Distributed Cache mode of BranchCache is the most easy to implement mode and it doesn’t require any infrastructure presence in the branch office. We will be discussing this mode of operation in this post.
The Story of Bob
Bob walks at the office 7 AM in the morning, fires up his windows 7 PC and wants to download the company newsletter that is hosted on a remote BranchCache enabled server in the main office. Since he is configured to use BranchCache, his laptop will start downloading identifiers or hashes that describe the data instead of the data itself and those identifiers are so small (Step 1).
So he pulls down those very quickly (couple of kilobytes) and he uses them to do something called multicast shout searching for a peer on the local subnet in the branch that has already downloaded that data (step 2). But since he is the first one who views this content, he shouts, nobody there, so he goes back to the WAN link and does a complete download of the data (Step 3).
It takes a little bit longer but once he is done, his computer keeps that data locally so that it can be made available to other peers.
Now, 15 minutes later, Alice comes at the office, fires her Windows 7 computer, and tries to access the same newsletter; she downloads the identifiers (Step 4), does a multicast shouts (Step 5). Bam… finds Bob PC, and downloads the content very quickly (Step 6).
You can see that you don’t need to have any servers in the branch office. All what need to be done, is to enable BranchCache on those branch clients which can be done easily via group policies.
Keep in mind that you need some disk space on client machines to host cache files, and some extra processing to reply to cache request from neighbor machines. Also you can notice that cache availability in the branch will drop when laptops go offline or hibernate. This mode of operation is recommended for branches up to 50 machines for Windows 7, but this has been changed in Windows 8.
This is part of the story. If you are interested to know more about this nice technology, come here again and filter posts with (BranchCache) tag.