Network and Telecom Strategies Blog

Handling Poor Application Performance over the WAN

Posted by: Eric Siegel

It's the end of my writing quarter, and I'm putting the finishing touches on a paper for management about WAN performance optimization (also called WAN Optimization Controller [WOC]) technologies.

That reminded me to make a note that WAN performance optimization isn't always the best solution, although I do think it's great! (See, for example, my previous blog entries "Final Catalyst WAN Performance Optimization Notes" and "Be a Hero! Cut costs to Zero!"; there are others.) (And, by the way, Catalyst is a great place to meet your colleagues! So let's put in an advert for them: Go To Catalyst!)

Here are some alternatives to WAN performance optimization that should always be considered:

• Application redesign or reselection: In some cases, it's better to replace a few poorly-designed applications instead of trying to alter the WAN characteristics. Backup and file transfer or distribution applications that don't remove long duplicate data strings ("deduplication") or that handle transmission errors or congestion inefficiently are prime examples. The Burton Group report “Designing Applications for the WAN” was written to assist programmers in designing applications properly for operation over the WAN, thereby avoiding the need for optimization. 

• Application remoting: Often called "terminal server" or "Citrix," this solution is best for applications that are tightly-intertwined with some remote service; for example, an application in a remote office that makes frequent calls on a database in the enterprise's central server location. Application remoting can also save money on licensing fees and has other advantages. Application Remoting data flows will probably require network QoS.

• System tuning: In some cases (e.g., inability to use all of the bandwidth in a high-latency path), simply tuning existing software or upgrading to more recent version (e.g., shifting to Microsoft Windows Vista from Windows/XP) can produce massive results at minimal cost. 

• WAN service modification: For some situations, the need for more bandwidth or better network delay or error characteristics is unavoidable or is the most cost-effective solution. In some cases, technology changes (e.g., to satellite from terrestrial links) are also involved. Renegotiation of carrier contracts and changing carriers are also options. 

See the Burton Group report "WAN Performance Optimization Quick Start" to learn about WAN performance optimization, and wait for my new Management Initiative document "WAN Performance Optimization" if you have to discuss things with your management. (As always, if you desperately need it now, and you're a Burton Group client, send me an email and I'll give you a pre-publication copy.)

WAN Performance Optimization for SaaS

Posted by: Eric Siegel

While I'm thinking about Software as a Service (SaaS) today, how about WAN Performance Optimization for SaaS?

Some SaaS websites are well-designed for the Web and perform well over poor bandwidth and high latency, but others don't, or they require the upload/download of large files. For those situations, WAN performance optimization can make the difference between usable and useless. (See, for example, my blog entry "Be a Hero! Cut costs to Zero!" for a discussion of optimization.)

Indeed, if you've created performance indicators in your service level agreement (SLA) with the SaaS provider, they may be more than happy to work with you to install WAN performance optimization between their server sites and your users. (See my blog entry "SaaS network performance SLAs.")

So. How should you install WAN optimization? There are a few things to keep in mind as you discuss this with your SaaS provider.

First, if your SaaS provider wants to use a double-ended appliance system (i.e., an optimizer appliance at the SaaS server site and an optimizer appliance at your site), how are you going to configure the device and integrate it into your branch offices? What happens if you have more than one SaaS provider? Will there be a tall, tottering stack of WAN optimizers from different vendors, and a maze of Ethernet cables plugging everything together? If the "appliance" at the branch office is a software application, how will you load it into your branch office server, and will it conflict with other software?

Second, if your SaaS provider wants to use a single-ended system (i.e., an optimizer appliance at the SaaS server site communicating with ActiveX, Java, or JavaScript running in a browser), then you have to be sure that your staffs' browsers will accept the plug-in, if necessary, and that it won't interfere with anything else.

Third, even if your SaaS provider doesn't want to install WAN optimization, you may still be able to improve performance with a branch office cache that will store commonly-downloaded files for use by all browsers in the office. Many branch office optimizers -- such as those that you might be using for communications with your central office -- can provide caches, as can Web traffic filtering devices, such as Blue Coat's ProxySG. Of course, there are also free caches, such as Squid; they can run on an inexpensive Unix or Windows box and make a big difference if you have a lot of users accessing the same set of Web files.

