3Com 2500 manual SAP Packet Structure

The Elements of IPX Routing 6-11

A workstation must first know a server’s network address before it can initiate a session with a file server.

SAP Packet Structure

SAP uses IPX and the medium-access protocols for its transport. The packet structure allows the following functions:

■A workstation request for the name and address of the nearest server of a certain type

■A router request for the names and addresses of all the servers or of all the servers of a certain type on the internetwork

■A response to a workstation or a router request

■Periodic broadcasts by servers and routers

■Changed server information broadcasts

Figure 6-5 provides an overview of the SAP packet structure. Note that the packet structure is encapsulated within the data area of IPX.

IPX Packet Format

IPX Header (30 bytes)

Packet Type = 4

Socket = 452h

Data

SAP Packet Structure

Operation	(2 bytes)
Server Entry (1)	(64 bytes)

.

.

.

Server Entry (n)	(64 bytes)
(n <= 7)

Figure 6-5 SAP Packet Structure

Server Entry Structure

Service Type	(2 bytes)
Server Name	(48 bytes)
Network Address	(4 bytes)
Node Address	(6 bytes)
Socket Address	(2 bytes)
Hops to Server	(2 bytes)