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admin on Sunday, May 17th, 2009 |
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1. Network interface(Data link) layer
2. Network layer
3. Transport layer
4. Application layer
Network interface layer
The lowest layer of the TCP/IP model. Its task is to provide access to the transmission physical medium and it differs according to the implementation of the medium.
Network layer
The network layer provides network addressing, routing and datagram transmission. Used protocols that will be of interest further regarding DHCP are IP and ARP.
IP protocol
It is the basic protocol of the network layer and in general the internet as a whole. It sends datagrams, which are independent units that contain information about the destination, source and the sequence number of the datagram. The sequence number is used for message reconstruction, since the delivery order of the datagrams might not be the same as their order in the message and delivery reliability isn’t guaranteed at all.
IP protocol versions:
” IP v4 – 32 bit addresses. Provides approximately 4 billion unique addresses which aren’t sufficient at present times.
” IP v6 – 128 bit addresses. The transition to v6 will bring (is bringing) higher security, QoS, packet segmentation and many more IP addresses. (the transition from IP v4 to IP v6 must be supported by the system provider)
ARP protocol
The ARP abbreviation stands for Address Resolution Protocol. This protocol is used to find the physical address (MAC) based on a known IP address. If required ARP sends information… Read the rest
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admin on Tuesday, May 12th, 2009 |
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If you already have a wireless network for your computers, you may be very interested in what’s coming next. Would you like it if your PDA, your mobile phone, your mp3 player and almost everything else you connect to your computer could be wireless too? It’s already a reality…
Personal Area Network.
Using wireless networking with your personal gadgets is often called PAN, which stands for Personal Area Network. The idea is that, in the future, we’ll all have laptop computers with their batteries charged and no more need to connect any wires to them at all — you just place your Bluetooth device near the computer, and the computer sees it and can use it straightaway.
Bluetooth has been around and in-use since 1999, and it’s only getting more popular. It was designed to be secure, low cost, and easy to use from day one.
There are two classes of Bluetooth that are in popular use: class 1 and class 2. Class 2 is the most common and cheaper standard, allowing you to use a device that is up to 10 metres (32 feet) away. Class 1 is rarer, but you can still find devices that use it easily enough, and it has ten times the range: 100 metres or 320 feet.
How Does It Work?
Bluetooth is more flexible than 802.11 wireless networking, in exchange for the shorter range. Essentially, a Bluetooth-enabled computer has one Bluetooth receiver installed in it, and this receiver can then be used with… Read the rest
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admin on Monday, May 11th, 2009 |
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Optic fibers are used widely in the medical field for diagnosing and treating a variety of ailments. Because optic fibers can be made extremely thin and made into flexible strands, they can be used for insertion into blood vessels, lungs and other parts of the body. Optic fibers have been enabling physicians to look and work inside the body through tiny incisions with an instrument called an Endoscope. An Endoscope is a medical instrument made to carry two bundles of optic fibers inside one long tube. One bundle of optic fiber directs light at the tissue being examined, while the other bundle of optic fiber transmits light reflected from the tissue, producing a detailed image. Endoscopes may be designed to look into specific areas of the human body. For example, physicians can use the optic fibers in the Endoscope to examine knees, shoulders and other joints in the body.
Arthroscopy (pronounced ahr-THROS-kuh-pee) is a technique of using another medical instrument called the Arthroscope. This instrument is straight and cylinder-like with a series of lenses and optic fiber bundles that come in sizes of 1/12 to 1/5 inch (2 to 5 millimeters.) The Arthroscope is used to examine a joint in a body, such as knee joints, ankles, elbows, hips and shoulders. This is done by the Arthroscope being inserted into a joint of the body through a small incision. A light is then transmitted by the use of the optic fibers to the tip of the Arthroscope to illuminate the… Read the rest