An Enriched Finite State Machine Model-based Formalism for Layer-5 Internet Protocols Modelling – An Investigation on Pr

1. An Enriched Finite State Machine Model-based Formalism for Layer-5 Internet Protocols Modelling – An Investigation on Protocol Performance Alexandru Catalin Ionescu 05.10.2008

2. Content • Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Conclusions • Personal Experience (How I wrote my MSc. Thesis)

3. Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Conclusions • Personal Experience (How I wrote my MSc. Thesis)

4. BackgroundMobile Services and Applications • New Mobile Networks providing High Data Rates • Fixed Internet Services are coming into the Mobile Environment • It is all about instant access to information • Ensure the Quality of Service (QoS) • Different applications need different QoS • In Mobile Networks resources are never enough  • The transition From GSM to UMTS • New Internet Engineering Task Force Multimedia Architecture The need to provide a model that allows a developer to first analyze and eventually optimize the application protocol.

5. Security SIP SDP SDP RTCP RSVP IETF Multimedia Architecture TCP / IP UPD / IP Video Equipment RTP / RTCP Encapsulation Audio Equipment Packet Network User Data Applications System Control User Interface

6. Problems and Methods Question 1: How could one formally model the communication protocols according to a specific use case? Question 2: How to estimate the generated network traffic for a specific use case when using a certain communication protocol? Question 3: How to improve a protocol in order to decrease the generated network traffic?

7. Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Conclusions • Personal Experience (How I wrote my MSc. Thesis)

8. Mobile Internet Communications • Mobile Communication - A way we see the world • Demand for Complete Connectivity • Service Evolution • First was the voice • Then came the basic messaging (SMS) • Data transfer followed (FAX) • Internet Applications in Mobile handsets

9. Effective Resilient Reliable Performance in Mobile Networks • Performance (efficiency) is hard to define formally, analyze and not easy to accept • Performance = Service Efficiency = Service Usability • Mobile Communications transmission Media is faulty – Reliable protocols • Error detection • Error correction • Topological Failures in Mobile Networks are common – Resilient protocols • Ability to test the Link • Effectives is defined as Easy to implement and Use • Easy and Use depend on the Context.

10. Resilience in Mobile Networks • Communication between End-points goes over various different physical media • Sending data - the first leg is the radio network • Receiving Data - the last leg of physical communication is again the radio wave • Level-5 Protocols cannot solve link loss in Mobile Networks • Resilience of Level-5 protocols translates to the ability of the protocol to test the availability of the link Example: A Voice over IP application uses SIP in order to perform the so called Registration. The Client registers its “location” to a Registrar Server. The server then knows how to contact the Client when there is an incoming call. In a GSM / UMTS environment the SIP protocol offers the possibility to both Client and Server to query the availability of each other. In case the Server notices a connection break it can reject all the incoming calls. At the same time a Client can try to re-Register.

11. Reliability in Mobile Networks • Radio resources in Mobile Networks are the most likely to create connectivity problems (e.g. bad signal or signal loss) • Bad signal quality – lower level protocols solve the reliability problem • Correction • Retransmission • All these at Level-4 and lower • Signal loss • No ability to handle correction and retransmissions • Level-5 needs to cope with these case • One could observe that Resilience and Reliability have the similar meaning in case of Level-5 protocols in mobile networks.

12. Effectiveness in Mobile Networks • Monetary vs. Non-monetary aspects • An effective Level-5 protocol is network friendly • Light • Not to case “too much” traffic • Monetary aspect • Direct – the amount of data sent and received is to expensive – • Indirect – the amount of data is too high and consumes resources that will otherwise be useful to other services • Non-monetary aspects need to be considered as well. • Mobile device resources are not costly but limited (e.g. processing power, battery)

13. Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Conclusions • Personal Experience (How I wrote my MSc. Thesis)

14. Resource Allocation in Mobile Networks • QoS classes • Conversational – Conversational pattern • Interactive – preserves the time relation between the informational elements • Streaming – Request / Response pattern • Background – Data is not expected with strict time limits • Protocol performance within a QoS class • Performance of a protocol needs to be considered in the context of the QoS class (e.g. A protocol can offer good performance when used by applications running under the Conversational Class but could be the wrong tool for the job within the Interactive Class) • Mobile Networks allocate the communication resources differently, depending on the QoS class. • In practice, means that an application running within the Conversational Class has more resources to spare compared to an application running within the Interactive Class • Protocols that have already been defined and perform well are not necessarily the best choice for the new applications being deployed.

