Evaluating, Selecting & Deploying WAN Acceleration Solutions White Paper
Rev. A 01/08
Inspired Innovation
White Paper
Evaluating, Selecting
and Deploying WAN
Acceleration Solutions
Real-World Testing Sifts Through Conflicting
Claims to Identify the True Performance of
Competing Solutions
January 2008
Spirent Communications, Inc.
1325 Borregas Avenue
Sunnyvale, CA 94089 USA
Email: sales@spirent.com
Web: http://www.spirent.com
Americas
T: +1 800.SPIRENT
+818 676.2683
Europe, Middle East, Africa
T: +33 1 6137.2250
Asia Pacific
T: +852 2511.3822
Copyright
© 2008 Spirent Communications, Inc. All Rights Reserved.
All of the company names and/or brand names and/or product names referred
to in this document, in particular, the name “Spirent” and its logo device, are
either registered trademarks or trademarks of Spirent plc and its subsidiaries,
pending registration in accordance with relevant national laws. All other registered
trademarks or trademarks are the property of their respective owners.
The information contained in this document is subject to change without notice
and does not represent a commitment on the part of Spirent Communications. The
information in this document is believed to be accurate and reliable; however,
Spirent Communications assumes no responsibility or liability for any errors or
inaccuracies that may appear in the document.
iSpirent Communications White Paper
Evaluating, Selecting and Deploying WAN
Acceleration Solutions
Real-World Testing Sifts Through Conflicting Claims to Identify the True
Performance of Competing Solutions
Contents
Overview ...............................................................1
Alleviating WAN Constraints ...............................................1
WAN Acceleration and Response Time .......................................2
Technology in the WAN ...................................................2
Traffic Shaping through QoS ............................................3
TCP Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Compression .........................................................6
Caching and Mirroring .................................................7
Off-loading CPU-Intensive Tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Forward Error Correction (FEC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Evaluating WAN Acceleration Solutions.......................................9
Configuring Real-World Network Emulation Profiles...........................10
Profiler/Playback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Standards-based Models ...............................................10
Deploying WAN Acceleration Solutions......................................11
Network Emulation Enables WAN Acceleration ...............................11
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Overview
As corporate networks continue to expand worldwide, the efficiency of the global
network becomes critical. The question arises, “How do you expand the corporate
network to a national or global scale without sacrificing usability and productivity?”
The most obvious solution for optimizing the wide area network (WAN) is the WAN
accelerator. But the wide range of technologies and solutions are often difficult to
differentiate and evaluate. And once a solution is selected, IT organizations face the
challenge of determining the optimum configuration.
Real-world testing allows IT organizations to cut through hype and reveal the
true performance of a technology, implementation or brand. During deployment,
real-world testing isolates factors affecting performance in a production network.
Insight into these factors enables proper configuration of a solution for optimum
performance.
This white paper highlights WAN performance issues, explains technologies
developed to address those issues and demonstrates the importance of real-world
testing when evaluating, selecting and deploying WAN acceleration tools or
technologies.
Alleviating WAN Constraints
The distributed workplace is a given in the 21st century. Beyond the corporate office
we find regional, branch or remote offices, off-site data centers (both primary and
backup), mobile users, telecommuters, off-shore offices and international offices. At
each location, a local area network (LAN) connects local users. Between locations,
a WAN connects the LANs.
Organizations rely on the WAN to support a highly diverse set of applications, from
best-effort delivery of email and Web pages to real-time traffic like Voice over IP
(VoIP) and video conferencing. Many other business-critical functions lie between
these two extremes including data synchronization, off-site backup, distributed
applications, collaboration applications, file sharing and others.
The bandwidth and latency constraints posed by the WAN often create performance
and responsiveness problems affecting top and bottom lines. Slow response from
online retail systems can result in abandoned shopping carts and reduced revenues.
Slow response from back-office systems, extended time for backups and mirroring,
and poor audio and video conferencing quality can translate into higher operating
costs and reduced profits.
Network Applications—Ensuring Performance and QoE with Network Impairment Emulation
Overview
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Network Applications—Ensuring Performance and QoE with Network Impairment Emulation
WAN Acceleration and Response Time
While some of these issues can be addressed simply by increasing bandwidth, others
require Quality of Service (QoS) classes to prioritize traffic. Others still are resolved
only by increasing the efficiency of the current network. WAN acceleration is one
method commonly used to increase network efficiency.
WAN Acceleration and Response Time
WAN acceleration reduces costs by increasing the effective throughput of the
existing network. Most WAN acceleration solutions use an array of techniques to
get a 10X to 40X improvement in response time or transaction processing rate.
