Lesson 5: AppleTalk and ArcNet

[Previous] [Next]

In lessons 3 and 4, we discussed the two most popular network architectures: Ethernet and Token Ring. Networking professionals also might encounter and be required to support two other architectures: AppleTalk and ArcNet. The AppleTalk architecture is used in the Apple Macintosh environment, while the ArcNet architecture is used in personal computer-based environments. Since the advent of Ethernet, the popularity of ArcNet has decreased.

After this lesson, you will be able to:

  • Identify the components and features of AppleTalk.
  • Identify the components and features of ArcNet.

Estimated lesson time: 40 minutes

The AppleTalk Environment

Apple Computer, Inc. introduced AppleTalk in 1983 as proprietary network architecture for small groups. Networking functions are built into Macintosh computers, which makes the AppleTalk network very simple to set up compared to other networks.

The primary terms used in the Apple environment can be confusing because they sound similar to terms used in other environments, but relate to different aspects of a network. The following aspects of Apple networking are addressed:

  • AppleTalk
  • LocalTalk
  • AppleShare
  • EtherTalk
  • TokenTalk

AppleTalk

AppleTalk is the Apple network architecture and is included in the Macintosh operating system software. Figure 3.29 shows a typical AppleTalk network configuration. This means that network capabilities are built into every Macintosh. Appletalk Phase 1 is obsolete. AppleTalk Phase 2 is the current release of AppleTalk. The architecture is a collection of protocols that correspond to the OSI reference model. The OSI reference model is discussed in detail in Chapter 5,"Introducing Network Standards."

Figure 3.29 AppleTalk network

When a device attached to an AppleTalk network comes online, three things happen in the following order:

  1. The device checks to see if it has stored an address from a previous networking session. If not, the device assigns itself an address chosen at random from a range of allowable addresses.
  2. The device broadcasts the address to determine if any other device is using it.
  3. If no other device is using the address, the device stores the address to use the next time the device comes online.

LocalTalk

AppleTalk networks are commonly referred to as LocalTalk networks. LocalTalk uses CSMA/CA as an access method in a bus or tree topology with shielded, twisted-pair cabling, but will also accept fiber-optic and UTP cable. LocalTalk is inexpensive because it is built into Macintosh hardware. But, because of its comparatively modest performance (the maximum communication data rate for LocalTalk is 230.4 Kbps), and because LocalTalk NICs for PC-compatible computers are obsolete, LocalTalk is not as widely used as Ethernet or Token Ring in large business networks. Figure 3.30 shows the LocalTalk cable and connectors.

LocalTalk also refers to the physical cabling components as well as to the data-link layer protocol. These include:

  • Cables.
  • Connector modules.
  • Cable extenders.

click to view at full size.

Figure 3.30 LocalTalk connector module with a LocalTalk cable

STP cabling is most often used in a bus or tree topology. A LocalTalk network supports a maximum of 32 devices.

Because of LocalTalk's limitations, manufacturers other than Apple are often preferred for cabling. Farallon PhoneNet, for example, can handle 254 devices. PhoneNet uses telephone cable and connectors and can be implemented as a bus network or plugged into a central wiring hub to form a star topology.

AppleShare

AppleShare is the file server on an AppleTalk network. The client software is included with every copy of the Apple operating system. There is also an AppleShare print server, which is a server-based print spooler.

Zones

Individual LocalTalk networks can be joined together into one larger network through the use of logical groupings called zones. Figure 3.31 shows three LocalTalk zones connected. Each connected subnetwork is identified by a zone name. Users in one LocalTalk network can access the services in another network simply by selecting that zone. This is helpful for accessing file servers in a variety of small networks, thereby expanding the size of the network. Networks using other architectures, such as Token Ring, can also be joined to an AppleTalk network in this way.

Conversely, working groups on a single LocalTalk network can be subdivided into zones to relieve congestion on a busy network. Each zone, for example, can have its own print server.

click to view at full size.

Figure 3.31 Three zones joined together to form a larger network

EtherTalk

EtherTalk allows the AppleTalk network protocols to run on Ethernet coaxial cable. As described in Chapter 2, "Basic Network Media," there are two types of coaxial cable: thinnet and thicknet.

The EtherTalk card allows a Macintosh computer to connect to an 802.3 Ethernet network. EtherTalk software is included with the card and is compatible with AppleTalk Phase 2.

