Enterprise users demanding high Quality of Service (QoS) together with high network availability rely on satellite broadband solutions from Hughes. To ensure the highest level of network availability, the Hughes HN and HX satellite broadband systems can be configured with a redundant hub which is geographically separate from the primary hub, and operating either in a hot standby or in a load sharing (diversity) mode. This paper describes the two available modes of implementing geographic hub redundancy.
This geographic redundancy is above and beyond the full and automatic component redundancy designed into the HN and HX hubs. The redundancy features discussed in this paper address potential network problems, such as significant rain fade at the hub station itself; failure of the hub station RFT equipment; or even catastrophic loss of the entire hub teleport. The essence of these redundancy features is to utilize geographical diversity of the hub stations to ensure continuous operation in the event of either rain fade or a catastrophic failure at one of the hub stations.
Modes of Operation
The modes for enabling geographic redundancy are:
- Automated Hub Redundancy (AHR). This mode of redundancy calls for two identically configured hubs, one operating “online” (supporting all the network traffic) and the other operating “offline” (in hot standby). In the event of rain fade or even catastrophic failure at the online hub, the offline hub is quickly activated and assumes all traffic load for the network.
- Hub Diversity. This mode of redundancy calls for two hubs to be simultaneously operational and sharing the network traffic. Remote terminals can be configured to “prefer” one of the two hubs, and are entitled to move to the alternate hub in the event of a failure at the preferred hub. Lower value remote terminals can be assigned to operate exclusively on only one of the hubs.
It is important to note that these modes are mutually exclusive and cannot coexist. In either case, after a remote terminal is switched from one hub to the other, it can be activated immediately on the new hub without the need for ranging and commissioning.
Automated Hub Redundancy
Automatic Hub Redundancy (AHR) is the mode where two hubs are installed in geographically separate locations. At any point in time, one of the hubs is online and the other is offline. In the event of a failure (or impending failure) at the online hub (for example, due to rain fade), the operator may initiate a switch to the offline hub to allow network operations to continue. Figure 1 illustrates the AHR setup.
The two hubs are identical with respect to all their baseband and IF equipment, and are functionally identical with respect to their RFT equipment. Identical configurations are used so that both hubs are capable of being fully operational without sacrificing traffic quality, or requiring reconfiguration of the hub equipment.
A terrestrial link between the two hubs is used for the command to activate the redundancy switchover. The terrestrial link also enables the synchronization of the databases so that changes made to the online hub are synchronized with the offline hub.
The time for completing the redundancy switchover is approximately 10 minutes. The process of hub redundancy switchover involves the following sequence of actions:
- Online hub goes offline.
- Remote terminals lose the outbound channel
- Offline hub goes online
- Remote terminals acquire the outbound channe
- TCP sessions are restoredl
In addition to the normal mode of AHR for rain fade conditions, the capability exists to force switchover in the event of a catastrophic loss of the online hub. This “failover functionality” allows the offline hub to be independently switched into active operation.
The Hub Diversity mode (sometimes referred to as “NOC Diversity”) allows two simultaneously active hubs to co-exist and manage a single Hughes HN or HX network. The remote terminals in the network will be configured to prefer one hub or the other, and may be configured to switch to the other hub in the event of a hub or transport failure. Remote terminals considered to be relatively low value can be configured to operate on only one hub and not be allowed to switch. Figure 2 shows the network layout for Hub Diversity.
When employing the Hub Diversity feature, the primary and secondary hub roles are fixed at the time of installation, and all terminal configurations are performed through the primary hub.
Remote terminals may be designated as one of the following:
- Assigned exclusively to the primary hub
- Assigned exclusively to the secondary hub
- Diverse (able to connect either to the primary or secondary hub)
Diverse remote terminals typically can switch to the alternate hub within approximately 3 minutes, during which time connectivity is lost.
In summary, Hub Diversity in the Hughes HN and HX Systems enables satellite broadband operators to provide their customers with a premium offering of remote terminals that are diversity-capable.
Both the Automated Hub Redundancy and the Hub Diversity modes require a terrestrial redundant LAN connection between the hubs in order to synchronize the databases. Automated Hub Redundancy also requires the Oracle Enterprise Edition to synchronize the databases.
The table below lists the HN and HX System releases supporting redundancy features: