IP addresses Classes

There are 5 classes of IP addresses, A, B, C, D, and E. These addresses have a standard range of addresses that are assigned to them, with specific network IDs and host IDs associated as the next table illustrates. Notice that all addresses that start with 127 are omitted, as these addresses are associated with loop back addresses and local hosts. Do not use any address that starts with 127
IP Subnet Mask
An IP address by itself is only one half of the required information for TCP/IP addressing to work. Every IP address class has a default subnet mask associated with it. The subnet mask is what differentiates the network ID and the host ID for a given TCP/IP address. In the table above, you can see that for a given class of address, there is a network ID and a host ID associated with it. The subnet mask is what breaks the address into these different pieces. The table below illustrates the default subnet mask for the three main TCP/IP address classes.Along with this, there are ways of supernetting, i.e., applying subnet masks that allow a specific class of addresses to be split up, providing more network addresses, and fewer host addresses, for network segmentation than does the default class subnet mask. The table below illustrates some common subnet masks for class C addresses.Using the 255.255.255.128 subnet mask for a class C address, we can figure the actual network numbers and the usable host addresses. The lowest high-order bit has a value of 128 for the subnet mask. If you divide the maximum number of addresses (256) by the lowest high-order bit (128) we find that the number of networks that we end up with is 2 (256/128=2). This lowest high-order bit value also tells us the number of nodes per network (128), but we cannot use the first address in a segment as this is the physical network number, and we cannot use the last address in a segment as this is the broadcast address for the physical network number. So the actual number of usable host addresses is the lowest high-order bit (128) minus 2 (the network number and the broadcast address) or 128-2=126 usable host addresses per segment. If the IP addresses use a subnet mask of 255.255.255.128, then the network segments would have addresses xxx.xxx.xxx.0 – xxx.xxx.xxx.127 and xxx.xxx.xxx.128 – xxx.xxx.xxx.255. Since the first address of each segment is the network number, and we cannot use this, so the first usable number is the next IP address of each segment, i.e., xxx.xxx.xxx.1 for network 0 and xxx.xxx.xxx.129 for network 128. We also loose the highest IP number for use as the network broadcast address in each segment. So the last IP address that we can use is xxx.xxx.xxx.126 for network 0 and xxx.xxx.xxx.254 for network 128. This gives you 2 networks with 126 usable IP addresses for hosts or devices.

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IP Addresses

IP Addresses

Every device that communicates on a network, utilizing the TCP/IP protocol, is identified by a unique IP address. The IP address identifies a host’s location on the network, much like a street address identifies a house location. The IP address must be unique for the network that it is a member of. Just like a house address, the IP address must be unique and be created using a uniform format.

Each IP address defines the network ID and the host ID of the device. The network ID defines devices that are on the same physical network. All devices on the same physical network must have the same network ID, and this ID must be unique for the network that the device is a member of. The host ID defines the actual device on the physical network, and must be unique for the network ID the device is a member of.

Each IP address is 32 bits long and made up of four 8-bit fields, called octets. Each of the four octets is separated by a period (.). Each of the four octets represents a decimal number between 0 and 255. This format is called dotted decimal notation. The following is an example:

Each bit position of an octet has an assigned decimal value or number. If a bit is set to 0 (zero), the bit position value is 0 (zero). If a bit position is set to 1 (one), then the bit position is converted to the decimal value or number assigned to that position. All of the decimal values of the bit positions of an octet are added together to get it’s decimal value. The low-order bit of the octet represents a decimal value of 1 (one), while the high-order bit represents 128. The highest decimal value that an octet may represent is 255 – or all bit positions set to 1 (one). The following table illustrates the bit position values of an octet.

Given the example above, to find the decimal number associated with this octet, we would add all of the decimal values of the bit positions that have a binary value of 1 (one) together to come up with the octet’s decimal value. So we would add 1 + 2 + 128 together, which equals 131. So this octets value is a decimal dotted notation of 131.