TokenTalk

The TokenTalk card is an expansion card that allows a Macintosh to connect to an 802.5 Token Ring network. TokenTalk software is included with the card and is compatible with AppleTalk Phase 2.

AppleTalk Considerations

Computers from companies other than Apple can also use AppleTalk. These include:

  • IBM personal computers and compatibles.
  • IBM mainframe computers.
  • Digital Equipment Corporation VAX computers.
  • Some UNIX computers.

Apple welcomes third-party product development. As a result, the AppleTalk environment is populated by products from a variety of vendors.

The ArcNet Environment

Datapoint Corporation developed the Attached Resource Computer Network (ArcNet) in 1977. Figure 3.32 shows a star-wired ArcNet. It is a simple, inexpensive, flexible network architecture designed for workgroup-size networks. The first ArcNet cards were shipped in 1983.

Figure 3.32 Simple star-wired ArcNet network

ArcNet technology predates IEEE Project 802 standards, but loosely maps to the 802.4 document. This specifies the standards for token-passing bus networks using broadband cable. An ArcNet network can have a star-bus or bus topology.

How ArcNet Works

ArcNet uses a token-passing access method in a star-bus topology (shown in Figure 3.33) passing data at 2.5 Mbps. ArcNet Plus, a successor to the original ArcNet, supports data transmission rates of 20 Mbps.

Because ArcNet is a token-passing architecture, a computer in an ArcNet network must have the token in order to transmit data. The token moves from one computer to the next according to the order in which they are connected to the hub, regardless of how they are physically located in the network environment. This means that the token moves from computer 1 to computer 2 (hub connections) in order, even if computer 1 is at one end of the building and computer 2 is at the other end of the building.

Figure 3.33 Token movement based on numerical order

The standard ArcNet packet (Figure 3.34) contains:

  • A destination address.
  • A source address.
  • Up to 508 bytes of data (or 4096 bytes of data in ArcNet Plus).

click to view at full size.

Figure 3.34 An ArcNet packet contains source and destination addresses

Hardware

Each computer is connected by cable to a hub. The hubs can be active, passive, or smart. As discussed in Chapter 1, Lesson 1: What is a Network?, passive hubs merely relay the signal. Active hubs can regenerate and relay signals. Smart hubs have all the features of active hubs and usually add diagnostic features such as reconfiguration detection and operator control-of-port connections.

The standard cabling used for ArcNet is 93-ohm RG-62 A/U, coaxial cable. ArcNet also supports twisted-pair and fiber-optic media. The distances between computers vary, depending on the cabling and the topology.

Using coaxial cable with BNC connectors and active hubs, a maximum cable distance of 610 meters (2000 feet) from a workstation to the hub can be achieved with a star topology. The maximum distance on a linear-bus segment is only 305 meters (1000 feet).

When unshielded twisted-pair cable with either RJ-11 or RJ-45 connectors is used, there is a maximum cable distance of 244 meters (800 feet) between devices on both star and bus topologies.

Lesson Summary

The following points summarize the main elements of this lesson:

  • AppleTalk is the network architecture of the Apple (Macintosh) computer environment.
  • AppleShare is the network operating system used by AppleTalk.
  • CSMA/CA is the access method for AppleTalk.
  • To use a Macintosh computer on an Ethernet with coaxial cable, you need an EtherTalk card and the EtherTalk software.
  • A TokenTalk card and software allow a Macintosh to connect to a Token Ring.
  • ArcNet is designed for workgroup-size networks.
  • ArcNet uses a token-passing bus topology.

The following table summarizes ArcNet specifications.

IMPORTANT
The following table includes the minimum set of standards required to conform to IEEE specifications. A particular implementation of the ArcNet network architecture might differ from the information in this table.

Table 3.11 ArcNet Specifications

IEEE specification ArcNet
Topology Series of stars
Cable type RG-62 or RG-59 (coaxial)
Terminator resistance, Ω (ohms) Not applicable
Impedance, Ω RG-62: 93 RG-59: 75
Maximum cable distance with coaxial cable, star topology 610 meters (2000 feet)
Maximum cable distance with coaxial cable, bus topology 305 meters (1000 feet)
Maximum cable distance with twisted-pair cable 244 meters (800 feet)
Minimum length between computers Depends on cable
Maximum connected segments Does not support connected segments
Maximum computers per segment Depends on cable used

Exercise 3.1: Case Study Problem

NOTE
Although this case study problem focuses on a particular architecture described in this chapter, you will need to draw on information presented in earlier chapters to formulate a solution.

