The session layer is level five of the seven level OSI model. It responds to service requests from the presentation layer and issues service requests to the transport layer. The Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model for short) is a layered, abstract description for communications and computer network protocol design. ... The application layer is the seventh level of the seven-layer OSI model. ... The presentation layer is the sixth level of the seven layer OSI model. ... In computing and telecommunications, the transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer. ... The network layer is third layer out of seven in OSI model and it is the third layer out of five in TCP/IP model. ... This article does not cite any references or sources. ... According to the IEEE 802 family of standards, Logical Link Control (LLC) is the upper sublayer of the OSI data link layer. ... The Media Access Control (MAC) data communication protocol sub-layer, also known as the Medium Access Control, is a part of the data link layer specified in the seven-layer OSI model (layer 2). ... This article does not cite any references or sources. ... The Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model for short) is a layered, abstract description for communications and computer network protocol design. ... The presentation layer is the sixth level of the seven layer OSI model. ... In computing and telecommunications, the transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer. ...

The session layer provides the mechanism for opening, closing and managing a session between end-user application processes, i.e. a semi-permanent dialogue. Communication sessions consist of requests and responses that occur between applications. Session layers are commonly used in application environments that make use of remote procedure calls (RPCs). In computer science, in particular networking, a session is either a lasting connection using the session layer of a network protocol or a lasting connection between a user (or user agent) and a peer, typically a server, usually involving the exchange of many packets between the users computer and... Remote procedure call (RPC) is a protocol that allows a computer program running on one computer to cause a subroutine on another computer to be executed without the programmer explicitly coding the details for this interaction. ...

An example of a session layer protocol is the OSI protocol suite Session Layer Protocol, also known as X.225 or ISO 8327. In case of a connection loss this protocol may try to recover the connection. If a connection is not used for a long period, the session layer protocol may close it and re-open it. It provides for either full duplex or half-duplex operation and provides synchronization points in the stream of exchanged messages.^[1] The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... A duplex communication system is a system composed of two connected parties or devices which can communicate with one another in both directions. ... A duplex communication system is a system composed of two connected parties or devices which can communicate with one another in both directions. ...

Other examples of session-layer implementations include Zone Information Protocol (ZIP) – the AppleTalk protocol that coordinates the name binding process; and Session Control Protocol (SCP) – the DECnet Phase IV session layer protocol. AppleTalk is a proprietary suite of protocols developed by Apple Computer for computer networking. ... AppleTalk is a proprietary suite of protocols developed by Apple Inc for computer networking. ... DECnet is a proprietary suite of network protocols created by Digital Equipment Corporation, originally released in 1975 in order to connect two PDP-11 minicomputers. ...

In brief: the session layer establishes, manages and terminates connections (sessions) among cooperating applications. It also adds traffic flow information.

Session layer support in the Internet

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The Session layer does not exist as a separate protocol layer or process in the four or five layer TCP/IP model, but its functionality is partly provided by the TCP/IP model transport layer, and partly by some TCP/IP model application layer protocols. However, a major part of its functionality is typically unused in Internet applications. The TCP/IP model or Internet reference model, sometimes called the DoD model (DoD, Department of Defense) ARPANET reference model, is a layered abstract description for communications and computer network protocol design. ... In computing and telecommunications, the transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer. ... The application layer is the seventh level of the seven-layer OSI model. ...

The OSI model made the session layer responsible for "graceful close" of sessions, which is a property of the TCP protocol, provided by the four-way SYN handshake process. The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ...

The OSI model also made the session layer responsible for session checkpointing and recovery, which is not usually used in the Internet protocols suite. However, there are a few applications layer protocols where the concept is useful. The idea is to allow information on different streams, perhaps originating from different sources, to be properly combined. In particular, it deals with synchronization issues, and ensuring nobody ever sees inconsistent versions of data, and similar things. To quote Matt Dillon (of DragonFly BSD), Checkpointing allows you to freeze a copy of an application so that, in theory, you can restore the program to that running state at a later point in time. ...

One application which is fairly intuitively clear is web conferencing. Here, we want to make sure that the streams of audio and video match up - or in other words, that we do not have lip synch problems. We may also want to do floor control - ensuring that the person displayed on screen and whose words are relayed is the one selected by the speaker, or by some other criteria. Web conferencing is used to conduct live meetings or presentations over the Internet. ... Lip synchronization is the synchronization of audio signals (sometimes with corresponding video signals) so that there is no noticeable lack of simultaneity between them. ...

Another big application is in live TV programs, where streams of audio and video need to be seamlessly merged from one to the other so that we do not have half a second of blank airtime, or half a second when we transmit two pictures simultaneously. Live television refers to television broadcasts of events or performances as they are happening, or on a delay of several seconds, rather than from video recordings or film. ...

List of Session layer services

• Authentication
• Permissions
• Session restoration (checkpointing and recovery)

For other uses of the terms authentication, authentic and authenticity, see authenticity. ... Look up Permission in Wiktionary, the free dictionary. ... To quote Matt Dillon (of DragonFly BSD), Checkpointing allows you to freeze a copy of an application so that, in theory, you can restore the program to that running state at a later point in time. ...

Examples

AppleTalk is a proprietary suite of protocols developed by Apple Inc for computer networking. ... AppleTalk is a proprietary suite of protocols developed by Apple Inc for computer networking. ... H.245 is the Control Protocol for Multimedia Communication within H.323. ... The title given to this article is incorrect due to technical limitations. ... L2F is a virtual private network system, developed by Cisco. ... In computer networking, the Layer 2 Tunneling Protocol (L2TP) is a tunneling protocol used to support virtual private networks (VPNs). ... NetBEUI redirects here. ... Password Authentication Protocol, sometimes abbreviated PAP, is a simple authentication protocol used to authenticate a user to a remote access server or Internet service provider (ISP). ... Point-to-point tunneling protocol (PPTP) is a protocol from Microsoft for virtual private networks. ... Remote procedure call (RPC) is a protocol that allows a computer program running on one computer to cause a subroutine on another computer to be executed without the programmer explicitly coding the details for this interaction. ... RTP Control Protocol (RTCP) is a sister protocol of the Real-time Transport Protocol (RTP). ... The short message peer-to-peer protocol (SMPP) is a protocol for exchanging SMS messages between SMS peer entities such as short message service centres. ... Secure Copy or scp is a means of securely transferring computer files between a local and a remote host or between two remote hosts, using the Secure Shell (SSH) protocol. ... The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. ... SSH redirects here. ... AppleTalk is a proprietary suite of protocols developed by Apple Computer for computer networking. ... The Sockets Direct Protocol (SDP) is an InfiniBand specific protocol defined by the Software Working Group (SWG) of the InfiniBand Trade Association (IBTA). ...

See also

• Session (computer science)

In computer science, in particular networking, a session is either a lasting connection using the session layer of a network protocol or a lasting connection between a user (or user agent) and a peer, typically a server, usually involving the exchange of many packets between the users computer and...

References

1. ^ Javvin, ISO-SP: OSI Session Layer Protocol (X.225, ISO 8327)