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Exchange 2003 Mobile Messaging Part 1 - A look at the Microsoft DirectPush technology

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Exchange 2003 Mobile Messaging Part 1 - A look at the Microsoft DirectPush technology

Written by David Noel-Davies

Thursday, 13 December 2007

Prior to Exchange 2003 SP2, you had two choices for synchronizing a mobile device with a mailbox; you could manually configure ActiveSync on the mobile device to issue synchronization on a scheduled basis, or you could make use of the Always-up-to-date (AUTD) technology. The problem with scheduled synchronizations is that you cannot schedule them for intervals less than five minutes, which means you will not always have the latest information on your device. Another problem is that you (depending on your mobile operator) will be charged for each established session, as new data will travel over the wire, each time a new session is established.

AUTD makes it possible to keep your device up to date by generating an Exchange store event in the user’s mailbox. When the store event detects a change in the mailbox, it triggers a Short Message Service (SMS) control message, which is then sent to the user’s mobile device. When the device receives the SMS message it initiates synchronization with the Exchange server. The idea behind the AUTD technology is good, but unfortunately it doesn’t work very well in reality, at least not in Europe where very few mobile operators supports AUTD. Microsoft IT became aware of this problem, when they deployed Exchange 2003 based mobile messaging in their own organization – an organization spread all over the world.

Based on customer feedback regarding the limitations of using SMS to notify a supported device, Microsoft improved the AUTD experience in Exchange Server SP2 based on the following goals:

A standard data plan is the only subscription you need to synchronize with Exchange (which must work globally)
No need to deploy additional infrastructure in your Exchange environment
No need for SMS notification or any other “out-of-band” schemes
No special configuration on the device

And this is basically what the Exchange DirectPush technology delivers. Microsoft has been testing this new technology on their own servers for a while, and with great results. The DirectPush technology keeps your mobile device up-to-date by delivering e-mail, Calendar, Contacts and Tasks directly to your device, allowing you to react quickly to changes in your mailbox. AUTD v1 did the same thing but DirectPush offers several benefits.

Note:
When enabling DirectPush on the Exchange 2003 Server, devices that are currently configured to use AUTD v1 are automatically switched/migrated from AUTD v1 to DirectPush. This means you don’t need to reconfigure anything on the device after enabling the feature.

The cool thing about the DirectPush technology is that it maintains an HTTPS connection between the Exchange server and the mobile device, a session which is kept alive by using heartbeats. This way the Exchange server can notify a mobile device whether or not there’s a change in the associated mailbox, and if a change occurs in the mailbox, the server can initiate a synchronization. Since the device keeps an open session to the Exchange server, some of you might think this could become rather expensive. But fear not because the device simply sits there and waits for a response, it doesn’t send or receive any data when it’s in this pending state. Said in another way, no data will travel over the wire, unless a change is detected in the mailbox, or the heartbeat expires. To get a more visualized picture of how the DirectPush technology works, see Figure 1 below.

Figure 1: Overview of the DirectPush Technology

Because the mobile device doesn’t send any empty syncs, as is the case with scheduled or manual syncs, the device reduces its power consumption which again increases battery life. Additionally data charges are reduced significantly. It’s also worth noting that any data synchronized between the mailbox and the devices are compressed using GZIP compression.

DirectPush requirements

Server-side
As the DirectPush feature is a new technology included in Exchange 2003 SP2, it’s required that you apply Exchange 2003 SP2 at least on the Exchange 2003 front-end servers in your organization. Note that I say front-end servers, because your back-end servers can run anything from Exchange 2003 RTM, SP1 to SP2 as long as you have one or more front-end servers with SP2 applied. But although DirectPush doesn’t require it, I still recommended you upgrade the back-end servers to SP2 as well, not because you will gain any advantage out of doing so when it comes to the DirectPush technology, but because the service pack is packed with new great features and improvements as well as a lot of bug fixes.

Note:
In addition to the above requirements it’s highly recommended you adjust the time-out values for HTTPS connection in your firewall (more on this later in the article).

In order to properly secure Exchange ActiveSync, it's best practice, as well as my personal recommendation, to publish the service using an ISA Server 2004 firewall, see Figure 2 below for a general best practice scenario.

