Method and arrangement for route cost determination and selection with link cost interaction
This invention extends routing mechanisms that use link metrics for route selection so that: A link metric cross correlation vector is determined for all links, where each element in the vector corresponds to some other link, and reflects the change in the link metric value if a data flow would already use this other link. The invention further describes a specific embodiment where all cross-correlating links are adjacent to each other, i.e., they terminate or originate in a common node. A mechanism is described to create an extended routing graph. This extended graph permits the use of standard polynomial time algorithms that simultaneously construct the optimal route and find the optimal route metric (such as shortest-path algorithms) also for the adjacent link cross-correlating case.
1. A method of selecting a route for a data transmission flow in a communication network, comprising:
defining a first route from a sender to a receiver comprising at least a first link having a first link metric, and a second route from the sender to the receiver comprising at least a second link having a second link metric;
determining a value of at least the first link metric based on a cross-correlation value representing an evaluated change that would occur in the first link metric value if a data flow would already use a link in the communication network other than the first link due to the first link and the other link transmitting on different channels or accessing common resources;
comparing route metrics for the first and second routes, the route metrics based on the link metric values of the links comprising the routes; and
calculating a corrected cross-correlation value σ a b (new) as:
σ a b (new)= g (σ a b ,α a b h ( m a , m′ a ))
where g and h are functions, α a b is a weight factor representing a probable influence of a link b on a link a, m a is a current link metric value for the link a, and m ′ a is a link metric value for the link a when a flow uses a path including the link a,
wherein one or more method steps are performed by a computational circuit associated with a network node.
2. The method of claim 1 wherein the first route comprises at least two links and the other link considered in the cross-correlation value is included in the first route.
3. The method of claim 1 wherein the first link metric value is calculated on the basis of a link metric cross-correlation vector comprising, for the first link, a cross-correlation value corresponding to another link, and reflecting the change in the link metric value for the first link if the data flow would already use the other link.
4. The method of claim 1 wherein the first link metric value is calculated on the basis of a set of values comprising pairs (b,σ a b ) for which there is a correlation or information exists, b being another link and (σ a b ) being the cross-correlation value reflecting the change in the first link metric value if the data flow would already use the other link.
5. The method of claim 4 wherein the first link metric value is calculated according to the function m a =ƒ a (m a ,σ a p ), where m a is the first link metric value to be calculated, m a is the current first link metric value and σ a b is the cross-correlation value reflecting the change in the first link metric value if the data flow would already use the other link b.
6. The method of claim 5 wherein the first link metric value is calculated according to the function
m
a
_
=
m
a
+
∑
b
∈
p
σ
a
b
,
where m a is the first link metric value to be calculated, m a is the current first link metric value, P is the set of all links to be considered, and σ a b is the cross-correlation value reflecting the change in the first link metric value if the data flow would already use the other link b.
7. The method of claim 1 further comprising calculating the first link metric value based on the change that would occur in the first link metric value if the data flow would already use the first link.
8. The method of claim 1 wherein defining the first route from the sender to the receiver comprises:
determining a set P of possible paths from the sender to the receiver by using link metrics m a associated with links and a standard k-shortest path construction method to find a predetermined number k of shortest paths;
including said k shortest paths in the set P; and
selecting the first route from the set P.
9. The method of claim 1 wherein the cross-correlation value is determined based on knowledge about how links affect each other.
10. The method of claim 1 wherein the cross-correlation value is determined based on observations over time of how link metrics are correlated.
11. The method of claim 1 further comprising:
creating an extended routing graph by introducing virtual nodes and virtual links;
determining a shortest path by applying a standard shortest path algorithm to the extended routing graph;
extracting a route along the determined shortest path by replacing each virtual node by its corresponding node and each virtual link by its corresponding link; and
extracting a route metric from a corresponding route metric in the extended routing graph.
12. The method of claim 1 wherein defining the first and second routes is performed by a path determining circuit associated with the network node.
13. The method of claim 1 wherein determining the cross-correlation value is performed by a cross-correlation value determining circuit associated with the network node.
14. The method of claim 1 wherein defining the first and second routes and determining the cross-correlation value are performed by a link metric function circuit associated with the network node.
