The Tait AS-IP solution uses significantly less equipment than a typical analog simulcast network solution because the voting and site control is already included in the TB9400 base station with intelligent resiliency.
An integrated solution reduces the possible points of failure, increases the reliability and therefore reduces maintenance operating cost. For example, the network is resilient to minor changes to link timing without additional equipment.
The Tait AS-IP provides connectivity with the IP network for simplicity. The TB9400 base station integrates a linear PA, used for P25 LSM (Linear Simulcast Modulation). This feature greatly improves inter-site separation network design.
The IP backbone interconnects the various elements of the network. It is a dedicated, private wide area network, which can be interfaced via a secure firewall to the organization's LAN.
Secure remote access to the network can be provided over the public Internet. The backbone consists of COTS IP-based building blocks. The public Internet itself is generally not suited to provide that backbone as it cannot guarantee performance or provide a high level of security.
A basic AS-IP network consists of a number of sites, with each site housing several base stations (one for each channel) linked via IP/Ethernet to form a local area network. For synchronization each site also has a GPS timing unit. The base stations are grouped together to form channel groups.
One of the base stations in a channel group is declared as the master and the other base stations are the satellites. The master controls the operation of the channel group and performs centralized voting. Transmissions are synchronized which means that the transmitters transmit exactly in unison. The master timestamps the voted voice signal to be transmitted and sends it to all channel group members.
The timestamp tells members when to transmit each voice packet. Each channel group requires its own console system which can be either a dispatch console connected to the central site via a console gateway, or an RF console which is a mobile on a desktop. The RF console allows the use of voice inversion scrambling.
GPS Timing Units
A GPS timing unit is located at each site. Simulcast networks must have a GPS-disciplined external frequency reference, a GPS-derived 1 PPS signal and access to an NTP server. The 1 PPS timing pulse and NTP ensure that simulcast transmissions from each physical site in the channel group are aligned with microsecond precision.
All base stations need to be connected to the GPS timing unit, and it is recommended for the console gateway to be also connected to NTP.
One GPS timing unit can support up to eight daisy-chained TB9400 base stations.
The console gateway consists of a TB9100 base station equipment used as a console gateway TN9110. Like the TB9400, it is also a common P25 equipment fully re-usable.
The console gateway can be managed remotely from a PC using a Windows application called the Customer Service Software (CSS).