· Overcrowding control Ø Realization Software and hardware controls.Ø Flow Control It manages therate of data transfer between two nodes and increases the speed of datatransfer. Figure 2: Transport layerIn above diagram, the data which isfirst divided into segments is sent from application layer to network layer andthese segments passes through network layer and receives by application layerand when data is received to the recipient.
It again merged into original form asit was before. 1.1.1. Issues with transport Ø Insecurity In transport layer, when data is being transferred through wirelessnetworks or other mediums.
We are not sure about the secure transmission ofdata because wireless devices are not always secure.Ø Lack of centralauthorityIn wired networks it would be possible to monitor or check the datatraffic by applying some central security checks but in wireless networks thesesecurity checks are not available, so lack of central check authority is theissue with transport layer. Ø Physicallyvulnerable Nodes used for the transmission purpose are easily breakable whichcan cause vulnerable threat to the loss of data being transmitted. 1.2. Session layerSession layer or port layer controlsthe connection between two computers or communication devices. Session layerdeals with the sessions and coordination of the applications and networks.
Themajor role of session layer is authentication, authorization and session restoration(Zimmermann, H. 1980). Figure 3: OSI model session layerIn above diagram, header and data isseparated and passed to the application layer. It performs the full duplex, half duplex and simplex duplication operation.Ø Full duplex Full duplex communication refers to the transmission of data in twodirections at same time means data can be sent and received at the same timethrough a single communication medium. Telephone is the example of full duplexmode.Ø Half duplexHalf duplex mode was used in old networks it refers thetransmission of data only in one direction over a medium at same time, walkietalkie is the example of the half duplex mode.
Other side of medium cannottransfer data until the data send by the first side is not received. Whenmessage from the first side is completely transferred and received by the otherside, then half duplex allows other side to transmit their data.Ø Simplex Simplex mode only allows the transfer of data in on direction. Itdoes not allow switching of direction while transmission of data. For examplein radio broadcast transmissions, information is only transfer in one directionto multiple receivers.
1.2.1. Protocols of session layer There are two protocols RPC and Netbiosand commonly found in use of LAN environments. These protocols normally sufferfrom any issue as they are in LAN environment. 1.2.
2. Functions of Session transport layer Session checkpoints and recovery inthe session layer is established through session layer. Different streamsinformation is allowed through this which may be originative from differentresource for proper synchronization. Synchronization of the information fromdifferent sources is also handled by session layer, for example sessions are usedin live television programs where video and audio streams coming from twodifferent sources merged together, sessions avoid overlapping and in case ofconnection loss it tries to recover or manage the failed connection. Role ofsession layer is important in keeping the track of the multiple telnetconnections, downloading of multiple files requested by the FTP applicationsand retrieval of the multiple web pages from a server at a time. Dialoguecontrol and synchronization are the functions of session layer. Check points insession layer are considered as recovery points in case of system failure;these check points are considered as recovery configurations and action and differentprotocols like NFS, NetBIOS names, RPC, SQL work at this layer.1.
2.2.1. Dialogue control Dialogue control allows two systemsto get start communication in half duplex or full duplex mode.1.2.
2.2. Synchronization Synchronization performs checkpointsinto streams of data for example if a system is sending a file of 1600 pages itapplies checkpoint after every 100 pages to ensure the quality andacknowledgement of data transmitted successfully or not. Web browsers and OSIprotocol known as X.225 or ISo8327 are the excellent examples of session layerprotocols. 1.3. Issues with transport Normally this layer is confused withsession of TCP/IP model session.
It upholds network traffic, make connection,and torn down connection. There are no such logical issues with the sessionlayer. 2. Conclusion