How Much Bandwidth Do You Really Need?

By Art Reisman – CTO –

Art Reisman CTO

When it comes to how much money to spend on the Internet, there seems to be this underlying feeling of guilt with everybody I talk to. From ISPs, to libraries or multinational corporations, they all have a feeling of bandwidth inadequacy. It is very similar to the guilt I used to feel back in College when I would skip my studies for some social activity (drinking). Only now it applies to bandwidth contention ratios. Everybody wants to know how they compare with the industry average in their sector. Are they spending on bandwidth appropriately, and if not, are they hurting their institution, will they become second-rate?

To ease the pain, I was hoping to put a together a nice chart on industry standard recommendations, validating that your bandwidth consumption was normal, and I just can’t bring myself to do it quite yet. There is this elephant in the room that we must contend with. So before I make up a nice chart on recommendations, a more relevant question is… how bad do you want your video service to be?

Your choices are:

  1. bad
  2. crappy
  3. downright awful

Although my answer may seem a bit sarcastic, there is a truth behind these choices. I sense that much of the guilt of our customers trying to provision bandwidth is based on the belief that somebody out there has enough bandwidth to reach some form of video Shangri-La; like playground children bragging about their father’s professions, claims of video ecstasy are somewhat exaggerated.

With the advent of video, it is unlikely any amount of bandwidth will ever outrun the demand; yes, there are some tricks with caching and cable on demand services, but that is a whole different article. The common trap with bandwidth upgrades is that there is a false sense of accomplishment experienced before actual video use picks up. If you go from a network where nobody is running video (because it just doesn’t work at all), and then you increase your bandwidth by a factor of 10, you will get a temporary reprieve where video seems reliable, but this will tempt your users to adopt it as part of their daily routine. In reality you are most likely not even close to meeting the potential end-game demand, and 3 months later you are likely facing another bandwidth upgrade with unhappy users.

To understand the video black hole, it helps to compare the potential demand curve pre and post video.

A  quality VOIP call, which used to be the measuring stick for decent Internet service runs about 54kbs. A quality  HD video stream can easily consume about 40 times that amount. 

Yes, there are vendors that claim video can be delivered at 250kbs or less, but they are assuming tiny little stop action screens.

Couple this tremendous increase in video stream size with a higher percentage of users that will ultimately want video, and you would need an upgrade of perhaps 60 times your pre-video bandwidth levels to meet the final demand. Some of our customers, with big budgets or government subsidized backbones, are getting close but, most go on a honeymoon with an upgrade of 10 times their bandwidth, only to end up asking the question, how much bandwidth do I really need?

So what is an acceptable contention ratio?

  • Typically in an urban area right now we are seeing anywhere from 200 to 400 users sharing 100 megabits.
  • In a rural area double that rati0 – 400 to 800 sharing 100 megabits.
  • In the smaller cities of Europe ratios drop to 100 people or less sharing 100 megabits.
  • And in remote areas served by satellite we see 40 to 50 sharing 2 megabits or less.

Can your ISP support Video for all?

By Art Reisman, CTO,

Art Reisman CTO

Art Reisman

As the Internet continues to grow with higher home user speeds available from Tier 1 providers,  video sites such as YouTube , Netflix,  and others are taking advantage of these fatter pipes. However, unlike the peer-to-peer traffic of several years ago (which seems to be abating), These videos don’t face the veil of copyright scrutiny cast upon p2p which caused most p2p users to back off. They are here to stay, and any ISP currently offering high speed Internet will need to accommodate the subsequent rising demand.

How should a Tier2 or Tier3 provider size their overall trunk to insure smooth video at all times for all users?

From measurements done in our NetEqualizer laboratories, a normal quality video stream requires around 350kbs bandwidth sustained over its life span to insure there are no breaks or interruptions. Newer higher definition videos may run at even higher speeds.

A typical rural wireless WISP will have contention ratios of about 300 users per 10-megabit link. This seems to be the ratio point where a small businesses can turn  a profit.  Given this contention ratio, if 30 customers simultaneously watch YouTube, the link will be exhausted and all 300 customers will be experience protracted periods of poor service.

Even though it is theoretically possible  to support 30 subscribers on a 10 megabit , it would only be possible if the remaining 280 subscribers were idle. In reality the trunk will become saturated with perhaps 10 to 15  active video streams,  as  obviously  the remaining 280 users are not idle. Given this realistic scenario, is it reasonable for an ISP with 10 megabits and 300 subscribers to tout they support video ?

As of late 2007 about 10 percent of Internet traffic was attributed to video. It is safe to safe to assume that number is higher now (Jan 2009). Using the 2007 number, 10 percent of 300 subscribers would yield on average 30 video streams, but that is not a fair number, because the 10 percent of people using video, would only apply to the subscribers who are actively on line, and not all 300. To be fair,  we’ll assume 150 of 300 subscribers are online during peak times.  The calculation now  yields an estimated 15 users doing video at one time, which is right on our upper limit of smooth service for a 10 megabit link, any more and something has to give.

The moral of this story so far is,  you should  be cautious before promoting unlimited video support with contention ratios of 30 subscribers to 1 megabit.  The good news is, most rural providers are not competing in metro areas, hence customers will have to make do with what they have. In areas more intense competition for customers where video support might make a difference, our recommendation is that  you will need to have a ratio closer to 20 subscribers to 1 megabit, and you still may have peak outages.

One trick you can use to support Video with limited Internet resources.

We have previously been on record as not being a supporter of Caching to increase Internet speed, well it is time to back track on that. We are now seeing results that Caching can be a big boost in speeding up popular YouTue videos. Caching and video tend to work well together as consumers tend to flock a small subset of the popular videos. The downside is your local caching server will only be able to archive a subset of the content on the master YouTube servers but this should be enough to give the appearance of pretty good video.

In the end there is no substitute for having a big fat pipe with enough room to run video, we’ll just have to wait and see if the market can support this expense.

%d bloggers like this: