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How to calculate the right Azure outbound capacity and choose the best egress option

From Outbound traffic to Egress

From the very beginning of Azure, incoming internet traffic was free of charge and outgoing traffic was and is being charged. In recent months, Microsoft has not only further tightened and improved the charging of the outbound data transfer, but also changed the name.

“Outbound traffic” is now labeled as ‘egress’. In the cloud, Internet egress means traffic that’s leaving from inside the private network out to the public internet Internet. More specific ‘egress’ exits an Azure region, while “ingress” is traffic that enters an Azure region.


Microsoft Global Network

In addition to the existing options such as routing egress via an ISP network or via an Express route, Microsoft now offers the possibility to route this traffic via its own Microsoft Global Network (WAN).


The Microsoft Global Network can be an attractive alternative for customers with offices and factories worldwide and a private MPLS network to connect them. All the more so that the Microsoft Global Network is routing the data around the world via cold-patato routing with the lowest and predictable latency, fully secure.




For most customers the Microsoft Global Network will not be an option and the choice is then to egress the Azure region via public internet or an Express Route.  Express Route is offering more reliability lower latencies, and higher security than typical connections over the public internet.


How to determine the necessary ExpressRoute bandwidth

Microsoft offers various Express Route options, depending on the desired bandwidth of this private connection between the customer network and the chosen Azure region. The question is how do you determine the necessary bandwidth and thus the correct ExpressRoute and what does that cost per month and is this indeed cheaper than the standard Azure egress costs over public internet?

The starting point for this calculation is data used monthly. Suppose 120 TB. The formula to convert this consumption into bandwidth = (TD*C2B)/RWT

Here is TD the amount of data transferred per month in GB, is 120TB*1000= 120.000 GB. C2B is the conversion from Bytes to Bit, because usage is measured in Bytes, bandwidth is measured in Bits. C2B is the factor 8,192.

The RWT is the windows of time in seconds the data is transferred in. Per month there are 2.628.000 seconds. But in practice, the largest amount of data is mainly sent during office hours, which is only 20% of the total available time. I use this 20% in my calculations to make a realistic estimate of the required bandwidth. Therefore the corrected RWT is then 525.600 seconds per month.

The required bandwidth is then (120.000*8,192)/525.600= 1,870 GBbps or 1870 Mbps. The Express Route of choice is then 2 GBbps.

ExpressRoute options

The next question is the which of the available ExpressRoutes is the best choice, from cost and SLA point-of-view.

There two options where you connect directly from your local premises into a Azure Region. The local option is limited to the region you tab in. The premium option gives you access to all Azure regions. Both options are available in in a metered version, where you pau per used GB and an unlimited option.

The third option is the ExpressRoute Direct, connecting your LAN/WAN to the closest Microsoft POP or edge-node and from there use the Microsoft Global Network, to connect to other customers offices or factories and any Azure Region. Be aware that the usage of the Microsoft Global Network is charged on top of the of the ExpressRoute Direct.

For the example of 120 TB data transfer the  monthly pricing for the different options looks as follows:

Zone 1  
ExpressRoute bandwidth 1870 Mbps/sec
Selected Bandwidth 2 Gbps  
ExpressRoute Metered Standard  $          3.944
ExpressRoute Unlimited Standard  $        11.400
ExpressRoute Metered Premium  $          5.444
ExpressRoute Unlimited Premium  $        12.900
ExpressRoute Direct Port:10 Gbps_2 Gbps  $        10.572

By the way, the Azure cost of the ‘standard’ 120 TB egress via an ISP network cost $ 7,373 per month.

Here a overview of most of the Azure egress options and the monthly cost.


Here the three main options compared. In all options the ExpressRoute Metered Standard is the most cost effective solution.


Conclusion: it starts with determine the right bandwidth requirements so you are able to make the right choice and you don’t pay too much for your outbound traffic!


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Herb Prooy
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