Also, keep in mind that there is no single right answer to this problem: there are too many variables to take into account. In fact, it is entirely possible that you will find another solution that works better than the one we suggest in Appendix A!

A small public relations firm leases two groups of offices in Building A and Building G of a suburban office park. The business staff, including the human resources and accounting departments, has 12 people and is located in two offices in Building A. The creative staff, including copy writing, graphics, and production departments, with a total of 22 employees, is housed in Building G. Building A and Building G are about 600 meters (about 1970 feet) apart.

The business staff is networked with a four-year-old coaxial bus that ties their PC-compatible computers together in a peer-to-peer workgroup. The creative staff in Building G has a conglomeration of computers including Apple Macintoshes and PC-compatibles; they are not networked.

The owners of the company would like to network all the computers for the creative staff and connect the creative-staff network to the business-staff network. They would also like to standardize the type of network used in both buildings to keep troubleshooting issues to a minimum.

  1. What kind of network should they install?
  2. Server-based ____

    Peer-to-peer ____

TIP
This case study can be solved with several different combinations of components and cable.

  1. What type of network should the company implement within the offices?
  2. Fiber-optic Ethernet ____

    Fiber-optic Token Ring ____

    Fiber-optic ArcNet ____

    Ethernet 10BaseT ____

    Ethernet 10Base2 ____

    Token Ring ____

    LocalTalk ____

    ArcNet ____

  3. What type of network should the company install between the two buildings?
  4. Fiber-optic Ethernet ____

    Fiber-optic Token Ring ____

    Fiber-optic ArcNet ____

    Ethernet 10BaseT ____

    Ethernet 10Base2 ____

    Token Ring ____

    LocalTalk ____

    ArcNet ____

Answers

Exercise 3.2: Troubleshooting Problem

You will need to draw on information presented in chapters 1 and 2 as well as this one to solve this problem. Use your knowledge of network architectures to troubleshoot the situation described below and create a possible solution.

Background Information

You have a 500-node 10BaseT network. It started with 50 nodes five years ago, and you have been expanding it constantly since then. Recently the network has started to suffer from slow response time to the end users, and you have identified the network as the bottleneck. The vendor that you have been working with for the last two years recommends moving to 100BaseX. The vendor says that all you need to do is put the new 100BaseX NICs in your computers, replace your hubs with 100BaseX hubs, and you will be up and running.

The Problem

You and several technicians from your vendor spend an entire weekend installing the new cards and replacing hubs on your network. When the staff arrive at work on Monday morning, most are ecstatic with the performance of the new network, but about 50 staff members report that they cannot connect to the network. When you investigate further, you notice that all 50 are working at stations that had been cabled at least four or five years earlier.

  1. List at least two things that could cause those nodes to fail to function.

NOTE
This list contains the most common errors that could be causing the problem, but these are not the only correct possibilities.

  1. What could you do to resolve each of the possible causes you listed above?

Answers

Exercise 3.3: Network Planning Problem

Research has shown that about 90 percent of all new network installations use Ethernet 10BaseT with Category 5 UTP. Category 5 allows you to install a 10-Mbps solution now and upgrade it to a 100-Mbps solution later. However, despite its popularity, Ethernet 10BaseT may not be suitable for all situations.

Because the cost of labor accounts for most of the expense of cable installation, there is little difference in cost between using Category 3 UTP and Category 5 UTP cable. Most new installations use Category 5 because it supports transmission speeds of up to 100 Mbps.

The IBM Cabling System is used in a Token Ring environment. The star-wired topology makes moves, changes, and additions simple and easy. Figure 3.35 shows a patch panel with three computers connected. Moving a patch cable on the distribution panel can make changes.

Additionally, a number of minicomputer and mainframe systems have built-in Token Ring connections. Cable manufacturers other than IBM also make Token Ring cabling, of which UTP is the most popular.

click to view at full size.

