Università degli Studi di Napoli Federico II. Corsi di Laurea Specialistica in Ingegneria Informatica ed Ingegneria delle Telecomunicazioni

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1 Università degli Studi di Napoli Federico II Corsi di Laurea Specialistica in Ingegneria Informatica ed Ingegneria delle Telecomunicazioni Corso di Applicazioni Telematiche Prof. 1

2 Some background: what is a servlet? Sun s definition: A Java program that runs as part of a network service, typically an HTTP server and responds to requests from clients Note well: typically an HTTP server this leaves space to other types of servers! 2

3 HTTP Servlets Used for developing Web Applications Servlets process HTTP Requests Responses are sent back to the client as HTTP responses containing web pages To provide custom functionality: developers just override the doget() and dopost() methods of the HTTP Servlet class HTTP Servlets, together with their deployment descriptor (e.g. web.xml file) are: packaged into a WAR (Web ARchive) file by the developer deployed to the server by administrators Container manages servlet s life cycle, replication of Session state, fail-over, authentication, security 3

4 HTTP Servlet API Client Web Container Servlet Methods init() HTTP Request Rules servlet service() destroy() doget() HTTP Response HTTP Response HTTP Response dopost() doput() Error Response Error Response 4

5 Why extending the Servlets model for SIP? Servlets API is an open standard supported by multiple vendors Containers manage Servlet s life cycle, session s state, fault-tolerance, scalability, security Application s developers can focus solely on their application HTTP Servlets are widely used in Web development large community of developers already familiar with the concepts of the Servlets API New Services developed as Servlets can interact with existing components, like HTTP Servlets or EJBs (Enterprise Java Beans) converged applications!! 5

6 SIP servlet goals Application composition one servlet can be called right after another servlet completes (execution chain ) Converged applications implementing applications that are both HTTP- and SIPenabled Caveats: Neither application composition nor converged applications are well defined in JSR (Java Specification Request), yet: JSR 116 (SIP servlet v1.0): JSR 289 (SIP servlet v1.1 Proposed Final Draft 2, May 2, 2008) Different SIP containers may act differently with respect to the above features 6

7 SIP Servlet Programming model SIP Servlet API: a specification developed by the communication industry in an attempt to standardize and speed up the development of services in SIP networks Similar to the HTTP Servlet API, it is based on two key figures: the SIP Servlet container the SIP servlet 7

8 SIP Servlet container An Application Server (AS) with a built in SIP stack that: is placed in a SIP network listens for incoming SIP messages When an incoming message arrives, the AS triggers one or more applications, which: deal with the signalling implement a certain service Applications include, among other resources, SIP Servlets 8

9 SIP servlets Like HTTP servlets, SIP servlets are pieces of java code contained and managed by the SIP Servlet Container They perform SIP signalling, by: either answering incoming requests or proxying them or even creating new ones This is a key difference with the HTTP Servlet API: HTTP servlets can only answer HTTP requests 9

10 SIP Servlet API Client SIP Container SIP Servlet Methods init() servlet service() destroy() SIP Message SIP Message Rules Create Request() Create Response() doinvite() doack() dooptions() docancel() doregister() doprack() doinfo() donotify() domessage() dosubscribe() dorequest() doprovisionalresponse() dosuccessresponse() doerrorresponse() doredirectresponse() doresponse() 10

11 HTTP servlets vs SIP servlets: differences HTTP SIP HTTP signaling less complex Only handles requests and generates responses HTTP servlets - the doservice() method is expected to send a response within the same method call HTTP request contains the name of the Servlet to invoke in the request URI SIP signaling is much more complex Handle and generate requests and responses, Session management, Proxying SIP servlets - response can be generated asynchronously Servlet mapping for SIP servlets is done by a set of rules evaluated at runtime. Client applications are not aware of applications installed on the server 11

12 HTTP servlets vs SIP servlets: similarities Servlets invocation is triggered by events: request response The container: hides the low level protocol exposes high level API selects the appropriate servlet to invoke manages servlet s life-cycle and session state Developers: override methods in the servlet s base class provide specific implementation Servlets are: grouped into applications: web archive (.war ), sip archive (.sar ) deployed with a deployment descriptor ( web.xml for HTTP, sip.xml for SIP) 12

13 SIP Servlet Abstractions ServletRequest ServletResponse javax.servlet SipServletMessage javax.servlet.sip SipServletRequest SipServletResponse SIP Servlet API: several abstractions in the form of classes and interfaces Pattern: SipServlet extends GenericServlet as a SIP specialization SipServletRequest extends ServletRequest SipServletResponse extends ServletResponse ServletMessage extends ServletMessage 13

14 Servlet Context A sandbox inside the container where applications are executed Every application has its own context where all its servlets run Every context has its own class loader: the isolation between applications is garanteed servlets of an application use the context primarily as a mechanism for communication between them 14

15 SipServlet The base class that developers subclass to implement their own servlets Defines: the lifecycle methods: init,destroy the message handling methods: dorequest, doresponse,... Implements the default behaviour of the methods above 15

16 Other classes SipServletRequest and SipServletResponse: encapsulate SIP requests and response messages respectively both provide access to: relevant request and response information handy methods for their process: createresponse, createack, createcancel, getproxy, send SipServletMessage: defines a number of methods which are common to SipServletRequest and SipServletResponse e.g.: setters and getters for message headers and content SipSession SipSessions are used to maintain dialog state every message belongs to a SipSession, i.e. the representation of the SIP dialog or call leg the message is engaged in 16

