Ch 2 Communication and Networking Technologies

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Communication and Networking Technologies

Ch 2


Communication and internet technologies Client server model of networked computers

A server provides resource or service while a client requests for service. Client and servers communicate over a computer network on separate hardware. Clients initiate communication sessions with servers and await incoming requests.

Examples of computer applications that use the client server model are email, network printing and World Wide Web.

Servers are classified by the services they provide e.web servers, serve WebPages and file server serves computer files. Client and servers exchange messages in request-response-messaging pattern. The language and rules of communication are defined in communication protocols.

A thin-client only provides input and receives output from the application,it has the following functions

• chooses an application to run on the server• sends input data to the server when requested by the application• receives output from the application.

World Wide Web and internet

www is a system of interlinked hypertext documents that are accessed via the internet. With a web browser, one can view web pages that may contain text, images, video and other multimedia and navigate between them via hyperlinks.

Internet is a global system of interconnected computer networks that use the standard protocol suit (TCP/IP) to link several billion devices worldwide. It is an international network of networks that consist of millions of private, public, academic, business and government packet switched networks, linked by wireless and optical media.

Networks Computer network or data network is a telecommunication network that allows computer to exchange data. Data is transferred in the form of packets. The connections between nodes are established using either cable media or wireless media. The known computer network is Internet.

Network types

LAN: it serves a small area, usually within a building or number of buildings within a small geographical area. A LAN is used to share software, hardware and files of data. usually owned by an individual or organization. twisted pair or WiFi are transmission mediums.

Thick-client: a client that carries out at least some of the processing itself,it has the following functions

• chooses an application provided by the server• possibly carries out some processing before running the application on the server and also aft er receiving

output from the application• It can possibly downloads the application from the server and runs the application itself.


• Installing application soft ware on each individual PC is expensive as compared toinstalling the soft ware on an application server attached to the LAN instead.

• Large files stored on a file server can a shared among users• Resources can be shared e.g one or more printers could be attached to a print server

instead of providing separate printer to each user

• Managers in organisations could use electronic mail to communicate with staff ratherthan sending round memos on paper.

• The ‘paper-less off ice’ where files were to be stored in digital form on a file serverrather than as paper copies in a filing cabinet.

Advantages of LAN

• a ‘job’ could be run on a remote computer that had the required application soft ware• a data archive that was stored on a remote computer could be accessed• a message could be transmitted electronically to a user on a remote computer.

Wide Area Network (WAN)In a WAN, the networked computers could be thousands of kilometers apart. Used to connect company's sites or branches,not owned by organization. usually leased from PSTN,a dedicated link is provided by PSTN,mostly fiber-optic is used as transmission medium.

Advantages of WAN

Network TopologiesA Network Topology is the arrangement of computer systems or network devices connected to each other.

data can be sent through medium in different modes

• simplex mode where data flow is one-way only• half duplex where data can flow either way but not simultaneously• full duplex where simultaneous both-ways data flow is possible.

A ‘message’ is any type of data, which can be sent as either:

• a broadcast, which is a one-to-all communication (as used traditionally for radio and television)• a multicast, which is from one source to many destinations• a unicast, which is a one-to-one communication.


Bus Topology

In Bus topology, all devices share single communication line or cable. Bus topology may have problem while multiple hosts sending data at the same time. Therefore, Bus topology uses CSMA/CD technology to solve the issue. It is one of the simple forms of networking where a failure of a device does not affect the other devices. But failure of the shared communication line can make all other devices stop functioning. Terminators are used to remove the data which reaches at extreme ends.There is no direct connection between any pair of end-systems. A message must therefore be broadcast even though it might only be intended for one end-system

Mesh TopologyIn this type of topology, a host is connected to one or multiple hosts. This topology has hosts in point-to-point connection with every other host. Transmission is duplex; messages might be unicast, multicast or broadcast.A mesh topology can be used when individual LAN switches are connected in a network. The topology is essential for the connection of routers within the infrastructure of the Internet.

Star TopologyIn a star topology, each end-system has a point-to-point connection to the central device,hub or switch. Transmission is duplex and messages from the central device might be unicast, multicast or broadcast. If hub fails, connectivity of all hosts to all other hosts fails.


Hybrid Topology

A hybrid topology uses two or more differing network topologies. These topologies can include a mix of bus topology, mesh topology, ring topology, star topology, and tree topology.

