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Numerous network are currently operating around the world:
Networks differs in their:
Novell NetWare is the most popular network system in the PC world. It was designed to be used by companies downsizing from a mainframe to a network of PCs. Novell NetWare is based on the client-server model.
NetWare uses a proprietary protocol stack (Fig. 1-22). It looks more like TCP/IP than like OSI.
Fig. 1-22. The Novell Netware reference model.
The physical and data layers can be chosen from among various industry standards (Ethernet, IBM token ring, ARCnet).
The network layer runs an unreliable internetwork connectionless protocol called IPX, functionally similar to IP.
Above IPX comes a connection-oriented transport protocol called NCP (Network Core Protocol) providing various other services besides user data transport. A second protocol, SPX, is also available, but provides only transport. The session and presentation layers do not exist. Various application protocols are present in the application layer.
The IPX packet consists of the following fields:
The maximum size of the packet is determined by the underlying network.
About once a minute, each server broadcasts a packet giving its address and telling what services it offers (by using SAP - Service Advertising Protocol). The packets are collected by special agent processes running on the router machines. The agents use the information contained in them to construct databases of which servers are running where.
When a client machine is booted, the following procedures take place:
NSF (the US National Science Foundation), seeing an enormous impact of the ARPANET, set up, by the late 1970s, a virtual network CSNET. It was centered around a single machine, supported dial-up lines, and had connections to the ARPANET and other networks. Using CSNET, academic researchers could call up and leave e-mail for other people to pick up later.
By 1984, NSF began designing a high-speed successor to the ARPANET for all university research groups. First, the supercomputer centers in San Diego, Boulder, Champaign, Pittsburgh, Ithaca, and Princeton were connected establishing the backbone of the network. Each supercomputer was given a little brother, consisting of an LSI-11 microcomputer called a fuzzball. The fuzzballs were connected with 56 kbps leased lines and formed the subnet, the same hardware technology as the ARPANET used. The software technology was different however: the fuzzballs spoke TCP/IP right from the start, making it the first TCP/IP WAN.
NSF also funded about 20 regional networks that connected to the backbone to allow users at thousands of universities, research labs, libraries, and museums to access any of the computers and to communicate with one another. The complete network, including the backbone and the regional networks, was called NSFNET. It was connected to the ARPANET through a link in the Carnegie-Mellon machine room (Fig. 1-26).
Fig. 1-26. The NSFNET backbone in 1988.
NSFNET was an instantaneous success and was overloaded from the word go. NSF immediately began planning its successor and the second version of the backbone was based on fiber optic channels at 448 kbps. In 1990, the second backbone was upgraded to 1.5 Mbps.
In 1990, a nonprofit corporation ANS (Advanced Networks and Services), initiated by NSF, took over the NSFNET and upgraded the 1.5 Mbps links to 45 Mbps to form ANSNET.
By 1995, the NSFNET backbone was no longer needed to interconnect NSF regional networks because numerous companies were running commercial IP networks. ANSNET was sold to America Online in 1995 and regional networks had to buy commercial IP services to interconnect.
To ease the transition, NSF awarded contracts to four different network operators to establish a NAP (Network Access Point). These NAP were established in San Francisco, Chicago, Washington and New York. Every network operator that wanted to provide backbone services to the NSF regional networks had to connect to all the NAPs. Consequently the network carriers were forced to compete for the regional networks business on the basis of service and price. The concept of single default backbone was replaced by a commercially driven competitive infrastructure.
In December 1991, the U.S. Congress passed a bill authorizing NREN, the National Research and Educational Network, the research successor to NSFNET, only running at gigabit speeds. The goal was a national network running at 3Gbps before the millennium. This network is to act as a prototype for the much-discussed information superhighway.
Other countries and regions are also building networks comparable to
NSFNET. In Europe, EBONE is an IP backbone for research organizations
and EuropaNET is a more commercially oriented network. Both connect numerous
cities in Europe with 2 Mbps lines. Upgrades to 34 Mbps are in
progress. Each country in Europe has one or more national networks, which
are roughly comparable to the NSF regional networks.
1.5.3. The Internet
The number of networks, machines, and users connected to the ARPANET grew rapidly after TCP/IP became the only official protocol on Jan. 1, 1983. When NSFNET and ARPANET were interconnected, the grows became exponential. Connection were also made to networks in Canada, Europe, and the Pacific.
Sometime in the mid-1980s, people began viewing the collection of networks as an internet, and later as the Internet, although there was no official dedication with some politician breaking a bottle of champagne over a fuzzball.
Some facts about the growth of the Internet:
The glue that holds the Internet together is the TCP/IP reference model and the TCP/IP protocol stack.
A definition what does it mean to be on the Internet: a machine is on the Internet if it runs the TCP/IP protocol stack, has an IP address, and has the ability to send and receive IP packets to all the other machines on the Internet.
With exponential growth, the old informal way of running the Internet no longer works. In January 1992, the Internet Society was set up, to promote the use of the Internet and eventually take over managing it.
Main applications provided by the Internet:
Up until early 1990s, the Internet was largely populated by researchers. One
new application, WWW (World Wide Web), changed all that and brought millions
of new nonacademic users to the net. This application was invented by
CERN physicist Tim Berners-Lee.
1.5.4. Gigabit Testbeds
The Internet backbones operate at megabit speeds. The next step is gigabit networking. With each increase in the network bandwidth, new application become possible, so it is wit gigabit networks.
Gigabit networks provide better bandwidth than megabit networks, but not much better delay. For example, sending a 1 Kbit packet from New York to San Francisco at 1 Mbps takes 1 msec to pump the bits out and 20 msec for the transcontinental delay, for total of 21 msec. A 1 Gbps network can reduce this to 20.001 msec (the bits go out faster, the transcontinental delay remains the same, given by the speed of light in optical fiber 200.000 km/sec independent of the data rate. So the gigabits networks may only help for wide area applications where the bandwidth is what counts and are not helpful for those, where low delay is critical.
Two of the possible gigabit applications are telemedicine (the transfer of high quality images for diagnostic purposes) and virtual meetings (using some methods of virtual reality).
Starting in 1989, ARPA and NSF jointly agreed to finance a number of university-industry gigabits testbed.