Lecture 18 – March 26, 2002 Synthetic criteria for evaluation of network traffic patterns. Open systems.

Open Systems Open systems…… Service overlay model  services are introduced at the edge of the virtual infrastructure supported by the Internet. The active network model  programmable network infrastructure. Active media model  media carries along the code necessary to transform the data.

Is the client-server paradigm sufficient? RPC limitations. The client is expected to know The interface presented by the server The exact location of the server The delay to get a response is low and client may wait for it. The servers are stateless no provisions for reliability. In an open system The client may not know The location of the server The API to invoke the service We have a resource-rich environment thus Reliability can be guranteed QoS guarantess are possible

Resource Management in an Open System Multiple administrative domains. Scalability of resource management. Impossibility to know accurately the state of all resources.

Active mechanisms  Directory or lookup services. Resource Discovery Active mechanisms  Directory or lookup services. Server register with the service at startup time. What happens when the server fails? Leasing of resources. May not be up to date. Passive mechanisms  Gossiping based upon epidemic algorithms

Population of fixed size – n. Epidemic Algorithms Population of fixed size – n. Deterministic model  the rate of change is proportional to: The size of the group infected  Y(t) The size of the group still healthy  n-Y(t). Y(t)’ = K Y(t) [ n – Y(t) ] Y(t) = n / [ 1 + (n-1) e –knt ]

Performance measures Flooding Swamping Name-dropper. Gossiping Algorithms Performance measures Running time Pointer communication complexity – number of pointers exchanged. Connection communication complexity – total number of connections between pairs of entities. Flooding Swamping Name-dropper.

Resource Leasing

Resource Virtualization Resource virtualization  abstraction of resources Operating Systems Virtual Memory Virtual Machine Socket Open Systems Higher Level abstractions Fuzzy resource specification

Objects are instances of abstract data types called classes. Inheritance Extended class Evolution Sharing Serialization Persistency

Network Objects Require Higher Levels of Abstractions Interfaces exposed by objects are language and system dependent. RPC are ill suited for distributed object applications; e.g. big endian versus little endian representations. Socket level programming is cumbersome.

Approaches for distributed object systems Accommodate the status quo  CORBA Ab initio – design a new platform that is architecture neutral  Java