AppleTalk
As you might have surmised, AppleTalk is the name given to the protocol used on Apple networks. The roots of the AppleTalk protocol can be traced back to the early 1980s. The first implementation of AppleTalk was limited and not suitable for internetworks. Late in the 1980s, however, significant improvements were made to the protocol; it then allowed for support of internetworking by supporting network addresses.
Like the IPX/SPX and TCP/IP protocol suites, the AppleTalk protocol suite is comprised of several protocols. The following are the AppleTalk protocols:
AppleShare— AppleShare provides application-layer services. It comprises three different protocols: AppleShare File Server, AppleShare Print Server, and AppleShare PC.
AppleTalk Address Resolution Protocol (AARP)— AARP maps the AppleTalk addresses to both Ethernet and Token Ring physical addresses.
AppleTalk Data Stream Protocol (ADSP)— ADSP is a session-layer protocol that also performs transport-layer functions. At the session layer, ADSP establishes and releases connections. At the transport layer, it provides sequencing and handles flow control.
AppleTalk Filing Protocol (AFP)— AFP manages file sharing on a network.
AppleTalk Session Protocol (ASP)— Like ADSP, ASP works at the session layer and is used to establish and release connections between devices.
AppleTalk Transaction Protocol (ATP)— ATP is a transport-layer connectionless protocol that is used to establish connections between computers.
Datagram Delivery Protocol (DDP)— DDP provides connectionless service on an AppleTalk network.
EtherTalk Link Access Protocol (ELAP)— ELAP is an implementation of the AppleTalk protocol that is compatible with the Ethernet protocol.
Name Binding Protocol (NBP)— NBP maps computer hostnames to network-layer addresses.
Printer Access Protocol (PAP)— PAP is a session-layer protocol that is used to facilitate printing on an AppleTalk network. PAP also allows connections between file servers and workstations.
Routing Table Maintenance Protocol (RTMP)— RTMP is a distance-vector routing protocol that is similar to the RIP, which is used by IPX/SPX and TCP/IP. RTMP maintains routing tables for a network.
TokenTalk Link Access Protocol (TLAP)— TLAP is an implementation of the AppleTalk protocol that is compatible with the Token Ring protocol.
Zone Information Protocol (ZIP)— ZIP divides network devices into logical groups called zones.
EXAM TIP
Know the Functions of the Protocols For the Network+ Exam, you should be sure you understand the functions of the protocols in the AppleTalk protocol suite.
AppleTalk Addressing
Like TCP/IP and IPX/SPX, AppleTalk requires two parts in the addressing system: the network part of the address and the node part. To get a node address, a system must simply be booted on an AppleTalk network. When the system is first brought up on the network, it generates a random node number that is then broadcast to the entire network. If by some unusual circumstance this number is already assigned to another system, a different node number is generated and broadcast to the network.
NOTE
LocalTalk AppleTalk is a complete networking protocol that can be made compatible with both Token Ring and Ethernet; LocalTalk was developed for AppleTalk in Apple-only networks. LocalTalk uses carrier-sense multiple-access with collision avoidance (CSMA/CA) as an access method. A LocalTalk network uses shielded twisted pair (STP) media but can be configured to use regular unshielded twisted pair (UTP) or fiber-based media. LocalTalk uses a bus topology and can support up to 32 devices.
The node number must be used in conjunction with a network number, which is assigned by the administrator. When these numbers are used together, they form the network address of the computer.
AppleTalk addresses are 24 bits long; 16 of the bits are used for the network address, and 8 are used for the node address. Having only 8 bits available for node addresses means that there can be a maximum of 254 nodes on each network. However, you can use a strategy called Extended AppleTalk Network to get around this limitation. To use this technique, you assign a network a range of addresses rather than a single address.
Another feature of AppleTalk networking that is worthy of note is the zone. Zones allow an administrator to divide an AppleTalk network into logical areas to simplify administration and make it easier for users to find network resources. Zones are generally used only in environments with large numbers of systems.
Mapping AppleTalk to the OSI Model
Like the other protocol suites, AppleTalk can be mapped to the OSI model. Table 5.1 shows the various AppleTalk protocols and the corresponding OSI levels.
AppleTalk Interoperability
Of the three protocol suites discussed in this chapter, AppleTalk is the least interoperable; only Macintosh systems use it as the default protocol. AppleTalk support can be provided on certain other platforms, such as Microsoft Windows, but additional software is required to enable it.
AppleTalk Routing
AppleTalk is a routable protocol (although early versions were not). The routing functionality is enabled by RTMP. Like RIP, which is used on IP- and IPX-based networks, RTMP is a distance-vector routing protocol.
AppleTalk Naming
Systems on an AppleTalk network are assigned names so that users can locate resources more easily than by using network addresses. This functionality is provided by the NBP, which handles the resolution of computer names to network addresses.