Title of Invention	A METHOD OF OVERLOAD CONTROL IN A COMMON CHANNEL SIGNALING LINK SYSTEM
Abstract	The invention relates to a method of overload control in a common channel signaling link system, comprising the steps of: a link control process detecting an amount of unprocessed signaling messages in a queue of messages regularly (201) and determining whether the amount of unprocessed signaling messages is more than an overload start threshold (203), if the amount of unprocessed signaling messages is more than the overload start threshold, the link control process dynamically controlling an amount of new services accessed by a service processing process by sending a message to the service processing process (205).

Title of Invention

A METHOD OF OVERLOAD CONTROL IN A COMMON CHANNEL SIGNALING LINK SYSTEM

Abstract

The invention relates to a method of overload control in a common channel signaling link system, comprising the steps of: a link control process detecting an amount of unprocessed signaling messages in a queue of messages regularly (201) and determining whether the amount of unprocessed signaling messages is more than an overload start threshold (203), if the amount of unprocessed signaling messages is more than the overload start threshold, the link control process dynamically controlling an amount of new services accessed by a service processing process by sending a message to the service processing process (205).

Full Text	TECHNICAL FIELD OF THE INVENTION The present invention relates to a method of overload control for signaling traffic in a common channel signaling link system during service processing in a communication system, and particularly to a method of overload control for service access processing and signaling traffic in the common channel signaling link system. BACKGROUND OF THE INVENTION la a common channel signaling link system, such as signaling interface No. 7, V5 interface, all the signaling are transmitted via signaling links. If the signaling traffic is too large and exceeds the processing capability of the signaling links, a large number of signaling links in the system are interrupted or the links are failed to be established, which would cause the frequent link establishment, thereby influencing whole performance of the system greatly. Therefore, a reasonable solution of overload control for signaling links is needed to reasonably control the amount of service access of the system when the signaling links are overloaded, to ensure the loads of the signaling links to maintain in relative steady and controllable state so mat the system can be operated normally with large call traffic and has a self-retrieval function for the signaling links. In the common channel signaling link system, local signaling messages are generated by a service layer and transmitted by a link layer. At an opposite end, the signaling messages are first received by the link layer and then transmitted to the service layer for processing. A process of acknowledgement from the opposite end is included in this process, that is, after a number of local signaling messages are sent to the opposite end, other signaling messages cannot continue to be sent until an acknowledgement message is received from the opposite end. When the local traffic is very large, since speed of generating the signaling messages locally is always faster than that of acknowledging the signaling messages at the opposite end, the signaling messages will be accumulated locally. A system will fail when the accumulation of signaling messages reaches a certain degree. A method of overload detection and control for Service Control Point (SCP) is disclosed in US patent No. 6510214. In this method, an overload control system estimates an overload rating in response to a latency and a queue depth of a service logic interpreter in the service control point and a Transaction Capabilities Application Part (TCAP) controls the service access according to the overload rating. An absolute value is used in the detection method of US patent No. 6510214 and the load of the system has been large when the overload is generated, so the processing manner is to discard the newly arrived services when the system is in overload state. SUMMARY OF THE INVENTION An object of the present invention is to provide a method of overload control in a common channel signaling link system, in which method a service processing process is informed of instantaneous overload information of signaling links by monitoring in real time a queue of signaling messages to be processed in a link layer, and traffic of signaling links is controlled by controlling an amount of new services accessed by a service layer, so that the problem that the signal links are frequently interrupted and the problem that the traffic of service processing fluctuates great and is unsteady can be solved to ensure reliability of the system's operation. For above purpose of the present invention, the technical solution is as follows. A method of overload control in a common channel signaling link system comprises the steps of: a link control process detecting an amount of unprocessed signaling messages in a queue of messages regularly; determining whether the amount of unprocessed signaling messages is more than an overload start threshold; and if the amount of unprocessed signaling messages is more than the overload start threshold, the link control process dynamically controlling an amount of new services accessed by a service processing process by sending a message to the service processing process. Preferably, the step of the link control process dynamically controlling an amount of new services accessed by a service processing