Congestion management in radio access networks
A method for congestion management in a radio access network is provided. The radio network controller maintains available bandwidth information for each of the downstream links towards the base stations. The radio network controller also measures incoming traffic for each such link and for various traffic classes and uses the traffic measurements and available bandwidth to predict congestion conditions. Upon detecting a congestion condition, congestion avoidance mechanisms such as controlled discard and back-pressure are activated.
1. A method for managing congestion in a network comprising an RNC (radio network controller) and a plurality of base stations over links comprising at least one respective link that is remote from the RNC for each base station, the method comprising:
measuring incoming traffic for each base station at the RNC of a plurality of traffic classes to produce traffic measurements;
for each base station, determining a total bandwidth available on the at least one respective link to the base station that is remote from the RNC and is along a signal path between the RNC and base station, said signal path including at least one other link having different characteristics from said respective link, and a transport component coupling said respective link and said at least one other link;
for each base station, detecting presence or absence of a congestion condition using the traffic measurements for the base station and the determined total bandwidth available on the at least one respective link to that base station; and
upon detecting the congestion condition, performing congestion avoidance at the RNC.
2. The method of claim 1 wherein:
for each base station, determining the total bandwidth available on the at least one respective link to the base station is done upon occurrence of an event that effects the total bandwidth available.
3. The method of claim 1 wherein said step of measuring incoming traffic for each base station comprises:
for each incoming packet, determining which link the packet will be transmitted on, and determining a traffic class for the packet, and incrementing a counter for the determined traffic class and link.
4. The method of claim 3 further comprising converting a size of the packet to a cell count, and incrementing a counter by the cell count.
5. The method of claim 3 wherein the traffic classes comprise DS (delay sensitive), NDS (non delay sensitive), and HSDPA (High speed downlink packet access).
6. The method of claim 5 wherein said step of detecting presence or absence of congestion conditions comprises:
every update period, updating the traffic measurements for DS, NDS and HSDPA to reflect traffic that has been transmitted;
comparing traffic balances of each of:
a) DS traffic to a first discard threshold;
b) DS+NDS traffic to a second discard threshold and first back-pressure threshold;
c) DS+NDS+HSDPA traffic to a third discard threshold and a second back-pressure threshold.
7. The method of claim 1 wherein determining a respective total bandwidth available on each link comprises:
adding up capacities of all active VCCs on the link.
8. The method of claim 7 wherein adding up capacities of all active VCCs on the link comprises computing:
LB =( T update /1 s)Σ( VCC ECR ) where VCC ECR =2*( PCR*SCR )/( PCR+SCR ),
where T update is the update interval, and PCR is a peak cell rate of a given active VCC, and SCR is a sustained cell rate of a given active VCC.
9. The method of claim 1 wherein for each base station, said step of detecting presence or absence of a congestion condition comprises:
every update period, updating the traffic measurements to reflect traffic that has been transmitted, comparing traffic balances of traffic classes or combinations of the traffic classes to respective thresholds.
10. The method of claim 9 wherein said updating and comparing step comprises:
comparing traffic balances of each of:
a) highest priority traffic;
b) sum of traffic of top two priorities;
c) sum of traffic of top three priorities;
to a respective at least one threshold.
11. The method of claim 10 wherein the respective at least one threshold comprises a discard threshold.
12. The method of claim 10 wherein the respective at least one threshold comprises a back-pressure thresholds.
13. The method of claim 10 wherein the respective at least one threshold comprises a controlled discard threshold and a back-pressure threshold.
14. The method of claim 1 wherein performing congestion avoidance at the RNC comprises at least one of:
performing controlled discards; and
applying back-pressure.
15. The method of claim 14 wherein performing controlled discards comprises:
discarding all traffic in excess of an exceeded controlled discard threshold.
16. The method of claim 14 wherein applying back-pressure comprises:
for a specified time period stopping transmission of a respective traffic type when a back-pressure threshold is exceeded.
17. A radio network controller (RNC) for performing congestion management of traffic transmitted towards a plurality of a base stations over links comprising at least one respective link that is remote from the RNC for each base station, the radio network controller comprising:
a congestion management function comprising:
a) a traffic measurement function for measuring incoming traffic destined for each base station;
b) a bandwidth tracker for tracking an available bandwidth for transmission to each base station on the respective link that is remote from the RNC and is along a signal path between the RNC and said each base station, said signal path including at least one other link having different characteristics from said respective link, and a transport component coupling said respective link and said at least one other link;
c) a congestion detector for detecting congestion using the traffic measurements and the tracked available bandwidth;
d) a congestion avoidance function for, upon detecting a congestion condition on the at least one respective link to a particular base station, performing congestion avoidance at the RNC.
18. The RNC of claim 17 wherein the congestion avoidance function performs congestion avoidance by applying back-pressure on selected streams for the at least one respective link upon which a congestion condition has been detected.
19. The RNC of claim 17 wherein the congestion avoidance function performs congestion avoidance by performing controlled discards on selected streams for the at least one respective link upon which a congestion condition has been detected.
20. The RNC of claim 19 wherein the congestion avoidance function performs congestion avoidance by applying back-pressure on selected streams for the at least one respective link upon which a congestion condition has been detected.
21. A UTRAN (UMTS terrestrial radio access network) comprising:
the RNC of claim 17 ;
an ATM network;
a high speed link interconnecting the ATM network and the RNC; and
a plurality of base stations, the at least one respective link interconnecting the ATM network to each of the plurality of base stations.