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Transcript of 1 The Internet and Networked Multimedia. 2 The Internet An interconnected set of networks A...
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The Internet and Networked Multimedia
The Internet and Networked Multimedia
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The InternetThe Internet
An interconnected set of networks A gigantic collection of millions of
computers, all linked together on a computer network
A home computer is usually linked to the Internet using a normal phone line and a modem that talks to an Internet Service Provider (ISP)freeservemsnfreeweb
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The InternetThe Internet
A computer in a business or university has a Network Interface Card (NIC) that directly connects it to a Local Area Network (LAN) inside the business
The business then connects its LAN to an ISP using a high speed phone line or optical cable
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The InternetThe Internet
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JANETJANET
The University is connected to the Joint Academic Network (JANET) via the LEarning Network South East (LENSE)
LENSE is a 622Mbit network connecting higher education sites in the south east
Sussex’s connection to LENSE is 155Mbit
JANET (superJANET 4) is a 2.4 – 20Gbit network backbone connecting academic LANs
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LENSELENSE
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JANETJANET
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Development of the Internet
Originally developed by the U.S. Department of Defence
Development started in 1969 with the Advanced Research Projects Agency ARPAnet
Enabled communication between geographically dispersed research centres funded by ARPA
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Development of the InternetDevelopment of the Internet
ARPAnet was the first Wide Area Network (WAN)
Electronic mail was soon introduced using the Simple Mail Transfer Protocol (SMTP)
With the developments of other networks such as MILNET a protocol was required to enable these networks to be linked
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Development of the InternetDevelopment of the Internet
In the early 1980’s the current versions of the core Internet protocols TCP and IP were introduced
In the late 1980’s the Domain Name System (DNS) was introduced
In 1992 The Centre for European Nuclear Research (CERN) released the first version of the World Wide Web software
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Growth of the InternetGrowth of the Internet
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Key Properties of the Internet
Key Properties of the Internet
Interoperable - any computer connected to the internet can communicate with any other computer connected to the internet - due to standardised protocols
Global - based on standardised and universal connectivity, using software that can be distributed throughout the Internet
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Key Properties of the Internet
Key Properties of the Internet
Easy to use - World Wide Web has made highly functional multimedia content easily available to users worldwide
Low cost - the cost of the network is shared across all users. A provider of information does not need to pay for the distribution system other than its own connection to the network
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Design Principles of the Internet
Design Principles of the Internet
The main problem for the internet is how to build a system that can handle communication between two computers which may:have any type of operating systembe connected using any type of physical
medium
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Design Principles of the Internet
Design Principles of the Internet
To complicate matters:no connected system has any knowledge
about the other systemsand there is no way of knowing
• the location of that system
• what kind of software it uses
• what kind of hardware platform it runs on
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Design Principles of the Internet
Design Principles of the Internet
The main principles can be split into 5 concepts :Interoperability Uniform naming and addressing Layering SimplicityEnd-to-end protocols
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InteroperabilityInteroperability
Independent implementations of internet protocols work together
Systems can be assembled using client and server computers and software from different vendors
Buyers and sellers are not required to update simultaneously and from the same vendor to conduct commerce
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Uniform Naming and Addressing
Uniform Naming and Addressing
The IP layer offers a uniform 32 bit addressing structure to each computer connected to the network
139.184.14.13Every device connected to the Internet
MUST have an IP address, whether it be a host, web server, name server or fridge
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Uniform Naming and Addressing
Uniform Naming and Addressing
The Domain Name Servers (DNS) offer a uniform way of translating IP addresses to human-readable names
139.184.14.13
www.sussex.ac.ukThe DNS system is a database – the
biggest distributed database on the planet and no other database on the planet gets this many requests
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Domain Name Servers (DNS)Domain Name Servers (DNS)
DNS has to cope with 5 major problems: There are billions of IP addresses currently in
use There are many billions of requests made to
domain name servers every dayDomain names and IP addresses change dailyNew domain names get created dailyMillions of people do the work to change and
add domain names and IP addresses every day
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Domain NamesDomain Names
The .COM, .UK and .NET portions of domain names are called the top-level domain or first-level domainThere are several hundred top-level domain names
Within every top-level domain there is a huge list of second-level domains. For example, in the COM first-level domain there are: microsoft fordplus millions of others...
