Many businesses became aware of networks when they bought an expensive laser
printer and wanted all the PCs to print to it, or when more than one person
needed to work in an accounting program at the same time. More recently have
come modem sharing, Internet access gateways, email, fax from the desktop and
many other networks applications. Soon even voice will be carried on data
networks. So essential have networks become, even garage operations with two
computers have found them necessary.
Circuit Switched Networks
POTS (Plain Old Telephone Service) is a switched network. When you make a call from one phone to another, switches make an actual connection between the two phones. That connection is dedicated to traffic between those two "nodes" until you hang up.
Today, the #9 crossbar is gone from the telephone system, and the telephone switches are all actually big Unix based computers.
The connection between a dumb terminal and a computer is a "switched" network (even if the only "switch" is plugging and unplugging cables). This includes terminals connected through a modem and computers acting as terminals (terminal emulation) over a modem connection or serial cable.
Packet Switched NetworksComputer to computer networks are "packet" networks. Computers may even act as dumb terminals over a packet network (using the "telnet" protocol) and some new dumb terminals now use telnet to work on a packet network.
A packet network works like the postal system. Information to be transmitted is cut into pages of convenient size. Each page is numbered, put in an envelope (packet) and the envelope is addressed (both destination and return address). It is then dumped into the network to find its way to its destination. At the destination, the pages are reassembled in numbered order. If any page is lost or damaged, it will be re-sent.
Obviously, to participate in a packet network, each "node" (workstation, server, router) must have an "address". Most familiar today is the "IP address" in the form 184.108.40.206. The real address is the "MAC" (Media Access Controller) address hard coded into the device by its manufacturer (say, 0000C0037DF8 for an individual Ethernet card). The IP address is an alias for the MAC address in the same way a url (www.aaxnet.com) is an alias for an IP address.
When you connect to your ISP (Internet Service Provider) through a modem, you establish a switched connection to the ISP, but it's actually carrying packets through a protocol called PPP (Point to Point Protocol) or (rarely now) SLIP (Serial Line Protocol).
Packet networks are somewhat more expensive to build, but tremendously cheaper to operate than circuit switched networks. Packet networks are now even being used for voice (VOIP (Voice Over IP)).
How it Works
Network "client" software running within each workstation includes a module called a redirector. The redirector intercepts data traffic which would normally go to a disk drive, printer, modem or other device attached to the computer and redirects it over the network to "resources" of similar type offered by some other computer.
In this way, a Windows computer which physically has only a "C:" hard disk, can be told it also has an "F:" hard disk. Any traffic intended for drive F: is actually intercepted by the redirector and redirected over the network to the hard disk of another computer. To the user and his software, it looks as though the F: drive is attached to his own workstation. The same works for printers and modems.
More "network aware" software doesn't need the "F:" alias, but can ask for a network resource by name. For instance, on a NetBIOS network it could ask for \\RHINO\CustData instead of F:. This might be a hard disk or directory server RHINO is offering on the network under the name CustData. Perhaps, for instance, it's actually RHINO's D: drive. Much software just isn't this smart, and it's also easier to tell users about their "F: drive" than it is to tell them about \\RHINO\CustData, but the resource name is more reliable.
A computer offering resources for use by other computers is called a
"server". A computer using the resources offered by others is called a
"client", or "workstation". In many networking systems, a computer can be
both a client and server at the same time.
In a peer-to-peer network all the computers are roughly equal. All are workstations, but each may offer its resources (hard disks, printers, modems, CD-ROMs) for use by the other computers on the network, thus being a part time server, or peer.
Even today, there are offices where the work is unstructured and peer-to-peer is appropriate for print sharing and general file transfer work. The main problems with peer-to-peer are:
Artisoft's LANtastic was king of peer-to-peer network software, and can connect DOS, Windows 3.1, Windows95/98, OS/2 and Windows NT workstations as equals. LANtastic, however, has faded because Microsoft set out to destroy it. Peer-to-peer networking capability now comes "free" with Windows95/98, NT and Windows 2000. LANtastic offers better performance, better management, better security, and includes many Internet and communications features, but it isn't "free".
