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

of 18 | Part 19#23 | ActiveSync and Exchange web service client protocol
connectivity flow in Exchange 2013/2007 coexistence environment | 4/4
Written by Eyal Doron | o365info.com | Copyright © 2012-2015
ACTIVESYNC AND EXCHANGE WEB SERVICE
CLIENT PROTOCOL CONNECTIVITY FLOW IN
EXCHANGE 2013/2007 COEXISTENCE
ENVIRONMENT | 4/4 |PART 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 main 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
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 mobile client is 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”.

Note – other Exchange clients such as Outlook and OWA, that can connect the
internal (or to the external) Exchange infrastructure.
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 is
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 is
hosted on the Exchange 2007 mailbox server).
 Exchange mailbox server location: the Exchange 2007 Mailbox server who hosts
the user mailbox, is located on the New York site.

Note – the special charter of mobile Exchange 2007 clients in an Exchange 2013
coexistence environment is that the Exchange 2013 CAS will not directly connect
the Exchange 2007 CAS but instead, proxy the Exchange 2007 ActiveSync client
request to Exchange 2013 Mailbox server.
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:
o The user mailbox version is: 2007
o The Exchange 2007 mailbox server that host the user mailbox, is located at
the New York site
o There is a 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 local CAS2007
by using the internal Exchange 2007 CAS ActiveSync URL address (Number 3).
5. The CAS2007 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 CAS2007 (Number 5).
7. CAS2007 proxy back the informationdata to Exchange 2013 Mailbox server
(Number 6).
8. Exchange 2013 Mailbox server proxy back the informationdata to CAS2013
(Number 7).
9. 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.
the user mailbox, is located on the Los Angles site.
 The Los Angles site is an Intranet site (non-Public facing Exchange site)
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.
o The Exchange 2007 mailbox server that host the user mailbox, is located at
the Los Angles site
o 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 informationdata to Exchange
2013 Mailbox server (Number 6).
8. Exchange 2013 Mailbox server proxy back the informationdata 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 specific 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 who
should be provided 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
host name of the Exchange server who will serve as: “ActiveSync server” but, 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 a1 host name or, use the host name 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 will be 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 basic 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.
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, is located on a
different Exchange site and additionally, the destination site is a “Public facing
Exchange site”

In former 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 is 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
were: 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 any more 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 method 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 will be successfully completed.
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.
o 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 informationdata 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).

Additional reading
 Understanding Proxying and Redirection
 Exchange ActiveSync Returned an HTTP 451 Error
 How Exchange Server 2007 CAS Proxy & Redirection works for Exchange
ActiveSync

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 a 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. Its truth that there are other 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 was 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 who is 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.
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 (FreeBusy 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 who is 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 will be 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) is located is 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).

Additional reading
 Understanding Proxying and Redirection
 Exchange 2013 interoperability with legacy Exchange versions
The Exchange 2013 coexistence article series index page

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

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