ETTC'2003 - SEE

L2/L3/L4 systems have to support ARP to solve the IP to MAC identification in Downloading Mode. L3
Switch also uses automatic learning from frames passing through it, to build its Unicast MAC table.
IENA SPECIAL FEATURES
Static Multicast
As seen above, the FTI LAN lies widely on Multicast addressing, which can be found in several
industrial applications, but more rarely with static configuration. Dynamic Multicast using IGMP was
prevented by some low-level technology L2 systems (without processor or Operating System). Static
Multicast also helps reducing damaging traffic of IGMP, what is always preferable for on-board real
time applications like Flight Tests.
Dynamic protocols de-activation
Even if some dynamic protocols are necessary for a good behaviour of the FTI LAN, there was a
constant search for reducing this kind of traffic to avoid disturbing the transfer of IENA packets. IGMP
(see above), STP, private protocols (CDP…) are therefore forbidden within the FTI LAN.
The only “extra” protocols supported by the network are ARP for Downloading Mode and ICMP for
debugging purpose.
IP Pin-programming
To avoid fastidious programming on board of the plane, most of the L2 systems integrate “Pin-prog
plugs” coding directly their Unicast Ip Address. This pin-prog allows these systems to be automatically
recognised on the LAN, and then to be downloaded via the network.
Network redundancy
Classically in FTI, the Mass Data Storage L4 is duplicated to ease data analysis and over all to secure
the installation. This redundancy can be easily extended to the FTI network itself : for the first A380
test planes, the L2 and L4 systems integrate a redundant Ethernet IO and the L3 are doubled. The
redundant L3 support the same commutation table as the first one, and the data flows are fully
identical on both networks.
Physical links
To take benefit of the new coming AFDX technology on A380, the same physical layer was chosen for
FTI LAN. The standard equipments (L3/L4) are customised to support the AFDX connectors and
cables. The cabling of the FTI is then identical as the one of the avionics systems, what eases the
cabling work at aircraft's assembly lines.
CHALLENGES
Technological challenges
At first, the ATM technology had been studied to forward IENA packets from L3-concentrator to L4
receivers.
This solution was given up for the benefit of a new architecture based on the use of switched
Ethernet. Several elements explain the abandon of this solution. First of all an ATM based architecture
is relatively complex to implement and expensive. Furthermore, the emergence of Ethernet as a
widely spread standard confirmed us in this way.
Quality of Service
The first need on FTI LAN is to ensure lost-less and guaranteed-delay data transmission between L2
and L4 : losses of data during Flight Tests could question the aircraft certification.
On one hand, PCM technology allowed a very controlled communication, based on synchronous
transmission with cyclic and predefined data exchanges, but performances are becoming insufficient
and communication is Half Duplex and mainly point-to-point. On the other hand, Ethernet brings
performance and flexibility in data transfers (asynchronous transmission, variable throughput…), but
needs to set up a real control of throughput, latency and non-congestion.
To perform this "QoS" management, the network statistics at L3 and L4 are re-injected at L2, and
treated as monitoring parameter of FTI network.