Exchange CAS server as information + Web service provider | Part 07#36

Page 1 of 13 | Exchange CAS server as information + Web service provider | Part 07#36

Written by Eyal Doron | o365info.com | Copyright © 2012-2015

Exchange CAS server as information +

Web service provider | Part 07#36

The current article will be focused on the two main responsibilities of the Exchange

CAS server:

Exchange CAS server as an information provider (Autodiscover information).

Exchange CAS server as Exchange web service provider.

The current article is the continuation of the former article –xx. In the former article,

we have reviewed the Exchange CAS server responsibilities that were described as

“providing Exchange client’s access to their mailbox”.

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Exchange CAS server as an information (Autodiscover

information) provider

In the following section, we will focus on the aspect of the Exchange CAS server as

an “information provider.”

Two main categories of Autodiscover information

We can classify the type information, which the Exchange CAS server provides to

Exchange clients into two main categories:

1. Configuration settings for Exchange mail client






The Exchange CAS server provides the required configuration settings for three

types of the mail client -Outlook, Mobile mail clients, and webmail client.

The configuration setting is used by Outlook and Mobile mail clients for creating a

mail profile automatically.

Regarding the subject of a webmail client such as – OWA, this Exchange client is not

configured using a mail profile and to be honest, I don’t know when and where the

OWA web client will use Autodiscover information.

2. Information about Exchange web services

The second type of information that the Exchange CAS server provides to his

Autodiscover client is a list of available Exchange web bases services.

This “list”, includes a description of the specific Exchange web service that is

provided and the URL address of the specific web services (the URL address

includes the host name of the Exchange CAS server who provides the specific web

service).

The Exchange CAS server provides the information about the existing web services

by using “different formats”.

One type of “format” for external mail clients that includes the public name of the

Exchange CAS server who provide the specific web service and additional types of

“URL format” which include the internal\private name of the Exchange CAS server

who provides the web service (internal\private name is not accessible or published

for external mail clients).






1. Information needed by Exchange clients, for creating a new mail profile.

Exchange clients such as Outlook and mobile devices, need to create a mail profile

for connecting their Exchange mailbox.

We can relate to a “mail profile” as a “collection of configuration settings and user

details” that are needed for creating the communication channel with the Exchange

CAS server.

In theory, the required configuration settings could be configured manually, but in

practice, the task of manual configuration of mail profile is not so simple because it

requires prior knowledge of the parameters and setting needed for the mail profile

and this task, is unsuitable for “standard user.”

Additionally, in case that the destination server is Exchange 2013, the option of

creating a manual mail profile becomes almost impossible, because the Outlook

mail profile is not configured using the Exchange CAS server name but instead,

using a session ID or GUID ID that is provided by the Exchange CAS server.

Given that the Exchange client provides his E-mail address and the user credentials,

all the rest of the required technical details, will be provided to the mail client such

as Outlook and will be used for the automatic creation of the new mail profile.






2. Information about available Exchange web services.

Exchange CAS server, serve as a “focal point” or “information center” for his

Exchange clients. We can say that mail client such as Outlook relates to the

Exchange CAS server a “Bulletin board.”

The Exchange CAS server has all the information about “who is doing what” and

how to get there.






If we want to be more technical, the Exchange client (the Autodiscover client)

submits a request for information, by asking a file named – autodiscover.xml or

autodiscover.csv file.

The Exchange CAS server “answer,” meaning the information that is provided by the

Exchange CAS server to the Exchange client such as Outlook, is “packed” and

delivered to the client as an – Autodiscover responds.






The Autodiscover.xml includes an important information about all the available

Exchange web services in the existing Exchange infrastructure.

The information that the Exchange CAS server provides includes a detailed

description of:

The names of the available Exchange web services.

The URL address of each of the web services – the URL address included the

name of the Exchange CAS server who provides the specific web service.

Different type of URL address for external and internal mail clients – Exchange

CAS server have two “identities” – internal identity that is “exposed” only to the

internal mail client and external identity that are exposed to external mail

clients.

The information that the Exchange CAS server provides is provided based on

the “type of the Exchange client.” In case that Exchange CAS server recognize

that the mail client is “internal mail client,” the information will include the

URL address with the “private names” of the Exchange CAS server\s.

Exchange CAS server, is responsible for generating the required information.

We use the term ”generating” because, the information is not a static, but instead,






“dynamic”. The meaning that the Exchange CAS server will need to “re-create” the

information for each Autodiscover client request.

