Hub and Spoke

The terms hub and spoke , spoke architecture and hub-spoke are used in transportation and information technology . Generally, what is meant is that the connection between two end nodes A and B do not directly, but via a central node Z, the hub (English: hub ), is guided. The compounds of the end node A, B to the node Z is referred to herein as spokes (English: spokes ). In a system with several hubs, the path leads from a node A in the area of the hub Z1 to a node B in the area of the hub Z2 from A via Z1 and Z2 to B, even if the direct connection A to B would be shorter and technically feasible. Minimizing the transport costs is the subject of the reloading problem , an optimization problem in the field of logistics .

Hub and spoke in transportation

In the transport sector , hub and spoke is a star-shaped arrangement of transport routes, whereby these all run to or from a central node in all directions in order to be able to serve the area (star topology).

Hub-and-spoke systems, a distinction single assignment ( single allocation ) and Multiple Assignment ( Multiple Allocation ). In the case of single allocation, each source (starting point of the charge) and each sink (receiving point of the charge) has exactly one connection to exactly one hub. In the case of multiple allocation, sources and sinks can establish connections to several hubs. The single assignment is therefore a special case of multiple assignment. In addition, there are hub & spoke systems without direct connections (pure hub & spoke systems) and systems with direct connections (hybrid hub & spoke systems) between the non-hub nodes.

This system was used in commercial air freight traffic within the USA in the late 1970s . The reason for this was and is the bundling of traffic flows and the corresponding demand, so that the utilization of the transport vehicles used is optimized by avoiding empty trips or empty flights. The system uses the law of fixed cost degression ; Cost savings compared to point-to-point traffic (direct connections) are possible. A disadvantage of this system is that the transport route is longer than that in direct traffic from point A to point B (see also transport network structure ).

This system is important for almost all means of transport:

Maritime traffic , where it is used indirectly for feeder traffic

Air freight transport , e.g. B. with the large courier express parcel services (CEP services) such as UPS (hub: Cologne / Bonn airport ) or Deutsche Post / DHL (hub: Leipzig airport ).

Rail passenger traffic : mainly in long-distance traffic, concentration on the connections between the airport locations and the associated closure of shorter direct long-distance connections (example: Hagen - Frankfurt am Main via Cologne instead of Siegen - Gießen ) and therefore decoupling of such larger cities from long-distance rail traffic on the direct routes Remaining local traffic with shorter routes and additional stops of the individual trains with therefore additional changes required as well as fare calculation exclusively via the hub even when using the shorter direct route; also shutdown of shorter routes that are close to hubs but at right angles to them;

Rail freight transport : both in single-wagon load transport with a concentration on very few marshalling yards as hubs and in container transport in combined transport .

Road freight transport, with all groupage forwarding companies , in order to be able to offer 24-hour transport in Germany and 48-hour transport throughout Europe ( groupage transport ).

Parcel service providers represent a further area of application. The parcels collected in the secondary run in the depots are consolidated in the so-called main run and handled via a hub. The spokes thus represent the connections between the hub and the depots. Usually, however, there is a mixed form of the two network alternatives, depots with a high mutual relationship due to a high volume of packets between the two are usually provided by point-to-point connections, also called direct traffic, interconnected; Above all, those parcels whose sender or recipient depots do not make up a complete truck load pass through the hub.

Overnight service of the city courier service: Since elimination of the appointment service (offered by the German Federal Railroad in 1990, since regional city courier services organized in various collaborations Association of German courier services , Ilonex, KEP AG, OPS, GO! ) And operate in central Germany near Bad Hersfeld each their central envelope ( HUB). You benefit from the fast "Sprinter" small vans and the German motorway network (spoke / spokes).

Systems with several hubs, which are connected to one another by means of direct traffic, are also possible. One example of this is the GLS Germany network ; the company describes the hubs as "central transhipment points" (ZUP).

In motorized private transport , the hub-and-spoke method is almost meaningless, since the driver usually drives the shortest route (at best with smaller detours via motorways instead of country roads). However, this is not the case with acquired car sharing (“hitchhiking”), where, depending on the method and traffic situation, cities, motorway stations and border crossings are given hub properties.

Hub and Spoke in Commercial Passenger Aviation

Almost all major commercial airlines use the hub-and-spoke method for their flights at their hubs. Exceptions are the so-called low-cost airlines that emerged in the 1980s and have been booming since the 1990s, and for the most part offer point-to-point connections. In contrast to the point-to-point method, the hub-and-spoke method makes it possible to offer a much larger number of connections, but with a correspondingly more frequent need to change.

Arithmetically

A system of transport endpoints with the connection paths can be abstracted as an undirected graph without multiple edges . The number of connections required to connect all nodes to each other in pairs results in: ${\ displaystyle n}$

For hub-and-spoke traffic:

${\ displaystyle n-1}$ Connections, the complexity is O ( n )

With only PP traffic:

${\ displaystyle (n-1) + (n-2) + \ dotsb + 1 = [n \ cdot (n-1)] / 2}$ Connections, the complexity is O ( n ² )

For hub-and-spoke traffic with hubs: ${\ displaystyle x}$

maximum connections ${\ displaystyle n-x + [x \ cdot (x-1)]}$

Example with airports

In a system of airports, the number of different individual connections required is in order to connect all airports to one another via a central hub selected from them 9, whereas different flight connections would be necessary for PP transports . ${\ displaystyle n = 10}$ ${\ displaystyle 9 + 8 + \ dotsb + 2 + 1 = (10 \ cdot 9) / 2 = 45}$

Hub and spoke in information technology

Enterprise application integration

As a hub-and-spoke architecture or hub-and-spoke architecture referred to in the information technology is a form of integration of business functions on the basis of exchange of messages or service requests, in which all traffic through a central integration platform is headed. It is one of the possible topologies for enterprise application integration . One speaks here of the business bus , although the terms are not completely synonymous.

network technology

In network technology, the star topology plays an essential role in networking with the help of twisted pair cabling. The individual network nodes are each connected to central hubs or switches , which in turn are connected to one another. The term hub in network technology is primarily used for a specific device type for the central network nodes. However, this type of device only plays a subordinate role in larger networks or when setting up new networks and is largely replaced by switches. However, this does not change the network topology, so that, from a topological point of view, switches are also hubs.

Telephony

Telephone networks are also largely structured in the form of a hub-and-spoke topology. The exchanges and telephone systems form the hubs and the terminals form the spokes. In the area of digital telephony based on ISDN , there are also bus architectures.

User interfaces

An example of user interfaces in a hub-and-spoke architecture is the home screen on smartphones, from which individual applications can be started. It is characterized by the fact that there is a central user interface from which other application parts are called. The individual parts then have little or no cross-connections. They don't show a navigation menu like Wikipedia does, for example.