process includes: performing the following steps of (i) ~ (ii) repeatedly at a predetermined time interval until an amount of signaling messages in the queue of messages is less than an overload retrieval threshold: (i) determining whether the amount of signaling messages in the queue of messages is less than the overload retrieval threshold, and if the amount of signaling messages in the queue of messages is less than the overload retrieval threshold, informing the service processing process that the system has retrieved normal state; (ii) if the amount of signaling messages in the queue of messages is more than the overload retrieval threshold, performing the following steps: determining whether a length of the current queue of messages is longer than that of a queue of messages previous to the predetermined time interval; if the length of the current queue of messages is longer than that of the queue of messages previous to the predetermined time interval, detennining whether an increment of the signaling messages in the queue of messages exceeds an overload increment threshold; if the increment of the signaling messages in the queue of messages exceeds the overload increment threshold, the link control process sending an overload controlling message to the service processing process; if the length of the current queue of messages is less than or equal to that of the queue of messages previous to the predetermined time interval, determining whether a decrement of the signaling messages in the queue of messages exceeds an overload decrement threshold; and if the decrement of the signaling messages in the queue of messages exceeds the overload decrement threshold, the link control process sending an overload relieving message to the service processing process. Preferably, the step of the link control process dynamically controlling an amount of new services accessed by a service processing process further includes: the service processing process receiving the message from the link control process, decreasing or increasing a predetermined amount in the amount of new accessed services and equally distributing calls allowed to be accessed to statistical windows for call access. Preferably, the step of informing the service processing process that the system has retrieved normal state further includes: the service processing process gradually increasing the amount of new accessed services at a predetermined time interval. Preferably, the step of the link control process dynamically controlling an amount of new services accessed by a service processing process further includes: the service processing process receiving the message from the link control process, and if the message is the overload controlling message, the service processing process decreasing the amount of new accessed services by m; if the message is the overload relieving message, the service processing process increasing the amount of new accessed services by n, wherein both m and n are natural numbers and m>n. Preferably, the overload start threshold is set to 50% ~ 70%, representing ratio of an amount of the current signaling messages in the queue of messages and the size of storage area for the queue of messages. Preferably, the overload start threshold is set to 60%. Preferably, the overload retrieval threshold approximates to and is less than the overload start threshold. The method of overload control in a common channel signaling link system according to the present invention implements overload control as early as possible according to capabilities of signaling processing and link transmission of the system, and detects in real time the variation of the amount of signaling messages in the queue of signaling messages to dynamically control the amount of new accessed services, so that the problem that the V5 signaling links between the BSS base station sub-system and the switch are interrupted is substantively solved by rapid decreasing and slow increasing as well as equally and randomly rejecting access of new call services, which causes the call traffic in the system steady and the fluctuation of signaling traffic small, thereby effectively reducing the impact on the switch and V5 interface and ensuring the steadiness and reliability of the system. Also, the method provided by the present invention may be applied to a SS7 (signaling No. 7) link system. BRIEF DESCRIPTION OF THE DRAWINGS The above features, advantages and objects of the present invention will become more apparent by describing embodiments thereof in detail with reference to the accompanying drawings in which: Fig. 1 shows a structural schematic diagram of a system in which a method of overload control in a common channel signaling link system according to an embodiment of the present invention can be implemented; Fig. 2 shows a flow diagram of a method of overload control in a common channel signaling link system according to an embodiment of the present invention; Fig. 3 shows a flow diagram of the process of dynamically controlling an amount of new accessed services in the method of overload control in a common channel signaling link system according to an embodiment of the present invention; Fig. 4 is a diagram showing a test result of overload in a common channel signaling link system to which the present invention is not applied; Fig. 5 is a diagram showing a test result of overload in a common channel signaling link system to which the present invention is applied. DETAILED DESCRIPTION OF EMBODIMENTS The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. Fig. 1 is a structural schematic diagram of a system in which a method of overload control in a common channel signaling link system according