Download Notes - Andrew

What is a Network
13 April 2015
15:09
A computer network is a number of computers linked together to allow them to
share resources. Networked computers can share hardware, software and data.
Most computer networks have at least one server. A server is a powerful computer
that provides one or more services to a network and its users. For example, file
storage and email.
LANs and WANs
There are two main types of network:
1. Local Area Network (LAN)
2. Wide Area Network (WAN)
LANs and WANs
There are two main types of network:
1. Local Area Network (LAN)
2. Wide Area Network (WAN)
LAN
A LAN covers a small area such as one site or building, eg a school or a college.
WAN
A WAN covers a large geographical area. Most WANs are made from several LANs
connected together.
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The internet is a WAN.
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A network of bank cash dispensers is a WAN.
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A school network is usually a LAN.

LANs are often connected to WANs, for example a school network could be connected to the internet.
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WANs can be connected together using the internet, leased lines or satellite links
Advantages and disadvantages of networks
Advantages
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Sharing devices such as printers saves money.
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Site (software) licences are likely to be cheaper than buying several standalone
licences.
Files can easily be shared between users.
Network users can communicate by email and instant messenger.
Security is good - users cannot see other users' files unlike on stand-alone machines.
Data is easy to backup as all the data is stored on the file server.
Disadvantages
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Purchasing the network cabling and file servers can be expensive.
Managing a large network is complicated, requires training and a network manager
usually needs to be employed.
If the file server breaks down the files on the file server become inaccessible. Email
might still work if it is on a separate server. The computers can still be used but are
isolated.
Viruses can spread to other computers throughout a computer network.
There is a danger of hacking, particularly with wide area networks. Security procedures
are needed to prevent such abuse, eg a firewall.
From <http://www.bbc.co.uk/schools/gcsebitesize/ict/datacomm/2networksrev1.shtml> and following pages
Teacher's URL:
http://127.0.0.1:800/Networking%20And%20Servers%20And%20Security%20And%20HTML/www.bbc.co.uk/schools/gcsebitesize/ict/da
tacomm/2networksrev1.shtml
What is Client-Server
13 April 2015
15:10
Video: (Basics)
Mr. Clarkson Talks About... Client-Server and Peer-Peer Network Models
Notes:
 Server side is more powerful on the dynamic generation of pages
 Peer to Peer makes things a lot easier on servers when downloading.
--------------------------------Structure of the Internet: Client server model
The history of computing started off with centralised computers (in many cases mainframes) or servers
performing all the calculations. Client computers were then attached to these centralised computers
(servers) and if you wanted to calculate something, you would have to wait for the central computer to
respond. As computing power got cheaper client nodes became more powerful and the central computer
less important. However, with the growth of the internet, there has been a shift back to a client server
model. Powerful central computers store information such as emails, documents, music and videos or
offer services such as file hosting, printing, game hosting and internet access; client computers fetch
information and use services from these central servers. In the next few years you are likely to see more
and more software moving away from running on your desktop to running on remote servers and you
accessing it as a client, this is called software as a service.
the client-server model
As an example of modern client server model consider a video sharing website. The website, let's call
it mutube, has a server that stores all the videos that are uploaded to the site. The website is used by
millions of clients a day and each of them connects to the server to watch videos. When a client connects
to mutube the server and asks for a particular video, the server loads the video into RAM from a large
array of hard disks and mutube sends the video to the client. The client on receiving the video, presses
play and watches the video.
Other examples of servers might be a shared printing service in a college. The print server will be hosted
on a single computer, and when anyone in the college wants to print, the request is sent to the server. In
this case the server will keep track of how much printing credit each user has and make sure that the
print queue is dealt with properly.
Extension: Cloud Computing
The current client-server model is starting to change, with companies being less likely to offer services
with a centralised server. Increasingly internet firms are reaching a global clientèle, it makes little sense
to have a server or servers based in one location as if your servers are in America and some of your
users in Armenia, these users will experience slow access to your services. Another problem is if a
power cut affects your server or the connection to that one server or set of servers goes down then the
service you are offering the internet will also stop.
With cloud computing the services may be distributed all over the globe, meaning that wherever you
are, you'll have a server reasonably close to you offering access to the data and services you need. It
also means that if one server goes down other servers in different locations can keep the service
running. Keeping databases synchronised across the globe, so your mail client has the same mails in
Switzerland as in Swaziland, is a complex task and firms such as amazon and rackspace offer services to
help you handle this. One downside with cloud computing is you are never quite sure where your data
is, and if you're not careful you might find data being stored in countries that have less stringent data
protection laws than your own.
