structure of the internet Flashcards
What is internet?
A network of computer networks and computers using unique IP addresses and TCP/IP
What is the difference between internet and the internet?
Any network of connected computers is an internet
The network used by the general public is the internet
What is the internet?
A network of interconnected computer networks (wide area and local area) and computers using a globally unique address space based on TCP and IP to support public access
What does IP stand for?
internet protocol
What does TCP stand for?
transmission control protocol
What is the core backbone of the internet?
very high speed connections between europe, north america, central and south america and the far east and pacific
What is the backbone of each continent?
very high speed links to interconnect routers in each country
What are routers?
Special switches that recieve incoming ‘packets’ of data on one link and use the destination IP address in the packet to make a decision about which outgoing link to send the packet along
What do routers connect?
Connect networks that use the same layer link protocol
Within national boundaries, what can be connected directly to the national backbone? How?
Networks belonging to large businesses and organisations such as universities
Connected using router gateways
What is a gateway?
A special kind of router used to connect networks that use different layer link protocols
=connects different networks, translating packages so that they will be compatible with the new network
How can small businesses and home users be connected to the national backbone?
Through an internet service provider (ISP) or internet access provider (IAP) which will have its own router gateway, selling internet access
What does ISP stand for?
internet service provider
Why are routers used?
It is impossible to connect every host to every other host
What is a host?
A computer which runs applications
What is a computer network?
machines (hosts and routers) interconnected by communication channels
What is a communication channel?
A means of transferring sequences of bits or bytes from one host or router to another
What is circuit switching?
Two points are connected with a complete end to end connection for however long that connection is needed. The connection cannot be used by other users whilst it is being used for this connection.
What kind of switching is used in the internet?
packet switching
What is another word for packet?
datagram
What three parts does a packet consist of?
source address
destination address
payload (the data)
What is a packet?
When a computer wishes to send data it splits it into chunks called packets
How are packets sent over the internet?
Each is sent through a router gateway and then travels INDEPENDENTLY through routers to the destination. At the destination they are put back in order and reassembled
What is the end-to-end principle?
The two end computers (start and finish point) are in control of the communication with the internet as a means to move packets
What are the advantages of the end-to-end model?
- A partial network failure can be survived, the packages can just be resent when it is detected they have not all arrived
- packets can be rerouted around failures by alternative paths
- The internet can grow easily because control does not reside in the internet
- Router design is simplified as they don’t have to notify each other when endpoint connections are formed or dropped
- Role of the internet is simplified as security and integrity of packets is monitored at the endpoints
- Each endpoint only has to be aware of the one router it is directly connected to
What is open architecture networking?
Designers are free to design networks in any way, all can communicate over the internet via a router gateway
What is an IP address?
A unique address that identifies a computer or other electronic device on a network
Which IP system is used today?
How many Ip addresses does it allow?
IPv4
2^32 ~4 billion
What two parts does an IP address include?
netID and hostID
In the IP address 196.100.11.4 which bit is the netID and which is the hostID?
network = 196.100.11
host=4
How are IP addresses often expressed?
32 bits written as bytes separated with dots
eg. 166.100.11.4
What information does each router have to help it send packets?
A table of other routers, computers and networks it is directly connected to as well as some information about the hierarchical structure of the internet
List in order the router hierarchy
-international
-national
-regional
-local
organisation networks (companies, schools, colleges etc)
What is the world wide web?
A system of interlinked hypertext documents accessed via the internet
How is the world wide web used?
A web browser is used to view webpages containing
text images and multimedia
Navigating between pages is done using hyperlinks
What is an intranet?
A private computer network that is used to share information or operations within an organisation only
What does DNS stand for?
domain name system
What is a domain name?
A memorable name corresponding to network IP address
What is a fully qualified domain name?
A domain name with the host ID and domain name
eg www. or mail. has the host ID added to the domain name which is the rest of the address
What is the hierarchical system which domain names use? (which is essentially written bottom to top)
- first-level
- second level
- third level
- fourth level
- public name of host
eg.mail.ags.bucks.sch.uk
Give four examples of level 1 domain names and what they mean
- com = commercial
- edu = educational
- org = non-commercial
- uk = in the uk
Give four examples of level 2 domain names and what they mean
-co = commercial ac = academic, higher education -sch = school
What is a DNS server?
A server accessed by hosts to convert fully qualified domain names into IP addresses to connect to other hosts on the internet
What does URL stand for?
uniform resource locator
What is a URL?
A short string representing the target of a hyperlink, specifying which server to access, access method and location in server
What is the structure of a URL?
HOW - which protocol to be used, eg. http:/
WHERE-the host server, eg. www.microsoft.com
WHAT - The path to what is needed on the given server eg. index/index.html
What does URI stand for?
uniform resource locator
What is a URI?
A way of specifying how to access a resource on the internet. Includes URLs and URNs (which can be outside of the internet such as books)
What does URN stand for?
uniform resource name
What is the difference between URLs and URNs?
