Before Buying a WAN Accelerator

In the last few pages, we showed various scenarios where organizations can

save cost by optimizing their WAN bandwidth. A key component for making this

happen is a WAN accelerator. In this article, we'll tell you about a few more

scenarios where WAN accelerators can be beneficial for your business. Plus,

we'll delve into what you should look for when choosing a WAN accelerator, and

finally we end the article with a few WAN accelerator solutions that are

available in the market.

Lets start by explaining what a WAN accelerator is. A WAN accelerators

improves WAN bandwidth usage and can be tuned to do it for specific

applications. In today's environment, where businesses are spread over large

geographical areas, and need to be better connected, WAN accelerators can be the

answer. They use several techniques for bandwidth optimization, which we'll get

into later in this article.

Business scenarios



Gone are the days when WAN links were only used for data transfers and web
access. Today, they can be used for many other applications, including voice and

video conferencing. So obviously, with more load coming on to the WAN links,

there's a need to optimize the bandwidth usage on them.

Here we will explain a few applications that are currently on top of IT

managers mind.

Voice over IP



This is one of the most common applications enterprises are considering to use
on their WAN links. The reason is simple: a significant portion of an

organization's communication cost is for inter-office phone calls and

conferences. If the organization's WAN links can be used to carry VoIP traffic

as well, then this cost can be completely eliminated.

Video conferencing



Graduall, organizations are beginning to feel the need to have video
conferencing on their networks. This is accentuated by the ecnomic slowdown,

because organizations want to cut down their travel budgets, without loosing the

impact of a face to face communication. Video conferencing technologies have

evolved to a level where they can provide a realistic virtual conference. But,

video requires higher bandwidth than data and can completely chew up an

organization's bandwidth. WAN accelerators therefore would be required to

provide smooth conferencing.

This shows the symmetrical way of deploying WAN accelerators. Here two appliances are used at both ends of the WAN.

File sharing



Information in the form of data is always critical to an organization, and
timely access to this information from authorized employees is critical. If your

organization is big with offices spread across different geographical areas,

access to data from one office to the other is necessary. This data is growing

by leaps and bounds in every organization, which places considerable amount of

stress on the WAN links.

Disaster recovery



Every organization today has a DR center, and there's a need to replicate data
to it. This makes for a very good case for having WAN accelerators, because they

can reduce the amount of bandwidth required to do the replication.

This shows how mobile software residing on the mobile device communicates with the WAN appliance.

Application acceleration



Every business today is dependant on certain business applications. These also
take up the maximum bandwidth over the WAN. If performance of these applications

is enhanced, this would automatically result in better output.

The good news is that most WAN accelerator vendors work closely with leading

application vendors to make their product work efficiently over the WAN

accelerator e.g. Riverbed Steelhead's latest software platform RiOS now supports

acceleration of Lotus Notes.

This shows the combination of WAN appliances along with the mobile software residing in the mobile devices in a typical enterprise.

Mobile users



Till here, we have discussed scenarios of office to office connectivity.
However, there's a growing need to provide WAN acceleration to a growing mobile

workforce. Suppose you work on oil rigs in the middle of the sea with most of

your work done on CAD application. Transfering these huge files over WAN again

is an issue. To overcome such issue, WAN accelerator vendors have created mobile

software for laptops that can act as WAN accelerators. These software

communicate with WAN accelerator appliances sitting in central office,

optimizing traffic between two.

On left hand side, is a typical file transfer using TCP. On the right side, TCP session is terminated at WAN accelerator making bandwidth utilization optimal.

What to look for in a WAN accelerator?



Now that we are familiar with a different business cases where WAN accelerators
can be of great help, let's see what questions need to be answered before making

any buying decision about these devices.

What applications is your organization using?



Besides doing general purpose acceleration, WAN accelerators come with feature
for application acceleration. Therefore before choosing any solution, check if

the extensively used applications in your organization like Lotus Notes or

Microsoft Office suite are accelerated or not.

This explains how caching can help in WAN scenario. Web pages are chached inside the WAN accelerator.

What type of usage?



WAN accelerators are often deployed in symmetrical manner, meaning that they are
effective in accelerating traffic between points that are fixed. Here by

symmetrical fashion we mean that two appliances are used one at branch office

and other at center office. But if most of your work force is mobile, using

symmetrical model is not possible.