Congestion Going Into Network Branches = Packet Loss

Posted by: Eric Siegel

End of the month, and I've been going over the list of the "dialogues" I had with Burton Group clients to see if there's something that might be of general interest.

So I uncovered one that I participated in with my colleague Ken Agress of Burton Group's consulting organization, and it's interesting because I think that the topic of QoS congestion on links into remote branches isn't given enough consideration in QoS network design.

The basic symptom of the problem was that despite QoS on the routers, there was excessive packet loss on high-priority flows into the branches on a hub-and-spoke network design.

But that's because the server-room router was trying to push too much data into the network cloud for a specific branch office. The discards weren't occurring at the server room boundary router into the cloud, because the fat access link from the server room will easily accommodate lots of traffic to the branch, especially if the other branches aren't receiving much traffic at that time.

If you have a large bandwidth access link into a cloud, but just a small bandwidth access link out of the cloud to a branch office destination, the cloud will need to discard data packets on high-bandwidth flows or during bursts, because the cloud itself (i.e., the backbone routers) has minimal buffering.

True, a single TCP flow will self-adjust (by "self-clocking") to a bandwidth-restricted exit from the cloud because its acknowledgements will be delayed, but if there are a lot of parallel flows, or there are non-flow-controlled UDP flows, you'll be in trouble. TCP flows will get the "global synchronization problem," in which all TCP flows ramp up in bandwidth concurrently, lose packets concurrently, reset their flow rates downwards concurrently, and then repeat. RED or WRED or FRED mechanisms can help avoid global synchronization, but you'll still lose packets.

So, how should this be handled? If you own the cloud or can signal to the cloud's administrator (e.g., by setting DSCP fields or EXP tags on packets going into a MPLS cloud), then the cloud can pick which packets to discard if the exit bandwidth isn't sufficient at the branch office. And the tags will, we hope, tell the cloud to discard packets from low-importance flows. RED / WRED / FRED on those flows will then get those low-importance flows to cut their bandwidth use. Those low-importance flows will be losing packets and will be miserable, but the higher-importance flows will get through.

A better idea, we think, is to avoid letting the cloud do your packet discards -- especially if you don't actually own/administer the cloud directly. Don't give it more traffic than it can handle; use traffic shaping on subinterface definitions to ensure that you never feed more data into the cloud than can exit at the destination. You will probably do a better job of discriminating among flow types and of smoothing brief traffic spikes (e.g., your routers probably have larger buffers than the cloud's routers have).

For example, see the following Cisco documents:

href="http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/reg_pkt_flow_shaping.html" target=_blank>Regulating Packet Flow Using Traffic Shaping

href="http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a0080114326.shtml" target=_blank>Applying QoS Features to Ethernet Subinterfaces

Or you could install a Blue Coat PacketShaper in the server room's exit path to do the traffic shaping for both TCP and UDP. And the new PacketShapers can also do compression.

Final Catalyst WAN Performance Optimization Notes

Posted by: Eric Siegel

OK, two final notes on WAN Performance Optimization from the Catalyst Conference.

(By the way, I'll be rewriting my 90-page, hyper-boring paper "Optimizing WAN Performance" starting in a week or so; it should be published in a couple of months. Ask me if you need a draft copy sooner than that. And post a reply to this blog entry if you have any suggestions for me or for anyone about WAN performance optimization!)

FIRST, be sure to test using realistic user scenarios. Don't just rely on vendor promises or magazine articles or your buddy's experiences or some simple "drag and drop across the Windows desktop" copies! I've been saying this for years, but it really bears repetition.