RepeatersRepeater is used when over long distances, signals become weak, making communication unreliable. A repeater receives an input signal and generates a new full-strength signal.

Bridgea bus network is constructed in what are called segments. Two segments are connected using a bridge. The bridge stores the network addresses for the end-systems in the two segments it connects.

Network Interface Card The LAN port on an end-system is connected to a component called Network Interface Card (NIC). The NIC is manufactured with a unique network address that is used to identify the end-system in which it has been installed

Hub a device in start topology which braodcasts any incoming communications to all connected end-systems

Switch a switch is a more intelligent decide and can keep track of addresses of all connected devices. aswitch can send an incoming transmission to a specific end-system as a unicast

The central device in a WiFi LAN is a Wireless Access Point (WAP). This can be an end-system in a wired network. The WAP can communicate with an end-system in the WiFi LAN provided that the end-system has a Wireless Network Interface Card (WNIC) installed.

Ethernet it is a dominant protocol. Ethernet transmitts data in frames,each frame has source and destination address. The address is a physical or MAC address. The use of shared medium can corrupt the message if two end-systems send the message at the same time and their voltage interfere each other,called a collision. The method adopted for dealing with this was CSMA/CD (carrier sense multiple access withcollision detection).To avoid collision, transmitter uses the following procedure.1 - Check the voltage on the transmission medium.2 - If this indicates activity, wait a random time before checking again.3 - If no activity is detected, start transmission.4 - Continuously check for a collision.5 - If no collision is detected, continue transmission.6 - If a collision is detected, stop transmission of the message and transmit a jamming signalto warn all end-stations; after a random time, try again.

Internet Service Provider(ISP)the initial function of an Internet Service Provider (ISP) was to give Internet access to an individual or company. This function is now performed by what we can call an ‘access ISP’. These access ISPs then connect to what we can call ‘middle tier’ or regional ISPs, which in turn are connected to tier 1 (or ‘backbone’)ISPs.


Routers

A router enables data to be routed between different networks, e.g between an Ethernet LAN and a

WAN of any description. It provides any necessary conversion of protocols from Ethernet to TCP/IP.

It can incorporate a firewall to provide network security. It stores information about which computer is

connected to which network. Router will inspect every packet of data being sent by any computer on

network connected to it. It connects at least two networks e.g. between LAN and WAN or a LAN and its

ISP.

Gateways

A gateway deals with different communication protocols between the receiving LAN and the other

networks. Gateway regulates traffic between two dissimilar networks while routers regulate traffic

between similar networks.e.g a device that allows a Windows NT network to communicate with a

NetWare network. Gateway acts as a network point that is entrance point to another network.

Servers

A network server is a computer designed to process requests and deliver data to other (client)

computers over a local network or the internet. Network servers are typically configured with additional

processing, memory and storage capacity to handle the load of servicing clients. Common types of

network servers include

Web servers

Proxy servers

FTP Servers

Numerous computers use the client/server networking model. An alternate model, peer-to-peer

networking enables all computers to act as either a server or client as needed.

PSTN (Public service telephone network)

The public switched telephone network is the aggregate of the world’s circuit switched telephone

networks that are operated by national, regional or local telephony operators, providing infrastructure

and services for public telecommunication.PSTN consists of telephone lines, fiber optic cables,

microwave transmission links, cellular networks communication satellites and undersea telephone

cables.

In relation to the internet, the PSTN actually furnishes much of the internet’s long distance

infrastructure. Internet service providers (ISP) pay the PSTN for access to their infrastructure and share

the circuit among many users though packet switching. Users pay usage tolls to their ISPs.

Connections between ISPs are handled by Internet Exchange Points (IXPs). The tier 1 ISPs are at the top of the hierarchy, along with major Internet content providers.


