Physical Layer Protocols; Link Layer Protocols; Network Layer Protocols; Transport Layer Protocols - 3Com CoreBuilder 2500 User Manual

Physical Layer
Protocols

Link Layer Protocols

Network Layer
Protocols
Transport Layer
Protocols
The Physical layer of the OSI protocol stack defines the connection with
network hardware. With AppleTalk, you can use standard network
hardware, such as that designed for Ethernet and token ring networks.
Apple has also defined its own network hardware, called LocalTalk, which
uses a synchronous RS-422A bus for communications.
The data link layer provides the interface between the network hardware
and the upper layers of the protocol stack. The AppleTalk data link layer
includes three link access protocols (LAPs):
TokenTalk LAP (TLAP)
Ethernet LAP (ELAP)
LocalTalk LAP (LLAP).
The AppleTalk Address Resolution Protocol (AARP), which translates
hardware addresses to AppleTalk addresses, also exists at the data link
layer because it is closely related to the Ethernet and token ring LAPs.
AARP is usually included in the definition of each LAP, so it does not
appear in the reference model. See "About AARP" on page 8-10 for
more information about this protocol.
The network layer accepts data from the layers above it and divides the
data into packets to send over the network through the layers below it.
The Datagram Delivery Protocol (DDP) transfers data in packets called
datagrams.
Datagram delivery is the basis for building other AppleTalk services such
as electronic mail. With DDP, AppleTalk runs as a process-to-process,
best-effort delivery system in which the processes running in the nodes of
interconnected networks exchange packets with each other.
The Transport layer and the Session layer provide end-to-end services in
the AppleTalk network. These services ensure that routers transmit data
accurately between one another. Each layer includes four protocols that
work together to support these services. This section describes these
protocols and provides more detail for the protocols that you can view
using the CoreBuilder 2500 Administration Console.
AppleTalk Protocols 8-5