Revenue by segment
Fiscal Year Ended March 31, 
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)
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 .

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)