Exchange CAS server “pack” the information into an XML format and send the data

to the Exchange mail client.

The “Exchange web services,” could be provided by a single Exchange CAS server or

could be distributed between many Exchange CAS servers.

Outlook client, use the information that he got from the Exchange CAS server (the

Autodiscover response) when he needs to get a specific Exchange web service such

as: Availability Service (Free\Busy time), Automatic reply (Out of office), Mail tips and

so on, by addressing the Exchange server who provides the specific web service.

In the following diagram, we can see the process in which the Exchange client

request for the information and the Exchange CAS server responds with an

“answer.”

The Exchange client, “use” the information that includes the URL address of a






specific Exchange web service for – addressing or connecting, the Exchange CAS

server who provides the required web service.

Providing Exchange web services \ access to the

Exchange web service.

An Exchange CAS server serves as the element that provides Autodiscover

information about the available Exchange web services and, at the same time, plays

the role of the “service provider” by providing Exchange web services.

This “mixture” of services is relevant only for Exchange server versions 2007 and

2010.

In Exchange 2013 architecture, the responsibility for providing Exchange web

service was allocated to the Exchange mailbox server.






The Exchange 2013 CAS server will forward Exchange client requests to for

Exchange web service to the Exchange mailbox server, but he is not the “element”

to provide the Exchange web service by himself.

The Autodiscover information that the Exchange CAS server provides to his

Exchange clients, can contain the URL address that point “to himself” or URL

address of other or additional Exchange CAS servers\s that provides a specific web

service.






EXCHANGE WEB SERVICE EXAMPLE | THE EXCHANGE AVAILABILITY

SERVICE (FREE\BUSY TIME) SERVICE.

The Exchange Availability Service (Free\Busy time) service is a very popular service

that is used daily, by many Exchange clients.

Every standard Outlook user, is familiar with the simple task of creating new

meeting and using the scheduling assistant for inviting additional participants and

view the information about the Free\Busy time of these Exchange recipients.

At first sight, this task seems to be very ordinary and simple. In reality, the “final

result” in which user A can sees the Free\Busy time of user B can be considered as a

compound task that requires many steps by the Exchange CAS server\s for

providing the required result.

The “mechanism” that enables these Exchange services, is the Exchange Availability

Service (Free\Busy time) service.






To be able to demonstrate the way that the Exchange Availability Service (Free\Busy

time) service “works” let’s use the following scenario.

On organization have two physical Active Directory and Exchange sites – New York

site and Los Angel’s site.

Alice is a recipient from the New York site, and Bob is a recipient from Los Angel’s

site.

In our scenario, Alice needs to invite Bob to a meeting is a specific date and, Alice

needs to get information about the availability status of Bob in that specific date.

Alice navigates to her Outlook calendar and, use the scheduling assistant to add

Bob’s name to the meeting.

In the following screenshot, we can see an example of the Free/Busy time

information that is present when inviting a specific organization user to a meeting.

Let’s assume that everything works correctly and, after a few second, Alice can see

that Bob is available on the specific date.

Now let’s take a second look and check what happened “Under the hood” of the

Exchange infrastructure.

1. Alice, send a request for information about the “Bob Free/Busy time” to her

Exchange CAS server (Alice Exchange CAS server is located at the New York site).






2. The New York Exchange CAS server accesses the local Active Directory to get

information about the Exchange mailbox server who host Bob’s mailbox.

3. When the New York Exchange CAS server gets the information from the Active

Directory, he “understand” that Bob’s mailbox is located at another site – the Los

Angel’s site.

4. The New York Exchange CAS server accesses the local Active Directory to get

information, about – who (and if) there is an Exchange CAS server who

represents the Los Angel’s site.

5. When the New York Exchange CAS server gets the information from the Active

Directory, he tries to connect the Los Angel’s site Exchange CAS server.

6. The Los Angeles Exchange CAS server accesses the local Active Directory to get

information about the Exchange mailbox server who hosts Bob’s mailbox.

7. The Los Angeles Exchange CAS server the Exchange mailbox server, which host

Bob’s mailbox and ask him for information about the Availability (Free\Busy

time) of Bob.

8. When the Exchange CAS server of the Los Angel’s site gets the required

information, he “forward” the information to the New York Exchange CAS server.

9. When the Exchange CAS server at the New York site gets the required

information, he “forward” the information to the user (Alice) mailbox.

10. Alice sees the information about Bob Free\Busy time in her calendar.




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Exchange CAS server as information + Web service provider | Part 07#36