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TCP/IP

TCP/IP is an industry standard suite of protocols designed for local and wide area networks (LAN – WAN). It was developed by the United States Department of Defense Advanced Research Projects Agency (ARPA) in 1969 for a research sharing project called ARPANET. Their purpose in creating TCP/IP was to provide high-speed communication links. The Internet was built on the foundation of the original ARPANET project.

The TCP/IP protocol suite can be mapped directly to the seven-layer Open Systems Interconnection (OSI) model.

Network Interface – responsible for putting frames on and pulling frames off the network wire.
Internet – responsible for addressing, packaging, and routing. Three protocols make up this layer:

• IP – responsible for addressing and routing packets between networks and hosts.
• ARP – responsible for obtaining hardware (NIC) addresses of hosts located on the same physical network.
• ICMP – responsible for messages and reporting errors regarding the delivery of packet(s).
  

Transport – responsible for providing communications between two hosts. Two protocols make up this layer:

• TCP – provides connection-oriented, reliable communications for applications that transfer large amounts of data at one time or that requires an acknowledgement of data received.
• UDP – provides connectionless communications and does not guarantee a packet will be delivered. Applications that use UDP transfer small amounts of data at one time, and pass responsibility of the reliable delivery of packet(s) to the application.
  

Application – responsible for allowing applications to gain access to the physical network.

When an application sends data to another host on the network, a data packet is assembled by combining the output of each of the TCP/IP protocol layers. The protocol layers adds their own information to a header that is encapsulated as data by the protocol in the layer below.

When the destination host receives the packet, the corresponding layer(s) strips off the header(s) and treat the remainder of the packet as data for the protocol that is above it.

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Media Bays

Media Bays

Media bays, or data suites are clusters of perhaps four desktop computers, a scanner and a printer.

Though self-sufficient in terms of peripherals, they would be connected to the main school network and have Internet access. This is one reason why they would be best sited in public areas around the school.

These suites would be used by students in small groups or individually and could accommodate task-oriented activities and self-directed learning.
Advantages are easy access to staff and students alike, Utilise areas of school without losing classrooms Public supervision

Disadvantages are Open access means security issues must be addressed .

Fig 3a: Movable or mobile Media Bays

Laptop and data-projector (Ref Fig 3b)
A combination of laptop and data-projector is a highly effective teaching model where a teacher wants to provide the whole class with visual or multimedia content . It can be used in conjunction with an existing LAN point in the room for best effect.Fig 3b: Movable or mobile Laptop PC with Digital Projector

Wireless LAN (Ref Fig 3c)

This scenario has the capability to connect multiple computers to the school LAN without providing direct LAN connections. No LAN cabling is required for the classroom; instead all computers are radio linked to the LAN. Wireless LAN technology is relatively new and generally more expensive and more limited than cabled LANs. There is the potential, however, to save on extensive cabling work with this option.

Wireless connections allow a region to be connected to a network by radiowaves, which link a wireless card in the computer to a wireless access point. One should remember that the access point itself must be connected by cable to the main network.

Advantages

• Flexibility of machines - usually laptops - linked even if students break into small workgroups in different parts of room.
• Wireless networking means that large common areas such as canteens or libraries can be easily connected to the network.
• Less unplugging of cables into sockets reduces wear and tear
  

Disadvantages

• Wireless networking may prove much more expensive if wiring large numbers of machines close together.
• Wireless hubs data rates (typically 11Mbps) are considerably less at present than their cable equivalent. Thus is unsuitable for high data volumes such as multimedia access by large numbers of machines.
• Manufacturers stated ranges of 100 - 300 metres is wildly optimistic. Ranges of less than 18 metres are not uncommon, Data rates drop off as distance increases.
  

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Models for Networking

Models for Networking
First let’s review some simple models where no networking exits and computers are used in standalone or ad-hoc mode. The following represent some simple models representing classrooms.

