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Computer Networks > Application Layer > Flashcards

Application Layer Flashcards

1
Q

Name 4 Network apps

A

Email
Streamed videos/audio
Social Networks
Search

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2
Q

Explain the Client-Server Architecture

A

The client communicates with the server and its IP address always changes.

The server acts as a Host, responding to requests from the client and its IP address is always the same.

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3
Q

What is a process?

A

Programs that are running within the host

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4
Q

Name three components of Email apps

A
  • User agents
  • Mail servers
  • SMTP(Simple Mail Transfer Protocol)
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5
Q

Name 4 mail access protocols

A

SMTP
POP (delete and download)
IMAP (allows manipulation of stored msgs on server)
HTTP(gmail, hotmail)

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6
Q

Name 3 things cookies are used for?

A

Authorization
Shopping carts
Recommendations

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7
Q

What is a web cache?

A

A cache is a place to store something temporarily in a computing environment. Cache acts as both client and server without involving the original server. (proxy server)

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8
Q

What is a DNS?

A

Used to locate internet domain names and translate them into IP addresses.

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9
Q

What is a socket?

A

Interface (a “door”) into which application process can both send and receive messages.

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10
Q

Explain the P2P architecture

A

Peers request service from other peers, peers provide service to other peers in return. P2P architecture is self scalable.

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11
Q

What is inter-process communication?

A

Two process’ communicate within the same host

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12
Q

Explain process communication in the P2P architecture

A

Both the client and server process can carried out by applications

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13
Q

Why are port numbers important?

A

They help to identify process accurately with the combination of the IP address.

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14
Q

List two common port numbers and what they belong to

A

HTTP server :80

Mail Server: 25

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15
Q

What’s the difference between Open protocols and Proprietary protocols?

A

Open protocols allow for interoperability e.g. HTTP

Proprietary protocols are not e.g. Skype

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16
Q

Name 4 transport services that an application needs

A

(1) Data Integrity- e.g. file transactions
(2) Timing e.g. interactive games
(3) Throughput e.g. multimedia
(4) Security

17
Q

What are the transport service requirements for: email, text messaging and interactive games?

A

Email- Data loss: none, Throughput: elastic, Time: none
Text Message-Data loss: none, throughput: elastic, time: none
Interactive games-Data loss: loss-tolerant, throughput: few kpbs, time: 100’s msec

18
Q

What is the application layer protocol for the following: E-MAIL, WEB, FILE TRANSFER and STREAMING MULTIMEDIA?

A

SMTP
HTTP
FTP
SIP, RTP, proprietary

19
Q

What is the transport layer protocol for the following: E-MAIL, WEB, FILE TRANSFER and STREAMING MULTIMEDIA?

A 
TCP
TCP
TCP
TCP or UDP
TCP or UDP
20
Q

What is a User agent?

A

Responsible for composing, editing and reading messages e.g. Outlook, iPhone email client

21
Q

What is a Mail server?

A

Responsible for storing incoming messages and creating a message queue of messages to be sent out.

22
Q

What happens when you send an email to someone?

A

1: Sender uses UA to compose a message
2: UA sends message to mail server it is then placed in a queue
3: Client side of SMTP opens TCP connection with recipients mail server
4: SMTP client sends the message to the recipient
5: Recipient’s mail server stores the messages in the mailbox
6: Recipient uses UA to read message

23
Q

What are the 3 phases of transfer that SMTP employ?

A
  • Handshaking
  • Transfer of messages
  • Closure
24
Q

Why must SMTP messages be in 7 bit ASCII?

A

It allows for images and documents to be included in the message

25
Q

What is MIME?

A

Multipurpose Internet Mail Extensions- supports non-text attachments, message bodies with multiple parts, non-ASCII text characters

26
Q

What is the difference between SMTP and other mail access protocols?

A

SMTP pushes out messages to recipients server
MEANWHILE…
Other mail access protocols retrieve message from server

27
Q

What does it mean to say that HTTP stateless?

A

The server maintains no information about past client requests.

28
Q

How does HTTP use TCP?

A

1- client initiates TCP connection to server
2- server accepts TCP connection from client
3- HTTP messages are exchanged between the browser and web server
4- TCP connection closed

29
Q

Why are protocols that maintain a ‘state’ complex?

A

If the server/client were to crash, their views of state may be inconsistent and must then be reconciled.

30
Q

What is non-persistent HTTP?

A

At most one object can be sent over TCP connection

31
Q

What are cookies used for in regards to HTTP?

A

To extend HTTP functionality and build state.

32
Q

What’s persistent HTTP?

A

Multiple objects can be sent over the TCP connection.

33
Q

What is RTT(Round Trip Time)?

A

Time taken for a small packet to travel from client to server and back

34
Q

What’s the difference between HTTP/1.0 and HTTP/1.1?

A

Both use GET, POST and HEAD but HTTP/1.1 can PUT and DELETE.

35
Q

What is the meaning of the following HTTP status codes: 200, 301, 400, 404, 505 ?

A

200: OK
301: Moved permanently
400: Bad request
404: Not found
505: HTTP Version not supported.

36
Q

How does the client get an IP address from a website?

A

1: Client queries root server to find .com DNS Server
2: Client queries .com DNS server to get amazon.com server
3: Client queries amazon.com to get the IP address

37
Q

Whats the difference between iterative and recursive queries in DNS name resolution?

A

Iterative query- Contacted server replies with name of server to contact. More widely used
MEANWHILE..
Recursive query- Puts the burden of name resolution on contacted server

38
Q

What is the RR(Resource Records) Format?

A

Name, Value, Type, TTL

39
Q

What does the application layer do?

A

Supports network applications

Computer Networks (5 decks)

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