Abstract:
A method and apparatus for handling an overload condition in a communication network are disclosed. For example, the method calculates a call target rate by at least one core signaling network element. The method then uses the call target rate by the at least one core signaling network element to start throttling signaling traffic if a total queueing delay of the at least one core signaling network element exceeds a predefined high threshold in a measurement interval.

Description:
The present invention relates generally to communication networks and, more particularly, to a method and apparatus for providing queue delay internal overload controls for signaling traffic in communication networks, e.g., packet networks such as Internet Protocol (IP) networks, Internet Protocol (IP) Multimedia Subsystem (IMS) networks, and Voice over Internet Protocol (VoIP) networks. 
     BACKGROUND OF THE INVENTION 
     Capacity of telephony networks is traditionally optimized to carry load during busy hour traffic while subject to some level of congestion and/or failure of network elements within a network. However, it is not engineered to account for extremely large traffic surges caused by exception events. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention enables a core signaling network element within a network to dynamically adjust a blocking rate of incoming calls received from a plurality of edge signaling network elements based on a target queueing delay parameter. For example, the method calculates a call target rate by at least one core signaling network element. The method then uses the call target rate by the at least one core signaling network element to start throttling signaling traffic if a total queueing delay of the at least one core signaling network element exceeds a predefined high threshold in a measurement interval. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teaching of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an exemplary packet network related to the present invention; 
         FIG. 2  illustrates an exemplary queue delay internal overload control system related to the present invention; 
         FIG. 3  illustrates a flowchart of a method for internal rate overload control in a packet network of the present invention; and 
         FIG. 4  illustrates a high level block diagram of a general purpose computer suitable for use in performing the functions described herein. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     Capacity of telephony networks is traditionally optimized to carry load during busy hour traffic while subject to some level of congestion and/or failure of network elements within a network. However, it is not engineered to account for extremely large traffic surges caused by exception events, such as the sudden increase in call volumes experienced after a major disaster, during contests of a highly popular television show in which viewers can participate by voting via telephony endpoint devices, or following an advertisement campaign after which a large number of customers calling to a particular toll free number within a short period of time. To cope with such exception events, operators rely on traditional network management capabilities to handle the sudden increase in traffic load effectively. However, in new and emerging packet based network, such as SIP based servers within IP networks, there are new challenges to be addressed. For example, the SIP protocol introduces new messages and requires a larger number of messages per call than in traditional telephony networks. In addition, routing within SIP networks often involves multiple routing choices to elements that can have varying capacities. SIP servers need to be able to protect against traffic surges, and need to maximize throughput during traffic overload. 
     To address this criticality, the present invention enables queue delay internal overload control for signaling traffic in a packet network, e.g., a VoIP network.  FIG. 1  illustrates an illustrative packet network  100 , e.g., a VoIP network, related to the present invention. In  FIG. 1 , three edge signaling network elements  120 ,  121 , and  122  are deployed at the edge of VoIP network  110  interconnecting access networks  130 ,  131 , and  132 , respectively. Core signaling network element  111  is interconnected with edge signaling network elements  120 ,  121 , and  122  via the VoIP network  110 . In general, a plurality of core signaling network elements and a plurality of edge signaling networks can exist in VoIP network  110 . 
     Note that examples of an edge signaling network element include a Media Gateway or a Session Border Controller that performs signaling, media control, security, and call admission control and related functions for calls originated from an access network and to be processed by a core signaling network element. The core signaling network element resides within the packet core infrastructure and communicates with the edge signaling network elements using e.g., the Session Initiation Protocol (SIP) over the underlying IP network  110 . 
     The core signaling network element  111  can be implemented for example as a Media Gateway Controller, a Softswitch, an Application Server (AS), or a Call Session Control Function (CSCF) in an Internet Protocol Multimedia Subsystem (IMS) network and performs network wide call control related functions. 
