Chapter 8: Voice Network Design Considerations (Part05)

References

For additional information, refer to these resources:

• Echo Analysis for Voice over IP, http://www.cisco.com/en/US/partner/tech/tk652/tk701/technologies_white_paper09186a00800d6b68.shtml.

  Note

  You must be a registered user on http://www.cisco.com/ to access this document.

• Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.4, http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hqos_c/index.htm.

• Introduction to voice, including telephony signaling documents, http://www.cisco.com/en/US/tech/tk652/tsd_technology_support_category_home.html.

• Traffic Analysis for Voice over IP, http://www.cisco.com/univercd/cc/td/doc/cisintwk/intsolns/voipsol/ta_isd.htm.

• Understanding Delay in Packet Voice Networks, http://www.cisco.com/warp/public/788/voip/delay-details.html.

• Voice Network Signaling and Control, http://www.cisco.com/warp/public/788/signalling/net_signal_control.html.

• Waveform Coding Techniques, http://www.cisco.com/warp/public/788/signalling/waveform_coding.html#subrstsix.

• Erlang tables on Westbay Engineers Limited Home Page, http://www.erlang.com/.

• Szigeti and Hattingh, End-to-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs, Indianapolis, Cisco Press, 2004.

• Cisco Unified Communications Manager (CallManager): Introduction, http://www.cisco.com/en/US/products/sw/voicesw/ps556/index.html.

• Cisco Unified Communications SRND Based on Cisco Unified CallManager 5.0, http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_implementation_design_guide_book09186a00806492bb.html.

• Understanding Codecs: Complexity, Hardware Support, MOS, and Negotiation, http://www.cisco.com/en/US/tech/tk1077/technologies_tech_note09186a00800b6710.shtml.

• Davidson, J., and J. Peters. Voice over IP Fundamentals. Indianapolis: Cisco Press, 2000.

• Voice Network Signaling and Control, http://www.cisco.com/warp/public/788/signalling/net_signal_control.html.

• Voice over IP—Per-Call Bandwidth Consumption, http://www.cisco.com/warp/customer/788/pkt-voice-general/bwidth_consume.html.

  Note

  You must be a registered user on http://www.cisco.com/ to access this document.

• Cisco IOS Voice Configuration Library, http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124tcg/vcl.htm.

• High-Density Packet Voice/Fax Digital Signal Processor Module, http://www.cisco.com/en/US/products/hw/univgate/ps501/products_data_sheet0900aecd80458049.html.

• Cisco Voice Codec Bandwidth Calculator, http://tools.cisco.com/Support/VBC/do/CodecCalc1.do.

  Note

  You must be a registered user on http://www.cisco.com/ to access this calculator.

Case Study: ACMC Hospital Network Voice Design

This case study is a continuation of the ACMC Hospital case study introduced in Chapter 2.

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Case Study General Instructions

Use the scenarios, information, and parameters provided at each task of the ongoing case study. If you encounter ambiguities, make reasonable assumptions and proceed. For all tasks, use the initial customer scenario and build on the solutions provided thus far.

You can use any and all documentation, books, white papers, and so on. In each step, you act as a network design consultant. Make creative proposals to accomplish the customer’s business needs. Justify your ideas when they differ from the provided solutions. Use any design strategies you feel are appropriate. The final goal of each case study is a paper solution.

Appendix A, “Answers to Review Questions and Case Studies,” provides a solution for each step based on assumptions made. There is no claim that the provided solution is the best or only solution. Your solution might be more appropriate for the assumptions you made. The provided solution helps you understand the author’s reasoning and allows you to compare and contrast your solution.

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In this case study you create a high-level voice design for the ACMC Hospital network.

Case Study Additional Information

The ACMC staff wants to replace its PBX and key systems and is eager to achieve cost reduction while providing better service to remote clinics. The replacement system needs to offer at least as many features as the present system. The staff is also very interested in unified voice-mail services for busy doctors and the potential for using phones with web-based menus as part of a quality care system.

Current features include standard PBX features, call conferencing, voice mail, and local calls. Remote clinics currently use some form of key system or remote PBX shelf with limited features. Figure 8-38 summarizes the ACMC design up to this point for your reference.

Figure 8-38: Case Study ACMC Hospital Current Design

Case Study Questions

Complete the following steps:

Step 1	Based on the design up to this point, what aspects of the infrastructure need to be considered when adding voice?
Step 2	Select the IP telephony design model most appropriate to ACMC, and indicate where you would place the various IP telephony components.
Step 3	Each remote clinic must be able to place local calls without going through the main campus. What devices will be needed at each site? What else must be added to be able to support local conference calls?
Step 4	WAN backup is by IPsec VPN across the Internet. What service characteristics might IPsec or the Internet lack that voice requires? What could be added to your design to remedy this?
Step 5	The ACMC current phone system uses a PBX at each clinic, with phone trunks to the main campus PBX. The Director of Telephony just had a call study done and is convinced she has sufficient capacity. Table 8-7 summarizes the number of calls currently supported for each remote site. Table 8-7: ACMC Call Study Results Open table as spreadsheet Remote Clinic Number of Calls on the Trunk to the Main Campus 1 8 2, 3, 4, 5 4 Estimate how much WAN bandwidth each ACMC site would need if the G.711 and G.729 codecs were used. Assume that with the required call parameters, a G.729 call uses about 25 kbps and a G.711 call uses about 92 kbps. Is there enough bandwidth in the ACMC WAN?