to an embodiment of the present invention can be implemented. As shown in Fig. 1, the common channel signaling link system in the embodiment includes a link control process 101 and a service processing process 103. Both processes transmit communication messages between each other through a communication platform 105. In the common signaling link system, service processing process 103 is in a service layer for controlling access of new services and generating corresponding signaling messages. The link control process 101 is in a transmission layer for controlling the transmission of local signaling messages to a link layer of an opposite end system 109 over a singling link 107. The link layer of the opposite end system 109 performs an acknowledgement process for the received signaling messages and then transmits these messages to the service layer for processing. After a number of signaling messages are sent to the opposite end system by the transmission layer of the local system, other signaling messages cannot continue to be sent until an acknowledgement message is received from the opposite end system 109. When the service traffic of the local system is very large, the signaling messages tend to be accumulated at the transmission layer of the local system because the speed of generating the signaling messages by the local system is always faster than that of acknowledging the signaling messages at the opposite end. Therefore, the overload in the signaling link system is needed to be controlled to rationally control an amount of accessed services of the system in the case that the system is overloaded, so that the load of the signaling link is ensured to be in relative steady and controllable state and the system can operate normally with large call traffic. Fig. 2 shows a flow diagram of a method of overload control in a common channel signaling link system according to the present invention. As shown in Fig. 2, first at Step 201, the link control process monitors an amount of unprocessed signaling messages. Then, at Step 203, the link control process determines whether the amount of unprocessed signaling messages exceeds an overload start threshold. If so, an overload controlling message will be sent to the service processing process. Specifically, since a message buffer for storing the unprocessed signaling messages in the system usually has large size and extremely goes beyond the capabilities of signaling processing and link transmission of the system, the overload control should be performed as early as possible on the basis of the capabilities of signaling processing and link transmission of the system, such that the system is able to control the link state and service access sufficiently. If the overload control is enabled late and a great number of services have accessed to the system, the services would generate a great number of signaling messages, which leads the link control process to lose the control capability of signaling link and thus the signaling link would be blocked. In this embodiment, the overload start threshold is set to 60%, representing ratio of an amount of current signaling messages in the queue of messages and the size of storage area for the queue of messages. When the link control process detects that the amount of unprocessed signaling messages in the current queue of messages exceeds 60% of the size of storage area for the queue of messages, the overload controlling message is sent to the service processing process to start the overload control. After receiving the overload controlling message from the link control process, the service processing process decreases the amount of new accessed services. In this embodiment, the service processing process decreases 2 new accessed services each time receiving the overload controlling message. In this embodiment, the overload control is implemented in a manner of refusing certain new services to access randomly, rather than discarding the generated signaling messages or releasing the established services. At Step 205, the link control process dynamically controls the amount of new services accessed by the service processing process. Specifically, the process of the link control process dynamically controlling the amount of new services accessed by the service processing process is shown as Fig. 3. Fig. 3 shows a flow diagram of the process of dynamically controlling the amount of new accessed services in the method of overload control in a common channel signaling link system according to an embodiment of the present invention As shown in Fig. 3, the link control process dynamically controls the amount of new services accessed by the service processing process by performing all the steps in Fig. 3 repeatedly at a particular time interval, until the amount of signaling message in the queue of messages is lower than or equal to an overload retrieval threshold. At first, At Step 301, the link control process initiates an overload monitor timer to set the time interval for detecting the queue of messages regularly. When the singling link is overloaded, the signaling traffic is very large and more signaling messages would be generated in a short time, thus the time interval should be set as short as possible to prevent from generating more new signaling messages due to such a long time interval. Moreover, the time interval is depended on the time interval of a scheduling process of an operation system. Generally, the time interval is set to 20 ms. At Step 302, when the overload monitor timer is up, the link control process detects the amount of signaling messages in the queue of messages and determines whether the amount of signaling messages in the queue of messages