Session
Identifiers 
As opposed to stateless HTTP requests, which can always be routed to any server determined by any load-balancing scheme, stateful requests have to be sent to the specific server that holds the corresponding session context. Unique session identifiers are used to establish a mapping between the session and its associated state stored on the server.
There are two kinds of SAP session identifiers used to uniquely identify user sessions residing on either the ABAP or JAVA/J2EE application engine on a specific application server. Note that in order to differentiate between ABAP and J2EE applications, the SAP Web Dispatcher uses a database table of all known ABAP URL-prefixes.
Both ABAP and J2EE session identifiers can be represented in the HTTP header either as cookies or as part of the URL in order to enable stateful sessions without cookies (URL-rewriting scheme).
The SAP Web AS Java 6.40 uses the Load balancing identifier instead of the J2EE session identifier.
For more information about the different identifiers, see