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

Adobe Lightroom 6.10.1 - Import, develop...
Adobe Lightroom is available as part of Adobe Creative Cloud for as little as $9.99/month bundled with Photoshop CC as part of the photography package. Lightroom 6 is also available for purchase as a... Read more
iPhoto Library Manager 4.2.7 - Manage mu...
iPhoto Library Manager allows you to organize your photos among multiple iPhoto libraries, rather than having to store all of your photos in one giant library. You can browse the photos in all your... Read more
Smultron 9.4 - Easy-to-use, powerful tex...
Smultron 9 is an elegant and powerful text editor that is easy to use. Use it to create or edit any text document. Everything from a web page, a note or a script to any single piece of text or code.... Read more
TextSoap 8.4 - Automate tedious text doc...
TextSoap can automatically remove unwanted characters, fix up messed up carriage returns, and do pretty much anything else that we can think of to text. Save time and effort. Be more productive. Stop... Read more
Merlin Project 4.2.3 - $349.00
Merlin Project is the leading professional project management software for OS X. If you plan complex projects on your Mac, you won’t get far with a simple list of tasks. Good planning raises... Read more
QuarkXPress 13.0.0.0 - Desktop publishin...
QuarkXPress 2017 is the new version that raises the bar for design and productivity. With non-destructive graphics and image editing directly within your layout, you no longer have to choose between... Read more
Path Finder 7.5 - Powerful, award-winnin...
Path Finder makes you a master of file management. Take full control over your file system. Save your time: compare and synchronize folders, view hidden files, use Dual Pane and full keyboard... Read more
Path Finder 7.5 - Powerful, award-winnin...
Path Finder makes you a master of file management. Take full control over your file system. Save your time: compare and synchronize folders, view hidden files, use Dual Pane and full keyboard... Read more
Merlin Project 4.2.3 - $349.00
Merlin Project is the leading professional project management software for OS X. If you plan complex projects on your Mac, you won’t get far with a simple list of tasks. Good planning raises... Read more
TextSoap 8.4 - Automate tedious text doc...
TextSoap can automatically remove unwanted characters, fix up messed up carriage returns, and do pretty much anything else that we can think of to text. Save time and effort. Be more productive. Stop... Read more

Latest Forum Discussions

See All

Magikarp Jump splashes onto Android worl...
If you're tired ofPokémon GObut still want something to satisfy your mobilePokémon fix,Magikarp Jumpmay just do the trick. It's out now on Android devices the world over. While it looks like a simple arcade jumper, there's quite a bit more to it... | Read more »
Purrfectly charming open-world RPG Cat Q...
Cat Quest, an expansive open-world RPG from former Koei-Tecmo developers, got a new gameplay trailer today. The video showcases the combat and exploration features of this feline-themed RPG. Cat puns abound as you travel across a large map in a... | Read more »
Jaipur: A Card Game of Duels (Games)
Jaipur: A Card Game of Duels 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: ** WARNING: iPad 2, iPad Mini 1 & iPhone 4S are NOT compatible. ** *** Special Launch Price for a limited... | Read more »
Subdivision Infinity (Games)
Subdivision Infinity 1.03 Device: iOS Universal Category: Games Price: $2.99, Version: 1.03 (iTunes) Description: Launch sale! 40% Off! Subdivision Infinity is an immersive and pulse pounding sci-fi 3D space shooter. https://www.... | Read more »
Clash of Clans' gets a huge new upd...
Clash of Clans just got a massive new update, and that's not hyperbole. The update easily tacks on a whole new game's worth of content to the hit base building game. In the update, that mysterious boat on the edge of the map has been repaired and... | Read more »
Thimbleweed Park officially headed to iO...
Welp, it's official. Thimbleweed Park will be getting a mobile version. After lots of wondering and speculation, the developers confirmed it today. Thimbleweed Park will be available on both iOS and Android sometime in the near future. There's no... | Read more »
Pokémon GO might be getting legendaries...
The long-awaited legendary Pokémon may soon be coming to Pokémon GO at long last. Data miners have already discovered that the legendary birds, Articuno, Moltres, and Zapdos are already in the game, it’s just a matter of time. [Read more] | Read more »
The best deals on the App Store this wee...
If you’ve got the Monday blues we have just the thing to cheer you up. The week is shaping up to be a spectacular one for sales. We’ve got a bunch of well-loved indie games at discounted prices this week along with a few that are a little more... | Read more »
Honor 8 Pro, a great choice for gamers
Honor is making strides to bring its brand to the forefront of mobile gaming with its latest phone, the Honor 8 Pro. The Pro sets itself apart from its predecessor, the Honor 8, with a host of premium updates that boost the device’s graphical and... | Read more »
The 4 best outdoor adventure apps
Now that we're well into the pleasant, warmer months, it's time to start making the most of the great outdoors. Spring and summer are ideal times for a bit of trekking or exploration. You don't have to go it alone, though. There are plenty of... | Read more »

