October 05, 2005
VoIP in the enterprise
VoIP provides carriers and customers with several advantages, these include:
• Reduction in toll charges that one has to pay when running calls over PSTNs. Combining of voice and data helps to conserve bandwidth.
• Pursuing open standards enables businesses to purchase the best available solution and achieve interoperability between products from different vendors, something that is not possible with traditional PSTN solutions, with most of them being proprietary in nature.
• By turning voice into an IP application, vendors provide companies with the opportunity to make maximum use of the latest developments in the world of telecommunications.
The early VoIP vendors concentrated on developing toll-bypass solutions to allow companies to reduce communication costs. However, as most of the solutions were proprietary in nature, interconnectivity was not easy to achieve. The four main independent standards are H.323, MGCP, SIP, and H.248.
Currently, the VoIP networks are being deployed using multiple protocols and architectures. The combination of protocols depends upon the type of services that a company wishes to deploy. Given below is a brief introduction to the various VoIP protocols:
• H.248/Megaco is a protocol for defining the centralized architecture used in the creation of multimedia applications such as VoIP.
• H.323 defines the distributed architecture of packet-based multimedia communication systems.
• MGCP is used to define the centralized architecture for creating multimedia applications such as VoIP.
• RTP is used to define the transport protocol for real-time applications.
• SIP is used for defining a distributed architecture used for creating multimedia applications.
VoIP networks can be either centralized or distributed. The flexibility regarding the choice of architecture allows companies to develop networks that can strike a balance between ease of management and innovative service. MGCP and Megaco are protocols used for a centralized device referred to as the media gateway controller, which manages the switching logic. The endpoints in a centralized network do not have any native features and the network intelligence is centralized. In order to develop SIP and H.323 networks in a centralized manner, back-to-back user agents (B2BUA) or gatekeeper routed call signaling (GKRCS) is used.
The advantages of a centralized architecture include centralized management and call control. Legacy voice features can be replicated with ease. The drawbacks include limiting of VoIP services to legacy voice features.
With a distributed architecture, the network intelligence for call handling is distributed to the end-points as well. Call handling implies features such as call state, calling features, call routing, billing, etc. A VoIP call can be initiated and terminated at the VoIP gateway, media server, IP phone, etc. The devices that do the call controlling are referred to as gatekeepers and redirect servers in H.323 and SIP networks, respectively. The disadvantage of a distributed architecture lies in its complexity. Companies looking at interconnecting the various segments by using VoIP protocols can do it in three ways:
• By using TDM tools or VoIP gateways for translating between protocol domains. This particular model is viewed as a stop gap arrangement till translators that are IP-based are available. Using this protocol increases latency and adds a protocol translation to the process.
• A single protocol architecture allows the company to run all the devices on a single protocol. This allows the company to keep the network simple but limits the ability to migrate the existing applications to the new protocol and connectivity to other networks that are using different VoIP protocols may be difficult.
• By employing IP-based protocol translation, two or more VoIP protocol domains can be connected. A company can continue to use its existing equipment while using IP translators; unlike TDM connections these do not introduce a delay. However, there are no standards for IP-based translators as yet.
In conclusion, it can be said that the selection of VoIP protocols depends upon the technical and service requirements of a company. In choosing a vendor, it is safer to select one that has developed its applications on open standards so that interoperability with other VoIP systems is not a problem. The applications should support multiple protocols to facilitate addition of new products or migration to other systems, without having to perform upgrades every time. A system that supports a multi protocol environment allows a company to develop a scalable network.
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