The classical example is assuming that all vendors handle Microsoft's remote file access protocol, CIFS (or its latest Vista version, SMB 2.0) in the same way. They don't. And there's a difference between string-based compression (e.g., Riverbed) and Wide Area File Services (WAFS)-based compression (e.g., Cisco WAAS and Expand Networks). If you just do a sequential copy (e.g., drag-and-drop across the Windows desktop from a remote file share to your local disk), all of the CIFS systems look good. BUT if you open a file from INSIDE Microsoft Word, Excel, or some other application (is that what your users do?), then you'll see major differences. An application doesn't usually do only sequential reads and writes; it'll do "random" reads and writes within the file, and it'll create temporary files. So the intelligence of the WAN performance optimization solution becomes relevant: it can greatly improve performance when using remote file shares, possibly using the inherent caching ability of CIFS (i.e., the "oplock" capabilities), but it'll also be more complex and vulnerable to possible failure if the programming is sloppy.

SECOND, don't underestimate the impact of Web caching. Even major vendors, such as Microsoft, don't set their cache tags for performance. You can make simply astounding improvements in performance by setting Web cache tags appropriately, and your application front end (AFE) or load balancer can even do that for you. Be sure to include an "Expires" header, or most caches will not cache your pages, or they'll have to check back with the server to check the expiration status of every single object (unless you're using a specialized Web accelerator). See my Burton Group paper "Optimizing WAN Performance" and http://www.mnot.net/cacheability/, http://www.squid-cache.org/, http://www.web-caching.com/, and http://webmaster.info.aol.com/caching.html for more information. (Also look at http://developer.yahoo.com/performance/rules.html, which Nick Fiekowsky recommends, for more caching hints and general performance suggestions for the Web.)

Building Applications for the WAN

Posted by: Eric Siegel

Our final session at Catalyst this year was a joint presentation between Network and Telecom Strategies and Richard Watson of Burton Group's Application Platform Strategies group. We talked about how programmers and network engineers can work together to improve application performance and problem diagnosis.

This session was based on the NTS report "Designing Applications for the WAN," which will be updated next week -- so go read it when the update comes out (it's out now!), but there are a two points that came out in the session that I think were rather surprising to us network folks and that should be emphasized here.

First, the applications developers are now using frameworks to enable them to develop applications more quickly. Those application frameworks completely hide ("abstract") the network. For example, an application developer will ask a "method" for a "data object." The developer doesn't even realize that the network is involved, or that there may be some SQL queries used by that method to create the data object. That's why when you have a crisis, and you put Wireshark or a Sniffer on the communications link and show the resulting trace to the developer, he or she has no idea what the heck is going on. I'll say it again: the developer didn't even realize an SQL query was generated by the method request, and has no idea whatsoever what that stuff in the query string, trapped by the trace, really means.

No wonder there's frustration and wasted time in diagnosis! The time has arrived for the network organization, the operations group, and the development organization to cooperate and purchase a diagnostic tool that will trace individual transactions through the production system for diagnosis. (An example is Quest Software's PerformaSure; there are others.) The programmers will understand what they're seeing, the network staff won't need to run around doing Wireshark or Sniffer traces for days on end, and the problem will be handled much more quickly.

And, as the second point, realize that performance is poor because of the "abstraction" of the network layer. The application framework has a lot of parameters that set timeouts, window sizes, buffer sizes, compression, whether to disable the Nagle Algorithm, etc. The programmers understand none of this, so they use the defaults. But the defaults aren't usually set by the vendor to ensure optimum performance; they're set to create the fewest trouble calls to the vendor regardless of the network characteristics. That may not be the optimum setting for your particular situation, and that's why the people who install and set up the framework should talk to the network staff to jointly decide how to set the networking parameters for the networks that the framework will be running over. That'll help quite a bit in creating good performance.

TCP stack Performance Tuning for Windows

Posted by: Eric Siegel

I held a Birds of a Feather (BoF) session on WAN performance optimization at Burton Group's Catalyst Conference this week in San Diego, and we had approximately 14 attendees, which was quite good. (Attendance at Catalyst is almost exactly the same as last year: approximately 1500 people! We're VERY happy.)

