Lab: Protocol Engineering

Transcription

1 Lab: Protocol Engineering Lab: Protocol Engineering Prof. Dr. Jürgen Jasperneite / M. S. Barath Kumar 1 Objective of the LAB to deepen your knowledge about the system theory and the basic building blocks of communication systems with a layered architecture. To get first hands-on experience how to design and validate communication protocols using UML Lab: Protocol Engineering Lab 1: Introduction to INRES/UML/TAU Lab 2: Design of INRES Lab 3: Validation of INRES 2 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 1

2 INRES INRES services and protocol: cannot be related to any specific layers of the OSI- Basic Reference Model (OSI-BRM) it does contain many basic OSI-BRM concepts it is used as a common example in the ISO/CCITT work on "Formal Methods and Conformance Testing it has originally been published by Dieter Hogrefe (now: University of Göttingen, Germany) [HOG89] it is an abridged version of the Abracadabra 1 system described in [TR 10167] 1 Abacadabra: Alternating Bit Protocol with Connection and Disconnection 3 Basic Structure of INRES 4 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 2

3 INRES Service General Informations INRES Service is: connection-oriented asymmetrical connection can be initiated through the service only by the Initiator-user, only the Initiator-user may send data once a connection is established, only Responder-user may terminate an established connection 5 INRES Service 6 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 3

4 INRES Service Primitives Phase Kind Name Parameter Connection Request ICONreq Indication ICONind Response ICONresp Confirmation ICONconf Data Transfer Request IDATreq Indication IDATind Disconnection Request IDISreq Indication IDISind 7 INRES Service Connection Phase Connection may be initiated only by the Initiator-user using ICONreq. An ICONreq should be issued only once to establish a connection and it may be repeated only once a connection has been terminated. 8 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 4

5 INRES Service Data Transmission Phase Once a connection is established the Initiator-user may send a IDATreq which will be delivered as IDATind to the Responder-user 9 INRES Service Disconnection Phase - (1) Successful disconnection of an established connection 10 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 5

6 INRES Service Disconnection Phase - (2) rejection of a connection establishment attempt 11 INRES Service Disconnection Phase spontaneous disconnection 12 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 6

7 INRES Service - User Errors Should the behavior of the service under incorrect usage by the service user be described? -- YES for robustness. An ICONreq should be ignored if issued when a connection is already established or is currently being established An ICONresp should be ignored if issued before any attempt to establish a connection was done, or if issued too late, after such an attempt was made A IDISreq should be ignored if issued before any attempt to establish a connection was done A IDATreq should be ignored if issued when a connection is not established. 13 General information INRES protocol is a connection-oriented protocol that operates between two protocol entities Initiator and Responder The protocol entities communicate by exchange of the protocol data units (PDU) CR, CC, DT, AK and DR The protocol renders the INRES service to users located in the imaginary next higher layer 14 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 7

8 Structure 15 Protocol data units (PDU) PDU Meaning Parameter Respective SPs CR Connection request none ICONreq, ICONind CC Connection Confirmation none ICONresp, ICONconf DT Data Transfer Sequence number, ISDU IDATreq, IDATind AK Acknowledgement Sequence number none DR Disconnection request none IDISreq, IDISind 16 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 8

9 Protocol Phases Communication between INITIATOR and RESPONDER takes place in three distinct phases: connection establishment phase data transmission phase disconnection phase an error processing phase exists which corresponds to the spontaneous disconnection's of the INRES service 17 Connection establishment phase Connection establishment phase is initiated by Initiatoruser by sending an ICONreq to Initiator Upon receipt of ICONreq Initiator sends a CR to Responder Responder can answer to Initiator with CC or DR If it responds by CC, Initiator issues an ICONconf to its user, and the data transmission phase can start If it responds by DR, the disconnection phase is entered If Initiator receives nothing at all within 5 seconds, CR is transmitted again to Responder If, after 4 attempts, still nothing is received by Initiator, it enters the disconnection phase 18 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 9

10 Connection establishment phase If Responder receives a CR from Initiator, the Responder-user gets an ICONind Responder-user can respond with ICONresp or IDISreq ICONresp indicates the willingness to accept the connection Upon receipt of an ICONresp, Responder sends a CC to Initiator, and the data transmission phase is entered Upon receipt of an IDISreq, Responder enters the disconnection phase 19 Data transmission phase (1) If Initiator-user issues an IDATreq, the Initiator sends a DT and is then ready to receive another IDATreq IDATreq has one parameter - a service data unit ISDU - transmitted by Initiator as a parameter of DT After having sent a DT, Initiator waits for an AK DT and AK carry a one-bit sequence number (0 or 1) First DT sent by Initiator carry sequence number 1 A correct AK of a DT has the same sequence number 20 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 10

11 Data transmission phase (2) After receipt of a correct acknowledgement, the next DT with the next (i.e. other) sequence number can be sent If Initiator receives an AK with incorrect sequence number, it sends the last DT once again Last DT is also sent again if the respective AK does not arrive within 5 seconds A DT can only be sent (retransmitted!!!) 4 times; afterwards Initiator enters the disconnection phase 21 Data transmission phase (3) Responder expects first DT with the sequence number 1 Upon receipt of a DT with the expected sequence number (and ISDU), Responder sends IDATind to its user (with the received ISDU as a parameter), and sends to the Initiator an AK with the same sequence number Upon receipt of a DT with an unexpected sequence number Responder sends an AK with the sequence number of the last correctly received DT The user data ISDU of an incorrectly received DT is ignored. 22 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 11

12 Disconnection phase It is initiated by Responder-user by sending an IDISreq to Responder Upon receipt of IDISreq Responder sends a DR to Initiator and it is ready to receive another connection establishment attempt CR from Initiator Upon receipt of a DR Initiator sends an IDISind to its use An IDISind is also sent by Initiator to its user after DT or CR have been sent unsuccessfully to the Responder 23 Medium INRES protocol have to be mapped on Medium service to realise INRES system Medium service is symmetrical and operates connectionless Medium service is unreliable (SPs can be lost) Medium Service Primitives (SPs) MDATreq and MDATind, carry a parameter Medium-Service Data Units (MSDU) 24 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 12

13 Medium Structure 25 Medium Service Unsuccessful data transfer in both direction Successful data transfer in both direction 26 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 13

14 The INRES System Structure 27 References [HOG89] Hogrefe, D.: Estelle, LOTOS und SDL, Springer Verlag, [TR 10167] ISO TC97/SC21: Guidelines for the application of Estelle, LOTOS and SDL (ISO TR 10167, 1990) 28 Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 14

15 And now: Enjoy Protocol Design with UML Prof. Dr. Jürgen Jasperneite/M.Sc. Barath Kumar 15