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Standard User mlmclaren
(experienced) Wed 01-Apr-15 12:28:57
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Throughput vs. Sync Rate


[link to this post]
 
So what would be the throughout one should expect to see from a speedtest or downloading if their VDSL line synced at 40000/10000kbps ?

and would the math also be the same for speeds from 2000/2000-> 80000/20000kbps?

Plusnet Unlimited 21CN 4200/800 @ 4.2Km > TP-Link TD-W8968v3 - BQM IPv4
Plusnet Fibre Extra 66000/20000 @ 450m > HG612 (Unlocked) > Linksys LRT224 - BQM IPv4
Standard User Chrysalis
(legend) Wed 01-Apr-15 12:40:02
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Re: Throughput vs. Sync Rate


[re: mlmclaren] [link to this post]
 
probably around 37mbit/sec if all is working ok.

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Standard User mlmclaren
(experienced) Wed 01-Apr-15 12:42:33
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Re: Throughput vs. Sync Rate


[re: Chrysalis] [link to this post]
 
Is their a specific math behind it all... a percentage maybe... do you know any sites where I can get this information?

Plusnet Unlimited 21CN 4200/800 @ 4.2Km > TP-Link TD-W8968v3 - BQM IPv4
Plusnet Fibre Extra 66000/20000 @ 450m > HG612 (Unlocked) > Linksys LRT224 - BQM IPv4


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Standard User mlmclaren
(experienced) Wed 01-Apr-15 13:18:03
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Re: Throughput vs. Sync Rate


[re: Chrysalis] [link to this post]
 
I calculate around 7.5% loss mark then for throughput over the sync rate

Plusnet Unlimited 21CN 4200/800 @ 4.2Km > TP-Link TD-W8968v3 - BQM IPv4
Plusnet Fibre Extra 66000/20000 @ 450m > HG612 (Unlocked) > Linksys LRT224 - BQM IPv4
Administrator MrSaffron
(staff) Wed 01-Apr-15 13:22:03
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Re: Throughput vs. Sync Rate


[re: mlmclaren] [link to this post]
 
Maximum TCP/IP throughput is 96.8% of the sync rate.

The other differences are down to the various overheads on your home network etc
Even 100 Mbps Ethernet does not deliver 100 Mbps but a couple of Mbps below this.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
Standard User mlmclaren
(experienced) Wed 01-Apr-15 13:24:51
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Re: Throughput vs. Sync Rate


[re: MrSaffron] [link to this post]
 
OK...

So I'm syncing at 66000kbps ... I can only achieve a max throughput of 60700kbps...

I feel this is around 2000kbps shy of its capability...

Nothing shocking I know but curiosity smile

Plusnet Unlimited 21CN 4200/800 @ 4.2Km > TP-Link TD-W8968v3 - BQM IPv4
Plusnet Fibre Extra 66000/20000 @ 450m > HG612 (Unlocked) > Linksys LRT224 - BQM IPv4
Standard User TheEulerID
(member) Wed 01-Apr-15 13:30:21
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Re: Throughput vs. Sync Rate


[re: mlmclaren] [link to this post]
 
Yes. The overhead is essentially down to overheads on the framing, IP and TCP overheads.

The usual maximum packet size is 1500 bytes (there are so-called "jumbo-packets", but they are only used for specialist purposes, like local storage over IP and require special support). However, within that 1500 byte packet there is a 20 byte IP packet header and a 32 byte TCP header. That gives you a payload of 1448 bytes. However, there is also an Ethernet framing overhead comprising another 38 bytes. So, for every 1448 bytes of data there are 1538 bytes sent over the link. That's 94.1% payload efficiency, which means for a 40mbps sync there is a maximum of 37.6mbps data throughput available.

The proportion is the same no matter what the sync speed. So an 80mbps will have a maximum TCP payload throughput of 75.2mbps.

*** edited as there was a slight mistake where I'd used 1440 as the payload size ***

Note that this is for IPV4. IPV6 has larger overheads.

Also, there is an overhead for "ack" packets in the opposite direction (About 4%, so downloading at 40mbps requires a minimum upload bandwidth of 1.6mbps).

UDP protocols have different overheads, but that's not normally used for speed tests.

Edited by TheEulerID (Wed 01-Apr-15 14:07:37)

Standard User b4dger
(knowledge is power) Wed 01-Apr-15 13:31:18
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Re: Throughput vs. Sync Rate


[re: mlmclaren] [link to this post]
 
Have you checked the current IP Profile rather than the sync?

Standard User mlmclaren
(experienced) Wed 01-Apr-15 13:34:06
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Re: Throughput vs. Sync Rate


[re: b4dger] [link to this post]
 
In reply to a post by b4dger:
Have you checked the current IP Profile rather than the sync?


64mbps (BTw IP Profile)

Plusnet Unlimited 21CN 4200/800 @ 4.2Km > TP-Link TD-W8968v3 - BQM IPv4
Plusnet Fibre Extra 66000/20000 @ 450m > HG612 (Unlocked) > Linksys LRT224 - BQM IPv4

Edited by mlmclaren (Wed 01-Apr-15 13:34:29)

Standard User TheEulerID
(member) Wed 01-Apr-15 14:03:20
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Re: Throughput vs. Sync Rate


[re: MrSaffron] [link to this post]
 
That calculation is surely only covering the TCP & IP headers. Surely it's necessary to include the Ethernet frame overheads too (unless the stats reported by the modem include an allowance for that).
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