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Domain NamesDomain Names
The left-most word, like www, encarta or cyril, is the host name
ames.central.sussex.ac.uk It specifies the name of a specific
machine or several machines which deal with requests to that host name
A given domain can, potentially, contain millions of host names as long as they are all unique within that domain
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Domain NamesDomain Names
All of the names in a given domain need to be uniqueNominet is the central authority that keeps
track of .UK top-level domainsNetwork Solutions is the domain registering
authority for .COMSussex Uni and EIT have several of their
own domain name servers and maintain the machines that implement their part of the DNS system
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Domain Name Servers (DNS)Domain Name Servers (DNS)
Every domain has a domain name server somewhere that handles its requests, and there is a person maintaining the records in that DNS
The DNS system is completely distributed throughout the world on millions of machines administered by millions of people, yet it behaves like a single, integrated database!
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The DNS ProcessThe DNS Process
When a request comes in, the name server can do one of four things with it: It can answer the request with an IP address because
it already knows the IP address for the domain It can contact another name server and try to find the
IP address for the name requested. It may have to do this multiple times
It can say, "I don't know the IP address for the domain you requested, but here's the IP address for a name server that knows more than I do"
It can return an error message because the requested domain name is invalid or does not exist
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The DNS ProcessThe DNS Process
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The DNS Look-up ProcessThe DNS Look-up Process
The name server would start its search for an IP address by contacting one of the root name servers
The root servers know the IP address for all of the name servers that handle the top-level domains and returns the appropriate IP address for that name serverE.g. the .UK name server if we are trying to find the IP
number for www.bandq.co.uk Your name server then sends a query to the
UK name server asking it if it knows the IP address for www.bandq.co.uk
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The DNS Look-up ProcessThe DNS Look-up Process
The name server for the UK domain returns the IP addresses for the name servers handling the banq.co.uk domain
Your name server then contacts the name server for banq.co.uk and asks if it knows the IP address for www.banq.co.uk
It actually does, so it returns the IP address to your name server, which returns it to the browser, which can then contact the server for www.banq.co.uk to get a web page
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IP AddressesIP Addresses The four numbers in an IP address are called
octets, because they are a byte long when viewed in binary form, giving a possible 256 values for each number
139.184.14.1310001011.10111000.00001110.00001101
The octets are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need
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IP AddressesIP Addresses
The octets are split into two sections: Net - contains the first octet. It is used to identify the
network that a computer belongs toHost - identifies the actual computer on the network.
The Host section always contains the last octet
139.184.14.13
Net or host information depending on class
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IP AddressesIP Addresses
There are five IP classes plus certain special addresses: Class A – Class ENetwork IdentificationLoopbackBroadcast
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Class A IP AddressesClass A IP Addresses
This class is for very large networks, such as a major international company might have
IP addresses with a first octet from 1 to 126 are part of this class 18.181.0.31
The other three octets are used to identify each host. Thus, there are 126 Class A networks each with 16,777,214 possible hosts
Class A networks account for half of the total available IP addresses
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Class B IP AddressesClass B IP Addresses
Used for medium-sized networks such as sussex.ac.uk – 139.184.14.13
IP addresses with a first octet from 128 to 191 are part of this class. Class B addresses also include the second octet as part of the Net identifier
The other two octets are used to identify each host. This means that there are 16,384 (214) Class B networks each with 65,534 possible hosts
Class B networks make up a quarter of the total available IP addresses
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Class C IP AddressesClass C IP Addresses
Used for small to mid-size businesses IP addresses with a first octet from 192 to 223
are part of this class 194.83.112.43 Class C addresses also include the second
and third octets as part of the Net identifier. The last octet is used to identify each host. This means that there are 2,097,152 (221) Class C networks each with 254 hosts
Class C networks make up an eighth of the total available IP addresses
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Class D IP AddressesClass D IP Addresses
Used for multicastsClass D is slightly different from the
first three classes. Its first 3 bit values are 1, and fourth bit value of 0 (224 – 239)
1110xxxxThe other 28 bits are used to identify the
group of computers the multicast message is intended for
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Class E IP AddressesClass E IP Addresses
Used for experimental purposes onlySimilar to Class D, but with it’s first 4 bit
values set to 1 (240 -247)
1111xxxxThe other 28 bits are used to identify the
group of computers the message is intended for
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Special IP AddressesSpecial IP Addresses
There are several special IP addresses which are not assigned to specific hosts
An all zero host refers to the network itselfE.g. 129.152.0.0 refers to the network 129.152
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Special IP AddressesSpecial IP Addresses
The IP address 127.0.0.0 is used as the loopback addressThis means that it is used by the host
computer to send a message back to itself. It is commonly used for troubleshooting and network testing
Broadcast - Messages that are intended for all computers on a network are sent as broadcasts. These messages always use the IP address 255.255.255.255
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