Session ID persistence based on SessionID parameter in Xml tag

Iam trying to write I-rule based on following requirement 

1. Client requests to initiate a session  F5 forwards the call to available Node in the pool.
2.  
3. Node sends response to F5 containing sessionid  F5 extracts sessionid from xml tag and creates a new persistence.
4.  
5. F5 then forwards the HTTP response to client  Client stores the sessionid .
6.  
7. Client uses the sessionid to create a new request using sessionid in the URL  F5 will parse the URL to retrieve the sessionid and use the existing persistence data to redirect the request to the right Node.
8.  The F5 script should be clever enough to retrieve sessionid in a case-insensitive way and persist. F5 can distinguish first call from the subsequent calls by parsing the URL as the first call will not contain any sessionid text. 

 Can some one please help iam completely new to F5 .

Thanks Amit