ActiveSync and Exchange web service client protocol connectivity flow in Exchange 2013/2007 coexistence | 4/4 | 19#23

The current article, is the fourth article of four articles series, on the subject of: “Exchange 2013/2007 coexistence environment and mail client protocol connectivity flow”.
In this article, our primary focus is reviewing two types of client protocol connectivity flow in Exchange 2013/2007 coexistence environment:

• ActiveSync client protocol connectivity flow
• Exchange web services client protocol connectivity flow

To be able to understand the different “Exchange clients” connectivity protocol flow in Exchange 2013/2007 coexistence environment, we will review five types of “relationships” that exist between Exchange 2007 client and the Exchange CAS 2013 server:

• Autodiscover client – protocol connectivity flow (Part 2#4)
• Outlook client – protocol connectivity flow (Part 2#4)
• OWA client – protocol connectivity flow (Part 3#4)
• ActiveSync client – protocol connectivity flow (Part 4#4)
• Exchange web service client – protocol connectivity flow (Part 4#4)

Exchange 2013/2007 coexistence | ActiveSync client protocol connectivity flow

Exchange ActiveSync clients (Mobile clients) are always considered as “external client” because the network infrastructure of the mobile client based on a public mobile network. Mobile Client (ActiveSync client) will always need to address the Public facing Exchange CAS server and for this reason, the “connection point” (Exchange CAS server) that will accept the Mobile (ActiveSync) client communication requests, must be configured as a “Public-facing Exchange CAS server.”

When the ActiveSync (Mobile) client connects the Public facing Exchange CAS server, based on the provided user credentials, the Public facing Exchange CAS server finds out where is the user mailbox is hosted and “route” (Proxy) the communication request to the internal Exchange infrastructure.

The “internal routing” of the ActiveSync (mobile) client communication request implemented by using the internal ActiveSync URL address.

Scenario 1: Mobile (ActiveSync) client | User mailbox located on New York site.

Scenario charters: an ActiveSync Exchange 2007 client, need to access his mailbox.

• Exchange user type: Exchange 2007 client (Exchange user whom his mailbox hosted on the Exchange 2007 mailbox server).
• Exchange mailbox server location: the Exchange 2007 Mailbox server which hosts the user mailbox, is located on the New York site.

The ActiveSync client protocol connectivity flow, will be implemented as follows:

1. Mobile (ActiveSync) client, connects the “New York Public facing Exchange CAS” by using the server name:mail.o365info.com and, provides his user credentials.
2. CAS2013 uses the user credentials and performs the Active Directory lookup.
   CAS2013 determines that:
3. The user mailbox version is: 2007
   • The Exchange 2007 mailbox server that host the user mailbox, is located at the New York site
   • There is a local Exchange CAS 2007 in the site (the New York site)
4. CAS2013 will proxy the ActiveSync client request + the ActiveSync user credentials to the local Exchange 2013 Mailbox server.
5. Exchange 2013 Mailbox server proxy the ActiveSync client to the local CAS2007 by using the internal Exchange 2007 CAS ActiveSync URL address (Number 3).
6. The CAS2007 will accept the request and “forward” (Proxy) the ActiveSync client connection request to the Exchange 2007 Mailbox server (Number 4).
7. Exchange 2007 mailbox server “fetch” the required user mailbox content and send back the data to the CAS2007 (Number 5).
8. CAS2007 proxy back the information\data to Exchange 2013 Mailbox server (Number 6).
9. Exchange 2013 Mailbox server proxy back the information\data to CAS2013 (Number 7).
10. CAS2013 provides the required information to the external ActiveSync client (Number 8).

Scenario 2: Mobile (ActiveSync) client | User mailbox located on Los Angles site | Destination site = Intranet site

Scenario charters: an ActiveSync Exchange 2007 client, need to access his mailbox.

• Exchange user type: Exchange 2007 client (Exchange user whom his mailbox is hosted on the Exchange 2007 mailbox server).
• Exchange mailbox server location: the Exchange 2007 Mailbox server which hosts the user mailbox, is located on the Los Angles site.
• The Los Angles site is an Intranet site (non-Public facing Exchange site)

The ActiveSync client protocol connectivity flow, will be implemented as follows:

1. Mobile (ActiveSync) client, connects the “New York Public facing Exchange CAS” by using the server name: mail.o365info.com and, provides his user credentials.
2. CAS2013 uses the user credentials and performs the Active Directory lookup.
   CAS2013 determines that:
   • The user mailbox version is: 2007
   • The Exchange 2007 mailbox server that host the user mailbox, is located at the Los Angles site
   • There is no local Exchange CAS 2007 in the site (the New York site)
3. CAS2013 will proxy the ActiveSync client request + the ActiveSync user credentials to the local Exchange 2013 Mailbox server.
4. Exchange 2013 Mailbox server proxy the ActiveSync client to the “Los Angles Exchange 2007 CAS” by using the internal Los Angles Exchange 2007 ActiveSync URL address (Number 3).
5. The Los Angles Exchange 2007 CAS will accept the request and “forward” (Proxy) the ActiveSync client connection request to the Exchange 2007 Mailbox server (Number 4).
6. Exchange 2007 mailbox server “fetch” the required user mailbox content and send back the data to the Los Angles Exchange 2007 CAS (Number 5).
7. Los Angles Exchange 2007 CAS proxy back the information\data to Exchange 2013 Mailbox server (Number 6).
8. Exchange 2013 Mailbox server proxy back the information\data to CAS2013 (Number 7).
9. CAS2013 provides the required information to the external ActiveSync client (Number 8).

