Case study on
IP PBX Solution through WiMax
Dr. Mashiur Rahman
Department of Computer Science & Engineering
Md. Sakhawat Hossain
ID – 062364056
North South University
This paper is intended at first to explain the various aspects of IP PBX. The possibility of
transmitting voice over IP-based networks, with all the challenges and associated
opportunities, such as voice and data integration.
In the second part, it describes why and how, WiMAX will be a key element in this new
important worldwide objective to provide a universal ubiquitous and equitable and affordable
1. Introduction 4
2. What is an IP PBX? 4
3. What are the Advantages of an IP PBX? 5
4. Where will an IP PBX be used? 5
5. Some Standards Used in IP PBX Software 6
6. WiMAX 6
7. Signaling Protocols 7
8. Security 7
9. Where does WiMAX play? 7
10. Solution Topology 10
11. Usage Scenarios 12
12. Conclusions 14
13. References 15
List of Figures
1. Fig1: IP PBX system 4
2. Fig2: WiMAX as the backbone of meshed networks 6
3. Fig3: The signaling protocols 7
4. Fig4: Security checking 7
5. Fig5: WiMAX system 8
6. Fig6: Network coverage 9
7. Fig7: VoWLAN Topology 11
8. Fig8: Education network 12
9. Fig9: Campus connectivity 13
10. Fig10: Rural connectivity 13
A PBX is a customer premises telephone system that manages telephones in the enterprise
and acts as the gateway to external voice networks. A switch/router directs incoming packets
to the appropriate data network. Traditionally, two separate networks are required: one for
voice and one for data.
This paper attempts to present the key technical features and applications of WiMAX, and
illustrate them by providing examples of usage scenarios in which WiMAX would be the
preferred solution. There are many usage scenarios that can be addressed by WiMAX. The
paper is primarily focused on fixed and portable usage; however, some examples of mobility
usage have also been included.
Instead of two separate networks, one each for data and voice, only one network is needed
if voice is packetized (Voice over IP) and sent over the data network.
2. What is an IP PBX?
An IP PBX is a combination of a switch/router and a PBX that handles Voice over IP (VoIP):
Fig1: IP PBX system
In an IP PBX, computers can be on a shared LAN that is connected to the IP PBX.
Telephones, on the other hand, should be directly connected to the IP PBX. This avoids
Quality of Service (QoS) issues that arise if both computers and telephones are on a shared
LAN. In such a case, voice packets will have to compete with data packets for the shared
LAN. Poor telephone voice quality will result if voice packets are not transmitted in a timely
An IP PBX also acts as a gateway that provides voice connections (voice lines, T1s) to a
LEC, a long distance company, etc. and data connections (cable, DSL, ISDN, E1) to a cable
operator, a LEC, an ISP, etc. IP PBXs can be used bypass the circuit-switched telephone
network by using the data network to connect to branch offices and other locations on the
Using a single converged network that carries both voice (packetized) and data allows
development of new services not typically available on the traditional network – for example,
the use of one central directory across multiple locations and unified messaging.
An IP PBX replaces a traditional PBX. It can be used with
• an IP phones (with a built-in DSP chip that converts voices to IP packets and vice
• a soft phone (software application on PCs that also converts voice to packets and
vice versa), which is used with a headset or a handset,
• existing phones along adapters that packetize voice, and standard phones connected
to PCs (PCs acts as the adapters).
As in case of computing devices, IP addresses are automatically assigned to phones as they
connect to the system. This means that a telephone can be moved from one location on the
network to another. The telephone number remains the same as it associated with the
VoIP packets can be packetized using protocols such as G.711 or G.723:
• G.711: an encoding standard for packetized voice; uses 64 kbs and can
communicate with other G.711 devices.
• G.723: an encoding standard for packetized voice that does compression; uses 6.4
kbs and can communicate with other G.723 devices but not G.711 devices.
3. What are the Advantages of an IP PBX?
Compared to a conventional PBX, an IP PBX
• handles both voice and data,
• is cheaper since it requires only one network to install and maintain instead of two,
• reduces equipment costs (only IP based products; no voice products needed),
• reduces long distance charges for inter-branch office calls (by using the data
• is easier to provision (just plug in from wherever),
• supports services such as unified messaging,
• is more flexible,
• is more scalable,
• makes it easier to provide new services, such as data and video collaboration,
• allows remote configuration (over the Web), and supports modular software
upgrades, new technologies (new CPUs, etc.) are easy to incorporate.
