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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