Home' RTCA Documents for Review : DO-230H FRAC Contents 258
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protocols such as Pragmatic General Multicast (PGM) have been developed to add loss detection and
retransmission on top of IP multicast.
IP multicast is widely deployed in enterprises, commercial stock exchanges, and multimedia content
delivery networks. A common enterprise use of IP multicast is for IPTV applications such as distance
learning and televised company meetings.
Multicasting implementations must be carefully engineered to avoid compromising switch performance,
including increased overall latency for all data across the fabric and undesirable losses in quality of service.
Virtual Private Network (VPN)
Virtual private networks ensure privacy and confidentiality of information using encryption. When a VPN
transmits information from one location to another, the VPN gateway at the first location encrypts
information into cipher-text before sending it on the Internet. At the other location, the receiving VPN
gateway decrypts the information into clear-text and sends it to the LAN. The system designer must first
identify and assess the needs of remote users, then specify the technology which best meets these needs:
IPSec-based VPN requires that software be pre-installed on remote users’ machines that may add
additional steps in order to gain access to the network.
SSL-based VPN uses a Web browser and an SSL connection to establish the connection, does not
require any software installation on remote PCs, can be less expensive to implement and/or operate
than its IPSec counterpart, but with tradeoffs that may limit how well it can address remote access
needs (e.g., many implementations do not permit a user to map drives directly and this limits the
user to whatever Web-based applications the IT Department has adopted)
If the network includes wireless services to be delivered to mobile ISSA responders and other persons
having PDAs and/or vehicles equipped with laptops who were not known when the VPN links were
established, the SSL-based VPN may be the best approach by virtue of not requiring the prior installation
of client software.
Network Backbone and Infrastructure
For a networked ISSA, information will be transmitted over a fiber optic backbone and over structured
copper cabling consisting of vertical segments from telecommunications rooms to distribution panels or
rooms and horizontal cabling to wall or floor plates serving end user devices.
Specifications should reference IEEE and TIA fiber and copper cabling for backbone, the structured copper
cabling, their terminations in telecommunication rooms, and how the cables are to be installed and tested.
The provisioning of fiber cabling and copper outlets should anticipate future service requirements and
network growth derived from a design requirements analysis.
Logical diversity and physical diversity should be considered in designing telecommunications rooms,
including network data centers and the telecommunications room which serves as the telephone M/POP
(Minimum Point of Presence). Logical diversity is relatively easy to specify. Physical diversity is often
costly, and its costs should be weighed against potential gains in system availability for likely disruptive
CCTV cameras which are networked may use copper or fiber to connect to an edge type network appliance,
the choice being driven by distance and cost considerations.
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