Server - a computer program running to serve the requests of other programs, the "clients"
includes:
 Printing
 File sharing
 Game hosting
 Websites
 Other web services
Client - an application or system that accesses a service made available by a server
Clients are software programs and processes that connect to servers, sending requests and receiving
responses. Client examples include:
 Web browser page requests
 Chat systems on mobile phones
 Online games
From <http://en.wikibooks.org/wiki/Alevel_Computing/AQA/Computer_Components,_The_Stored_Program_Concept_and_the_Internet/Structure_of_the_Inter
net/Client_server_model>
Teacher's URL:
http://127.0.0.1:800/Networking%20AND%20Internet%20And%20Servers%20And%20Security%20And%20HTML/en.wikibooks.org/wiki/A
level_Computing/AQA/Computer_Components,_The_Stored_Program_Concept_and_the_Internet/Structure_of_the_Internet/Client_serv
er_model
Client-Server - Examples (W)
13 April 2015
15:44
Below:
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SAP
ORACLE ERP
BANKS
SARS
GoogleDrive
GoogleDocs
MS Cloud
SAAS
What is the Internet, WWW, Intranet
13 April 2015
15:11
Video: Basics
Mr. Clarkson Talks About... The WWW, The Internet &amp; Intranets
Notes:
 WWW
 Emails
 File Structures
 Newsgroups
 IRC
 FTP

Distinction:
o Internet: about computer
o Collection of web pages on the Internet
======================================================
Structure of the Internet: Internet, Intranet and World Wide Web
The Internet - a global system of interconnected computer networks that use the standard Internet Protocol
suite (TCP/IP)
The internet impacts heavily upon the way that we live, study and work. But it hasn't always been that way.
In the 1960s ARPA, a part of the American Department of Defence, funded several large computing projects.
These projects were very expensive and situated in different parts of the USA. It was unreasonable to expect
research groups to travel to each of these sites, and it was far too expensive to build more of them, what was
needed was a method to link them together so that information could be easily exchanged. ARPANET was
created, basing communication on packet switching. This system of communication broke messages into
chunks which were then passed to other sites using a network of interlinked computers. Due to the
unreliable nature of connections, if any link in the network broke, a packet could be re-routed around the
problem to reach its destination. The concept is similar to how drivers can take different routes when they
meet a blocked off road.
ARPANET logical map, March 1977
Extension: Cold War Rumours
A popular myth is that the internet was started because the American Department of Defense were looking
at how they could maintain control of military installations in the event that they were on the receiving end
of a Soviet Nuclear strike. This would mean that communications between sites would have to be
maintained even if one or more of the sites connecting installations were knocked out. A sound idea, but
not the reason for starting ARPANET. The network never carried any classified material and was
predominantly used for research purposes, connecting research institutions, including Universities in the
UK.
In the 70s ARPA funded other experimental networks and made an effort to unite them. At the same time
the limits of the initial network to 63 nodes and 252 hosts were reached and so the TCP/IP protocol was
created. This protocol, or set of rules, allowed different networks to talk to each other. This protocol still
forms the main link between networks in the internet to this day.
As the internet consists of many different networks interlinking with each other, the internet has no central
structure or governing body. This makes it very robust, meaning that if one connection between two hosts is
lost, you can probably find another route to send information by. It also poses a threat to some governments,
as they struggle to restrict information available to their citizens. Countries such as North Korea and China
funnel their internet links through a few connections to the outside world, this means the government can
control what comes in an out of the country, giving them the ability to filter which websites are available and
allow them to switch the internet 'off' at times of crisis, by cutting these connections. This happened during
the 2011 Arab Spring, where Tunisia, Egypt and Libya tried to stop their citizens from getting information
from the outside world.
Diagram of routing paths through a portion of the Internet, notice the multiple routes you can take to get from one
network to another
World Wide Web (WWW)[edit]
World Wide Web - a system of interlinked hypertext documents accessed via the Internet
The first thing to notice is that the World Wide Web is not the internet, but a subset of what the internet
offers. The internet hosts all forms of data, including games, video, telecommunications etc. while the WWW
only transmits hypertext documents. The WWW is accessed through a web browser linking files together
using hyperlinks and was invented by a British computer scientist, Sir Tim Berners-Lee in 1989.
Intranet[edit]
Intranet - a private network within an organisation which may offer printer sharing, file sharing,
communication, private websites etc...which uses internet technologies such as TCP/IP and web browsers
the relationships between the internet, intranets and the World Wide Web
From <http://en.wikibooks.org/wiki/Alevel_Computing/AQA/Computer_Components,_The_Stored_Program_Concept_and_the_Internet/Structure_of_the_Internet/
Internet,_Intranet_and_World_Wide_Web#The_Internet>
Teacher's URL:
http://127.0.0.1:800/Networking%20AND%20Internet%20And%20Servers%20And%20Security%20And%20HTML/en.wikibooks.org/wiki/Alevel_Computing/AQA/Computer_Components,_The_Stored_Program_Concept_and_the_Internet/Structure_of_the_Internet/Internet,_Intran
et_and_World_Wide_Web#The_Internet
Internet from Wiki - Comprehensive Overview
13 April 2015
15:53
(Comprehensive overview as well: http://en.wikipedia.org/wiki/Internet_access_ )
==================================
Internet
From Wikipedia, the free encyclopedia
T
The Internet is a global system of interconnected computer networks that use the standard Internet protocol
suite(TCP/IP) to link several billion devices worldwide. It is a network of networks[1] that consists of millions of
private, public, academic, business, and government networks of local to global scope, linked by a broad array of
electronic, wireless, and optical networking technologies. The Internet carries an extensive range of information
resources and services, such as the inter-linked hypertext documents and applications of the World Wide
Web (WWW), the infrastructure to supportemail, and peer-to-peer networks for file sharing and telephony.
