Exercise 5.1: Traffic Engineering | Rick Gallahers MPLS Training Guide: Building Multi Protocol Label Switching Networks

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The customer has four classifications of traffic: real-time voice and video, VoIP, time-critical data traffic, and nontime-critical data traffic. The customer currently has three T1 lines that run at 1.555Mbs:

The first T-1 has the best SLA with 9000 hours MTBF and an MTTR of 2 minutes. The POC is .0001.
The second T-1 is the second grade of traffic with 6000 hours MTBF and an MTTR of 5 minutes. The POC is .001.
The third T-1 is the third grade of traffic with 4000 hours MTBF and an MTTR of 15 minutes. The POC is .01.

Note: Use the related traffic engineering RFCs, Erlang tables, and necessary reference documents found on the Web.

Part 1: Voice

The customer has 200 voice circuits with a mean call duration of 10 minutes and peak traffic of 35 simultaneous calls. They require a POC of .001, with an MTBF of 7000 hours and an MTTR of less than 5 minutes.

How many voice channels are required?

Answers

BHT = Average call duration (s) * Calls per hour/3600
10 minutes = 600 seconds
600 * 35 /3600 = 5.8 Erlangs

Use the Erlang B calculator www.erlang.com/calculator/erlb/

For POC .01 to determine that 9 lines are needed

Because of the MTBF the first T-1 is required. So 1⁄2 of the T1 would be needed for standard PCM coding.

Nine (9) voice channels are required.

Part 2: Video

The video used for videoconferencing uses one voice channel for each video channel. For one videoconference, two channels are required. The company expects not to exceed the need for 5 simultaneous videoconferences with an average duration of 1.5 hours.

The company requires a POC of .01, with an MTBF of 700 hours and an MTTR of less than 10 minutes.

1.	How many video channels are required?
2.	How much bandwidth is required?

Answers

Video conference = 1 channel for voice and 1 for Video
2 channels required for each conference

Up to 5 conferences so the calculation is 5 * 2 voice channels

That is (5* 2) * 64K or 640K

Only five (5) video channels are required; however, in this case we combine voice with video for a total of two (2) channels per videoconference for a total of ten (10) channels.

10* 64 K or 640K

Part 3: Streaming Data

Streaming data is used for real-time stock market reports, news feeds, and some limited VoIP. The data streams consist of a data stream of 5Kbps for the stock market for 8.5 hours a day (business hours). The news feed is 15Kbps, and the average VoIP calls are 16K, with no more than 10 VoIP calls connected simultaneously. The average call duration of the VoIP calls is 2 hours.

The company requires a POC of .01, with an MTBF of 6000 hours and an MTTR of less than 5 minutes.

How much bandwidth is required?

Answers

1.	5 k data stream + 15k news + 160k VoIP = 180K

Part 4: Time-Critical Data

The company uses time-critical data for critical business information. They connect using SAP, Oracle, and PeopleSoft software in their daily business requirements.

The sessions are relatively short, with an average duration of 5 minutes. The average amount of data sent per session is 250K. This is user data and does not include overhead.

There are 2000 user terminals, with the average call duration being 5 minutes. The average number of calls per terminal operational hours is five. (Assume an eight-hour day.)

The company requires a POC of .001, with an MTBF of 7000 hours and an MTTR of less than 5 minutes.

What is the required bandwidth?

Answers

In order to solve this problem, several factors must be calculated . Let’s say that the overhead is 20 percent, then the 250K per session becomes 300K over 5 minutes.

There are 2000 terminals at five (5) sessions per hour or 10,000 sessions per hour using 1K per session. The bandwidth required would be 10,000K.

Average call duration (s) X Calls per hour / 3,600 =?
300 X 10,000 /3,600 = 833 channels at 1K

Part 5: Nontime Critical Data

The company uses e-mail and Web browsers to conduct daily business. It has 14,000 employees, each with access to the Internet and e-mail accounts. This data is not necessarily time sensitive; however, it is critical to operations.

The average employee checks his or her e-mail four times a day for 10 minutes per time.

The average employee surfs the Web five times a day for 5 minutes at a time, loading less than 150Kbps of data per hour per active connection.

The company requires a POC of .05, with an MTBF of 2000 hours and an MTTR of less than 20 minutes.

How many kilobytes of bandwidth are required to support the nontime-sensitive data?

Answers

Assume that e-mails are primarily rapid loading and that most of the 10 minutes is used for the end users reading their e-mail. Since it is not stated, let’s assume that each e-mail takes 300K for one minute. The number of calls is 4 times a day or .5 times per workday hour.

14,000 * .5 * 60 seconds /3600 = 1.9

Rounding up let’s allocate 2 channels of 300K for e-mail.

Surfing-the-web time does not directly translate to network use. Web pages are loaded within seconds while the users may spend several minutes reading the page.

Since, HTTP use may create less of a load than e-mail, let’s conservatively estimate 3 channels of 300K for HTTP.

They require a POC of .05, with an MTBF of 2000 hours and an MTTR of less than 20 minutes.

We have calculated best guess estimates; a better method would be to measure the bandwidth actually used for HTTP and e-mail.

Using this best guess estimate, we should reserve 5 channels of 300K for e-mail.

Part 6: Review Questions

Answer the following questions:

1.	What is the maximum bandwidth required to support all the customer’s requirements?
2.	How would you classify the traffic?
3.	Explain your provisioning and over-provisioning strategies for each classification of traffic.
4.	Describe how you would allocate the traffic to the various channels. Show your calculations.

Answers

1.	Voice (9 voice channels) round up to 10 channels 640K Video conference traffic 640K Data Streaming 5 K data stream + 15K news feed + 160K VoIP 180K Real-time data 833K Non-real time 5 channels at 300 K 15K
2.	Each T1 = 1.5 Megs or 1544K 1^st T-1: Voice and video conference and data streaming will fit well in to the first T1. 2^ndT-1: Real time data of 833K for the second T1. 3^rdT-1: The non-real time data fits nicely into the third T1.
3.	Services are allocated to the T1 based upon traffic analysis, as well as the MTBF and MTRT requirements.
4.	Shown in the previous answers.

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