## Are Those Bandwidth Limits on Your Router Good Enough?

Many routers and firewalls offer the ability to set rate limits  per user by IP. On a congested network, simple rate limits are certainly much better than doing nothing at all. Rate limits will force a more orderly distribution of bandwidth; however, if you really want to stretch your bandwidth, and  thus the number of users that can share a link, some form of dynamic fairness will outperform simple rate limits every time.

To visualize the point I’ll use the following analogy:

Suppose you ran an emergency room in a small town of  several hundred people. In order to allocate emergency room resources, you decide to allocate 1 hour, in each 24 hour day, for each person in the town to come to the emergency room. So essentially you have double/triple booked every hour in the day, and scheduled everybody regardless of whether or not they have a medical emergency. You also must hope that people will hold off on their emergency until their allotted time slot. I suppose you can see the absurdity in this model? Obviously an emergency room must take cases as they come in, and when things are busy, a screening nurse will decide who gets priority – most likely the sickest first.

Dividing up your bandwidth equally between all your users with some form of rate limit per user, although not exactly the same as our emergency room analogy, makes about as much sense.

The two methods used in the simple set rate limit model are to equally divide the bandwidth among users, or the more common, which is some form of over subscription.

So, for example, if you had 500 users sharing a 50 megabit trunk, you could:

1) Divide the 50 megabits equally, give all your users 100kbs, and thus if every user was on at the same time you would ensure that their sum total did not exceed 50 megabits.

The problem with this method is that 100kbs is a really slow connection – not much faster than dial up.

2) Oversubscribe, give them all 2 megabit caps – this is more typical. The assumption here is that on average not all users will be drawing their full allotment all the time, hence each user will get a reasonable speed most of the time.

This may work for a while, but as usage increases during busy times you will run into the rolling brown out. This is the term we use to describe the chaotic jerky slow network the typifies peak periods on an over subscribed network.

3) The smart thing to do is go ahead and set some sort of rate cap per user, perhaps 4 or 5 megabits, and combine that with something similar to our NetEqualizer technology.

Equalizing allows users to make use of all the bandwidth that is on the trunk and only slows down large streams (NOT the user) when the trunk is full. This follows more closely what the triage nurse does in the emergency room, and is far more effective at making good use of your Internet pipe.

Related Article using your router as a bandwidth controller

I believe this excerpt from the Resnet discussion group last year exemplifies the point:

You have stated your reservations, but I am still going to have to recommend the NetEqualizer. Carving up the bandwidth equally will mean that the user perception of the Internet connection will be poor even when you have bandwidth to spare. It makes more sense to have a device that can maximise the users perception of a connection. Here are some example scenarios.

NetEQ when utilization is low, and it is not doing anything:
User perception of Skype like services: Good
User perception of Netflix like services: Good
User perception of “ajaxie” webpages that constantly update some doodad on the page: Good
User Perception of games: Good

Equally allocated bandwidth when utilization is low:
User perception of Skype like services: OK as long as the user is not doing anything else.
User perception of Netflix like services: OK as long as long as the user is not doing anything else.
User perception of “ajaxie” webpages that constantly update some doodad on the page: OK
User perception of games: OK as long as the user is not doing anything else. That is until the game needs to download custom content from a server, then the user has to wait to enter the next round because of the hard rate limit.

NetEQ when utilization is high and penalizing the top flows:
User perception of Skype like services: Good
User perception of Netflix like services: Good – The caching bar at the bottom should be slightly delayed, but the video shouldn’t skip.  The user is unlikely to notice.
User perception of large file downloads: Good – The file is delayed a bit, but will still download relatively quickly compared to a hard bandwidth cap.  The user is unlikely to notice.
User perception of “ajaxie” webpages that constantly update some doodad on the page: Good
User perception of games: Good – downloading content between rounds might be a tiny bit slower, but fast compared to a hard rate limit.

Equally allocated bandwidth when utilization is high:
User perception of Skype like services: OK as long as the user is not doing anything else.
User perception of Netflix like services: OK as long as long as the user is not doing anything else.
User perception of “ajaxie” webpages that constantly update some doodad on the page: OK as long as the user is not doing anything else.
User perception of games: OK as long as the user is not doing anything else. That is until the game needs to download custom content from a server, then the user has to wait to enter the next round because of the hard rate limit.

As far as the P2P thing is concerned, while I too realized that theoretically P2P would be favored, in practice it wasn’t really noticeable. If you wish, you can use connection limits to deal with this.

One last thing to note: On Obama’s Inauguration Day, the NetEQ at PLU was able to tame the ridiculous number of live streams of the event without me intervening to change settings.  The only problems reported turned out to be bandwidth problems on the other end.

I hope you find this useful.

Network Engineer
Information & Technology Services
Pacific Lutheran University

### 5 Responses to “Are Those Bandwidth Limits on Your Router Good Enough?”

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