Cross-layer optimization
Encyclopedia
Cross-layer optimization is an escape from the pure waterfall
-like concept of the OSI communications model
with virtually strict boundaries between layers. The cross layer approach transports feedback dynamically via the layer boundaries to enable the compensation for e.g. overload, latency or other mismatch of requirements and resources by any control input to another layer but that layer directly affected by the detected deficiency.
Especially in information routing with concurrent demand for limited capacity of channels there may be a need for a concept of intervention to balance between e.g. the needs of intelligible speech transmission and of sufficiently dynamic control commands. Any fixed allocation of resources will lead to a mismatch under special conditions of operations. Any highly dynamic change of resource allocation might affect the intelligibility of voice or the steadiness of videos. However, as with other optimizing strategies, the algorithm consumes time as well .
management is currently subject of various patent applications, as e.g.
The cross-layer control mechanism provides a feedback on concurrent quality information for the adaptive setting of control parameters. The control scheme apply
layer (which manages actual transmission and reception of data over the media).
In some communications channels (for example, in power lines), noise may be non-stationary and might vary synchronously with the 50 or 60 Hz AC current cycle. In scenarios like this, overall system performance can be improved if the MAC can get information from the PHY regarding when and how the noise level is changing, so that the MAC can schedule transmission during the periods of time in which noise levels are lower.
An example of a communications system that allows this kind of Cross-layer optimization is the ITU-T
G.hn
standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables).
Waterfall model
The waterfall model is a sequential design process, often used in software development processes, in which progress is seen as flowing steadily downwards through the phases of Conception, Initiation, Analysis, Design, Construction, Testing, Production/Implementation and Maintenance.The waterfall...
-like concept of the OSI communications model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
with virtually strict boundaries between layers. The cross layer approach transports feedback dynamically via the layer boundaries to enable the compensation for e.g. overload, latency or other mismatch of requirements and resources by any control input to another layer but that layer directly affected by the detected deficiency.
Especially in information routing with concurrent demand for limited capacity of channels there may be a need for a concept of intervention to balance between e.g. the needs of intelligible speech transmission and of sufficiently dynamic control commands. Any fixed allocation of resources will lead to a mismatch under special conditions of operations. Any highly dynamic change of resource allocation might affect the intelligibility of voice or the steadiness of videos. However, as with other optimizing strategies, the algorithm consumes time as well .
Adjusting quality of service
Cross-layer optimization shall contribute to an improvement of quality of services under various operational conditions. Such adaptive quality of serviceAdaptive quality of service
In multi-hop networks, Adaptive Quality of Service routing protocols have become increasingly popular and have numerous applications. One application in which it may be useful is in Mobile ad hoc networking ....
management is currently subject of various patent applications, as e.g.
The cross-layer control mechanism provides a feedback on concurrent quality information for the adaptive setting of control parameters. The control scheme apply
- the observed quality parameters
- a fuzzy logic based reasoning about applying the appropriate control strategy
- the statistically computed control input to parameter settings and mode switches
Tailoring to resource efficiency
The quality aspect is not the only approach to tailor the cross-layer optimization strategy. The control adjusted to availability of limited resources is the first mandatory step to achieve at least a minimum level of quality. Respective studies have been performed and will continueAdapting MAC scheduling based on PHY parameters
Communication systems that need to operate over media with non stationary background noise may benefit from having a close coordination between the MAC layer (which is responsible for scheduling transmissions) and the PHYPhysical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
layer (which manages actual transmission and reception of data over the media).
In some communications channels (for example, in power lines), noise may be non-stationary and might vary synchronously with the 50 or 60 Hz AC current cycle. In scenarios like this, overall system performance can be improved if the MAC can get information from the PHY regarding when and how the noise level is changing, so that the MAC can schedule transmission during the periods of time in which noise levels are lower.
An example of a communications system that allows this kind of Cross-layer optimization is the ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
G.hn
G.hn
G.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...
standard, which provides high-speed local area networking over existing home wiring (power lines, phone lines and coaxial cables).