As it is also used in traditional telecom operator networks, MPLS-based traffic forwarding provides virtual tunnels to separate the traffic of different network slices as well as traffic classes. Each data packet is associated with an MPLS label, which is associated with a specific traffic class. Even when forwarded between the same radio nodes on the same radio links, a voice packet will experience different handling than a data packet and typically be transmitted first. Sophisticated traffic-engineering concepts ensure high network performance, efficient usage of available resources among multiple network slices, and provisioning of guaranteed end-to-end quality of service (E2E QoS) at the same time.
Transparent Layer2 forwarding, incl. support for IEEE802.1q VLAN trunking, ensures compatibility with a higher-layer protocol such as IPv4 and IPv6. To that end, segments of a WiBACK network form QoS-aware broadcast domains.
A WiBACK network may the partitioned to support network slicing or multi-tenancy, thus allowing multiple operators to share the same physical infrastructure and its costs.
Plug-and-Play Network Management
IEEE 802.21, an international standard originally developed for inter-technology handovers, was extended by Fraunhofer to provide an extended set of control functions. This extension is used to manage the MPLS paths across the network and to collect and provide network monitoring information. Its technology-independent nature allows WiBACK to integrate any type of radio network technology, provided that an appropriate control interface has been made available. A central component, the Interface Management Function (IMF), provides a Unified Technology Interface (UTI) to higher layers. So-called Technology Adapters located logically below the IMF are responsible for mapping a set of generic primitives onto technology-specific features and mechanisms. The higher layer modules on top of the IMF provide functionalities of traditional routing protocols and beyond, such as monitoring, topology discovery, radio planning, channel assignment, or QoS-aware path computation.
The control plane is based on a centralized management approach, where so-called Controller nodes manage a set of outdoor-nodes in the field. Dedicated management entities maintain the resource allocation and forwarding state of their network areas. Multiple Master nodes might be operational within each administrative area in a primary/backup configuration. Contrary to the rather distributed routing protocols such as Open Shortest Path First (OSPF) or Optimized Link State Routing (OLSR), the centralized approach offers the opportunity to perform network-wide optimizations allocating radio resources or when assigning the overall network capacity to best match payload demands.
Automated topology management, provided by the Topology Management Function (TMF), dynamically discovers neighboring nodes, sets up (redundant) control paths between each node and a Master node, reacts to new nodes and node failures, and provides mechanisms for fast re-routing if necessary. The WiBACK Controller uses TMF information to assign radio channels (frequencies) or select optimal end-to-end paths based on selectable criteria or policies. Monitoring information such as signal quality, link errors, or end-to-end QoS violations may trigger self-healing processes. TMF implements a ring-based approach where a Controller node first brings up its radio interfaces and determines the optimal radio configuration. This is computed based on the radio interfaces' capabilities, possible regulatory restrictions (e.g. TxPower, DFS), and the ambient spectrum usage assessed by passive channel utilization analysis. Additionally, TMF may coordinate with external spectrum allocation databases (i.e., TVWS). Once this process is complete, the Controller starts sending WiBACK beacons via all its active interfaces to inform adjacent nodes about its availability.
Outdoor nodes determine their configuration during the bootstrap phase and then switch into a passive beacon scan mode. The scan mode periodically scans all administratively permitted channels for WiBACK beacons sent by a Controller node or other already associated nodes. Once they detect WiBACK beacons, they will attempt to associate with the sending node. If multiple WiBACK beacons have been detected, they will be sorted, and associations will be attempted starting with the highest rated sender. Once associated, the Controller node may alter the channel or the point of association.
Link Property Estimation
An automated Link Calibration is performed for each newly activated link to determine, for example, the proper range, modulation and coding (MCS) and TxPower settings. The resulting logical link properties, such as capacity and latency, are estimated based on this information. Those properties serve as the basis of the RMF's constraint-based path computation. In the WiBACK cross-layer design, the TMF may specify the maximum TxPower allowed on a given link. Simultaneously, the respective technology is free to optimally adjust itself to the present channel conditions within the limits set forth by the TMF.
Logical Resource (i.e., capacity) management is provided by the Resource Management Function (RMF) to ensure that a link's capacity is well utilized but rarely exceeded. Based on configurable policies, RMF may adjust its resource allocations to best match end-user demands. Upon association of a new node, the TMF re-computes the optimal channel configuration for all available physical radio links in the WiBACK network and may trigger network reorganizations to optimize the overall network performance (i.e., capacity or latency).
WiBACK maintains extensive network monitoring statistics of its nodes, radios, links, and MPLS LSPs, its so-called Pipes. The UTI-supported self-management modules continuously examine this information to detect possible network problems such as link errors or end-to-end QoS violations. Statistics on the monitoring data are maintained by the Statistics Functions (SF). A Web Interface provides access to this information for administrators. Passive monitoring is used where possible to keep the load caused by monitoring/probing frames at a minimum.