SUMMARY
This article discusses the various methods that you can use
to increase the performance and response of Microsoft Outlook Web Access (OWA)
when you use OWA with Exchange 2000.
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Use the Reach Version of OWA
There are two versions of OWA, the
rich version and the
reach version. The version that you use depends on the Web browser that
you use to access OWA. If you use Microsoft Internet Explorer 5.0 or later, you
receive the rich version. If you use Internet Explorer 4.02 or earlier, you
receive the reach version.
The rich version supports rich features,
such as dynamic HTML (DHTML), the Web Distributed Authoring and Versioning
(WebDAV) protocol, XML, and Extensible Stylesheet Language (XSL). Internet
Explorer 5.0 and later are rich browsers, which are sometimes called
uplevel browsers.
The reach version does not support these
extended feature sets, but does support basic capabilities, such as HTML 3.2
and European Computer Manufacturers Association (ECMA) script standards.
Internet Explorer 4.02 and earlier versions of Internet Explorer are reach
browsers, which are sometimes called
downlevel browsers.
The reach version uses a simpler user
interface than the rich version. Because the reach version is designed for
browsers that do not have DHTML and XML support, it does not include some of
the features that are available in the rich version, including the following
versions:
- Advanced view options, such as the preview pane and
sorting
- New mail notification
- Search
- Calendar reminders
- Advanced calendar controls and printing
- Public folders
- Drag-and-drop editing
- Tree control
If you use the rich version of OWA, you can take advantage of
the client-side Microsoft XML control and make custom HTTP-DAV requests to the
server by using verbs such as SEARCH and PROPFIND.
NOTE: Some older proxy servers do not support HTTP-DAV requests and
block these requests, which prevents the Web browser from accessing OWA. The
reach client is not affected because it only uses standard HTTP verbs, such as
GET and POST.
The server determines the version of the client browser
by using the User-Agent HTTP header that is sent with every browser request.
Based on the information in the User-Agent HTTP header, the server returns the
appropriate OWA version for the client browser.
Because of the
simpler user interface and limited feature set, the reach version of OWA
requires less bandwidth. If you use the rich browser and you experience OWA
performance that is not acceptable, you might experience better performance if
you use a reach browser of OWA.
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Segment Your OWA Installation
You can use OWA segmentation, which is available in Exchange 2000
Service Pack 2 (SP2), to selectively turn on the rich client features of OWA,
such as calendaring, contacts, public folders, calendar reminders, and new mail
notification. OWA segmentation can also provide server-side control of the rich
version of OWA by forcing the use of the reach version, even if the client uses
a rich browser.
You can also configure OWA segmentation individual
servers and individual users. Settings for individual users override the
settings that are configured for individual servers.
For more information about how to write an
add-in to segment OWA on an HTTP virtual server, click the following article number to view the article in the Microsoft Knowledge Base:
310594
How to hard code the reach client for Internet Explorer 5.0 and later
For more information about how to segment OWA on a server or for an
individual user, click the following article number to view the article in the Microsoft Knowledge Base:
311154
Outlook Web Access segmentation in Exchange 2000 Server
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Upgrade to OWA 2000
OWA 2000, which is available with Exchange 2000, has been
redesigned to provide a more scalable, performance-oriented client. For
more information about OWA 2000, visit the following Microsoft Web site:
For more information about upgrading to Exchange 2000, click the following article number to view the article in the Microsoft Knowledge Base:
295922
Considerations when you upgrade to Exchange 2000 Server
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Front-End and Back-End Planning Considerations
You can distribute Exchange 2000 server tasks between front-end
and back-end servers to balance tasks and to make the best use of available
network resources, such as bandwidth. A front-end server responds to OWA client
requests, and then works with back-end Exchange 2000 servers and Microsoft
Active Directory directory service servers to retrieve the information that the
client requested. If the OWA client has a fast connection to the front-end
server, the client can download Web content from the front-end server while the
front-end server proxies requests to the correct back-end server.
You
can also configure the front-end server to authenticate users. Microsoft
recommends that your network plan includes a domain controller near the
front-end server to speed the authentication process.
NOTE: Exchange 2000 Enterprise Edition must be used on the front-end
server.
For more information about how to configure front-end servers with Exchange
2000, click the following article number to view the article in the Microsoft Knowledge Base:
326268
White paper - Microsoft Exchange 2000 front-end server and SMTP gateway hardware scalability guide
326276 White paper - Using Microsoft Exchange 2000 front-end servers
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Use SSL
The use of Secure Sockets Layer (SSL) to encrypt OWA data while
it is in transit has a small performance impact on the OWA server. Both the
server and the client must complete additional processing to encrypt and
decrypt the data.
NOTE: If your users gain access to OWA over a dial-up connection, the
user's perceived performance is slower because the hardware compression that is
used in most modem models cannot compress SSL traffic.
Some of the
processing load can be relieved if you put the front-end server between your
clients and the back-end Exchange 2000 servers. If you do so, the front-end
server performs all of the SSL encryption and decryption processing.
You can also increase OWA performance if you add an SSL accelerator to your
front-end and back-end topology. SSL accelerators generally come in two forms:
- Accelerator cards: Accelerator cards are typically used on
the front-end server, and they offload the encryption and decryption overhead.
This increases the throughput of each connection and reduces the work that the
software on the server has to do.
- External accelerator devices: External accelerator devices
sit between the clients and the front-end servers. Traffic that comes from the
client is decrypted on the accelerator device, and then it is sent to the
front-end server unencrypted. Likewise, traffic from the front-end server is
sent to the accelerator device unencrypted, and then it is encrypted for
transmission to the client.
NOTE: Make sure that the Microsoft Windows 2000 License Logging
Service is running on the front-end server. Microsoft Internet Information
Services (IIS) does not permit more than 10 simultaneous SSL connections unless
this service is running.
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