Benefits and drawbacks of using copper cables, fiber optic, radio waves, microwaves nd satellites

Copper cables

Common types are coaxial cable and twisted pair or unshielded twisted pair(UTP)

Advantages

Least expensive media for transmission for short distances

Can be used for both analogue and digital data transmission

Disadvantages

More chances of electromagnetic interferences

Can’t be used for long distance communication

Fiber optics

Consist of a large number of very fine glass strands down which pulses of light can be sent

Advantage

Because means of communication is light rather than electrical signal, the data will remain

inference free

They are also very difficult to hack into

The cables do not corrode

They have much greater bandwidth than metal cables

Disadvantages

Expensive to install but last longer than copper cables

Can be broken or have transmission loses when wrapped around only a few centimeters

Requires more protections around the cable compared to copper

Radio waves

Radio waves have lower frequencies and longer wavelengths than microwaves. They are used to

transmit television and radio programs. They cannot transmit a lot of data simultaneously because they

are low frequency. continued exposure to large amount of radio waves can cause health problems.

Despite these setbacks these can be used to transmit information from space t earth. Its frequency

ranges from 3 kHz to 300 kHz.

They travel at the speed of light in vacuum most commonly used in mobile radio communication,

computer networks, communication satellites, radar and broadcasting.

Microwaves

Microwaves are the electromagnetic or radio waves having higher frequencies so it can carry large

quantities of data. It is highly directional and transmits data between fixed positions. Wide bandwidth.

Less power requirement .some disadvantages include expensive towers and repeaters required also

subject to interference such as air plan, rain or building can disrupt microwave.


Satellites

It is a microwave repeater in space .it is a high bandwidth, coverage over a large geographical area and

can be cheaper over long distance. disadvantages include, huge initial cost, noise and interference,

propagation delay

The highest altitude satellites are in geostationary Earth orbit (GEO) ,provide long-distance telephone and computer network communication. ‘Geostationary’ means that the satellite orbits at the same speed as the Earth spins, so from a point on the Earth the satellite always appears to be at the same point in the sky. Only three GEO satellites are needed for full global coverage. Closer to Earth are a group of medium-Earth-orbit (MEO) satellites some of which provide the global positioning system (GPS). Ten MEO satellites are needed for global coverage.

Finally, low-Earth-orbit (LEO) satellites work in ‘constellations’ to supplement the mobile phone networks. Fifty LEO satellites are needed for full global coverage but currently there are several hundred LEO satellites in orbit.

Bit streaming

A bit stream is a sequence of bits representing a stream of data transmitted continuously over a

communication path, serially. Live streams are provided by means of called “true streaming”. It sends

the information straight to the computer without saving the file to hard disk e.g. during a football

game.

On-demand streaming is provided by means of “progressive streaming”. It saves the file to a hard disk

and then is played from that location.

Issues with bit-streaming

The connectivity of various devices

The software to provide the service

Quality of service

Bandwidth and storage

A broadband speed of 2.5mbits/s or more is recommended for streaming movies. Storage size in

calculated from streaming bandwidth and length of media e.g.

storage size(MB) =length(seconds)𝐱 bit rate(

bits )

8𝐱1024𝐱1024

Practical example: calculate the storage of one hour of video encoded at 300 Kbits/s

storage size(MB) =3600𝐱 300,000(

bits )

8𝐱1024𝐱1024

=128 MB


(1.1.2) IP Addressing, Format of an IP address

An internet protocol address is a numerical label assigned to each device e.g. computer, priner in a

computer network that uses internet protocol for communication.

IP addresses are binary numbers but they are usually stored as text files and displayed in human readable

notations such as 172.16.254.1

The maximum address is 255.255.255.255.in practice these are not enough for all the possible computes

so other techniques are used e.g. local addressing and subnetting

IP address has two parts. The first part of an IP address is used as network address, the last part as a host

address e.g.

192.168.123.____ network

___.___.____.132 host

Public IP address

A public IP address is assigned to every computer that connects to the internet where each IP is unique.

User has no control over the public IP address that is assigned to the computer. It is assigned by an ISP

(internet service provider).A public IP can be either static or dynamic. A static IP address does not change

and is used primarily for hosting WebPages or services on the internet

A dynamic IP address is chosen from a pool of available addresses and changes each time one connects to

the internet

Private IP address

The internet assigned numbers authority (IANA) has reserved ranges of IP addresses for private networks.

Private IP addresses are used for numbering the computers in a private network including home, school

and business LANs in airports and hotels. Private IP addresses are used to exchange files and share

resources within the private network. Different private networks could use the same IP addresses because

computers in different networks don’t directly communicate. A network router passes the data back and

forth. The router is assigned a public IP address by ISP.tis single IP address identifies the entire network on

the internet.