Many concepts and debates on technology, which shaped the Internet, date back to research commissioned by
theUnited States government in the 1960s to build robust, fault-tolerant communication via computer
networks.[2] This work evolved into efforts in the United Kingdom and France, that led to the primary precursor
network, the ARPANET, in the United States. In the 1980s, the work of Tim Berners-Lee, in the United Kingdom on
the World Wide Web, theorised the fact that protocols link hypertext documents into a working system,[3] hence
marking the beginning the modern Internet.[4]From the early 1990s, the network experienced sustained
exponential growth as generations of institutional, personal, and mobile computers were connected to it.
The funding of a new U.S. backbone by the National Science Foundation in the 1980s, as well as private funding for
other commercial backbones, led to worldwide participation in the development of new networking technologies,
and the merger of many networks.[5] Though the Internet has been widely used by academia since the 1980s,
thecommercialization of what was by the 1990s an international network resulted in its popularization and
incorporation into virtually every aspect of modern human life. As of December 2014, 37.9 percent of the world's
human population has used the services of the Internet within the past year--over 100 times more people than
were using it in 1995.[6][7] Internet use grew rapidly in the West from the mid-1990s to early 2000s and from the
late 1990s to present in the developing world. In 1994 only 3% of American classrooms had access to the Internet,
while by 2002 that figure was 92%.[8]
Most traditional communications media, including telephony and television, are being reshaped or redefined by
the Internet, giving birth to new services such as voice over Internet Protocol (VoIP) and Internet Protocol
television (IPTV). Newspaper, book, and other print publishing are adapting to website technology, or are reshaped
into blogging and web feeds. The entertainment industry, including music, film, and gaming, was initially the
fastest growing online segment. The Internet has enabled and accelerated new forms of human interactions
through instant messaging, Internet forums, and social networking. Online shopping has grown exponentially both
for major retailers and small artisans and traders.Business-to-business and financial services on the Internet
affect supply chains across entire industries.
The Internet has no centralized governance in either technological implementation or policies for access and
usage; each constituent network sets its own policies.[9] Only the overreaching definitions of the two
principal name spaces in the Internet, the Internet Protocol address space and the Domain Name System (DNS),
are directed by a maintainer organization, the Internet Corporation for Assigned Names and Numbers (ICANN). The
technical underpinning and standardization of the core protocols is an activity of the Internet Engineering Task
Force (IETF), a non-profit organization of loosely affiliated international participants that anyone may associate
with by contributing technical expertise.[10]
From <http://en.wikipedia.org/wiki/Internet>
Internet Architecture
13 April 2015
16:13
In Company:
http://www.gcsecomputing.org.uk/support/network/NWB_SIM.swf
Teacher's URL:
http://127.0.0.1:800/Networking%20And%20Servers%20And%20Security%20And%20HTML/www.gcsecomputing.org.uk/support/network/NW
B_SIM.swf
Watch out for:
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What can you use:
o PC
o Printers
o Servers: File, Multimedia, Email, Cache
o Backups
o
o
o
o
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Connections
Internet
Switches
Hubs
Shared Resources: Printers, File Servers etc
What makes it faster
Switch or Hub or Fast Switch
=======================================================================
Outside
To understand the Internet, it helps to look at it as a system with two main components. The first of those
components is hardware. That includes everything from the cables that carry terabits of information every second to
the computer sitting in front of you.
Other types of hardware that support the Internet include routers, servers, cell phone towers, satellites, radios,
smartphones and other devices. All these devices together create the network of networks. The Internet is a
malleable system -- it changes in little ways as elements join and leave networks around the world. Some of those
elements may stay fairly static and make up the backbone of the Internet. Others are more peripheral.
