Communication and Internet Technologies
The options for a cable are twisted pair, coaxial or fibre-optic
Comparisons of different cable types
|Twisted pair||Coaxial||Fibre Optic|
|Data rate||Lowest||Higher||Much Higher|
|Attenuation||Affected||Most affected||Least affected|
|Interference||Worst affected||Less affected||Least Affected|
|Repeaters||More often||More often||Less often|
The alternative to cable is wireless transmission. The three options here are radio, microwave or infrared
(forward arrow means increases with choice and backward arrow means decreases with choice)
|Frequency Range||Radio Microwave Infrared 3KHz-3GHz 3-300GHz 300GHz-400THz|
|Need for repeaters||—————————————————————————————————>|
|Directional focusing capability||—————————————————————————————————>|
|Penetration through a wall||—————————————————————————————————>|
Comparing Cable and Transmission
- The use of specific wireless transmission frequencies is regulated by government agencies and so permission has to be obtained before wireless transmission is used.
- Outside these frequencies, no permission is needed to use the air for transmission but cables can only be laid in the ground with the permission of landowners.
- For global communications, the two competing technologies are transmission through fibre optic cables laid underground or on the sea bed and satellite transmission currently neither of these technologies is dominant.
- Interference is much more significant for wireless transmission and its extent is dependent on which frequencies are being used for different applications
- Repeaters are needed less often for wireless transmission.
- Mobile (cell) phones now dominate Internet use and for these only wireless transmission is possible.
- For home or small office use, wired or wireless transmission is equally efficient; the lack of cabling requirement is the one factor that favors wireless connections for a small network.
The World Wide Web (WWW)
The web consists of an enormous collection of websites each having one or more web pages. The special feature of a web page is that it can contain hyperlinks which, when clicked, give direct and essentially immediate access to other web pages.
Router: a device that acts as a node on the Internet
Gateway: a device that connects networks of different underlying technologies
Server: a device that provides services via a network
1Pv4 address: a 32-bit long, hierarchical address of a device on the Internet
The 1Pv4 addressing scheme is based on 32 bits (four bytes) being used to define an 1Pv4 address. It is worth putting this into context. The 32 bits allow 232 different addresses
Classless inter-domain routing (CIDR)
The first approach developed for improving the addressing scheme is called ‘classless interdomain routing’ (CIDR). This retains the concept of a netlD and a hostlD but removes the rigid structure and allows the split between the netlD and the hostlD to be varied
The simple method used to achieve this is to add an 8-bit suffix to the address that specifies the number of bits for the netlD. If, for instance, we define the suffix as 21, that means that 21 bits are used for the netlD and there are 11 bits remaining (of a 32-bit address) to specify hostlDs allowing 211
Subnetting is the process of stealing bits from the HOST part of an IP address in order to divide the larger network into smaller sub-networks called subnets. We always reserve an IP address to identify the subnet and another one to identify the broadcast subnet address.
This uses a 128-bit addressing scheme allowing 2128 different addresses, a huge number! In practice, this will allow more complex structuring of addresses
Domain name system (DNS): a hierarchical distributed database installed on domain name servers that is responsible for mapping a domain name to an IP address
The system is implemented as a hierarchical distributed database which is installed on a large number of domain name servers covering the whole of the Internet. The domain name servers are connected in a hierarchy, with powerful replicated root servers at the top of the hierarchy supporting the who le Internet. DNS name space is then divided into nonoverlapping zones. Each zone has a primary name server with the database stored on it. Secondary servers get information from this primary server.
The domain name is included in a universal resource allocator (URL), which identifies a web page, or an email address