Will WAAS be worth it?

[Pete89]

Hello,

We have our headquarters in New York and a remote office in Chennai India. The circuit between the offices is a 10mbps MPLS with a big provider.

The performance of web applications is fine. Users start to complain when it comes to Windows file transfers or admins trying to deploy software packages to PCs in Chennai. I used this math to figure out what the best throughput could be given the latency and the TCP Window size:

TCP-Window-Size-in-bits / Latency-in-seconds = Bits-per-second-throughput

And what I got was a little over 2.0 mbps of maximum throughput for a tcp session. Not surprising given the latency of 235ms. Window size was around 50,000 bits.

So my questions is could a WAAS device in each office make any difference at all for the apps that are transferring data? I mean you cant cheat the speed of light right?

I have tried to show MGMT the math and I get rolling eyes. They just want it to go faster, and the worst thing that could happen is we spend the money on WAAS and there is no noticeable improvement. Instead of rolling eyes, they'll be rolling me out the door.

Any advice is much appreciated.

P.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Yes, WAAS might help.

Keep in mind, often these devices cache/compress already seen traffic.  I.e. first transfer isn't faster but repeat transfer can be much, much faster.  (e.g. Same software push to multiple hosts.)

Some device can also improve 1st time transfer performance by using techniques such as compression (w/o caching), increasing TCP RWIN (which you can do to on your hosts), and/or using a "faster" TCP variant that works well with LFNs (long fat network).

PS:

BTW, if using Windows hosts, Vista and later have a "next Gen" stack which can improve file transfer performance over LFNs.  However, their compound TCP, isn't fully enabled on workstations, you need to manually activate it (netsh interface tcp set global congestionprovider=ctcp).  (NB: of course, you'll want both hosts to support compound TCP to fully leverage it.)

[Pete89]

Joseph,

Thanks so much for your input. Our workstations are all Windows 7. The file servers are Server 2008. I will have a talk with the Windows team to see if we can get both server and client to use the setting you mentioned.

In addition, if we decide to go with WAAS, is it recommended to use dedicated piece of hardware? The headquarters Edge routers are ASR1004s and the Edge router in India is a 2921. I  know Cisco offers some WAAS modules for the 2900s. Not too sure about WAAS for the ASRs. My experience with integrated modules is not great and thus I prefer dedicated hardware.

I presume if we went the route of dedicated hardware it would be one device in each location correct?

Again many thanks for your help!

P.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Windows Server 2008 should already have CTCP enabled; but Windows 7 hosts might not.

Using a module has the all the normal pros and cons.  So, cannot say a stand alone unit would be better, although the latter does provide you more selection options, including 3rd party.

Normally, yes, you need WAAS hardware at each site.

PS:

Just increasing a host's RWIN will often allow it to push a LFN to capacity.  However, slow start really does become slow start when latency is high.  This can also be a problem if sending lots of little files, i.e. each one starts slow.  Small files might not even allow the transfer rate to reach full speed.

Also a problem is standard TCP's adaptive flow rate, which increases very slowly when latency is high after a packet is lost.

I believe there are file transfer utilities, that transfer a file using multiple TCP sessions.  This can greatly increase the transfer rate on a LFN.