Some specialized techniques targeted to specific protocols, such as the Messaging
Application Programming Interface (MAPI) and the Common Internet File System
(CIFS), can achieve up to a 100X improvement in performance.
Consider the experience of one North American organization that partnered with
a team in Asia. They discovered that it took 160 times longer to send a document
over the WAN, as transfer time increased from 30 seconds to 80 minutes. TCP
optimization and compression reduced the overseas transfer time to 2 minutes. With
dramatic improvements like this, it is not surprising that WAN accelerators are
attractive to organizations facing WAN issues.
Technology in the WAN
The primary effects the WAN introduces are bit errors, packet loss, and latency
also known as delay. To a lesser degree, packets may be reordered or duplicated
while traversing the WAN. These impairments have varying effects on different
types of traffic. For example, as latency increases beyond 80 ms, throughput on a
TCP session begins to degrade regardless of available bandwidth. VoIP, on the other
hand, handles twice that latency without problems as long as the delay variation is
low. As a result, the technique used to increase performance and throughput varies
based on the type of impairment and the type of traffic.
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Network Applications—Ensuring Performance and QoE with Network Impairment Emulation
Traffic Shaping through QoS
Traffic Shaping through QoS
Traffic shaping improves throughput for preferred traffic at the expense of lower-
priority traffic. Delay-sensitive traffic such as video or voice is prioritized and
guaranteed delivery. Other data traffic, such as email or Web page requests, are
delivered if available bandwidth permits or are dropped if higher priority traffic
has consumed available bandwidth. Some WAN accelerators offer QoS features to
prioritize traffic.
Ethernet
Switch
Ethernet
Switch
IP Phone
Web
Server
E-mail
Server
Video
Server
Router
Router
PC PC
Internet
Best Effort
Differentiated
Services
Guaranteed
Bandwidth
Best Effort
Differentiated
Services
Guaranteed
Bandwidth
Figure 1. Network QoS
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Network Applications—Ensuring Performance and QoE with Network Impairment Emulation
TCP Optimization
TCP Optimization
Internet Protocol (IP) sends packets to the destination without checking to see
if they arrived. The Transport Control Protocol (TCP) maintains the end-to-end
connection by requiring periodic acknowledgments from the destination. TCP uses a
sliding window to avoid congestion. The window size denotes the number of packets
that can be sent before an acknowledgement from the receiver is required. A larger
window size means more data can be transmitted before waiting, which results in
greater throughput.
When the sender receives an acknowledgement (ACK) before it times out, it
increases the window size for the next transmit. (Scenario A in Figure 2) If the
transmit or ACK is lost, the sender times out and re-transmits. (Scenario B in
Figure 2) If the ACK is delayed due to network latency and arrives after the time-
out value, the sender assumes the packet was lost and re-transmits. (Scenario C in
Figure 2) Re-transmissions cause TCP to reduce the window size and/or increase
the time-out value, which can result in inefficient use of bandwidth.
TCP uses a slow-start method to gradually ramp up the window size, which
can cause sluggish performance. Enabling RFC 1323 TCP Extensions for High
Performance can improve throughput, but for high-latency connections the round-
trip time can cause long waits for acknowledgement even if bandwidth is available
and there is no congestion.
WAN
LAN A LAN B
A
B
C
Transmit 1
Transmit 2
ACK 1
ACK 2
Retransmit 2
Retransmit 2
WAN
Accelerator A
WAN
Accelerator B
Router A Router B
Figure 2
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Network Applications—Ensuring Performance and QoE with Network Impairment Emulation
TCP Optimization
WAN acceleration solutions use connection optimization and aggressive windowing
methods to improve performance. Rapid accelerate-and-fallback windowing
can achieve 700 Mbps throughput even on intercontinental links. Connection
optimization reduces the wait for acknowledgements by terminating the TCP session
at the local accelerator rather than at the destination, resulting in near-instantaneous
responses rather than long waits for acknowledgments (Figure 3).
In addition, connection pooling re-uses WAN-side connections for multiple
requests, saving setup and teardown time and CPU cycles. Unlike many of the other
acceleration techniques, TCP optimization doesn’t necessarily require a pair of
devices, one on each end of the connection. It can be implemented on a server-side
appliance, improving throughput for anyone who accesses the server – be it an entire
remote office or just a single remote user.
