How does one diagnose packet loss ?

All day today I have had packet loss spikes. When I contacted LL support, they said there is no problem. One sim I was on had 100 people and that was related to packet loss (?). 100 people lag I can understand really easily, but packet loss ?

At any rate, I was told to recycle my broadband modem and perhaps to contact my ISP. Contacting my ISP is the last resort, because they recently replaced some local equipment for me and have tested my line.

Any links you can give me or a short course on packet loss ? Thanks.

Steve

on edit: some basic information below from wikipedia.org

Packet loss can be caused by a number of factors, including signal degradation over the network medium, oversaturated network links, corrupted packets rejected in-transit, faulty networking hardware, maligned system drivers or network applications, or normal routing routines.

Effects

When caused by network problems, lost or dropped packets can result in highly noticeable performance issues or jitter with Streaming Technologies, Voice over IP, Online Gaming and Videoconferencing, and will affect all other network applications to a degree. However, it is important to note that packet loss does not always indicate a problem. If the latency and the packet loss at the destination hop are acceptable then the hops prior to that one don't matter. [1]

Packet recovery

Some network transport protocols such as TCP provide for reliable delivery of packets. In the event of packet loss, the receiver asks for retransmission or the sender automatically resends any segments that have not been acknowledged. Although TCP can recover from packet loss, retransmitting missing packets causes the throughput of the connection to decrease. This drop in throughput is due to the sliding window protocols used for acknowledgment of received packets. In certain variants of TCP, if a transmitted packet is lost, it will be re-sent along with every packet that had been sent after it. This retransmission causes the overall throughput of the connection to drop.

Protocols such as UDP provide no recovery for lost packets. Applications that use UDP are designed to handle this type of packet loss.

http://en.wikipedia.org/wiki/Packet_loss

If there is packet loss for any lenght of time I usually ask people around me. Mind you most of the time everyone starts commenting on it at the same time so no need to ask. That will tell you who's end its on. Otherwise it would be your isp and its possible they just dont recover it well. I have not had packet loss come from my end ever so I dont know, but I doubt I would contact my isp about it. The amount of data coming to your computer from second life and the bandwidth consumption rates are pretty huge anyhow and some isp's just dont allow that amount of stuff to go through regularly, but then you would get an email. In any event it would have to be really severe for me to say anything especially at this time of year because internet traffic usually jumps exponentially as summer draws to a close in the northern hemisphere and this is usually when stuff breaks

This is the part to pay close attention to..

You've got SL software running on your computer. LL has server software that talks to your copy of SL. All packet loss really means is that something between your client and LL's servers got lost or didn't make it to the other end quickly enough. Could be network, your end or LLs or somewhere in between. Could be the sim is hurting and slow.

I've never really like the SL term "packet loss" - it's just too generic for me. Kinda like the "check engine" light in cars, it just says something is (or _might_ be) wrong but doesn't really give you any idea what the problem is.

If I start lagging, I look at the sim fps, not at packet loss. If that's low, I look at the time numbers at the bottom of the stats bar as they give a decent idea of what the sim is spending time on. If I'm lagging but the sim stats seem ok, the problem is usually on my end.

Are the packet loss spikes causing any trouble?

I think the packet loss figures SL displays include factors other than transmission problems between SL and you and includes problems related to SL's inability to produce the packets quickly enough. So I think that if one of the 100 people in a sim has problem like a bad router or defective cable that impairs that user's ability to provide SL with the packets it needs to send to you that that can cause the SL packet loss display that you see to spike.

There's a program called VisualRoute Lite from http://www.visualroute.com that will give you a nice little graph that shows response time and packet loss. You can get the url to use for testing from the Help About Second Life dialog.

Search around for Internet ping tests, latency, traceroute, and tracert.

SL uses (or used to use) a lot of what is called UDP datagrams. Basically, a packet is sent, and if no ACKnowledgement is received after some length of time, it is assumed that either it was not delivered, or the reply was not delivered. in either case, the sender probably tries again.