We started the BoF with a talk by Nick Fiekowsky of Wyeth; he also has a talk coming up on WAN optimization, but the BoF was a great opportunity for us to have a more unstructured discussion (it lasted over an hour) about some of the detailed technical issues.

Nick made some great new observations about TCP performance on Windows; they're very interesting and also seem to have a large impact on performance. So here, with his permission, are some of them:

First, as Nick says, "Latency doesn't end at the RJ-45." When you're computing the required buffer size (receive window, RWIN) for long fat networks (i.e., large bandwidth and large latency), we always think of just the latency on the path and the bandwidth. I hadn't previously thought about the time that the received packet spends inside the receiving station's TCP buffers, waiting to be processed and then waiting to be read by the application. But that's an important factor in the latency; after all, the RWIN can open until there's space in the receive buffer, and the receive buffer won't have space until the application has read something out of it!

So Nick looked at what actually happened, and he discovered that although the bandwidth delay product (and therefore the receive buffer size) was approximately half a megabyte for a particular path, there were still long pauses waiting for acknowledgements to be returned to the sender -- throughput was lower than it could be. He had to increase the receive buffer size to almost THREE MEGABYTES before the sniffer (actually, Wireshark) trace showed that the bandwidth was being fully utilized. Wow.

And that led to Nick's other major point: it's important to optimize Windows performance to keep it from stalling while processing those incoming packets:

• "Non-Paged Pool" (NPP), where the buffers are located, is a precious resource. Nick says that in a 32-bit Windows OS, the NPP = RAM/16. That's not very large, especially if you need large receive buffers. (Look at the Task Manager to see how much of the NPP is being used. Or you can just notice that the TCP stack is requesting a small RWIN when a new connection comes in, because it's under memory pressure.) The only way to increase that is to increase the total RAM in the processor. In the 64-bit Windows OS, the NPP allocation is handled much better, TCP auto-tuning in Vista, Windows 7 and Windows Server 2008 makes better use of NPP, and finally the 64-bit OS also makes the entire system run better because system processes are faster. So the 64-bit OS is a big improvement here.
• Defrag the hard drive to be sure that fragmentation isn't slowing down the processes and the stack.
• Use updated NIC drivers. Nick says that recently he's noticed that there's a new emphasis on performance in the drivers, possibly being driven by iSCSI and datacenter requirements. Also increase the number of transmit and receive descriptors in the driver configuration.

Nick had a lot of other recommendations, such as the big improvement made by ensuring that Web cache expiration tags are properly used, and I'll try to get to them in a later blog.

Meanwhile, thanks, Nick!

Backup for WAN performance optimizers at remote offices

Posted by: Eric Siegel

(This is the first of a few blog entries that I'm going to post to share some ideas that came out of the Birds of a Feather (BoF) session on WAN performance optimization at Burton Group's Catalyst Conference this week in San Diego.)

A primary advantage of WAN performance optimization appliances is that they cut down the bandwidth needs of a remote branch office -- usually by 50% or more. And they reduce response time to make remote file shares, etc., actually usable instead of being a miserable, irritating experience that destroys productivity.

But what happens when the optimizer breaks? Bandwidth requirements spike upwards, and response time instantly becomes lousy.

My suggestions in the past involved QoS in the branch office boundary router to ensure that critical traffic would still flow despite the worsened bandwidth restrictions, and recommendations that the enterprise make arrangements with vendors or resellers to have spares available in-country (to avoid delays in customs and in transit) and configuration information available on a USB flash drive or by downloading as an email attachment. There would be a day or so of worse-than-normal performance as the compression directories are rebuilt, and then things would be OK.

But Nick Fiekowsky, while sharing his slides at the BoF, had a great idea: use the new software client optimizers, such as Blue Coat's Proxy Client, Cisco's WAAS Mobile, Expand Network's Mobile Accelerator Client, and Riverbed's Steelhead Mobile to serve as emergency backups. These software optimizers run on the users' laptops and provide the function of the optimization appliance. They're not as good, because (except for the new Expand Networks Mobile Accelerator Client! More later...) they don't share their compression directories and caches. But they're a lot better than nothing, and they also provide the ability for the user to use acceleration from home or on the road. This is especially great if the software optimizer system licenses are inexpensive or can be turned on and off easily from the central server location, with billing only when they're used.

