Case Study: Your Turn to Put the Pieces in Place


To help you get a better feel for voice network design, consider a sample high-level design scenario. A suggested solution is provided after the scenario. However, remember, when it comes to the design of a voice network, there is no one solution. The flexibility of voice technology allows many different design approaches to achieve the same goal. So, don't be concerned if your solution differs from the suggested solution.

Consider the following scenario:

The XYZ Company comes to you wanting your advice for designing a telephone network to interconnect the XYZ Company headquarters with two of its remote offices. Even though the XYZ Company already has a data network interconnecting these offices, at this point, it isn't completely convinced it should pursue a VoIP telephony network, as opposed to a traditional PBX/key system network. Therefore, you are asked to recommend a traditional telephony (PBX or key system) solution based on the criteria outlined in Table 1-3.

Table 1-3. XYZ Company Requirements for a Telephony System

Location

Number of Telephones

Required Features

Headquarters

4500

Voice mail
A conference bridge capable of supporting a conference of 20 simultaneous participants

Remote Office 1

2000

Access to the corporate voice mail system
Access to the corporate conference bridge
Capability to support 72 simultaneous voice paths back to the headquarters

Remote Office 2

30

Access to the corporate voice mail system
Access to the corporate conference bridge
Capability to support 12 simultaneous voice paths back to the headquarters


Because you are such an advocate of VoIP technologies, as opposed to a traditional PBX/key system approach, the XYZ Company asks you to add to your traditional telephony design your arguments as to why a VoIP network would be preferable. Use the space provided to diagram and document your design. Also, write a paragraph describing why a VoIP network might be preferable.

Design Diagram for XYZ Company:

Design Description for XYZ Company:

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Rationale for a VoIP Solution:

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Suggested Solution

Figure 1-10 illustrates a suggested solution for the case study. Remember, however, there isn't just a single solution to voice network designs. Don't be concerned if your design doesn't exactly match the suggested solution. Rather, read through the suggested solution to see whether it triggers any ideas you might be able to use to tweak your design.

Design Diagram for XYZ Company

Figure 1-10. XYZ Company Suggested Solution


Design Description for XYZ Company

Due to the number of phones located at the company headquarters (4500), the headquarters requires a PBX. When selecting a PBX, prospective vendors need to specify the extra hardware and software required to support the stated conference bridge and voice mail requirements.

Remote Office 1 also requires a PBX because this site contains 2000 phones. Separate voice mail and conference systems are not required for this remote office, however. This remote office can simply access the voice mail and conferencing resources located at the company headquarters. Because the trunks connecting the remote office PBX to the headquarters PBX need to support 72 simultaneous voice paths, three T1 circuits will be used to interconnect these two PBXs (that is, 24 channels per T1 * 3 = 72 channels).

Remote Office 2 only requires a key system due to its relatively small number of phones (30 phones). Like Remote Office 1, there is no need for Remote Office 2 to have its own voice mail and conferencing systems. Remote Office 2 can access the resources that reside at the company headquarters. Because only 12 simultaneous voice paths are required between Remote Office 2 and the headquarters, a full T1 is not required. Instead, a fractional T1, containing 12 voice channels, will be used to interconnect Remote Office 2 to the company headquarters.

Rationale for a VoIP Solution

A VoIP solution might be able to use the existing data network to simultaneously send voice and data traffic, thus eliminating the need for the three T1s and one fractional T1 specified in the design, which saves on recurring monthly expenses.

A VoIP network would also lay the foundation for enhanced services. For example, instead of simply having a voice mail system, the XYZ Company may be able to use a product such as Cisco Unity (described in Chapter 7, "VoIP Supporting Roles"), which provides unified messaging. Unified messaging is more than just voice mail. It provides a single repository for voice mail, e-mail, and fax messages.




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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