WAN
LAN A LAN B
Transmit 1
ACK 1
Transmit 2
ACK 2
Transmit 3
ACK 3
Transmit 4
ACK 4
Transmit 5
ACK 5
Transmit 6
ACK 6
Transmit 1
ACK 1
Transmit 2
ACK 2
Transmit 3
ACK 3
Transmit 4
ACK 4
Transmit 5
ACK 5
Transmit 6
ACK 6
Transmit 1
Transmit 2
Transmit 3
Transmit 4
Transmit 5
Transmit 6
WAN
Accelerator A
WAN
Accelerator B
Router A Router B
Figure 3
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Network Applications—Ensuring Performance and QoE with Network Impairment Emulation
Compression
Compression
Typical compression techniques replace repeating bit patterns with a short label
before sending the data across the WAN. On the receiving side the label is removed
and the original pattern is inserted back into the bit stream (Figure 4). Depending
on the compression scheme and the data type, the number of bits transmitted can
be reduced by 20% to 70%. Some proprietary techniques that use parsing and
hierarchical trees claim to reduce data size by up to 98%. In addition, by offloading
compression to the WAN accelerator, servers can serve more requests thereby
improving throughput and response time.
WAN
LAN A
WAN
Accelerator A
WAN
Accelerator B
Router A Router B
LAN B
No compression
With compression
Figure 4
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Caching and Mirroring
Caching and Mirroring
Caching is used at many levels in computing and networking, from onboard caches
in system processors to print job spooling. Client-side WAN accelerators store Web
pages and other data as it passes through so subsequent requests can be answered
locally by the accelerator rather than requiring retransmission from the remote
server. Database applications can provide read-ahead caching to transmit additional
pages for a query before they are requested. Caching improves response time and
reduces demand on the servers (Figure 5).
High-availability mirror systems provide synchronized copies of entire databases
at multiple locations. When a change is made locally, it is replicated at all the other
sites in the background so that requests from users in those locations can provide the
most recent data without having to query a remote server.
WAN
LAN A LAN B
Request 1
Response 1
Request 1
Response 1
Request 2
Response 2
Request 2
Response 2
WAN
Accelerator A
WAN
Accelerator B
Router A
A. Caching
B. No caching
Router B
Web
page
Web
page
Web
page
Web
page
A
NO CA
CHING
B
CA
CHING
Figure 5
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Off-loading CPU-Intensive Tasks
Off-loading CPU-Intensive Tasks
Multi-processor systems are typically licensed per processor, adding hardware
and software costs as more processors are required. As the number of transactions
increase, so increases the demands on processors that may already be pushed
to their limits with ancillary tasks such as compression, encryption and XML
processing. By offloading CPU-intensive tasks to an appliance, organizations
improve WAN performance and handle increased traffic without the expense of
licensing additional processors (Figure 6).w
Forward Error Correction (FEC)
Some WAN acceleration solutions use FEC to reduce the need for retransmissions
on lossy networks. FEC sends recovery information in-band with data for indexing
to allow for reconstruction of lost packets.
WAN Accelerator
Server Server
E-mail Server
Web Server
Encryption
Compression
XML Processing
E-mail Server
Web Server
Encryption
Compression
XML Processing
Figure 6
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Evaluating WAN Acceleration Solutions
Evaluating WAN Acceleration Solutions
During the early stages of acquiring a WAN acceleration solution, efforts are
focused on identifying products with the desired features and capabilities,
comparing costs and other off-line methods of reducing the wide array of options to
a manageable short list. Between the short list and the purchase is a critical step –
performance evaluation in a test lab.
All the various WAN acceleration techniques have one thing in common: They
improve the performance of systems running across a WAN. Consequently, testing
the solutions under real-world WAN conditions is the only true method of validating
the claims of the various vendors. While WAN acceleration solutions usually
promise a significant ROI, they also pose a significant CapEx investment. An
objective evaluation reduces dependence on a vendor’s claim for ROI and increases
confidence in meeting ROI goals.
Unfortunately, live networks (or production networks) even if available are not
suitable for testing. Conditions at any given time cannot be controlled or, in some
cases, cannot even be known. This reality poses significant problems in evaluating
or benchmarking one WAN Acceleration solution vs. another when the same
scenario cannot be repeated between tests.
However, designing a test bed to replicate the “real-world” is possible. It provides
an environment that produces meaningful and repeatable tests and results. The
test bed includes the system under test, a traffic generator/analyzer and a network
emulator. The test-bed emulates the behavior of the production network – including
delay, jitter, packet loss, corruption, etc. – through user, traffic and network profiles.