Model 1a: One computer in a classroom with its own private printer. It is recommended that schools with computers in this situation would network the classrooms in question as shown. Networking will more effectively make use of commonly shared resources such as file servers and school printers, internet , email etc. When a mobile PC or PC with projector is require in a room the network points are already present.
In this scenario, there could be a single LAN-connected point for the teacher and an additional LAN connection to allow for a portable switch. Refer to diagram 2a

Model 1a:

Fig 2a: From single PC to networked LAN Points

Model 1b: This scenario is similar to Model 1a, but where other equipment such as printers, scanners are used in ad-hoc and inefficient configuration. It is recommended that schools with computers in this situation would network the classrooms in question . Networking will more effectively make use of commonly shared resources such as scanners, printers, internet , email etc. In this scenario there may be a single LAN-connected point for the teacher and a limited number of LAN connection points throughout the room to allow students access to the school LAN. The connection points may be situated as required around the room depending upon class learning requirements and the availability of existing power outlets. Refer to diagram 2b

Model 1b:

Fig 2b: Networking other commonly used equipment

Networked Computer Room
Model 1c: A non networked computer room or resource area with an ad-hoc and inefficient use of printers, scanners etc. Networking computer rooms is essential so that all PCs can access printers, the internet, email etc. This scenario represents a school computing room which can be timetabled for classes, and with each computer networked to the LAN. There may be a single LAN-connected presentation point for the teacher and LAN-connected computers throughout the classroom. Traditionally, ICT in Irish secondary schools has been concentrated in dedicated computer rooms. Primary schools have more varied deployment. From an administrative point of view, this setup is attractive. An entire class can be timetabled, avoiding problems of extra teachers for split classes. Refer to diagram 2c

Model 1c:
Fig 2c: Networked computer lab

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Server Functionality Model

Fig 4: Server Functionality Model

The network connects to a File and Print Server, Fig 4. The File server stores common files, The Print Server manages the different requests for printing. A Multimedia or CD server is used to store and distribute Multimedia - Sound, Video, Text , applications etc . Internet access is handled via a modem or router, while internet Filtering , Proxy and Web Caching are all handled via a dedicated server. Read More...

Networking Models

Networking Models: Towards a Networked School

This model shows a diagram of a networked school indicating the various types of networking models used. These include computer rooms, networked classrooms, networked specialist rooms for specific subjects. Mobile solutions are shown in the Resource room, the General Purpose room and Building # 2. Note: To improve readability only network points are shown, rather than cabling itself. Refer to Fig 1.Fig 1: Representation of a Whole School Network Model

Fig 2: Typical Network Model for a Primary or Special school.

Figure 2 shows a model for a Primary or Special school. This includes connectivity to all classrooms back to a central network. The network connects to a File and Print Server. Internet access is handled via a modem or router, while internet Filtering , Proxy and Web Caching are all handled via a dedicated server.

Fig 3: Typical Network Model for a Post Primary school

Figure 3 shows a model for a Post Primary school. This includes connectivity to all classrooms back to a central network. The network connects to a File and Print Server. Internet access is handled via a modem or router, while internet Filtering , Proxy and Web Caching are all handled via a dedicated server.

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Advantages of Networking

Speed.
Networks provide a very rapid method for sharing and transferring files. Without a network, files are shared by copying them to floppy disks, then carrying or sending the disks from one computer to another. This method of transferring files in this manner is very time-consuming.

Cost.
The network version of most software programs are available at considerable savings when compared to buying individually licensed copies. Besides monetary savings, sharing a program on a network allows for easier upgrading of the program. The changes have to be done only once, on the file server, instead of on all the individual workstations.

Centralized Software Management.
One of the greatest benefits of installing a network at a school is the fact that all of the software can be loaded on one computer (the file server). This eliminates that need to spend time and energy installing updates and tracking files on independent computers throughout the building.

Resource Sharing.
Sharing resources is another area in which a network exceeds stand-alone computers. Most schools cannot afford enough laser printers, fax machines, modems, scanners, and CD-ROM players for each computer. However, if these or similar peripherals are added to a network, they can be shared by many users.