15. The method of claim 1 wherein the cross-correlation value represents the change that would occur in the first link metric value due to the first link and the other link transmitting on different channels, wherein the different channels are transmitted by different Radio Access Networks.
16. The method of claim 15 wherein the different channels transmitted by different Radio Access Networks share the same spectrum.
17. The method of claim 1 wherein the cross-correlation value represents the change that would occur in the first link metric value due to the first link and the other link accessing common computational resources.
18. The method of claim 1 wherein the cross-correlation value represents the change that would occur in the first link metric value due to the first link and the other link accessing common memory resources.
19. A telecommunications network node, comprising:
a link metric function (LMF) computational circuit operative to monitor or control a link characteristic needed for determining a link metric for a first link starting at the node, the LMF computational circuit further operative to calculate a link metric value of the first link on the basis of a link metric cross-correlation vector comprising a cross-correlation value corresponding to a link other than the first link and reflecting an evaluated change in the first link metric value if a data flow would already use the other link due to the first link and the other link transmitting on different channels or accessing common resources, wherein the LMF computational circuit is operative to calculate the first link metric value according to the function m a =ƒ a (m a ,σ a p ), where m a is the first link metric value to be determined, m a is a current first link metric value, and σ a b is a cross-correlation value reflecting the change in the first link metric value if a data flow would already use other link b.
20. The node of claim 19 wherein the LMF computational circuit is operative to calculate the link metric value on the basis of a set of values comprising pairs (b, σ a b ) for which there is a correlation or information exists, b being another link and (σ a b ) being the cross-correlation value reflecting the change in the first link metric value if the data flow would already use the other link.
21. The node of claim 19 wherein the LMF computational circuit is operative to calculate the first link metric value according to the function
m
a
_
=
m
a
+
∑
b
∈
p
σ
a
b
,
where m a is the first link metric value to be calculated, m a is the current first link metric value, P is the set of all links to be considered, and σ a b is the cross-correlation value reflecting the change in the first link metric value if the data flow would already use the other link b.
22. The node of claim 19 wherein the LMF computational circuit is operative to calculate the link metric value of the first link based on the change that would occur in the first link metric value if the data flow would already use the first link.
23. The node of claim 19 wherein the LMF computational circuit is operative to determine a set P of possible paths by:
using link metrics m a associated with links and a standard k-shortest path construction method to find a predetermined number k of shortest paths; and
including said k shortest paths in the set P.
24. The node of claim 19 wherein the LMF computational circuit is operative to use the cross-correlation value determined based on knowledge about how the links affect each other.
25. The node of claim 19 wherein the LMF computational circuit is operative to use the cross-correlation value determined based on observations over time of how link metrics are correlated.
26. The node of claim 19 wherein the LMF computational circuit is operative to calculate a corrected cross-correlation value as σ a b (new) as follows:
σ a b (new)= g (σ a b ,α a b h ( m a , m′ a ))
where g and h are functions, α a b is a weight factor representing a probable influence of a link b on a link a, m a is the current link metric value for the link a, and m′ a is the link metric value for the link a when a flow uses a path including the link a.
27. The node of claim 19 wherein the LMF computational circuit is operative to:
create an extended routing graph by introducing virtual nodes and virtual links;
determine a shortest path by applying a standard shortest path algorithm to the extended routing graph;
extract a route along the determined shortest path by replacing each virtual node by its corresponding node and each virtual link by its corresponding link; and
extract a route metric from a corresponding route metric in the extended routing graph.
28. A communications network comprising at least one node including a link metric function (LMF) computational circuit operative to monitor or control a link characteristic needed for determining a link metric for a first link starting at the node, the LMF further operative to calculate a link metric value of the first link on the basis of a link metric cross-correlation vector comprising a cross-correlation value corresponding to a link other than the first link and reflecting an evaluated change in the first link metric value if a data flow would already use the other link, wherein the LMF computational circuit is operative to calculate the first link metric value according to the function m a =ƒ a (m a ,σ a p ), where m a is the first link metric value to be determined, m a is a current first link metric value, and σ a b is a cross-correlation value reflecting the change in the first link metric value if a data flow would already use other link b.