Thanks for the responses. I'll go into a little more detail:
We have been running several profilers against OpenSimulator on the MOSES grid, and on my development machine. The tests were to examine the loading on the server under several different loads, specifically mesh and physics loads. What we found appears to be that no matter what kind of load we placed on the region, even to the point of becoming unresponsive due to physics and mesh, that scripting and physics load were nowhere near the amount of time spent in OpenSim.Region.ClientStack.LindenUDP once we had more than one or two avatars logged in. We know from previous investigations at our firewall that network traffic for OpenSim is not that heavy, especially with low numbers of users.
I ran several Wireshark captures against a Firestorm viewer logging into the MOSES public grid ABWIS region, where we hold our office hours. I saw that with our current configuration, all traffic between the server and my client, with the exception of http CAPS and fsapi calls, were UDP traffic. This is not immediately concerning, as we have simian serve our mesh and textures directly. The messages are mostly binary information, so I could not examine closely, but I did see a lot of messages containing identical ASCII strings, such as the name of my avatar.
My primary concern is the amount of time spent handling networking, not necessarily the networking its-self. But there is at least a portion of messages on the UDP pipeline that are either reliable, or perhaps should be; and re-implementing a reliable transport over udp introduces load at the application layer, instead of letting a low-level reliable transport such as tcp handle it. I went to university with a guy who implemented a java networking library completely over UDP, believing that it was faster than a normal TCP socket; but he was neglecting that the networking hardware handles the ACK and retransmission transparently, and without needing for the messages to be handled manually by the application.
This may just be my opinion, but since I was going to be ecamining the network stack anyways, and typically in a client-server scenario the ability to maintain a persistent reliable connection where the server can push important events to the client, that it would be a good idea. The points about network throttling and QoS are taken, but wouldn't they also typically affect the UDP stream? Working on MOSES I have plenty of problems dealing with external users who operate on restricted networks, and they cannot see traffic aside from 80 and 443 without dealing with their own IT personnel. The fact that it is HTTP over TCP instead of raw TCP makes no difference once it is on a non-standard HTTP port.
I agree that it would be more prudent to look at improving the websocket code and the http server, rather than replace it with a raw TCP socket, especially given that there are multiple plugins, such as jsonsimstats, that use the http functionality directly.
I hope that explains my position a little better. I would love to hear if there are other plans/ideas in the community to address time-sinks like this one, networking simply appears to us as a good starting point to increase performance and scalability of the system.
-- Michael Heilmann Research Associate Institute for Simulation and Training University of Central Florida
Date: Thu, 13 Nov 2014 13:50:32 -0800 From: Diva Canto<[email protected]> To:[email protected] Subject: Re: [Opensim-dev] Modifying the networking stack Message-ID:<[email protected]> Content-Type: text/plain; charset=ISO-8859-1; format=flowed What problem are you trying to solve? It's hard to comment without knowing what you want to achieve, but here are some random observations that you may want to take into account. As far as I remember, the reliable packets are a very small percentage of the UDP traffic at this point, so I'm not sure it's worth creating a dedicated TCP channel for them. Moving the HTTP traffic to the same TCP connection seems like a bad idea, as the HTTP traffic tends to be dominated by big data (textures, assets, etc) which would then get in the way of the small packets like AgentOnline, etc. I suspect it would make the client less responsive than what it is now. There is already support for WebSockets in OpenSim. It may not be complete, so I would encourage you to build on that. I am aware of WebGL clients that use WebSockets with OpenSim, and they have the same problem as described above: the big data gets in the way of the small packets, making the clients less responsive at points. But since WebGL is inevitable, your effort is probably best invested in this than in a TCP channel. Best, Diva On 11/13/2014 1:18 PM, Michael Heilmann wrote:Greetings everyone I and another MOSES developer are going to be looking at the client/server network stack, as well as the processing queue's used for incoming and outgoing packets. I am going to see if I can implement a client stack on opensim and firestorm that uses the traditional TCP/UDP pairing for this type of client<->server relationship. I have two thoughts, but I am interested in hearing if you have ideas or insight into this particular space. Idea 1: Add a dedicated tcp port next to the UDP port, and move reliable transport transmissions to the tcp port. I am uncomfortable increasing the required ports for each region, but the http server is in the way. I can look to move all communications from http to a tcp socket-server type of deployment, at the expense of simple POST/GET operations idea 2: Look into increasing the performance of the http server of the regions, as well as testing/implementing a full websockets implementation, and using the websockets upgrade for consistent client connections. This could eventually lead to javascript-based clients, and does not remove http functionality. Either idea would see any traffic requiring reliable transport shifted off of the current UDP stack, and onto the tcp reliable transport. Either idea also will require modifications to a client to match. I, and another developer here, would be developing the client code, the region code, and testing against a MOSES deployment. As we are MOSES developers, we would be working against simian instead of Robust; so there would be a gap for regular Robust-based grids. If you could lend me your opinions about these ideas, the management queues, associated problems in opensim, etc, I would really appreciate it. We would be working completely in the open on github, and obeying all licensing. We would welcome any and all cooperation, and we will cooperate ourselves wherever we are welcome, but we are not interested in avoiding positive changes to maintain SecondLife compatibility. Thanks.
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