Three Alternatives For Connecting A Macintosh Network

Description: 

Networking Macintosh personal computers

Main Article Text

Apple Talk has made history with 250,000 nodes installed worldwide by the end of 1987 and with a forecast of 750,000 more workstations connected by the end of 1988. We are dealing with modern network architecture and a system of interconnectivity that is practical and easy to install, especially for those who want to share the services of a laser printer or a disk server within a work group. However, even the simple things are sometimes meant to be made complicated, so in these past few months we have begun to hear about LocalTalk, EtherTalk, and even TokenTalk. Therefore, it is legitimate to ask, what of the original AppleTalk system, and what choices are to be made for those whom today would want to connect several Macintosh computers with one another, or to integrate the Apple world with the MS-DOS environment.
There are of course, other aspects of the problem concerning the connection of the Mac with the mini and mainframe computers, but these are beyond the scope of these notes. The heart of the matter central to AppleTalk, is that it is a network system, which is a set of software programs, protocols and hardware interfaces that allow the transfer of information and messages along a connecting cable. Following the modern model Open System interconnect (OSI) codified by the International Organization for Standardization (Iso), AppleTalk divides into seven levels, of which the highest is reserved for operations performed by the software while the other six concern themselves with the management of the actual network. In the upper band, we find the four levels that act as a buffer between programs and network, performing all the logical interface functions and routing packets of information. This is the heart of AppleTalk that takes care of sending information over the network ensuring that they arrive at their destination intact. Below this range we find two levels that directly govern the physical medium of transmission. In this second zone, the electrical signals are manipulated necessitating that they must travel on the cable that connects the various nodes of the network. Of course, varying the type of conductor and transmitting mode, changes the characteristics of these two lower system layers. In the original version of AppleTalk, there was only one type of conductor, the shielded twisted pair cable, and only one protocol transmission, 230.4 Kbits per second. Therefore, originally, it was not necessary to distinguish between upper and lower levels. Today, however, with the availability of the Ethernet card for Macintosh and with the announced production of Token-Ring interface for the world of Apple, new names are being used. So let’s call LocalTalk, the network which is based on the original shielded twisted pair cable provided by Apple, and EtherTalk a LAN which makes use of the coaxial cable capable of transmitting at 10 MBit per second. TokenTalk, finally, is the name of a product that does not exist yet, but that will allow the world of Apple them to take advantage of actualizing the network ring of IBM. The only difference existing between these three types of LAN is in the cable and in the mode of transmitting the physical signal, but the four upper levels remain the domain of AppleTalk.
LocalTalk or EtherTalk
The user chooses which cable to adopt in function of size and network load. Where LocalTalk is ideal for small workgroups that want to communicate within short distances (the maximum length of a section of cable is 300 meters and the number of stations that can be connected are 32), EtherTalk is suitable for large networks, where the speed of transfer and reliability of the lines is a critical factor. Naturally, the price of the two solutions is different. In the first case, we are talking about 95,000 Lire for each LocalTalk connection, in addition to 950,000 Lire, for AppleShare file sharing software and 300,000 Lire for the LaserShare package which allows Printer sharing. The alternative offered by 3Com Ethernet (via Durres 2, 20134 Milan, tel. 02 26410112)the price becomes 1,270,000 Lire for the EtherLink Nb interface card to be mounted on each Macintosh II (this version for Mac, maybe will be available in September), plus 50,000 Lire for the cable (7 meters long) and the special connector that is needed. In addition to these minor costs , one must also add the investment of at least 16,900,000 Lire for the dedicated 3Com server and 985,000 Lire for the Macintosh 3Plus software that needs to be installed. This configuration not only provides the ability to link different Macintosh II machines together, but also opportunities to integrate the worlds of Apple and MS-DOS. Kinetics, imported from List in Italy (Piazza Mazzini 6, 56100 Pisa, tel. 050 44023), offers an economic alternative as it allows one to benefit from the speed of 10 MBps while continuing to use AppleShare software and the Mac II as a network server. Both the EtherPort II and EtherPort SE cards by Kinetics cost 1,450,000 Lire, while the cost of the cables and connectors are roughly equal in cost to that of the cables offered by 3Com. The Kinetics version of the EtherTalk network, can also be connected via special little box of external interfaces (EtherSc) to the MacPlus, and costs 2,100,000 Lire, or 1,900,000 Lire if there is no internal adapter for the coaxial cable (transceiver). The landscape, in reality, is more extensive than described so far, and in the next issue we’ll see how it is possible to achieve good levels of reliability and speed while remaining within the LocalTalk environment.

Roberto Mazzoni