Transcript l18_march26

Lecture 18 – March 26, 2002
Synthetic criteria for evaluation of network
traffic patterns.
Open systems.
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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.
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Electronic
Remote
File
Financial
Mail
Login
Transfer
Video & Audio
Videoconferencing
Services
Layer 4 - Applications
Layer 3 - Middleware Services
Web
Telemedicine
Services
Financial
Distance
Services
Electronic
Learning
Commerce
Teleconferencing
Event Directory
Authentication
Coordination
Storage
Layer 2 - Transport Services
Layer 1 - Network Services
Text
Video
Audio
IP
ATM
Layer 0 - Technology Substrate
Dial-up
Modems
LANs
Wireless
Direct
Cable
Broadcast
Frame
Sateliite
Relay
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Is the client-server paradigm sufficient?
RPC limitations.
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The client is expected to know
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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
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The client may not know

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The location of the server
The API to invoke the service
We have a resource-rich environment thus
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Reliability can be guranteed
QoS guarantess are possible
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Resource Management in an Open System
Multiple administrative domains.
Scalability of resource management.
Impossibility to know accurately the state of
all resources.
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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
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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 ]
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Gossiping Algorithms
Performance measures
Running time
 Pointer communication complexity – number of
pointers exchanged.
 Connection communication complexity – total
number of connections between pairs of entities.
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Flooding
Swamping
Name-dropper.
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Resource Leasing
Resource
lease request
lease request
renewal request
renewal request
Resource
Proxy
Client
Client
(a)
time
(b)
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Resource Virtualization
Resource virtualization  abstraction of
resources
Operating Systems
Virtual Memory
 Virtual Machine
 Socket
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Open Systems
Higher Level abstractions
 Fuzzy resource specification
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Objects
Objects are instances of abstract data types
called classes.
Inheritance
Extended class
 Evolution
 Sharing

Serialization
Persistency
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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.
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Approaches for distributed object systems
Accommodate the status quo  CORBA
Ab initio – design a new platform that is
architecture neutral  Java
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Interface
Repository
Object
IDL stub
ORB
Interface
Object
Object
Object
Object
IDL stub
IDL stub
IDL stub
IDL stub
Dynamic
Invocation
Client
Server
Dynamic
Invocation
Static
Skeletons
ORB, Object Request Broker
Implementation
Repository
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