Flexible Access.
School networks allow students to access their files from computers throughout the school. Students can begin an assignment in their classroom, save part of it on a public access area of the network, then go to the media center after school to finish their work. Students can also work cooperatively through the network.

Security.
Files and programs on a network can be designated as "copy inhibit," so that you do not have to worry about illegal copying of programs. Also, passwords can be established for specific directories to restrict access to authorized users.

Main challenges of installing a School Network
Costs
Although a network will generally save money over time, the initial costs can be substantial, and the installation may require the services of a technician.
Requires Administrative Time.
Proper maintenance of a network requires considerable time and expertise. Many schools have installed a network, only to find that they did not budget for the necessary administrative support.

File Server May Fail.
Although a file server is no more susceptible to failure than any other computer, when the files server "goes down," the entire network may come to a halt. When this happens, the entire school may lose access to necessary programs and files.

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Wireless Network Components

There are certain parallels between the equipment used to build a WLAN and that used in a traditional wired LAN. Both networks require network interface cards or network adapter cards. A wireless LAN PC card, which contains an in-built antenna, is used to connect notebook computers to a wireless network. Usually, this is inserted into the relevant slot in the side of the notebook, but some may be internal to the notebook. Desktop computers can also connect to a wireless network if a wireless network card is inserted into one of its internal PCI slots.
In a wireless network, an 'access point' has a similar function to the hub in wired networks. It broadcasts and receives signals to and from the surrounding computers via their adapter card. It is also the point where a wireless network can be connected into an existing wired network.
The most obvious difference between wireless and wired networks, however, is that the latter uses some form of cable to connect computers together. A wireless network does not need cable to form a physical connection between computers.

Wireless Network Configurations
Wireless networks can be configured in an ad hoc/peer-to-peer arrangement or as a local area network.

Ad Hoc/Peer-to-Peer Configuration
This is the most basic wireless network configuration. It relies on the wireless network adapters installed in the computers that are communicating with each other. A computer within range of the transmitting computer can connect to it. However, if a number of computers are networked in this way, they must remain within range of each other. Even though this configuration has no real administration overhead, it should only be a consideration for very small installations.

Benefits and Educational Uses
The installation of cables is time consuming and expensive. The advantages of not doing so are apparent:
the amount of work required and the time taken to complete it are significantly reduced the network is accessible in places where wiring would have been difficult or impossible with no cables linking computers together, cable-related faults and network downtime are minimised Where a wireless network is in place, teachers or students can have continuous access to the network, even as they move with their equipment from class to class.
The space over which a wireless network operates is not planar but spherical. Therefore, in a multi-level site, network access is available in rooms above or below the access point, without the need for additional infrastructure.
In a location within a school where network access is required occasionally, desktop computers fitted with wireless network cards can be placed on trolleys and moved from location to location. They can also be located in areas where group work is taking place. As they are connected to the network, documents and files can be shared, and access to the Internet is available, enhancing group project work.
As the range of the wireless network extends outside the building, students and teachers can use wireless devices to gather and record data outside, e.g., as part of a science experiment or individual performance data as part of a PE class.

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advantages and disadvantages of a Wireless LAN?

What are the advantages and disadvantages of a Wireless LAN?

Wireless LANs have advantages and disadvantages when compared with wired LANs. A wireless LAN will make it simple to add or move workstations, and to install access points to provide connectivity in areas where it is difficult to lay cable. Temporary or semi-permanent buildings that are in range of an access point can be wirelessly connected to a LAN to give these buildings connectivity. Where computer labs are used in schools, the computers (laptops) could be put on a mobile cart and wheeled from classroom to classroom, providing they are in range of access points. Wired network points would be needed for each of the access points.