My updated recommendation is therefore to install the WAN accelerator vendor's mobile client in branch office desktops. If the office's WAN accelerator fails, the desktop clients will step in to reduce WAN traffic and provide an acceptable user experience. It is necessary to have enough license capacity to cover all the client devices that may become active when a single branch office's WAN accelerator fails.

XML Compression

Posted by: Eric Siegel

XML compression came up recently in one of my conversations with a client. It's an interesting topic that a lot of us will need to deal with as XML replaces other forms of process-to-process messaging.

XML is inefficient in its use of bandwidth, a tradeoff that was made to gain ease of use and generality. However, that need for a lot of bandwidth can be a problem, especially on paths with restricted bandwidth or high error rates, such as mobile wireless communications.

Some vendors, such as Stampede and Accelenet (ViaSat/ICT), provide advanced compression solutions that can be extremely effective -- and they also improve the transport protocol, which can help on wireless links. These are quite different from classical "zip" compression. They're proprietary and there are no "standards" involved; you can't pair up compression from two different vendors and expect them to interoperate. However, in exchange for the proprietary nature of these things, you get great compression. These systems maintain compression dictionaries at both end of the path, substituting short pointers for data strings. You can also pre-load these dictionaries with XML phrases; e.g., Stampede's Web 2.0 Performance Series has special features for SOA, including pre-loading of XML compression dictionaries, persistent TCP connections despite the tendency of AJAX (asynchronous Java and XML) to disconnect and reconnect frequently, and extensive security that includes XML schema validation, message anomaly detection, and denial of service attack detection. Indeed, most WAN performance optimization vendors provide advanced compression solutions that can assist with XML.

An alternative is to use binary XML, such as the Efficient XML Interchange format (EXI), which is being specified and evaluated by the Efficient XML Interchange (EXI) Working Group of W3C and is available from vendors such as AgileDelta. AgileDelta says that they provide software that supports standard XML APIs and they can also provide HTTP and TCP Socket proxies to convert XML to Efficient XML (EXI) without any change whatsoever to the application. The software could be used for applications that you can get the vendor to write with EXI; the proxies could be used to convert EXI to standard XML for applications that you don't have control over.

A big question, of course, is whether EXI will become broadly used. Although the EXI standard hasn't been formally approved, it's just one step away from that approval (it's in "Last Call"). The wikipedia article on binary XML has some discussion of these standards -- both EXI and others.

Note, of course, that any encryption or non-standard compression (e.g., proprietary compression, or possibly, EXI) can interfere with network devices that are trying to do "deep packet inspection" of data flows to detect policy violations and attacks, or to route data flows depending on flow contents. And any flow conversion system (compression or protocol acceleration) must usually intercept both flow directions; that can be tricky if flows travel asymmetrically. So use of any encryption, interception, or compression device means you have to think about precisely where you're going to place that device.

My colleague Chris Haddad also says that edge CPU processing speed for XML is important; it can be a problem that binary XML can help. An article referenced by the wikipedia binary XML entry is interesting here: "i-Technology Viewpoint: The Performance Woe of Binary XML" by Jimmy Zhang in SOA World Magazine, August 5, 2008.

Be a Hero! Cut costs to Zero!

Posted by: Eric Siegel

Is there anyone who hasn't felt the threat of layoffs this last few months? Everyone is digging foxholes, worrying about the future. That's the natural tendency, I know. (Hey, I'm typing this from the warm security of my desk's kneehole, and my cats have gathered around me, prepared to show their fangs to anyone who might endanger their food supply.)

But if you really want to avoid Trouble, the thing to do is to get out there and save your company money, or set it up to make money quickly! Winning enterprises are using this period to prepare to launch at rocket speed out of the recession, leaving their foxhole-dwelling competitors chewing dirt and breathing rocket exhaust. And there's an easy way to help position your company for that launch, at the exact same time that you save megabucks immediately! It's called WAN Performance Optimization.

