[Nel] TCP vs. UDP

Thu, 5 Jul 2001 18:04:42 +0200

According to Vianney Lecroart:
+> On Anarchy Online game, they only use TCP protocol between client and server
+> (other commercial online game use UDP) and it seems that it causes lot of
+> problem like horrible ping or connection lost:
+> http://aoforums.funcom.com/showthread.php?threadid=26297
+
+
+This post (and the rest of the discussion) do highlight the problems of
+AO. However, only one post, in the whole thread, seems to be close to the
+real "problem".
+
+I have two friends who are playing AO together. They often experience
+"bad lag" (i.e. 20-30s delays between a command and it's execution).
+However, there's one strange thing during these periods of bad lag.
+
+They still chat with each other.
+
+And I've done checking with tcpdump: you do not talk directly between clients.
+Everything goes thru the AO servers.
+
+My guess is that their architecture is based on a front-end/zone service
+model. Clients connect to a front end, and said front-end connects to a
+zone service, depending on the zone you are in. This is further supported
+by various analysis points during beta, notably when the zone service
+crashed while I was in it (and the whole mission dungeon got resert and
+randomly re-rolled), and the numerous problems people have for zoning
+(zone... after a strangely fixed 45s - the default TCP connection timeout -
+ you get "Area Change not initiated on server).
+
+So you have:
+
+Client ---- TCP ----> Front End ---- TCP ----> Zone server
+                          ^                  /
+                          |                 /
+                          V                /
+Client ---- TCP ----> Front End ---- TCP -/
+
+which is probably the worst architecture I can imagine, specially as there
+appears to be one front-end per client, and front ends closes and opens
+communication to zone servers. :(
+
+> In a first step, we would like to know your opinion about this choice. And
+> in a next step, we'll do some test about ping/packet lost and so on to
+> compare TCP and UDP, and we'll need your help to do that.
+
+Packet loss is a non-sequitur under TCP. You *cannot* lose packets under TCP :)
+(you lose connection first)
+
+-- 
+	Vincent Archer			Email:	archer@frmug.org
+
+All men are mortal.  Socrates was mortal.  Therefore, all men are Socrates.
+							(Woody Allen)
+
+