ViaSat ArcLight, Руководство пользователя, Страница: 62 / 368

ArcLight Hub User’s Guide
General System Description
1-26 1081006 Rev. 001
summary message. The dummy packets are constructed in the same
fashion as a traffic packet would be from that VMT (i.e. “xft2” dummy
packets will not work since the VCI is hardcoded for all VMTs). Also,
the destination IP address is selected so that the packet is routed
through the physical layer to the hub but does not exit the router to the
internet.
1.5.3 User Traffic management
The basic user traffic routing in the ArcLight hub is divided into two
directions; to the VMT and from the VMT, and segregated into two
protocol types; TCP and non-TCP. IP traffic from the Internet or a
private intranet, enters the hub through the enterprise router, which is
part of the Routing and TCP PEP subsystem. The router determines if
the IP traffic is TCP or non-TCP by using Cisco’s policy routing
capability. Non-TCP traffic for the VMTs is forwarded directly to the IP
encapsulator in the uplink chain, and from the encapsulator to the
modulator.
IP traffic from the VMTs arrives at the MCD encapsulated in ATM cells.
The ATM encapsulation is removed by the MCD and the reassembled IP
packets are forwarded to the router, or to the local host at the hub,
based on their IP destination addresses. TCP traffic from the VMTs
usually arrives encapsulated in UDP packets. Non-TCP traffic from the
VMTs arrives with the final destination IP address and is forwarded to
the router for additional handling. Figure 1-12 shows the user traffic
flow through the ArcLight hub for TCP and non-TCP traffic.
Figure 1-11. IP Traffic Diagram (Non-TCP).