Learn real-world voice-over-IP deployment solutions and strategies from the Cisco experts
Deploying Cisco Voice over IP Solutions covers:
* Definitive guidelines on real-world VoIP deployments, the fundamentals of the latest VoIP solutions, and a look into the future of VoIP services
* Different techniques for engineering and properly sizing traffic-sensitive voice networks
* Basic concepts applicable to echo analysis, echo cancellation, and locating and eliminating echoes
* Various QoS features applicable to voice
* Detailed information on call admission control (CAC)
* Dial plan configuration recommendations on Cisco H.323 gateways and gatekeepers used to support large dial plans
* Basic tasks of designing a long-distance VoIP network
* The two classes of hosted voice networks: Managed Multiservice (MMS) networks and packet voice VPNs
* Fax services store and forward as well as real-time relay fax services
* Sample configurations and step-by-step examples to help you learn how to build a VoIP network
Deploying Cisco Voice over IP Solutions provides networking professionals the knowledge, advice, and insight necessary to design and deploy voice over IP (VoIP) networks that meet customers’ needs for scalability, services, and security. Beginning with an introduction to the important preliminary design elements that need to be considered before implementing VoIP, Deploying Cisco Voice over IP Solutions also demonstrates the basic tasks involved in designing an effective service provider-based VoIP network. You’ll conclude with design and implementation guidelines for some of the more popular and widely requested VoIP services, such as prepaid services, fax services, and virtual private networks (VPNs).
This book is a collaboration of Cisco Systems CCIE(r) engineers, technical marketing engineers, and systems engineers. You’ll find design experience from people who have designed some of the world’s largest VoIP networks.
Networks, whether voice or data, are designed around many different variables. Two of the
most important factors that you need to consider in network design are service and cost.
Service is essential for maintaining customer satisfaction. Cost is always a factor in
maintaining pro?tability. One way you can maintain quality service and rein in cost in
network design is to optimize circuit utilization.
This chapter describes the different techniques you can use to engineer and properly size
traf?c-sensitive voice networks. You’ll see several different traf?c models and explanations
of how to use traf?c probability tables to help you engineer robust and ef?cient voice
networks.
Traf?c Load Measurement
In traf?c theory, you measure traf?c load. Traf?c load is de?ned as the ratio of call arrivals
in a speci?ed period of time to the average amount of time it takes to service each call
during that period. These measurement units are based on Average Hold Time (AHT). AHT
is de?ned as the total amount of time of all calls in a speci?ed period divided by the number
of calls in that period. For example:
3976 total call seconds / 23 calls = 172.87 sec per call = AHT of 172.87 seconds
The two main measurement units used today to measure traf?c load are the following:
• Erlangs
• Centum Call Seconds (CCS)
In 1918, A.K. Erlang developed formulas that could be used to make predictions about
randomly arriving telephone traf?c. The Erlang—a measurement of telephone traf?c—was
named in honor of him. One Erlang is de?ned as 3600 seconds of calls on the same circuit,
or enough traf?c load to keep one circuit busy for 1 hour.
Traf?c in Erlangs = (number of calls × AHT) / 3600
Example: (23 calls × 172.87 AHT) / 3600 = 1.104 Erlangs
CCS is based on 100 seconds of calls on the same circuit. Voice switches generally measure
the amount of traf?c in CCS.
Traf?c in CCS = (number of calls × AHT) / 100
Example: (23 calls × 172.87 AHT) / 100 = 39.76 CCS
Which unit you use depends on the equipment you use and the unit of measurement it
records in. Many switches use CCS because it is easier to work with increments of 100
rather than 3600. Both units are recognized standards in the ?eld. The following is how the
two relate:
1 Erlang = 36 CCS
Although you can take the total call seconds in an hour and divide that amount by 3600
seconds to determine traf?c in Erlangs, you can also use averages of various time periods.
These averages allow you to utilize more sample periods and determine the proper traf?c.
More info?Deploying Cisco Voice over IP Solutions (Networking Technology)
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