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chapter 2 - application layer Flashcards

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1
Q

What does the application layer do?

A

provides services for applications to communicate over the network

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2
Q

What are the two main application architectures?

A

Client-server and peer-to-peer (P2P)

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3
Q

What is a client-server model?

A

client contacts an server with a fixed IP -> server answers

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4
Q

What is peer-to-peer (P2P)?

A

hosts both request and provide services to each other

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5
Q

What is a socket?

A

interface between the application layer and the transport layer
like a door to the network

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5
Q

How do processes on different hosts communicate?

A

By exchanging messages through sockets

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6
Q

What info is needed to identify a process?

A

IP address + port number

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7
Q

Common port numbers: HTTP? Mail?

A

HTTP = 80, Mail = 25

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8
Q

What does an application-layer protocol define?

A

Message types
syntax
semantics
rules for sending/receiving

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9
Q

What are open protocols?

A

communication rules and standards that are public, anyone can use them

like HTTP, SMTP

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10
Q

What are common transport needs for apps?

A

reliable

low dealy

Throughput (some need high bandwidt)

Security

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11
Q

Key features of TCP?

A

Reliable
flow control
congestion control
connection-oriented

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12
Q

Key features of UDP?

A

Unreliable
no flow/congestion control
no setup
faster

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13
Q

Does TCP guarantee timing or security?

A

No, only reliable delivery

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14
Q

How can TCP be secured?

A

Using TLS (Transport Layer Security)

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15
Q

What does TLS do?

A

Encrypts data
authenticates server
ensures data integrity

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16
Q

What is HTTP?

A

Web’s application layer protocol -

rules for how client talks to a webserver

TCP on port 80

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17
Q

Where is TLS implemented?

A

Application layer

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18
Q

What is a web page made of?

A

A base HTML file + referenced objects (images, stylesheets..)

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19
Q

Is HTTP stateful or stateless?

A

Stateless

server does not store past request info

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20
Q

What are the two types of HTTP connections?

A

Non-persistent and persistent

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21
Q

What is non-persistent HTTP?

A

One TCP connection per object

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22
Q

What is persistent HTTP?

A

One TCP connection for multiple objects

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23
Q

HTTP response time (non-persistent)?

A

2 RTTs + file transmission time

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24
HTTP response time (persistent)?
1 RTT for all referenced objects
25
What are common HTTP request methods?
GET, POST, HEAD, PUT
26
What does HTTP status code 200, 301, 400, 404mean?
200 - request succeeded 301 - Moved Permanently – the object has moved 400 - Bad Request – request not understood by server 404 - Not Found – the requested object doesn't exist
27
Why are cookies used in HTTP?
fix that server remeber you between requests identfies users, track behavour | fix that http is stateless
28
What are the 4 components of cookies?
Cookie line in HTTP response Cookie line in next HTTP request Cookie file on client Backend database at the server
29
What is the goal of a web cache?
If requests same resource again, it can be sent from the cache, not from original server
30
How does a web cache work?
If object is cached, send it If not, fetch from server, cache it, and return to client
31
What is a conditional GET used for?
To check if the cached object is still valid
32
What’s the goal of HTTP/2?
Reduce delay in handling multiple HTTP requests
33
does does HPPT/2 work
takes several requests at the same time Server push - sends resources before you ask for them binary frames - easier for data to understand
34
What’s the key improvement in HTTP/3?
uses UDP/CUIC instead of TCP faster connection setup no HOL | faster -> combines TCP + TLS handshake in one step
35
What are the 3 main components of email?
User agents, mail servers, and SMTP
36
What is SMTP?
Protocol for sending emails over TCP (port 25)
37
Is SMTP push or pull?
Push – sends mail from client to server
38
How is SMTP different from HTTP?
SMTP pushes messages; HTTP pulls objects
39
What is IMAP?
Internet Mail Access Protocol – allows users to manage email on the server
40
What does DNS do?
Translates hostnames to IP addresses
41
What are the 3 types of DNS servers?
Root servers, TLD servers, Authoritative servers
42
What is a local DNS server?
caches recent lookups - to respond faster
43
What is a DNS record type A?
Maps hostname to IP address
44
What does DNS caching do?
Saves lookups temporarily (controlled by TTL value)
45
Advantages of P2P?
scalability and resource sharing
46
What is Dynamic Adaptive Streaming over HTTP (DASH)?
video quality adapts to your Internet speed in real time
46
What are CBR and VBR video?
CBR: Constant Bit Rate VBR: Variable Bit Rate (adapts to video complexity)
46
What is a Content Delivery Network (CDN)?
caches data at multiple locations near users
47
What’s the difference between “enter deep” and “bring home” CDN strategies?
Enter deep: many small servers deep inside access networks Bring home: larger server clusters in fewer location
48
What must a TCP client do to connect to a server?
Create a socket -> specify IP and port
49
Can one TCP server handle multiple clients?
Yes, each client gets a separate socket
50
What is included in an HTTP request line?
Method, path, and version
51
What is included in the HTTP response status line?
Version, status code, and reason phrase | ( HTTP/1.1 404 Not Found)
52
What does the Host header in HTTP request do?
Specifies domain name of the server
53
What’s the difference between recursive and iterative DNS queries?
Recursive: server gets full answer for client Iterative: server refers client to another server.
54
What is a Type NS record in DNS?
domain name -> authoritative name server
55
Why is caching important in DNS?
Reduces load on DNS servers and speeds up response time
56
What is the DASH manifest file?
tells video player: what media is available where chunks are located What qualities exist timing and duration
57
Why is P2P more scalable than client-serv
Peers contribute bandwidth, storage as the network grow

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