Home > CCNP, ONT > ONT – Policing and Shaping

ONT – Policing and Shaping

As you can see I’m back in business and started to get back into QoS (and my studies).

This post will go over the basics of Policing and Shaping, the next step when designing and building QoS on a router.

Policing is used to drop or remark exceeding traffic. This is the more advanced way.
Shaping queues excess traffic to send at a desired rate. This is a much older technique that been used with older protocols (that required specific bandwidth limits).

Shaping used to work per interface but can be used per traffic type on more advanced IOS. It will queue the excess traffic and will send them later, if possible. Working per traffic expand the capabilities of this tool and make it more flexible and powerful.

Policing will never try again, there is no queue – if traffic exceed it will permanently drop it.

Few definitions related to Policing:
Tc = Time committed, how much traffic will be sent in a specific time frame
Bc = Burst committed, you get what you paid for and will never get extra traffic
Be = Burst excess, extra bandwidth the ISP allow (beyond the paid traffic)

To understand Be we have to look at the way ISP allow our traffic. On a regular (no bursting allowed) connection it will allow X amount of data at any given moment. This is the amount you paid for and even when the ISP network is free and can pass extra traffic it will not allow it. It is like an iron pipe that cannot expand under any circumstances.

When using Bursting the ISP allow sending extra traffic to allow full usage of the line. It is a way to avoid time intervals that are not being used. This is like a rubber pipe that can expand under high pressure. As long as you keep bursting in reasonable amounts the ISP allow all traffic to go through. Over time you will not get extra traffic, the average will be the 100% or less but at some peaks you’ll get some help from the ISP.

Other definitions you should be familiar with are:
Conform – sending traffic bellow Bc
Exceed – traffic between Bc and Be
Violate or De = Discard Eligible – this is the traffic beyond Be. It is marked by the ISP as possible discarded traffic.

  1. No comments yet.
  1. No trackbacks yet.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: