Introduction
1-1
Section 1: Introduction
SDN System Description
The Serial Distribution Network (SDN) is a local area communications
network designed to share patient physiological parameters and other
data among bedside instruments, information centers (IC), recorders,
thermal printers, computer systems, and other information systems
connected to the system. The SDN is a digital communications network
that allows real-time transfer of digitized patient data between these
instruments. The communication protocol, data formatting, and hardware
implementation is intended to be flexible enough to accommodate a
variety of communication needs in the patient monitoring environment for
present and future expansion.
SDN
Components
The components of the SDN consist of the model 78581B Agilent CareNet
Controller (ACC), the SDN interface circuitry located within each
instrument connected to the SDN, and the system distribution cables
(branch cables), local distribution cables, and the associated wallbox
hardware, connectors and receptacles. The components of the SDN are
shown on page 1-2, and a typical SDN configuration is illustrated in Figure
1-2 on page 1-3.
SDN Operation
The SDN functions automatically without user interaction and without
direct patient connections. Digitized patient information from each
instrument (branch) is transmitted serially at regular intervals (called poll
cycles) over branch cables to the ACC. The ACC sequentially receives,
synchronizes, and rebroadcasts the digitized patient information to all
instruments connected to the SDN. This patient data is received for use by
each instrument via the SDN interface circuity resident in each
instrument. Patient data are not restricted or allocated by the network,
but are accepted from, and transmitted to, all instruments within the
system. Each instrument decides for itself which patient information it
wants to acquire and process. Each instrument gets a chance to transmit
and receive patient information every poll cycle. A poll cycle lasts 32 ms,
thus, there are approximately 32 poll cycles per second.
Digitized patient information transmitted over the SDN may be either
waveforms (for ECG, pressure, and respiration) or parametric information
(for heart rate/pulse, pressure valves, and respiration rate). The SDN data
transmission rate of 3.6 Mbits can provide up to 7700 usable 12-bit data
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