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BUILDING LARGE CAMPUS ASTERISK-BASED PABX SYSTEMS 1.0 Background The abundance of Local Area Networks such as those found on most African Universities, and recent advances in Computer and Telephony integration has further created the opportunity to explore multimedia (voice in the first instance) to enhance communication in medium and large organizations, such as academic institutions. IP based telephone systems are increasingly becoming attractive due to 1. The proliferation of IP based networks, and the added advantage that such networks are always on 2. The expensive cost models of circuit switched telephone networks, which discourages extended use of such networks 3. Availability of Free and Open Source Telephony toolkits such as the Asterisk Open-Source PBX software. 4. Abundance of inexpensive interface hardware such as those of Digium, Sangoma, Grandstream etc. This write-up outlines an IP technology-based, scaleable and cost effective PABX switch solution that is being developed and maintained by the Telephony Group of General Data Engineering Services, Ibadan – Nigeria (aka SKANNET). It is suitable for medium to large campuses, and incorporates all the features available in large enterprise telephone switches.
2.0 PABX Architecture The PABX system is based on the Asterisk Open-Source PBX Software, using industry grade interface equipment. It is engineered to a high degree of reliability and simplicity. The architecture achieves Voice communication via Internet Protocol (IP) and Time Division Multiplexing (TDM) using an incremental implementation approach. This allows organizations protect their investments in existing cable plant, yet maintain high level of user satisfaction because they (the organization) can move to VoIP at a convenient pace using their networking infrastructure and IP services as a solid foundation for the PBX implementation. SKANNET PABX solutions are modular in nature, allowing incremental PABX system configuration for high quality voice over an IP network on one side, and an optional trunk side of the existing Infrastructure. (Circuit-Switched PSTN and or existing PABX where it exists). For example, a single CPU with channel Banks (CB) can serve as the PBX, which can then be expanded to serve multiple configurations and specifications. A clustered or distributed topology of PBXs can also be used, to expand to the number of lines and connections required. 3.0 PABX Features IP based PABX systems enable businesses have a very simple, reliable, robust, easy, expandable and feature-rich PABX. Organizations can enjoy the benefits of cost savings via the enhanced capabilities of VoIP.
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Asterisk-Based PABX Solutions meet the specific needs of businesses while keeping expenditure to a very low level, guaranteeing the protection of investment. Enterprises can migrate at the pace that best suites their needs, reaping the many benefits of VoIP without compromising their vital communication service. With value added applications such as voicemail, the PABX helps organizations lower their total cost of ownership and improve user satisfaction. Features that are matured and easily customizable include: • Multiple Technology Dialing Application, which makes it possible to make calls through the PBX system using either soft phones or hardware phones. • Voicemail:, which allows user to have personal mail boxes which could only be accessed either through the phone, or via the web. Call Transfer and Call Conferencing, which allows users the freedom of who to include in a conversation. With the conferencing feature, users can talk to multiple callers at the same time. Enterprise-wide directory lookup feature, based on LDAP databases, or global ENUM Access to global VoIP services, for affordable International communications. Call Detail Recording, which logs and reports all incoming and outgoing calls for proper accountability. Interactive Voice Response (IVR) system, which allows voice prompts for selecting various options. 4.0 Sketches of Sample Configurations 4.1 Basic IP Configuration (No Telephone Wires) Following the server/Client model, all computers on the organization’s network can utilize soft phones to make and receive phone calls. This solution expects that the computers have audio capabilities.
CallProcessor
Workstation 1 Workstation 2
Workstation 3
Workstation 4
Workstation 5
Workstation N
Computer based PBX Network (No Telephone Wires)
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4.2 Small Office Configuration The Small Office Configuration, apart from offering the entire configuration option available in 4.1 above, also has the capability to connect to the PSTN network, via the Plain Old Telephone Interface (POTS). Phone boxes can be connected, which can operate independently from a computer.
Call Processor PSTN(2 Lines)
2X8 Deployment Fig 1
Line 1
Call Processor
Line 7 Line 8
PSTN(8 Lines) 1 2 3 4
16
8X16 Deployment Fig 2
Line 1
Call Processor
Line 15 Line 16
PSTN(16 Lines) Channel Bank
1 2 3 4
24
16X24 Deployment
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4.3 Enterprise PABX Solutions Designed for large companies existing with high telephone structures with high telephony requirements, the enterprise solutions have multiple call processors and can be scaled to whatever configuration is required. Where TDM technology is employed, conversion from IP to TDM can be centrally located, or dispersed, depending on the existing cable plant structure. Example configurations are 16X24 – Up to 16 PSTN lines, and 24 Extensions 24X120 – Up to 24 PSTN lines and 120 Extensions 24X240 – Up to 24 PSTN lines and 240 Extensions 48X240 – Up to 48 PSTN lines and 240 Extensions 48X480 – Up to 48 PSTN lines and 480 Extensions 96X960 – Up to 96 PSTN lines and 960 Extensions 96X1920 – Up to 96 PSTN lines and 1920 Extensions
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4.4. Multi-Location System This configuration is ideal for Institutions or organizations who have multiple campuses, all linked by IP, or different organizations who want to share a common telephony system, probably because of the volume of calls that they exchange at any point in time. The Basic requirement is an existing IP network. Cluster A
Cluster B
Sokoto
Calabar
Cluster C
Lagos
Hybrid PBX
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5.0 Costs Since scalability is a very important component of the Asterisk-Based system, the following are sample ball-park costs, and means of estimating the cost of a typical installation, based on the types of equipment employed. The Following table lists the various components, their costs, impact in terms of lines and Extensions, and the configuration in which such equipment can be used. Most of these costs are from popular VoIP online supplystores. The costs are exclusive of shipping and duty to the destination country
Call Processor 1-4 POTs Interface Card 1-24 POTs Interface Card 1 TDM Interface Card 1-4 TDM Interface Card IP to TDM Converter TDM to POTs Converter IP to POTs Converter IP Phones
USD ($) Extensions Useful in Configs Min Cost Max Cost Minimum Maximum 4.1 4.2 4.3 4.4 $1,500.00 $2,000.00 1 144 Y Y Y Y $120.00 $400.00 1 4 Y $550.00 $1,800.00 1 24 Y Y $600.00 $900.00 1 24 Y Y Y $1,400.00 $1,800.00 1 96 Y Y Y $1,000.00 $1,400.00 1 24 Y Y $1,400.00 $1,900.00 1 24 Y Y Y $58.00 $320.00 1 144 Y Y Y Y $100.00 $400.00 1 144 Y
6.0 References http://ws.afnog.org/afnog2004/t2/930-telephony/telephony.ppt 1. 2. http://www.digium.com 3. http://www.asteriskpbx.org 4. http://voip-supply.com
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