Case Study: Your Turn to Choose the Bandwidth


The XYZ Company, in the previous chapter's case study, asked for a design based on PBX and key system technology. The suggested solution from Chapter 1, "Touring the History Museum of Telephony," is shown in Figure 2-14. However, you were such a proponent of VoIP technology, XYZ Company is considering interconnecting the proposed PBXs and key system over the IP WAN, as opposed to dedicated T1 and fractional T1 lines, which were specified in Chapter 1's original proposal.

Figure 2-14. XYZ Company's Suggested Solution


We saw in the previous case study that we need to support 72 simultaneous calls between the XYZ Company headquarters and XYZ Remote Office 1. The connection between the XYZ Company headquarters and XYZ Remote Office 2 needed to support 12 simultaneous calls.

Therefore, your task in this case study is to determine the required WAN bandwidth between the XYZ Company headquarters and each of the remote offices. Use the Cisco Voice Bandwidth Calculator located at the following URL:

http://tools.cisco.com/Support/VBC/do/CodecCalc1.do

When calculating the required bandwidth amounts, make the following assumptions:

  • CODEC: G.729a

  • Voice Protocol: VoIP

  • Voice Payload Size: 20 Bytes (default)

  • RTP Header Compression: Disabled

  • Media Access: PPP

  • Tunnel/Security/Misc. Overhead: None

Enter your answers below:

  • How much bandwidth is required on the link between the XYZ Company headquarters and XYZ Remote Office 1? _______

  • How much bandwidth is required on the link between the XYZ Company headquarters and XYZ Remote Office 2? _______

Case Study Suggested Solution

Let's walk through the steps to calculate the bandwidth required for the two links in this scenario. First, we log in to the Cisco Voice Bandwidth Calculator, using our CCO login credentials. We select g729_All_Variants as the Codec and VoIP as the Voice Protocol. For the link between the XYZ Company headquarters and the XYZ Remote Office 1, we enter 72 as the Number of Calls parameter. After filling out this initial screen, we click the Next button, as shown in Figure 2-15.

Figure 2-15. Case Study: Voice Bandwidth Calculator Screen 1


From the next screen, we select PPP for the Media Access parameter. In this scenario, we leave all other parameters at their default settings, as shown in Figure 2-16.

Figure 2-16. Case Study: Voice Bandwidth Calculator Screen 2


After clicking the Submit button, we are presented with a screen showing us a breakdown of the VoIP calculation. The Total Bandwidth (including Overhead) value tells us the amount of bandwidth that we should provision. In this example, the bandwidth is 2026.08 kbps, as shown in Figure 2-17.

Figure 2-17. Case Study: Voice Bandwidth Calculator Screen 3


We repeat the process for the link between the XYZ Company headquarters and XYZ Remote Office 1, this time specifying 12 as the Number of Calls. This calculation gives us a result of 337.68 kbps. Finally, you can enter your results in the case study as follows:

  • How much bandwidth is required on the link between the XYZ Company headquarters and XYZ Remote Office 1?

    2026.08 kbps

  • How much bandwidth is required on the link between the XYZ Company headquarters and XYZ Remote Office 2?

    337.68 kbps




Voice over IP First-Step
Voice over IP First-Step
ISBN: 1587201569
EAN: 2147483647
Year: 2005
Pages: 138
Authors: Kevin Wallace

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