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TechNote: AppleTalk and Macintosh |
AppleTalk
AppleTalk was developed by Apple Computers in the early 1980s
to allow file and printer sharing and mail functionality between
Macintosh computers. A Mac that shares resources is called a
server, and the computer connecting to it a client. Like TCP/IP,
AppleTalk is not just one protocol, but a suite of several protocols
for different functions. It is built-in in every Macintosh computer
and requires virtually no user interaction, therefore it is
very easy to administer in small network environments. As with
any other protocol, AppleTalk is best explained in correlation
to the 7-layer OSI model.
At the Physical and Data Link layer several specifications are
defined to allow AppleTalk to run over several network types
with different media-access technologies. EtherTalk allows AppleTalk
to run over Ethernet, TokenTalk allows AppleTalk to run over
Token Ring, FDDITalk allows AppleTalk to run over FDDI, and
LocalTalk is Apple's own media-access technology, and uses CSMA/CA
as the access-method. LocalTalk uses UTP or STP cabling and
has a maximum data transfer rate of 230 Kbps, you can still
find this in today's networks, typically in very small environments
for simple file and printer sharing. The image below shows a
connector used in LocalTalk networks to connect network nodes.
At one side it connects to a computer or printer using a min-din
connector or DB-9 serial connector. The other side connects
to a phone cable, which in turn, connects to another LocalTalk
connector or a terminator. This type of media is known a PhoneNet,
and is similar to building a 10Base2 bus network topology.
At the Network layer, two main protocols are defined:
| Datagram Delivery
Protocol (DDP) |
A connectionless datagram
protocol providing best-effort delivery and layer 3 addressing.
Similar to the function of IP. |
| AppleTalk Address Resolution
Protocol (AARP) |
Maps (Network) layer 3
addresses to (Data Link) layer 2 MAC addresses. Analogous
to the function of the ARP protocol in TCP/IP. |
At the Transport layer a big difference with the TCP/IP suite
becomes noticeable. In TCP/IP the routing protocols are defined
at the Network layer, with AppleTalk this is not the case:
| Routing Table
Maintenance Protocol (RTMP) |
Allows AppleTalk routers
to exchange information and build their routing tables.
The routing tables contain entries of possible routes
in the network and their attributes. RTMP routers broadcast
their routing table to neighboring routers every 10 seconds
causing a lot of overhead. RTMP is the equivalent of the
Routing Information Protocol (RIP) typically used in TCP/IP
networks. |
| AppleTalk Update-based
Routing Protocol (AURP) |
Allows AppleTalk networks
to be connected over a TCP/IP WAN link. AURP wraps AppleTalk
datagrams into UDP datagrams allowing them to be tunneled
over IP connections. |
| AppleTalk Echo Protocol
(AEP) |
Used to verify if remote
hosts are reachable. This is similar to ICMPs Echo messages
used by the PING utility in TCP/IP networks. |
| AppleTalk Transaction Protocol
(ATP) |
This is the transport protocol
in AppleTalk. Provides reliable delivery service for transaction-oriented
operations. ATP handles acknowledgements, flow control
and sequencing. |
| Network Binding Protocol
(NBP) |
Maps AppleTalk names to
AppleTalk network layer addresses. This protocol is largely
responsible for the large overhead on AppleTalk networks
because of the broadcast method it uses. NBP is somewhat
similar to DNS and WINS in TCP/IP. |
At the Session layer, the next 4 protocols are defined:
| Printer Access
Protocol (PAP) |
A protocol
created for client to printer communication, which manages
the virtual connection to printers and print servers.
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| AppleTalk Data Stream Protocol
(ADSP) |
Provides a data channel
between hosts. It is a full-duplex, connection-oriented
protocol that provides its own transport layer services
(therefore ADSP functions reside partly on OSI's Transport
layer) |
| AppleTalk Session Protocol
(ASP) |
A Session protocol that
manages sessions for higher layer protocols and uses the
AppleTalk Transaction Protocol (ATP) for transport services. |
| Zone Information Protocol
(ZIP) |
Manages the relationship
between network numbers and zone names and allows applications
to use zones. |
At the Presentation and Application layer the AppleTalk
Filing Protocol (AFP) is defined. AFP provides an interface
between an application and a file server. AFP allows a workstation
on an AppleTalk network to access files on an AFP file server,
such as an AppleShare file server. When the user opens a session
with an AppleShare file server over the network, it appears
as if the files were located on a local disk drive.
AppleTalk Addressing
The following network diagram shows an example of a simple AppleTalk
network using EtherTalk:
An AppleTalk network consists of three main components:
| Nodes |
A uniquely identified host
on the network, includes Macintosh computers, printers,
Windows PCs and routers. |
| Networks |
Multiple network numbers
can be assigned to a single segment, known as an extended
cable range. |
| Zones |
Similar
to the concept of VLANs, they are used to control broadcast
traffic by dividing internetworks into logical
groups. When a client request resources such as shares
and printers, only those in the same zone of the client,
will appear by default. |
An AppleTalk address is 24 bits in length and as with all routable
protocols needs a network and a host portion. The first 16 bits
denote the network portion of the address, and is learned automatically
from an AppleTalk router or computer. The other 8 bits denote
the node portion. When a client is added to the network,
it will make up the node portion itself and broadcasts requests
to see if the number is already in use. If the number is in
use, the client will generate a new number and start over again
until an unused node number is found. The complete AppleTalk
network address of node 37 is 58.37. The 16 bits network portion
allows for 65000 networks and the 8 bits node portion allows
for 254 hosts (0 can't be used, 255 is the broadcast address).
The current version of AppleTalk is named AppleTalk phase 2,
allowing multiple network numbers to be assigned
to a single segment, known as an extended cable range,
and eliminates the limit of 254 nodes per network. Sometimes
the address includes the socket number, for example 58.37.254
or 58.37/254. An AppleTalk socket is similar to the concept
of ports in TCP/IP.
Using the Network Binding Protocol's
services, AppleTalk objects can be named. AppleTalk names consist
of a object, type and zone field, where each of these three
parts are limited to 32 characters in length. An example of
a printer name could be: Finance1:LaserWriter@Executive, where
Finance1 is the name configured for the object, LaserWriter
the object type, and Executive the zone name.
MAC OS
The current operating system running on Macintosh computers
is MAC OS X and supports TCP/IP. Macintosh computers are often
used for graphical and other multimedia related purposes. MAC
OS runs only on Macintosh computers, not on general x86 based
machines. Mac OS X uses an access permission system based on
a UNIX. Every file and folder on a hard disk has an associated
set of permissions that determines who can do what. The three
types of permissions are Read (r--), Write (-w-), and Execute
(--x).
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Current
related exam objectives for the Network+ exam:
1.5 Choose the appropriate media type and connectors to add
a client to an existing network.
2.3 Differentiate between the following network protocols in
terms of routing, addressing schemes, interoperability and naming
conventions:
- AppleTalk
3.1 Identify the basic capabilities (i.e. client support,
interoperability, authentication, file and print services, application
support, and security) of the following server operating systems:
- Macintosh
4.4 Given specific parameters, configure a client to
connect to the following servers:
- Macintosh
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Click
here for the complete list of exam objectives.
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Discuss this TechNote here |
Author:
Johan Hiemstra |
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