Microsoft networking is based on IBM's antique PCNet (you didn't think Microsoft invented it themselves, did you?), and is pure Microsoft - just "good enough" but "free", so it drives competitors with better products out of business. Win95/98 networking has no security (none), is unstable, frustrating, feature poor, and it's performance sucks - but when you finally can't take it any more, Microsoft has just the solution for your problems - Windows NT/2000 Server! Not at all free, but "compatible".
At the high end, Unix and Linux support both peer-to-peer and server based networking simultaneously (and serial terminals too). The Internet is the world's largest peer-to-peer network. (top)
CS networks were the darling of the industry a few year ago, and if you weren't deploying Client/Server, you just weren't "with the program". Unfortunately, the way Client/Server was deployed resulted in absolutely stunning administration costs (see Failure on a Grand Scale for details), and it is now commonly considered dead.
A new generation of Client/Server is being quietly deployed. The most advanced version is IBM's WSOD (WorkSpace On Demand) but it is being deployed mainly by banks, airlines and other highly critical businesses, because no one else wants to admit to running OS/2 when "Windows NT is clearly the future". WSOD eliminates client administration problems, making Client/Server not only practical, but economical.
The other new version of Client/Server is the Java/NC (Network Computer)
environment. Because this environment didn't take over the world in 90 days,
the computer magazines have all declared Java/NC dead, but it is being
successfully deployed by corporations at an accelerating rate and will soon be
working its way down into small business.
The proliferation of Servers: In the past, a modest sized business would have one server, a larger business one at each branch or campus building. Now even modest sized companies have swarms of servers scattered all to Hell and back. This is caused by the growing popularity of Microsoft's Windows NT as server operating system of choice. Its poor performance and instability mean companies must have (and Microsoft strongly recommends) a separate physical server for each significant server process. This has become a major administration and security headache.
Among enterprises that have gone the Windows NT route, there is now a counter
movement to consolidate most server processes on a big honk'n high performance
Sun Enterprise or IBM AS/400 server, or even an IBM 360 (the dinosaurs are back,
"stronger then ever!"). These machines do not do Windows.
With the exception of NetWare, the server and client parts of the NOS are distinct processes running under a general operating system such as Unix or Windows NT. A single computer may host both server and client parts and may simultaneously act as a server and as a workstation. This configuration is referred to as a peer.
Here are the common NOS, listed roughly in order of overall power. .
Microsoft Networking is Microsoft's interpretation of IBM's old PC-Net network (you didn't think Microsoft actually "innovated", did you?). It is variously known as a NetBIOS, NetBEUI (Enhance User Interface) or SMB (Server Message Block) network.
Microsoft's Windows95/98 Networking is prone to many ailments, such as suddenly forgetting where other computers are. It has NO security, and, in fact, compromises the security of any other network it is attached to. Management and performance tuning features are almost non-existent.
Microsoft Networking Supports peers: DOS (client only), Windows 3.1x, Windows95/98,Windows NT, OS/2 (reluctantly).
AAx Recommendation: Think real hard about putting in a
Linux/SAMBA server to get some stability.
LANtastic provides a good degree of security, stability and management features. The Windows95/98 version has, however, been wounded by Microsoft's insistence Artisoft go through their services (limiting how much better LANtastic can be). Every time Windows is updated Microsoft will break LANtastic (as they did with Windows98), and you will have to update to the latest version of LANtastic to get a fix.
Lantastic Supports peers/workstations: DOS, Windows 3.1x, OS/2, Windows95/98, and Windows NT. If you have a situation where a DOS machine must act as a server, you have few other options. Microsoft Networking can't do that.
AAx recommendation: before Windows95 we enthusiastically
endorsed LANtastic, but, because Microsoft deliberately sabotaged it, we
have had to temper that enthusiasm. If you already have LANtastic, stick
with it until you're ready for a server based network.
OS/2 peer networking is compatible with Windows NT Server and Windows workstations running Microsoft Networking. Microsoft has tried to make Microsoft Networking incompatible, but they have only created a few annoyances - it is IBM's network, after all, and they are limited by what they can do without breaking their own stuff.
Of course, you have to be running OS/2 workstations to use it.
OS/2 peer supports peers/workstations: OS/2, Windows 3.1x, Windows95/98, Windows NT, and DOS (client only).
AAx recommendation: This is what we use in our office, and
we like its trouble free operation (We are also networked to a Linux host where
our accounting software lives).
