Computer Science Chapter 4: Networking and the Internet

networks
linked computer systems
local area network (LAN)
univeristy campus, house
Metroploitan Area network (MAN)
Wide area network (WAN)
proprietary
closed or private network
access points
focal points around which all communication is coordinated
hub
connects computers to a central location through running links and bus networks
protocols
established rules in which activites are conducted
Carrier Sense, Multiple Access with Collision Detection
protocol that controls the right to transmit messages
dictates that each message be broadcast to all the machines on the bus.
each machine monitors all the messages but keeps only those addressed to itself.
hidden terminal problem
signals from the different machines are blocked from each other by objects or distance even though they can all communicate with the central AP.
Carier Sense, Multiple Access with Collision Avoidance
designed to avoid collisions and may not eliminate them completely
when collisions do occur the messages must be retransmitted.
repeater
a device that simply passes signals back and forth between the two original buses without considering the meaning of the signals
bridge
more complex than a repeater
connects two busses, and looks at the destination address that accompanies each message and forwards a message across the connection only when that message is destined for a computer on the other side.
switch
is essentially a bridge with multiple connections, allowing it to connect several buses rather than just two.
produces a network consisting of several buses extending from the with as spokes on a wheel
internet
a network of networks
the original networks maintain their individuality and continue to function as autonomous networks
routers
connection between networks to form an internet
special purpose computers used for forwarding messages
forwarding table
contains router’s knowledge about the direction in which messages should be sent depending on their destination addresses.
gateway
the point at which one network is linked to an internet
serves as a passageway between the network and the outside world.
interprocess communication
communication between processes
client/server
defines the basic roles played by the processes
client
makes requests of other processes
server
satisfies the requests made by clients
peer to peer model
involves processes that provide service to and recieve service from each other
involves processes on a temporary basis
distributed systems
meaning that they consist of software units that execute as process on different computers
cluster computing
describes a distributed system in which many independent computers work closely together to provide computation or services comparable to a much larger machine
high-availablity
because it is more likely that at least one member of the cluster will be able to answer a request, even if other cluster members break down or are unabailable
load-blancing
the workload can be shifted automatically from members of the cluster that have too much to do to those that may have too little
grid computing
refers to distributed systems that are more loosely coupled that clusters but that still work together to accomplish large tasks
can involve specialized software to make it easier to distribute data and algorithms to the machines participating in a grid.
cloud computing
google cloud space can switch
huge pools of shared computers on the networks can be allocated for use by clients as needed.
Internet
originated from research projects going back to the early 1960s
Internet Service Providers (ISP)
organizations that maintain and constructs these networks.
intranet
independent internet
operated by a single authority that is in the business of supplying internet access to individual users
end systems
devices that indicidual users connect to the access ISP
not necessarily computers in a traditional sense
hot spot
area within the AP’s range.
modems
convert digital data to be transferred into a form compatible with the transmission medium being used
dial-up
used for temporary connections in which the user places a traditional telephone call to an access ISP’s router
IP addresses
“internet protocol”
unique identifying address to each computer in the system
Internet Corporation for ssigned Name and Number (ICANN)
a nonprofit corporation established to coordinate the internets operation
dotted decimal notation
the bytes of the adderess are separated by periods and each byte is expressed as an integer represented in traditional base ten notation
domain
a “region” of the internet operated by a single, authority such as a university, club, company, or government agency
registrars
handles the process of registering each domain
domain name
mnemonic name that is unique among all the domain names throughout the internet.
subdomains
used as a means of organizing the names within a domain
domain name system (DNS)
names servers are used as an internet-wide directory
DNS lookup
process of using the DNS to perform a translation
email
a system by which messages are transferred among internet unsets
mail server
established within domains operated by access ISPs for the purpose of providing mail service to users within its realm
Simple Mail Transfer Protocol (SMTP)
initially designed for transferring text messages encoded with ASCII
Multipurpose Internet Mail Extensions (MIME)
developed to convert non ASCII data to SMTP compatible form
Post Office Protocol version 3(POP3)
user transfers messages to his or her local computer where they can be read, stored in various folders, edited and otherwise manipulated as the user desires
Internet Mail Access Protocol
allows a user to store and manipulate messages and related materials on the same machine as the mail server
File Transfer Protocol (FTP)
a client/sever protocol for transferring files across the internet
to transfer a file using this method a user at one compute in the internet uses a software package that implements ftp to establish contact with another computer.
telnet
protocol system that was established to allow computer users to access computers from great distances
a user can contact the telnet server at a distant computer then follow that operatings systems login procedure to gain access to the distant machine
secure shell (SSH)
alternative to telnet that offers a solution to an eavesdropper intercepting a pssword and later misuing the information.
provides encryption of data being transferred as well as authentication
VoIP (voice over Internet Protocol)
the internet infastructure is used to provide voice communication similar to that of traditional telephone systems
soft phones
P2P software that allows 2 or more PCs to share a call with no more special hardware than a speaker and a microphone
i.e. skype
analog telephone adapters
VoIP devices that allow a user to connect his/her traditional telephone to phone service provided by an access ISP
N-unicast
a single sender involved with multiple unicasts
multicast
transfers the distribution problem to the internet routers
hypertext
text documents, images, video, and audio that contains links
World Wide Web(www)
the web that has evolved on the internet
website
a collection of closely related webpages
HTTP
hypertext transfer protocol
transfer between browsers and web servers
url
uniform resource locator
contains information needed by a browser to contact the proper server and requested desired documents
tags
special symbols that describe how the document should appear on the display screen, what multimedia resources and which items are linked to others
HTML
hypertext markup language
system of tags
search engine
websites that assist users in locating web material pertaining to a subject of internet
client-side activities
browser
server-side activities
web server
web mail
access email by web browser
XML
extensible mark up language
standardized style for designing notational systems for representing data as text files
markup languages
developed for representing math, and multimedia presentations and music
source
HTML encoded version
application layer
message originates here
software units such as clients and servers that use internet communicatioin to carry out their tasks
not restricted to software in application classification
transport layer
accept messages from the application layer
ensure the messages are properly formatter for transmission over the internet
divides long messages into small segments which are transmitted over the internet as individual units

