VoIP

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1. Introduction

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1.1 Telephone and Data Networks ....................................................3
1.2 The classic Telecommunication System and Connections ......4
1.3 The Voice over IP Concept (1/2) ..................................................5
1.3 The Voice over IP Concept (2/2) ..................................................6
1.4 Advantages of IP-Telephony (1/2) ...............................................7
1.4 Advantages of IP-Telephony (2/2) ...............................................8
1.5 Worries about IP-Telephony........................................................9
1.6 Field of Applications of IP-PBXs (1/2).......................................10
1.6 Field of Applications of IP-PBXs (2/2).......................................11

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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.

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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.

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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).

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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.

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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.

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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.

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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.

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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.

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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.