VoIP Intro - Next

2 Voice over IP Network 

2.1 VoIP Network Elements

In order to create a Voice over IP infrastructure, three basic components are needed. The end user needs an IP phone, also known as terminal. 

This can either be an IP phone or an IP client installed on user's PC. The centre element is an IP public branch exchange server (IP-PBX server) together with a gatekeeper. They are responsible for connection request management and switching. 

Finally, a gateway is needed as a third component to establish a packet-oriented connection between the IP network elements and the Public Switched Telecommunication Network, PSTN. Additionally, a Multi-point Control Unit, MCU, can be implemented to support voice and video conferences with more than two terminals. 

2.2 Single-Site VoIP Location 

A company's organizational structure strongly determines the requirements for an IP-PBX. A single site location only requires a stand-alone solution with one central IP-PBX server and gateway. The IP-PBX hosts all subscriber data whereas the gateway connects the company to the legacy PSTN or to other IP networks. An integration of the IP-PBX with an existing standard PBX creates no problems for the IP-PBX hardware.

2.3 Multi-Site VoIP Location

Multi-site solutions have different requirements for a convergent infrastructure. Both, IP-PBX and gateway have to support multi-site environments. This could lead to dedicated IP-PBX servers and gateways at each location. All components are interconnected all the time to constantly align server data and states as a common numbering plan and common phone directory are used. For cost efficiency reasons, the IP-PBX servers route the call as long as possible within the IP network and deliver the call to the PSTN as close as possible to its final  destination.  Additionally,  the  IP  gateways  must  support  dialling-in  from  any  PSTN signaling point to any branch office and call delivery to the PSTN gateway according to a least cost routing plan in order to save costs. 

2.4 PBX Networking via IP 

The interconnection of legacy PBXs in different branch offices using a company intranet is a major  domain  of  IP-based  telephony.  One  of  the  most  significant  features  is  the independence from any time-based cost structures and the parallel use of resources for data traffic. Hence, IP-based PBX networking provides a lot of economic advantages. A Voice over IP gateway is the heart of IP networking. It compresses a synchronous stream of speech data, encapsulates these speech data in IP packets and transmits them with a low data rate via the packet-oriented IP network.

This transmission is a transparent one, with the gateway neither analyses the signaling info nor  making  any  routing  decisions.  From  the  PBX's  view,  the  gateway  only  acts  as  an additional switching node. 

2.5 PBX Migration towards VoIP 

Many companies own a quite powerful legacy PBX infrastructure with long-term service agreements and a defined period for capex depreciation. Therefor, it is uneconomic to put it out-of-service and replace it by new IP-PBX equipment. In many cases, IP-PBXs are used to complement an existing PBX, also known as "PBX migration towards VoIP". A gateway is used to connect the local area network to the existing internal telephone network. Step by step, different departments are equipped with IP-PBXs as a subset of the existing switchboard and with IP phones instead of standard terminals. Branch offices and home offices can be integrated easily using IP-dial-in access to the company' s network. As IP telephony is accepted by the users, new extensions are activated directly within the IPPBX.  Step  by  step,  the  legacy  PBX  can  be  replaced  totally  by  the  IP-PBX  using  teh company's experience with the new technology and with copeing network load problems or system break-down periods.

2.6 VOIP and ISP

Internet services providers (ISPs) have already achieved a good position in a tough market fighting for end users. Unfortunately, the ISPs' margins have gone down as the fight for subscribers has been price-driven and is still continuing . Hence, value added services are badly need to assure additional revenue. This services could include access to non-data communication, e.g., voice and fax services. This requires an upgrade of the backbone infrastructure to be able to support this kind of service and assures a proper connection to the PSTN using the gateways used.