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On the line a noise burst can destroy a frame completely. If frame is destroyed the data link layer software on the source machine can retransmit the frame. However, multiple transmissions of the same frame cause the possibility of duplicate frames. If the acknowledgement frame from the receiver to sender were lost then duplicate frame could be sent. It is function of this layer to solve the problems caused by damaged, lost and duplicate frames. The data link layer provides number of different service classes to the network layer, each of a different quality and with a different price.

Another design issue that takes place within data link layer is how to keep a fast transmitter from drowning a slow receiver in data. Some traffic control mechanism must be applied to let the transmitter know how much buffer space the receiver has at the moment. Frequently, this flow control and the error handling are incorporated.
Broadcast networks possess some additional issue in the data link layer: how to control access to the shared channel. The medium access sub layer, a special sub layer of the data link layer related with this problem.

3) Network Layer
The Network layer is designed for controlling the operation of the subnet. An important design issue of network layer is determining how packets are routed from one route to another route. Routes are dependent upon static tables that are "wired into" the network and rarely changed. At the start of each conversation routes are determined. They can be highly dynamic, being determined additionally to reflect the current network load for each packet.

If in the subnet too many packets are present at the same time, they will get in each other’s way, forming bottleneck. The control of such congestion of packets is done by the network layer.
When a packet travel from one source to another destination many problems may arise. The addressing used by the first network may be different from the destination. The destination may not accept the packet at all because it is too large. The protocol used may differ and so on. It is function of network layer to overcome all these problems to permit heterogeneous networks to be interconnected. In Broadcast network, the routing provided is simple, so the network layer is often thin or even nonexistent.

4) Transport Layer
Its main function is to take data from the session layer and divide the data into smaller units and pass these to the network layer and check that the pieces all arrive correctly at the other end. Transport layer perform all this function efficiently and in such way that separates the upper layers from the inevitable changes in the hardware technology.

The transport layer creates a distinct network connection under normal condition for each transport connection required by the session layer. If the transport connection needs a high throughput then the transport layer might create multiple network connection, dividing the data among the network connection to improve throughput. On the other hand if creating or maintaining a network connection is expensive then in order to reduce the cost the transport layer might multiplex several transport connections onto the same network connection. It makes the multiplexing transparent to the session layer.

It also determines what type of services to provide to upper session layer and indirectly to users of the network. The transport connection must be an error free point to point channel that transports message or bytes the order in which they sent. Other transport services are delivery of isolated messages with no guarantee about the order of delivery and broadcasting of message to multiple destinations.
It is a true end to end layer from source to destination

There are many brands of portable GPS receivers that people use, however Magellan GPS is one of the better known ones. Most people install GPS systems in their automobiles to assist with directions, monitor what their teenage kids are doing, or track their car in the event of a theft.

Some other reasons that people carry these portable GPS units would be to take hiking or hunting to prevent them from losing their directions. Regardless of the reason that you wish to utilize a Magellan GPS, you should do your research prior to shopping around for one that is at the right price with the right features.

Initial Considerations

Before you buy you a GPS system decide what features you need. Is it more significant to you that it be light or rugged? Is battery longevity a consideration? Is there a manufacturers guarantee in regards to the hardware itself? Additionally, the majority of GPS systems will require periodic software updates.

In other words, you will need to install updated maps onto your GPS receiver periodically. Also, the same as with any type of software, it will require some minor patches at times. Regardless of where you purchase it, learn about the type of tech support the dealers give you, and do a comparison for the prices when it comes to any monthly monitoring prior to making your choice.

Shopping in a Retail Outlet

The majority of stores, particularly outdoor and automotive stores have Magellan GPS systems in stock. If you have a store discount card or some other method of getting a better price, making your purchase this way may be the best method. Particularly when the holidays are near, you may find exceptional discounts in prices. Discounts on GPS prices can range from as little as $100 to as high as $1000. Keep in mind that you should use promotions that allow for a certain percentage discount instead of a set amount off for large ticket products.

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News & Evens
vehicle tracking system is an electronic device installed in a vehicle to enable the owner or a third party to track the vehicle's location. Most modern vehicle tracking systems use Global Positioning System (GPS) modules for accurate location of the vehicle. Many systems also combine a communications component such as cellular or satellite transmitters to communicate the vehicle’s location to a remote user. Vehicle information can be viewed on electronic maps via the Internet or specialized software.
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