Amount of Bandwidth required to run Outlook Client remotely

Hi there,

The company I work for is considering centralizing their MS Exchange infrastructure and I was wondering what the miminmum network bandwidth would have to be to support a full Outlook client (say Outlook 2003 with Exchange 2003 backend) remotely.
There are 24,000 users across 70 sites, they send on average 15 emails and receive 30 emails per day. The majority of the emails (30%) are approx between 4kb to 10kb in size but around 3000 messages a day are over to 2mb.

What I need to know is if we were to centralize, how much bandwidth would I require for a small site (1 to 50 users), a medium site (50 to 200 users) and a large site (200+ users) as a minimum?

The client would be the full version and not OWA and the servers would be based in data centre.

Thanks a lot in advance, I appreciate any help or advice you can give.
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Pete LongConnect With a Mentor Technical ConsultantCommented:
OK Step One work out what protocols you are going to use..........................

Protocols and throughput considerations

Internet Mail Access Protocol 4: Is the most complex protocol used, it works by only downloading the message “header” from the server. It is suitable for both offline and online working. Its overhead on the system is MUCH higher than POP3 and also needs the SMTP (Simple Mail Transfer Protocol) for it to operate.

Post Office Protocol version 3: Using this method ALL the mail is downloaded from the server to the users machine, and deleted from the central server. This is a very simple protocol. Its drawback is it will only support offline working and CANNOT be used with a “Roaming Profile”. However it has the LEAST impact on network throughput.

Microsoft Application Protocol Interface: This uses another Microsoft service (which runs on all our Microsoft computers) called the RPC (Remote Procedure Call) service. This protocol PERIODICALLY synchronises the uses mail with the server. This method is very efficient but has a LARGE message “Overhead”
Hypertext Transfer Protocol: Only online working is available with http, the overhead on http depends on the client’s ability to cache web information locally, but generally this protocol has the HIGHEST overhead.
If the client browser is not performing caching the overhead can be multiplied by a factor of 3

Step Two Determine how many users are using what type of protocols
(I may loose some formatting here cause this is out of a table)

Mail Protocol      Client      User OR Administrator      Offline or Online      Overhead      Size of Message Kb
POP3                      Outlook      User                                      Offline                       Low      0.03
IMAP4                      Outlook      User and Administrator      Offline and Online      Medium      2
HTTP                      Internet Explorer      User and AdministratorOnline                      High      10
MAPI                      Outlook      Administrator                       Offline and Online      High      4

Step Three You then need to make allowances for the following

Additional Network factors for consideration.

Calendar and Directory Queries
Although less frequent than mail messaging this must be taken into consideration, most of these queries are via HTTP.

Encryption and RPC traffic
IE 5.5 and above support (128 bit encryption) this uses a system called SSL (Secure Sockets Layer) and is used for IMAP4, POP3 and HTTP
RPC encryption is employed when using MAPI
Both methods have a VERY SMALL impact (1 kb on each message)

Mail moving/Mail deletion
Has a VERY small bandwidth impact (1 Kb on each message)

Current mail statistics
Under my existing Mail system average mail size is 30Kb – This figure can be misleading most mail transfers are between 1-10 Kb in size. The figure has to be increased to take into account the amount of LARGE attachments that are periodically sent. Worst-case scenario (Using HTTP) would an extra 33% to existing http traffic.

Peak throughput
At Peak usage times throughput increases by a factor of six.

Amount of users
This is not an easy concept to understand, because of the way traffic is handled, and DOES NOT work in the way you would expect. Generally SMALLER amounts of users sharing the same connection require MORE bandwidth i.e. 1-20 users increases the bandwidth by a factor of four, 20-100 users increases bandwidth by a factor of TWO.
Broadly speaking, the faster the connection the faster the mail downloads response times on mail transfers of 1-3 seconds are considered acceptable, where 10-20 seconds are not

To quantify all the above our users must be classified into categories based on their system usage. Classifying Low, Medium and High sytem users does this.
(Table coming again sorry :(

Per Day                                      Low user      Medium User      High User
Messages Sent                      5      15                      30
Messages Relieved                     10      20                      30
Messages Deleted or Moved      8      15                      25
Calendar Lookups                      1      3                       5
Directory Lookups                      1      2                       4
Logons                                      1      5                       10

Now for the cool bit putting it all together :)

Estimation Technique Of future Bandwidth Utilisation
First calculate the amount of data for each user group sent per day.
This is calculated by

Total Messages X Average message size (30kb) X Protocol Overhead
                                         Added to
                            Total Logons per day X 40 Kb
                                        Added to
              Total Messages Deleted/Moved per day X 1 Kb
                                       Added to
                  Total Calendar lookups per day X 10Kb
                                       Added to
                    Total Directory lookups per day X 10 Kb

To save You time Ive worked it out for you :)

Mail/Calendar/Directory      Low User (Kb)      Medium User(Kb)      High User (Kb)
POP3/HTTP/HTTP                           518                                1315      2315
HTTP/HTTP/HTTP                           668                                  1665      2915
MAPI/MAPI/HTTP                           578                                 1455      2555

YOU NEED TO DO SOME WORK NOW :) You need to find out how many staff you have and how many are high meduim and low users, I cannot do this for you but we will contunue with my figures as an example

Total Number of staff      Low Users      Medium Users      High Users
3100                         2170         620                        310

The Data is then divided by 24, to give a daily rate, and multiplied by six to give a peak hourly rate. This figure is then converted into bits per second

1476 kbps                            1882 kbps          1583 kbps

So to handle the throughput above your looking at a 2048kbps    (Thats 2Mb to us normal people) throughput to handle future bandwitth.

The above was used to work out future bandwidth requirements for a Health Trust Spanning about 70 sites over a large geographic area, I have all the original notes for the analysis and the documents I derived the above method from, If you want a copy of these documents, then feel free to E@Mail me (see my profile) though it may take me a while to get to it (I get a LOT of Mail)  LOL

Regards and good luck
Hope Ive saved you some work


Everything you need is contained in the link below.  Enjoy.

aneilson_ukAuthor Commented:
Thanks for that link, I've seen that document and it contains good information but I was wondering if anyone had any "real life" figures...

Pete LongTechnical ConsultantCommented:
Yup went through this myself hang on while I dig the notes out......................................................
Pete LongTechnical ConsultantCommented:
Wow that was fast ThanQ
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