chapter 3 [ RPC ]

Question 1

what is the most used model for organizing distributed applications?

Answer 1

client-server model

Question 2

what is a Chained Client-Server Interactions?

Answer 2

when a server acts as a client for another server

Question 3

what is the downside of a Client-Server Model?

Answer 3

• usually doesn’t run faster than a centralized application
• client waits while server works

Question 4

what are advantages of a Client-Server Model?

Answer 4

• specialized resources [ faster cpu, larger memory ]
• splits up the application
• allows server use by multiple clients

Question 5

what is RPC?

Answer 5

the extension of local procedure calls into the context of a distributed system

Question 6

how does RPC work?

Answer 6

by converting procedure call invocations into network messages and vice versa

Question 7

what is a stub?

Answer 7

a piece of code on the client side that converts:
- function call to network req
- network resp to function returns

Question 8

what is a skeleton?

Answer 8

is a piece of code on the server side that converts:
- net req to function call
- function return to net response

Question 9

how are stubs and skeletons generated?

Answer 9

automatically by the RPC

Question 10

what are limitations of RPC?

Answer 10

clients and servers do not share:
- address space
- file descriptors
- global vars
- func params

Question 11

what constraints does RPC place on client-server model?

Answer 11

• server needs to have function prototypes
• both client and server can have internal data that can not be accessed by the other

Question 12

what is sun RPC?

Answer 12

is a mechanism that automatically generates client stub and server skeleton using RPC compiler rpcgen.

Question 13

sun rpc is _________ dependent and ________ independent?

Answer 13

language [ c ] and platform

Question 14

what is port mapper?

Answer 14

a protocol that permits a client to look up the port number of programs hosted on the server

Question 15

What port is port mapper?

Answer 15

port 111

Question 16

what do we mean by RPC runtime is unaware?

Answer 16

• it doesn’t know about function prototypes, procedure names, what the procedures are doing or what arguments they take

Question 17

what is the only thing an RPC is concerned with?

Answer 17

managing requests and shipping response buffers

Question 18

what is the downside of using UDP based RPC?

Answer 18

• lose of req and resp

Question 19

what happens if a request gets lost in a UDP based RPC?

Answer 19

• client automatically resends request until it receives a response

Question 20

what happens if a response gets lost in a UDP based RPC?

Answer 20

• server will be invoked several times [ however many times it takes ] until response is sent

Question 21

what type of server is recommended if using UDP based RPC?

Answer 21

idempotent server : performing an operation once is the same as performing it multiple times

Question 22

what is (Un)Marshalling Parameters?

Answer 22

process of converting parameters from a lower level representations to a higher level representations and vice versa

Question 23

what is the lower level and higher level representation of parameters respectively?

Answer 23

• buffers and C variables

Question 24

what is in charge of parameter conversion?

Answer 24

XDR [ external data representation ] layer

Question 25

what is the role of client Stub in XDR context?

Answer 25

calls XDR function to:
- marshal procedure params to buffers
- un marshal function return to variables

Question 26

what is the role of server Skeleton?

Answer 26

1. defines a function that handles incoming requests
2. creates TCP and UDP server sockets and registers them to the port mapper
3. registers function created at 1 to RPC system
4. waits for incoming requests from RPC