The Importance of Sliding Window Protocol Generalisation in

The Importance of Sliding Window Protocol Generalisation in a Communication Protocols Course Drago Hercog University of Ljubljana, Faculty of Electrical Engineering Ljubljana, Slovenia Drago. Hercog@fe. uni-lj. si Drago Hercog, Slovenia ICEE 2010, Gliwice

Importance of Communication Protocols n n n Digital packet Based Communication Systems Layered Architecture Communication Protocols Basic Knowledge of Communication Engineers Communication Protocols Course Drago Hercog, Slovenia ICEE 2010, Gliwice 2

Properties of Communication Protocols n What is a Protocol n n n a set of rules for message exchange a distributed algorithm Important Aspects from Pedagogic Viewpoint n n n systematic presentation algorithmic aspect specification logical correctness efficiency Drago Hercog, Slovenia ICEE 2010, Gliwice 3

ARQ Protocols n n Reliable Transfer of Packets Automatic Repeat re. Quest Protocols Retransmit Corrupted/Lost Packets Sliding Window Protocols n n n ARQ protocols management of input/output buffer memory real-life protocols very much used in practice different complexities taught in basic communication protocols courses Drago Hercog, Slovenia ICEE 2010, Gliwice 4

Systematics of Sliding Window Protocols n n Transmit and Receive Windows Classical Sliding Window Protocol Types n n Stop-and-Wait protocol Go-Back-N Protocol Selective-Repeat Protocol Go-Back-N & Selective-Repeat protocols behave differently! Drago Hercog, Slovenia ICEE 2010, Gliwice 5

Generalised Sliding Window Protocols n n n Combination of go-back-N and selective-repeat Any combination of transmit and receive window widths Stop-and-wait, go-back-N, selective-repeat are special cases Unified and simplified theory Unified specification Single simulator Drago Hercog, Slovenia ICEE 2010, Gliwice 6

Protocol Efficiency n n Measure of the use of resources Efficiency of the generalised protocol: Equal or even better than with selective-repeat protocol, but with less resources n More freedom for efficiency-resource compromise Drago Hercog, Slovenia ICEE 2010, Gliwice 7

Formal Specification of a Protocol n n Importance of formal protocol specification Special case protocols were specified in different languages Generalised protocol was specified in SDL This specification also specifies the three special case protocols Drago Hercog, Slovenia ICEE 2010, Gliwice 8

Pedagogic Importance of Sliding Window Protocols n n n Typical distributed algorithms Much used in practice Protocol algorithm, correctness, efficiency and specification can be taught using this protocol family as example Drago Hercog, Slovenia ICEE 2010, Gliwice 9

Pedagogic Importance of Protocol Generalisation n n n Unified theory Clear and systematic presentation The three specific protocols can be compared as members of a common family Explanation of protocols can be based on the explanation of transmit/receive buffer management Typical protocols to be specified, verified, simulated analysed A good example of engineering compromise Drago Hercog, Slovenia ICEE 2010, Gliwice 10

The Generalised Protocol Presentation n n n n ARQ protocols principles Sliding window protocol: distributed algorithm Transmit/receive buffer management Generalised protocol, special cases Typical scenarios Protocol specification Logical correctness and verification Protocol efficiency and verification Generation and presentation of efficiency diagrams Drago Hercog, Slovenia ICEE 2010, Gliwice 11

Conclusion n n Sliding window protocols are core topic of a communication protocols course Protocol generalisation provides for n n Unified theory Possibility to present stop-and-wait, go-back-N and selective-repeat as special cases Easier presentation of protocol operation based on transmit/receive buffer management Flexibility in efficiency - resource compromise Drago Hercog, Slovenia ICEE 2010, Gliwice 12

Thank You for Your attention Drago Hercog, Slovenia ICEE 2010, Gliwice 13