AT&T 7100 series manual Session Layer, Presentation Layer, Application Layer, Standard Protocols

COMMUNICATIONS PROTOCOLS D-5

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Session Layer

The session layer, or layer 5, provides a mechanism for controlling dialogue between applications. It establishes, manages, and terminates connections between cooperating applications.

Presentation Layer

The presentation layer, or layer 6, provides independence to the application processes from differences in syntax. This layer defines the syntax used for communication between applications and provides for the selection and subsequent modification of the type of communication to be used. Encryption is a type of presentation layer protocol.

Application Layer

The application layer, or layer 7, provides a means for distributed applications to access the OSI environment. Examples of protocols at this level are file transfer and electronic mail protocols (for example, X.400).

STANDARD PROTOCOLS

Standards organizations differ according to how they name the standards they formulate. For you to determine whether a standard applies, it may be helpful to you to become familiar with the following naming conventions:

∙Names of digital standards formulated by the CCITT start with X.

∙Names of analog standards formulated by the CCITT start with V.

∙Names of ISDN standards formulated by the CCITT start with I or Q.

∙Names of standards formulated by the EIA start with RS (for recommended standard).

∙Names of telecommunication standards formulated by the U.S. federal government start with FED-STD.

∙Names of information processing standards formulated by the U.S. federal government start with FIPS.

∙Names of standards formulated by the IEEE start with IEEE.

∙Names of standards formulated by ANSI start with X.

CCITT Standards

Tables 1-1,1-2,and 1-3name some CCITT digital, analog, and ISDN standards. If the CCITT standard is equivalent to any other standard, the name of the equivalent standard is also given.