     SIP is an example signaling protocol used between signaling network elements, and is discussed here to illustrate a signaling communications network. Broadly defined, SIP is an Internet Engineering Task Force (IETF) signaling protocol standard for creating, modifying, and terminating call sessions. These sessions include, but are not limited to, internet telephone calls, multimedia distributions, and multimedia conferences etc. SIP invitations (used to create sessions) carry session descriptions that allow entities to agree on a set of compatible media types. SIP makes use of elements called proxy servers to help route call requests, authenticate and authorize users for services, implement provider call-routing policies, and provide features to users. In  FIG. 1 , edge signaling network elements  120 ,  121 , and  122  are edge proxies and core signaling network element  111  is a core proxy according to the SIP protocol standard. IMS is an architectural framework for delivering Internet Protocol (IP) multimedia to mobile users defined by the standard body, 3rd Generation Partnership Project (3GPP). 
     In one example, during an exception event in which a large volume of calls are placed by callers destined to access network  132 , edge signaling network elements  120  and  121  process call requests originating from access networks  130  and  131  and forward the requests to core signaling network element  111  for further processing using flows  150  and  151 , respectively. If the total call volume far exceeds the processing capacity of the core signaling network element  111 , core signaling network element  111  can become so congested that it results in a catastrophic failure in which no calls can be processed at all. In this case, call requests destined to edge signaling network element  122  will not be processed by core signaling network element  111  for call completion to access network  132 . 
       FIG. 2  illustrates an illustrative queue delay internal overload control mechanism  200  related to the present invention. In order to prevent the aforementioned catastrophic failures from occurring at a core signaling network element, the present invention enables the core signaling network element to internally reject incoming traffic. In  FIG. 2 , an offered load of rate, λ offered , arrives at the core signaling network element  202  from the edge signaling network element  201 . Under overload conditions, the call target load of rate, λ target , processed by the core signaling network element  202  is internally and dynamically adjusted to prevent the core signaling network element  202  from being overloaded. 
       FIG. 3  illustrates a flowchart of a method  300  for providing an internal overload control in a packet network, e.g., a VoIP network, of the present invention. For example, one or more steps of method  300  can be performed by a core signaling network element. 
     Method  300  starts in step  305  and proceeds to step  310 . In step  310 , in a measurement interval t, the method  300  measures the message service rate, μ t , (e.g., in units of messages per second) and the total queueing delay of the core signaling network element. In one embodiment, the message service rate is calculated by dividing the number of signaling messages processed in a predefined time interval T by the total busy processor time within T. In one embodiment, the total queuing delay, d t , is calculated by dividing the signaling message queue length by the measured message service rate, μ t , at the end of the predefined time interval T. Note that T is a user configurable parameter representing the duration of a sampling interval and, for example could be set to 0.1 second. The minimum value of μ t  is zero. It should be noted that when μ t  is less than or equal to 0, then d t  is set to 0. It should be noted that the various values that are provided above and below are only illustrative and should not be interpreted as a limitation of the present invention. Namely, these values can be selected in accordance with the requirements of a particular implementation. 
     In step  330 , the method checks if the total queuing delay, d t , is below a predefined low threshold. If the total queuing delay is below the predefined low threshold, the method proceeds to step  380 ; otherwise, the method proceeds to step  340 . In one embodiment, the predefined low threshold is calculated by multiplying a predefined low watermark factor, β, with a predefined target queueing delay parameter, d e , where β and d e  are user configurable parameters that can be set, for exemplary purposes only, to 0.1 and 0.2 second, respectively. 
     In step  340 , the method checks if the measured total queuing delay, d t , exceeds a predefined high threshold. If the total queueing delay has exceeded the predefined high threshold, the method proceeds to step  350 ; otherwise, the method proceeds back to step  310  to process the next measurement time interval. In one embodiment, the predefined high threshold is calculated by multiplying a predefined high watermark factor, α, with a predefined target queueing delay parameter, d e , where α and d e  are user configurable parameters that can be set to 0.9 and 0.2 seconds, respectively, for illustrative purposes. 
     In step  350 , the method calculates the message target rate for internal rate overload control purposes. In one embodiment, the message target rate, λ t , is defined as:
 
λ t =λ t *(1−( d   t   −d   e )/ C ), where
 
d e  is the user configurable target queueing delay and C is a user configurable control interval duration that can be set to 0.2 seconds and 0.1 seconds, respectively, for illustrative purposes. The expression μ t *(d t −d e )/C is equivalent to the signaling message queue backlog. The message target rate is the desired signaling message service rate (e.g., measured in units of messages per second) at or below which the core signaling network element is targeted for processing incoming signaling messages from a plurality of edge signaling network elements.