Layer 4-7 Tester
(Client Tier)
Application Tier
Server
Application Tier
Server
Data Tier
Server
Data Tier
Server
Data Tier
Server
Spirent Network Emulator
(WAN)
Test Bed
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Configuring Real-World Network Emulation Profiles
A test methodology is a definitive procedure to identify, measure, and evaluate
a product, system, or service that produces a test result. Test solution vendors
can provide a set of methodologies targeted at testing specific capabilities. The
configuration of the user, traffic and network profiles will vary based on the
capabilities under test. For example, TCP optimization is evaluated using a network
profile that emulates a range of realistic settings for latency and packet loss. FEC is
evaluated using a network profile that emulates a range of realistic bit error rates.
Following the methodology provides a test result that includes a set of observed
metrics. The results are compared to target metrics. The specific metrics of
interest vary based on the capabilities under test. For example, when testing TCP
optimization, data throughput rates are the primary metric of interest. If the
observed throughput doesn’t meet or exceed the target throughput, other metrics
such as the number of concurrent sessions or the number of timeouts correlated to
latency and packet loss are reviewed during troubleshooting.
When the IT department has hard data in the form of test results obtained under
known and repeatable conditions, a purchasing decision is based on recorded
metrics rather than vendor promises. The performance of competing solutions can
be directly evaluated in an apples-to-apples comparison. Consequently, the risk of
unpleasant surprises after purchase and deployment is reduced, and the confidence
that ROI targets will be met significantly increases.
Configuring Real-World Network Emulation Profiles
There are two ways to configure realistic network emulation profiles.
Profiler/Playback
To replay actual network conditions on a production network, use Profiler/Playback
to capture the end-to-end packet loss, delay and jitter for each profile. Then play
back the conditions dynamically during testing so the emulator replicates actual
production network conditions on a packet-per-packet basis.
Standards-based Models
IP networks don’t present deterministic, periodic disruptions to traffic. Instead,
impairments vary over time, presenting problems in bursts resulting from such
issues as route flaps, queue discards and buffer overruns. The Network Model for
Evaluating Multimedia Transmission Performance over Internet Protocol, adopted
by TIA as TIA-921 and by ITU-T as Recommendation G.1050, is a time-varying
model that emulates the dynamic nature of impairments in an IP network.
This model has been adopted by several standards organizations for testing real-
time applications and protocols. It is a statistical model based on actual network
information obtained from anonymous service providers. It uses an impulse-driven
time series model to emulate impairments introduced by each leg of an end-to-end
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Deploying WAN Acceleration Solutions
network. The dynamic nature of the emulated conditions reflects the time-varying
conditions found on actual production networks.
Deploying WAN Acceleration Solutions
The value of real-world testing extends beyond evaluation and purchase. WAN
accelerators are integrated solutions that implement multiple configurable
technologies to improve WAN throughput and performance. To achieve performance
goals, network engineers configure the parameters to address issues specific to a
production network. Refining the settings is often an iterative process. The devices
must be configured under production network conditions. However, due to the risk
of adverse effects from configuration errors, establishing the optimum configuration
should not be done on the production network.
The test lab’s controlled environment provides the ability to precisely and accurately
emulate the environment where the solution will be deployed, but without risk to
productivity on the production network. In addition, the test lab provides repeatable
emulation of network conditions, making it possible to experiment with multiple
configurations to identify the optimum settings for a specific network. The result is
an optimum configuration that increases the likelihood of meeting ROI goals.
Network Emulation Enables WAN Acceleration
WAN acceleration devices address the issue of maintaining usability and
productivity while expanding the corporate network into the global workplace. IT
departments looking to purchase and deploy WAN acceleration solutions face a
complex and confusing array of technologies, vendors and performance claims.
Once a solution is selected, the challenge of determining the optimum configuration
can be equally daunting.
By creating a test bed of traffic generator/analyzers, network emulators, and
production applications, testing under “real-world” testing can take place –
providing the benefits of testing on a production network without the inherent risks.
These components, combined with a test methodology that incorporates realistic
user behavior, traffic mixes and network conditions produce a controlled, precise
and repeatable environment that makes meaningful test results possible. This
enables proper selection of WAN Acceleration solutions to meet your needs.
The use of Network Emulators in your test-bed provides a cost-effective and
efficient method of identifying the true performance of a solution. In addition,
real-world testing assists in determining the proper configuration of a solution
for optimum performance. Real-world testing increases confidence in meeting
performance and ROI targets. It also reduces the likelihood of buying an ineffective
solution while minimizing risk from performance and productivity issues due to
configuration errors.
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Inspired Innovation
