cancel
Showing results for 
Search instead for 
Did you mean: 

Routerstats speeds

shure
Grafter
Posts: 509
Thanks: 1
Registered: 21-01-2013

Routerstats speeds

Hi,
on my Routerstats summary (as well as my router's own stats page) it claims my download speeds are 7,616 up and 448 down, while I never get anywhere near those speeds.  The best I can get at the moment are 6.5 up and 0.35 down.  When I moved to Plusnet I was given an estimated sync speed of 8Mbps.  I know things can change but why do the routerstats give such differing figures to the speedtest sites?  The sync speeds page on Routerstats also gives around 7,600 (I'm assuming 7,616 for consistency but my graph's not that detailed!), so if it's measuring that speed why am I only seeing 1Mb less?
6 REPLIES
Estragon
Rising Star
Posts: 811
Thanks: 10
Registered: 07-02-2012

Re: Routerstats speeds

That sounds like you are on a 20CN exchange, using IPSC, (in layman's terms the latest way of delivering ADSL Max).
All BT-Wholesale based connections such as Plusnet's are subject to an IP Profile system and other effects of BT Wholesale Dynamic Line Management.
The maximum connection speed is 8128kbps. However if Interleaving is turned on by the DLM, for most combinations of exchange kit and the user's router that reduces to 7616kbps, which is what you have.
Then you get the normal IP Profiling, which in your case is according to the table on this page. Giving you a maximum throughput of 6500kbps. I expect your Plusnet "Current line speed" show 6.4Mbps, losing you another 100kbps.
The sick bit is that on a WBC-enabled exchange you line should connect at well over 20Mbps.
Edit - you have your down and up speeds wrong way round in your post.
shure
Grafter
Posts: 509
Thanks: 1
Registered: 21-01-2013

Re: Routerstats speeds

ah, silly me.  I do know the difference between up and down, honest! Embarrassed
That all sounds fair enough, and many thanks for the excellent explanation (yes, I am on 20CN Angry), but what I don't get is if my actual speed is reduced to 6.5Mbps down (which is fine if that's the way it works), then why does the router tell me I'm getting 7,616kbps?  Doesn't the profiling happen before it gets to my router, if you get what I mean?  Shouldn't the router report on what I'm actually receiving?  Otherwise, the router stats sync speed is always going to be at odds with what I'm actually getting and not worth much as a diagnostic tool, or am I seeing it wrong?
pengbo
Grafter
Posts: 104
Registered: 15-01-2013

Re: Routerstats speeds

shure from memory I think the router reports the synch rate with the exchange but when you use the connection there is an overhead between what you can actually get and the data needed by the adsl process itself to make sure the the real tcp/udp packets data gets to you if that makes sense.
I will leave it to the more knowledgeable to give you the actual maths
Estragon
Rising Star
Posts: 811
Thanks: 10
Registered: 07-02-2012

Re: Routerstats speeds

The speed, attenuation and the other stats that you see are for the actual connection of the modem component of your ADSL router to a modem at the exchange. The sync/connection speed is the rate "bits" are travelling up and down the line all the time your router is synchronised with the exchange modem. So that is the speed reported at that stage.
Data on the internet as a whole is generally transmitted in digital TCP/IP packets. A TCP/IP packet has a header containing the target IP address and other stuff, data, and some end bits. These packets are of variable length but need to be no bigger than the MTU settings of the kit they pass through, otherwise they have to be split up. (Which is why MTU size matters).
When those get to the DSLAM at the exchange (which holds loads of modems with you connected to one) they have to be further packaged into ATM packets.
Assume you are not downloading anything - zilch, No browsing, email or anything. In the first paragraph I said bits are travelling up and down all the time. Those bits are organised into empty ATM packets.  In other words the on-off pattern of the bits lays out a header, empty body and end. 53 bits in total.
When you are receiving something the TCP/IP packets (including the wrapper parts as well as the data) are split up into chunks to form the body of those ATM packets.  IIRC the body is 48 bits. So some ATM packets will still have empty space in them as if a TCP/IP packet does fit into a whole number of them the last one isn't full. The next TCP/IP packet doesn't start in there, it starts at the beginning of the next ATM one.
There's a lot of overheads there. The IP Profile accounts for a lot of the overheads as it tries to define the data speed. Which is why Plusnet call their copy of the IP Profile "Current line speed", being the fastest that real data can get to you.
From that little lot, I think you will see why speed test results, (measuring data bits), will always be a bit less than IP Profile, which is inevitably considerably lower than sync speed?
Superuser
Superuser
Posts: 9,133
Thanks: 537
Fixes: 46
Registered: 06-04-2007

Re: Routerstats speeds

It's a bit technical but AAISP's Knowledge Base article ATM/IP and overheads provides the numbers to explain how sync rate translates into payload (data) rate when protocol overheads are allowed for. However even this doesn't allow for the overheads of managing data transmission to and from a particular host - establishing the link, requesting a file, confirming packet receipt or requesting retransmission of damaged packets and closing the link.
David
shure
Grafter
Posts: 509
Thanks: 1
Registered: 21-01-2013

Re: Routerstats speeds

Thanks all for your feedback.  Much appreciated.  I understand about the packets but I was under the (mistaken!) impression that all that happened before reaching the router and the speed which it registered should be the actual one i was getting.  Learn something new every day Cheesy