AppleTalk Protocols 6-9
The AppleTalk Transaction Protocol (ATP). ATP, along with the AppleTalk
Data Stream Protocol (ADSP), ensures that DDP packets are delivered to a
destination without any losses or corruption.
The Name Binding Protocol (NBP). The NBP translates alphanumeric
entity names to AppleTalk addresses. The NBP maintains a table that
references the addresses of nodes and named entities that reside in that
node. Because each node maintains its own list of named entities, the
names directory within an AppleTalk network is not centralized. It is a
distributed database of all nodes on the internet.
The Session Layer Protocols
The four session layer protocols are these:
■The Zone Information Protocol (ZIT)
■The AppleTalk Data Stream Protocol (ADSP)
■The AppleTalk Session Layer Protocol (ASP)
■The Printer Access Protocol (PAP)
The Zone Information Protocol (ZIP). ZIP works with RTMP to maintain a
table that maps network numbers to network zones for the entire AppleTalk
internet. Network zones are the logical groupings of AppleTalk networks.
The table created by ZIP is called the Zone Information Table (ZIT). The
Administration Console allows you to view the zone information table by
network number or network zone.
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, it includes the zone name which
the router compares with entries in the zone table. The router then matches
the network number from the matching ZIT tuple to that in the RTMP table
to find the interface where it can route the packets.