The problem could be anywhere between you and Linden Lab.

Oh yeah, are there any consequences to the packet loss spikes you are seeing, or is it justtha the packet loss indicator is going up high and it bugs you?

This is probably LL's favorite lie. It is sort of like "It is Microsoft's fault" when you can't find what to blame.

They know their output needs exceed their capacity, but they'd rather make you think that you've done something wrong. It keeps you from bothering them until you've diagnosed the entire internet. I had done that a few years ago and they told me I was mistaken.

Remember:
1. Clear your cache
2. It is your ISPs fault that we have oversubscribed our output
3. Reinstall the client
4. Re-enter your billing information
5. Send mail to support for no reason at all
6. Whatever you do, don't call them "phone weasels"

Probably some lag. I did WinMTR and there was packet loss all up and down the network, from my ISP and including LL.

The sim I am on now has only 9 people on it, and packet loss is still spiking really badly. If no one else really cares about it, then I'll forget about it.

Its not just about the sim.. its all linked through the 'Grid'.. your inventory is held on an assest server which is remote from the sim server unless you are wearing the goods, or using them in the event of animations/weapons etc. Rez a prim, thats the sim server that creates that, put it into your inventory, that is held on the assest server. TP and you leave a residue on the sim server you left and are transfered across the internal network to the new sim server, and not forgetting, it is also shadowed to any adjoining sims as you are visible there... add that to the map updates, again colated onto a realtime server.. then there is the tracking of your IM's, voice chat, group notices.... etc etc..

Do Help->About SL to get the name of the server that sim is on. From there, a tracert will show you how 'far' you are to that sim - more hops = more chance of losing packets - and a ping -t left to run for a few minutes will show you how steady your connection to the server is.

Network problems aren't always the cause of packet loss, though.. Just about anything (bad disk, overloaded sim, etc, etc, etc) can contribute to it.

I once had packet loss of around 374%.

I still don't understand what its all about, but that was pretty bad. Now if I have packet loss of 30-60% I'm thinking, "I've had worse."

/me guesses this is from a single packet having to be resent several times.

I suspect that SL uses a protocol where packet reordering causes it to think that packets were lost. Reordering of packets is explicitly allowed in an IP network, but nevertheless service providers and network equipment vendors work very hard to avoid this as much as possible because it causes many protocols to operate less efficiently. (I work for Cisco, and believe me we work very hard to avoid this.)

However, a well-designed protocol should have minimal degradation due to packet reordering in the network, as long as the reordering isn't extreme.

I've read on this forum that wireless links cause packet reordering, and that it adversely affects SL. That's just hearsay, and I seem to get about the same behavior wired versus wireless, but YMMV and it's worth a try.

In my experience, high packet loss causes slow rezzing after TP and effects like that.

I agree.... Time Dilation (the latency between the LL grid network) is probably responsible for 'lag related' issues more than any other.

phone company/DSL came in and tested my pc and traced all thier lines running in here from the office, it's not them, or my pc, it's on the other end which they have noted we're having the issues, on the SL end.

The only remedy I know of is to reduce the "Bandwidth" parameter in Preferences -> Network. However, that slows things down even when they'd be running without much packet loss. This *seems* to reduce packet loss, but I'm not sure it ends up speeding things up much overall.

Also, if possible try hard-wired rather than wireless, in case the rumor was correct.

BTW, your service provider probaby didn't test for packet reordering (if that is indeed the problem). That's a more sophisticated test, and I don't know of any way you could test this yourself.

Finally, SL is migrating towards using TCP rather than UDP. Hopefully, the TCP implementations on our PCs is relatively tolerant of packet reordering, and if so, things might improve. With UDP, it's all up to the application (SL) to handle packet reordering, and SL doesn't seem to be very good at it.

trace from the main office to here, and he/they came into the house, went online tested there, as well after I logged for him SL he went in world for me to test our end further there. I'm am sure it will be solved it does have it's peeks.

But I do thank you and am in great hope of it's potential of use in the future in many venues.
Many Blessings,,