HOW WEB WORKS Flashcards
is a set of rules that partners use when they communicate.
PROTOCOL
A set of rules, for routing and addressing packets of data so that they can –across networks
and – at the correct destination.
travel, arrive
A suite of communication
protocols used to interconnect
network devices on the internet
Transmission Control
Protocol / Internet
Protocol (TCP/IP)
TCP/IP is originally abstracted as a –layer stack.
four
(TCP/ IP)Later abstractions subdivide it further into five or – layers
seven
Transmits raw bit stream over the physical medium
- PHYSICAL LAYER
Defines the format of data on the network
- DATA LINK LAYER
Decides which physical path the data will take
- NETWORK LAYER
Transmits data using transmission protocols including TCP and UDP
- TRANSPORT LAYER
Maintains connections and is responsible for controlling ports and sessions
- SESSION LAYER
Ensure that data is in a usable format and is where data encryption occurs
- PRESENTATION LAYER
Human-computer interaction layer, where application can access the network services
- APPLICATION LAYER
INTERNET
PROTOCOLS
APPLICATION LAYER
TRANSPORT LAYER
INTERNET LAYER
LINK LAYER
the lowest layer, responsible for both the physical transmission of data/raw bits
across media (both wired and wireless) and establishing logical links.
LINK LAYER
Link layer handles –like packet creation, transmission, reception, error
detection, collisions, line sharing, and more.
issues
The one term here that is sometimes used in the Internet context is that
of – addresses. These are unique 48- or 64-bit identifiers assigned to network.
MAC (media access control)
▪ sometimes also called the IP Layer, routes packets between
communication partners across networks.
INTERNET LAYER
Internet layer establishes connection, routing, and –
addressing
Internet layer provides “–” communication. It sends out a message to its destination, but expects –, and provides no guarantee the message will arrive intact, or at all
best effort, no reply
▪ The Internet uses the – addresses, which are
numeric codes that uniquely identify destinations on the
Internet.
Internet
Protocol (IP)
is composed of 32-bit address
length and is the fourth version of
the Internet Protocol (IP).
IPv4
is composed of 128-bit
address length and is the latest
updated version of the Internet
Protocol (IP).
IPv6
Who Gives an ISP its ISP addresses?
Internet Assigned Numbers Authority (IANA)
IANA a department of ICANN,
the Internet Corporation for Assigned Names and Numbers, which is an
internationally organized – responsible for the global coordination of IP addresses, domains, and –.
nonprofit organization, Internet protocols
▪ IANA allocates – from pools of unallocated addresses to Regional Internet Registries, such as AfriNIC (for Africa) or ARIN (for North
America) or APNIC (the Asia Pacific Network Information Centre)
IP addresses
ensures transmissions arrive in order and
without error
The transport layer
used by end-user software such as web browsers and email clients.
APPLICATION LAYER
Application Layer provides protocols that allow software to – and –
information and present meaningful data to users.
send , receive
Application Layer Protocols
HTTP
SSH
FTPPOP/IMAP/SMTP
DNS
is used for web
communication
HTTP. The Hypertext Transfer Protocol
allows remote command-line
connections to servers
SSH. The Secure Shell Protocol
is used for transferring files between
computers.
FTP. The File Transfer Protocol
the Internet’s system for mapping alphabetic names
to numeric Internet Protocol (IP) addresses like a phone book maps a person’s name to a phone number.
Domain Name System
Generic top-level domain (gTLD)
Unrestricted
Sponsored
New
TLDs include .com, .net, .org, and .info.
Unrestricted
TLDs including .gov, .mil, .edu, and others. These domains can have requirements for ownership and thus new second-level domains must have permission from the sponsor
before acquiring a new address.
Sponsored
From January to May of 2012, companies and individuals could
submit applications for new TLDs. TLD application results were announced in June 2012, and include a wide range of both
contested and single applicant domains. These include corporate ones like .apple, .google, and .macdonalds, and contested ones like
.buy, .news, and .music
New
These codes are under the control of the countries which they represent,
which is why each is administered differently
Country code top-level domain (ccTLD)
Some IDNs include –, –, and – domains (among others)
which have test domains at http://παράδειγμα.δoιμή, http:// 例え.テス
ト, and http:// ,مثال.إختبارrespectively
Greek, Japanese, and Arabic
was the first assigned top-level domain. It is still assigned and used for reverse DNS lookups (i.e., finding the domain
name of an IP address)
arpa
The owner of a second-level domain can elect to have – if
they so choose, in which case those subdomains are prepended to
the base hostname.
subdomains
define what application protocols
to use
Protocol
identifies the server
from which we are requesting
resources.
Domain
is a familiar concept to
anyone who has ever used a computer file system. The root of a web server corresponds to a folder somewhere on that server
Path
They are a critical way of passing
information, such as user form input from the client to the server. In URLs, they are encoded as key value pairs delimited by & symbols
and preceded by the ? symbol
Query String
The components for a query string
encoding a – and
password
username
The last part of a URL is the
optional fragment.
This is used as a way of requesting
a portion of a page.
Fragment
is an application protocol
for distributed, collaborative, hypermedia information
systems that allows users to communicate data on the
World Wide Web.
Hypertext Transfer Protocol (HTTP)
are sent in the request from the client and received in
the response from the server. These encode the parameters for
the HTTP transaction, meaning they define what kind of
response the server will send.
Headers
Request headers include data about the – machine (as in
your personal computer)
client
The HTTP protocol defines several different types of
requests, each with a different intent and characteristics
Request Methods
one is asking for a
resource located at a specified URL
to be retrieved
GET request
This method is
normally used to transmit data to
the server using an HTML form
▪ POST request
Request
Methods
GET request
POST request
HEAD request
is similar to a GET except that the response
includes only the header information, and not the body
that would be retrieved in a full GET.
HEAD request
integer values returned by the server as part of the
response header. These codes describe the state of the
request, including whether it was successful, had errors,
requires permission, and more.
Response Codes
response code means that the request was successful
200:OK
Tells the client that the requested resource has moved. Codes like this allow search engines to update their databases to reflect the new location
of the resource. Normally the new location for that resource is returned in
the response.
301: Moved Permanently
If the client requested a resource with appropriate Cache-Control headers,
the response might say that the resource on the server is no newer than the one in the client cache. A response like this is just a header, since we expect the client to use a cached copy of the resource.
304: Not Modified
This code is similar to 301, except the redirection should be considered
temporary.
2307:
Temporary redirect
If something about the headers or HTTP request in general is not correctly
adhering to HTTP protocol, the 400 response code will inform the client.
400: Bad
Request
Some web resources are protected and require the user to provide
credentials to access the resource. If the client gets a 401 code, the request
will have to be resent, and the user will need to provide those credentials.
401: Unauthorized
are one of the only ones known to web users. Many browsers
will display an HTML page with the 404 code to them when the requested
resource was not found.
404: Not
found
URLs have a length limitation, which varies depending on the server software in place. A 414 response code likely means too much data is likely
trying to be submitted via the URL.
414: Request URI too long
This error provides almost no information to the client except to say the server has encountered an error.
500:
Internal server error
