Layer 4-7 Testing

The upper layers of the Open System Interconnection (OSI) protocol stack are referred to as Layers 4-7. They apply to the type of application rather than the lower layers which are designed to transfer data packets from place to place.

Layer 4, also known as the Transport Layer, provides transparent transfer of data between hosts. It is usually responsible for end-to-end connection, error recovery, flow control and for ensuring complete data transfer. It provides a transparent transfer of data between users and while relieving the upper layers (Layer 5 through 7) of any concerns with providing reliable data transfers.

Layer 5 is also known as the Session Layer that manages dialogue between end-user applications. It provides for either full duplex or half-duplex operation and establishes check pointing, adjournment, termination and restart procedures.

Layer 6 is the Presentation Layer responsible for the delivery and formatting of information to the application layer for either further processing or display.

Layer 7, the Application Layer, provides services for user applications to employ. Even though a Web browser is an application, it does not "reside" in the application layer. Rather, the web browser makes use of a protocol operating in that layer; this protocol is the Hypertext Transfer Protocol (HTTP).

Layer 4-7 Testing Solutions
Layers 4-7 can all be tested simultaneously. Testing the capacity of your network to handle Triple Play's requirements of voice, video and data will ensure that each respective layer is tested. Also, performing security tests by either incorporating viruses in e-mails and/or introducing Denial of Service (DoS) attacks with real traffic will also test the attributes of Layers 4-7. Another way to test Layers 4-7 is by testing web applications.

It is possible to test Layer 4 separately by introducing delay, duplication, reordering, fragmentation, loss, errors and jitter while transporting packets across the network.

More Information on Layer 4-7
In the Internet Protocol Suite, Layer 4 is most commonly achieved by the connection oriented Transmission Control Protocol (TCP) and the datagram-type transport, User Datagram Protocol (UDP). Though UDP does not provide error recovery or flow control.

Layer 5 is typically unused, but it does have a few places where it is useful. The idea is to allow information on different streams, perhaps from different sources, to be properly combined.

Layer 6 is the first layer where people really start to care about what is being sent at a more advanced level than ones and zeros. For example, Layer 6 deals with the issues of how a string is represented. In Visual Basic, a string is represented as "13\thisisastring" while in C/C++ it is represented as "thisisastring\0".
To ensure that each respective layer is tested, Spirent tools test the capacity of your network to handle voice, video and data and perform security tests with real traffic

   To ensure that each respective layer is tested,
   Spirent tools test the capacity of your network
   to handle voice, video and data and perform
   security tests with real traffic

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