Remote Procedure Calls (RPCs) allow a process to cause a procedure to execute in another address space, either locally or remotely. The client stub packs parameters into a message and sends it to the server stub, which unpacks the parameters and calls the server procedure. The server stub then packs the result into a message back to the client stub. RPCs hide the details of message passing between client and server stubs to make the remote procedure call appear local to the client.

1. Remote
Procedure Calls
By
P.SAHITHI CHAITANYA (1551210075)
A.RAMPRAKASH REDDY(1551210077)
G.V.R.SHASHANK(1551210080)

2. Introduction
 Inter-process communication (IPC).
 Another virtual address space.
 Another process on the same machine.
 Another process on different machine.
 Hides remote interaction.
 Network programming standard 1980s
 Builds on named pipes or Winsock.
 Remote Method Invocation (RMI)

3. How RPC Operates

4. Cont….
 When client code calls a remote
procedure, the client stub code
 Retrieves the required parameters from the
client address space.
 Marshals1
the parameters as needed into a
standard NDR2
format for transmission over the
network.
 Calls functions in the RPC client run-time
library to send the request and its parameters
to the server.
1 Marshalling (similar to serialization) is the process of transforming the memory
representation of an object to a data format suitable for storage or transmission
2 Network Data Representation (NDR) is an implementation of the presentation layer in
the OSI model.

5. Cont…
 The server performs the following steps to
call the remote procedure:
 The server RPC run-time library functions
accept the request and call the server stub
procedure.
 The server stub retrieves the parameters from
the network buffer and converts (i.e.
unmarshals) them from the network
transmission format to the format the server
needs.
 The server stub calls the actual procedure on
the server.

6. Stubs
 Client stub
 Packs parameter into message.
 Calls : Send & Receive.
 Server Stub
 Calls : Receive & Send.
 Unpacks parameter from the message.
 Details of message passing are hidden – two
libraries.

7. Cont…

8. Steps
1. The client procedure calls the client stub in the normal way.
2. The client stub builds a message and traps to the kernel.
3. The kernel sends the message to the remote kernel.
4. The remote kernel gives the message to the server stub.
5. The server stub unpacks the parameters and calls the server.
6. The server does the work and returns the result to the stub.
7. The server stub packs it in a message and traps to the kernel.
8. The remote kernel sends the message to the clients kernel.
9. The client’s kernel gives the message to the client stub.
10. The stub unpacks the result and returns to the client.

9. Parameter Passing
 Parameter Marshaling.
 Ex: Remote procedure “sum( i, j)”.
 Identical machines.

10. Problems - Parameter Passing
 Different Machine Types
 Ex: IBM mainframes (EBCDIC) & IBM PCs(ASCII).
 Different representation of Integers (1s
compliment & 2s Compliment), Floating point
numbers.
 Numbering of bytes
 Right to Left (Ex: Intel 486) – Little Endian.
 Left to Right (Ex: Sun SPARC) – Big Endian.

11. Example - 1

12. Example - 2

13. Representation of Information
 Canonical Form
 Convert internal representation while
marshaling.
 Ex:
 2’s compliment for integers.
 0 for ASCII.
 1 for Boolean.
 IEEE format for floating point no.

14. Pointer Passing
 One way is to forbid the pointers & reference parameters in
general. – Highly undesirable
 One strategy is copying the whole array/structure (simple)
into message.
 Call by reference is replaced by copy/restore.
 Optimization – Buffer knows if stub is an input / output
parameter. (Twice as efficient).
 Pointer is followed (dereferenced) by putting it in the
register. – Highly Inefficient.

15. Dynamic Binding
 Hardwiring network add. of server into client –
Extremely Inflexible
 To avoid problems like
 Replication of server
 Relocation
 Migration
 Interface Change

16. Terms
 Exports Interface
 Imports Interface
 Binder
 Registering
 Unique Id – Typically 32 bit long
 Handle
 System Dependent
 IP Add. , Ethernet Add. , etc.

17. Disadvantages
 Overhead Exporting & Importing
 Costs Time
 Many short lived client process may have to start over
again.
 Binder may act as bottleneck in distributed system.
 Registering / Deregistering of interfaces creates more
overhead.

18. RPC semantics-presence of failures
 Unable to locate the server
 Lost request message
 Lost reply message
 Server crashes
 Client crashes

19. Unable to locate the server
 When server is down it intimate the value
-1
 Client is unable to locate the server

20. Lost request message
 Message send from client to server is lost

21. Lost reply message
 Reply message from server to client is lost

22. Server crashes
 Server crashes after receiving a request
 Solutions
 Atleast one semantic
 Atmost one semantic
 Exactly one semantic

23. Client crashes
 Client crashes after sending a request
 Solution is extermination

24. Protocols for RPCs
1. Request protocol
2. Request / Reply protocol
3. Request /Reply /Acknowledge-Reply
protocol

25. Request (R) protocol
Client Server
First
RPC
Next
RPC
Request message
Request message Procedure
execution
Procedure
execution

26. Request / Reply (RR) protocol
Client Server
First
RPC
Next
RPC
Request message
Request message
Procedure
execution
Procedure
execution
Reply message
Reply message
Also serves as acknowledgement
for the request message
Also serves as acknowledgement
for the request message
Also serves as acknowledgement
for the reply of the previous RPC

27. Request / Reply / Ack. (RRA) protocol
Client Server
First
RPC
Next
RPC
Request message
Request message
Procedure
execution
Procedure
execution
Reply message
Reply message
Reply acknowledgement message
Reply acknowledgement message