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

calibre 4.17.0 - 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
MacPilot 11.1.4 - $15.96
MacPilot gives you the power of UNIX and the simplicity of Macintosh, which means a phenomenal amount of untapped power in your hands! Use MacPilot to unlock over 1,200 features, and access them all... Read more
Transmission 3.00 - Popular BitTorrent c...
Transmission is a fast, easy, and free multi-platform BitTorrent client. Transmission sets initial preferences so things "just work", while advanced features like watch directories, bad peer blocking... Read more
Doom 3 1.3.1 - First-person shooter acti...
A massive demonic invasion has overwhelmed the Union Aerospace Corporation's (UAC) Mars Research Facility, leaving only chaos and horror in its wake. As one of only a few survivors, you must fight... Read more
Box Sync 4.0.8004 - Online synchronizati...
Box Sync gives you a hard-drive in the Cloud for online storage. Note: You must first sign up to use Box. What if the files you need are on your laptop -- but you're on the road with your iPhone? No... Read more
LibreOffice 6.4.4.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
Day One 4.14 - Maintain a daily journal.
Day One is an easy, great-looking way to use a journal / diary / text-logging application. Day One is well designed and extremely focused to encourage you to write more through quick Menu Bar entry,... Read more
Doxie 2.12.2 - Scan, share, and store do...
Introducing Doxie, the new, modern paper scanner that's so simple, it'll revolutionize the way you think about sharing and storing docs and photos forever. Doxie is ultra-portable, fully automatic,... Read more
Tinderbox 8.7.0 - Store and organize you...
Tinderbox is a personal content management assistant. It stores your notes, ideas, and plans. It can help you organize and understand them. And Tinderbox helps you share ideas through Web journals... Read more
Viber 13.0.0 - Send messages and make fr...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device, so... Read more

Latest Forum Discussions

See All

SINoALICE, Yoko Taro and Pokelabo's...
Yoko Taro and developer Pokelabo's SINoALICE has now opened for pre-registration over on the App Store. It's already amassed 1.5 million Android pre-registrations, and it's currently slated to launch on July 1st. [Read more] | Read more »
Masketeers: Idle Has Fallen's lates...
Masketeers: Idle Has Fallen is the latest endeavour from Appxplore, the folks behind Crab War, Thor: War of Tapnarok and Light A Way. It's an idle RPG that's currently available for Android in Early Access and will head to iOS at a later date. [... | Read more »
Evil Hunter Tycoon celebrates 2 million...
Evil Hunter Tycoon has proved to be quite the hit since launching back in March, with its most recent milestone being 2 million downloads. To celebrate the achievement, developer Super Planet has released a new updated called Darkness' Front Yard... | Read more »
Peak's Edge is an intriguing roguel...
Peak's Edge is an upcoming roguelike puzzle game from developer Kenny Sun that's heading for both iOS and Android on June 4th as a free-to-play title. It will see players rolling a pyramid shape through a variety of different levels. [Read more] | Read more »
Clash Royale: The Road to Legendary Aren...
Supercell recently celebrated its 10th anniversary and their best title, Clash Royale, is as good as it's ever been. Even for lapsed players, returning to the game is as easy as can be. If you want to join us in picking the game back up, we've put... | Read more »
The Magic Gladiator class arrives in MU...
The Magic Gladiator class is now available in MU Origin 2 following the most recent patch. It also marks the start of Abyss Season 11 and the introduction of Couple Skills and Couple Dungeons. [Read more] | Read more »
The 5 Best Racing Games
With KartRider Rush+ making a splash this past week, we figured it was high time we updated our list of the best mobile racing games out there. From realistic racing sims to futuristic arcade racers (and even racing management games!), check out... | Read more »
KartRider Rush+ Guide - Tips for new rac...
KartRider Rush+ continues to be a surprisingly refreshing and fun kart racer that's entirely free-to-play. The main reason for this is just how high its skill ceiling is. Check out the video above if you're curious to know what top level play looks... | Read more »
KartRider Rush+ might be good, actually?
It's hard to find good racing games on mobile. Most of them are free-to-play, and free-to-play racers generally suck. Even Nintendo couldn't put together a competent Mario Kart game, opting instead for a weird score chaser that resembles--but feels... | Read more »
LifeAfter, NetEase's popular surviv...
A new map will be making its way into NetEase's popular survival game LifeAfter. The map is set to arrive on May 28th and will introduce a volcano that's teetering on the verge of eruption, bringing a host of added challenges to the game. [Read... | Read more »