4. Where will an IP PBX be used?
IP PBXs are good candidates for being used particularly in
• new businesses which will avoid the costs of installing and maintaining two networks
(its hard to replace equipment that works in existing offices) businesses that have
many branches will reduce costs by
- avoiding long distance charges incurred by calls between the branches and
- using one centralized directory (which will be cheaper to maintain than many
5. Some Standards Used in IP PBX Software
• G.711: An international standard protocol used for encoding (packetizing) telephone
voice on an 64 kbps channel
• G.723: An international standard protocol for compressing voice to 6.4 kbs. The
compression quality is very good with voice quality is as good as normal telephone
voice quality. It is supported by virtually all IP telephone equipment.
• H.323: Signaling & telephone services protocol for the transmission of IP packets
representing any combination of voice, video and data.
• IVR (Interactive Voice Response): An telephone voice system that interacts with
callers using with a voice menu
• SIP (Session Initiation Protocol): A signaling & telephone services protocol similar to,
but simpler than, H.323.
WiMAX, the Worldwide Interoperability for Microwave Access, is a telecommunications
technology aimed at providing wireless data over long distances in a variety of ways, from
point-to-point links to full mobile cellular type access. It is based on the IEEE 802.16
standard, which is also called WirelessMAN. The name WiMAX was created by the WiMAX
Forum, which was formed in June 2001 to promote conformance and interoperability of the
standard. The forum describes WiMAX as "a standards-based technology enabling the
delivery of last mile wireless broadband access as an alternative to cable and DSL."
Fig2: WiMAX as the backbone of meshed networks
WiMAX is a versatile technology with relevance to all operator segments in all regions of the
world whether it be a mature market with demanding utilization needs or an emerging market
with challenging price constraints.
WiMAX is equally well suited to serve a broad range of application scenarios spanning from
fixed, nomadic, mobile, indoor and outdoor communications.
WiMAX can be used for wireless networking in much the same way as the more common
WiFi protocol. WiMAX is a second-generation protocol that allows for more efficient
bandwidth use, interference avoidance, and is intended to allow higher data rates over
7. Signaling Protocols
Fig3: The signaling protocols
The signaling protocols H.323, SIP are used to setup the route for the transmission over the
IP network, the Gateway protocols like the Media Gateway Control Protocol are used to
establish control and status in the media and signaling gateways. Routing (UDP, TCP) and
transport protocols (RTP) are used once the route is established for the transport of the data
stream as shown in Figure
Securing the voice communication is also a big challenge for VoIP over WiMAX as care has
to be taken that it cannot be eavesdropped or intercepted. The Double encryption process -
X.509 for Authentication and 152-bit AES, 3DES or 56-bit DES for data flow ensure the
transmission is secure and eavesdropping is very difficult on the traffic.
Fig4: Security checking
9. Where does WiMAX play?
Whether you are a service provider, network operator or an enterprise, WiMAX enables to
deliver the differentiated high-speed and high-bandwidth data services your customer’s
value. Fixed WiMAX is ideally suited for:
Broadband access to underserved areas, and extending DSL/cable modem services
to rural areas
Replacing more expensive means of Broadband access such as DSL, cable modem
services, and satellite TV.
Backhauling traffic for wireless service providers or cable operators at a reduced cost
Interconnecting and backhauling WiFi hot zones.
Enabling ISPs, cable and satellite operators to deliver existing content through a new
Enterprise: Providing robust, secure bandwidth for data traffic and communications
for financial and educational institutions, municipalities and in-the-field military or
public safety institutions
The high bandwidth of WiMAX delivers real-time applications much faster than other
technologies do today, including:
Streaming video: movies, TV, videos
Fig5: WiMAX system
WiMAX: the flexibility
Wireless is more flexible and thus easier to deploy according to the market demand (Capex
follows the needs). Although most of the existing wireless technologies suffer from limited
range and coverage (usually a few hundred meters around the base station) resulting in very
costly combination of technologies (wired and/or wireless), WiMAX technology benefits of a
wide coverage and can be deployed as a Point Multi Point .last mile. connection but also as
part of the backhaul to the PSTN and Internet access points. With potential range of 30 to 50
kilometers in Line Of Site (LOS) conditions, WiMAX offer a huge improvement over all
existing broadband wireless technology. With the addition of the capability for the operator
to adapt its network configuration to his marketing strategy (coverage, throughput, services,
and grade of service) WiMAX provides a very powerful solution.
WiMAX: a multi-application technology
Following the normal trend of digitalization and packet transmission and switching, WiMAX
uses the Internet protocol and thus supports all multimedia services from Voice over IP
(VoIP) to high speed internet and video transmission. WiMAX allows service providers to
offer all the latest generation of services and beyond, thanks to a throughput up to ten’s of
Mbps. With regard to the potential users, this means that WiMAX have the capacity to
deliver services from households to SME.s, SOHO.s, Cybercafés, Multimedia Telecentres,
Schools and Hospital.
