Local Area Networks (LANs) in Aircraft - FTP Directory Listing - FAA

Consequently, protocol translation gateways have repeatedly been shown to have high
operational overhead, often requiring significant administrative oversight even when translating
between two such similar systems. Most other legacy systems are significantly different from
TCP/IP than CLNP/TP4, which increases the difficulty of doing protocol translation between
them. This often results in the need for increased administrative oversight of those translation
gateways for them to remain operationally viable over time.
4.7.1 Significant Semantic Differences to Allegedly Similar Concepts.
Figure 10 introduced the concept that different protocol families can be connected into the same
network system by leveraging protocol translation gateways. This section discusses protocol
translation gateways themselves. The key point of this section is that even when protocol
families have similar concepts, there are often subtle but important differences between the
semantics of those concepts within the protocol family milieu in which they operate that
obfuscate translations between these protocol systems. For example, it was previously explained
how the OSI CLNP/TP4 variant that the ATN network uses is based upon TCP/IP. Despite the
great deal of similarities between these two approaches, section 4.7 stated that the protocol
systems are not mutually interoperable nor do they have identical underlying protocol state
machines, which causes some translation difficulties for the protocol translation gateway.
4.7.2 Integrating Dissimilar Protocol Families.
As was mentioned in section 4.7, deployments that seek to integrate multiple different
communication families into an interoperable network traditionally accomplish this via common
mechanisms. This section discusses these generic mechanisms in terms of a notional airborne
infrastructure that includes both military and civilian aviation protocol systems.
Figure 12 shows that environments that do not try to connect their dissimilar network families
into a common structure have created a deployment characterized by “islands of
communications.” For example, military Link16 communicating systems are only natively able
to communicate with other Link16 devices, but not with HAVE QUICK or Link4 devices.
These islands of communications are traditionally bridged by protocol translator gateway
devices (depicted as G/W in figure 12). As was previously mentioned, protocol translator
devices are operationally expensive to deploy and require an unusual amount of administrative
attention. They also create single points of failure, communications bottlenecks, and deprecate
(e.g., added extra latency and processing needs) the total system performance. Nevertheless,
these devices are an essential part of bridging islands of communications, at least initially, for
environments that (1) have network-centric operations requirements, (2) have requirements for
humans or applications to communicate between (or across) these islands, or (3) have
collaborative requirements to communicate with entities beyond the communications reach of
legacy protocol systems.
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