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Calculate Exchange Online requirements for bandwidth

Bandwidth planning for Exchange Online migrations may seem boring, but it's essential for a successful move to Office 365.

A badly planned move to Office 365 can cripple an organization if the bandwidth requirements aren't investigated...

before migrating. Although services such as Exchange Online aren't bandwidth heavy in daily use, services such as Lync can be, depending on workloads.

Bandwidth planning for Exchange Online migrations can be a dry subject, but it's essential for a successful move. It isn't as simple as plugging the values into the Microsoft calculators. Admins need to use values and other data to understand where the weak points are and remediate.

It's important to look at end users across the organization and perform calculations using Microsoft tools to understand the impact of these Exchange Online requirements. Admins can then use the results to understand if they'll need to make upgrades. We'll focus on how to perform this planning and understand the ongoing requirements for using Office 365.

Before we begin, it's essential to understand how clients access Office 365. Typically, an Outlook client will connect from its local site directly to the Internet, or, if it's on a wide area network (WAN), at the closest site with Internet breakout. The client will perform a DNS lookup to obtain the nearest Office 365 point of presence and connect over HTTPS to the service. This typically provides reasonably low latency when accessing the service.

During a migration, it's typical to switch on features such as Cached Mode and upgrade clients in advance. The Offline Cache stays intact after a hybrid migration, so this removes the need for every client to re-download the mailbox en masse.

Collect information to use as input

Before calculating the bandwidth necessary for these Exchange Online requirements, we need good input data. Collect the following information about each site with end users, each data center with Exchange and each site with an Internet breakout that end users will use (or used to migrate mailboxes):

  • List of sites with end users, Exchange and Internet breakouts;
  • List of end users at each site;
  • Define the route to the Internet from each site;
  • For each site that traverses the WAN to another site with Internet breakout, define the WAN link speed;
  • For each site with an Internet breakout, define the Internet link and WAN link speeds;
  • Determine the average mailbox profile for end users either as a whole or based on a site. Admins can use one of Microsoft's tools to perform this analysis, such as the Generate Message Profile script for Exchange 2010 and Exchange 2013; and
  • Collate the average and total mailbox sizes per site.

The goal for collecting the above data should be to have a picture of the end users, mailboxes, Exchange sites and enough information to determine the bandwidth likely to be required.

Calculate Exchange workloads

Admins can use the raw data collected with Microsoft's Exchange Client Network Bandwidth Calculator to understand the per-site requirements for end users. On the Input sheet, update the Exchange Service field to state Office 365; if required, admins can then use their Exchange mailbox message profile data to update the User Profile information (Figure 1).

Update User Profile in Exchange Client Network Bandwidth Calculator
Figure 1

On the Client Mix sheet, enter each site, accompanied by the site's user profile and the number of end users. This should give you the per-site bandwidth requirements (Figure 2). We'll use the results in the next step.

Per-site bandwidth requirements
Figure 2

Collating per-site user requirements

For the per-site end user requirements, we'll collate the results from the previous step along with other information about the site into a new spreadsheet. We'll typically expect this to have the following fields.

Country: To help group sites together in larger organizations.

Site Name: The physical site name as used in the Exchange calculator.

Number of Users: The same number of end users used in the Exchange calculator.

Exchange Download Bandwidth Required: The Exchange-to-Client bandwidth required in the calculator.

Exchange Upload Bandwidth Required: The Client-to-Exchange bandwidth required in the calculator.

Site Type (Internet Breakout / Downstream WAN): If the clients access the Internet directly at this site, choose Internet Breakout. If the Internet is accessed via another site or data center, choose Downstream WAN.

Total Download Bandwidth: The total download bandwidth available.

Total Upload Bandwidth: The total upload bandwidth available.

Average Download Bandwidth Utilization: The average download utilization of the relevant link.

Average Upload Bandwidth Utilization: The average upload utilization of the relevant link.

Upstream Internet Breakout Site Name: If this is a downstream WAN site, then record the site this connects to the Internet through.

After adding the appropriate fields and then entering data, the results should appear (Figure 3).

Calculations for per-site user requirements
Figure 3

In the diagram, we've captured the data from the Exchange Client Network Bandwidth Calculator across the first fields and then entered additional data collected above.

This immediately provides us with important information about our Exchange Online requirements, such as whether downstream sites connecting via the WAN have enough bandwidth available and whether sites with their own Internet breakout have enough bandwidth.

Collate per-Internet breakout requirements

What the per-site user requirements don't tell us is whether sites that have multiple sites connecting through to the Internet can cope. We'll need to collate the information on a second worksheet to make this determination. This summary spreadsheet will have the following fields and contain only Internet breakout sites.

Country. To help group sites together in larger organizations.

Site Name. The physical site name used in the previous spreadsheets.

Combined Number of Users. The total number of end users, including end users on this site and those who use this site as Internet breakout.

Combined Exchange Download Bandwidth Required. The combined Exchange download bandwidth required across this site and those connecting through it.

Combined Exchange Upload Bandwidth Required. The combined Exchange upload bandwidth required across this site and those connecting through it.

Total Internet Download Bandwidth. The total download bandwidth available.

Total Internet Upload Bandwidth. The total up load bandwidth available.

Average Internet Download Bandwidth Utilization. The average download utilization of the relevant link.

Average Internet Upload Bandwidth Utilization. The average upload utilization of the relevant link.

Downstream Capacity Available? Checking to see if the combined Exchange download bandwidth and average current utilization is less than the total available download bandwidth.

Upload Capacity Available? This should include the same as above, but it checks if enough upload capacity is available.

After collating the data, we're able to easily identify the Internet breakout sites that will have capacity problems in our example (Figure 4). Our next step as part of our preparation will be to upgrade both the Internet links that fall short and in downstream WAN sites.

Internet Breakout sites with potential capacity problems
Figure 4

About the author:
Steve Goodman is an Exchange MVP and works as a technical architect for one of the U.K.'s leading Microsoft Gold partners. Goodman has worked extensively with Microsoft Exchange since version 5.5 and with Office 365 since its origins in Exchange Labs and [email protected]

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