[AusNOG] Speeds to international - acceptable minimum

[Glenn Lake]

As per Damien's response - TCP throughput (single stream) will depend on window size.  Default on Microsoft Windows is 64KB from memory.


Latency dramatically impacts the throughput.


Based on a 250Mb/s link the below is likely to USA West Coast (with latency of 169ms which just happened to be a random host I picked - I am in Melbourne)


Bandwidth / latency (250 Mbit/sec, 169.0 ms)
required tcp buffer to reach 250 Mbps with RTT of 169.0 ms >= 5157.5 KByte
maximum throughput with a TCP window of 64 KByte and RTT of 169.0 ms <= 3.10 Mbit/sec.


You either need to adjust window / buffer size or use multiple streams.


Glenn

________________________________
From: AusNOG <ausnog-bounces at lists.ausnog.net> on behalf of Damien Gardner Jnr <rendrag at rendrag.net>
Sent: Friday, 13 October 2017 7:04:08 PM
To: Dino Sosic
Cc: ausnog at lists.ausnog.net
Subject: Re: [AusNOG] Speeds to international - acceptable minimum

Depends on whether you've tuned the TCP stack on the machine you're testing from..  With default window sizes etc, I'd expect maybe 10-20mbps per stream from the US, less from Europe?   With nice large window sizes and receive buffers, I'd be expecting 100-150mbps per stream, provided the server on the other end isn't limiting window sizes to something stupidly low?  (Have had that issue a few times with SaaS providers in the US..  Usually an email to their helpdesk with some pcaps, and an explanation of how window sizes work, and how they need to tune their servers, will result in a huge jump in performance)

A short look with tcpdump, ethereal, etc should tell you whether it's a window size issue, or something further upstream.  If you can, adding an adjust-mss rule on your router to say drop your negotiated mss on outbound connections to say 1400, may make a (large) difference if your provider is using a GRE-based DDoS mitigation platform in the US, and they're doing transparent packet fragmentation, rather than just sending back frag-needed packets.

On 12 October 2017 at 18:22, Dino Sosic <Dino.Sosic at datacom.com.au<mailto:Dino.Sosic at datacom.com.au>> wrote:
Hi,

Out of curiosity, if you get a 250 mbps circuit from an ISP (IP transit service) and all is fine within ANZ but as soon as you go international speed tests show 2/2 mbps, FTP transfers show 7/8 mbps, would that be acceptable? (Same towards multiple US, Europe and Asia destinations)
What is the minimum you would deem acceptable to international destinations?

Cheers
Dino





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Damien Gardner Jnr
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