is lower than or equal to the overload retrieval threshold. If the amount of signaling messages in the queue of messages is lower than or equal to the overload retrieval threshold, the process is advanced to Step 303; otherwise Step 305 will be performed. In this embodiment, in order to early and dynamically control the overload of the signaling link of the system to make the system still has great control capability under overload state, the overload retrieval threshold is set to approximate to and be lower than the overload start threshold so that the system can detect new overload state as soon as possible and control it if the traffic of signaling messages is large after the system is relieved of overload state. At Step 303, the link control process informs the service processing process of entering into the overload retrieval phase. The service processing process begins to retrieve the services and sets a service retrieval timer, by which the amount of the accessed services is gradually increased until the system retrieves normal state (Step 304). In this embodiment, the service retrieval timer can be used to control a time interval, such as 2 seconds, for the service processing process to retrieve the amount of new accessed services. Slight adjustment may be adopted to make the increment of the new accessed services each time not too big to prevent the system from fluctuating greatly, for example, the increment of the new accessed services each time is one. The service retrieval phase is not stopped until the system retrieves normal state or the service processing process receives the overload controlling message again. At Step 305, the link control process initiates the overload monitor timer again and then, at Step 306, the link control process determines whether the amount of signaling messages in the queue of messages is more than the overload start threshold and determines whether the length of the current queue of messages is shorter than that of the queue of messages detected when the overload monitor timer is up last time. If yes, the process is advanced to Step 307; otherwise Step 309 will be performed. At Step 307, the link control process further determines whether the decrement of the signaling messages in the queue of messages is more than a predetermined overload decrement threshold during the period defined by the overload monitor timer. If yes, the process is advanced to Step 308 in which the amount of the new accessed services is increased; otherwise Step 311 will be performed. The overload decrement threshold is determined based on the size of storage area for the queue of messages as well as capabilities of service access and link control of the system. The overload decrement threshold is set to 45 in this embodiment. At Step 308, the link control process sends an overload relieving message. After the service processing process receives the message, the amount of the new accessed service is increased and the overload retrieval timer is reset. In this embodiment, after the service processing process receives the overload relieving message, the amount of the new accessed service is increased by one. Then, the process is advanced to Step 311. At Step 309, the link control process further determines whether the increment of the signaling messages in the queue of messages is more than a predetermined overload increment threshold during the period defined by the overload monitor timer. If yes, the process is advanced to Step 310 in which the amount of the new accessed services is further decreased and the overload retrieval timer is reset; otherwise Step 311 would be performed. The overload increment threshold is determined based on the size of storage area for the queue of messages as well as capabilities of service access and link control of the system. The overload increment threshold is set to 40 in this embodiment. At Step 310, the link control process sends the overload controlling message to the service processing process. After the service processing process receives the message, the amount of the new accessed services is further decreased. In this embodiment, after receiving the overload controlling message, the service processing process decreases 2 new accessed services. Then the process is advanced to Step 311. In this embodiment, in order to prevent the system from fluctuating greatly, slight adjustment for overload is used to ensure that the changed service traffic each time is not very large, thus the speed of decreasing the new accessed services of the system is faster than that of increasing the new accessed services. At Step 311, the process returns to Step 302 and repeats above steps to continue the regular detection of the amount of signaling messages in the queue of messages and dynamical control of the amount of the new services accessed by the service processing process, until the system retrieves normal state. In this embodiment, the service processing process limits the access of new calls equally according to the overload controlling message and overload relieving message sent from the link control process. The control of the access of new calls by the service processing process is as follows: the service processing process sets the number of statistical windows in accordance with the ratio of overload control service access. Generally, the number of statistical windows is set to 32, i.e. the amount of accessed calls is counted with a cycle of every 32 calls. The amount of calls allowed by the current statistical window to be accessed is set and it is determined that whether the newly accessed call numbers are allowed to be accessed. The call numbers allowed to be accessed are equally