Congestion control in network systems

Details Congestion control in network systems Congestion control in network systems

1998-07-20

2002-03-26

Vincent, David R. (Department: 2661)

Multiplex communications

Data flow congestion prevention or control

Control of data admission to the network

C370S244000, C379S008000

Reexamination Certificate

active

06363052

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a congestion control technique for use in network systems.
FIG. 1
is a block diagram representing a modern communications network
100
. The network
100
is populated by a number of communication switches
110
-
170
. Switches
110
-
170
are interconnected by communication trunks according to a predetermined arrangement. To establish a communication link between, for example, two telephones
10
,
20
the communication network
100
establishes a call path therebetween. One such call path is illustrated in
FIG. 1
, traversing switches
120
,
140
,
160
and
170
.
As is known, at the beginning of a call, the call path is established incrementally through the network
100
. For example, an originating telephone
10
generates an off-hook signal and enters a telephone number of a destination telephone
20
. Switch
120
interprets the telephone number and determines to route the call in the direction of switch
140
. Switch
120
signals switch
140
with a call request message identifying telephone
20
as the destination of the call path. In response, if switch
140
possesses available capacity sufficient to route the call, switch
140
may reply within an acknowledgment message to switch
120
. If not, switch
140
signals switch
120
with a call reject message.
If switch
140
determines that it can process the call, it determines that it will route the call through switch
160
. Switch
140
repeats the process that was used by switch
120
. It generates a call request message to switch
160
which may be responded to by either an acknowledgment message or a call reject message. Thus, a call path is established incrementally through network
100
to establish a communication link between two telephones. Initiation of call paths in communication networks is well-known.
In a signaling network, the known “Automatic Congestion Control” algorithm (ACC) is used during switch overloads to maintain network throughput. Studies demonstrate that the known ACC algorithm performs poorly. Indeed, these studies suggest that switch throughput can be improved by disabling the ACC algorithm entirely.
The following is taken from the ITU Standards (Blue Book):
“Automatic Congestion Control (ACC) is used when an exchange [switch] is in an overload condition. Two levels of congestion are distinguished, a less severe congestion threshold (congestion level 1) and a more severe congestion threshold (congestion level 2). If either of the two congestion levels is reached, an automatic congestion control information message may be sent to the adjacent exchanges indicating the level of congestion (congestion level 1 or 2). The adjacent exchanges, when receiving an automatic congestion control information message, should reduce their traffic to the overload affected exchange.”
See, CCITT-Blue Book,
Specification of Signaling System Number
7 (1998).
The ACC level is typically based on the real time utilization and queue length thresholds in a “Congested Switch.”The ACC levels are passed back to a source switch in the known Release (REL) and Address Complete (ACM) messages. When a source switch determines that a congested switch is in overload, it blocks calls directed to the congested switch. If the congested switch's ACC level is 1, then the source switch blocks 75% of Hard-to-Reach (HTR) calls destined for the congested switch. If the ACC level is 2, then the source switch blocks all HTR calls and 75% of Not-Hard-to-Reach (NHR) calls destined for the congested switch. Call blocking remains in effect for a period of 3 seconds. Additional details of the ACC algorithm may be found in ITU-T Recommendation Q.542
, Digital Exchange Design Objections—Operations and Maintenance.
Studies demonstrate that the known ACC algorithm performs poorly. See, Houck, et al.,
Failure and Congestion Propagation Through Signaling Control
, Proc. 14th Int'l Teletraffic Congress (June 1994). Houck draws the following conclusions:
The present implementation of the ACC algorithm is non-optimal and higher throughput can be achieved by turning it off;
The ACC algorithm over-controls traffic which, in turn, leads to congestion propagation from congested switches to non-overloaded switches; and
The control duration (3 seconds) is too long and the control granularity (two blocking levels for HTR and NHR) is too coarse.
Houck recommends increasing the granularity of the control (from two values) and decreasing the control duration interval (from 3 seconds). However, a change in the number of levels would require message format changes in the ACC standard. Accordingly, Houck's recommendation requires agreement from all major switch venders.
A network congestion controller was suggested by Furmann, et al. See, “An Adaptive Antonomous Network Congestion Controller,” Proc. ITC Specialists Seminar on Control in Comm. (1996). Furmann's approach uses congestion control at a source switch based on locally available information rather than from commands originated from a congested switch. Its controller attempts to maintain a call acceptance rate at a predetermined value.
There is a need in the art for a congestion control technique in a communication system that maintains high network throughput and that prevents switches from experiencing severe congestion events while, at the same time, working within the framework of the present ACC signaling standard.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide a congestion control method in which a source switch measures the number of calls sent by the source switch to a congested switch that are rejected by the congested switch. In response to a report from the congested switch identifying its level of congestion, the source switch blocks calls destined for the congested switch based upon the measured number of rejected calls, the number of calls it may have previously blocked and the value of the ACC level it most recently received from the congested switch.
A given switch may act as both a congested switch and a source switch. The switch routes call traffic to one or more switches in a network; the switch is a source to those other switches. At the same time, the same switch may receive call traffic from the other switches. The switch may be a congested switch and the other switches may be source switches.


REFERENCES:
patent: 5068892 (1991-11-01), Livanos
patent: 6047118 (2000-04-01), Sofman et al.
S. Fuhrmann et al., “An Adaptive Autonomous Network Congestion Controller,”IEEE Proc. of 35thConf. on Decision and Control, Kobe, Japan, Dec. 1996, vol. 1, 1996, pp. 301-306.
B. Wallstrom and C. Nyberg, “Transient Model of Overload Control and Priority Service in SPC-system,”Teletraffic and Datatraffic in a Period of Change, ITC-13, A. Jensen and V. B. Iversen (Eds.), Elsevier Science Publishers B.V. (North-Holland), 1991; pp. 429-434.
S. Thierry et al., “Overload Control In A Distributed System,”Teletraffic and Datatraffic in a Period of Change, ITC-13, A. Jensen and V. B. Iversen (Eds.), Elsevier Science Publishers B.V (North-Holland), pp. 421-427.
“Digital Exchanged: Digital Exchange Design Objectives—Operations and Maintenance,” ITU-T Recommendation Q.543,International Telecommunication Union, Mar. 1993.
D. J. Houck et al., “Failure and Congestion Propagation Through Signaling Control,” Proc. of the 14thInternational Teletraffic Congress, Antibes, France, Jun. 1994, J. Labetoulle and J. W. Roberts (Eds.), pp. 367-376.
J. E. Burns and D. Ghosal, “Automatic Detection and Control of Media Stimulated Focused Overloads,” ITC 15, V. Ramaswami and P. E. Wirth (Eds.), Elsevier Science B.V., 1997, pp. 889-900.
M. Kihl and M. Rumsewicz, “Analysis of overload control strategies in combined SSP-SCPs in the Intelligent Network,” ITC 15, V. Ramaswami and P. E. Wirth (Eds.), Elsevier Science B.V., 1997, pp. 1209-1218.
P. Hosein, “An Improved Automatic Congestion Control Algorithm for Telecommunication Networks,” submitted toTelecommunication Systems, 1998.
S. Fuhrmann et al., “An Adaptive

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