AFP Over TCP

This chapter describes how the Transmission Control Protocol (TCP) can be used to transport AFP packets efficiently. With TCP as the transport protocol, AFP services can be made available over the Internet just as they are made over AppleTalk networks. When a user mounts a remote volume over TCP, the type of network over which the volume is mounted is completely transparent to the user. On local area networks, providing AFP services over TCP/IP effectively utilizes the bandwidth of high speed network media such as Fiber Distributed Data Interface (FDDI) and Asynchronous Transfer Mode (ATM).

TCP can be used as the transport protocol for AFP version 2.1 and later.

Implementation

A layer known as the Data Stream Interface (DSI) is used to provide AFP services over TCP. With minimal overhead, the DSI establishes an interface between AFP and TCP that is generic enough to be used over any data stream protocol. The DSI has the following characteristics:

DSI Commands

DSI commands are similar to ASP commands, and they preserve all of the ASP commands except ASPWriteContinue. The DSI commands are listed in Table 6-1.

Table 6-1  DSI commands

Command name

Command code

Originator of command requests

DSICloseSession

1

Client and server

DSICommand

2

Client only

DSIGetStatus

3

Client only

DSIOpenSession

4

Client only

DSITickle

5

Client and server

DSIWrite

6

Client only

DSIAttention

8

Server only