These elements are connections. Some are end points -- the computer, smartphone or other device you're using to
read this may count as one. We call those end points clients. Machines that store the information we seek on the
Internet are servers. Other elements are nodes which serve as a connecting point along a route of traffic. And then
there are the transmission lines which can be physical, as in the case of cables and fiber optics, or they can be
wireless signals from satellites, cell phone or 4G towers, or radios.
http://www.conceptdraw.com/mosaic/draw-lan-and-wan
=================================================================
: http://computer.howstuffworks.com/internet/basics/internet.htm and PP
Teacher's URL:
http://127.0.0.1:800/Networking%20AND%20Internet%20And%20Servers%20And%20Security%20And%20HTML/computer.howstuffworks.co
m/internet/basics/internet.htm and PP
======================================================================================================
Cabling
13 April 2015
16:32
Types of Cable
(NB: Watch the (Dis)Advantages)
Coaxial cable
This consists of a solid copper core surrounded by insulation which is then surrounded by a
copper shielding and finally covered with a plastic sheath. Coaxial cable is widely used for
television wiring as it has enough bandwidth to handle a television signal over a typical run
from antenna to television..
Twisted Pair
There are 8 colour-coded wires with each related pair twisted around one another. Twisting
it in this way reduces signal loss over any given length of cable.
Twisted pair cable is widely used in 100 Mbps and 1 Gbps networks.
Shielded Twisted Pair
In order to improve performance even more, shielded twisted pair cable (STP) has copper
shielding wrapped around each twisted pair and another shield wrapped around the whole
cable.
Fibre Optic
Fibre-optic cable has an astounding bandwidth, it is limited more by the electronics either
side of the cable than the bandwidth of the cable itself. For instance in recent experiment, a
160 km length of high performance fibre-optic cable carried up to 14 Tera bits per second!
Fibre optic cable uses light to transmit information rather than electrical signals. Unlike
copper cable it is not prone to electrical interference.
Wireless
An alternative to setting up a network with copper or fibre cable is Wireless. Connection
between computer and router is achieved using radio waves.
This has the strong advantage of not requiring cables to be laid through a building. On the
other hand radio is very prone to being weakened by walls and other objects.
The bandwidth of a wireless network is lower than a physical network.
Wireless technologies[edit]
Computers are very often connected to networks using wireless links
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Main article: Wireless network
Terrestrial microwave – Terrestrial microwave communication uses Earth-based transmitters and
receivers resembling satellite dishes. Terrestrial microwaves are in the low-gigahertz range, which limits
all communications to line-of-sight. Relay stations are spaced approximately 48 km (30 mi) apart.
Communications satellites – Satellites communicate via microwave radio waves, which are not deflected
by the Earth's atmosphere. The satellites are stationed in space, typically in geosynchronous orbit
35,400 km (22,000 mi) above the equator. These Earth-orbiting systems are capable of receiving and
relaying voice, data, and TV signals.
Cellular and PCS systems use several radio communications technologies. The systems divide the region
covered into multiple geographic areas. Each area has a low-power transmitter or radio relay antenna
device to relay calls from one area to the next area.
Radio and spread spectrum technologies – Wireless local area networks use a high-frequency radio
technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread
spectrum technology to enable communication between multiple devices in a limited area. IEEE
802.11 defines a common flavor of open-standards wireless radio-wave technology known as Wifi.
Free-space optical communication uses visible or invisible light for communications. In most cases, lineof-sight propagation is used, which limits the physical positioning of communicating devices.
From <http://en.wikipedia.org/wiki/Computer_network>
http://www.teachict.com/as_a2_ict_new/ocr/A2_G063/333_networks_coms/bandwidth/miniweb/pg2.htm
and following pages
Teacher's URL: http://127.0.0.1:800/Networking%20And%20Servers%20And%20Security%20And%20HTML/www.teachict.com/as_a2_ict_new/ocr/A2_G063/333_networks_coms/bandwidth/miniweb/index.htm and following pages
===================================================================
Also See: http://en.wikipedia.org/wiki/Computer_network
================================================
Routing (Optional)
13 April 2015
17:04
Routing[edit]
Routing calculates good paths through a network for information to take. For example from node 1 to node 6 the
best routes are likely to be 1-8-7-6 or 1-8-10-6, as this has the thickest routes.
Routing is the process of selecting network paths to carry network traffic. Routing is performed for
many kinds of networks, including circuit switching networks and packet switched networks.
In packet switched networks, routing directs packet forwarding (the transit of logically
addressed network packets from their source toward their ultimate destination) through
intermediate nodes. Intermediate nodes are typically network hardware devices such
as routers, bridges, gateways, firewalls, or switches. General-purpose computers can also forward
packets and perform routing, though they are not specialized hardware and may suffer from limited
performance. The routing process usually directs forwarding on the basis of routing tables, which
maintain a record of the routes to various network destinations. Thus, constructing routing tables,
which are held in the router's memory, is very important for efficient routing. Most routing algorithms
use only one network path at a time. Multipath routing techniques enable the use of multiple
alternative paths.
There are usually multiple routes that can be taken, and to choose between them, different elements
can be considered to decide which routes get installed into the routing table, such as (sorted by
priority):
1. Prefix-Length: where longer subnet masks are preferred (independent if it is within a routing protocol or
over different routing protocol)
2. Metric: where a lower metric/cost is preferred (only valid within one and the same routing protocol)
3. Administrative distance: where a lower distance is preferred (only valid between different routing
protocols)
Routing, in a more narrow sense of the term, is often contrasted with bridging in its assumption
that network addresses are structured and that similar addresses imply proximity within the network.