Figure 2: Microsoft DirectPush Topology

Client-side
Another requirement in order to make use of the DirectPush technology is that the mobile devices need to run Windows Mobile 5.0. In addition the devices need to have the Messaging and Security Feature Pack (MSFP) installed. Although Microsoft shipped firmware that included the MSFP to mobile device manufactures back in October 2005, new firmware releases with the MSFP included have been heavily delayed. But March 2006 seemed to be the month where things started to kick off. Both i-mate and Qtek as well as Orange have finally released new firmware updates with the MSFP included, although so far only for their newer models.

Note:
The Messaging and Security Feature Pack (MSFP) is also known as the Adaption Kit Update 2 (AKU2).

Enabling DirectPush on the Exchange 2003 Server(s)

When Exchange 2003 SP2 has been applied, the DirectPush feature will be enabled by default. The feature can be found in the same place as the other Exchange mobility features are located, which is on the property page of the Mobile Services object in the Exchange System Manager (see Figure 3 below).

Figure 3: Enabling DirectPush in the Exchange System Manager

Note that even though the DirectPush feature has been enabled, mobile devices without the MSFP installed are still capable of doing synchronizations using either the manual and/or scheduled methods, or via AUTD.

Exchange 2003 Server heartbeat time-out values

In order to maintain a persistent connection between an Exchange server and a mobile device, DirectPush makes use of so called heartbeat intervals. This is so that the server can keep a connection open to a device all the time, even though no changes occur in a mailbox. The Exchange server adjusts this heartbeat interval automatically, it keeps the last heartbeat interval received from a device. But you can also configure the value for the heartbeat intervals in a set of registry keys on the Exchange server, although it shouldn’t be nescessary. For details on how you configure these values, I recommend you take a look at MS KB article 905013.

Firewall considerations

In order to maximize performance as well as provide a better always-up-to-date experience for the end-users, it’s highly recommended that you increase the time-out values for HTTPS connections on your firewall. Depending on what type of firewall is used in your organization, this is of course done differently. For steps on how to do so on an ISA Server 2004 firewall see MS KB article 905013, these steps should give you an idea of how you should approach this with another firewall product as well.

Note:
Failing to set the time-out on the firewall to minimum 15 minutes (MS recommends 30 minutes) will among other things result in poor battery life time on the mobile devices as well as increase data transfers over the wire.

Enabling DirectPush on the mobile device

It’s time to see what is required on the mobile device in order to get it to synchronize with the Exchange server using DirectPush. Let me be honest and tell you there’s nothing new when it comes to configuring ActiveSync on the device, actually you only need to enable Microsoft DirectPush under the Comm Manager as shown in Figure 4 below, and the device will issue an HTTP (ping) request to the Exchange server and we’re pretty much there.

Figure 4: DirectPush on a mobile device with the MSFP installed

When DirectPush has been activated on the device, an icon consisting of two small vertical arrows appears in the top right corner of the screen (see Figure 5). When a change is detected in the mailbox, or if the heartbeat expires, the server will issue a response back to the device, which will then do a synchronization of the respective mailbox, or re-issue an HTTP request.

Figure 5: DirectPush enabled on the mobile device

DirectPush Performance Counters

When you install Exchange 2003 SP2 on an Exchange Server, several DirectPush related performance counters are added to the server as well. These counters can be found under the Microsoft Exchange ActiveSync performance object, as can be seen in Figure 6 below.

Figure 6: DirectPush related performance counters

Notice all the counters measuring so called Ping commands. Ping (which shouldn’t be confused with a traditional Ping command) is the command or request that’s sent by the mobile device to the server via an HTTP(S) connection. This request will then be in a pending state until a change occurs in a mailbox, or until the heartbeat interval expires.

As with any other performance counter you can get a description of each DirectPush related counter by marking it, then click the Explain button (see Figure 6).

Conclusion

The new DirectPush technology provides a much richer experience for your end-users, and even though DirectPush isn’t real push technology (like is the case with RIM’s Blackberry product), the end-user will never notice as it is a matter of seconds before a change occurring in a mailbox (e-mail, calendar, contacts and tasks) is synchronized to a mobile device. Due to the fact that the DirectPush technology is an integrated part of Exchange 2003 Servers with SP2 applied, the investments required can be kept at a minimum, as the only thing you need to invest in is mobile devices running Windows Mobile 5.0 and have the MSFP installed.