Interconnecting networks

      Providing access to created electronic collections is inherent in the development of digital libraries. Unlike physical libraries with books and journals sitting on a shelf, digital libraries occupy space on computers that are accessible from end-user workstations connected through local and global networks. For example, a signal traveling through a simple network connection between the host server and the end-user follows this typical path: from the server through a network card, to a cable connected to a series of routers and switches comprising the local, regional, national and global Internet backbones. Then depending on the destination is directed back down the hierarchy to the national, regional, and local backbones through routers and switches to a cable connected to the network card in the desktop computer of the end-user. A modem-connected PC would use the public telephone system to connect to the Internet backbones.

      The communication between so many layers of networking equipment and software is facilitated by a set of complex protocols. That set of protocols (TCP/IP – transmission control protocol/Internet protocol) is based on international open standards which are commonly referred to as the Internet. The dominant Internet protocol is HTTP (hypertext transmission protocol) upon which the World Wide Web is based.

      The capacity, bandwidth and speed of the local and global network to deliver data from the server to the end-user are major concerns when designing and planning for digital libraries. Just as a chain is only as strong as its weakest link, a network is only as fast as its slowest link. Fortunately, commercial and e-business development entities share these concerns and extensive capital investments are being made in global network systems. For example, a PC connected to the Internet with a 56.6 KB modem can communicate at approximately 5.7 KB per second. To transmit a 10 KB text article over a public network would take less than a minute, however, a 600 KB-1,500 KB audio or video clip could take several minutes to transmit to the end-user. Streaming audio and video with efficient compression techniques can reduce transmission times, however, future developments to increase network capacities such as Internet-2 and xDSL will contribute more to the success of digital libraries. Noerr (2000, p.63) provides an excellent discussion of networking issues in the Digital Library Toolkit.