Definition of bandwidth capacity for an internet connection

Question

First, I want to test the data rate of a fibre-optic internet connection, but I understand that results are affected by the circumstances of the test, like number of hops between the CPE and the other end-node, time of day, etc, which ultimately impact the test results. Also, I need the most standard, universally accepted definition of bandwidth capacity of an internet connection to ensure that the test is performed and measures the most formal correct way possible, to make sure the test pass scrutiny.

Second, I must make a report with the results. So I need to refer to the definition in the literature. Therefore the question is simple, what is the most universally accepted definition of the term ‘bandwidth capacity’ of an internet connection? Please also include a reference from relevant litterature that you recommend for the purpose.

Answer 1

There are two aspects for bandwidth:

1. The link speed as indicated by the interface presents the upper limit of what that interface can transport.
2. The practical throughput (maximum capacity) you can achieve using that interface. This is much harder to determine and there is no generally accepted method for measuring.

High-speed Internet uplinks beyond 100 Mbit/s often reach their maximum capacity only with multiple flows from different servers. Many servers have limited uplinks with 100 Mbit/s or 1 Gbit/s and can't provide faster flows than that. So, unless you know a server's uplink capacity and its current spare capacity you can't be sure which bottleneck limits a certain flow from/to a server at hand. Potential bottlenecks include: your uplink, access ISP infrastructure (provisioning), access ISP peering, server ISP peering, server uplink, server capacity, and anything between access ISP and server/hosting ISP including congestion anywhere on the path.

Often, smaller ISPs document their peering capacities so you can scale your throughput expectations for your most important flows. Larger ISPs are expected to have sufficient capacities for at least gigabit speeds. In any case should you define your expectations in a mutual service-level agreement and not rent an uplink because of its low price and then expect performance that wasn't guaranteed.