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IP Telephony Components And Protocols
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IP Telephony solutions are applicable in all environments in which legacy telephony installations can be found, including home users, SMBs, large enterprises, and carriers. Even though the deployment environment and customer requirements for IP Telephony solutions differ, the design approach remains the same. Topology, performance, and budget considerations drive the choices of equipment and protocols following the identification of the stakeholder requirements. The key solution components, although they differ in scalability and capability, share the same characteristics and principles of operation. Viewing voice as an application implies that a viable IP infrastructure must be in place to support any successful IP Telephony solution deployment.
In developing an IP Telephony solution, you must also maintain a clear distinction between IP Telephony and Voice over IP (VoIP). Although the two expressions are frequently used as synonyms in casual technical discussions, consider VoIP as an enabler of IP Telephony in the context of design. An IP Telephony solution relies on VoIP standards, protocols, and equipment to create as complex or as simple a telephony system as has been determined by the user requirements and the available budget.
Consider the following key IP Telephony components:
• Gateways
• Gatekeepers
• Software
• IP phones
• VoIP protocols
Gateways:
Generically, a gateway converts between the same layer protocols from different computing architectures or technologies. The H.323 recommendation identifies a number of gateway types (access, trunking, media, composite, and decomposed) that reflect a high degree of gateway versatility in packet-based multimedia communications systems that include IP Telephony. Yet, this gateway versatility inevitably implies that in the course of designing IP Telephony or any other communications solution; you need a clear understanding of each gateway's functionality. In the context of H.323, gateways are also referred to as endpoints, meaning that they can initiate and terminate calls.
Finally, in an IP Telephony deployment without TDM, PSTN, or POTS interfaces, gateways are not needed. If an SMB's internal phone system is entirely IP-based, and the interface to the provider for local, long-distance, and international calls outside of the SMB network is also via IP, that SMB will not require gateways. To integrate legacy phone instruments into an IP-based telephone system, a voice gateway is required. The analog voice gateway allows for the integration of analog phones, faxes, and modems with the IP-based Call processing platforms.
Because gateways represent the points of convergence between different communications systems, they can be deployed individually or in groups as a function of the size of the networks and the number of points (locations) where the different networks need to interconnect.
Posted by ROOT Technologies
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