Lecture 1

= Transmission Control Protocol (is connection oriented
)

Establishes a point-to-point connection between two entities in the network

= Internet protocol (principal communications protocol on the internet)

Delivers packets of data across network boundaries

numerical label assigned to devices in a network that use the internet protocol to communicate with other devices

= Domain Name System

It translates hostnames to IP Addresses

Hyper Text Transfer Protocol

TCP and IP

• Client (web browser) sends request

• Web server replies with appropriate answer 
 (could also be an error)

• Each request-response pair is independent

• No permanent connection between server and browser

  (allows for a high number of users per server)

It is a:

• Synchronous request-response protocol

• "Stateless" protocol

• Proxies mediate between browser and server

  (caching, filtering, etc.)

• Everything is sent and received as clear text

They are an abstract concept for nodes in hypertext (HTML files, documents, images, etc)

-> Data types are defined by MIME (RFC 2045)

e.g. "text/html", "image/png", “application/xml“, etc.

= Uniform Resource Locator

• Standardized way of identification and addressing of any resource on the internet

• Subtype of Uniform Resource Identifier (URI)

<scheme>://[<user>[:<password>]@]<server>[:<port>]/[<path>][?<query>][#<fragment>]

-> https://usr:pwd@tennis-club-wieden.at:3000/members/rackets?year=2020#vintage

It’s a protocol to be used when connecting to a server
 (http(s), ftp, mongodb, etc.)

They’re optional:

• Credentials to access a protected resource

As the Domain name or IP address of the server

It’s the port at which the server is listening for requests

It’s the local path to a resource on the server

Parameters that can be passed to server app

Name of an entity within the resource

-> This is only used by clients

• Refers to a certain resource (identified by its URL)

• Contains a certain type/method (Most common methods for access: GET, POST, PUT)

Optional:

• Application data = the “body” (e.g., the data of a form (POST, PUT)

• Application metadata

  • Preferred data type and language (for GET, POST - e.g., JSON/ HTML)

  • Data type of the body (for POST, PUT - what kind of data)

• request metadata (headers) (e.g., Targethost, User authentication, Cookies, etc.)

Each access to a resource has a certain request type ("method")

request a resource (only retrieves data)

submit data to a resource

• Data is included in body of the request

• May result in creation of new resource or 
update of existing resource

replaces target resource with sent payload (Idempotent)

deletes a resource (Idempotent)

provides a set of instructions to modify the target resource

access to the metadata of the servers, the Internet connection, the resource, etc.

• text/plain

• text/html

• image/jpeg

• application/pdf

• application/xml

what kind of response type to accept (e.g. Accept: application/json)

what kind of request payload are we sending (in POST and PUT)

tells server a list of acceptable encodings (e.g. Accept-Encoding: gzip, deflate)

Authorization method and credentials (e.g. Authorization: Basic QWxhZGRpbjpPcGVuU2VzYW1l)

Sends a cookie to the server

• Always follows a request message

• Contains a status code

• application data („body“)

• application metadata

  • Data type and encoding of the application data

  • Caching possibilities and expiring date

  • Current URL of a transferred resource (for GET)

• response metadata (e.g.: Server, TCP connection state, date)