How URL is used to locate resources on www and role of DNS

A URL is a formatted text string used by web browsers, email clients to identify a network resource on the

internt.URL string consists of three parts (sub strings)

I. Network protocol

II. Host name and address

III. File or resource location

E.g.protocol://host/location

The most commonly used protocols are http for viewing WebPages and FTP for transferring files over

the internet.


A DNS server provides name resolution for TCP/IP based networks. It makes it possible to use name

rather than numeric IP addresses to identify remote hosts. A client computer sends the name of remote

host to a DNS server which responds with a corresponding IP address. If the DNS server does not have

an entry in its database for the remote host, it can respond to the client with the address of DNS sever

that is more likely to have information about that remote host or it can forward the request to a

different DNS server at next higher level in the hierarchy.

IPV4 addressing

Currently the internet functions with IP version 4 addressing. This scheme is based on 32 bits or four bytes. The 32 bit allows 232 different addresses which is approximately four billion addresses. IPv4 is a connectionless protocol for use on packet-switched networks. A group of bits defining a network (a netlD) and another group of bits defining a host on that network (a hostID). The aim was to assign a unique universally recognized address for each device on the Internet. The separation into two parts allows the initial transmission to be routed according to the netlD. The hostID only needs to be examined on arrival at the identified network.

The logic was straight forward. The largest organisations would be allocated to Class A. There could only be 27 i.e. 128 of these but there could be 224 distinct hosts for each of them. This compared with 221 approximately two million, organisations that could be allocated to ClassC but each of these could only support 28 i.e. 256 hosts.

Classless inter-domain routing (CIDR) The first app roach developed for improving the addressing scheme is called 'classless inter domain routing' (CIDR). This retains the concept of a netlD and a hostID but removes the rigid structure and allows the split between the netlD and the hostID to be varied to suit individual need. 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 hostID allowing 211 , i.e. 2048, hosts


Sub-netting

A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.

Network address translation large organisations use private networks(intranet)which provides extra security due to isolation from the internet but they also want internet connectivity. NAT box has one IP address which is visible over the internet as a sending and receiving address.

Internally IP address has to be chosen from one of the following three ranges of IP addresses.

Each IP address can be simultaneously used by any number of private networks. The interface in the NAT box has a software installed to examine incoming and outgoing transmission.

Lower bound Upper bound

10.0.0.0 10.255.255.255

172.16.0.0 172.31.255.255

192.168.0.0 192.168.255.255

https://en.wikipedia.org/wiki/IP_network


IPv6 It is a 128-bit address which provides greater address space. The addresses are written in colon hexadecimal notation. The code is broken into 16bit parts with each part consists of four hexadecimal character

IPv6 address Comment

68E6:7C48:FFFE:FFFF:3D20:1180:695A:FF01 A full address

72E6::CFFE:3D20:1180:295A:FF01 :0000:0000: has been replaced by ::

6C48:23:FFFE:FFFF:3D20:1180:95A:FF01 Leading zeros omitted

::192.31.20.46 An IPv4 address used in IPv6

DNSDomain name service (DNS): a hierarchical distributed database installed on domain nameservers that is responsible for mapping a domain name to an IP address. Also known as domain name system.The DNS service allocates readable domain names for Internet hosts and provides a system for finding the IP address for an individual domain name.


world wide web (www):

is a collection of (multimedia) web pages or documentshttp/protocols used to transmit data, web pages are written in HTMLURLs specify the location of the web pages,web documents are accessed using browsers

Cloud Computing is the provision of computing service usually via Internet.

Private Cloud: The organization takes full responsibility or outsources to a third-party forcreating and managing the cloud installed on-site and connected to a private network

public cloud. This is created, managed and owned by a third-party cloud service provider.accessible via a browser by individual or by organization from any suitable device in any location

The services provided ,may include,provision of infrastructure,platform and software

Advantages:

For the infrastructure provision, the advantages include the better performance when running soft ware and the increased storage capacity.

For the platform provision, the cloud can offer facilities for soft ware development and testing.

For the soft ware provision, the cloud will be able to run applications that require high performance Saves cost of buying and installing a software

Disadvantages

for public cloud,the cloud service provider has complete access to all of the data stored on the cloud.

The security of data is also an issue.

Ch 2 Communication and Networking Technologies

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