Hello Running Exchange 2007 SP2. We have four regions in our company - America (AMER), Latin America (LTAM), AsiaPac (APAC) and Europe (EMEA). At the moment, our OAB setup is with the OAB Generation Server in AMER, with web-based distribution to regional CAS servers. We want to look into have one OAB per region - that is each region would have their own OAB generation server and CAS distribution. One of the main reasons is because admins can troubleshoot their own OAB problems, but I guess other advantages are 1 - Reduced network traffic between OAB Generation server and CAS servers 2 -OAB failure on one will not affect other regions Are there any more? What I'm curious to know is, if we did go for this model, how does this work in terms if A - There can only be one Default OAB can't there? So if we kept the Default in AMER, how could we prevent APAC users from downloading that? The only way I can think is to remove the APAC CAS servers from the distribution list of the Default OAB? B - But, let's say that we didn't want to amend the CAS distribution list of the OAB, but we did create an APAC OAB Generation server as well with APAC CAS's. So now we have APAC CAS servers involved the distribution of two OAB's. Which one will clients download? C - When the CAS servers distribute the OAB, is this compressed when being transmitted? D - If I wanted to work out how much data was transferred in a full download of an OAB for a client, how could I work that out, bearing in mind this compression too?

You can create multiple OABs. Generate and distribute to the repective CAS per region and name the OABs appropriately. As far as the other questions, hopefully this will help: http://technet.microsoft.com/en-us/library/bb232155.aspx Understanding Offline Address Books

Appreciate the link. But what I don't understand is - say we have OAB (AMER) and OAB (APAC). Both OAB's have APAC CAS servers as their distribution servers, but the Default OAB is the OAB (AMER). Does this mean that APAC clients will pick up the OAB (AMER)? I'm unsure about - i. How the Default OAB and regional OABs fit into this. From what I understand, new mailboxes will pick up the Default OAB providing a local CAS server is set to distribute it Secondly, back to the example of the above OAB's with APAC CAS distribution servers. But this time, the default OAB is OAB (EMEA) - which doesn't have any CAS distribution servers in APAC. Does this mean that APAC clients will pick up a mix of the OAB (AMER) and OAB (APAC) OAB's? Is the only way to prevent clients picking up another OAB to remove APAC CAS servers from that OAB's distribution list?

I would distribute the correct repsective OABs to the CAS in the respective AD sites. APAC CAS get the APAC OAB, NA get the NA OAB etc... On each mailbox database, you then set which OAB the mailboxes on that store will use under client settings. Make sense?

Ah ok, so we'll have to amend that value on each Mailbox Store as well? Out of interest - if, say we configure the Mailbox Stores to use the OAB (APAC) address book, but there are no CAS distribution servers set for that OAB, will all the clients connect across the WAN to other CAS distribution servers that ARE set to distribute that OAB?

Ah ok, so we'll have to amend that value on each Mailbox Store as well? Out of interest - if, say we configure the Mailbox Stores to use the OAB (APAC) address book, but there are no CAS distribution servers set for that OAB, will all the clients connect across the WAN to other CAS distribution servers that ARE set to distribute that OAB? Yep. Because you are telling it to use that OAB for that store. For example: NA OAB: Generate on NA Server -> Distribute to NA CAS -> Set as OAB for mailbox stores in NA under client settings. APAC OAB: Generate on APAC Server -> Distribute to APAC CAS -> Set as OAB for mailbox stores in APAC under client settings. Default OAB: Either one. Up to you.

Ah ok, so we'll have to amend that value on each Mailbox Store as well? Out of interest - if, say we configure the Mailbox Stores to use the OAB (APAC) address book, but there are no CAS distribution servers set for that OAB, will all the clients connect across the WAN to other CAS distribution servers that ARE set to distribute that OAB? Yep. Because you are telling it to use that OAB for that store.