Communication Black Holes in Ground Segment Networks

Kurzfassung

The ISS Columbus Ground Segment is a complex MPLS-based WAN communication network witch connects sites located in USA (NASA), Russia (RSA), France (ATV-CC), Germany (COL-CC) and several user centres across Europe (network consists of more than 17 sites). For the communication between the different control centres and facilities a proprietary network is used. This network is called IGS (International/interconnected Ground Segment). The Columbus IGS WAN was migrated - in 2007/2008 - from ATM/ISDN-technology using presently MPLS as network communication platform. The change in the technology used for the network communications implied big changes in the concept used to support operations. The migration from ATM/ISDN to MPLS reduced the communication costs and a made a new technology available, but implied also new challenges while delivering quality assured end-to-end operational services. Here we would like to address one challenge resulting from the usage of complex network communication structures and protocol interactions in the MPLS backbone network that may result in complete “silent” outages of communication between various sites. The silent outages also called “black holes” are outages that are not discovered by the “normal” network monitoring tools as the network and physical layers are still operational. Communication “black holes” in most cases are not seen by network monitoring instances – therefore their detection, localization and elimination is a time consuming process needing often also manual intervention correcting them. For critical operations they represent a risk that needs to be addressed. In this article we will present the reasons why such outages occur together with their effect on network availability and operations. We also describe how such events can be detected and - in case of redundant sites - automatically bypassed. The presented procedures and event avoidance is IGS-WAN network specific but the experience gained here can definitely be implemented in other proprietary networks.