URLs identify resources by network location
URNs identify resources by name
What are internet registries?
Stores for registered domain names, tracking the association between IP addresses and domain names so that they can be mapped onto each other
Each major domain (eg .com) has its own registry
What are internet registrars
Private companies responsible for registering domain names to people and organisations
What is JANET?
What is nominet?
joint academic network
internet registrar for all .ac.uk and .gov.uk domain names
Registrar for all other domain names
What is the client-server model?
A client software process initiates a request for a service from a server software process, the server responds to the request
In the client-server model are the client and server hardware or software?
software
What is a server?
A software process which provides a service requested by a client
What is a client?
Software process that requests and uses services provided by a server
What is a protocol?
A set of agreed signals, codes and rules for data exchange between systems
What is a protocol stack?
A collection of protocol layers, each responsible for part of the process governed by the stack
What is the basic protocol used in the internet?
TCP/IP
What is the TCP/IP protocol stack?
A protocol stack specific to TCP/IP protocol
What are the layers of TCP/IP protocol stack?
- application (telnet, email, web browsing etc)
- transport (TCP)
- Network (IP)
- Link (device driver and interface card)
What is the role of the transport layer in a TCP/IP stack?
TCP software in the layer connects hosts and ensures a reliable flow of data by detecting when errors occur, re-transmitting packets and detecting when a connection is broken
It also splits data being sent into packets and reassembles packets in the right order for use when they are recieved
What is a port?
A typical host on a TCP/IP network runs multiple processes at once, data packets have to be sent to the right process (by TCP software)
An additional address element (the port) is added for the software process needed
What is a socket?
A combination of host IP address and port number
The connection between two sockets provides bi-directional communication between end processes or applications
What is the network layer?
Ip software takes packets from the transport layer and adds destination and source IP addresses
Takes packets from the link layer and removes source and destination IP addresses
What is the link layer?
Adds the source and destination hardware addressesto packets from the network layer before sending them onto the local cable
Handles all the physical details of interfacing with the cable, including the network interface card and a device driver
In an ethernet local area network (LAN) what are the hardware addresses the link layer deals with?
Ethernet card addresses or MAC addresses
A hardware address would be assigned as the ethernet card address , then the ethernet card address of the gateway connected
What is application layer?
Handles the details of the particular networking application, using different protocols for different applications
eg. http for a web browser application
What is the payload?
The actual data sent in a packet
What are client port numbers?
A temporary port number assigned to each client process
How are client port numbers allocated?
Incrementally from 1024 to 4095
What are well known port numbers?
Universally known port numbers in the range of 0 to 1023
eg 80 or 8080 are web server
What does HTTP stand for?
hypertext transfer protocol
What is HTTP?
A very simple application-level protocol
A client sends a GET request to a server and the server responds with a message that can contain many forms of data but probably includes text formatted with HTML
What does HTML stand for?
hypertext markup language
What does a request to view a basic webpage look like with HTTP?
GET/
What is the default webpage for a site (found with a GET request)?
index.html
What happens to a connection when a response message is sent to a GET request?
HTTP is finished with the connection and the TCP connection will be broken unless it is specifically requested to remain connected
What does a web page returned by an HTTP GET request consist of?
A text file containing content and how the content should be displayed
What does a web browser do when sending an HTTP GET request ?
- Accepts URI from user
- Extracts FQDN and uses a DNS server to find the corresponding IP address
- Sends a GET request to this IP address (port 80 unless told otherwise)
- Receives a file returned by the server
- Uses style and structure instructions to render file’s contents in the browser window
- If the file contains other URIs (eg references to graphics), another GET request will be issued to request that resource
What does FTP stand for?
file transfer protocol
What is FTP?
An application level protocol which enables files on one host to be copied to another host, one host running an FTP client and the other an FTP server
Which ports does FTP use?
21=commands
20=data
What must be typed into the address bar to use FTP in a web browser?
ftp://
How do some FTP servers restrict access?
They require a registered username and password
If the username is ‘anonymous’ for an FTP server what is the password?
An email address
What is telnet?
A text based protocol that can be used to manage a remote machine and edit files etc as if it was the clients own machine, read HTML text of a webpage and send/retrieve email
What is the well known port of telnet listening servers?
23
What does SMTP stand for?
simple mail transfer protocol
What is SMTP?
A relatively simple text based protocol
One or more recipients of mail are specified and the text is transferred to a mail server listening on port 25
What does POP3 stand for?
post office protocol version 3
What is POP3?
An application layer protocol used to receive stored mail sent from a destination mail server
Email is stored in a mailbox and the user does not have to be connected for mail to be received
The server holds the mail until the user connects and requests the mail
What does HTTPS stand for?
hypertext transfer protocol over secure socket layer
What is HTTPS?
A web protocol developed by netscape to encrypt ad decrypt user page requests and the pages returned by a server
Uses the secure sockets layer beneath the HTTP application layer, using port 443 instead of 80
Used for sensitive communication such as payment transactions and corporate logons
