TweetFollow Us on Twitter

AppleTalk Fundamentals
Volume Number:3
Issue Number:4
Column Tag:Connections

AppleTalk: Fundamentals

By Dave Kosiur, Editor & Publisher, Connections Newsletter

Connections is a new industry newsletter in the MacInTouch style that covers issues related to networking on the Mac. Connections and MacTutor have agreed to promote each other as "sister" publications and we will be re-printing articles from Connections in MacTutor from time to time. This article is re-printed from the first issue. Connections is edited and published by Dave Kosiur. Bob Denny of Alisa Systems serves on it's advisory board, as he does for MacTutor. Subscriptions are $60 per year for the bimonthly publication, available from Connections, PO Box 5894, Fullerton, CA 92635. This is a valuable source of network specific information and we encourage your support.

AppleTalk is Apple's design of a simple, inexpensive and flexible network for connecting computers, peripheral devices, and servers. AppleTalk's flexibility allows it to be used to connect peripherals such as the LaserWriter, or act as a stand-alone local-area network for up to 32 nodes, or form portions of a larger network by using bridges and gateway devices.

Fig. 1 The Physical Connection

What is AppleTalk? At a purely physical level, AppleTalk is a network with a bus topology that uses a trunk cable between connection modules. Interfacing with the network is handled by the Serial Communications Control chip found in every Mac. Any device (computer, peripheral, etc.) attaches to a connection box via a short cable (called a drop cable), as shown in figure 1. This type of network is known as a multidrop line or a multipoint link. AppleTalk is capable of supporting up to 32 nodes (devices) per network and can transmit data at a rate of 230,400 bits per second. Nodes can be separated by a maximum cable length of 1000 feet.

AppleTalk, as specified by Apple, is wired using relatively inexpensive shielded, twisted-pair cable and Apple's connection boxes. One box is required per device; in the case of the Mac, the box plugs into the serial printer port in the back of the Mac using an attached drop cable. A trunk cable segment from one node on the network plugs into one port on the connection box, and another cable segment leading to the next node in the network plugs into the other port on the box.

One of the advantages of AppleTalk relates to the design of these connection boxes. The boxes are designed so that the continuity of the trunk cable and the network is maintained even if a device is disconnected from the network by unplugging it from the connection box. (Unplugging the trunk from the connection box does disrupt the integrity of the network, however.) The physical layout of an AppleTalk network can therefore be designed by locating the connection boxes where desired without worrying if a device will be initially connected to each one of the boxes. Additional devices can be added to the network at any time simply by plugging them into the boxes.

There are alternatives to using Apple's connection boxes. Farallon Computing markets their PhoneNET system, which fully supports the AppleTalk protocols. In the case of PhoneNET, the physical transmission medium is ordinary telephone wire, allowing the user to use the in-house telephone wiring for his network. PhoneNET uses the two of the unused wires found in a normal telephone installation, supporting both a telephone and a Mac connected to the same telephone wall box. In addition, PhoneNET links are capable of supporting 3000-foot distances between nodes. Farallon has a series of devices (repeaters, Star Controller) for extending the network.

With the recent announcement of DuPont's system for AppleTalk, users can also use fiber optic connections for an AppleTalk network. A concentrator is also available for constructing star networks. Two advantages of the fiber optics system are its immunity to EMI-RFI interference and improved data security; nodes may be a maximum of 4900 feet apart.

AppleTalk Protocols and the OSI Model

The Physical Layer has the responsibility of bit encoding/decoding, synchronization, signal transmission/ reception and carrier sensing. As mentioned previously, the Serial Communications Control chip in the Mac takes care of the AppleTalk port, which happens to be the printer port on current Macs. As long as connection modules conform to the signal descriptions of the Physical Layer, any transmission medium can be used for the actual network.

The AppleTalk Link Access Protocol (ALAP) must be common to all systems on the network bus and handles the node-to-node delivery of data between devices connected to a single AppleTalk network. ALAP determines when the bus is free, encapsulates the data in frames, sends its data, and recognizes when data should be received. ALAP is also responsible for assigning node numbers to each station on a network. The ALAP software assigns a random node number when the Mac is booted and keeps that number as long as it does not conflict with a previously assigned node number (if it does conflict, ALAP tries again).