 
     In one embodiment, the calculated message target rate is further divided by the estimated messages per call parameter, r t , to obtain the call target rate, λ t /r t , (e.g., measured in units of calls per second). The call target rate is the desired call service rate (e.g., measured in units of calls per second) at or below which the core signaling network element is targeted for processing incoming calls from a plurality of edge signaling network elements. Note that r t  is the Exponentially Weighted Moving Average (EWMA) estimate derived from dividing the measured incoming message rate by the measured incoming call rate. 
     It should be noted that message and call rates are the counts of incoming messages and calls during the measurement interval T. It should be noted that any method for estimating messages per call can be used. The weight, w, used in calculating the EWMA estimate of r t  is a user configurable parameter, for example set to 0.8. It should be noted that EWMA or any equivalent smoothing algorithm can be used. 
     In step  360 , the method starts or updates discarding incoming signaling traffic based on the calculated call target rate. The method then proceeds back to step  310  to process the next measurement time interval. Note that the core signaling network element throttles signaling traffic at the call level. In other words, the core signaling network element rejects signaling messages on a combination of call and signaling message type. For example, the core signaling network element may reject the messages based on the type of signaling message for any given call. This allows the ability to give priority to messages related to calls that are already in progress and discarding only new call messages. 
     In one embodiment of the present invention, the core signaling network element throttles offered signaling traffic based on a blocking percentage derived from the call target service rate parameter. For instance, in one embodiment of the present invention, the blocking percentage used to discard offered traffic can be expressed as ((offered load in units of calls per second/call target rate in units of calls per second)−1). In another embodiment of the present invention, the core signaling network element throttles offered signaling traffic using a leaky bucket algorithm according to the calculated call target rate parameter. Furthermore, blocking algorithms such as window algorithms, or gap algorithms can also be used. It should be noted that any commonly known throttling algorithms can be used. 
     In step  380 , the method checks if queue delay internal overload control is already active. If the overload control is already active, the method proceeds to step  390 ; otherwise, the method proceeds back to step  310  to process the next measurement time interval. 
     In step  390 , the method deactivates the queue delay internal overload control and stops throttling signaling traffic received from edge signaling network elements. The method then proceeds back to step  310  to process the next measurement time interval. 
     It should be noted that although not specifically specified, one or more steps of method  300  may include a storing, displaying and/or outputting step as required for a particular application. In other words, any data, records, fields, and/or intermediate results discussed in the method  300  can be stored, displayed and/or outputted to another device as required for a particular application. Furthermore, steps or blocks in  FIG. 3  that recite a determining operation, or involve a decision, do not necessarily require that both branches of the determining operation be practiced. In other words, one of the branches of the determining operation can be deemed as an optional step. 
       FIG. 4  depicts a high level block diagram of a general purpose computer suitable for use in performing the functions described herein. As depicted in  FIG. 4 , the system  400  comprises a processor element  402  (e.g., a CPU), a memory  404 , e.g., random access memory (RAM) and/or read only memory (ROM), a module  405  for providing an internal rate overload control, and various input/output devices  406  (e.g., storage devices, including but not limited to, a tape drive, a floppy drive, a hard disk drive or a compact disk drive, a receiver, a transmitter, a speaker, a display, a speech synthesizer, an output port, and a user input device (such as a keyboard, a keypad, a mouse, and the like)). 
     It should be noted that the present invention can be implemented in software and/or in a combination of software and hardware, e.g., using application specific integrated circuits (ASIC), a general purpose computer or any other hardware equivalents. In one embodiment, the present module or process  405  for providing a queue delay based internal overload control can be loaded into memory  404  and executed by processor  402  to implement the functions as discussed above. As such, the present process  405  for providing a queue delay based internal overload control (including associated data structures) of the present invention can be stored on a computer readable medium, e.g., RAM memory, magnetic or optical drive or diskette and the like. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.