In late 1970s to late 1980s, ATT offered a pure private line digital data service called Dataphone Digital Service, or DDS. Supported rates of 2.4, 4.8, 9.6, and 19.2 were standard with higher rates such as 56kbps; and nx56kbps also possible but rarely. These circuits although legacy, are still quite common today – because they really work. Specialized channel cards called OCU-DP (Office Channel Unit Data Port) are connected to standard CSU/ DSUs with datacomm interfaces.
Both synchronous and asynchronous data is formatted and fit cleanly into a 64kbps time-slot (by repeating the data bits or bytes). The bit repetition had the added advantage of providing error correction and thus better performance. The channel data is then inserted into time-slots of a standard T1. In this manner many data circuits can be packed into a private line T1.”
“GL supports non-intrusive monitoring and analysis of DDS frames using T1 Analyzer hardware. The captured data can be decoded and analysed by GL’s DDS Protocol Analyzer,” Vijay Kulkarni, the CEO of the company said, “Non-intrusive TAPs are used to passively duplicate the signal between two end points on a network link without disturbing the actual network activity. GL’s T1 Analyzer hardware can be used with RJ48 Y Bridge – splits one RJ48 into two complete and non-intrusively tap and capture the DDS frames on a T1 line.”
He added, “The DDS data is formatted into frames separated by one or more bytes. The data channel may utilize multiple, all or a fractional timeslot of the T1 line. Also, there may be multiple data channels within the T1 line. The captured data is analyzed using GL’s DDS Protocol Analyzer.”