Adding Value to a SIP Trunk

Adding Value to a SIP Trunk
A XOP Networks White Paper
September 2007
Contents
Contents ..................................................................2
Abstract ...................................................................2
What is a SIP Trunk? ..............................................2
Who sells SIP Trunks?...........................................2
Abstract
Voice over Internet Protocol (VoIP) has come a long way
from its origins that allowed cheap phone calls over the
Internet. With appropriate QoS mechanisms in place and
support for rich signaling, the packet based data network
can now be relied upon for supporting commercial grade
voice telephony.
Deploying Value Added Services..........................3
What is a SIP Trunk?
Adding a SIP Trunk.................................................3
Session Initiation Protocol (SIP) refers to is the common
signaling standard for real-time communications using
Voice over Internet Protocol (VoIP). SIP is an openstandard which allows network carrier voice equipment to
interoperate seamlessly with customer premise equipment
(CPE). The voice channel established between the two is
what is referred to as a SIP Trunk - a virtual phone line
that utilizes a Broadband connection for access.
SIP Trunk based Network ......................................3
Benefits of a SIP Trunk ..........................................4
Summary .................................................................4
SIP is a rich signaling protocol capable of supporting not
only voice, but can also be used to set up multi-media
connections involving data and video streams.
Who sells SIP Trunks?
There are several Internet Telephony Service Providers
(ITSP) that offer SIP trunks. An ITSP typically deploys a
Soft-switch based architecture. The Soft-switch serves as
a gateway between the SIP based packet network and the
TDM based Public Switched Telephone Network (PSTN).
The larger the foot print of an ITSP, the longer the distance
a call can be carried in packetized form on its network.
And the longer a call stays on the packet network, cheaper
it is due to inherent bandwidth efficiencies of the packet
network. This in turn results in lower per minute price for
the end user.
ITSPs offer several different pricing models for SIP trunks.
The most prevalent model is ‘pay as you use’. In other
words there is no fixed monthly recurring charge. An
enterprise only pays for the calls that it makes. The local
intra-lata calls are free. The long distance calls are billed
40-70% cheaper compared with the traditional service
providers.
TDM trunks are usually sold in increments of T1’s (or
PRIs) or for smaller enterprises as fractional T1s with a
minimum number of voice channels. On the other hand
SIP trunks can be added in increments of one. Hence an
enterprise can order exactly what it needs.
Therefore by switching to a SIP trunk based network, an
enterprise can save a considerable amount of money on
its voice telephony related operational expenses.
the enterprise pays long distance charges in the range of
5-8 cents per minute.
Deploying Value Added Services
The scenario described above is typical of the telephony
environment in a medium to large size enterprise today.
Figure 1 shows a typical legacy PBX environment.
Adding a SIP Trunk
In order to leverage the advantages of SIP trunking, an
enterprise needs to upgrade its telephony equipment to
support SIP. This involves; a) replacing the TDM PBX with
an IP PBX or b) augmenting the existing TDM PBX with a
packet module so that it can support a SIP trunk.
PBX
TDM Trunk
PSTN
TDM Trunk
Voicemail
Conference
Bridge
If the enterprise uses in-house value added sub-systems
such as an external Voicemail system and Audio
Conference Bridge, then newer SIP based alternatives that
are now available should be explored.
SIP Trunk based Network
TDM PBX
with SIP Trunk
Figure 1: Enterprise Legacy PBX Deployment
As shown, the PBX is connected via TDM based
trunks (CAS T1 or ISDN PRI) to the PSTN. The
enterprise has also deployed its in-house Voicemail
and Audio Conference Bridge. The interface
between the legacy PBX and the in-house Voicemail
system and Audio Conference Bridge is also based
on a TDM based trunk.
The enterprise uses outsourced web conferencing
and video conferencing services as needed.
The TDM trunk connected to the PSTN has a block
of 100 Direct Inward Dialed (DID) numbers
associated with it. The PBX routes the calls to
individual employees based on the incoming DID
number. If an employee is busy or does not answer
the incoming call, the PBX routes that call over to
the Voicemail system.
One specific DID number is set up as a lead number
for the Audio Conference Bridge. When multiple
people call the same number for joining a
conference, the PBX routes those callers based on
the lead number to the PRI connecting to the Audio
Conference Bridge.
The TDM based trunks connected to the PSTN incur
a monthly recurring charge. These charges can
range from $500-$1000 /Month per T1 depending on
the carrier and the geographical location. In addition,
SIP Trunk
ITSP
SIP Trunk
USN
Figure 2: Enterprise IP PBX Deployment
Figure 2 shows the same enterprise network as before
with two changes.
1) A packet based module has been added to introduce
the SIP trunk on the PBX. This SIP trunk is then connected
to the ITSP via the enterprise’s data network.
2) A SIP based value added service platform has been
added. The platform also interfaces with the PBX via the
same SIP trunk. The particular platform shown in Figure 2
is XOP Network’s Universal Service Node. Along with
providing Meet-me conferencing, the platform also
provides Web conferencing, Voicemail and Group Alerting
applications. Therefore, between the PBX and the USN,
the Enterprise can not only use IP telephony for regular
phone calls, but also use it for providing all previously
available value added services.
Benefits of a SIP Trunk
About XOP Networks
•
Easier management – one data connection
for both voice and Internet.
•
Same ITSP for both local and long distance
service.
•
Ease of switching between ITSPs.
Enterprise can get best rates for the
services as they switch easily between
service providers just by pointing to a
different IP address.
•
Hard Dollar savings. Significant reduction in
monthly telephony related expense due to
‘pay for what you use’ model.
•
Reduction in the cost of service platforms
due to availability of SIP based appliances
that can provide multiple services in one
platform.
•
Retain the same phone numbers as ITSPs
support local number portability.
•
Location Independence. In the event the
office needs to relocate across the city or
across the country, the pain of the move will
be minimal as the same SIP trunk will be
available at the new location as long as
Internet service is available.
•
Enables converged services such as multimedia collaboration and video conferencing.
Also sets the stage for further
enhancements such as presence and
location based services.
XOP Networks is a leading supplier of TDM and IP based
value added services platforms for Enterprises and
Independent Telephone Companies. Its unique product
architecture allows smooth migration of value added
services from legacy circuit switched TDM networks to
VoIP based packet networks. Its products support Audio
Conferencing, Web Conferencing, Group Alerting,
Enhanced Firebar, Voicemail and a few other services.
XOP Networks is headquartered in Plano, Texas.
Additional information on XOP Networks is available at
www.xopnetworks.com
Summary
VoIP and SIP technology have come a long way
from the early days of making cheap phone calls
over the Internet. The true benefits of packet based
networking are now in reach of most Enterprises.
This paper describes how an enterprise can use SIP
trunking to lower its monthly telephone bill and also
introduce value added services via a SIP based
applications platform.
For any inquiries, please contact:
XOP Networks, Inc
5508 West Plano Parkway,
Suite B
Plano, Texas 75093
Main: 972-590-0200
Alt: 214-564-2263
Fax: 972-590-0215