1. Unit-IV Distributed Computing Systems Distributed Computing models
Issues in designing distributed operating systems
DCE

2. Computer Architecture Multiprocessors Types
Tightly Coupled Multiprocessor System (Parallel )

3. Computer Architecture Multiprocessors Types
Loosely Coupled Multiprocessor System(Distributed )

4. Parallel v/s Distributed Systems
Parallel Systems
Distributed Systems
Memory
Tightly coupled shared memory
UMA, NUMA
Distributed memory
Message passing, RPC, and/or used of distributed shared memory
Control
Global clock control
SIMD, MIMD
No global clock control
Synchronization algorithms needed
Processor interconnection
Order of Tbps
Bus, mesh, tree, mesh of tree, and hypercube (-related) network
Order of Gbps
Ethernet(bus), token ring and SCI (ring), myrinet(switching network)
Main focus
Performance
Scientific computing
Performance(cost and scalability)
Reliability/availability
Information/resource sharing

5. What is a distributed system?
Tanenbaum’s definition of a distributed system: “
A distributed system is a collection of independent computers that appear to the users of the system as a single coherent system.”

6. An example of a Distributed System
Nationalized Bank with multiple Branch Offices

7. Requirements of Distributed systems
Security and reliability.
Consistency of replicated data.
Concurrent transactions (operations which involve accounts in different banks; simultaneous access from several users, etc)
Fault tolerance

8. What is a Distributed Computing System?
"a collection of processors interconnected by a communication network in which each processor has its own local memory and other peripherals and the communication between any two processors of the system takes place by message passing over the communication network"    (Sinha97)

9. Evaluation of Distributed Computing System
Loading monitor
1950s-1960s
Batch system
1960s
Multiprogramming
1960s-1970s
Time sharing systems
Multics, IBM360
WAN and LAN
ARPAnet, Ethernet
1960s-early1980s
Minicomputers
PDP, VAX
Early 1980s
Workstations
Alto
1980s – present
Workstation/Server models
Sprite, V-system
1990s
Clusters
Beowulf
Late 1990s
Grid computing
Globus, Legion

10. Distributed Computing System Models
Minicomputer model
Workstation model
Workstation-server model
Processor-pool model
Cluster model
Grid computing

11. Minicomputer Model Extension of Time sharing system
ARPA
net
Mini-
computer
Mini-
computer
Extension of Time sharing system
User must log on his/her home minicomputer.
Thereafter, he/she can log on a remote machine by telnet.
Resource sharing
Database
High-performance devices

12. Workstation Model Process migration
100Mbps
LAN
Workstation
Process migration
Users first log on his/her personal workstation.
If there are idle remote workstations, a heavy job may migrate to one of them.
Problems:
How to find an idle workstation?
How to migrate a job?
What if a user log on the remote machine?

13. Workstation-Server Model
Client workstations
Diskless
Graphic/interactive applications processed in local
All file, print, http and even cycle computation requests are sent to servers.
Server minicomputers
Each minicomputer is dedicated to one or more different types of services (print, database,…etc).
Client-Server model of communication
RPC (Remote Procedure Call)
RMI (Remote Method Invocation)
A Client process calls a server process’ function.
No process migration invoked
Example: NFS
Disadvantage : capability of idle workstations is not utilized.
100Gbps
LAN
Workstation
Mini-
Computer
file server
http server
print server

14. Processor-Pool Model Clients:
They log in one of terminals (diskless workstations or X terminals)
All services are dispatched to servers.
Servers:
Necessary number of processors are allocated to each user from the pool.
Better utilization but less interactivity
Server 1
100Mbps
LAN
Server N

15. Cluster Model Client Takes a client-server model Server
100Mbps
LAN
Workstation
Master
node
Slave 1 N 2
1Gbps SAN
http server1
http server2
http server N
Client
Takes a client-server model
Server
Consists of many PC/workstations connected to a high-speed network.
Puts more focus on performance: serves for requests in parallel.

16. Grid Computing
Goal
Collect computing power of supercomputers and clusters sparsely located over the nation and make it available as if it were the electric grid
Distributed Supercomputing
Very large problems needing lots of CPU, memory, etc.
High-Throughput Computing
Harnessing many idle resources
On-Demand Computing
Remote resources integrated with local computation
Data-intensive Computing
Using distributed data
Collaborative Computing
Support communication among multiple parties
Workstation
Super-
computer
High-speed
Information high way
Mini-
computer
Cluster
Super-
computer
Cluster
Workstation
Workstation

17. Why are Distributed Computing Systems Gaining Popularity?
Inherently distributed applications
Distributed DB, worldwide airline reservation, banking system
Information sharing among distributed users
CSCW (Computer Supported Cooperative Works )or groupware
Resource sharing
Sharing DB/expensive hardware and controlling remote lab. devices
Better cost-performance ratio / Performance
Emergence of Gbit network and high-speed/cheap MPUs
Effective for coarse-grained or embarrassingly parallel applications
Reliability
Non-stopping (availability) and voting features.
Scalability, Extensibility and Incremental Growth
Loosely coupled connection and hot plug-in
Flexibility
Reconfigure the system to meet users’ requirements

18. Distributed Computing Environment (DCE)
What is DCE?
DCE Architecture
DCE Components

19. DCE Vendor Independent Environment
Defined by OSF a consortium of computer manufacturers .
Nither OS or an application ,integrated set of services
software that supplies a framework and toolkit for developing client/server applications
The framework includes
a Remote Procedure Call (RPC) mechanism,
a naming (directory) service,
a time service,
authentication service,
authorization service
Distributed File System.

20. Distributed Computing Environment
DCE Applications
Threads
Distributed File Service
RPC
Security
Name
Distributed Time Service
Platforms

21. DCE
Support the development of distributed application in a single system
Platform independent ,runs on all OS and heterogeneous DS
Middle ware software between OS and networking layer and DCE applications layer.
Hides the difference between machines by automatically performing data type conversion

22. DCE Architecture

23. DCE(Components )
Fundamental distributed services provide tools for software developers to create the end-user services needed for distributed computing. They include
Remote Procedure Call, which provides portability, network independence, and secure distributed applications.
Directory services, which provides a single naming model to allow programmers and maintainers to identify and access distributed resources more easily.
Time service, which provides a mechanism to monitor and track clocks in a distributed environment and accurate time stamps to reduce the load on system administrator.
Security service, which provides the network with authentication, authorization, and user account management services to maintain the integrity, privacy, and authenticity of the distributed system.
Thread service, which provides a simple, portable, programming model for building concurrent applications.

24. DCE
Data-sharing services provide end users with capabilities built upon the fundamental distributed services. These services require no programming on the part of the end user and facilitate better use of information. They include
Distributed file system, which interoperates with the network file system to provide a high-performance, scalable, and secure file access system.
Diskless support, which allows low-cost workstations to use disks on servers, possibly reducing the need/cost for local disks, and provides performance enhancements to reduce network overhead.

25. DCE components

26. DCE Cell
Largest management unit in DCE is cell.(group of users, machines and other resources)
The highest privileges within a cell are assigned to a role called cell administrator
Breakdown a large system into small ,manageable units called cell.
Major components of DCE within every cell are:
The security server that is responsible for authentication
The Cell Directory Server (CDS) that is the repository of resources and Access Control Lists
The Distributed Time Server that provides an accurate clock for proper functioning of the entire cell.

27. DCECell Setting up a DCE system ,decide cell boundaries Four factors
Purpose :users and m/c’s with same task must be put in same cells.
Administration: to register new users in the system.
Security : machines of those users have trust in each other put in same cell
Overhead : m/c’s of users frequently interacting put in same cell