Scenario 3: Mobile (ActiveSync) client | User mailbox located on Madrid site | Destination site = Public facing Exchange site | Regional namespace

Before we start with the specific details of the “Madrid ActiveSync user” briefly review the charters of this particular scenario.

By default, ActiveSync (Mobile) client will use the Exchange Autodiscover infrastructure for getting the “server name” that will accept their request. In a scenario of a “Madrid ActiveSync user”, the name of the Exchange server which should provide for the ActiveSync client as part of the Autodiscover process is, the name of “Madrid Public facing Exchange CAS server”: europe.mail.o365info.com

By default, the preferred method for ActiveSync client is to use the Exchange Autodiscover services for getting all the required ActiveSync profile settings and the hostname of the Exchange server who will serve as -“ActiveSync server.” In some scenarios, ActiveSync client the Autodiscover services are not used and instead, the mobile user uses a “manual method” in which he provides the “Exchange server name”.

For example, when a “Madrid ActiveSync user” want to access his mailbox, he can provide the primary namespace: mail.o365info.com (option A in the diagram) as the Exchange host name. Another option is to use the hostname of the “Madrid Public facing Exchange CAS server”: europe.mail.o365info.com (option B in the diagram)

In case that the “Madrid ActiveSync user” use the primary namespace: mail.o365info.com, the connection request accepted by the “New York Public facing Exchange CAS server.”

The “New York Public facing Exchange CAS server” will need to know how to “handles” this request because, in our scenario, the ActiveSync user mailbox is hosted on another Exchange site: the Madrid site.

The underlying assumption could be that in this case, the “New York Public facing Exchange CAS server” will “redirect the “Madrid ActiveSync user” to his Exchange server but Exchange 2013 CAS will not use the redirection method.

In this scenario, the “New York Public facing Exchange CAS server” will not redirect the ActiveSync request, but instead, proxy the connection request to the “Madrid Exchange CAS server”.

Scenario charters: Mobile (ActiveSync) client, need to get access to his mailbox.

• Exchange user type: Exchange 2007 client (Exchange user whom his mailbox hosted on the Exchange 2007 mailbox server).
• Exchange mailbox server location: the Exchange 2007 Mailbox server which hosts the user mailbox, is located on the Madrid site.
• The Madrid site considers as Public facing Exchange site and the “Madrid Public facing Exchange CAS server” are published with a regional namespace: mail.o365info.com

The special charter of this scenario is – that the user’s mailbox located on a different Exchange site, and additionally, the destination site is a “Public-facing Exchange site.”

In previous versions of Exchange server, in a scenario in which the mobile (ActiveSync) client connects a Public facing Exchange CAS server and the Exchange server recognizes that the mobile (ActiveSync) client mailbox located in a different Exchange site + the “other Exchange site” considers as Public facing Exchange site, the “response” of the Public facing Exchange CAS server was a: redirection message to the Mobile (ActiveSync) client.

The Mobile (ActiveSync) client was supposed to accept the “redirection message” and create a new communication channel with the “other Public facing Exchange CAS server (the “Madrid Public facing Exchange CAS server” in our scenario).

The method of redirecting mobile (ActiveSync) client was implemented by using a message that described as: ”451 redirect message”.

The problem with the ”451 redirect message” was that – many ActiveSync clients (mobile client), did not know how to “digest” the redirection message, and the result was – communication failure of ActiveSync clients.

For this reason, the behavior of Exchange CAS 2013 server is different because the Exchange CAS 2013 server will not implement anymore the redirection method (451 redirect message) for ActiveSync clients.

In our scenario, the New York Public facing Exchange CAS server “know” that the user mailbox is located at the Madrid site and additionally, that the Madrid site has a Public facing Exchange CAS server.
Theoretically, the New York Public facing Exchange CAS server can redirect the Exchange ActiveSync to this server, but instead, the New York Exchange 2013 CAS will choose to use the Proxy method.

It’s clear that this approach is not efficient from the point of view of the “New York Public facing Exchange 2013 CAS server” because theoretically, the “Madrid Public facing Exchange CAS server” should have served the “Madrid ActiveSync (mobile) client, but using the “Proxy method”, will ensure that the Mobile (ActiveSync) client communication successfully completed.

