Presentation Layer Protocols - 3Com 4007 Implementation Manual

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HAPTER PPLE ALK OUTING
AppleTalk Data Stream Protocol (ADSP) The ADSP works with the
ATP to ensure reliable data transmission. Unlike ATP, however, ADSP
provides full-duplex, byte-stream delivery. Therefore, two nodes can
communicate simultaneously. ASDP also includes flow control, so that a
fast sender does not overwhelm a slow receiver.
Zone Information Protocol (ZIP) ZIP works with RTMP to map
network numbers to network zones for the entire AppleTalk
intranetwork. Network zones are the logical groupings of AppleTalk
networks. The table created by ZIP is called the Zone Information Table
(ZIT). You view the ZIT by network number or network zone from the
Administration Console.
ZIP creates a zone information table in each router. Each entry in the ZIT is
a tuple, or pair, that includes a network number and a network zone
name. When an NBP packet arrives at the router, the router compares the
zone name in the packet with zone names in the ZIT entries. The router
then compares the network number in the matching ZIT entry with the
network number in the RTMP table to find the interface for routing the
packet.
AppleTalk Session Protocol (ASP) The ASP passes commands
between a workstation and a server after they connect to each other. ASP
ensures that the commands are delivered in the same order that they
were sent and returns the results of these commands to the workstation.
Printer Access Protocol (PAP) The PAP maintains communications
between a workstation and a printer or print service. The PAP functions
include setting up and maintaining a connection, transferring the data,
and tearing down the connection on completion of the job. Like other
protocols at the session layer, PAP relies on NBP to find the addresses of
named entities. PAP also depends on ATP for sending data.

Presentation Layer Protocols

The presentation layer maintains information about files, formats, and
translations between formats. An AppleTalk intranetwork has two
protocols at the presentation layer: the AppleTalk Filing Protocol (AFP) and
PostScript. AFP provides remote access to files on the network. PostScript
is a graphic page description language used by many printers.