Week 4

Question 1

What are layers of a network?

Answer 1

Each layer implements a service, relying on services implemented by a layer below

Question 2

Why is layering good?

Answer 2

• modularization
• ease of maintenance

Question 3

What are the 5 Internet Layer Stacks

Answer 3

1. App
2. Transport
3. Network
4. Link
5. Physical

Question 4

What does the Application Layer do?

Answer 4

supporting network apps through HTTP, IMAP, SMTP, DNS

Info: MESSAGE

Question 5

What does the Transport Layer do?

Answer 5

Process to process data transfer (TCP and UDP)

Info: SEGMENT

Question 6

What does the Network Layer do?

Answer 6

moving packets known as DATAGRAMS.

Question 7

What does the Link layer do?

Answer 7

Data transfer between neighboring elements (within the same network) called FRAMES

Question 8

What does the Physical Layer do?

Answer 8

bits “on the wire”

Question 9

Order of layering?

Answer 9

App > Transport > Network > Link > Physical

Question 10

What are the 2 Main Network Architechtures?

Answer 10

1. Client-Server Architecture
2. P2P Architecture

Question 11

Explain the Client-Server structure

Answer 11

Server:
- always on host, permanent IP address
- ideally data centers

Client:
- initiates contact with the server.
- Clients do not interact with other clients

example: HTTP, IMAP, FTP

Question 12

Explain the P2P Architechture

Answer 12

• minimal or no reliance on dedicated servers
• direct communication between hosts.

Question 13

How do Client-Servers processes interact with each other?

Answer 13

Through SOCKETS. send/receive through sockets, like a door.

Question 14

What are sockets?

Answer 14

where a process sends messages into and receives messages from.

“door” of 2 houses, connecting the inside, outside, + road (link)

Question 15

What info do we need to identify a process?

Answer 15

1. Host’s address
2. Port number

Question 16

4 types/dimensions of transfer service an app needs?

Answer 16

1. Reliable data transfer
2. Throughput
3. Timing / delay
4. Security

Question 17

What are the 2 Main Transport services provided by the internet?

Answer 17

TCP and UDP

Question 18

For text-apps, what transfer servies would it need?

Answer 18

-No data loss
- Time sensitive (FOR TEXTS)

Question 19

For images/video apps, what transfer services would it need?

Answer 19

• Throughput
• Timing / delay sensitive

Question 20

Explain the TCP service.

Answer 20

• Connection oriented
• Has congestion control

Question 21

Pros of TCP

Answer 21

• No loss (provides reliability)
• Congestion controlC

Question 22

Cons of TCP

Answer 22

• does NOT provide:
• guaranteed timing, security, throughput

Question 23

Explain the UDP service model

Answer 23

• lightweight transport protocol with minimal services
• no handshaking required

Question 24

Pros of UDP

Answer 24

• UDP has no constraints unlike TCP, you can send as much as you wantC

Question 25

Cons of UDP

Answer 25

• unreliable data transfer
• Does not provide timing, throughput guarantee, congestion control

Question 26

Which types of apps can use UDP?

Answer 26

• Internet telephone
• Interactive games

Question 27

What are the 2 types of a network app?

Answer 27

1. Open Network (rules dictated by RFC)
2. Properiety Network

Question 28

What are the parts of a destination address?

Answer 28

IP address and port number of BOTH client and server.

Question 29

Parts of a Client Program with UDP: How do you create the client socket?

Answer 29

1. initialize server name and port
2. create client socket: USING SOCK_DGRAM

Question 30

Parts of a Client Program with UDP: How do you send a message?

Answer 30

1. encode message
2. use .sendto() function

Question 31

Parts of a Client Program with UDP: How do you receive message?

Answer 31

1. use .recvfrom()
2. close the socket

Question 32

Parts of a Server Program with UDP: What socket do you need to make?

Answer 32

Server socket!

Using SOCK_DGRAM

Question 33

Parts of a Server Program with UDP: How do you receive packets?

Answer 33

INSIDE THE INFINITE LOOP:

• use .recvfrom()
• decode the message!
• use .sendto()

Question 34

Parts of a Client Program with TCP: How do you create the client socket?

Answer 34

1. initialize servername and port
2. Create client socket through SOCK_STREAM

Question 35

Socket programming for TCP, how does client -> server handshake work exactly?

Answer 35

1. client and server handshake before sending data
2. client drops data into TCP connection
3. server “hears” the data and creates a new socket dedicated for that client

Question 36

Parts of a Client Program with TCP: How to sent request to server?

Answer 36

using socket.send()

Question 37

Difference between TCP and UDP client?

Answer 37

Nothing, just the SOCK_STREAM vs SOCK_DGRAM

Question 38

Parts of a Server Program with TCP: How does accepting requests from a client work?

Answer 38

In a LOOP FOREVER:

Server has to wait for incoming connection request: socket.accept()

then, a NEW SOCKET must be created for the server

Question 39

Parts of a Server Program with TCP: How does sending messages to a client work?

Answer 39

send an encoded messages to the client and close the connection.