prop. 144 more implementation notes

i2p2www/spec/proposals/144-ecies-x25519-aead-ratchet.rst

@@ -3207,6 +3207,30 @@ non-mod-16 padding, things will need to be done differently.
 
 
 
+Protocol-layer Responses
+-------------------------
+
+Initial implementations rely on bidirectional traffic at the higher layers.
+That is, the implementations assume that traffic in the opposite direction
+will soon be transmitted, which will force any required response at the ECIES layer.
+
+However, certain traffic may be unidirectional or very low bandwidth,
+such that there is no higher-layer traffic to generate a timely response.
+
+Receipt of NS and NSR messages require a response;
+receipt of ACK Request and Next Key blocks also require a response.
+
+A sophisticated implementation may start a timer when one of these
+messages is received which requires a response,
+and generate an "empty" (no Garlic Clove block) response
+at the ECIES layer
+if no reverse traffic is sent in a short period of time (e.g. 1 second).
+
+It may also be appropriate for an even shorter timeout for
+responses to NS and NSR messages, to shift the traffic to
+the efficient ES messages as soon as possible.
+
+
 
 Analysis
 ========