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

2. 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.

4. 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

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

6. 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

7. 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 ]

8. 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.

9. Resource Leasing

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

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

12. 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.

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