AppleTalk

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AppleTalk is a group of network protocols and was developed by Apple Computer in late 1983 to allow easy access to shared resources such as files or printers on the network . AppleTalk is a registered trademark of Apple, Inc.

Due to the initial exclusive connection of AppleTalk with the network hardware later renamed LocalTalk , AppleTalk is often incorrectly used as a synonym for LocalTalk cabling.

The decision to establish its own network protocols and LocalTalk as a proprietary transmission medium resulted from the prevailing conditions in 1983: Network hardware was rarely standardized and very expensive; the cost often reached the cost of a personal computer itself.

In view of the widespread use of IP- based networks, AppleTalk was abandoned by Apple as of Mac OS X 10.6. All essential services were either mapped to TCP / IP (example: file access via AFP, TCP Port 548) or replaced by other, already existing protocols (example: printer access via LPR or JetDirect ports or IPP , finding devices and services in the network with Bonjour ). Bonjour, however, is limited in its capabilities to one network segment, and there is no longer any possibility to logically organize network-compatible devices via zones .

For non-Apple PCs, there were also ISA , MCA and SBus cards with LocalTalk interfaces, so that such PCs could be integrated into an AppleTalk network and data could be exchanged and printers shared.

history

AppleTalk is largely based on the (unpatented) Cambridge Ring .

overview

AppleTalk has two addressing modes: Extended (Phase 2) and Nonextended (Phase 1).

AppleTalk addresses devices using a dynamically assigned address. This address consists of a 16-bit network address (phase 2 only) and an 8-bit node ID. The network address can be specified by a router within a contiguous range . The network address 0 stands for the local network segment , the network addresses 65280-65534 are reserved. The node ID 0 is invalid, 1-127 are intended for users, 128-254 for servers, 255 for broadcast . This is followed by an 8-bit socket number to differentiate between the individual services on the respective device. Sockets 0 and 255 are invalid, 1-127 are for static and 128-254 are for dynamic allocation.

A typical AppleTalk address would be 1248.33: 4.

AppleTalk knows the concept of zones . These enable a logical grouping of devices that does not have to match the physical structure of network segments. Phase 2 networks support more than one zone per segment. The user can then choose the zone membership. This zone list appears in the user program Selection .

A dynamic name service (NBP) is provided so that users do not have to grapple with unrecognizable numeric addresses. Server services register with the respective local NBP service. On the network side, this is based on multicasts . The selection sends out multicasts and compiles the individual responses into a list view.

The AppleTalk protocols

The AppleTalk family comprises the following protocols (grouped according to network layers ):

Application and presentation layer

Session shift

Transport layer

Network layer

Security and physical layer

Several link access protocols (LAP) are supported, which are managed by the so-called LAP manager .

The physical layer comprises the drivers for network interfaces.

The AppleTalk protocol stack

The AppleTalk protocols can be divided into several layers that form a protocol stack . The protocols can be classified in the ISO-OSI reference model as follows :

OSI layer AppleTalk protocol stack
7th AFP PAP
6th
5 ZIP ASP ADSP
4th          ATP AEP NBP RTMP
3 DDP
2 LLAP ELAP TLAP FDDI ← AARP
1 LocalTalk Ethernet
driver 		Token Ring
Driver 		FDDI
driver

Relation to other protocols

AppleTalk can be routed, all routers involved must support AppleTalk, but are considered "chatty", i.e. they produce constant packet transmissions, whereby some AppleTalk-capable routers (e.g. from Cisco or Netopias from Farallon) were able to do this above all emulate data traffic consisting of keepalive packets (AppleTalk spoofing ) so that a permanent connection could be bypassed. Connections via X.25 networks were also possible.
The connection of two remote AppleTalk networks, e.g. B. via the TCP / IP -based Internet is therefore not possible directly, but only through encapsulation (e.g. using Kinetics Internet Protocol ), see the product description of the Apple Internet Router .

Trivia

Due to the small packet size of the underlying Datagram Delivery Protocol (13 byte header , 587 bytes of user data ) , AppleTalk scales poorly on transmission routes faster than 10 Mbit / s Ethernet, the data throughput on Fast Ethernet is around a third of the possible with fast network components involved .

literature

  • Gursharan S. Sidhu, Richard F. Andrews, Alan B. Oppenheimer: Inside AppleTalk, Second Edition . Ed .: Apple Computer, Inc. 2nd edition. Addison-Wesley Publishing Company, Inc., 1990, ISBN 0-201-55021-0 (English).
  • Apple Computer Inc .: Inside Macintosh: Networking , 2nd, Addison-Wesley, 1994 , Chapter 1 - Introduction to AppleTalk (online version)

Individual evidence

  1. ↑ Missing The Big Time (German translation) by Wendy Grossman from Personal Computer World Magazine (May 1993)
  2. ↑ Description of AIR  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / docs.info.apple.com