Structured addresses allow a single routing table entry to represent the route to a group of devices. In
large networks, structured addressing (routing, in the narrow sense) outperforms unstructured
addressing (bridging). Routing has become the dominant form of addressing on the Internet. Bridging is
still widely used within localized environments.
From <http://en.wikipedia.org/wiki/Computer_network>
===========================
Definitions:
More on hubs, switches etc
Hubs, Bridges, Switches and Routers are used to build networks. If you are trying to
design your own LAN (Local Area Network) at home, then you probably need to know
what they do and the main differences between them. I will try to cover all that in
addition to some networking details to cultivate the article and provide better
understanding of how the internet works. After all, always remember that the internet as
you know it is nothing more than a network of networks!
Hubs are used to build a LAN by connecting different computers in a star/hierarchal
network topology, the most common type on LANs now a day. A hub is a very simple
(or dumb) device, once it gets bits of data sent from computer A to B, it does not check
the destination, instead, it forwards that signal to all other computers (B, C, D…) within
the network. B will then pick it up while other nodes discard it. This amplify that the
traffic is shared.
There are mainly two types of hubs:
1. Passive: The signal is forwarded as it is (so it doesn’t need power supply).
2. Active: The signal is amplified, so they work as repeaters. In fact they have been
called multiport repeaters. (use power supply)
Hubs can be connected to other hubs using an uplink port to extend the network.
OSI Model: Hubs work on the physical layer (lowest layer). That’s the reason they can’t
deal with addressing or data filtering.
Switches on the other hand are more advanced. Instead of broadcasting the frames
everywhere, a switch actually checks for the destination MAC address and forward it to
the relevant port to reach that computer only. This way, switches reduce traffic and
divide the collision domain into segments, this is very sufficient for busy LANs and it
also protects frames from being sniffed by other computers sharing the same segment.
They build a table of which MAC address belongs to which segment. If a destination
MAC address is not in the table it forwards to all segments except the source segment.
If the destination is same as the source, frame is discarded.
Switches have built-in hardware chips solely designed to perform switching capabilities,
therefore they are fast and come with many ports. Sometimes they are referred to as
intelligent bridges or multiport bridges.
Different speed levels are supported. They can be 10 Mb/s, 100 Mb/s, 1 Gb/s or more.
Most common switching methods are:
1. Cut-through: Directly forward what the switch gets.
2. Store and forward: receive the full frame before retransmitting it.
OSI: Switches are on the data link layer (just above physical layer) that’s why they deal
with frames instead of bits and filter them based on MAC addresses. Switches are
known to be used for their filtering capabilities.
VLANs (Virtual LANs) and broadcast domains: Switches do not control broadcast
domains by default, however, if a VLAN is configured in a switch it shall have its own
broadcast domain.
*VLAN is a logical group of network devices located on different LAN physical
segments. However they are logically treated as if they were located on a single
segment.
Bridges are used to extend networks by maintaining signals and traffic.
OSI: Bridges are on the data link layer so in principle they are capable to do what
switches do like data filtering and separating the collision domain, but they are less
advanced. They are known to be used to extend distance capabilities of networks.
In a comparison with switches, they are slower because they use software to perform
switching. They do not control broadcast domains and usually come with less number of
ports.
Routers are used to connect different LANs or a LAN with a WAN (e.g. the internet).
Routers control both collision domains and broadcast domains. If the packet’s
destination is on a different network, a router is used to pass it the right way, so without
routers the internet could not functions.
Routers use NAT (Network Address Translation) in conjunction with IP Masquerading
to provide the internet to multiple nodes in the LAN under a single IP address.
Now a day, routers come with hub or switch technology to connect computers directly.
OSI: Routers work on the network layer so they can filter data based on IP addresses.
They have route tables to store network addresses and forward packets to the right
port.
Gateways are very intelligent devices or else can be a computer running the
appropriate software to connect and translate data between networks with different
protocols or architecture, so their work is much more complex than a normal router. For
instance, allowing communication between TCP/IP clients and IPX/SPX or AppleTalk.
OSI: Gateways operate at the network layer and above, but most of them at the
application layer.
P.S. The term Gateway is used to refer to routers in some articles so beware. In this
case, the router has gateway software. And Default Gateway is used to refer to the
node (e.g. router) connecting the LAN to the outside (e.g. internet).
Repeaters are simple devices that work at the physical layer of the OSI. They
regenerate signals (active hubs does that too).
There is an important rule to obey while using repeaters/hubs to extend a local network
and is called the 5-4-3 rule or the IEEE way. The rule forces that in a single collision
domain there shouldn’t be more than 5 segments, 4 repeaters between any two hosts in
the network and only 3 of the segments can be populated (contain user connections).