An NT/2000 server tends to stabilize Microsoft Networking and provides a reasonable degree of security at the server. Security at the workstations is still between zilch and none. Properly set up, an NT 4.0 server can run for weeks without being rebooted, but that is not as good as NT 3.51, which could run months. Windows 2000 server can run for months.
All in all, Windows NT Server is a decent and capable departmental server, though not outstanding in any way. It provides basic file and print services suitable for a small business, comes with a lot of Internet stuff most people don't use, and is manageable by a version of the familiar Windows95 user interface. The problem is not with What Windows NT is, but in what Microsoft claims it is. It is not a fully scalable, rock stable, enterprise grade operating worthy of betting a corporation on.
Windows 2000 Server and Advanced Server are much more stable than Windows NT 4.0, and can scale to larger networks, but there are some very distinct downsides to Windows 2000, which you will find in our article Adopting Windows 2000.
Window 2000 Datacenter is designed to compete with Unix in large datacenters. It will not be available separately, but pre-installed on certain high-end Intel based servers. It has just been released and has not yet established a track record.
Microsoft has made some of its key software modules to run only on NT/2000 Server. In the case of Microsoft Exchange (email messaging), Microsoft Back Office, Microsoft SQL Server, and Microsoft Internet Information Server (IIS) are some of the other packages that will run only on NT Server. The coming Office 2000 will also be dependent on NT/2000 Server for full function (colaboration features and such). If you choose any of these Microsoft products you have no choice but to run them on NT/2000 Server. Your main file and print server could still be NetWare, Warp Server or Linux, though.
NT Supports clients: DOS (client only) Windows 3.1, Windows95/98, Windows NT, OS/2 (reluctantly).
AAx recommendation: Why? You can get so much more with
WarpServer or Linux/SAMBA - unless you have chosen to use Microsoft Back
Office, Microsoft SQL Server, Microsoft Exchange or Microsoft IIS (there are
better, cheaper alternatives to all of these).
NetWare is excellent as a high performance file and print server, but is seldom used as an applications server (client/server database server). Novell Directory Services make it highly manageable in large organizations, but are overkill for smaller organizations. NetWare is highly stable and servers have been known to run for years without a reboot. Novell has been having a hard time getting users of older versions to upgrade because they work too well.
NetWare 5.1 has now succeeded the very well received 5.0. It was supposed to come out at the same time as NT 5.0 (Windows 2000), but beat it by more than a year (and has all the features that were promised). Novell is banking heavily on Java to bring it forward and into the application server market.
A very large pool of people familiar with NetWare, including many CNEs (Certified NetWare Engineers) is available. The problem of "paper CNEs" with no experience has largely solved itself - they've either gained experience or moved on to Microsoft.
NetWare Supports clients: DOS, Windows 3.1x, Windows95/98, Windows NT, OS/2, Linux (Caldera).
AAx Recommendation: If you already have or are comfortable
with NetWare, stay with it. It is problematical for new installations because
Novell has ignored the small business market for so long. Linux/SAMBA is
a lot easier to understand and administer.
Linux can be configured as a workstation, a peer, or a server. It can also be configured as a performance cluster to achieve supercomputer level performance at a ridiculously low price. The U.S Postal service does all its OCR reading and sorting on 900 Linux clusters at centers across the U.S., and all the difficult image rendering for the film Titanic was done on a Linux cluster.
Linux servers can easily be administered remotely with a modem or telnet connection. This is a great cost saver for a small business because no administrative staff is needed on-site, the company's VAR or integrator can do it from his/her office, even from thousands of miles away.
Outfitted with the SAMBA module, a Linux server can act as an SMB (Server Message Block) server. SMB - SAMBA, get it? In other words, workstations can't tell it from a Windows NT Server, except it's faster and doesn't crash. Note, however that Linux cannot host Microosft Server modules (SQL Server, Exchange, SII, Back Office).
Linux supports clients/peers/terminals: any computer supporting TCP/IP networking (basically, everything this side of the Apple II), ASCII terminals, or anything that can emulate an ASCII terminal (Apple II, microwave ovens, digital clocks, coffee makers, etc.).
Linux/SAMBA supports clients: native support for DOS, Windows 3.1x, Windows95/98, Windows NT, OS/2.
