VoIP - Intro

1. Introduction

1.1 Telephone and Data Networks

 Up to now, companies had two separate communication infrastructures. On one side, there was the public branch exchange (PBX), featuring voice services provided by the company's own switchboard. On the other side, we had the LAN (Local Area Network), providing data communication. As a rule both networks had interfaces for communicating with the outside world. 

This separation is very inefficient and uneconomical, because each network needs its own technology. Two sets of know-how are needed for operation and maintenance. Futhermore it prevents the rapid evelopment of  new applications, as the basic technology of  the two systems is so different. 

1.2 The classic Telecommunication System and Connections

Classic PBXs are proprietarily based on the system architecture of the respective provider. Only the manufacturer of a PBX can provide and market upgrades for both hardware and applications. For example, it's impossible to use a system-telephone from one manufacturer with another system. Common wired telephone connections use a direct connection between the callers. This is called connection oriented communication. 

The sequential dataflow always follows the same path from the source to the recipient, and the delay always remains the same. The connection - usually a 64 kbit/s line - is not available for other information transfer. Pauses in speech, which make up to 60% of a standard phone call, mean that the connection is not being used at full capacity. 

1.3 The Voice over IP Concept (1/2)

The IP-PBX is a new type of PBX. Here speech is not routed over a separate infrastructure. Instead,  it's  an  integrated  component  of  a  common  infrastructure  for  speech  and  data communication in a multimedia network.

The packet-oriented and connectionless communications protocol IP  (Internet protocol) is fundamental for linking these infrastructures. With the rapid development of the internet, IP has become very important in the world of communications. Speech is compressed, wrapped in IP packets and simultaneously transported on the same network along with other data. If speech is transmitted, the bandwidth of the data-network is used only partially. As audio and video data are transferred by IP, this is often referred to as IP telephony or Voice over IP (VoIP). 

1.3 The Voice over IP Concept (2/2)

IP-PBX itself is a software kit running usually on a server in the LAN. This kit controls all dialling and connection processes inside and outside of the local multimedia network. The most important advantage of an IP-PBX is the fact that no special switching hardware is needed. So, unlike a classical PBX, there is no switching network. The IP-PBX provides the switching functionality of a PBX simply by assigning IP addresses and substation numbers to the  IP  telephony  devices.  These  are  linked  to  the  LAN  and  coordinate  the  connection requests. So IP telephony can take advantage of the advanced and established routing and network technology of IP networks. 

1.4 Advantages of IP-Telephony (1/2) 

There are many advantages to IP telephony but the most significant is the cost-saving potential, which has two main components.

 Decreased infrastructure costs: As speech and data now share their infrastructure, the maintenance of a parallel telephone network, which requires a costly switching technology and its own wire distribution system, is much cheaper.

 Savings on fees: The cheap connection routes, which until now only handled internal data traffic, can now be used for the internal speech traffic as well. Least Cost Routing (LCR) is used with external calls. This means that the currently cheapest provider is chosen and that external calls are routed for as long as possible over the internal network before switching to the external provider. For example, imagine a call from a company's central office in Berlin to an external participant in Nuremberg. The call is routed internally to the company's own branch in Nuremberg and there switches to the external network.

1.4 Advantages of IP-Telephony (2/2) 

Higher flexibility: When a company relocates, costly charges for the redirection of speech and data traffic, or for user administration can be saved. IP telephony is far simpler than having two separate speech and data networks. All user information is kept in a single data structure and can be used for computer purposes as well as for telephony. Another advantage is the linking of separate applications like email, telephony, voice mail and fax within one single communication platform.

The inclusion of the internet increases performance over legacy PBXs. E-commerce offers with special speech functions are possible. These can be activated by the customer by clicking special call-me buttons on the website. 

Also,  a  company  using  VoIP  is  no  longer  bound  to  equipment  made  by  a  particular manufacturer, as VoIP uses international standards. 

1.5 Worries about IP-Telephony 

Alongside all the advantages of IP telephony there are also some unanswered questions. For example, IP telephony still has to prove its reliability and fail-safe qualities - a strong point of classic PBXs. Doubts focus on PC technology and the stability of the software making up network elements like elements and terminals within VoIP. But VoIP has the option of using PC independent phones alongside PC based phones. Critical components, like gateways to the public phone network or IP-PBX servers, can be made more fail-safe using clustering. Speech quality in IP networks depends mainly on three factors:

1.  Speech coding and compression, also called codec. Codecs compress the scanned digital speech signal using special algorithms and so decrease the amount of data to be transmitted. 

2.  Packet delay, also called jitter. There is always delay when compressing the speech signal. Delay also occurs along the transmission route whenever speech packets are cached in network elements like gateways, routers or IP terminals. Every time this is done, latency time is increased. 

3.  Packet loss of speech transmissions, which mostly results in the late delivery of  speech packets.

1.6 Field of Applications of IP-PBXs (1/2)

 IP-PBXs can be deployed in a number of ways in a local multimedia network. In a Unified Messaging System, IP-PBX is the central element. Speech communication can be carried out by one single client. For example, it is possible to have mobile access to a company's internal network, listen to saved messages and directly establish the resulting speech connections. Besides voice messages, the IP-PBX can also read emails and fax. With the integration of speech and data, all messages can now be managed centrally by a PC. 

Special client software turns the PC into an IP telephone, incorporating all the functions of a legacy  system  telephone.  Using  a  free-form  user  interface,  this  functionality  can  be customised in a flexible and individual way for each employee. 

1.6 Field of Applications of IP-PBXs (2/2) 

A common system telephone has no connection to PC applications and is thus limited to its speech functions. An IP telephone, on the other hand, can be connected to email programs, electronic  calendars  or  the  internet.  This  turns  it  into  a  digital,  multimedial,  intelligent message centre. All the different information types merge in the IP-PBX. An IP-PBX can much better integrated into a company´s workflow than an ordinary IP-PBX. The IP-PBX can tell an external caller if the person they are looking for is reachable or not. This ability is based on the following information:

1.  Knowing if the person has logged into the LAN and 2.  Knowing if the person has an appointment by analysing his pc-diary 

The internet presence of a company could be enhanced to include navigation with voice support, directly called up from the website. All the advantages of the globalisation of the internet are thus transferred to voice telephony.