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csc3002f > application layer > Flashcards

application layer Flashcards

1
Q

As a service, what is the internet’s main roles

A

provides service to applications
provides programming interface to applications - hooks that allow sending and receiving app programs to connect to internet - think post service

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2
Q

What are network applications?

A

programs that :

  • run on different end systems - exchange msgs
  • communicate over a network
  • e.g. web server communications with browser
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3
Q

do we need to write software for network core devices?

A

no - net core devices dont run on user applciations

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4
Q

what are 2 application architectures?

A

client-server

peer-to-peer (P2P)

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5
Q

Describe client-server architecture

A

server - always on host, permanent ip address, data centers for scaling

clients

  • communicate with server
  • doesnt need to be on all the time
  • dynamic IP
  • no direct communication with other clients
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6
Q

Describe P2P architecture

A 
no always on server
end systems communicate directly
peers request service from other peers
peers intermittently connected
dynamic IP
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7
Q

what is p2p self-scalability?

A

new peers bring new service capacity and resources as well as new service demands

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8
Q

what is a service

A

capabilities provided by system to users

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9
Q

what is a service access point

A

instantiation of the port set with an IP that identifies the device/host

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10
Q

what is the transport service

A

allows networked applications to exchange messages

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11
Q

what are 3 things that identify applications

A

host IP address
port number
protocol - type of trans protocol

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12
Q

some transport primitives

A

request
indication - request for connection
response
confirm

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13
Q

connectionless service

A

src just sends information without first establishing a connections

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14
Q

problems with connectionless service

A

message lost, message transformed, duplication, order of message changed

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15
Q

connection-oriented service

A

connection request sent and confirmed before trying to send data packets

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16
Q

message mode transfer

A

messages sent is received in the same unit format that it was sent in

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17
Q

stream mode transfer

A

not concerned about units just concerned that messahes are received in the same order that they were sent

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18
Q

TCP properties

A

reliable
flow control - sender doesnt overwhelm receiver
congestion control - throttle sender when network is overloaded
connection-oriented

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19
Q

what does TCP not provide?

A

timing, minimum throughput guarantee, security

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20
Q

UDP properties

A

unreliable

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21
Q

what does udp not provide

A

reliability, flow/congestion control, timing, throughput guarantee, security, connection setup

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22
Q

why bother with udp

A

quick messaging

message units

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23
Q

what is a process

A

program running within a host - two processes communicate using inter-process communication

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24
Q

how do processes within the same vs different hose communicate?

A

same - interprocess comm

diff - exchange messages

25
Q

difference between server and client process

A

server - waits to be connected to

client - initiates communication

26
Q

what is a socket

A

networks send/receive messages to/from its socket - door between application process and end-end transport protocol

27
Q

what is used to identify processes

A

port and IP address

28
Q

describe the process of socket programming with TCP

A

specfiy ip and port
client creates socket and client TCP establishes connection to server TCP
when contacted by client, server creates new socket for server process to connect to that particular client
- server can talk with multiple clients
- source port numbers used to distinguish clients

29
Q

how to distinguish between different clientes

A
  • source port numbers used to distinguish clients
30
Q

what does http stand for

A

hyper text transfer protocol

31
Q

what does http do

A

web application layer software

32
Q

what connection model does http follow and how does it work in this case

A

client server
client - browser requests and receives using http and displays web objects
server - web server sends objects in response

33
Q

how does http use tcp

A

client initiates tcp connection to server port 80
server accepts request
http messages are exchanged
connection closed

34
Q

is http stateless? what does that mean?

A

Yes

stateless: server maintains no information about past client requests

35
Q

explain persistent http

A

multiple objects can be sent over single tcp connection

36
Q

explain non-persistent http

A

one object sent over a tcp connection, connection then closed - download multiple objects = multiple connections

37
Q

what is RTT

A

round trip time - time takes for small packet to travel from client to server and back

38
Q

what is http response time? Non persistent

A

2 RTT + file transmission time

39
Q

issues with non-persistent http

A

OS overhead for each TCP connection

browsers often open parallel TCP connections to fetch referenced objects

40
Q

what is http response time? persistent

A

min on 1 RTT

41
Q

two types of http messages

A

request, response

42
Q

how are cookies used - describe the whole process of how the server and client interact and how cookies play a role in this interaction

A

client: tcp connection
server: response - sends cookie
client: accepts cookies, sends request
server: sees cookie, check DB and responds with customized response based on client’s previous uses

43
Q

what is the goal of a web cache

A

satisfy client request without involving origin server

44
Q

how does the web cache work?

A

browser sends all http requests to cache
obj in cache: cache returns object
else: cache requests from origin server

45
Q

What is DNS

A

Domain name server

46
Q

define dns

A

distributed database implemented in hierarchy of many name servers

47
Q

what layer protocol is dns?

A

app layer - name servers communicate to resolve names - address/name translation

48
Q

where is core internet function implemented (layer name)

A

application

49
Q

what are some dns services

A

map host name to ip address
host aliasing - diff names map to same address
mail server aliasing
load distribution - not all activity will go to same server e.g. facebook has lots of users and will take users to different servers but all users use facebook

50
Q

why not centralize (have one system doing all the dns functionality) dns?

A 
single point of failure
traffic volume
distant database 
maintenance
doesnt scale
51
Q

hierarchical view of dns - root name servers

A

contacted by local name server - cannot resolve name

  • contact authoritative name server is name mapping is not known
  • gets mapping
  • returns mapping to local name server
52
Q

what are authoritative DNS servers

A

organizations own dns server(s) - for providing ip mapping to orgs own named hosts
maintained by org or service provider

53
Q

what are top-level domain servers

A

responsible for org net edu ero jobs and all country domains

54
Q

what are local DNS name servers

A

not strictly part of hierarchy
each isp has one - also default name server
host makes dns query - sent to local dns server
- has local cache of recent name to address conversions
- acts as a proxy into heirarchy

55
Q

explain the process of iterated query dns resolution

A

host - local dns - root dns - local - topleveldomain - local - authoratative - local - host

56
Q

explain the path of a recursive dns resolution

A 
host
local
root
tld
auth
tld
root
local
host
57
Q

what does RR stand for with regards to dns?

A

resource record

58
Q

name and explain different types of resource records

A

A - name= host name, value = ip
NS - name - domain, value - hostname of auth server
CName - name - alias for some real name, val - real name
MX - val name of mail server associated with the name

59
Q

How can one insert into DNS

A

register name with DNS registrar - names, ip address of auth server
registrar inserts two RRs into TLD server (NS and A)

csc3002f (16 decks)

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