15. Communication Channels • Common Channels • Caring the signalling within the network but In some cases they are also used for user data • Low setup time - Fast to establish in order to send and receive data and then tear-down • Cannot handle the so called soft handover – no cell to cell hoping • The network will not allocate them when the data amounts to be sent or received is high - work with small individual packets • Dedicated Channels • Exact opposite of the Common Channels • Long time to set up • High bit rates and the bit rate can be changed during the transmission • Improved radio performance • Any protocol can be used on these channels • Issues can arise only when the entities involved in the communication expect responses to their request within a certain time interval • Shared Channels

16. Communication Channels (cont) • Shared Channels • Share a channel in time between different users • Bit rate is lower in comparison with the achieved rates on the dedicated channels • Good for applications that generate bursty traffic • Capacity of the air interface is shared among many users at the same time

17. Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Conclusions • Personal Experience (How I wrote my MSc. Thesis)

18. Layered Model

19. Relay Open System

20. IP Suite Stack Host to Host communication over Internet Application Application PEER TO PEER Communication Transport Transport Network Network Network Network Data Link Data Link Data Link Data Link Internet Internet Internet Physical Layer

21. Internet Reference Model in Mobile Networks Application Server Mobile Device Application Application PEER TO PEER Communication Transport Transport Network Network Network Ethernet GPRS Data Link Data Link Data Link Radio Network Internet Gateway GPRS Support Node

22. Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Conclusions • Personal Experience (How I wrote my MSc. Thesis)

23. Protocol Modelling • Informal methods • Successfully used • Do not handle well high complexity • Formal methods • Analyze rigorously and efficiently • Several papers in the literature • Extremely valuable for Validation and Verification • Performance evaluation has not been addressed much • Done in an informal manner • Acknowledge issues but do not offer clear fact and figures • Lack of formalism makes comparison between two set of results impossible

24. Protocol Modelling Techniques • High-level Programming Languages • Convenient tool – Communication party represented as a program • Can represent data, variables, counters, etc… • Cannot represent complex structures – general metrics • Do not serve the purpose of calculating traffic • Finite State Machines • Use in the early stages of Protocol definition • Single-machine model vs. Multi-machine approach • The model is applicable to any protocol having a finite number parties involved in communication • Petri Nets • Petri Nets can model a protocol that has an infinite number of states • We can develop a model that allows messages to have size using the so called Coloured Petri Nets extension • The size of the graph can become a problem • Even in the case of simple protocols this can result in growing to complexities that are not easy to manage

25. Finite State Machine Model Process 2 (server) Process 1 (user) IDLE Not Logged-in + LOGIN - LOGIN + ACK_LOGOUT - ACK_LOGOUT + ACK_LOGIN + LOGOUT Service_Request Authenticated Wait Logged-in - ACK_LOGIN - LOGOUT

26. Petri Nets Model Client Network Server Login Idle Msg1 Send Login Login Received Wait1 Service Login Request Logged-in Ack1 Login Ack Authenticated Ack Login Received Msg2 Send Logout Logout Received Logout Wait2 Service Logout Request Ack2 Logged Out Logout Ack Ack Logout Received Logged Out

27. Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Conclusions • Personal Experience (How I wrote my MSc. Thesis)

28. Context The System Entity A Entity B Network Measure the traffic flowing through the network Protocol Measurement System

29. Handling an external event in the measuring environment The System Entity A Entity B Network External Event (data) The protocol implementation transforms the external event in a protocol primitive / message packing the data carried by the event Message 1 Relay Message 1 Entity B Processes the Message and creates response Response Message 1 Relay Response Message 1 External Response (data) External Event (data)

30. A User – Client – Server Model Access to information User The System Entity A (client) Entity B (server) Network Use client Application Measure the traffic flowing through the network

31. Connect / Subscribe / Notify / Disconnect Connect User The System Entity A (client) Entity B (server) Network Notify Use client Application Disconnect