Price Scanner via MacPrices.net

Sale! 15-inch 2.6GHz Silver Touch Bar MacBook...
DataVision has the 15″ 2.6GHz Silver Touch Bar MacBook Pro (MLW72LL/A) on sale for $2199 including free shipping. Their price is $200 off MSRP, and it’s the lowest price available for this model (... Read more
A Kaby Lake Processor Upgrade For The MacBook...
Now they tell me! Well, actually Apple hasn’t said anything official on the subject, but last week Bloomberg News’s Mark Gurman and Alex Webb cited unnamed “people familiar with the matter”... Read more
Kodak’s Camera-First Smartphone EKTRA Launche...
The Eastman Kodak Company and Bullitt Group have announced the availability of a U.S. GSM version of the KODAK EKTRA Smartphone. The U.S. launch coincides with a software update addressing requests... Read more
Apple Launches App Development Curriculum for...
Apple today launched a new app development curriculum designed for students who want to pursue careers in the fast-growing app economy. The curriculum is available as a free download today from Apple... Read more
Check Apple prices on any device with the iTr...
MacPrices is proud to offer readers a free iOS app (iPhones, iPads, & iPod touch) and Android app (Google Play and Amazon App Store) called iTracx, which allows you to glance at today’s lowest... Read more
9.7-inch 2017 iPad available for $298, save $...
Sams Club has 32GB 9.7″ Apple iPads available for $298 for Sams Club members. That’s $21 off MSRP. Order online and choose free local store pickup (if available) or free shipping. Read more
touchbyte Releases PhotoSync 3.2 for iOS With...
Hamburg, Germany based touchbyte has announced the release of PhotoSync 3.2 for iOS, a major upgrade to the versatile and powerful app to transfer, backup and share photos and videos over the air.... Read more
Emerson Adds Touchscreen Display and Apple Ho...
Emerson has announced the next evolution of its nationally recognized smart thermostat. The new Sensi Touch Wi-Fi Thermostat combines proven smarthome technology with a color touchscreen display and... Read more
SurfPro VPN for Mac Protects Data While Offer...
XwaveSoft has announced announce the release and immediate availability of SurfPro VPN 1.0, their secure VPN client for macOS. SurfPro VPN allows Mac users to protect their internet traffic from... Read more
13-inch Touch Bar MacBook Pros on sale for $1...
B&H Photo has 13″ MacBook Pros in stock today for up to $150 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 13″ 2.9GHz/512GB Touch Bar MacBook Pro Space Gray (... Read more

Jobs Board

Data Engineer - *Apple* Media Products - Ap...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
*Apple* Store Leader Program - Apple, Inc (U...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on Read more
*Apple* Integration Specialist - A3 Solution...
Apple Integration Specialist Contract-To-HireWe are searching for dedicated, well-experienced and energetic individuals for an information technology corporation Read more
Sr. Software Engineer, *Apple* Online Store...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
Senior Engineering Project Manager, *Apple*...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.