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Inside Macintosh: Networking /

Chapter 1 - Introduction to AppleTalk / Deciding Which AppleTalk Protocol to Use

Measuring Packet-Delivery Performance

You can use the AppleTalk Echo Protocol (AEP) to measure the timing of send-receive cycles and to determine if another node is online. There is no application programming interface to AEP. However, to measure the round-trip packet delivery time from your node to another node, your application or process can send a packet that is addressed to the AEP socket, referred to as the AEP Echoer, on the destination node, and AEP will return a copy of that packet directly to you.

You can use this echo test as part of a diagnostic tool application, for example. A diagnostic tool could troubleshoot a suspect node and report how long it took the packet to travel to and from the node. Your application could use repeated transmissions to determine if a packet takes longer than the typical amount of time to reach the node,
if it contains corrupted data, or if it doesn't make it back at all.

To determine if another node is on the network, you can send a packet to that node's AEP socket. For a conclusive test, you should send more than one packet, in case the first packet is lost or discarded by DDP.