An Introduction to Voice Over IP (VOIP) & IP Telephony

Have you seen the phones in your office being plugged to the computer network (RJ-45 Jack) and wondered why enterprises have moved to IP Telephony/ VOIP System? In this article we discuss exactly that. We have also included an introduction and a short note on the various components used to build an IP Telephony/ VOIP system. The IP Telephony architecture diagram just below would give a good insight in to the connectivity architecture and how exactly the IP Telephony Servers and IP Phones get integrated in to the computer networks.

Voice Over IP - IP Telephony Architecture and Connectivity Diagram
VOIP/ IP Telephony - Architecture and Connectivity Diagram


Voice Over IP Networks (VOIP) / IP Telephony:

What is IP Telephony?

IP Telephony is basically a concept where all the voice communications within and outside an enterprise network is carried over the Computer Network (4 Pair UTP Cables) instead of the Single Pair Voice Cable Network.

A VOIP (Voice Over IP Networks) System / IP Telephony system has become the basis of a converged network, where a single computer network is used to carry voice, multimedia and video applications in real time in addition to the data traffic they are expected to carry.

Why has IP Telephony System become very popular?

  • IP Telephony system utilizes the same network as the computer network and hence the cost of creating and maintaining a separate voice network is not there. So, there is a single converged network for transmitting both voice and data traffic.
  • With IP Telephony, Inter-branch calling and long distance calling become very cost effective as the WAN IP Networks (Internet, Leased Lines, MPLS Circuits) that carry data are used to carry voice as well.
  • The IP Telephony system scales up very well and quickly – New extensions are created based on software licenses and hence it is very fast and a large number of extensions can be created and implemented quickly.
  • IP Telephony System enables a lot of voice applications out of the box (Like IVR, Voice Mail, Call Recording etc) and makes it easier to implement new applications and business process integration (Integration with Google Maps, CRM Systems for example).
  • IP Telephony system enables presence information to be shared across the network to identify who is available and how they wish to be contacted (over their Desk IP Phone, Soft Phone, Home phone, Cell phone, IM, video call, Voice Mail, Email etc). It also enables single number reach.
  • IP Telephony system integrates with corporate directories like Active Directory, LDAP and enables users to dial from their outlook contacts list and even web pages!
  • IP Telephony system can accommodate a variety of end points (IP phones, Dual Mode Cell Phones, Soft Clients, Wi-Fi Phones) and they can also be enabled over a variety of network interfaces (Wired Networks, Wi-FI networks, 3G Networks etc). IP Telephony system can also connect to the older analog phones and fax machines using ATA’s – Analog Telephony Adapters.
  • IP Telephony systems can connect to a variety of voice trunk lines from the service providers – PRI Lines, FXO Trunks, SIP Trunks etc and choose which line to use for which call based on a Least Cost Routing Analysis at any given point of time.
  • Redundancy can be created at multiple levels and remote hosting services (for disaster recovery, pay-as-you-use subscription models) are also available for IP Telephony systems.
  • IP Telephones enable multi-party meet-me conferences with password protected access.
  • Open Source based IP Telephony Call Control softwares are available, some of which are free of cost to download. They can be run on any standard Server/PC hardware.

What are the components of an IP Telephony System?

  • IP Telephony Server(s) – This is the heart of the IP Telephony systems which provides complete Call Control, Dial Plan control and all the basic vocie applications (In case of smaller systems, all the functionalities of the below mentioned application servers can also be bundled with this)
  • Application Servers – Some times applications like IVR (Interactive Voice Response – Auto Attendant), Call Recording, Voice Mail, Data Base Integration require to be hosted in separate servers – Especially for larger VOIP installations.
  • IP Phones – These IP Phones connect directly to the IP Network (RJ-45 based UTP Cables) and provide all the voice functionalities hitherto provided by analog phones like caller ID display, speaker phones, speed dial keys, memory etc.
  • Soft Phones – These are basically software utilities that have all the telephony functions but use the computer, head-set with microphone to make and receive calls.
  • Wi-Fi Phones/ Dual Mode Cell Phones – Wi-Fi phones are based on IP Technology and connect to the wireless network and act as mobile extensions. Certain Cell phones come with Wi-Fi adaptors and can be used as a Wi-Fi Phone (if the manufacturer supports the same). Cell Phones can also connect to the IP Telephony server through 3G Networks/ CDMA networks for making a VOIP Call.
  • Analog Telephony Adapters (ATA) – These are specialised devices that connect to the LAN at one end and connect to FXO (Analog Trunks) or FXS (Analog Extensions) at the other end.
  • PRI Cards – These are used to connect PRI/E1/T1 Trunk Lines to IP Telephony Servers – Usually they connect directly with the PCI/ PCI Express Slot in the server.
  • Computer IP Network – An IP based Computer Network is used to carry the voice signals across the enterprise and sometimes even to remote locations.
  • IP Phones are much more expensive when compared to the cost of analog phones.
  • The voice call quality (over IP Networks) depends on a number of parameters like the configuration of right QoS parameters, latency, jitter, available bandwidth etc across the network.
  • IP Networks need to be built with sufficient redundancy and security for continuous availability of IP Telephony services – If there is a DOS attack on the network (for example), the telephones also become inactive along with the computers.
  • Scaling of IP Telephony systems needs to be planned properly – Failing which, the IP telephony server may not be able to handle high concurrent call loads. There are hardware/ license based restrictions on the maximum number of concurrent calls that a single server can handle/ maximum number of end points that can connect to a single server.

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