanation / Answer

1. According to the OSI Model, the session layer is where connections are established, managed, and torn down. For connection-oriented network protocols, understanding how the session layer works, and what symptoms would help you identify when it's not working, is an important part of your job as a network administrator. However, because TCP doesn't respect the OSI model, we have to sort of carve TCP/IP out of this conversation, which really limits its practical application in most environments.

When you think about session-oriented communications vs. connectionless conversations, you might compare them to a telephone conversation vs. using a walkie-talkie. With a telephone, you call the person who you want to talk to, establish a connection -- or session -- and then you hang up, severing the connection once the conversation is completed. With a walkie-talkie, you simply speak into the device and hope that the person on the other end is listening and that they respond in kind. There's no session established.

2 . remote procedure call ( RPC):is a network programming model for point-to-point communication within or between software applications.

In RPC, the sender makes a request in the form of a procedure, function, or method call. RPC translates these calls into requests sent over the network to the intended destination. The RPC recipient then processes the request based on the procedure name and argument list, sending a response to the sender when complete.

RPC applications generally implement software modules called "proxies" and "stubs" that broker the remote calls and make them appear to the programmer the same as local procedure calls (LPC).

RPC calling applications usually operate synchronously, waiting for the remote procedure to return a result.

RPC incorporates timeout logic to handle network failures or other situations where RPCs do not return.

RPC has been a common programming technique in the Unix world since the 1990s. The Open Systems Foundation (OSF) Distributed Computing Environment (DCE) and Sun Microsystems Open Network Computing (ONC) libraries both were widely deployed. More recent examples of RPC technologies include Microsoft DCOM, Java RMI, and XML-RPC and SOAP.

3.SESSION LAYER:The session layer allows session establishment between processes running on different stations. It provides: Session establishment, maintenance and termination: allows two application processes on different machines to establish, use and terminate a connection, called a session.

Session support: performs the functions that allow these processes to communicate over the network, performing security, name recognition, logging, and so on.

4.session layer tracks connections, also called sessions. The session layer should keep track of multiple file downloads requested by a particiular FTP application, or multiple telnet connections from a single terminal client, or web page retrievals from a web server.

With TCP/IP this functionality is handled by application software addressing a connection to a remote machine and using a different local port number for each connection.

The session layer performs the following functions:

Communication with the Presentation layer above.
Organize and manage one or more connections per application, between hosts.
Communication with the Transport layer below.

EXAMPLE

Sessions are used to keep track of individual connections to remote servers. Your web browser is an excellent example of the use of sessions.

Your web browser (an application layer object) opens a web page. That page contains text, graphics, Macromedia Flash objects and perhaps a Java applet. The graphics, the Flash object and the Java applet are all stored as separate files on the web server. To access them, a separate download must be started. Your web browser opens a separate session to the web server to download each of the individual files. The session layer keeps track of which packets and data belong to which file and keeps track of where they go (in this case, to your web browser).

In most modern Internet applications, the session, presentation and application layers are usually rolled together inside the application itself, thus, your web browser performs all functions of the session, presentation and application layers.

5.A NAT (Network Address Translation or Network Address Translator) is the virtualization of Internet Protocol (IP) addresses. NAT helps improve security and decrease the number of IP addresses an organization needs.

6.Dialog Control Language (DCL) is a high-level description language and interpreter within AutoCAD for creating simple graphical dialogs. AutoLISPextensions use it to interact with the user in the AutoCAD environment.

7.Simplex, half-duplex and full-duplex connections

There are 3 different transmission modes characterised according to the direction of the exchanges:

A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions (for example, from your computer to the printer or from the mouse to your computer...).

A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time. With this type of connection, each end of the connection transmits in turn. This type of connection makes it possible to have bidirectional communications using the full capacity of the line.

A full-duplex connection is a connection in which the data flow in both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission.

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