In such scenarios, usage of software based WAN accelerators residing on

mobile devices of users is recommended. These software communicate with the WAN

appliance sitting in a fixed point (central office).

How many users?



WAN accelerators categorization is done based on number of concurrent users that
can be supported. There are many WAN appliances in market today with each vendor

having its own set of WAN appliances supporting different number of clients with

different set of features, like number of processors, cache size, etc. One needs

to take into account the number of current users, and possible future size

before purchasing these appliances.

Though a secure tunnel is created before transferring data over WAN

accelerators, one concern that needs to be seriously taken care of is that the

WAN appliance might not go well with the security compliance of your

organization, as techniques like caching keep copies of data locally. The way

WAN appliances overcome this situation is by usage of encryption.Check whether

your WAN accelerator vendor offers this feature or not.

Single or Multifunctional?



WAN accelerators can also perform other functions besides acceleration. A single
appliance can now do acceleration with up to five virtual machines running on

top of it. These virtual machines can run firewall, mail server and other

servers. This not only reduces management issues but also increases effective

usage of resources. Such factors should be taken into account before buying an

appliance.

Myth buster: Bandwidth Bottleneck Vs Latency In this section we will show you, through a small experiment, how an increase in bandwidth will not enhance performance across WAN. For this, we have used WAN simulator and transferred 10 Mb data through it. First we used a link speed of 500 kbps with 100 millisecond latency, and then we doubled the bandwidth (1000 Kbps) and increased the latency four times i.e. 400 milliseconds. The results were amazing. We found out that the time taken for data transfer was almost equal i.e. 211 and 227 seconds respectively. These results further strengthen the need of WAN accelerators as they considerably reduce this latency resulting in better performance.

The graph shows the behaviour of 2MB file at different link speeds along with different latencies.

Software or appliance based?



There are two types of WAN accelerators present today--appliance based and
software based. Here by appliance based we mean there is a hardware box having

all the necessary software and hardware needed for WAN acceleration. Software

based WAN accelerators on the other hand are packages that are deployed on a

machine that acts as accelerator.

Technology used in WAN Accelerators



Let's analyze how WAN accelerators are able to improve performance of your
applications and other traffic. Here are some of the techniques.

TCP optimization



Transport Control Protocol or TCP maintains an end to end connectivity between
two nodes on the network by periodically requesting an acknowledgement from

destination. On the other hand, Internet Protocol (IP) does not require any

acknowledgement to check if data has arrived at destination. TCP uses sliding

window technique to accomplish this task, where size of window defines number of

packets that can be transmitted before getting acknowledgement from the

receiver.If sender receives acknowledgement before it times out, it increases

window size for next transmission. On the other hand if sender does not receive

acknowledgement before time, it performs some actions i.e. sender decreases

window size, increases time out period and retransmits packets. All this leads

to inefficient usage of bandwidth. WAN accelerators overcome this situation by

using aggressive windowing technique. In this method, TCP session is terminated

at local accelerator thus getting instantaneous responses eliminating long wait

time for acknowledgement.

Traffic shaping



One smart way of improving performance over WAN is by categorizing traffic on
the bases of priority. Essentially, it means that WAN accelerators can perform

QoS operations. We've explained QoS concepts in more detail in a separate

article in this cover story.

Compression



Transfer of redundant data across WAN can be overcome by replacing identical
bits with a label. On the receiver side, this label is again replaced with

original bit patterns. Considerable amount of bits can be reduced using

different compression techniques available inside WAN accelerators.

Caching



Yet another simple technique to enhance performance over WAN is by using caching
techniques. Client side WAN accelerators locally store data (e.g. web pages)

that is often requested, thus eliminating unnecessary usage of bandwidth.

Intelligent caching like read ahead caching requests additional pages from

server to answer local query, thus increasing performance. Another way is to

mirror complete database locally.

Off loading CPU intensive tasks



Apart from the above, processing power of WAN accelerator appliances can also be
used to offload CPU tasks from server. Thus these appliances give additional

processing power to complete system making it more effective.These were a few

things you shound know before choosing a WAN accelerator. In the next page,

we've given the specs of some WAN Accelerator products that are available in the

market.