This rule ensures that a signal sent over the network will reach every part of it within an
acceptable length of time.
If the network is bigger, the collision domain can be divided into two parts or more using
a switch or a bridge.
Conclusion
What have been introduced so far are the main traditional devices used to build
networks, understanding how they work helps to understand the logic behind networks
designing, however, now that technology advance quickly, it is possible to find new
products in the market combining two or more of these devices into one.
Examples are:
– Brouter: Works as a Bridge and as a Router.
– IP Switch or MultiLayer Switch (MLS): New switches with routing capabilities, they
forward data based on IP addresses, work at the network layer too.
References used are the following in addition to my previous readings and background
study.
[1] TCP IP in 24 hours by SAMS
[2] http://www.techexams.net/technotes/ccna/lan_technologies.shtml
From <http://blog.creativeitp.com/posts-and-articles/networking/hubs-switches-routers-and-bridges/comment-page-1/>
Extra: Pages on Hardware And LAN
20 April 2015
12:12
Connectors:
Modems
Modem (from modulator-demodulator) is a device that turns the digital 1s and 0s of a personal
computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone
Systems (POTS), and once received on the other side, converts those sounds back into a form
used by a USB, Ethernet, serial, or network connection. Modems are generally classified by the
amount of data they can send in a given time, normally measured in bits per second, or "bps".
NIC (Network Interface Card)
A network interface card is a computer hardware component designed to allow computers to
communicate over a computer network. It is both an OSI layer 1 (physical layer) and layer 2
(data link layer) device, as it provides physical access to a networking medium and provides a
low-level addressing system through the use of MAC addresses. It allows users to connect to
each other either by using cables or wirelessly. Most motherboards today come equipped with
a network interface card in the form of a controller, with the hardware built into the board
itself, eliminating the need for a standalone card.
Hub
Hubs connect computers together in a star topology network. Due to their design, they increase
the chances for collisions. Hubs operate in the physical layer of the OSI model and have no
intelligence. Hubs flood incoming packets to all ports all the time. For this reason, if a network
is connected using hubs, the chances of a collision increases linearly with the number of
computers (assuming equal bandwidth use). Hubs pose a security risk since all packets are
flooded to all ports all the time. If a user has packet sniffing software, they can extract data
from the network and potentially decode it and use it. Hubs make it easy to "spy" on users on
the same LAN as you.
Routers
Routers operate at the network layer of the OSI model and efficiently route information
between Local Area Networks. Since routers operate in the third layer, the network layer, they
must understand layer 3 addressing... such as TCP/IP. A router will divide a broadcast domain by
not forwarding broadcasts on one connected network to another connected network. Routers
operate in two different planes: the control plane, in which the router learns the outgoing
interface that is most appropriate for forwarding specific packets to specific destinations, and
the forwarding plane, which is responsible for the actual process of sending a packet received
on a logical interface to an outbound logical interface.
Bridges
Bridges can be identified by the fact that they operate at the data link layer of the OSI model.
Bridges have intelligence and can "bridge" two of their ports together at very high speed. They
use a database of MAC addressesto determine where computers are located and very efficiently
send frames only where they need to go. The database is created dynamically as computers
communicate on the network. A bridge simply watches the incoming frame and memorizes the
MAC address and port a frame arrives on. It uses this information to locate a computer if a
packet comes in that must be forwarded to it. If a frame arrives at the bridge and the bridge
does not know where to send it, the bridge will flood the frame just like a hub does. Bridging is
often inaccurately called switching.
Switches
Switches are often confused with bridges because they also operate at the data link layer of
the OSI model. Similar to a hub, switches provide a central connection between two or more
computers on a network, but with some intelligence. They provide traffic control for packets;
rather than forwarding data to all the connected ports, a switch forwards data only to the port
on which the destination system is connected. They use a database of MAC addresses to
determine where computers are located and very efficiently send packets only where they
need to go. The database is created dynamically as computers communicate on the network.
The switch simply watches the incoming packets and memorizes the MAC address and port a
packet arrives on. If a packet arrives with a destination computer that the switch does not have
an address for in its MAC address table, it will flood the packet out all connected ports. A switch
creates separate collision domains for each physical connection. A switch will only create
separate broadcast domains if separate VLANs (Virtual Local Area Networks) are assigned to
different ports on the switch. Otherwise, a broadcast received on one port will be flooded out all
ports except the one it came in on.
Firewalls
A firewall is a part of a computer system or network that is designed to block unauthorized
access while permitting outward communication. It is also a device or set of devices configured
to permit, deny, encrypt, decrypt, or proxy all computer traffic between different security
domains based upon a set of rules and other criteria.
Firewalls can be implemented in both hardware and software, or a combination of both.