A WLAN has some specific advantages:

• It is easier to add or move workstations
• It is easier to provide connectivity in areas where it is difficult to lay cable
• Installation can be fast and easy and can eliminate the need to pull cable through walls and ceilings
• Access to the network can be from anywhere in the school within range of an access point
• Portable or semi-permanent buildings can be connected using a wireless LAN
• Where laptops are used, the ‘computer suite’ can be moved from classroom to classroom on mobile carts
• While the initial investment required for wireless LAN hardware can be similar to the cost of wired LAN hardware, installation expenses can be significantly lower
• Where a school is located on more than one site (such as on two sides of a road), it is possible with directional antennae, to avoid digging trenches under roads to connect the sites
• In historic buildings where traditional cabling would compromise the façade, a wireless LAN can avoid drilling holes in walls
• Long-term cost benefits can be found in dynamic environments requiring frequent moves and changes
• They allows the possibility of individual pupil allocation of wireless devices that move around the school with the pupil.
  

WLANs also have some disadvantages:

• As the number of computers using the network increases, the data transfer rate to each computer will decrease accordingly
• As standards change, it may be necessary to replace wireless cards and/or access points
• Lower wireless bandwidth means some applications such as video streaming will be more effective on a wired LAN
• Security is more difficult to guarantee, and requires configuration
• Devices will only operate at a limited distance from an access point, with the distance determined by the standard used and buildings and other obstacles between the access point and the user
• A wired LAN is most likely to be required to provide a backbone to the wireless LAN; a wireless LAN should be a supplement to a wired LAN and not a complete solution
• Long-term cost benefits are harder to achieve in static environments that require few moves and changes
• It is easier to make a wired network ‘future proof’ for high data transfer.
  

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Wireless Networks

The term 'wireless network' refers to two or more computers communicating using standard network rules or protocols, but without the use of cabling to connect the computers together. Instead, the computers use wireless radio signals to send information from one to the other. A wireless local area network (WLAN) consists of two key components: an access point (also called a base station) and a wireless card. Information can be transmitted between these two components as long as they are fairly close together (up to 100 metres indoors or 350 metres outdoors).

Suppliers would need to visit the schools and conduct a site survey. This will determine the number of base stations you need and the best place(s) to locate them. A site survey will also enable each supplier to provide you with a detailed quote. It is important to contact a number of different suppliers as prices, equipment and opinions may vary. When the term 'wireless network' is used today, it usually refers to a wireless local area network or WLAN. A WLAN can be installed as the sole network in a school or building. However, it can also be used to extend an existing wired network to areas where wiring would be too difficult or too expensive to implement, or to areas located away from the main network or main building. Wireless networks can be configured to provide the same network functionality as wired networks, ranging from simple peer-to-peer configurations to large-scale networks accommodating hundreds of users.

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Hub and Switch

A hub is a device used to connect a PC to the network. The function of a hub is to direct information around the network, facilitating communication between all connected devices. However in new installations switches should be used instead of hubs as they are more effective and provide better performance. A switch, which is often termed a 'smart hub'.
Switches and hubs are technologies or ‘boxes’ to which computers, printers, and other networking devices are connected. Switches are the more recent technology and the accepted way of building today's networks. With switching, each connection gets "dedicated bandwidth" and can operate at full speed. In contrast, a hub shares bandwidth across multiple connections such that activity from one PC or server can slow down the effective speed of other connections on the hub.

Now more affordable than ever, Dual-speed 10/100 autosensing switches are recommended for all school networks. Schools may want to consider upgrading any hub based networks with switches to improve network performance – ie speed of data on the network.

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Network Interface Card (NIC)

A NIC (pronounced 'nick') is also known as a network card. It connects the computer to the cabling, which in turn links all of the computers on the network together. Each computer on a network must have a network card. Most modern network cards are 10/100 NICs and can operate at either 10Mbps or 100Mbps.

Only NICs supporting a minimum of 100Mbps should be used in new installations schools.
Computers with a wireless connection to a network also use a network card (see Advice Sheet 20 for more information on wireless networking).

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