How Outlook traveling clients connect to a local Exchange 2010 server?

Dear all,
 
I have questions regarding the Exchange architecture, design and functionment.
We have 3 sites on 3 different continents with an Exchange 2010 server on each site (CAS, Mailbox server and hub transport roles).
The 3 exchange servers are in the same DAG and all databases are replicated on all sites.
We domain controllers on each site with a single AD Forest with different sites.

I assume below that our users connect to a LAN with a VPN between each site.
 
1- When one user from site A travels to site B (where resides a copy of the database for HA) , on which Exchange server does the outlook client connect?
 I cannot imagine that a user travelling in China (where our internet bandwidth is really slower than in US or Europe) would connect to the remote server and have very slow response.
 
2- When one user from site A travels to site B (where resides a copy of the database for HA) , and sends an email to another user in site B, what is the route of the mail ? Site B--> site B OR site B--> site A --> site B ?
 
3- If the server in site A fails, where will connect my traveling user if he is on site B (with an exchange server on site) but without internet connection? In other words, will he be able to send emails to another local user on site B?

4- If internet connection between Site A and Site B is down and the database on Site B is promoted as active, what happens when the link is restored? Does Site B send its updates to Site A then become inactive again?

 
Thank you for your help :-)
LVL 2
abissaAsked:
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James HIT DirectorCommented:
1. The user has no choice with your given setup. Since each server has a CAS role and none are in an array, the user that is setup at a particular site has to connect back to that specific server in order to get his mail. DAG is only for database resiliency and not for client connectivity.
2. Again, since this user has to connect back to his exchange server, it will go from A to B.
3. No, not without manually changing the CAS to point to one of the other DAG members.
4. No, once a site becomes the active member, you will have to manually switch it back once the site has been restored.

This link explains it with some diagrams as well.

http://www.shudnow.net/2010/03/04/exchange-2010-rpc-client-access-service-and-multiple-sites/

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abissaAuthor Commented:
Hi Spartan,

Thank you for your reply.
I do agree with most of your answers  (1 and 4) but would like some highlight on 2 and 3:

2. Does the hub transport used is the one of the sender or the recipient?
If our user authenticate with a CAS array on server B, ig uess that he would use the Hub transport on server B? And in that case, the emails sent to other users on site B wouldn't route to server A. Your opinion ?
Microsoft Technote: "If the recipient's mailbox is located on a Mailbox server in the same Active Directory site as the Hub Transport server and the version of the Mailbox server matches the Hub Transport server, the message is delivered directly to that mailbox"

3. If we have a CAS array, i guess that this traveling user could connect and authenticate to site B.

Ludovic
abdulalikhanCommented:
For the 2 point, The hub transport used is of sender and you understand it correctly.

For point 3, spartan_1337 already explained that you have to manually change the CAS to site B. CAS Array cannot be configured intersite. Every site must have a different CAS Array.
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