With the proliferation of I-Macs, the legacy network protocol, known as AppleTalk is seeing a bit of resurgence. Due to the fact that AppleTalk utilizes unique names for various sub-components of AppleTalk, it can be a little daunting to understand. In this section, AppleTalk is detangled.
Just as TCP/IP is a collection of protocols and utilities, the same can be said about AppleTalk. For example, instead of saying Domain Name Service (DNS), which is the TCP/IP computer to logical address mapping system, Apple calls this the Name Binding Protocol (NBP). However, the operations are similar. Instead of Address Resolution Protocol (ARP) the firm coined the term, Apple Address Resolution Protocol (AARP). Just as Microsoft NT has workgroups, Apple has a zone, or in more complex cases, zones (more than one zone). Since AppleTalk is peer to peer in nature, the domain model of Microsoft does not translate well.
Since AppleTalk has been around a while, the AppleTalk protocol has been extended from the original specification. The first one is known as Phase 1. A Phase 1 Apple network operates in a single zone. Computers running AppleTalk in a Phase 1 network share a common network number and zone name. What distinguishes each computer is an eight bit binary number (2^8=256, allowing for 253 nodes with the other 3 mathematical combinations being reserved for logistics such as broadcasts). The network name is defined with a 16-bit number. Apple supports sockets with an 8-bit number. Addresses are delivered to the net-tech in the form of ZZZ.NNN, where Z is the Zone or network number and N is the node number (specific device).
AppleTalk gets a bit dicer with Phase 2 or Extended Networks. This mode supports multiple zones, via unique network numbers. As with TCP/IP or IPX, physical cable is (typically) divided into segments, and AppleTalk uses network numbers to identify cable segments. Cable segments can be labeled between 1 and 65,279. Higher numbers are reserved for Phase 1 (legacy) AppleTalk networks.
A non-extended network simply starts numbering the network at 65,280, and node numbers beginning with 1. In a Phase 2 network, one or more routers are declared seed routers. The seed router defines the network numbers and zones, similar in fashion to a DHCP server. Actually, if you are familiar with the dirty details of multicasts in TCP/IP (Class D), extended or Phase 2 AppleTalk networking is very similar. (If not, skip that last sentence!) Once a seed router is part of the AppleTalk network, other routers learn from the seed router(s) and do not propagate network ID information.
Successful routing occurs when routers on a network segment have valid network number ranges and zone lists for that segment. Network range numbers must be contiguous, and this defines the upper limit of nodes on the network. No more than 255 zone name can be stuffed into the zone list, and one must be considered the default zone. All the routers must know what the default zone are as well as the network range and what zones were stuffed in the zone list.
All this data is slung around via the Routing Table Mapping Protocol (RT NT/W2K and AppleTalk NT 4 Server and Windows 2000 (including Professional) support the AppleTalk protocol. The server versions of NT/W2K can either learning or seed router, found in the routing table. Because AppleTalk is "chatty", when entering configuration data, keep entries to the smallest possible and still support the AppleTalk devices.
Since the behavior of AppleTalk is much like NetBEUI with NetBIOS built-in (bummer), the detection of devices being there or not in anything approaching real-time is something not happening. One trick to minimize this Twilight Zone behavior is to realize that in the NT kernel, AppleTalk is a device that can be stopped and restarted in the Control Panel.
As in the PC world, a common source of errors is between the Seat and Keyboard, when entering configuration data. After that, another source of errors would be driver conflicts. Additionally, user-level (not configuration related) errors between the Seat and Keyboard can also occur. For example, the extension folder is the MAC the functional equal to a DOS config.sys file or NT services. Because the MAC is so simple to the end user, the (O/S) extensions folder can be stuffed to the point of exploding. Once (and I am not exaggerating) I found 4 different fax/modem programs stuffed into the extension folder, all-competing for the same fax/modem. And the user was wondering why the MAC was slow to boot and had sluggish performance....
Having said this lets move on to the all-important TCP/IP discussion.
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