Call records (or CDR - Call Data Record)) are the raw material from which a telephone management service produces reports. No data quite simply means no reports and incomplete data gives useless reports. Data Acquisition is an engineering discipline in itself and is sometimes taken for granted by the industry as a whole.

Each call data record CDR has a real value as it contributes to the accuracy of the Telephone Management system as a whole. If call records are lost the accuracy of reports suffers as a consequence.

A PBX outputs CDRs by one of three methods, IP data, Serial data and as a file. Each format must be handled very differently.

Via Serial

Using an RS232, the specification limits the cable length between the sender and receiver to 15 meters. In reality this can be much further, and can often work up to distances of 50 meters. However for reliable transfer of CDR we should stay within the recommended limitations.

IP data:

Within this category there are two methods. The first, a PBX may produce call records and simply drop them onto the network in addressed packets. This method has no service guarantees at all. Taking this method to the extreme, it is possible to transport addressed packets over the Internet however, with valuable data, this is unreliably and not recommended. Even data transported over an Intranet in this manner may suffer from packet loss and therefore the Telephone Management system useless. The second method uses hand shaking between the devices creating a reliable data collection channel.

Via a File

Usually found on server based PBX, for example Asterisk, the PBX writes CDR to a file in a shared directory, where the Telephone Management system can access the data.

Both IP and serial data delivery methods need addition equipment for dependable data acquisition. This equipment is designed to receive call records, store them safely and then transport the data reliably to the host application. The device is called a 'call buffer', or 'data collection device'.

Types of call buffer

Serial data in - Serial data out. The device receives call records at a particular baud rate store the data until the host application is ready to receive it, then forwards it a baud rate suitable to the host.

Serial to IP: This device collects Serial data, converts it to IP and drops packets onto the network in the form described. This type call buffer is only suitable for transporting the data to a technologically close (on the same local area network) Telephone Management system. CDR transported over an Intranet or the Internet in this manner will suffer from packet loss.

Internet enabled device. This data collection device will receive either IP or serial data, store it and then send it to an Internet based telephone management service . The device uses secure protocols to ensure dependable data delivery.

Data collection devices come in the form of either a solid state ultra reliable purpose built box, or can be a software program running on a PC within the client environment.

The price of Data Collection Devices varies wildly between suppliers with a high of around US$500 and a low of US$200.