MPLS Traffic Engineering

Traffic Engineering

In data and voice networks, traffic engineering is used to direct traffic to the available resources.  If achieving a smooth-flowing network by moving traffic around were simple, then our networks would never experience slowdowns or rush hours.

On the Internet (as with highways), there are four steps that must be undertaken to achieve traffic engineering: measuring, characterizing, modeling, and moving traffic to its desired location.

Figure 5.2: Four Aspects of Traffic Engineering

Measuring traffic is a process of collecting network metrics, such as the number of packets, the size of packets, packets traveling during the peak busy hour, traffic trends, applications most used, and performance data (i.e., downloading and processing speeds).

Characterizing traffic is a process that takes raw data and breaks it into different categories so that it can be statistically modeled. Here, the data that is gathered in the measurement stage is sorted and categorized.

Modeling traffic is a process of using all the traffic characteristics and the statistically analyzed traffic to derive repeatable formulas and algorithms from the data. When traffic has been mathematically modeled, different scenarios can be run against the traffic patterns.  For instance, “What happens if voice/streaming traffic grows by two percent a month for four months?”  Once traffic is correctly modeled, then simulation software can be used to look at traffic under differing conditions.

Putting traffic where you want it: To measure, characterize, and model traffic for the entire Internet is an immense task that would require resources far in excess of those at our disposal.  Before MPLS was implemented, we had to understand the characteristics and the traffic models of the entire Internet in order to perform traffic engineering.

When addressing MPLS traffic engineering, articles and white papers tend to focus on only one aspect of traffic engineering.  For example, you may read an article about traffic engineering that addresses only signaling protocols or one that just talks about modeling; however, in order to perform true traffic engineering, all four aspects must be thoroughly considered.

With the advent of MPLS, we no longer have to worry about the traffic on all of the highways in the world. We don’t even have to worry about the traffic on Interstate 5. We just need to be concerned about the traffic in our express lane – our MPLS tunnel. If we create several tunnels, then we need to engineer the traffic for each tunnel.

Provisioning and Subscribing

Before looking at the simplified math processes for engineering traffic in an MPLS tunnel, a brief discussion of bandwidth provisioning and subscribing is needed. 

First, let’s look at the definitions. Over-provisioning is the engineering process in which there are greater bandwidth resources than there is network demand.  Under-provisioning is the engineering process in which there is greater demand than there are available resources.  “Provisioning” is a term typically used in datacom language.

In telecom language, the term “subscribe” is used instead of “provision.” Over-subscribing is the process of having more demand than bandwidth, while under-subscribing is a process of having more bandwidth than demand.  It is important to note that provisioning terms and subscription terms refer to opposite circumstances.

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