Compression method for TDM frames in a packet network
Example embodiments provide a compression method for TDM frames transported over a packet network. The method is based on mapping of allocated TDM slots but not all un-allocated slots into a transport structure, which thereby reduces the needed amount of data transported over packets and hence reduces the required packet rate and packet capacity during transport of the TDM frame. The mapping is further arranged to allow dynamic changes of packet rate and packet capacity, thus the mapping is performed such that a working size of the transport TDM frame is allowed to increase or decrease over time.
1. A method for node-to-node transfer of a plurality of Time Division Multiplex (TDM) frames over packet transfer from a transmitting node to a receiving node, said method comprising:
in said transmitting node for each TDM frame:
identifying ranges of allocated and unallocated slots in said TDM frame;
determining an initial working size of said TDM frame;
mapping said allocated slots and a subset of said identified ranges of unallocated slots to a transport TDM frame according to a mapping configuration; and
performing synchronized dynamic mapping configuration change, thereby allowing a dynamic effective capacity of the working size of the transport TDM frame over time.
2. A method according to claim 1 , wherein said mapping or a change in mapping configuration is performed without data loss.
3. A method according to claim 2 , wherein said mapping further comprises providing a mapping configuration defining slots to be transferred; and
a subset of said defined ranges of unallocated slots not to be transferred in a mapping configuration.
4. A method according to claim 2 , wherein in said mapping configuration, a first unused TDM slot of a defined range of unallocated slots is encoded to indicate the number of continuous unallocated slots within that defined range which are not transferred in the transferred TDM frame.
5. A method according to claim 2 , further comprising:
for a low packet rate transport signal,
decreasing the transport TDM slot working size in order to maintain a current packet rate, thereby ensuring a predetermined packet delay limit.
6. A non-transitory computer readable storage medium storing computer readable instructions that are executable by a computer processor to cause the computer processor to perform the method according to claim 2 .
7. A method according to claim 1 , further comprising identifying a first unallocated slot of a range of unallocated slots at the tail of said TDM frame, and wherein said increase of the working size is provided by adding slots after said identified first unallocated slot, and said decrease of the target working size is provided by not mapping slot numbers starting at said determined first unallocated slot.
8. A method according to claim 7 , further comprising:
performing a pre-negotiation between said transmitting node and said receiving node to initiate a change in the working size of the transport TDM frame.
9. A method according to claim 1 , wherein said mapping further comprises:
shifting or copying allocated slots within said TDM frame to slot numbers corresponding to a subset of said identified ranges of unallocated slots which are identified within said initial working size.
10. A method according to claim 9 , wherein the shifting or copying of allocated slots within said TDM frame is synchronized by messages passed between said transmitting node and said receiving node.
11. A method according to claim 1 , wherein said mapping further comprises providing a mapping configuration defining slots to be transferred; and
a subset of said defined ranges of unallocated slots not to be transferred in a mapping configuration.
12. A method according to claim 11 , further comprising:
performing a pre-negotiation between said transmitting node and said receiving node to initiate a mapping configuration change.
13. A method according to claim 11 , wherein said mapping configuration is exchanged between said transmitting node and said receiving node in the form of a bitmap table encoding the transfer/non transfer of said TDM frame per TDM slot.
14. A method according to claim 11 , wherein said mapping configuration is exchanged between said transmitting node and said receiving node in the form of changes of the transfer/non transfer of said TDM frame per TDM slot.
15. A method according to claim 1 , further comprising providing said receiving node with a synchronizing signal to initiate a coordinated mapping configuration change.
16. A method according to claim 1 , wherein in said mapping configuration, a first unused TDM slot of a defined range of unallocated slots is encoded to indicate the number of continuous unallocated slots within that defined range which are not transferred in the transferred TDM frame.
17. A method according to claim 1 , further comprising:
at said receiving node,
de-mapping based on said mapping configuration, said allocated slots and said subset of said identified ranges of unallocated slots from said transport TDM frame to recreate said TDM frame.
18. A method according to claim 1 , further comprising:
combining independent channels to form said transport TDM frame as an aggregate transport TDM frame, thereby enabling a reduced packet buffer delay.
19. A method according to claim 1 , further comprising:
for a low packet rate transport signal,
decreasing the transport TDM slot working size in order to maintain a current packet rate, thereby ensuring a predetermined packet delay limit.
20. A non-transitory computer readable storage medium storing computer readable instructions that are executable by a computer processor to cause the computer processor to perform the method according to claim 1 .