WiMAX: the Worldwide Standardization benefits
Developed and supported by the WiMAX forum (more than 300 members), WiMAX will
become the worldwide technology based standard for broadband and will guaranty
interoperability (i.e.multivendor CPEs), reliability and evolving technology, but also, thanks to
high volumes and integration, will ensure equipments with very low cost. With CPEs under
100 $ as one of the first objective, business model can easily be profitable even in
WiMAX: the Spectrum flexibility
In line with the objective to become the worldwide standard based technology for broadband,
WiMAX will use a single radio covering all licensed and unlicensed frequency bands
allocated by the ITU for such services i.e.:
• The two licensed bands 3.3-3.8 GHz and 2.3-2.7 GHz
• One license exempt band 5.725-5.85 GHz.
In addition to the flexibility offered to address all national spectrum situations, this single
radio, thanks to the volume effect, will makes base stations and customer premises
equipment costs very attractive.
Fig6: Network coverage
10. Solution Topology
It is an architecture that, unlike traditional network design, can change or “adapt” to meet
changing network needs, so that organizations can adopt new technologies and solutions.
The Adaptive WiMAX Architecture is a strategy for solution design that contrasts to the
traditional design in which all intelligence decision-making capability is located at the core of
The system maintains complete command of the network in a centralized manner, and
pushes out control—and intelligence—to the network edge where users connect. Complete
command from the center along with intelligence at the edge of the network, enables a user-
centric solution and is the hallmark of the Adaptive WiMAX Architecture.
Intelligence at the edge enforces security, QoS, and bandwidth allocation processes,
enabling appropriate network connectivity when and where needed, and maintaining session
persistence as mobile users move across wireless zones.
The Adaptive WiMAX Architecture’s control from the center provides another distinctive
benefit for VoWLAN solutions: The ability to manage a communications infrastructure in a
consistent fashion, including both the wired and wireless portions and, within the wireless
sphere, both standalone (“heavy”) access points and coordinated (“lightweight”) radio ports.
In the world of the Adaptive EDGE Architecture, wired and wireless, standalone access
points and coordinated radio ports, are all managed in a unified way. ProCurve Identity
Driven Manager (IDM) functionality, along with ProCurve Manager Plus (PCM+) determines
how the network applies security, QoS, bandwidth limits, and ACLs, based on user identity
or device type, regardless of where and how users connect to the network. This results in a
network that is customized for the user and which follows the user wherever he or she
attaches to the network. This contrasts to competitive approaches that require entirely
separate management systems for different types of network equipment.
Figure presents a network topology that extends VoWLAN capability across both the
corporate headquarters and remote office of an enterprise, and integrates wireless voice
capability using ProCurve Networking equipment to leverage the existing IP telephony
infrastructure at each site.
Both offices are connected to a WiMAX to provide local phone service using IP PBX to give
an enterprise a smooth migration to IP telephony.
ProCurve Networking switches provide IP connectivity and power to IP phone handsets and
wireless access points over standard Cat-5 Ethernet cable via the IEEE 802.3af Power over
Ethernet (PoE) Standard, with redundant PoE power. This solution highlights the benefit of
using both coordinated radio ports in the corporate headquarters and standalone access
points in the remote office, all managed in a unified way using PCM+ and IDM. For the
corporate site, a Redundant Wireless Services xl Module is deployed for increased reliability
and availability of voice and other important business applications.
NetLink SVP Server – The SpectraLink NetLink SVP Server provides admission control to
avoid over-subscription of access points, ensuring that excellent voice quality is maintained
on a shared wireless voice and data network. The NetLink SVP Server can support
thousands of users depending on the number of NetLink SVP Servers and the average
wireless telephone usage.
NetLink Telephony Gateway – The SpectraLink Telephony Gateway provides the interface
between the LAN and the traditional PBX (telephone switch). Each NetLink Telephony
Gateway supports up to 16 wireless telephone users. Up to 40 NetLink Telephony Gateways
can be linked for a system capacity of 640 active users.
Traditional PBX and IP PBX – The SpectraLink NetLink solution supports digital and IP
station interfaces to a variety of telephone systems by emulating proprietary digital telephone
sets. It also supports connections through direct IP interfaces to leading IP telephony
platforms via licensed protocols and OEM agreements. These digital and IP interfaces
deliver most of the features and functions of a wired desk phone on the NetLink wireless
Fig7: VoWLAN Topology
ProCurve Wireless Edge Services xl Module — The ProCurve Wireless Services xl
Module seamlessly integrates WLAN RF management and IDM role based policy
enforcement into the 5300xl intelligent edge switch enabling network administrators to easily
deploy and centrally manage a multi-service network. It provides coordinated control for
ProCurve Radio Ports (described below) connected either directly to the switch 5300xl or via
any standard PoE Ethernet switch such as the ProCurve 2600-PWR series or 3500yl series.
