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adiabatic
join:2009-01-24
Victoria, BC

adiabatic

Member

BB100 - upload rate affects download?

Before I start looking at my equipment... is this normal for BB100? If I'm uploading at 5 Mbps my simultaneous download speed drops to about 15 Mbps. With no uploading happening my download speed is over 75 Mbps (depends on the speedtest).

I've got a gigabit NIC, full-duplex gigabit router and SB 6120 modem. I think everything in the chain is full-duplex capable...
AnonShawUser
join:2006-06-17
Calgary, AB

AnonShawUser

Member

when your upstream is saturated with other traffic, your network is unable to send acks for the received packets in a timely manner. This causes the download to slow down to what it can accept.

If you're using torrents, limit the upstream connections and bandwidth, so there's still overhead to have data pass by through regular channels and you'll have a mostly seamless experience.
adiabatic
join:2009-01-24
Victoria, BC

adiabatic

Member

What do you mean by "my network"? 5 Mbps up shouldn't be saturating my gigabit LAN (I easily stream 50 Mbps videos internally). Is this saturation at the cable modem?

It's not torrents... this is during RDC sessions when I have security camera video visible on the remote machine desktop (not a normal situation to view the video that way, just when I'm configuring cameras).
AnonShawUser
join:2006-06-17
Calgary, AB

AnonShawUser

Member

It's entirely a lack of being able to send proper acks to the general internet, by saturating your upstream. I had a few calls with a very similar situation, where the user was trying to set up and monitor security cameras. His downstream was more than adequate, but his upstream was limited, which was causing the entire network to choke itself when he had more than 1 camera going for remote view. Within the local network, on gigabit connections, you're not at all limited by your external connection speed, but the upstream on the internet side is so much lower, it's barely adequate for sustaining the datastream.

XT0RT
S3x, Drugs, War
join:2001-07-28
Edmonton, AB

XT0RT to adiabatic

Member

to adiabatic
That SB6120 should be retired to be quite honest. It only supports 4 QAM downstream channels while the new Cisco's support 8 QAM downstream channels. Something to think about when you want to upgrade to BB250.
ravenchilde
join:2011-04-01

ravenchilde to adiabatic

Member

to adiabatic
said by adiabatic:

What do you mean by "my network"? 5 Mbps up shouldn't be saturating my gigabit LAN (I easily stream 50 Mbps videos internally). Is this saturation at the cable modem?

If you are saturating your 5mbps upstream, then you can't acknowledge packets on your downloads. This is a function of TCP. If you want to download at 100mbps you need almost the full 5mbps of upstream bandwidth available for TCP ack packets.

»www.google.ca/url?sa=t&r ··· 1_C1sG8A

The above YouTube link is a video of Steve Gibson explaining how TCP works on the Security Now! podcast.

Using 3-4 mbps of your 5 mbps of uploading capacity will severely limit how fast you can download as you cannot acknowledge receipt of packets back to the sender, so they'll stop sending you packets as fast.
ilianame
join:2002-06-05
Burnaby, BC

ilianame

Member

Poor Shaw...

Where and when did you get your Internets license OP?
I'd like to speak to your examiner/instructor...

Jumpy
@shawcable.net

Jumpy to ravenchilde

Anon

to ravenchilde
You don't acknowledge every packet. TCP allows for a series of packets to be sent and is constantly negotiating buffer space with the sender, called the Receive Window. For 100Mbit down, you really don't need more than 1Mbit up in most situations.

That said, you still NEED the upstream available to do exactly what everyone here is saying. Unless you send an acknowledgement to the sender that you've received the data they've sent they won't send you new data and will just resend old data if you take too long.

The consequences of this are that:
A - If you have a small buffer (your equipment's TCP Receive Window) you cannot accept large quantities of data without generating your own upstream ACK packet.
B - If you've got a large amount of upstream traffic, your ACK packets will wait in queue, stalling the TCP stream, reducing your effective throughput.
C - Because of A and B, if you're generating excessive ACK packets because your Receive Window is small, AND you're uploading a large amount of data, you're compounding the problem.
ravenchilde
join:2011-04-01

1 edit

ravenchilde

Member

said by Jumpy :

For 100Mbit down, you really don't need more than 1Mbit up in most situations.

Citation please. I'd love to read up on that.

To my understanding as TCP windows are based on number of packets sent before waiting for an ack (with some going over just to probe for extra speed). So depending on the SIZE of the downstream packets, you may need a lot more upstream (or less). Small packets down will require more ACK packets sending up.

Also using your upstream will cause ACKs to possibly delay sending, which will cause delay in more packets coming down. So delay is a second factor in TCP download speed.

I don't think we can easily say that for 100 mbps down you need only 1 mbps up. I'm not saying that's wrong, but it's a moving target. More is better?

Jumpy
@shawcable.net

Jumpy

Anon

Can you cite where you got your 5Mbit number from?

With a server that has 40 active SSH sessions (of which at least 4 are being used a SOCKS proxy), 34 active irssi (command line IRC) clients, a DNS server, a mail server, and a web server running, I conducted this test.

On a gateway reached by a 100Mbit link, create a 100MByte file in its management webpage path:
$dd if=/dev/urandom of=largefile.dat bs=1M count=100
|100+0 records in
|100+0 records out
|104857600 bytes transferred in 2.878715 secs (36425141 bytes/sec)

and temporarily enable non HTTPS access to the device.