distributed into the statistical windows. When a new service is accessed, if its call number is the one allowed to be accessed, the new service is allowed to be accessed; otherwise, if its call number is the one rejected to be accessed, the new service is rejected. Moreover, Fig. 4 shows a test result of overload in a common channel signaling link system to which the present invention is not applied. In the common channel signaling link system, a program for simulating large call traffic is used for call test. A front end controls continual calls and simulates initiation of calls in 240 lines (total 480 lines including lines for initiating calls and lines for receiving calls). The duration of a call is 6 seconds and the interval between calls is 4 seconds. It can be seen that the call traffic is fluctuated greatly in the common channel signaling link system when the embodiment of the present invention is not applied. The interface tends to be interrupted due to the overload of the system Fig. 5 is a diagram showing a test result of overload in a common channel signaling link system to which the present invention is applied. In this embodiment, the program for simulating large call traffic is used for call test. A front end controls continual calls and simulates initiation of calls in 240 lines (total 480 lines including lines for initiating calls and lines for receiving calls). The duration of a call is 6 seconds and the interval between calls is 4 seconds. It can be seen that the call traffic is fluctuated slightly in the common channel signaling link system to which the embodiment of the present invention is applied. The traffic of the system is steady. While the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that various modifications and substitutions can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims. WE CLAIM: 1. A method of overload control in a common channel signaling link system, said method comprising the steps of a link control process detecting an amount of unprocessed signaling messages in a queue of messages regularly (201) and determining whether the amount of unprocessed signaling messages is more than an overload start threshold (203); and if the amount of unprocessed signaling messages is more than the overload start threshold, by sending a message to a service processing process, the link control process also dynamically controlling an amount of new services accessed by the service processing process (205); wherein the step of the link control process dynamically controlling an amount of new services accessed by a service processing process comprises: performing the following steps of (i) and (ii) repeatedly at a predetermined time interval until an amount of signaling messages in the queue of messages is less than an overload retrieval threshold: (i) determining whether the amount of signaling message in the queue of messages is less than the overload retrieval threshold (302); (ii) if the amount of signaling message in the queue of messages is more than the overload retrieval threshold, comparing a length of current queue of messages with a length of a queue of messages previous to the predetermined time interval, and decreasing or increasing the amount of new accessed services according to the comparing result. 2. The method as claimed in claim 1, wherein in steps (i) and (ii): determining whether a length of current queue of messages is longer than that of a queue of messages previous to the predetermined time interval (306), if the length of current queue of messages is longer than that of the queue of messages previous to the predetermined time interval, determining whether an increment of the signaling messages in the queue of messages is more than an overload increment threshold (309), if the increment of the signaling messages in the queue of messages is more than the overload increment threshold, the link control process sends an overload controlling message to the service processing process, if the length of current queue of messages is less than or equal to that of the queue of messages previous to the predetermined time interval, determining whether the decrement of the signaling messages in the queue of messages is more than an overload decrement threshold (307), and if the decrement of the signaling messages in the queue of messages is more than the overload decrement threshold, the link control process sends an overload relieving message to the service processing process. 3. The method as claimed in claim 1 or 2, wherein, if the amount of signaling message in the queue of messages is less than the overload retrieval threshold, informing the service processing process that the system has retrieved normal state. 4. The method as claimed in claim 1, wherein the step of the link control process dynamically controlling an amount of new services accessed by a service processing process comprises: the service processing process receiving the message from the link control process, decreasing or increasing a predetermined amount in the amount of new accessed services and equally distributing calls allowed to be accessed into statistical windows for call accessing. 5. The method as claimed in claim 3, wherein the step of informing the service processing process that the system has retrieved normal state of the system comprises: the service processing process gradually increasing the amount of new accessed services at a predetermined time interval (303). 