How are requirements of network specified to ensure QoS? [closed]

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When I review the hardware requirements of many database backed enterprise solutions, I find requirements for the application server (OS, processor, RAM, disk space, etc), for the database server (versions, RAM, etc) and requirements for the client.

Here is an example of Oracle Fusion Middleware.

I cannot find requirements on network speed or architecture (switch speed, SAN IOPS,RIOPS, etc). I do not want a bad user experience from my application but caused by network latency in the clients environment.

When sending clients required hardware requirements specifications, how do you note the requirements in these areas? What are the relevant measures of network performance? (Or is it simply requiring IOPS=x )

Answer 1

Generally, there is more than one level of detail for requirements. You'd typically differentiate the levels of detail into a range from 0 (rough mission statement) to 4 (technical details), for example.

So if you specify that your SAN shall be operating with at least a bandwidth capacity of x, that would be a high number on that scale. Make sure to break down your main ideas (The system shall be responsive, in order to prevent clients from becoming impatient and leaving for competitors....) into more measurable aims (as the one above).

Stephen Withall has written down good examples in his book "Software Requirement Patterns". See chapter 9, page 191 ff., it is not that expensive. He breaks it down into recommendations on, and I quote, Response Time, Throughput, Dynamic Capacity, Static Capacity and Availability.

Of course, that's software! Because basically, you'd probably be well advised to begin with defining what the whole system asserts under specified circumstances: When do we start to measure? (e.g. when the client request comes in at the network gateway); what average network delay do we assume that is beyond our influence? from how many different clients do we measure and from how many different autonomous systems do these make contact? Exactly what kind of task(s) do they execute and for which kind of resource will that be exceptionally demanding? When do we stop to measure? Do we really make a complete system test with all hardware involved? Which kinds of network monitoring will we provide at runtime? etc.

That should help you more than if you just assign a value to a unit like transfer rate/ IOPS which might not even solve your problem. If you find the network hardware to perform below your expectations later, it's rather easy to exchange. Especially if you give your hosting to an external partner. The software, however, is not easy to exchange.

Be sure to differentiate between what is a requirement or constraint that you have to meet, and what is actually a part of the technical solution you offer. There might be more solutions. Speed is a requirement (a vague one, though). Architecture for hardware is a solution.