Firewalls are frequently used to prevent unauthorized Internet users from accessing private
networks connected to the Internet. All messages entering or leaving the Local Area
Networkpass through the firewall, which examines each message and blocks those that do not
meet the specified security criteria. Without proper configuration, a firewall can often become
worthless. Standard security practices dictate a "default-deny" firewall ruleset, in which the
only network connections which are allowed are the ones that have been explicitly allowed.
From <http://en.wikibooks.org/wiki/Network_Plus_Certification/Devices/Common_Devices>
From <http://en.wikibooks.org/wiki/Network_Plus_Certification/Devices/Common_Devices>
http://en.wikiversity.org/wiki/Network_Administration
Teacher's URL:
http://127.0.0.1:800/Networking%20AND%20Internet%20And%20Servers%20And%20Security%20And%20HTML%20and%20IP%20Address%20
and%20URL/en.wikibooks.org/wiki/Network_Plus_Certification/Devices/Common_Devices
Activity: PSTN, Telkom, ISP, Cell Phone Providers (45mi)
13 April 2015
16:31
Find the definitions and the uses for the following:
a. Network
b. Router
c. Bridge
d.
e.
f.
g.
Gateway
Server
PSTN
ISP
Prepare a diagram about how they fit together
Comprehensive Reference
13 April 2015
17:18
Contents
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[hide]
1 History
2 Properties
3 Network packet
4 Network topology
4.1 Network links
4.2 Network nodes
4.3 Network structure
5 Communications protocols
5.1 IEEE 802
5.2 Internet Protocol Suite
5.3 SONET/SDH
5.4 Asynchronous Transfer Mode
6 Geographic scale
7 Organizational scope
7.1 Intranets
7.2 Extranet
7.3 Internetwork
7.4 Internet
7.5 Darknet
8 Routing
9 Network service
10 Network performance
10.1 Quality of service
10.2 Network congestion
10.3 Network resilience
11 Security
11.1 Network security
11.2 Network surveillance
11.3 End to end encryption
12 Views of networks
13 See also
14 References
15 Further reading
16 External links
From <http://en.wikipedia.org/wiki/Computer_network>
Streaming
13 April 2015
17:33
Background
Streaming media is multimedia that is constantly received by and presented to an end-user while being
delivered by a provider. The verb "to stream" refers to the process of delivering media in this manner; the
term refers to the delivery method of the medium rather than the medium itself.
A client media player can begin playing the data (such as a movie) before the entire file has been transmitted.
Distinguishing delivery method from the media distributed applies specifically to telecommunications
networks, as most of the delivery systems are either inherently streaming (e.g., radio, television) or
inherently non streaming (e.g., books, video cassettes, audio CDs). For example, in the 1930s, elevator
music was among the earliest popularly available streaming media; nowadays Internet television is a
common form of streamed media. The term "streaming media" can apply to media other than video and
audio such as live closed captioning, ticker tape, and real-time text, which are all considered "streaming text".
The term "streaming" was first used in the early 1990s as a better description for video on demand on IP
networks; at the time such video was usually referred to as "store and forward video",[1] which was
misleading nomenclature.
From <http://en.wikipedia.org/wiki/Streaming_media>
Teacher's URL:
http://127.0.0.1:800/Networking%20AND%20Internet%20And%20Servers%20And%20Security%20And%20HTML/en.wikipedia.org/wiki/Stream
ing_media
Note:
 The file does not have to be completely downloaded before it can be played
 Watch the bandwidth!
Applications:
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lectures, seminars
on-demand instruction
entertainment: specialty content
remote digital editing
voice mail
YouTube!
http://www.cs.columbia.edu/~hgs/teaching/ais/slides/2003/RTSP.pdf
Advantages / Disadvantages:
Advantages:
 Can access when needed
 Power business-enhancement tool
Disadvantages:
 Very high bandwidth requirements
 Special equipment
 Can be very expensive
 Billing can be complex (See e.g. MTN)
 Can be "Lossy" - Poor quality - due to packet loss
 Protocol Problems
http://www.cs.columbia.edu/~hgs/teaching/ais/slides/2003/RTSP.pdf
http://en.wikipedia.org/wiki/Streaming_media
Real-Time and On-Demand
On-demand streaming is provided by a means called progressive streaming orprogressive download.
Progressive streaming saves the file to a hard disk and then is played from that location. Ondemand streams are often saved to hard disks and servers for extended amounts of time;
On-demand streaming is provided by a means called progressive streaming orprogressive download.
Progressive streaming saves the file to a hard disk and then is played from that location. Ondemand streams are often saved to hard disks and servers for extended amounts of time;
Live streaming (Real-Time) are only available at one time only (e.g., during the football game).[8]
Live streaming, which refers to content delivered live over the Internet, requires a form of source
media (e.g. a video camera, an audio interface, screen capture software), an encoder to digitize
the content, a media publisher, and a content delivery network to distribute and deliver the
content.