AAx recommendation: With major networking companies like
Cisco ripping out NT in favor of Linux/SAMBA, with so much of the Internet
running on Linux, and with corporate IS departments sneaking it into NT
networks so they have something that works, and considering its low cost, we
can only give Linux and Linux/SAMBA our highest recommendation as a small
WarpServer is highly compatible with NT Server networks - they are both based on IBM's PC-Net and further developed cooperatively between IBM and Microsoft (before the split). IBM's version is simply implemented a lot better than Microsoft's version. The new Aurora (v5.0) WarpServer has added features for managing NT Servers, making it a good master server when you must have NT servers (because you have MS SQL Server, MS Back Office, MS Exchange Server or MS Internet Information Server (IIS) - all NT specific).
While OS/2 WarpServer is normally administered using graphic tools, just as NT is, it can easily be administered from afar by modem, either using the graphic interface like NT, or from the command line like Unix. You can use a WarpServer computer as a workstation (peer) but it is not recommended (see disadvantages of peer-to-peer).
When PC magazines first compared WarpServer to NT, they panned Warp Server for not supporting multiple processors. They did, though, have to note that WarpServer on a single processor out performed NT on a multiple processor. Since WarpServer now supports multiple processors, and does so far more effectively than NT, no magazine dares do a comparative review (it would produce the "wrong" answer).
OS/2 WarpServer supports clients: OS/2, DOS, Windows 3.1x, Windows95/98, Windows NT.
AAx recommendation: This is simply one of the best servers
money can buy, and we recommend it highly. If you prefer a graphical
administration interface rather than Linux/SAMBA's text mode, and still want
a server that performs, this is for you.
Everything said above in the Linux section applies to Unix except Unix is sold by major corporations (IBM, Compaq, SCO, Sun Microsystems, SGI, Data General, etc.).
As with Linux, a Unix box can run SAMBA so it can look just like an amazingly fast, amazingly stable NT Server
High security versions of Unix are available for special situations.
Note: Caldera, a major Linux vendor, has purchased the Unix assets of SCO, the largest Unix vendor. Caldera will be blending it's Unix and Linux holdings into a single coherent product line running from desktop PC to corporate datacenter.
Unix supports clients/peers/terminals: any computer supporting TCP/IP networking (basically, everything this side of the Apple II), ASCII terminals, or anything that can emulate an ASCII terminal (Apple II, microwave ovens, digital clocks, coffee makers, etc.).
Unix/SAMBA supports clients: native support for DOS, Windows 3.1x, Windows95/98, Windows NT, OS/2.
AAx recommendation: Highly recommended. More expensive
than Linux, but you can get well integrated communications and server suites
fully backed by a major corporate vendor.
AS/400 scales with your growth, offering models starting at about $7,000 and going well beyond $700,000 for the enterprise crowd.
If you need the advantages of the AS/400, but really, really need NT Server too, the AS/400 offers plug-in boards that run NT. You can have as many as 14 of these running as 14 NT Servers in a single AS/400 box. Of course, those NT Servers aren't going to be more reliable or any faster than NT Server on any other box, but you can reboot them individually without shutting down the AS/400 side.
A funny story: Microsoft has so conditioned people to the dismal quality of their products, one consultant reports a client who insists on rebooting his AS/400 every morning because, "the PCs act funny if we don't reboot every day, so we'd better do the AS/400 too". Most AS/400s are rebooted only every few years. You can replace hard disks, install applications, even upgrade the operating system without rebooting.
AS/400 Supports clients: OS/2, DOS, Windows 3.1x, Windows95/98, Windows NT, 5250 class terminals.
AAx recommendation: If you need total security, absolute
virus immunity and extreme uptime in a high performance package, what other
choice do you have? (NOS)
A Topology is a wiring layout. The current preferred topology is a Star layout done to a specification called "Structured Cabling". See Wire and Cable for more detail.
A Protocol is a convention by which devices agree to communicate with each other. There are many protocols in various "layers" of every network. For convenience, you can ignore the ISO 7-layer protocol cake and just divide them into two categories: Physical (related to a specific kind of network card and its associated wiring "topology") and Logical (all others). We will ignore the fact that any bozo that read a book can (and will) make a case for the "incorrectness" of this terminology.
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