adds sequence numbers to the small segments it produces so that the segments can be reassembled at the messages destination

network layers
decides which direction a packet should be sent at each step along the packet’s path through the internet
in charge of maintaining the router’s forwarding table and using that table to determine the direction in which to forward packets
link layer
responsibly for transferring the packet
deals with the communication details particular to the individual network in which the computer resides
packet
small segments of long messages that is transported through the application, transport, network, and link layers.
Open System Interconnection (OSI)
standard based on a seven-level heirarchy as opposed to the four-level hierarchy
carries the authority of an international organization, but it has been slow to replace the four-level point of view
Transmission Control Protocol (TCP)
a version of the transport layer.
provides more than one way of implementing the transport layer
User Datagram Protocol (UDP)
does not offer retransmission services and said to be unreliable protocol
sends the message to the address it was given and forgets about it.
connectionless protocol
flow control
TCP transport layer at a message’s origin can reduce the rate at which it transmits segments to keep from overwhelming its counterpart at the destination
congestion control
a TCP transport layer at a message’s origin can adjust its transmission rate to alleviate congestion between it and the message’s destination
forwarding
relaying packets through the internet
routing
updating the layers forwarding table to reflect changing conditions
hop count
value is a limit to the number of times the packet should be forwarded as it tries to find its way through the internet
malware
malicious software
software can be transferred to, executed on, the computer itself, or it might attack the computer from a distance
virus
software that infects a computer by inserting itself into programs that already reside in the machine
when the host program is executed the virus is also executed
some may perform devastating actions such as degrading portions of the operating systme, erasing lare blocks of mass storge, or corrupting data ad o programs
worm
autonomous program that transfers itself through a network, taking up residence in computers and forwarding copies of itself to other computers
what is a characteristic consequence of a worm?
an explosion of the worms replicted copies that degrades the performance of legitimate applications and can ultimately overlaod an entire network or internet
Trojan horse
a program that enters a computer system disguised as a desirable program such as a game or useful utility package that is willingly imported by the victim
typically arrive in the form of attachments to enticing emal messages
spyware
software that collects information about activities at the computer on which it resides and reports that information back to the instigator of the attack
used for recording the symbol sequences typed at the computers keyboard in earch of passwords or credit crd numbers
phishing
a technique of obtaining information explicitly by simply asking for it
play on word for fishing becuase the prcess involved is to cast numerous lines in hopes that someone will take the bait
often carried out via email and in this form it is little more tan an old telephone con
denial of service (DoS)
the process of overloading a computer with message
spam
abundance of unwanted messages is the proliferation of unwanted junk email
effect of spam is to overwhelm the person receiving the spam
firewall
filter traffic passing through a point in the network may be installed at the gateway of an organizations intranet to filter messages passing in and out of the region
spoofing
saying you are someone you are not
spam filters
firewalls designed to block unwanted email
proxy server
software unit that acts as an intermediary between a client and a server with the goal of shielding the client from adverse actions of the server
antivirus software
used to detect and remove the presence of known viruses and other infections
FTPS
a secure version of FTP, and SSH
HTTPS
secure version of HTTP
used by most financial institutions to provide customers with secure internet access to their accounts
Secure Sockets Layer (SSL)
backbone of HTTPS
originally devleoped by netscape to provide secure communication links between web clients and servers
public-key encryption
incolves techniques by which encryption sysstems are designed so that having knowledge about how messages are encrypted does not allow one to decrypt messages
keys
two values that are used in the public-key encryption system
public key
used to encrypt messages
private key
required to decrypt messages
certificate authorities
maintains an accurate list of parties an their public keys, they then act as servers provide reliable public-key informationto their clients in packages known as certificates
certificate
package containing a partys name and that partys public key
authentication
making sure that the author of a message is in fact the party that it claims to be
digital signature
a bit pattern producesd by the holder of the private key