1. REQUEST/REPLY COMMUNICATION
BHAVIN KANSARA

2. OBJECTIVE Request/Reply Communication RPC ( Remote Procedure Call )
RPC Operation
Issues Associated with RPC
parameter passing
binding
compilation
failure handling
security
Sun’s secure RPC
GridRPC

3. REQUEST/REPLY COMMUNICATION
Most widely used request/reply communication model is Remote Procedure Call (RPC)

4. Neither message passing nor I/O at all are visible to the programmer
WHAT IS RPC
Process on Procedure P
machine M1 on machine M2
Calls
M1 is suspended
M2 executes P
When M2 returns, controls back to M1
Neither message passing nor I/O at all are visible to the programmer
This method is known as Remote Procedure Call (RPC)

5. RPC: STUB COMPONENTS
-- Program subsystems used by client or server to initiate an RPC request
-- The stubs are responsible for managing all details of the remote communication between client and server
Client calls client stub residing on local machine ,responsible for packing the call and its parameters into a message format
On server side, a server stub unpacks the message into call request

6. RPC OPERATION

7. ISSUES ASSOCIATED WITH RPC
Parameter passing
Binding
Compilation
Failure handling
Security

8. PARAMETER PASSING Parameter passing methods
Functions in an application that runs in a single process may collaborate via parameters and/or global variables
Passing parameters is typically the only way that RPC-based clients and servers share information
Parameter-passing has following possible modes:
IN: pass info from caller to callee
OUT: callee writes a value in the caller
IN/OUT: caller tells callee value of var, which may be updated by callee
Parameter passing methods
Call by value
Call by reference
Call by copy/restore

9. PARAMETER PASSING Call by Value Call by copy/restore IN Mode
simple to handle
Value passed to procedure is copied to local variable
can’t have an effect on caller variable
Call by reference
IN/OUT mode
Much harder to handle
Pass pointer address
Same memory location is referred
Call by copy/restore
Call by value + call by reference
Call by value at entry of procedure and restricts the call by reference to the exit of the call
Results are copied back to the calling procedure at the completion of the called procedure

10. Manages mapping between program number and port number
BINDING
Manages mapping between program number and port number
When server machine is unknown, the client will need to locate the server machine by contacting directory server to locate address of server system

11. BINDING
Server starts  registers its communication endpoint by sending request to port mapper  that contains server’s program, version number and port number

12. BINDING
Client process contact port mapper to obtain handler for accessing server with specific program and version number. This is done by RPC run-time library routine create.

13. BINDING
The port mapper returns the port number of the server to the client system after verifying the program and version number.

14. BINDING
Client system builds client handle for the client process for subsequent use in the remote procedure call.
Binding process establish socket connection between client and server

15. RPC COMPILATION
The compilation of RPC requires three major components in the RPC package
An interface specification file
RPC generator which takes the interface specification file as input and produces the client and server stub procedure source code as output
A run-time library for the supporting execution of RPC

16. RPC COMPILATION

17. RPC COMPILATION

18. RPC COMPILATION

19. RPC FAILURE HANDLING Failures can be of three types Lost message
Server crash
Client crash

20. RPC FAILURE HANDLING Lost Message
Sever is allocated and request message has been sent
Message may delay or lost
Lost message are eventually detected by time out or no response form server
Retransmission
Request was not lost but delayed  server will receive two request
SOLUTION
--- Request can be executed any number of times with same effect
--- using sequence numbers

21. Most desirable  Exactly once  difficult to achieve
RPC FAILURE HANDLING
Server Crash
Three possible assumptions for the RPC semantics in the presence of failure :
" Exactly once?
Server crashes before request arrives
server crashes before reply
server crashes after reply, but reply dropped
" At most once?
If server crashes, can’t know if request was done
" At least once?
Keep retrying across crashes, but may be done multiple times
Most desirable  Exactly once  difficult to achieve
SOLUCTION
--- Problem lies in the loss of cache table
--- Use at least once semantics and to log the cache table
--- When the server recovers  it reloads cache table from log

22. RPC FAILURE HANDLING Client Crash
Before server completes the client request, the server has an orphan computation and its reply is undeliverable.
No easy way for the server to detect the disappearance of clients except by using a time-out or by waiting for the failed client to reboot
Orphan computations consume server resources
Can be eliminated by :
By Client : upon reboot of failed client
By Server : the server occasionally tries to locate the owners of its remote operations and abort those whose owners can not be found
By Expiration : each remote operation is given a maximum lifetime

23. SECURITY
RPC is a form of remote execution that allows programs or commands to be executed on other systems. But it also opens doors for attacks from unfriendly remote users
Mutual authentication
--- identities of clients and server are verified Request Message Client server Reply message server client
Message integrity, confidentiality, and originality
--- request/reply messages have not been tampered with (integrity), their contents are not revealed ( confidentiality) , and the same message has not appeared more than once ( originality )
Truly generated by
Intended for

24. SUN’S SECURE RPC

25. GRIDRPC One of grid programming models
Supports remote procedure calls (RPCs) on the Grid
Standardized at GridRPC
Standardizing only minimal set of APIs
Higher-level features can be built on top
Providing several reference implementations
Usage scenarios
Remote library calls for executing compute-intensive tasks
Executing large scale task-parallel processing

26. NINF-G SYSTEM (2000..) Reference implementation of GridRPC
Constructed on top of Globus
Globus is introduced in many sites
No more security halls are required in introducing Ninf-G2
Ninfied applications can be executed on many sites
Globus provides primitive functions/tools for grid computing
Concentrating on the development of RPC specific functions
Easy to use other tools on Globus
Ninf-G2 hides complicated mechanisms of Globus
Grid applications/middleware can be easily constructed

27. GRID APPLICATIONS USING NINF-G
Chemical simulation
Replica Exchange Monte Carlo
Surveying potential energy of molecules
Time Dependent Density Functional Theory
Simulating time evolution of electron system in molecules
Optimization problem
Vehicle Routing
Searching optimal route for delivery
Weather simulation
S-model
Forecasting global weather change

28. REFERENCES
Distributed operating system and algorithms Randy chow, Theodore johnson
Remote procedure call - Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Remote_procedure_call
Sun RPC
GridRPC: A Remote Procedure Call API for Grid Computing
Grid technology research center