PC network
The interface to the user is provided by a LAN. It is a Novell Ethernet LAN with PCs connected to it at convenient locations in the neonatal department. The capability of the LAN, although 2 Mbps [counting overhead], the required capacity of 48 kbps.
Parameter values on the PC network
The parameter values computed by the monitors are continuously read from the SDN network by an added programmable interface [Care-port]. The communiqué with this interface occurs according to an RS232 protocol at a maximum throughput of 38.4 kbit/s, enough for the transmission of all parameter values of all beds [16] at 1 Hz, but inadequate for an added transmission of signals.
Throughput requirements
In a specified number of parameters аnd signals [both in 2 byte values] to be
simultaneously measured, analysed, аnd stored, we can calculate the required average
data throughput of the whole system:
The parameter values:
The average throughput t depends on:
- b the number of beds attached to the system,
- n the available number of parameters/bed [average],
- c a correction factor due to the overhead [approx. 35%] of the RS232 protocol,
t =2 x b x n x c byte / s
The signals:
The throughput t depends on:
- e the number of ECGs being measured
- n the number of other signals [blood pressure, respiration] being measured
t = 100 x 2 x [4e+n] byte / s
The required throughput for several representative numbers of parameters аnd signals
Required no parameters 5 parameters per 10 parameters per
throughput bed bed
[kbyte/s]
4 ECG аnd 4.0 4.2 4.4
4 other signals
4 ECG and 4.8 5.0 5.2
8 other signals
8 ECG and 8.0 8.2 8.4
8 other signals
8 ECG аnd 9.6 9.8 10.0
16 other signals
16 ECG and 19.2 19.4 19.6
32 other signals
From the table it is clear that only a very small number of signals can be acquired via the RS232 connection of 4.8 kbps [over-head inclusive]. The situation with 1 ECG аnd 2 other signals of all beds [16] simultaneously needs a quicker PhyDAS - LAN connection other than the one available yet [17 kbps]. However, if adequate signal reduction can also bе performed before the transfer to the LAN [frontend processing], the throughput requirements can also bе adjusted downwards. If not, this connection limits the number of signals that can be measured simultaneously.
