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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
difference between server and client process
server - waits to be connected to | client - initiates communication
26
what is a socket
networks send/receive messages to/from its socket - door between application process and end-end transport protocol
27
what is used to identify processes
port and IP address
28
describe the process of socket programming with TCP
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
how to distinguish between different clientes
- source port numbers used to distinguish clients
30
what does http stand for
hyper text transfer protocol
31
what does http do
web application layer software
32
what connection model does http follow and how does it work in this case
client server client - browser requests and receives using http and displays web objects server - web server sends objects in response
33
how does http use tcp
client initiates tcp connection to server port 80 server accepts request http messages are exchanged connection closed
34
is http stateless? what does that mean?
Yes | stateless: server maintains no information about past client requests
35
explain persistent http
multiple objects can be sent over single tcp connection
36
explain non-persistent http
one object sent over a tcp connection, connection then closed - download multiple objects = multiple connections
37
what is RTT
round trip time - time takes for small packet to travel from client to server and back
38
what is http response time? Non persistent
2 RTT + file transmission time
39
issues with non-persistent http
OS overhead for each TCP connection | browsers often open parallel TCP connections to fetch referenced objects
40
what is http response time? persistent
min on 1 RTT
41
two types of http messages
request, response
42
how are cookies used - describe the whole process of how the server and client interact and how cookies play a role in this interaction
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
what is the goal of a web cache
satisfy client request without involving origin server
44
how does the web cache work?
browser sends all http requests to cache obj in cache: cache returns object else: cache requests from origin server
45
What is DNS
Domain name server
46
define dns
distributed database implemented in hierarchy of many name servers
47
what layer protocol is dns?
app layer - name servers communicate to resolve names - address/name translation
48
where is core internet function implemented (layer name)
application
49
what are some dns services
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
why not centralize (have one system doing all the dns functionality) dns?
``` single point of failure traffic volume distant database maintenance doesnt scale ```
51
hierarchical view of dns - root name servers
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
what are authoritative DNS servers
organizations own dns server(s) - for providing ip mapping to orgs own named hosts maintained by org or service provider
53
what are top-level domain servers
responsible for org net edu ero jobs and all country domains
54
what are local DNS name servers
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
explain the process of iterated query dns resolution
host - local dns - root dns - local - topleveldomain - local - authoratative - local - host
56
explain the path of a recursive dns resolution
``` host local root tld auth tld root local host ```
57
what does RR stand for with regards to dns?
resource record
58
name and explain different types of resource records
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
How can one insert into DNS
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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