6. The method as claimed in claim 2, wherein the step of the link control process dynamically controlling an amount of new services accessed by a service processing process comprises: the service processing process receiving the message from the link control process, if the message is the overload controlling message, the service processing process decreasing the amount of new accessed services by m (310), if the message is the overload relieving message, the service processing process increasing the amount of new accessed services by n (308), wherein both m and n are natural numbers and m>n. 7. The method as claimed in claim 1, wherein the overload start threshold is set to 50% ~ 70% of a size of storage area for the queue of messages occupied by an amount of current signaling messages in the queue of messages. 8. The method as claimed in claim 7, wherein the overload start threshold is set to 60% of the size of storage area for the queue of messages occupied by the amount of current signaling messages in the queue of messages. 9. The method as claimed in claim 7, wherein the overload retrieval threshold approximates to and is less than the overload start threshold. ABSTRACT A METHOD OF OVERLOAD CONTROL IN A COMMON CHANNEL SIGNALING LINK SYSTEM The invention relates to a method of overload control in a common channel signaling link system, comprising the steps of: a link control process detecting an amount of unprocessed signaling messages in a queue of messages regularly (201) and determining whether the amount of unprocessed signaling messages is more than an overload start threshold (203), if the amount of unprocessed signaling messages is more than the overload start threshold, the link control process dynamically controlling an amount of new services accessed by a service processing process by sending a message to the service processing process (205).

Full Text

TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of overload control for signaling traffic in a common
channel signaling link system during service processing in a communication system, and
particularly to a method of overload control for service access processing and signaling traffic in the
common channel signaling link system.
BACKGROUND OF THE INVENTION
la a common channel signaling link system, such as signaling interface No. 7, V5 interface, all
the signaling are transmitted via signaling links. If the signaling traffic is too large and exceeds the
processing capability of the signaling links, a large number of signaling links in the system are
interrupted or the links are failed to be established, which would cause the frequent link
establishment, thereby influencing whole performance of the system greatly. Therefore, a reasonable
solution of overload control for signaling links is needed to reasonably control the amount of
service access of the system when the signaling links are overloaded, to ensure the loads of the
signaling links to maintain in relative steady and controllable state so mat the system can be
operated normally with large call traffic and has a self-retrieval function for the signaling links.
In the common channel signaling link system, local signaling messages are generated by a service
layer and transmitted by a link layer. At an opposite end, the signaling messages are first received by
the link layer and then transmitted to the service layer for processing. A process of
acknowledgement from the opposite end is included in this process, that is, after a number of local
signaling messages are sent to the opposite end, other signaling messages cannot continue to be sent
until an acknowledgement message is received from the opposite end. When the local traffic is very
large, since speed of generating the signaling messages locally is always faster than that of
acknowledging the signaling messages at the opposite end, the signaling messages will be
accumulated locally. A system will fail when the accumulation of signaling messages reaches a
certain degree.
A method of overload detection and control for Service Control Point (SCP) is disclosed in US
patent No. 6510214. In this method, an overload control system estimates an overload rating in
response to a latency and a queue depth of a service logic interpreter in the service control point and
a Transaction Capabilities Application Part (TCAP) controls the service access according to the
overload rating. An absolute value is used in the detection method of US patent No. 6510214 and
the load of the system has been large when the overload is generated, so the processing manner is to

discard the newly arrived services when the system is in overload state.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of overload control in a common
channel signaling link system, in which method a service processing process is informed of
instantaneous overload information of signaling links by monitoring in real time a queue of
signaling messages to be processed in a link layer, and traffic of signaling links is controlled by
controlling an amount of new services accessed by a service layer, so that the problem that the
signal links are frequently interrupted and the problem that the traffic of service processing
fluctuates great and is unsteady can be solved to ensure reliability of the system's operation.
For above purpose of the present invention, the technical solution is as follows.
A method of overload control in a common channel signaling link system comprises the steps of:
a link control process detecting an amount of unprocessed signaling messages in a queue of
messages regularly;
determining whether the amount of unprocessed signaling messages is more than an overload
start threshold; and
if the amount of unprocessed signaling messages is more than the overload start threshold, the
link control process dynamically controlling an amount of new services accessed by a service
processing process by sending a message to the service processing process.