Figure 3.35 A patch panel makes moving computers easy

This UTP star-wired Token Ring network transmits data at 16 Mbps. Changes can be made easily by simply moving a modular patch cord on the patch panel. This network simplifies management by using an intelligent MSAU. Some intelligent MSAUs allow distances of up to 100 meters (330 feet) to each network lobe (the cable distance between the MSAU and a computer). This cabling scheme follows AT&T wiring standards, which make it fully compatible with all 10BaseT applications. It is also compatible with 4-Mbps Token Ring networks.

Because 10BaseT is currently the most popular implementation of the Ethernet architecture, it should be chosen unless there is a compelling reason to choose something else. Therefore, in a case where any architecture will work, 10BaseT should be given first consideration.

Make a check mark on the line next to the choice that applies to your site. To determine which type of architecture would be most appropriate for your site, simply total the number of check marks for each indicator. The indicator with the most check marks should be the first option you consider.

NOTE
In the following questions, 10 indicates 10BaseT; T indicates Token Ring; F indicates fiber-optic; C indicates coaxial; A indicates that any will do; and D indicates that the appropriate choice depends on other factors.

  1. Are ease of troubleshooting and the cost of long-term maintenance important?
  2. Yes ____ 10

    No ____ A

  3. Are most of your computers situated within 100 meters (330 feet) of your wiring closet?
  4. Yes ____ 10

    No ____ A

  5. Is ease of reconfiguration important?
  6. Yes ____ 10

    No ____ A

  7. Do any members of your staff have experience with UTP cable?
  8. Yes ____ 10

    No ____ A, D

NOTE
Even if no one on staff has experience with UTP cable, someone may have transferable experience with another type of cable such as coaxial, STP, or even fiber-optic cable.

  1. Do you have existing coaxial cabling in your network?
  2. Yes ____ C, if existing cabling is extensive. Otherwise, switch to 10BaseT.

    No ____ A

  3. Is your network very small (fewer than ten computers)?
  4. Yes ____ C

    No ____ A

  5. Will your network be installed in an open area using cubicles to separate work areas?
  6. Yes ____ C, 10, D

    No ____ A

  7. Do you need cable that is more resistant to EMI (electromagnetic interference) than UTP is?
  8. Yes ____ C, F, D

    No ____ A

  9. Do you need longer cable runs than are supported by UTP?
  10. Yes ____ C, F, D

    No ____ A

  11. Do you need to cable longer distances than those supported by copper media? For example, do you need to connect two buildings in a campus environment? Or do you need to connect two wiring closets in a single building that are more than 185 meters (607 feet) apart?
  12. Yes ____ F

    No ____ A, D

  13. Do you need network cabling that is relatively secure from most eavesdropping or corporate intelligence-gathering equipment?
  14. Yes ____ F

    No ____ A

  15. Does your network have any existing STP cabling?
  16. Yes ____ T

    No ____ A

NOTE
While it is possible to use STP cabling with more than one architecture, it is most closely associated with token passing, specifically with IBM's Token Ring implementation. IBM refers to it as Type 1. It is much more expensive than UTP.

  1. Do you have any equipment that needs Token Ring cards (such as an IBM mainframe, and so on)?
  2. Yes ____ T

    No ____ A

  3. Do you have any equipment already installed that uses Token Ring?
  4. Yes ____ T

    No ____ A

  5. Do you need a network cable system that has built-in redundancy?
  6. Yes ____ T

    No ____ A

  7. Do you need cable that is more resistant to EMI than UTP is?
  8. Yes ____ T

    No ____ A

  9. Do you have existing ArcNet infrastructure you need to connect to?
  10. Yes ____ Use ArcNet

    No ____ A

  11. Do you have an existing LocalTalk network?
  12. Yes ____ Use LocalTalk or create a multivendor network (see Chapter 4, Lesson 5: Network Operating Systems in Multivendor Environments).

    No ____ A

  13. Do you have Macintosh computers that do not have an Ethernet or Token Ring interface?
  14. Yes ____ Use LocalTalk or create a multivendor network.

    No ____ A

  15. Based on the information generated in this exercise, your network architecture should be: ______________________________________


MCSE Training Kit Networking Essentials Plus 1999
MCSE Training Kit: Networking Essentials Plus, Third Edition (IT Professional)
ISBN: 157231902X
EAN: 2147483647
Year: 2005
Pages: 106

Similar book on Amazon

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net