Revenue by segment
IBW segment revenue decreased $10.8 million, in fiscal year 2019 when compared to fiscal year 2018, primarily due to lower sales of DAS conditioners, commercial repeaters, and related ancillary products (passive RF system components and antennas).
Lower sales of DAS conditioners, which includes our Universal DAS Interface Tray (UDIT) active conditioner, were the largest contributor to the year-over-year decline. The overall market for these stand-alone conditioners is expected to continue to decline over time, as their key function, the attenuation of the RF signal from its high-power source to low-power required for a DAS, becomes more integrated into the DAS head-ends themselves (or in some applications, a low enough power level may already be provided by the RF source). Further, in the fourth fiscal quarter of 2018, one service provider that had previously been a large UDIT buyer made an unexpectedly abrupt network architecture shift to an alternative, non-DAS solution for their in-building coverage. This resulted in an even sharper decline during fiscal year 2019 compared to fiscal year 2018. We expect the current lower levels of UDIT revenue to be flat-to-down in the future, with its primary market coming from capacity expansions at existing sites where embedded DAS networks included UDIT.  Lower sales of DAS conditioners, which includes our Universal DAS Interface Tray (UDIT) active conditioner, were the largest contributor to the year-over-year decline. The overall market for these stand-alone conditioners is expected to continue to decline over time, as their key function, the attenuation of the RF signal from its high-power source to low-power required for a DAS, becomes more integrated into the DAS head-ends themselves (or in some applications, a low enough power level may already be provided by the RF source). Further, in the fourth fiscal quarter of 2018, one service provider that had previously been a large UDIT buyer made an unexpectedly abrupt network architecture shift to an alternative, non-DAS solution for their in-building coverage. This resulted in an even sharper decline during fiscal year 2019 compared to fiscal year 2018. We expect the current lower levels of UDIT revenue to be flat-to-down in the future, with its primary market coming from capacity expansions at existing sites where embedded DAS networks included UDIT.
Lower sales of commercial repeaters, while still a reliable and proven solution for amplifying cellular coverage inside a building, are reflective of the continuing downward-demand trend as our larger customers have had a stronger preference for small cells to provide in-building cellular coverage. We expect this trend to continue.
The decrease from ancillary products (passive RF system components and antennas) revenue is largely a function of the decline in sales of DAS conditioners and commercial repeaters. Future ancillary product revenue can follow the same flat-to-down trend as DAS conditioners and commercial repeaters, or potentially increase in tandem with an increase in public safety revenue.
In fiscal year 2019, the Company spent considerable resources, with a partner, to bring a new suite of public safety products to market. When compared to our current public safety repeaters, these products would include additional capacities, frequency ranges, features, and channelization that would significantly expand our offering to a larger public safety addressable market. We continue to work with our partner on product testing and delivery time frames and, if successful, we would expect future revenue growth in this market.
ISM segment revenue decreased$2.1 million in fiscal year 2019 when compared to fiscal year 2018. The year-over-year decrease was primarily due to a decline in deployment (i.e., installation) services revenue. Deployment services revenue had been largely dependent on one domestic customer that continues to buy our ISM remotes and support services but that, subsequent to a price increase, no longer places orders with us for deployment services. Secondarily, the ISM revenue decrease was also attributable to lower sales of our Optima network management software. Due to the project-based nature of our ISM business, it is difficult to make a determination on future trends.
CNS segment revenue decreased$2.1 million in fiscal year 2019 when compared to fiscal year2018, due primarily to the expected lower sales of integrated cabinets, which are heavily project-based and historically high in customer concentration. There was a significant decrease in fiscal year 2019 from two of our historically larger customers for integrated cabinets - one where we customized integrated cabinets for a neutral host operator providing wireless coverage in the New York City subway and the other, a rural broadband service provider.
The expected lower sales of T1 NIUs and TMAs, as the products serve declining markets, also contributed to the CNS segment revenue decline.
Partly offsetting the declines from integrated cabinets, T1 NIUs, and TMAs, was increased revenue from our copper/fiber network connectivity products as well as revenue from products newly introduced during fiscal year 2019 as part of our fiber access growth initiative.
For CNS, we expect fiber access revenue to grow; power distribution and network connectivity products to remain flat; T1 NIU and TMA revenue to continue to decrease; and sales of integrated cabinets, which are heavily project-based, to remain uneven.
Table:
Revenue by segment |  | Fiscal Year Ended March 31,  | Increase (Decrease)
(in thousands) | 2019 | 2018 | 2019 vs. 2018
IBW | $12,474 | $23,265 | $(10,791)
ISM | 17,263 | 19,350 | (2,087)
CNS | 13,833 | 15,962 | (2,129)
Consolidated revenue | $43,570 | $58,577 | $(15,007)


Question: Why did IBW segment revenue decrease in 2019 compared to 2018?
Answer: lower sales of DAS conditioners, commercial repeaters, and related ancillary products (passive RF system components and antennas)