Internet connection bandwidth

You have purchased a 2Mbit/s Internet connection from your ISP, does this mean you are guaranteed 2Mbit/s at all times? If not, what does it mean?

First, let's start with a short description of what the Internet really is.

The Internet was invented in the 1960s by the US military, but since around 1990 it is completely commercialized. Today, the Internet is not one network that is controlled by one entity.

The Internet of today consist of many networks connected together. The networks can be a corporation, some government organisation or an Internet Service Provider (ISP). The ISPs own most of the Internet today.

ISPs can be huge, covering large parts of the world (e.g. Worldcom, AOL or Level 3), or they can be tiny and only cover a small part of a city. ISPs and other networks of the Internet are connected together in multiple places, for redundancy and capacity reasons.

So, what does this mean for our 2Mbit/s Internet connection?

Let's start at the beginning. Your company network is connected to the ISP access router (a router is a network device). To the same router, many other customers are connected. This router has a limited capacity to process traffic, and a limited bandwidth to the rest of the ISP network.

Most customers to an ISP will not use all of the bandwidth they have purchased all of the time, therefore it is possible for the ISP to sell more bandwidth than they can actually deliver. This is called overbooking.

Typically, in an access router as described above, the ISP will overbook 7-10 times for corporate connections and up to 100 times for home users. This may sound bad, but actually it is a good thing. This means that the cost for the ISP will be lower, and therefore the cost for you will be lower.

The reason that this works are several. First of all, the network protocols that the Internet are based on (TCP/IP) are built to handle bottlenecks in the network. Without congestion management, traffic peaks would be a disaster, but on the Internet, it just means that things go a bit slower for a short while.

The second reason this works is because the ISPs will monitor the bandwidth of all their network connections and the load on their routers, so that they can upgrade connections or move customers around. If a specific set of customers use a higher percentage of their connection on average, the overbooking factor will be smaller for them.

Still, despite the ISPs monitoring bandwidth, during traffic peaks your 2Mbit/s connection may not give you 2Mbit/s even past the first router in the ISP network. You should definitely monitor the bandwidth you get on your connection yourself, because there is a difference in the quality of ISPs, and you can always switch.

So, the next step. Your traffic has a final destination, it may be close and it may be far, far away. Your traffic may have to travel over the ISPs backbone network, via some connection to another ISP, over that ISPs backbone, through that ISPs access router to reach the final destination. Each one of these components uses overbooking.

So, as a rule of thumb, the further away your destination, the less likely you are to get full capacity, because you can bump into some congestion along the way. Within the same ISP is typically better, within your country is typically ok, but if your destination is some small country in Africa or Eastern Europe, you will probably have a lousy capacity.

It all comes down to numbers. You want to pay as little as possible for your network connection. Your ISP wants to make money. Overbooking is what makes it possible to deliver fast connections at low costs.

One important implication of this is if you want to use applications like Voice Over IP (VOIP). The Internet was not designed for this type of traffic from the beginning. For this type of traffic, there are several problems if the network is congested, so special care needs to be taken. In most cases, it will work just fine, because short periods of congestion will just cause some white noise.

However, if you want to ensure good voice quality you should make sure that your ISP prioritizes the VOIP traffic. Furthermore, your ISP can not tell another network to prioritize some traffic, so for best quality, your VOIP traffic should stay within the same network.

So, to summarize, there are no guarantees for your bandwidth. Just because you buy 2Mbit/s of capacity, you could end up with a lot less to a specific destination. Hower, most of the time you should be able to peak at 2Mbit/s bandwidth usage, otherwise you should consider switching ISP. Monitoring your bandwidth will help you see if you have a good ISP or not.