Application Layer Flashcards
Name 4 Network apps
Email
Streamed videos/audio
Social Networks
Search
Explain the Client-Server Architecture
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.
What is a process?
Programs that are running within the host
Name three components of Email apps
- User agents
- Mail servers
- SMTP(Simple Mail Transfer Protocol)
Name 4 mail access protocols
SMTP
POP (delete and download)
IMAP (allows manipulation of stored msgs on server)
HTTP(gmail, hotmail)
Name 3 things cookies are used for?
Authorization
Shopping carts
Recommendations
What is a web cache?
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)
What is a DNS?
Used to locate internet domain names and translate them into IP addresses.
What is a socket?
Interface (a “door”) into which application process can both send and receive messages.
Explain the P2P architecture
Peers request service from other peers, peers provide service to other peers in return. P2P architecture is self scalable.
What is inter-process communication?
Two process’ communicate within the same host
Explain process communication in the P2P architecture
Both the client and server process can carried out by applications
Why are port numbers important?
They help to identify process accurately with the combination of the IP address.
List two common port numbers and what they belong to
HTTP server :80
Mail Server: 25
What’s the difference between Open protocols and Proprietary protocols?
Open protocols allow for interoperability e.g. HTTP
Proprietary protocols are not e.g. Skype
Name 4 transport services that an application needs
(1) Data Integrity- e.g. file transactions
(2) Timing e.g. interactive games
(3) Throughput e.g. multimedia
(4) Security
What are the transport service requirements for: email, text messaging and interactive games?
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
What is the application layer protocol for the following: E-MAIL, WEB, FILE TRANSFER and STREAMING MULTIMEDIA?
SMTP
HTTP
FTP
SIP, RTP, proprietary
What is the transport layer protocol for the following: E-MAIL, WEB, FILE TRANSFER and STREAMING MULTIMEDIA?
TCP TCP TCP TCP or UDP TCP or UDP
What is a User agent?
Responsible for composing, editing and reading messages e.g. Outlook, iPhone email client
What is a Mail server?
Responsible for storing incoming messages and creating a message queue of messages to be sent out.
What happens when you send an email to someone?
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
What are the 3 phases of transfer that SMTP employ?
- Handshaking
- Transfer of messages
- Closure
Why must SMTP messages be in 7 bit ASCII?
It allows for images and documents to be included in the message
What is MIME?
Multipurpose Internet Mail Extensions- supports non-text attachments, message bodies with multiple parts, non-ASCII text characters
What is the difference between SMTP and other mail access protocols?
SMTP pushes out messages to recipients server
MEANWHILE…
Other mail access protocols retrieve message from server
What does it mean to say that HTTP stateless?
The server maintains no information about past client requests.
How does HTTP use TCP?
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
Why are protocols that maintain a ‘state’ complex?
If the server/client were to crash, their views of state may be inconsistent and must then be reconciled.
What is non-persistent HTTP?
At most one object can be sent over TCP connection
What are cookies used for in regards to HTTP?
To extend HTTP functionality and build state.
What’s persistent HTTP?
Multiple objects can be sent over the TCP connection.
What is RTT(Round Trip Time)?
Time taken for a small packet to travel from client to server and back
What’s the difference between HTTP/1.0 and HTTP/1.1?
Both use GET, POST and HEAD but HTTP/1.1 can PUT and DELETE.
What is the meaning of the following HTTP status codes: 200, 301, 400, 404, 505 ?
200: OK
301: Moved permanently
400: Bad request
404: Not found
505: HTTP Version not supported.
How does the client get an IP address from a website?
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
Whats the difference between iterative and recursive queries in DNS name resolution?
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
What is the RR(Resource Records) Format?
Name, Value, Type, TTL
What does the application layer do?
Supports network applications
