Local Area Networks (LANs) generally connect the imaging equipment, manage and storage devices, and displays within an institution.

Wide Area Networks (WANs) provide connections with users outside of a local institution.  The internet is a major component of many WANs.

An important characteristic of a network is the speed with which it can transmit the bits (pulses).

As we will soon see, this depends on the type of network.

As we know, this depends on the number of pixels and the number of bits per pixel (the pixel bit depth).

The matrix size is generally a characteristic of each specific imaging modality and covers a considerable range as shown here.

Speed is a major issue with WANs, especially with the network connections to the internet.

A fiber optic cable is made-up of transparent strands of glass fibers.

Data is transmitted as a series of light pulses through the fibers.

It is usually practical to install this type of network within an institution.

An alternative is to use electronic cables for LANs.

Many LANs (universities, airports, coffee shops, etc) also provide the capability  for wireless connections to laptop computers, PDAs, etc.

One approach, especially for institutions not located in major metropolitan areas where fiber optical cable connections are practical, is to lease a group of telephone lines. 

These can be made-up of different numbers of lines, depending on the required capacity (speed).

A so-called T1 line is a common configuration.

The Internet Service Provider (ISP) is the institution or commercial organization that has a high-speed connection to the internet "backbone" and then provides internet services to the individual users.

There are a variety of methods than can be used to connect to the ISP.

Each connection method has some limitations on speed as we are about to discover.

The modem converts the digital data (bits) into sound (tones) that will pass over the telephone line.

The advantage of this type of connection is that telephone lines are available just about everywhere.

The disadvantage is that conventional telephone circuits have a limit on how fast they can transmit data.  That is usually a maximum of 56,000 bits per second, but is often much less because of the condition of the line, distance, etc. 

It is based on some special equipment that makes it possible to transmit the digital data, at high speeds, over the local telephone lines.  It does not conflict with normal use of the telephone line for voice communications.

One limitation is that the user must be relatively close (within three miles) of the telephone company facility.

Therefore, TV cable companies can be high-speed internet service providers.

Special equipment, usually called a Cable Modem, can be installed to separate the digital data from the TV signals.

Each method has speed limitations that must be considered.

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