Computer Networks Chapter 2

Question 1

API

Answer 1

Application programming interface. A set of functions and procedures allowing the creation of applications that access the features or data of an operating system, application, or other service.

Question 2

Process

Answer 2

Program running within a host (end system).

Question 3

Communication Within the Same Host

Answer 3

Within the same host, two processes communicate using inter-process communication, defined by the OS.

Question 4

Communication Between Different Hosts

Answer 4

Processes in different hosts communicate by exchanging messages.

Question 5

Client Process

Answer 5

Process that initiates communication.

Question 6

Server Process

Answer 6

Process that waits to be contacted.

Question 7

Open Protocols

Answer 7

Defined in RFCs. Everyone has access to protocol definition. Allows for interoperability.

ex. HTTP, SMTP.

Question 8

Proprietary Protocols

Answer 8

Private protocol definition.

ex. Skype, Zoom.

Question 9

Client-Server Paradigm

Answer 9

Server:
-always-on host
-permanent IP address
often in data centers, for scaling

Clients:
-contact, communicate with, server
-may be intermittently connected
-may have dynamic IP addresses
-do not communicate directly with each other
ex. HTTP, IMAP, FTP

Question 10

Peer-Peer (P2P) Architecture

Answer 10

-no always-on server
-arbitrary end systems directly communicate
-peers request service from other peers, provide service in return to other peers
-self-scalability - new peers bring new service capacity as well as new service demands
-peers are intermittently connected and change IP addresses
-complex management compared to client-server paradigm

*Applications with P2P architecture have both client and server processes, depending on the task they are currently carrying out.

Question 11

Sockets

Answer 11

A socket is analogous to a door:
-process sends/receives messages to/from its socket.
-sending process relies on transport infrastructure on other side of door to deliver message to socket at receiving process.
-two sockets involved: one on each side.

Question 12

Identifiers

Answer 12

To receive messages, a process must have an identifier. An identifier includes both IP address and port number associated with the process on the host.

*Host devices have a unique 32-bit IP address.
*example port numbers include: HTTP server (80) and mail server (25).

Question 13

An Application-Layer Protocol Defines…

Answer 13

How an application’s processes, running on different end systems, pass messages to each other.

-types of messages exchanged.
-message syntax.
-message semantics.
-rules for when and how processes send and respond to a message.

Question 14

Transport Services an App Needs

Answer 14

-data integrity
-timing
-throughput
-security

Question 15

Internet Transport Protocols Services

Answer 15

-TCP
-UDP

Question 16

TCP Service

Answer 16

“Transmission control protocol” service.
-reliable transport between sending and receiving process.
-flow control: sender won’t overwhelm receiver.
-congestion control: throttle sender when network overloaded.
-connection-oriented: setup required between client and server processes.
-does not provide: timing, minimum throughput guarantee, security.

Question 17

UDP Service

Answer 17

“User Datagram Protocol” services.
-unreliable data transfer between sending and receiving process.
-does not provide: reliability, flow control, congestion control, timing, throughput guarantee, security, or connection setup.

Question 18

Vanilla TCP and UDP Sockets

Answer 18

-no encryption.
-cleartext passwords sent into socket traverse Internet in cleartext.

Question 19

HTTP

Answer 19

Hypertext transfer protocol. Web’s application-layer protocol. Based on the client/server model.

Question 20

Client/Server Model

Answer 20

client: browser that requests, receives (using HTTP protocol), and “displays” Web objects.
server: Web server sends (using HTTP protocol) objects in response to requests.

Question 21

Non-persistent HTTP

Answer 21

-TCP connection opened.
-At most one object sent over TCP connection.
-TCP connection closed.

*downloading multiple objects requires multiple connections.

Question 22

Persistent HTTP

Answer 22

-TCP connection opened to a server.
-Multiple objects can be sent over single TCP connection between client and that server.
-TCP connection closed.

Question 23

RTT

Answer 23

“Round Trip Time.” Time for a small packet to travel from client to server and back.

Question 24

HTTP Response Time (per object)

Answer 24

-one RTT to initialize TCP connection.
-one RTT for HTTP request and first few bytes of HTTP response to return.
-object/file transmission time.

Question 25

Non-persistent HTTP Issues

Question 26

Application Architecture

Answer 26

Designed by the application developer and dictates how the application is structured over the various end systems.

-Client-server Architecture
-P2P Architecture

Question 27

Handshaking

Answer 27

Client and server exchange transport-layer control information with each other before the application-level messages begin to flow.

Question 28

Full-Duplex

Answer 28

Two processes can send messages to each other over the connection at the same time.

Question 29

Pipelining

Answer 29

Requests for objects can be made back-to-back, without wait
ing for replies to pending requests.