Connect a second SSH session for myself to must test server, run bwm-ng, set to display max observed throughput, set to give me 1 second deltas.
Run wget on my fist SSH session:
$wget »10.1.0.1/largefile.dat
|--2012-02-15 16:42:20-- »10.1.0.1/largefile.dat
|Connecting to 10.1.0.1:80... connected.
|HTTP request sent, awaiting response... 200 OK
|Length: 104857600 (100M) [application/octet-stream]
|Saving to: `largefile.dat'
|100%[==============================================================================>] 104,857,600 11.2M/s in 8.9s
|
|2012-02-15 16:42:29 (11.2 MB/s) - `largefile.dat' saved [104857600/104857600]

Results from bwm-ng:
94.36Mb/s down
2.1Mb/s up

Keep in mind, all those other services I mentioned were still active and count in the 2.1Mb/s up. This was done in a few minutes, and I haven't done any tuning for large file transfers (my receive window is set to 112K - the default for this distro of Linux). This means that I'm only getting data in up to 112K chunks (spread across many packets). If I double that I halve my requires ACKs, etc.
Jumpy

Jumpy

Anon

The other thing I forgot to mention is that the lower your latency to the server providing you your content, the more ACK you'll send.

Yes, it is a moving target. My BSD based firewall at home (also on Shaw's BB100 package) only requires ~900Kbit up for me to run over 90Mbit down.
ravenchilde
join:2011-04-01

ravenchilde to Jumpy

Member

to Jumpy
said by Jumpy :

Can you cite where you got your 5Mbit number from?

Yes. Shaw's 100 mbps package has a 5 mbps upload speed. (10 MBPS soon after their network upgrade)

I cite: »www.shaw.ca
said by Jumpy :

Yes, it is a moving target. My BSD based firewall at home (also on Shaw's BB100 package) only requires ~900Kbit up for me to run over 90Mbit down.

I think what you're saying is that we agree, more is better? :P

To the OP: If you want to Max 100 mbps you'll have more luck if your upstream is free (I think Jumpy would agree).

Jumpy
@shawcable.net

Jumpy

Anon

Just because the package has a 5Mbit upload doesn't mean that you need it to achieve 100Mbit down.

And yes, we agree : having more upstream available is better. I was just pointing out that you don't need all 5Mbit to achieve 100Mbit down. What the OP is doing (saturating their upstream) is having a direct and significant impact on how fast they are able to download.
ravenchilde
join:2011-04-01

ravenchilde

Member

said by Jumpy :

Just because the package has a 5Mbit upload doesn't mean that you need it to achieve 100Mbit down.

I never said you did. Not sure where you are getting this from. I _did_ say that if you saturate your 5Mbps upload capability then you're essentially, as they say in the sticks, "Hosed."

Lets quote me here:
said by ravenchilde:

If you are saturating your 5mbps upstream, then you can't acknowledge packets on your downloads.

said by ravenchilde:

Using 3-4 mbps of your 5 mbps of uploading capacity will severely limit how fast you can download as you cannot acknowledge receipt of packets back to the sender, so they'll stop sending you packets as fast.

I still stand behind those statements. Nowhere did I say 5 mbps was a requirement of 100 mbps download. 'Severely' might have been the wrong choice of word.

Keeping in mind that on a 5mbps upload contract you often won't get a full 5mbps (at least on speed tests).

Jumpy
@shawcable.net

Jumpy

Anon

Quoting from 2012-02-15 16:29:15:
said by ravenchilde:

---snip---
If you want to download at 100mbps you need almost the full 5mbps of upstream bandwidth available for TCP ack packets.
---snip---

That's what I was trying to clarify. You can be using 3-4 mbps of your upload and still achieve close to 100mbit in the right situation.

Still, as we've already agreed, saturating your upload is going to make your download crawl.

zeroumus1
@shawcable.net

zeroumus1

Anon

yup, if you max your upload beyond about 85-100% capacity, your download will start suffer

if you have a way to throttle your upload a little, it is wise to do so. For example, many torrent clients allow you to cap your up and down. this will result in better performance on your computer and reduce un-needed bottle necks on the ISP's gear ( which effects everyone ), even setting your upload to 90%-95% capacity can improve overall network performance greatly
adiabatic
join:2009-01-24
Victoria, BC

adiabatic

Member

If it's stated above I apologise but I'd still like to know where the choke point is. Is it the modem? My router? Shaw's node?

With BB100 and DOCSIS 3.0 I have 4 channels down and 1 up so is the upstream channel not independant of the downstream?

Assuming I limit upload to 4 Mbps to protect download speed, when BB100 upgrades to 10 Mbps will I still be choking that one upstream channel at 5 Mbps or am I going to be able to go to 7-8 Mbps upload speed?

Jumpy
@shawcable.net

Jumpy

Anon

The choke point is with your contract - it isn't a failure, or saturation issue. It is a functional property of how any network works.

You're allocated 5Mbit up. You need to use a part of that to facilitate your downloads. If you use it all for another action you can't tell the other side to send more, slowing your download speed.

When BB100 goes to 10Mbps up the 5Mbps "choke" moves up to 10Mbps with it. Remember that you're not limiting your upload to a specific value for it to work, you're reserving capacity for normal network communication. That same capacity needs to exist regardless of where that "choke" lies. That is, if you need 2Mbit available with a 5Mbit upload, you will need 2Mbit available with a 10Mbit upload.

Baud1200
join:2003-02-10

Baud1200

Member

The best (also most expensive) Internet connection is symmetrical , provided by true cable modem connections, optical fiber systems, and SDSL.