Method of resynchronizing streams benefiting from circuit emulation services, for use in a packet-switched communications network
A packet-switched communications network (PSN) includes a multiplicity of nodes (Ni) adapted to switch streams of packets benefiting from circuit emulation services, known as CES packets. The network uses a particular method of resynchronizing the CES streams. According to that method, for a CES stream intended to take an associated path (CE) from an ingress node (N 1 ) passing through a set of nodes including a subset of nodes adapted to resynchronize CES streams selectively, effective resynchronization of said stream by a node selected from said subset is conditioned by a value representative of the cumulative jitter suffered by said stream as far as that node.
1. A method of resynchronizing streams of packets in a packet-switched communications network including a multiplicity of nodes and a stream of packets (“CES stream”) related to a circuit emulation service which takes an associated path from an ingress node which implements circuit emulation services to an egress node which implements circuit emulation services through a set of said network nodes, said method comprising:
selecting a subset of the set of nodes as intermediate synchronization nodes, wherein each intermediate synchronization node of said subset is selected as a function of a value representative of cumulative jitter suffered by said CES stream as far as said intermediate synchronization node, wherein said each intermediate synchronization node resynchronizes said CES stream and sends the resynchronized CES stream to a next node along said associated path,
wherein said each intermediate synchronization node of said subset is selected when setting up the associated path,
wherein the method further comprises the step of:
determining said value representative of cumulative jitter for one node of the set through which said associated path passes as a function of a sum of a first predetermined maximum jitter that is introduced by said one node and a second predetermined maximum jitter that is introduced by the nodes of said set between said one node and a preceding intermediate synchronization node that precedes said one node, and
wherein the method further comprises the steps of:
determining that said sum becomes greater than a selected threshold and selecting a node that precedes said one node as an intermediate synchronization node for said associated path in response to said determination.
2. A method of resynchronizing streams of packets in a packet-switched communications network including a multiplicity of nodes and a stream of packets (“CES stream”) related to a circuit emulation service which takes an associated path from an ingress node which implements circuit emulation services to an egress node which implements circuit emulation services through a set of said network nodes, said method comprising:
selecting a subset of the set of nodes as intermediate synchronization nodes, wherein each intermediate synchronization node of said subset is selected as a function of a value representative of cumulative jitter suffered by said CES stream as far as said intermediate synchronization node, wherein said each intermediate synchronization node resynchronizes said CES stream and sends the resynchronized CES stream to a next node along said associated path,
wherein said each intermediate synchronization node of said subset is selected when setting up the associated path, and
wherein the method further comprises the steps of:
estimating, at one node of said set through which the associated path passes a value of a sum of a jitter introduced by said one node and jitters introduced by nodes of said set through which the associated path passes between said one node and a preceding intermediate synchronization node that precedes said one node, and
determining that said sum is greater than a selected threshold, and in response to said determination, selecting a node that precedes said one node as an intermediate synchronization node.
3. The method according to claim 1 characterized in that said each intermediate synchronization node of said subset is determined as said CES stream progresses along the associated path.
4. The method according to claim 3 , further comprising the steps of:
estimating, at one node through which the associated path carrying the CES stream passes, a value of a sum of a jitter introduced by said one node and jitters introduced by nodes of the set through which said associated path passes between said one node and an intermediate synchronization node that precedes said one node, and then
comparing said sum to first and second thresholds, if said sum is less than the second threshold, considering a following node of said associated path as the one node for repeating previous steps, and
if said sum is between said first and second thresholds, selecting the one node as an intermediate synchronization node for said associated path.
5. The method according to claim 2 , characterized in that the value of jitter that each one node of the set introduces is estimated at that node as a function of the value of a selected local parameter.
6. The method according to claim 4 , characterized in that the value of jitter that one node of the set introduces is estimated at that node as a function of the value of a selected local parameter.
7. The method according to claim 5 , characterized in that said local parameter is a level of use of a buffer used by said node to process a multiplicity of CES streams.
8. The method according to claim 1 , further comprising the step of selecting said threshold as a function of a quality of service associated with said CES stream.
9. The method according to claim 2 , further comprising the step of selecting said threshold as a function of a quality of service associated with said CES stream.
10. The method according to claim 4 , further comprising the step of selecting said first and second thresholds as a function of a quality of service associated with said CES stream.
11. The method according to claim 6 , characterized in that said local parameter is a level of use of a buffer used by said node to process a multiplicity of CES streams.
12. The method according to claim 1 wherein said set of nodes through which the associated path passes comprises at least one node which is not selected as an intermediate synchronization node, wherein said at least one node sends the CES stream to a next node along said associated path without resynchronizing said CES stream.