The Wireless Edge Services xl Module scales to meet future demands; the network
administrator can simply add more Radio Port licenses, up to 36 per module, to
accommodate growing infrastructure needs. The Wireless Edge Services xl module and
Radio Ports support both WMM and SVP.
ProCurve Redundant Wireless Services xl Module — For increased availability of
wireless voice and data services, the ProCurve Redundant Wireless Services xl Module can
be placed in an open slot of the 5300xl, which houses the primary Wireless Edge Services xl
Module, or any other 5300xl on the same subnet, to automatically adopt Radio Ports should
the primary module fail or become unavailable.
ProCurve Radio Ports 210, 220 and 230 – Working in conjunction with the ProCurve
Wireless Edge Services xl Module, ProCurve Radio Ports enable advanced wireless
services to assure a resilient and highly secure, mobile multi-service network that is easy to
deploy and manage. The ProCurve family of radio ports provides choice and flexibility to
address a wide range of deployment needs. Network architects can choose between flexible
dual radio (802.11a and 802.11b/g) and highly cost-effective single radio (802.11b/g)
designs, integrated or external antenna configurations, as well as customized housings for
office area and in-ceiling deployment. Installation is as simple as plug-and-play. The Radio
Ports include the following:
• Radio Port 210: Single radio 802.11b/g Radio Port with integrated diversity antennas
• Radio Port 220: Dual radio 802.11a + b/g Radio Port with external antenna selection,
• Radio Port 230: Dual radio 802.11a + b/g Radio Port with integrated diversity
available for both radios ProCurve Access Point 530— The ProCurve Access Point 530 is
a dual-radio 802.11b/g and 802.11a/b/g access point that offers flexible radio and antenna
configuration, security, user authentication and IDM-driven access control policies ideally
suited for small branch or satellite offices. The Access Point 530 supports both WMM and
The Access Point 530 can deliver simultaneous dual 2.4 GHz radio operation, allowing for
one radio to be dedicated to voice clients, while the other radio can service data traffic and
periodic rogue AP scanning. This capability addresses a key challenge in running VoWLAN:
in order to achieve QoS, the network must avoid interference between voice and data
packets. In dual 802.11b/g mode, the 530 virtually eliminates the possibility of voice/data
packet interference, thereby improving voice quality and performance. The 530’s dual
802.11b/g mode also holds a financial benefit to companies, particularly companies seeking
to extend wireless voice and data coverage to a large number of small branch offices.
Deploying a single 530 to each office, rather than having to use two separate access points,
or a more complex controller-based system, can significantly reduce the cost of deployment.
11. Usage Scenarios
School boards can use WiMAX networks to connect schools and school board offices within
a district, as shown below. Some of the key requirements for a school system are NLOS,
Fig8: Education network
high bandwidth (>15 Mbps), Point-to-Point and Point-to-Multipoint capability, and a large
coverage footprint. WiMAX-based education networks, using QoS, can deliver the full range
of communication requirements, including telephony voice, operating data (such as student
records), email, Internet and intranet access (data), and distance education (video) between
the school board office and all of the schools in the school district, and between the schools
Government agencies, large enterprises, industrial campuses, transportation hubs,
universities, and colleges, can use WiMAX networks to connect multiple locations, sites and
offices within their campus, as shown below. Campus systems require high data capacity,
low latency, a large coverage footprint, and high security:
Fig9: Campus connectivity
Service providers use WiMAX networks to deliver service to underserved markets in Rural
areas and the suburban outskirts of cities, as shown below:
Fig10: Rural connectivity
The delivery of rural connectivity is critical in many developing countries and underserved
areas of developed countries, where little or no infrastructure is available. Rural connectivity
delivers much-needed voice telephony and Internet service. Since the WiMAX solution
provides extended coverage, it is a much more cost-effective solution than wired technology
in areas with lower population densities. WiMAX solutions can be deployed quickly,
providing communication links to these underserved areas, providing a more secure
environment, and helping to improve their local economies.
As shown in the preceding sections, WiMAX technology and products are poised to address
a wide range of applications and usage scenarios, over a broad range of markets and
geographies. The above usage scenarios should be considered representative, not
comprehensive. As noted in the Introduction, the length of this paper precludes a discussion
of all possible usage scenarios, and my focus has, by necessity, been limited to fixed and
portable usage scenarios.
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