Method and arrangement for determining transmission delay

1. An arrangement for determining mutual differences of transmission delays experienced by received protocol data units and for performing control actions related to ingress ports of a network element, each protocol data unit being associated with an order indicator arranged to indicate the position of that protocol data unit in a mutual sequential order of said protocol data units, and each protocol data unit being sent earlier than or simultaneously with a protocol data unit next in said sequential order, the arrangement comprising:

a processor unit arranged to:

determine, based on a first order indicator associated with a first protocol data unit received earlier and a second order indicator associated with a second protocol data unit received later, whether the first protocol data unit is later in said sequential order than said second protocol data unit, said first protocol data unit being a protocol data unit received at a first ingress port of the network element, and said second protocol data unit being a protocol data unit received at a second ingress port of said network element, and

in response to a situation in which said first protocol data unit is later in said sequential order than said second protocol data unit, calculate a time difference of receiving moments of said second protocol data unit and said first protocol data unit, said time difference representing a lower limit for a difference between transmission delays experienced by said second protocol data unit and said first protocol data unit

wherein said processor unit is further arranged to remove said second ingress port from among ingress ports available to a routing protocol in response to a situation where said first protocol data unit is later in said sequential order than said second protocol data unit and an indicator value updated on the basis of said time difference exceeds a predetermined threshold value.

2. An arrangement according to claim 1 , wherein said first ingress port is a physical ingress port or a logical ingress port and said second ingress port is a physical ingress port or a logical ingress port.

3. An arrangement according to claim 1 , wherein said processor unit is arranged to compare said time difference with said indicator value and to set said time difference as said indicator value in response to a situation where said time difference and a predetermined number of corresponding time differences calculated earlier are greater than said indicator value.

4. An arrangement according to claim 1 , wherein said processor unit is arranged to use said time difference as an input quantity for low-pass filtering, an output quantity of said low-pass filtering being said indicator value.

5. An arrangement according to claim 1 , wherein said first protocol data unit and said second protocol data unit are one of the following: IP (Internet Protocol) packets, ATM (Asynchronous Transfer Mode) cells, Ethernet units, or Frame Relay units.

6. An arrangement according to claim 1 , wherein said order indicator associated with each protocol data unit is one of the following: transmission time stamp indicating the transmitting moment of the protocol data unit in question, and an ordinal number of the protocol data unit in question.

7. A network element comprising:

a first ingress port and a second ingress port for to receive protocol data units each of which is associated with an order indicator arranged to indicate the position of that protocol data unit in a mutual sequential order of said protocol data units, and each of which is sent earlier than or simultaneously with the protocol data unit next in said sequential order, wherein the network element has a processor unit arranged to:

determine, based on a first order indicator associated with a first protocol data unit received earlier and a second order indicator associated with a second protocol data unit received later, whether the first protocol data unit is later in said sequential order than said second protocol data unit, said first protocol data unit being a protocol data unit received at the first ingress port of the network element, and said second protocol data unit being a protocol data unit received at the second ingress port of the network element,

in response to a situation in which said first protocol data unit is later in said sequential order than said second protocol data unit, calculate a time difference of receiving moments of said second protocol data unit and said first protocol data unit, said time difference representing a lower limit for a difference between transmission delays experienced by said second protocol data unit and said first protocol data unit, and

remove said second ingress port from among ingress ports available to a routing protocol in response to a situation where said first protocol data unit is later in said sequential order than said second protocol data unit and an indicator value updated on the basis of said time difference exceeds a predetermined threshold value.

8. A network element according to claim 7 , wherein the network element is one of the following: an IP (Internet Protocol) router, Ethernet switch, ATM (Asynchronous Transfer Mode) switch, base station of a mobile communications network, or an MPLS (Multi Protocol Label Switching) switch.

9. A method for determining mutual differences of transmission delays experienced by received protocol data units and for performing control actions related to ingress ports of a network element, each protocol data unit being associated with an order indicator arranged to indicate the position of that protocol data unit in a mutual sequential order of said protocol data units, and each protocol data unit being sent earlier than or simultaneously with the protocol data unit next in said sequential order, the method comprising:

determining, based on a first order indicator associated with a first protocol data unit received earlier and a second order indicator associated with a second protocol data unit receiver later, whether the first protocol data unit is later in said sequential order than said second protocol data unit, said first protocol data unit being a protocol data unit received at a first ingress port of the network element and said second protocol data unit is a protocol data unit received at a second ingress port of the network element,

in response to a situation in which said first protocol data unit is later in said sequential order than said second protocol data unit, calculating a time difference of receiving moments of said second protocol data unit and said first protocol data unit, said time difference representing a lower limit for a difference between transmission delays experienced by said second protocol data unit and said first protocol data unit, and

removing said second ingress port from among the ingress ports available to a routing protocol if said first protocol data unit is later in said sequential order than said second protocol data unit and an indicator value updated on the basis of the time difference of said receiving moments exceeds a predetermined threshold value.

10. A method according to claim 9 , wherein said first ingress port is a physical ingress port or a logical ingress port and said second ingress port is a physical ingress port or a logical ingress port.

11. A method according to claim 9 , wherein said time difference is compared to said indicator value and if said time difference and a predetermined number of corresponding time differences calculated earlier are greater than said indicator value, said time difference is set as a new indicator value.

12. A method according to claim 9 , wherein said time difference is used as an input quantity for low-pass filtering, an output quantity of said low-pass filtering being said indicator value.

13. A method according to claim 9 , wherein said first protocol data unit and said second protocol data unit are one of the following: IP (Internet Protocol) packets, ATM (Asynchronous Transfer Mode) cells, Ethernet units, or Frame Relay units.

14. A method according to claim 9 , wherein said order indicator associated with each protocol data unit is one of the following: transmission time stamp indicating the transmitting moment of the protocol data unit in question, and an ordinal number of the protocol data unit in question.

15. A non-transitory computer readable medium encoded with a computer program for controlling a programmable processor to determine mutual differences of transmission delays experienced by protocol data units received and to perform control action related to ingress ports of a network element, each protocol data unit being associated with an order indicator arranged to indicate the position of that protocol data unit in a mutual sequential order of said protocol data units, and each protocol data unit being sent earlier than or simultaneously with the protocol data unit next in said sequential order, the computer program comprising:

software means for controlling said programmable processor to determine, based on a first order indicator associated with a first protocol data unit received earlier and a second order indicator associated with a second protocol data unit received later, whether the first protocol data unit is later in said sequential order than said second protocol data unit, said first protocol data unit being a protocol data unit received at a first ingress port of the network element to be controlled, and said second protocol data unit being a protocol data unit received at a second ingress port of the network element,

software means for controlling said programmable processor to calculate, in response to a situation in which said first protocol data unit is later in said sequential order than said second protocol data unit, a time difference of receiving moments of said second protocol data unit and said first protocol data unit, said time difference representing a lower limit for a difference between the transmission delays experienced by said second protocol data unit and said first protocol data unit, and

software means for controlling said programmable processor to remove said second ingress port from among ingress ports available to a routing protocol in response to a situation where said first protocol data unit is later in said sequential order than said second protocol data unit and an indicator value updated on the basis of said time difference exceeds a predetermined threshold value.