Distributed systems architectures

• See slides on communication systems architectures
• The main points are the following:
• Architecture of one protocol layer (within a layered architecture)
• Service definition: global view including several access points; abstract interface at each access point
• Protocol defined in terms of the behavior of both protocol entities ; coding of messages is an important aspect, order of interactions is also important (example of connection establishment prior to using the connection for data transfer)
• "concrete" service access interface is also important (in the form of an API), e.g. socket interface in C provided under Windows to access the TCP service
• Consider some standards: what do they define ? - (abstract) service, protocol, "concrete" interface, message coding or what ?
• Here are some diagrams from an example protocol: TCP (taken from the book "Data Communications, Computer Networks and Open Systems" by Fred Halsall, Addison Wesley, 1992)