The ActiveSync client protocol connectivity flow, will be implemented as follows:

1. Madrid Mobile (ActiveSync) client, connects the “New York Public facing Exchange CAS” by using the server name: mail.o365info.com and provides his user credentials.
2. CAS2013 uses the user credentials and performs the Active Directory lookup.
   CAS2013 determines that:
   • The user mailbox version is: 2007
   • The Exchange 2007 mailbox server that host the user mailbox is located at the Madrid site
3. CAS2013 will not send a redirection request to the Madrid ActiveSync client, but instead, proxy the ActiveSync client request + the ActiveSync user credentials to the “Madrid Public facing Exchange CAS server” by using the external “Madrid Public facing Exchange CAS server” ActiveSync URL address (Number 2).
4. The “Madrid Public facing Exchange CAS server” will accept the request and “forward” (Proxy) the ActiveSync client connection request to the “internal Madrid Exchange 2007 Mailbox server” (Number 3).
5. The “internal Madrid Exchange 2007 Mailbox server” “fetch” the required user mailbox content and send back the data to the “Madrid Public facing Exchange CAS server” (Number 4).
6. “Madrid Public facing Exchange CAS server” proxy back the information\data to “New York Public facing Exchange CAS server” (Number 5).
7. “New York Public facing Exchange CAS server” provides the required information to the external ActiveSync client (Number 6).

Exchange 2013/2007 coexistence | Exchange web service client protocol connectivity flow

The subject of Exchange web services connectivity flow In Exchange 2013/2007 coexistence environment could be a bit confusing because it’s not clear who is the “element” that provides the Exchange web services to the Exchange 2007 clients.
The element is – Exchange 2013 CAS that implements the standard Proxy mechanism of proxy, Exchange 2007 clients request to the Exchange 2007 CAS or another scenario in which the Exchange 2007 client connects directly to the Exchange 2007 CAS and asks for specific exchange web services?

Note – In the current article, we will not get into detailed explanations of this concept, and if you want a more thorough review, please read the articles:

• Exchange web services in an Exchange 2013 coexistence environment | Part 1/2
• Exchange web services in an Exchange 2013 coexistence environment | Part 2/2

Just a general note: the most “important Exchange web service client” is the Outlook client. It’s truth that there are another Exchange web service clients, but the Exchange client that is most dependent on the Exchange web service is the Outlook mail client.

For this reason, when we mention the subject of “Exchange web services and client protocol connectivity flow,” most of the time, the client that we are refereeing is Outlook.

We can start with a basic rule: in Exchange 2013/2007 coexistence environment Exchange 2007 CAS is the element that provides Exchange web services to the Exchange 2007 clients.

The implementation of Exchange web services in Exchange 2013/2007 coexistence environment, is implemented by using a combination of the Exchange 2013 CAS Autodiscover services + the Exchange 2007 CAS web services.

In an Exchange 2013/2007 coexistence environment, the Exchange 2007 clients will connect the Exchange 2007 CAS using the legacy namespace, based upon the Autodiscover information that provided to them by the Exchange 2013 CAS.

Scenario 1: Internal Exchange 2007 client | Exchange 2007 user mailbox located on New York site.

Scenario charters: an internal Exchange 2007 client, need to get Exchange web services.

• The Exchange 2007 user mailbox, is hosted on the New York site (Exchange 2007 Mailbox server which located on the New York site).

Scenario charters: an external Exchange 2007 client, need to get Exchange web services.

1. Internal Exchange clients connect the Exchange 2013 CAS server and asking for Autodiscover information.
2. CAS2013 uses the user credentials and performs the Active Directory lookup. CAS2013 determines that: the user mailbox version is: 2007
3. CAS2013 sent to the Exchange 2007 Autodiscover information that includes the information on the Exchange web services URL address. The URL address is based on the Exchange 2007 legacy namespace.
4. The Exchange 2007 client gets the Autodiscover information and saves it for later use.
5. When the Exchange 2007 needs specific Exchange web services, such as Availability Service (Free\Busy time), he will contact the Exchange 2007 CAS server using the Exchange 2007 CAS legacy namespace (Number 3).

Scenario 2: External Exchange web service’s client | Exchange 2007 user mailbox on the same Active Directory site

Scenario charters: an external Exchange 2007 client, need to get Exchange web services.

• The Exchange 2007 user mailbox, is hosted on the New York site (Exchange 2007 Mailbox server which located on the New York site).
• New York includes two Public facing Exchange CAS server: the “Exchange 2007 CAS Public facing Exchange CAS server” that is published using the public name: legacy.mail.o365info.com and the “Exchange 2013 CAS Public facing Exchange CAS server” that is published using the public name: mail.o365info.com

The Exchange web services connectivity flow implemented as follows:

1. The external Exchange 2007 client, connect CAS2013 server and provide user credentials.
2. CAS2013 will authenticate the user and perform an Active Directory lookup.
3. CAS2013 determines that: the user mailbox version is 2007 + the user Exchange Mailbox server (and CAS2007 server) located on the same AD site.
4. CAS2013 will proxy the Exchange web service request to the CAS2007 in the local site (Number 2).
5. The CAS2007 will generate the required information and send it back to the CAS2013 server (Number 3).
6. CAS2013 “provide” the Exchange web services information to the external Exchange 2007 client (Number 4).