Price Scanner via MacPrices.net

Memorial Day Weekend Sale: Take $300 off thes...
Apple resellers are offering $300 discounts on select 16″ MacBook Pros as part of their Memorial Day Weekend 2020 sales. Prices start at $2099: – 16″ 2.6GHz 6-Core Space Gray MacBook Pro: $2099 at... Read more
Best Memorial Day Weekend 2020 Apple AirPods...
Apple resellers are offering discounts ranging up to $50 off MSRP on AirPods as part of their Memorial Day Weekend 2020 sales. These are the best deals today on various AirPods models. See our... Read more
Memorial Day Weekend Sale: 10″ Apple iPads fo...
Amazon is offering new 10.2″ iPads for $80-$100 off Apple’s MSRP as part of their Memorial Day Weekend 2020 sale, with prices starting at only $249. These are the same iPads sold by Apple in their... Read more
Memorial Day Weekend Sale: 2020 Apple iPhone...
Sprint is offering Apple’s new 2020 64GB iPhone SE for $0 per month for 18 months as part of their Memorial Day Weekend 2020 sale. New line of service and trade-in required. Offer is valid from 5/22/... Read more
Amazon’s popular $100 Apple Watch Series 5 di...
Amazon has Apple Watch Series 5 GPS + Cellular models on sale for up to $100 off Apple’s MSRP today. Shipping is free. These are the same Apple Watch models sold by Apple in their retail and online... Read more
2020 13″ 4-Core MacBook Air on sale for $949,...
Apple reseller Adorama has the new 2020 13″ 1.1GHz 4-Core Space Gray MacBook Air on sale today for $949 shipped. Their price is $50 off Apple’s MSRP, and it’s the lowest price currently available for... Read more
Apple Retail Chief Announces Staggered Reopen...
NEWS: 05.20.20 – In the midst of a global pandemic, after its retail outlets were shuttered temporarily in mid-March as a mitigation measure enacted by Apple during the peak of the spread of COVID-19... Read more
Apple’s Pro Display XDR models in stock today...
Abt Electronics has Apple’s new 32″ Pro Display XDR models in stock and on sale today for up to $305 off MSRP. Shipping is free. Their prices are currently the lowest available for these new models... Read more
Apple restocks refurbished iPhone 8 for $339
Apple has restocked Apple Certified Refurbished 64GB iPhone 8 models for only $339. Apple dropped their price on this phone last month by $160, from $499 to $339. Each refurbished iPhone comes with a... Read more
New at AT&T: 50% off iPhone 11 for new cu...
AT&T is offering a 50% off the 64GB iPhone 11 for new customers who switch to AT&T and open a new line of service. Discount applied over a 30 month period The fine print: “iPhone 11 64GB for... Read more

Jobs Board

Cub Foods - *Apple* Valley - Now Hiring Par...
Cub Foods - Apple Valley - Now Hiring Part Time! United States of America, Minnesota, Apple Valley New Retail Operations Post Date 5 days ago Requisition # Read more
Senior Data Engineer - *Apple* - Theorem, L...
Job Summary Apple is seeking an experienced, detail-minded data engineeringconsultant to join our worldwide business development and strategy team. If you are Read more
Cub Foods - *Apple* Valley - Now Hiring Par...
Cub Foods - Apple Valley - Now Hiring Part Time! United States of America, Minnesota, Apple Valley New Retail Operations Post Date 4 days ago Requisition # Read more
Medical Screener - *Apple* Hill - Evenings...
Medical Screener - Apple Hill - Evenings Tracking Code D-MS-AH-E Job Description Medical Screener - Temporary We Are Hiring: WellSpan Health has a temporary Medical Read more
*Apple* Systems Administrator - Solidus Tech...
Solidus is searching for an Apple Systems Engineer. The engineer will be responsible for desktop and server infrastructure. This includes support for operating Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.