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When designing a network with the obvious use of Servers or whatever else etc, how is bandwidth calculated?

- Is it based on the actual network design ready to be implemented?

Bandwidth will obviously only be an issue across a WAN/INTERNET as in if it is just local connections presumably within the same building then it is just down to memory on each device etc ie server, router, switch etc?

Im not sure about from one building to the next ?

what is it:  2 + 2 = 4, plus 10% for residual - although a REAL bad example i know!!!
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Bandwidth is usually calculated based on the speeds of the various links in the network with the slowest one likely causing a bottleneck down to its speed. You are correct in pointing out that the speed of the devices involved also play a part and are just as likley to be the slowest point.
>When designing a network with the obvious use of Servers or whatever else etc, how is bandwidth calculated?

One of the most important requirements when designing a network; the bandwidth. This is no doubt one of the requirements that is always overlooked. It is not just related to WAN and Internet links. You also have to have the bandwidth requirements for the LAN as well. This becomes important to the scalability of the network. It is always easier to design a network with allot of bandwidth based on the application. Take for instance a network admin that is designing a network for a client that is a video editing company with 40 workstations and 5 servers in a cluster; the majority of the data sent via the LAN is 1080p data. The local admin does a quick search on Google and determines that the required bandwidth for 1080p data is typically 4-5Mbps based on best quality. Network is designed based on 100/1000Mbps switchports and is finally deployed, long story short, the customer uses 1080p uncompressed data which requires about 1.5Gbps of bandwidth; required bandwidth should have been around 20Gbps, ouch! So one of the first steps in calculating bandwidth is to have a meeting with the customer and discuss the application, understand what it is the customer will be using the network for, how many data sources and server locations exists on the network, etc

A. What are the bandwidth requirements?
Typically, the customer has no idea, you have to calculate this on your own.
1. What is the application
a. How many servers are related to the application
2. What is the protocol used for the communication session (TCP, UDP, RTP, etc)
3. How many users on the network will access the application.
a. How many users will use the network at the same time
This deals directly with oversubscription (should you design with it or without):
There are no hard set values and only what I go by, it has yet to fail me.
Desktop: 3:1 (this is assuming not all users are using the network at the same time, however, during the customer meeting, this should be a question for the customer of do you want a worst case scenario, if so, the ratio would be 1:1)
Segment: 2:1
Server: 1:1
Core: 1:1

Designing without oversubscription depends on the customers pockets and whether they
can afford it and obviously on the application, how much data bandwidth is required and how quickly
they need to access the data.

4. You also have to consider microburst of data which can affect the network devices in your network, so consider network devices that can support the traffic patterns of the application:
a. buffers, queue, switch fabric, backplane, etc
5. Always consider QoS on a network (especially with oversubscription).
a. With oversubscription, you should design the network with a non-blocking architecture.

These are the basics and they change depending on the customer; years of experience is one way to calculate bandwidth accurately the rest is OJT.

Good Luck
mikey250Author Commented:
what does "1080p" mean? one thousand and eighty packets maybe?

Is there some kind of calculator I can use to work out the calculations of required bandwidth?

how do you even calculate bandwidth requirement on 1 or more servers as Im assuming although you mention, this is down to what features are used within win 2003, ie dhcp, terminal server, file & print server, dns, application server, vpn, ipsec etc etc, which would also depend on how many people use the network and how often as you mentioned already.  So im assuming out of 1 server being configured for everything say on an sbs 2003, MS already know the max bandwidth, also based on 75 users for sbs 2003?

This would then act as a guide for anything less than 75 users, and maybe only creating domain, terminal server, dns, dhcp, but maybe no application server, no vpn, nop ipsec etc etc am i on the right track?

thanks for that useful information!!!!!!
>what does "1080p" mean? one thousand and eighty packets maybe?
disregard, it was an example of the "application"; 1080p is the video; 1080p uncompressed, it allot of bandwidth.

>Is there some kind of calculator I can use to work out the calculations of required bandwidth?
Depends on the application; you are asking a very tough question that honestly comes with experience.

Here is an example for the bandwidth requirements for exchange:


Here is another for websites:

Here is one for VoIP:

the list goes on, you gather the data and you then aggregate all that data to get your required bandwidth for the network

mikey250Author Commented:
ok this looks useful thanks!!!!!!!!
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