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Computer Networks > Application Layer > Flashcards

Application Layer Flashcards

1
Q

Network Application is

A

Any application running on one host providing communication to the application running on the other host. Helps to manage and monitor network traffic, analyze data

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2
Q

Describe client-server architecture

A

In client-server architecture, one remote process acts as a client and requests some resources from another application process acting as server

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3
Q

Describe Peer-to-peer architecture

A

Both remote processes are executed on the same level and exchange data using shared resources

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4
Q

In client-server architecture, server is

A

Always on host, one or many permanent IP addresses, data centers for scaling

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5
Q

In client-server architecture, client

A

May Communicate with the server, maybe intermittently connected, have dynamic IP addresses, do not communicate directly with each other

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6
Q

A system can acts as client and server simultaneously? True or False? Why?
If same host? If different host?

A

True. One process acts as a server, another as a client.

Communicate with each other via interprocess communication. If host different - exchange messages

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7
Q

What are sockets? How are sockets identified? What is the size of identifier?

A

Process sends and receives messages via the socket. Port numbers to identify the socket. 32-bit

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8
Q

Which of the following is not the TCP services? (Multiple answers):
Reliability, flow control, congestion control, timing, minimum throughput, security, connection-orientedness

A

Timing, minimum throughput, securoty

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9
Q

Which of the following is not the UDP services? (Multiple answers):
Reliability, flow control, congestion control, timing, throughput guarantee, security, connection setup

A

ALL

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10
Q

Web page URL contains

A

Host name, path name

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11
Q

Two features that make HTTP is simple, but powerful because of:

A

use of TCP, statelessness

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12
Q

How does the TCP used in HTTP?

A
  1. client initiates TCP connection (creates socket) to server, port 80
  2. server accepts TCP connection from client
  3. HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server)
  4. TCP connection closed
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13
Q

What does stateless means in HTTP

A

No information about the client’s previous requests

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14
Q

What are the two types of HTTP connections? Describe each of them

A

Non-persistent HTTP: one object sent over TCP connection

Persistent HTTP: multiple objects sent over a TCP connection

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15
Q

What is RTT? How many RTTs does Non-persistent HTTP have? For what steps are RTTs calculated? What is the non-persistent HTTP response time?

A

RTT (definition): time for a small packet to travel from client to server and back. One to initiate connection, one RTT for HTTP request and first few bytes of HTTP response. 2RTT + file transmission time

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16
Q

Compare Non-persistent and persistent HTTP in terms of RTTs?

A

Non-persistent HTTP takes 2 RTTs for a single object, while Persistent needs only one RTT for all referenced objects

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17
Q

What are 2 types of HTTP messages?

A

Request, Response

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18
Q

What is the content of request message? What each part of the message have?

A

Single request line and multiple header lines. Request line has method, URL and HTTP Version fields.
Header lines have host, user agent, condition fields

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19
Q

What kind of HTTP methods exist?

A

GET, POST, HEAD

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20
Q

How does a browser know if browsers wants to use persistent connection?

A

Include Connection: keep-alive in header

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21
Q

Entity body method is used with what method

A

POST method to fill out the form and send it to the server

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22
Q

What are the differences between HTTP 1.0 and HTTP 1.1

A

HTTP 1.1 has PUT and DELETE, to upload and delete file to/in path specified in URL field

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23
Q

Which method in HTTP is used for debugging?

A

HEAD

24
Q

What are the sections of HTTP response message?

A

Status, header, data

25
Q

Status line has what kind of fields?

A

Protocol version field, Status code and status message.

26
Q 
What do the following status codes mean: 
200
301
400
404
505
A 
200 - OK
301 - Moved Permanently
400 - Bad Request
404 - Not found
505 - HTTP version not supported
27
Q

What is the cookie?

A

User-server interaction, small bit of information that travels from browser to the web server.

28
Q

What is the cookie used for?

