Second Life News 2013-7

We have had about a week with the new rollouts. There doesn’t seem to be any major problems. Nothing had to roll back. I’m not clear whether the Interest List or the maintenance package will roll to the main channel this week. We’ll see something post later today when the Lindens make a final decision.

This seems so like SL -

This seems so like SL –

Interest List

The bot users have seen a huge drop in the data being delivered to them. Even beyond the amount added with the Interest List bug. Andrew Linden was considering what changes, other than the bug fix, may account for the saving in bandwidth use.  Some of those items are:

  • Removal of the data needed for the old particle clouds.
  • Fewer wind data updates.
  • Improved server side culling.

The whole point of the Interest List update was to improve server side culling, meaning to have the server only send object information for the objects an avatar can see. That has improved.

Often there is the problem of a fix creating new problems. One such is a visual glitch that some people are noticing. But, the Lindens are not hearing complaints. So, while the Lindens do have a fix in the works, they are interested in how many people are bothered by the problem.

You may notice the problem but only in areas with the Interest List upgrade. Currently and last week that would be in the Magnum RC channel. The glitch happens when there is a prim that is moving or changing and you turn your back on it, take it out of the avatar’s field of view. The server stops sending you updates for that object in a second or two. When you turn around and look at the object again, it is still in the state you last saw it. It then takes a second or less for the server to realize you can see it and send an update. Once you get the update, it snaps to the ‘current’ state.

I suppose a clock could snap to the correct time or a trolley could jump to its current position. So, if you see something like this in Magnum RC regions, let Andrew know in the Deploys thread. But, remember. If you go looking for it, that isn’t really the ‘noticing’ I think he is looking for.

Not Interest List

There is another thing we sometimes notice. If you have been in a shop looking a things in one end then move to the other end, the texture at the original end with de-rez. When you turn around they are grey. They quickly rez, but it is a bit of a bummer.

There is a point at which the viewer decides to unload textures from your graphics card to prepare for the new ones that are bound to come. The less video ram you have the sooner this is likely to happen. It has nothing to do with the recent Interest List changes.

Network Packet Sizes

Some of the recent HTTP Protocol work and Interest work has dealt with packet sizes used by Second Life. You probably know that all the information moving across the Internet is carried in packets of data. Just like letters used to be in paper envelopes, which could be thought of as a packet, with a destination and return addresses, so data moves across the Internet in ‘packets’ with destination and return addresses.

Just as there was a weight limit on paper letters there is a similar limit on how much data can be placed in a packet. For some time the size of these packets was pretty much set to be a total of 1492 bytes for Ethernet networks, the Internet. But, with the advent of streaming media, think Netflix and COX cable services, we started to move toward network congestion, mean we were push all the data into the system that it could carry. As things got more congested there was the possibility of a network crash, just like a wreck on a freeway at rush hour jams traffic.

While 2012 was the year for converting from IPv4, the style of writing address on packets, to IPv6 the problem of traffic congestion has been in the works even longer. Windows XP made some effort at being able to handle data packets of variable lengths. Vista, Win 7 and 8 improved on their ability to handle variable packet sizes. While the dominant paper envelop is still the #10 the USPS, UPS, and FedEx can all handle a variety sizes. The same is true of the Internet.

But, old routers and switches slow things down. So, the Lab is in the place of deciding how much of the new tech they can use and how to deal with old equipment used by customers. I am one that hopes they are handling variable size network packets.

Andrew says that most of the UDP packets are only carrying a few hundred bytes of data, so size is not a concern. But, the streaming packets delivering textures and mesh fill up the packets to the max. Currently the code is written to target 1500 bytes as the completed packet size for UDP packets rather than the typical 1492. Andrew is looking at redoing there code.

Prior to Andrew’s fix some cases would force the packet size to 3,000 bytes. Routers will typically split these large packets into smaller ones, which later get reassembled. Unfortunately not all routers are smart enough to know they need to do that. So, it is possible to get some fails as packets are clipped.

Second Life Viewer

The next thing heading into the viewer-development channel is CHUI, Chat Hub User Interface. The Materials System has some bugs on the viewer side that are being worked on. So, it is still in a separate channel of its own.

The avatar baking project is currently in load testing. I suppose the Lindens are figuring out how much hardware will be needed for the ‘bake backend.’

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