17 SipApplicationSession In many SIP applications (e.g. B2BUA) an incoming message sets up a dialog that leads to the initiation of other dialogs, each of them represented by their own SipSession: such SipSessions are independent, yet related to the same execution of the service we could think of them as an application instance SipApplicationSession: the above identified application instance holds references to all the SipSessions (as well as HttpSessions in the case of converged applications) provides methods to store application instance data 17

18 Factory and Proxy SipFactory used to create new application sessions, requests, addresses and URI objects servlets obtain a reference to it through a ServletContext attribute: Proxy javax.servlet.sip.sipfactory represents a proxy operation offers methods to configure several proxy aspects whether it should be stateless or stateful, parallel or sequential, record routed or not, etc. setting the proxy supervision flag configures how controlling servlet is to be invoked for subsequent events related to this proxying transaction: incoming responses, CANCELs and ACKs 18

19 SIP Servlet life cycle 19

20 SIP Servlet methods 20

21 SipSessions and Dialogs SipSession: can be roughly considered as the representation of a SIP dialog it maintains dialog state can be used to create subsequent requests inside a dialog via its createrequest(method) 21

22 Working as UAC Create an initial request from scratch: the servlet has to: retrieve the SipFactory from the ServletContext invoke the createrequest method modify the SipServletRequest as appropriate send the newly created request Create a subsequent request: the only thing we need is the SipSession; then we can proceed like this: //Sending BYE because we're done mysipsession.createrequest("bye"); //Send the request req.send(); Create ACK requests use the SipServletResponse method createack Create CANCELs from the request that we want to cancel: SipServlet Request cancelrequest = inviterequest.getcancel(); cancelrequest.send(); 22

23 Working as UAS To generate a response to an incoming request UAS servlets simply have to: invoke createresponse() on the request object being processed modify the SipServletResponse obtained, if needed invoke its send method protected void doinvite(sipservletrequest req) throws javax.servlet.servletexception, java.io.ioexception{ }... SipServletResponse resp = req.createresponse(486, Pippozzo server is so busy now. Sorry'); resp.send();... 23

24 Working as Back-to-Back User Agent (B2BUA) Useful any time you need to appropriately orchestrate interaction among two or more parties: e.g. 3 rd Party Call Control (3PCC) To implement this kind of behaviour a SIP Servlet: uses the SipFactory method createrequest(sipservletrequest origrequest, boolean samecallid) to: process an initial request coming from the upstream create the request that will be sent downstream 24

25 Working as Proxy The SIP Servlet API abstracts the proxy operation by means of the Proxy object obtained from the SipServletRequest via the getproxy() method any other message involved in the proxy operation carried out by this proxy object wil return the same Proxy instance The Proxy objects offers several setters to configure its behaviour recurse: tells the proxy to automatically retry when a 3xx response is received recordroute: whether the application is supposed to stay in the signalling path of the dialog parallel: when proxying to multiple destinations this flag indicates whether the proxy should fork or retry sequentially stateful: indicates whether the proxying should be carried out statelessly or statefully supervised: if set to true responses coming from the downstream are delivered to the servlet if set to false: they are forwarded upstream (if applies) by the container without application involvement sequentialsearchtimeout: how long will the proxy wait for one of its branches to send a final response before cancelling it 25

26 Accessing the SIP message content Often, developers need access to the content of the SIP messages The SIP Servlet API provides a set of methods to read and write such content They are all methods of the SipServletMessage interface: to read or set the length of the message: int getcontentlength() void setcontentlength(int len) to read or set the content type: String getcontenttype() void setcontenttype(string type) to gain direct access to the content: Object getcontent() byte[] getrawcontent() void setcontent(object obj, String type) 26

27 SDP Management SIP applications very often have to deal with SDP The JAIN familiy of specifications includes JAIN-SDP (JSR 141) designed to help developers with SDP multimedia session descriptions offers a set of objects and interfaces wich developers can use to create, read or modify the SDP content of SIP messages a free implementation can be found at protected void doinvite(sipservletrequest req) throws javax.servlet.servletexception, java.io.ioexception{ }... //Save the SDP content in a String String sdpcontent = new String(req.getRawContent(),req.getCharacterEncoding()); //Use the static method of SdpFactory to //parse the content SessionDescription requestsdp = SdpFactory. createsessiondescription(sdpcontent);... 27

28 SIP Application Server example: WeSIP ( WeSIP is a Converged SIP Servlet Application Server built on top of OpenSER it basically adds a SIP Servlet programming layer to Openser users can develop their own services and applications using existing OpenSER modules: nat_traversal registrar etc......while at the same time enjoying the java programming language facilities: Web services (SOAP) Java Beans (EJB) Database Connectivity (JDBC)... WeSIP helps integrate OpenSER with other systems and protocols, enabling the offer of a new portfolios of services 28

29 WeSIP OpenSER Integration 29

30 Alternatives to SIP servlets: CPL! "#!$# %& # '#( ) *+, 30

31 Alternatives to SIP servlets: SIP CGI - *%.% # * ) *+, // 31

32 A few more pointers: CCXML and JSLEE! * * # "!##$ %#&!#!%!! + 32