Design and implementation of analog telephone on IPPBX network interconnection

The use of PABX between buildings existed in State Polytechnic of Malang consists of 3 types, which are produced by the same manufacturer. However, the three types of PABX have different characteristics and specifications from one another. Therefore, its merging is done by numbering method which must use prefix to be able to contact users in other PABX. Every PABX is always provided with an interface that aims to combine with different systems, so that adjustments can be made. To overcome this problem, by software-based central installation, namely IPPBX, so that if the change (migration process) occurs, a device called the internet telephone gateway can be installed. This device with one IP address can connect more than one analogue telephone number. So far the product has 32 ports. This research uses ITG with 16 ports due to the connection characteristics of the same connector as the conventional PABX. This condition will be easily implemented and does not change the existing network system in State Polytechnic of Malang. The results of the design based on the number of connected services required a number of 32 devices ITG 16 ports plus 4 ports connection to the public services telephone network (PSTN).


Introduction
The PABX combined between buildings existed in State Polytechnic of Malang, are produced by the same manufacturer. The first modular design of the PABX Super Hybrid System and 8 lines to as many as 448 extensions and 192 CO lines by adding expansion cards (512 ports maximally). The system can be installed as one, two or three shelf configurations, providing economical expansion from 192 ports (1 cabinet) to 384 ports (2 cabinets). The second and third PABXs use the Pure IPPBX type, but differ in capacity as shown in table 1 and table 2 [1].  Therefore, its merging is done by numbering method which must use prefix to be able to contact users in other PABX. Every PABX is always provided with an interface that aims to combine with different systems, so that adjustments can be made.  To solve this problem, the PABX is replaced by the internet protocol private branch exchange (IPPBX) [2], so that all processes can be done automatically, by operating application software via the WEB Graphic User Interface [3].
Then without changing the existing cable network and telephone equipment, an IPPBX server can centrally be connected through the intranet computer network.
The application uses an internet telephone gateway, each of which consists of 16 ports instead of ESLC or SLC16 cards as much as the capacity has been installed with the basic network architecture as shown below [4].  Figure 2. Network model offered.

Method
The design and implementation in this research includes:  Selecting Internet Protocol Private Branch Exchange (IPPBX) devices that can register up to 800 users or more.  Designing and selecting the internet telephone gateway device that matches the previously replaced card.  Designing and implementing telephone networks using a computer network that is already installed.

Required device specifications
The IPPBX comes with an asterisk-based system, the IPPBX software, offering not only full PBX functionality, but also a new feature that enables new stability for your unified communication systems. It can seamlessly integrate VoIP trunks and your existing PSTN lines with 4 port analog connections and 2 Ethernet ports. They are developed with a wide selection of codecs and signaling protocols, including G711 (alaw/ulaw), G722, OPUS, AMR-NB/WB, SILK, G723.1 G726, G729, GSM, ADPCM, iLBC, H263, H263P, H264, VP8 [5]. Taking full advantages of open source platform, the IPPBX Series appliances support industry standard SIP trunks, IAX2 trunks, analog PSTN trunks, and analog station trunks. Moreover, with IPPBX system software, the fully featured IPPBX is an ideal solution for the office. Detailed device specifications are shown in table 3.

VoIP server settings
There are some configurable VoIP (SIP/IAX) Server templates on this page. The number of VoIP Server templates is the half of FXS ports on TA FXS Gateway. The VoIP server settings help the FXS ports to register to the VoIP server. After being configured, the templates can be chosen on FXS port setting page. There are 3 register modes for VoIP server. Users could select one mode for the VoIP server and apply it to FXS ports.
 Service Provider -IP Based VoIP Provider, do not generally require the TA gateway to register with the provider. Only IP address or domain is needed to configure on TA gateway.  Port Register -the VoIP server requires TA gateway to register with the provider  using an authentication ID and password. If you choose the VoIP server, you need to fill in User Name, Authentication Name and Password to register the FXS port.  Template Register -register to your VoIP server and apply the template to FXS ports. The FXS ports will register to the server with the same account.  Figure 5. VoIP server.

Architecture of plan.
This setting is to connect two or more servers that use Asterisk IP PBX (using Elastix version 4.0), so that dialling between extensions on both servers can be done easily, namely by simply pressing the extension number directly [6]. This method can still be used for 2 to 7 servers. The number of trunks that must be set up to produce a full mesh trunk network can be obtained by the formula: n x (n -1) Therefore, if we want to connect 7 IP PBX at once, it will take as much as 7 x (7-1) = 42 trunks. What needs to be prepared is as follows:  If the two sites are on two different networks / places / cities, it is recommended that connections between the sites use VPN (PPTP, L2TP, Open VPN, VPLS, MPLS, EoIP etc.). And if you really have to use a public IP address, put the IP PBX server under the router/ firewall and just do port forward (not 1: 1 Network Address Translated). Trunk using IAX2, port forwarding is easy because only one port is needed for signalling and media streams, the TCP / UDP 4569 port.  Extension number planning is very important because it is to facilitate the routing of calls. If you have two IP PBXs that you want to interconnect, use different extension heads, for example server A uses 4 digits with head 1 (1001, 1002, 1003, etc.), then server B uses 4 extensions with head 2 (2001, 2002, 2003, etc.) As an additional suggestion, or if the site reaches more than 7 and will still use interconnection this way, add extension digits, for example to 5 or 6 digits. Later it will be very helpful if we want to use additional prefixes (for example to trunk to PSTN / ITSP), or the number of sites reaches more than 10 sites. The reason for using IAX2 is because it only uses one port for signalling and media streams (SIP uses a different signalling port rather than the media stream), so that setting up a firewall is quite easy. Besides, IAX2 is indeed designed to overcome the NAT problem.

Results and discussion
The results applied two IPPBX interconnections. This system was divided into two groups of users. The first group was with 1XXX number of 216 extensions, and the second with 2XXX number of 301 extensions that could be registered. It was shown in Figure 5 above. The settings of each IPPBX are illustrated below.  The complete diagram of the results is described below.  Figure 9. Diagram of connection of full system design.

Conclusion
 This research uses ITG with 16 ports due to the connection characteristics of the same connector as the conventional PABX. This condition will be easily implemented and does not change the existing network system in State Polytechnic of Malang. The results of the design based on the number of connected services required a number of 32 ITG devices 16 ports plus 4 ports connection to the Public Service Telephone Network (PSTN). However, only 2 ports are used.  Some cables on the previous network could still be used.  A mobile phone can be used as an extension.