32. Use Case Execution The System Entity A (client) Entity B (server) (1) Start use case User stable state 0 stable state 0 (2) message 1 (3) (3) server state x client state x (4) message 2 (5) (5) server state y client state y (6) message 3 (7) (7) server state z (8) message 4 client state z (9) (9) stable state 1 stable state 1

33. Process 1 (server) Process 1 (user) Time Not Logged-in IDLE - LOGIN + LOGIN Wait Service_Request - ACK_LOGIN + ACK_LOGIN Logged-in Authenticated - LOGOUT + LOGOUT Wait Service_Request + ACK_LOGOUT - ACK_LOGOUT Not Logged-in IDLE A Graphical Representation of FSP

34. Presence Server Presence Client IDLE IDLE Time Connect to Service State 1 State 1 Publish Presence Information State 2 State 2 Subscribe for Presence Information State 3 State 3 State 1 – Connected State 2 – Connected & Published State 3 - Connected & Published & Subscribed Abstract Time-line Mode for Presence

35. Presence Server Presence Client Connect to Service IDLE IDLE SIP Register Time SIP 401 Unauthorized SIP Register SIP 200 OK State 1 State 1 State 1 – Connected State 2 – Connected & Published State 3 - Connected & Published & Subscribed SIMPLE Connection to Presence Service

36. Presence Server Presence Client … IDLE IDLE Time Publish Presence Information State 1 State 1 SIP Publish SIP Publish SIP 200 OK SIP 200 OK Publication expires or user changes the Information State 1 – Connected State 2 – Connected & Published State 3 - Connected & Published & Subscribed SIMPLE Presence Publication

37. Presence Server Presence Client … IDLE IDLE Time … State 1 State 1 Publish Presence Information State 1 State 1 SIP Subscribe SIP 200 OK SIP Notify SIP 200 OK Subscription expires or Connection is lost the Information State 1 – Connected State 2 – Connected & Published State 3 - Connected & Published & Subscribed SIMPLE Presence Subscription

38. First Results

39. Improvements

40. Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Conclusions • Personal Experience (How I wrote my MSc. Thesis)

41. ConclusionsGeneral • New directions in Mobile Communications are shaped by the business requirements optimization needs for profitable investments • Increase complexity – introduce fixed-Internet technologies to the Mobile Domain • IETF protocols and especially the level-5 ones are becoming the de facto protocols for mobile services • Solve the performance or efficiency evaluation • Need to understand how a certain technology works • Improves the performance • Quality of the Services • Impact on the operational costs

42. ConclusionsProtocol Modelling • Finite State Machines and Petri Nets - in their original form - did not suite all our needs • Good for validation and verification • Not good for measurements due to lack of metric • Colored Petri Nets • Good for measurements • Hard to use • Potentially will alienate some of the stakeholders • Improvement of the Finite State Machines - METRICS

43. Future Work • The performance measurements need to address two aspects • Number of messages sent over the network • Amount of data exchanged in the communication • FSP model proposed by this work is able to handle well the first aspect • The amount of data aspect is not handled in an elegant way • An improved model to deal with this aspect is needed • Coloured Petri Nets are a good candidate for this particular aspect • Extended versions of the general automata, such as X-machines, provide computability and therefore direct implementability and testing.

44. Surf the MSc Thesis • Background, Problems and Methods • (Mobile) Internet Communications • Packet Data Access in Mobile Networks • Layered Network Architectures • Protocol Modelling • Protocol Modelling for Performance Measurements • Personal Experience (How I wrote my MSc. Thesis)

45. The Subject • Choose the subject early enough • Stick with it – do not give up when things get tough • Get your references well in advance • Read all your references and the some • Attend the Scientific Writing in Human-Computer Interaction (Kari-Jouko Räihä OR Howell Istance)

46. Work and Study • A real problem • How to get the work done and how to get the work done  • Difficulties • Share time in the office / time at the University / time at home / travelling • Confidentiality management • Relationship with the management • Time management • How many hours do you allocate per week to your studies • Try to find a day when you spend most of those hours – preferably a working day • Save your evening for reading • The feeling after    