Note: they are the same size. It is only the delivery that is different
From <http://en.wikipedia.org/wiki/Streaming_media>
Bitrates and Bandwidth
Note the difference between MB (MegaByte), Mb (Megabit), KB (KiloByte), Kb (Kilobit)
 FM Radio: 56kb/sec
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Ticker-tape: Very little
Video: 1.5Mb/sec
Blue-Ray: 2.5Mb/sec
Dolby True HD : 18Mb/sec
HD Video: 10Mb/s
(Check iTunes Playback)
http://en.wikipedia.org/wiki/Dolby_TrueHD
Bandwidth and storage[edit]
A broadband speed of 2.5 Mbit/s or more is recommended for streaming movies, for example to
a Roku, Apple TV, Google TV or a Sony TV Blu-ray Disc Player, 10 Mbit/s for High Definition content.[10]
Unicast connections require multiple connections from the same streaming server even when it streams the same
content
Streaming media storage size is calculated from the streaming bandwidth and length of the media using the
following formula (for a single user and file):
storage size (in megabytes) = length (in seconds) × bit rate (in bit/s) / (8 × 1024 × 1024)
8bits per Byte
1024 Bytes per KiloByte
1024 KiloBytes per MegaByte
Real world example:
One hour of video encoded at 300 kbit/s (this was a typical broadband video in 2005 and it was usually
encoded in a 320 × 240 pixels window size) will be:
(3,600 s × 300,000 bit/s) / (8×1024×1024) requires around 128 MB of storage.
If the file is stored on a server for on-demand streaming and this stream is viewed by 1,000 people at the
same time using aUnicast protocol, the requirement is:
300 kbit/s × 1,000 = 300,000 kbit/s = 300 Mbit/s of bandwidth
This is equivalent to around 135 GB per hour. Using a multicast protocol the server sends out only a single
stream that is common to all users. Therefore such a stream would only use 300 kbit/s of serving bandwidth.
See below for more information on these protocols.
The calculation for live streaming is similar.
Assumptions: speed at the encoder, is 500 kbit/s.
If the show lasts for 3 hours with 3,000 viewers, then the calculation is:
Number of MBs transferred = encoder speed (in bit/s) × number of seconds × number of viewers /
(8*1024*1024)
Number of MBs transferred = 500 x 1024 (bit/s) × 3 × 3,600 ( = 3 hours) × 3,000 (number of viewers) /
(8*1024*1024) = 1,977,539 MB
From <http://en.wikipedia.org/wiki/Streaming_media>
Adaptive bitrate streaming
is a technique used in streaming multimedia over computer networks. While in the past most video
streaming technologies utilized streaming protocols such as RTP with RTSP, today's adaptive streaming
technologies are almost exclusively based on HTTP[1] and designed to work efficiently over large distributed
HTTP networks such as the Internet.
It works by detecting a user's bandwidth and CPU capacity in real time and adjusting the quality of a video
stream accordingly. It requires the use of an encoder which can encode a single source video at multiple bit
rates. The player client[2] switches between streaming the different encodings depending on available
resources.[3] "The result: very little buffering, fast start time and a good experience for both high-end and lowend connections."[4]
More specifically, and as the implementations in use today are, adaptive bitrate streaming is a method of
video streaming over HTTP where the source content is encoded at multiple bit rates, then each of the
different bit rate streams are segmented into small multi-second parts.[5] The streaming client is made aware
of the available streams at differing bit rates, and segments of the streams by a manifest file. When starting,
the client requests the segments from the lowest bit rate stream. If the client finds the download speed is
greater than the bit rate of the segment downloaded, then it will request the next higher bit rate
segments. Later, if the client finds the download speed for a segment is lower than the bit rate for the
segment, and therefore the network throughput has deteriorated, then it will request a lower bit rate
segment. The segment size can vary depending on the particular implementation, but they are typically
between two (2) and ten (10) seconds.[3][5]
From <http://en.wikipedia.org/wiki/Adaptive_bitrate_streaming>
Teacher's URL:
http://127.0.0.1:800/Networking%20AND%20Internet%20And%20Servers%20And%20Security%20And%20HTML/en.wikipedia.org/wiki/Adapti
ve_bitrate_streaming
Extra: Build a Network
16 April 2015
13:06
http://www.gcsecomputing.org.uk/support/network/NWB_SIM.swf
Teacher's URL:
http://127.0.0.1:800/Networking%20And%20Servers%20And%20Security%20And%20HTML/www.gcsecomputing.org.uk/support/network/NW
B_SIM.swf
Watch out for:
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What can you use:
o PC
o Printers
o Servers: File, Multimedia, Email, Cache
o Backups
o Connections
o Internet
o Switches
o Hubs
Shared Resources: Printers, File Servers etc
What makes it faster
Switch or Hub or Fast Switch
Review Mindmap
13 April 2015
14:52
• explain the client-server model of networked computers
• give examples of applications which use the client-server model
• describe what is meant by the World Wide Web (www) and the internet