A

Personal tracking, authentication, personalization, user session state, recommendation, shopping carts

29
Q

Describe each component of cookie and what it is responsible for

A
  1. Header line in the HTTP response message
  2. Header line in the next HTTP request message
  3. Cookie file kept on user’s host, managed by the user browser
  4. Back-end database on the server
30
Q

Which feature of HTTP simplifies the implementation of cookies?

A

Statelessness

31
Q

What does a site do when a client initially visits their website?

A

When initial HTTP requests arrive at site, site creates a unique ID and entry in the backend for the ID.

32
Q

How to keep state of a cookie?

A

Protocol endpoints: maintain state at sender/receiver at multiple transactions
cookies: http messages carry state

33
Q

Is an email system synchronous or asynchronous?

A

Asynchronous

34
Q

Three major components of email are? Describe each of them

A

User agents, mail servers, simple mail transfer protocol(SMTP)

35
Q

Who is the user agent in emails?

A

Just a default user, who reads and sends messages

36
Q

What is the mail server in emails? What does the mail server have?

A

The component that forms the core of email infrastructure. Has mailbox containing messages, mail queue for outgoing mail messages, SMTP protocol between mail servers to send email messages.

37
Q

Mail servers use TCP? True or False?

A

True

38
Q

What is the port that SMTP use?

A

25

39
Q

How are the emails transferred? Is it persistent or not-persistent?

A

Three phases: handshaking(establishing connection), transfer of messages, closure. Persistent

40
Q

What is the main similarity of SMTP and HTTP

A

Use command/response interaction

41
Q

Is there any restriction of email messages? How is this restriction solved?

A

7-bit ASCII. Solved via MIME.

42
Q

What is the purpose of DNS?

A

To identify servers. Maps between IP address and the name.

43
Q

What is the DNS? How is it implemented?

A

Implemented in the hierarchy of many name-servers? Application-Layer protocol, core Internet protocol. DNS can only employ other by application layer protocol like HTTP, SMTP to translate user supplied host names to IP addresses

44
Q

List the DNS services?

A
  1. Hostname to IP address translation
  2. Host Aliasing(host can have one or more alias names)
  3. Mail Server Aliasing
  4. Load distribution(many IP addresses can correspond to one name)
45
Q

Why one should not centralize the DNS?

A
  1. Single point of failure
  2. Traffic Volume
  3. Distant Centralized Database
  4. Maintenance
    Doesn’t scale
46
Q

What does root name server do?

A

Contact authoritative name server if does not know the mapping, get the mapping, return mapping to local name server

47
Q

What are the types of DNS?

A

Root name server, authoritative name server, local(default) name server

48
Q

What is the top level domain server do?

A

responsible for com, org, net etc.

49
Q

What is the authoritative domain server?

A

organization’s own DNS server for providing the authoritative host name to IP mappings for organization’s named hosts

50
Q

List each name resolution method and describe each of them? Which is better? Why?

A

iterated and recursive. iteratively and recursively :).

51
Q

Why is the caching needed in DNS?

A

To store the mappings

52
Q

What are the types in DNS records? What are the domains of A, NS, MX and CNAME?

A

Identifiers responsible for identifying the domain and the parameters required
IP Address, Name server, mail service and canonical name

53
Q

Peer to Peer Architecture is?

A

No always on server, arbitrary end systems directly communicate, peers can change IP addresses

54
Q

What is the formula for distribution time in client servers?

A

N file copies
F file
u_s upload speed of server
d_min minimum client download rate

D_cs >= max(NF/u_s, F/d_min)

55
Q

What is the formula for distribution time in P2P?

A

N file copies
F file
u_s upload speed of server
d_min minimum client download rate

u_max(maximum upload rate) is u_s + sum(u_i)
D_p2p >= max(F/u_s, F/d_min, NF/u_max)

56
Q

extra assignment problem 1

A

extra assignment problem 1

57
Q

extra assignment problem 2

A

extra assignment problem 2

Computer Networks (6 decks)

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