The Link Access Protocol uses a method called CSMA/CA, or carrier-sense multiple access with collision avoidance, for access control. Carrier sense means that a sending node first listens to the network to hear if any other node is using the bus and defers to the ongoing transmission. Collision avoidance means that the protocol attempts to minimize collisions between transmitted data packets. In AppleTalk CSMA/CA, all transmitters wait until the bus is idle for a minimum time plus a random amount of added time before transmitting (or retransmitting after a collision).

While the ALAP protocol provides delivery of data over a single AppleTalk network, the Datagram Delivery Protocol (DDP) extends this mechanism to include a group of interconnected AppleTalk networks, known as an internet. An internet can be formed, for example, by using a bridge between two, or more, AppleTalk networks.

AppleTalk's address header (a part of each data packet) is used for identification of a process on the network and consists of a socket number, node number, and network number. A socket is a communication endpoint within a node on the network. Sockets belong to processes or functions that are implemented within software in the node. One Mac may have several AppleTalk connections open at one time, so the node number is not enough to identify a network address. In addition, node numbers are unique only within a single physical network, so DDP requires that each network be assigned a network number. The Datagram Delivery Protocol takes care of assigning socket numbers, as well as node numbers and network numbers, to provide a unique identification for every process occurring on the AppleTalk network.

As we move on to the Transport Layer, several protocols exist to add different types of functionality to the underlying services. The Routing Table Maintenance Protocol (RTMP) allows bridges and internet routers to dynamically discover routes to the different AppleTalk networks in an internet. The routing tables pair network numbers with the local node number of the bridge through which the shortest path to that net exists.

The AppleTalk Transaction Protocol, or ATP, is part of the Transport Layer and is responsible for controlling the transactions (flow of data) between requestor and responder sockets. This transaction-oriented protocol can be contrasted to other types of transport layers which support a two-way link between clients that can act as though they had an error-free hardwired link between them.

The basic function of the Name Binding Protocol (NBP) is the translation of a character string name into the internet address of the corresponding client. A key feature of the network is that most objects are accessible by name rather than by address (better for the user). NBP also introduces the concept of a zone, which is an arbitrary subset of networks in an internet where each network is in one and only one zone. The concept of zones is provided to assist the establishment of departmental or other user-understandable grouping of the entities of the internet. AppleTalk names consist of three fields: the object name (e.g., Dave), the type name (e.g., printer), and the zone name (e.g., Bldg. 1).

The Echo Protocol (EP) is a simple protocol that allows any node to send data to any other node on an AppleTalk internet and receive an echoed copy of that data in return. The Echo Protocol is mainly meant for network maintenance functions.

The specifications for the AppleTalk Data Stream Protocol (ADSP) have not yet been published (Inside AppleTalk, current version dated July 14, 1986). ADSP is designed to provide byte-stream data transmission in a full duplex mode between any two sockets on an AppleTalk internet. The Zone Information Protocol (ZIP) is used to maintain an internet-wide mapping of networks to zone names. Most of ZIP's services are transparent to the normal (non-bridge) node; the majority of ZIP is implemented in the bridges of an internet. ZIP is used by the Name Binding Protocol to determine which networks belong to a given zone.

In the Session Layer, the AppleTalk Session Protocol (ASP) is a general protocol designed to interact with ATP to provide for establishing, maintaining and closing sessions. Central to ASP is the concept of a session; two network entities, one in a workstations and the other in a server, can set up an ASP session between themselves (identified by a unique sessions identifier). ASP is an asymetric protocol in that the workstation initiates the session connection and issues sequences of commands, to which the server responds; the server may not send commands to the workstation.

The specifications for the AppleTalk Filing Protocol (AFP) have not been generally publicized. However, AFP has been finalized with the introduction of the AppleShare file server software from Apple, which uses AFP. AFP is a presentation layer protocol designed to control access to remote file systems.

