Home' RTCA Documents for Review : DO-230H FRAC Contents 251
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Certain operational upgrades, such as increased memory and processing power on the network routers and
switches, may also be required during the network lifetime, but none of this should require a radical
overhaul of the network infrastructure to support projected growth during the network’s lifetime.
The operating environment must ensure that the existing systems maintain their access security for the local
environment while they are interconnected to the central or regional center. Provisions for the networking
environment must include local, regional, and/or centralized management and control of the ISSA via the
Prioritization of traffic, preferably developed from a security system operational analysis prepared for the
ConOps, must be designed into the proposed network infrastructure. Mission-critical traffic should be
identified and afforded the highest level of availability, redundancy and resiliency in network resources.
The ISSA availability goal in a shared IT network environment should be at least 99.9 percent. For most
ISSA applications, this will require IT network availability of 99.99 percent or higher depending on the
network architecture and the network resources required to support the ISSA. When this level of network
availability is not possible, the ISSA design should focus on ways of attaining close to zero down time for
critical security functions, including information flow to incident responders.
Average, minimum, and maximum response time goals, to be determined during the requirements process,
must be maintained throughout the operations period of the network including periods of moves, additions,
and changes that impact database records.
The network should be sized to have enough excess operating capacity to maintain the initial operating
traffic parameters (to be determined) and accommodate sustained peak loads during download/upload of
information without impact on operational response times. In addition, there must be reserved capacity for
traffic reroutes during the failure of an inter-connecting node within the network.
Priority reserved capacity (outside of the excess capacity for peak operations) is required for periods of
National Emergency to allow multiple locations to be accessed from a central command center to coordinate
database lookup and updates.
Target values should also be set for network availability or downtime, in unambiguous terms and including
how such targets are to be validated and tested. In a shared IT environment, where security is one of several
applications on the network, IT policies for availability and downtime should be revised against security
requirements, including zero downtime for critical functions.
The following steps provide guidelines for approaching the fundamental tasks of the design process:
Determine those performance parameters which best specify each of the design goals; for example,
application response time, percentage packet loss, latency, and application availability.
Identify the scope of design constraints such as budget, implementation timescale, support of legacy
equipment, incorporation of specialized departments that require unique network specification, and
policies resulting from a shared IT environment.
Set target values for the relevant network performance parameters in the context of the identified
Start with high-level design to resolve major issues such as the selection of WLAN technology,
equipment, and user permissions; the IP addressing plan; the degree to which routing is used instead
of switching; backup and recovery provisions and procedures; etc.
Formulate a network architecture which combines the best features of distributed nodes and edge
devices and centralized management. Edge devices are especially useful for high bandwidth
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