For years work on improving networks has focused on reducing the risk of disruption to a minimum. In terms of network concepts, this reduction can be realised by doubling the number of network connections, doubling the network equipment at core locations, splitting services across two nearby locations and using better protection/restoration mechanisms.
Reducing risk is also a factor in selecting hardware suppliers, with requirements that important equipment functions be resilient, such as double power supplies, redundant control cards, redundant switch fabrics and advanced protection schedules.
Such improvements have also been implemented in SURFnet7, such as double core switches, the redundant PoP roll-out, combined with availability requirements for the Carrier Ethernet switches.
Nevertheless, a significant risk of single points of failures (SPoFs) exists in the “invisible” link between the various network layers, such as the Ethernet layer, C/DWDM infrastructure and fibre. How does the Ethernet layer map on to the C/DWDM layer, and then on to the fibre footprint? This stacking of physical layers means SURFnet7 has fibre routes accommodating upwards of 20 links. These links may never be combined with either the primary or backup paths, as that may cause a SPoF.
Defining a SPoF-free path
There is also the ever-present risk of the geographic overlapping of different fibres, which can also result in a SPoF. Hence, the links running on these fibres must also never be combined in the primary and backup paths. Links that share a similar risk of a SPoF are categorised in the same Shared Risk Link Group (SRLG).
In the past few years, SURFnet has therefore ensured that more than 95% of fibre routes have been geographically mapped. It is precisely during the building phase of a new service when this geographic information should be used – preferably automatically – to define a SPoF-free path.
SPoF-free routing of a backup path in relation to the primary path
Two systems play a vital role here: the Configuration Management Database (CMDB, IMS application of VC4) the system that defines the entire SURFnet7 network, and the Network Management System (NMS), the system that builds the network services in SURFnet7.
With precisely the same geographic location of the fibres and configuration as the SURFnet7 equipment, CMDB has everything necessary to determine the SRLG groups using a SPoF algorithm. This list with SRLG groups is then automatically loaded in the NMS where the SURFnet7 IP and light path services are built,
creating a link between the geographic location of the fibres and the NMS logical path computation engine and revealing the stacking from physical to logical topology in the NMS. For each path computation that the NMS provisioning engine performs, the SRLG list is consulted in order to ensure entirely SPoF-free routing of the backup path in relation to the primary path.
Automated SRLG function
SURFnet7 customers that want to set up their own light path in the future using self-service cannot see the found path or its geographic location. SURFnet7’s built-in fully automated SRLG function is therefore an absolute must-have for end-users who want to operate the provisioning controls themselves.