At this time, third-party products are available for connecting Macintoshes and IBM PCs to AppleTalk, as well as using gateways for access to EtherNet as a backbone network to larger computers. Future articles in Connections will deal with these products and the diversity of products (file servers, spoolers, etc.) that can take advantage of such connections. For additional information, see MacTutor, Vol. 1, Numbers 10 and 11 for articles by Bob Denny & Alan Wootton.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Tor Browser 11.5.8 - Anonymize Web brows...
Using Tor Browser you can protect yourself against tracking, surveillance, and censorship. Tor was originally designed, implemented, and deployed as a third-generation onion-routing project of the U.... Read more
Alarm Clock Pro 15.0 - $19.95 (91% off)
Alarm Clock Pro isn't just an ordinary alarm clock. Use it to wake you up in the morning, send and compose e-mails, remind you of appointments, randomize the iTunes selection, control an internet... Read more
Google Chrome 107.0.5304.121 - Modern an...
Google Chrome is a Web browser by Google, created to be a modern platform for Web pages and applications. It utilizes very fast loading of Web pages and has a V8 engine, which is a custom built... Read more
calibre 6.9.0 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Safari Technology Preview 16.4 - The new...
Safari Technology Preview contains the most recent additions and improvements to WebKit and the latest advances in Safari web technologies. And once installed, you will receive notifications of... Read more
FileZilla 3.62.2 - Fast and reliable FTP...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface. The FileZilla Client not only supports FTP, but also FTP over TLS... Read more
djay Pro 4.0.13 - Transform your Mac int...
djay Pro provides a complete toolkit for performing DJs. Its unique modern interface is built around a sophisticated integration with iTunes and Spotify, giving you instant access to millions of... Read more
Opera 93.0.4585.21 - High-performance We...
Opera is a fast and secure browser trusted by millions of users. With the intuitive interface, Speed Dial and visual bookmarks for organizing favorite sites, news feature with fresh, relevant content... Read more
AppCleaner 3.6.6 - Uninstall your apps e...
AppCleaner allows you to uninstall your apps easily. It searches the files created by the applications and you can delete them quickly. Supports macOS Ventura. Fixed an issue causing failed updates... Read more
QuickBooks 21.0.7.1248 - Financial manag...
QuickBooks helps you manage your business easily and efficiently. Organize your finances all in one place, track money going in and out of your business, and spot areas where you can save. Built for... Read more

Latest Forum Discussions

See All

‘Top Hunter Roddy & Cathy’ Review –...
The NEOGEO is generally characterized by, with only a few notable exceptions, fighting games and Metal Slug. Within a couple of years of its launch, the vast majority of the output on the console seemed to be mining (quite successfully) a few... | Read more »
SwitchArcade Round-Up: Reviews Featuring...
Hello gentle readers, and welcome to the SwitchArcade Round-Up for November 28th, 2022. In today’s article, we’ve got a pair of reviews to check out. Full reviews of Pokemon Scarlet and Violet and The Oregon Trail are waiting for you to read. There’... | Read more »
‘OPUS: Echo of Starsong’ Interview: Port...
With OPUS: Echo of Starsong ($8.99) having finally launched on iOS after hitting PC and consoles, I had a chance to talk to Scott Chen who is the co-founder and executive producer of Sigono. In our chat, I touched on topics like game subscription... | Read more »
Best iPhone Game Updates: ‘Rush Rally 3’...
Hello everyone, and welcome to the week! It’s time once again for our look back at the noteworthy updates of the last seven days. As November breaths its last, the holiday season is right around the corner. That means we should start seeing more... | Read more »
‘Total Football’ is an Arcade-Style Socc...
GALA SPORTS recently launched its brand new soccer title, Total Football, and, true to its name, it is a pure arcade-style soccer game in the same vein as FIFA Mobile and PES Mobile. It also features official licensing from FIFPro and Manchester... | Read more »
Genshin Impact will recieve two new char...
HoYoverse has announced that Genshin Impacts version 3.3 will be arriving on December 7th. Titled All Senses Clear, All Existence Void, the update will bring two powerful new characters and a brand new card-based minigame. [Read more] | Read more »
‘Wreckfest’ Mobile Compared With Console...
HandyGames’ mobile version of Bugbear’s demolition derby-style racer Wreckfest ($9.99) released on iOS and Android recently, and we featured it as our Game of the Week. | Read more »
Black Friday Deals Here – The TouchArcad...
After taking a couple of weeks off we return on this glorious Black Friday with another episode of The TouchArcade Show. We get into a big discussion about virtual assistants like Alexa, Siri, and Google, and their place in the greater smarthome... | Read more »
TouchArcade Game of the Week: ‘Station 1...
I’m a big fan of Glitch Games and their unique brand of point-and-click adventure/escape room/puzzle games, and while they’re a tiny outfit and there’d typically be a couple years gap in-between their new releases, they were always worth the wait.... | Read more »
SwitchArcade Round-Up: ‘Super Lone Survi...
Hello gentle readers, and welcome to the SwitchArcade Round-Up for November 25th, 2022. Today we look at the remaining releases for the week, and I’ll be honest with you: it’s not a great assortment. Still, there are at least a couple of things... | Read more »

