Home' RTCA Documents for Review : DO-230H FRAC Contents 246
© 2017, RTCA, Inc.
The communications medium used in an ISSA should have the following characteristics:
Physical protection so as to prevent or delay access to the communications line and equipment in
Line security with reliable supervisory methods to detect and isolate communication failure thro ugh
equipment malfunctions and power failure.
Line integrity with proper installation practices and signal conditioning to eliminate external
Environmental protection of the communications system components against disturbances such as
electrical transients, electromagnetic interference, or radio frequency interference.
Wherever applicable, the ISSA owner shall ensure the communications cable medium is further
protected or supported by such physical objects as duct bank, pipe, conduit, inner-duct, cable
ladder, cable tray, etc.
If the ISSA is implemented on a WAN, then technologies such as VLAN, VPN, or encryption
should be employed to segment security traffic from that of other stakeholders and to secure the
traffic against accidental or deliberate unauthorized access.
Access to a WAN by a commercial telecommunications and network service provider should include both
guaranteed minimum bandwidth and guaranteed surge bandwidth, the latter to handle incident management.
The guarantees of bandwidth should be set forth in a written Service Level Agreement (SLA) with the
service provider to ensure sufficient bandwidth, network availability, and a secure data transfer, all of which
should be verified by periodic testing stipulated in the SLA.
In situations where high availability and high-speed bandwidth are required, a broadband
telecommunications infrastructure, such as Synchronous Optical Network (SONET) and Dense
Wavelength Division Multiplexing (DWDM) over fiber can be utilized.
It is imperative to set clear design objectives at the outset of the design process by identifying performance
parameters and setting target values, which will ultimately be dictated by the application requirements. To
assign meaningful targets, the application requirement should be expressed at both a quantitative and a
qualitative level, e.g., stating the transmission bandwidth needed for the application, its sensitivity to packet
loss, packet delay and variation in delay, etc. – which are especially important on IP networks that support
multiple heterogeneous applications including voice and video.
An ISSA can be network-based to operate over a LAN/WAN or over a private network. ISSA
communications should be scaled for the size and complexity of the system. Operational requirements for
voice, data and video services should be established before system design begins. Selection of system
architecture and system technologies should assure that the design will meet current requirements and be
scalable for future requirements; that it will perform reliably over its lifetime; and that support will be
readily available to diagnose and resolve system problems that may arise.
The process of translating system architecture into a design should address data integrity, data security, full
connectivity among all system components, appropriate system monitoring and diagnostics, and growth
potential. Where system components are supplied by different vendors, the design specifications must
provide for, and post-installation testing must validate that all components that are properly integrated and
realize the required performance. The system provider should also be contractually bound to support,
maintain and ensure that all components are properly integrated.
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