Yes, the same drum I've been beating for years, this time with extra added incentives!

I'll make this short, so we can all get back to work. But there isn't much to say.

ONE: WAN Optimization really DOES pay for itself in under a year. (In these times, payback in more than a year doesn't impress management at all. You need instant payback, and then big savings.) Those charts showing 50%, 80% and larger bandwidth savings aren't fake. In a surprising number of cases, the bandwidth savings are immense. So you'll be a hero for saving costs, and your procurement department will be singing your praises!

TWO: Your users will be delirious with joy at the performance improvements, especially if they've been suffering with remote file shares or with the pain of sending huge files back and forth among team members. Because it now takes only minutes, not hours, to send project files back and forth, there will be closer teamwork and they'll win more deals and avoid more screwups. Server centralization will be enabled, too, which is more money saved. So you're a hero for improving productivity and morale, and your HR and operations departments and your branch office managers and project managers will be singing your praises!

Just remember to forward all of those love notes to your management; this is not the time to be shy.

The technology can be somewhat complex, so be sure to find some reference accounts with a similar architecture and network design to yours. The vendors will love to show you around the technology, and they'll even loan you equipment to try it out. Different vendors specialize in different optimization situations; it's a good idea to look around. Some leading vendors are:

• Blue Coat
• Certeon
• Cisco (WAAS and AVS)
• Citrix (WanScaler and NetScaler)
• Exinda
• Expand Networks
• F5 (WANJet and WebAccelerator)
• Juniper (WX)
• Riverbed
• Silver Peak
• Stampede

See my previous blog entry, "WAN Optimization Whitelists and Blacklists"  for more information on this topic. Burton Group clients should look at my 80-single-spaced-page hyper-boring "Optimizing WAN Performance" report. And in a few weeks a new report, "Evaluating and Deploying WAN Performance Optimization," will be out in print. (Ask me for a pre-production copy.) It talks about how to pitch WAN optimization to management, how to select and evaluate contenders, and how to go through a rollout without crises. Or go to Burton Group's Catalyst Conference, July 27-31 in San Diego, where we're going to have tutorials and sessions on this, and a Birds-of-a-Feather meeting. Or call me for a free "dialogue." Gee, there are lots of ways to get started; no excuses here!

Please TEST before inflicting your app on the network!

Posted by: Eric Siegel

Here's another pet peeve of mine: lack of realistic pre-deployment testing.

How many development organizations use zero-latency infinite-bandwidth LANs and top-of-the-line switches in their development shop, then, when their tightly-coupled client-server application goes into production, they blame lousy performance on the network? As the saying goes, "If I had a nickel....." Well, I'd be writing this blog entry from a penthouse suite on Fifth Avenue.

A leading cause of friction between network operations staff and development staff could be removed if all applications were realistically tested before being placed into production. Real production network environments differ greatly from typical development environments; they include high-latency WAN and cellular links, bandwidth restrictions, congestion, link errors, packet duplication and misordering, and packet fragmentation caused by devices in the communications path, encryption, and virtual private network (VPN) connections. Bandwidth optimization appliances such as caches, compression devices, and protocol-acceleration devices also interact with data flows. All of these affect application performance.

If the application is accessible from the public web, designers must also consider and handle the possibility of a flash load. Flash loads occur when overwhelming numbers of users try to connect to a web server simultaneously, possibly in response to a news event or a television advertisement. The flash load inevitably leads to widespread abandonment of slow transactions, causing resource recovery problems (transaction abandonment is difficult to detect in web environments) and probably further degrading performance. Public web applications must also consider the universe of possible browser types and the fact that a small percentage of users disable cookies on their browsers.

WAN emulation and load generation devices and services can reproduce all of these problems, and it is much less stressful for everybody if problems are discovered before the application is put into production. Surprising things happen to data flows on production WANs: Always test before deployment.