Price Scanner via MacPrices.net

Cyber Monday: 24″ Apple M1 iMacs for $150 off...
Amazon has Apple’s 24″ M1 iMacs on Black Friday sale for $150 off MSRP. Their prices are currently the lowest available for new iMacs among the Apple retailers we track: – 24″ M1 iMacs (8-Core CPU/7-... Read more
Cyber Monday Sale: 25% off Apple MagSafe acce...
Apple retailers are offering MagSafe accessories for up to 25% off MSRP for Cyber Monday. Here are the best deals available, currently from Verizon and Amazon: (1) Verizon has Apple MagSafe Chargers... Read more
Cyber Monday Sale: Apple AirPods for up to $1...
Looking for Apple AirPods, AirPods Pro, or AirPods Max this Cyber Monday? Look no further than our Apple AirPods Price Tracker. We track prices from 20+ Apple retailers and update the tracker... Read more
Final day for Apple’s Black Friday/Cyber Mond...
CYBER MONDAY Apple’s four day Black Friday/Cyber Monday 2022 event is now live and will run from November 25, 2022 to November 28, 2022 (ends today!). Receive a free $100-$250 Apple Gift Card with... Read more
Cyber Monday: Apple 13″ M2 MacBook Airs for $...
Apple retailers have posted their Cyber Monday prices on 13″ MacBook Airs. Take up to $200 off MSRP on M2-powered Airs with these sales with prices starting at only $1049. Free shipping is available... Read more
The best Cyber Monday iPhone sale? This $500...
If you switch to Xfinity Mobile and open a new line of service, they will take $500 off the price of a new iPhone, no trade-in required. This is the best no trade-in Cyber Monday Apple iPhone 14 deal... Read more
Cyber Monday Sale: Apple 16″ MacBook Pros for...
Amazon is offering $500 off MSRP discounts on Apple 16″ MacBook Pros with M1 Pro CPUs as part of their Cyber Monday sale. Their prices are the lowest available for these models from any Apple... Read more
Cyber Monday Sale: Apple 14″ MacBook Pros for...
Amazon is offering $300-$500 off MSRP discounts on Apple 14-inch MacBook Pros with M1 Pro CPUs as part of their Cyber Monday sale. Their prices are the lowest available for these models from any... Read more
Cyber Monday Sale: Apple Watch Ultra for $60...
Amazon has Apple Watch Ultra models (Alpine Loop, Trail Loop, and Opean Bans) on sale for $60 off MSRP as part of their Cyber Monday sale, each including free shipping, reducing the price for an... Read more
Cyber Monday MacBook Sale: 13″ M1 Apple MacBo...
Amazon has Apple 13″ M1 MacBook Airs back on sale for $200 off MSRP, starting at only $799, for Cyber Monday 2022. Their prices are the lowest available for new MacBooks this Cyber Monday. Stock may... Read more

Jobs Board

*Apple* Electronic Repair Technician - PlanI...
…a highly motivated individual to join our Production Department as an Apple Electronic Repair Technician. The computer repair technician will diagnose, assemble, Read more
Product Manager II - *Apple* - DISH (United...
…you will be doing We seek an ambitious, data-driven thinker to assist the Apple Product Development team as our new Retail Wireless division continues to grow and Read more
Staff Engineer 5G Protocol, *Apple* - DISH...
…metrics. Essential Functions and Responsibilities for a Staff Engineer 5G protocol( Apple ) Knowledge of 5G and 4G/LTE protocols and system architectures Experience Read more
Cashier - *Apple* Blossom Mall - JCPenney (...
Cashier - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Blossom Mall Read more
Omnichannel Associate - *Apple* Blossom Mal...
Omnichannel Associate - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.