Application Layer

Question 1

What are the two possible structures of applications?

Answer 1

Client-Server

Peer to Peer (P2P)

Question 2

The behaviours of a server are:

Answer 2

Always-on host
Permanent IP address
data centres for scaling

Question 3

The behaviours of clients are:

Answer 3

communicate with server
may be intermittently connected
may have dynamic IP addresses
do not communicate directly with each other

Question 4

Specifics of a P2P architecture?

Answer 4

no always-on server
arbitrary end systems directly communicate
peers request servie from other peers
provide service in return to other peers

Question 5

What is ‘self scalabilty’?

Answer 5

In P2P architecture, new peers bring new service capacity, as well as new service demands.

Question 6

what is a process

Answer 6

program running within a host

Question 7

Within the same host, how do two processes communicate?

Answer 7

Using inter-process communication, which is defined by the OS.

Question 8

How do processes in different hosts communicate?

Answer 8

By exchanging messages

Question 9

What is the client process?

Answer 9

Process that initiates communication

Question 10

What is the server process?

Answer 10

Process that waits to be contacted

Question 11

How does a process send/receive messages?

Answer 11

To/from its socket

Question 12

Why does a process need an identifier?

Answer 12

To receive messages

Question 13

To receive messages, a process must have an :

Answer 13

An identifier

Question 14

Does IP address of host on which process runs suffice for identifying the process?

Answer 14

Many processes can be running on same host

Question 15

Identifier includes both:

Answer 15

IP address

Port numbers associated with process on host

Question 16

App-layer protocol defines:

Answer 16

types of messages exchanged
message syntax
message semantics
rules
open protocols
proprietary protocols

Question 17

What transport service does an app need?

Answer 17

data integrity
timing
throughput
security

Question 18

What is data integrity?

Answer 18

Some apps require 100% reliable data transfer

Other apps can tolerate some loss (audio)

Question 19

What is timing in relation to transport service?

Answer 19

Some apps require low delay to be effective (games)

Question 20

What is throughput in relation to transport service?

Answer 20

Some apps require minimum amount of throughput to be effective.

Other apps make use of whatever throughput they get (elastic apps)

Question 21

What is an elastic app?

Answer 21

An app that makes use of whatever throughput it can get

Question 22

Transport protocol specs of TCP service:

Answer 22

Reliable transport
flow control
congestion control
does not provide:timing, minimum throughput guarantee, security
Connection - oriented

Question 23

UDP service transport protocol specs:

Answer 23

unreliable data transfer
does not provide: reliabiity, flow control, congestion control, timing, throughput guarantee, security, of connection setup.

Question 24

Why is there UDP?

Answer 24

Good to get a simple answer to another server quickly.

Delivering data that will quickly be replaced/updated. Like weather, gaming data.

Question 25

what is the security of TCP & UDP?

Answer 25

No encryption

cleartext passwords sent into socket traverse internet in cleartext

Question 26

What is the security of SSL?

Answer 26

provides encrypted TCP connection
data integrity
end-point authentication