Preferably, the step of the link control process dynamically controlling an amount of new services
accessed by a service processing process includes: performing the following steps of (i) ~ (ii)
repeatedly at a predetermined time interval until an amount of signaling messages in the queue of
messages is less than an overload retrieval threshold:
(i) determining whether the amount of signaling messages in the queue of messages is less than
the overload retrieval threshold, and if the amount of signaling messages in the queue of messages
is less than the overload retrieval threshold, informing the service processing process that the system
has retrieved normal state;
(ii) if the amount of signaling messages in the queue of messages is more than the overload
retrieval threshold, performing the following steps:
determining whether a length of the current queue of messages is longer than that of a queue of
messages previous to the predetermined time interval;
if the length of the current queue of messages is longer than that of the queue of messages
previous to the predetermined time interval, detennining whether an increment of the signaling
messages in the queue of messages exceeds an overload increment threshold;
if the increment of the signaling messages in the queue of messages exceeds the overload

increment threshold, the link control process sending an overload controlling message to the service
processing process;
if the length of the current queue of messages is less than or equal to that of the queue of
messages previous to the predetermined time interval, determining whether a decrement of the
signaling messages in the queue of messages exceeds an overload decrement threshold; and
if the decrement of the signaling messages in the queue of messages exceeds the overload
decrement threshold, the link control process sending an overload relieving message to the service
processing process.
Preferably, the step of the link control process dynamically controlling an amount of new services
accessed by a service processing process further includes: the service processing process receiving
the message from the link control process, decreasing or increasing a predetermined amount in the
amount of new accessed services and equally distributing calls allowed to be accessed to statistical
windows for call access.
Preferably, the step of informing the service processing process that the system has retrieved
normal state further includes: the service processing process gradually increasing the amount of new
accessed services at a predetermined time interval.
Preferably, the step of the link control process dynamically controlling an amount of new services
accessed by a service processing process further includes: the service processing process receiving
the message from the link control process, and if the message is the overload controlling message,
the service processing process decreasing the amount of new accessed services by m; if the message
is the overload relieving message, the service processing process increasing the amount of new
accessed services by n, wherein both m and n are natural numbers and m>n.
Preferably, the overload start threshold is set to 50% ~ 70%, representing ratio of an amount of
the current signaling messages in the queue of messages and the size of storage area for the queue of
messages. Preferably, the overload start threshold is set to 60%.
Preferably, the overload retrieval threshold approximates to and is less than the overload start
threshold.
The method of overload control in a common channel signaling link system according to the
present invention implements overload control as early as possible according to capabilities of
signaling processing and link transmission of the system, and detects in real time the variation of the
amount of signaling messages in the queue of signaling messages to dynamically control the amount
of new accessed services, so that the problem that the V5 signaling links between the BSS base
station sub-system and the switch are interrupted is substantively solved by rapid decreasing and
slow increasing as well as equally and randomly rejecting access of new call services, which causes

the call traffic in the system steady and the fluctuation of signaling traffic small, thereby effectively
reducing the impact on the switch and V5 interface and ensuring the steadiness and reliability of the
system. Also, the method provided by the present invention may be applied to a SS7 (signaling No.
7) link system.
BRIEF DESCRIPTION OF THE DRAWINGS
The above features, advantages and objects of the present invention will become more apparent
by describing embodiments thereof in detail with reference to the accompanying drawings in which:
Fig. 1 shows a structural schematic diagram of a system in which a method of overload control in
a common channel signaling link system according to an embodiment of the present invention can
be implemented;
Fig. 2 shows a flow diagram of a method of overload control in a common channel signaling link
system according to an embodiment of the present invention;
Fig. 3 shows a flow diagram of the process of dynamically controlling an amount of new accessed
services in the method of overload control in a common channel signaling link system according to
an embodiment of the present invention;
Fig. 4 is a diagram showing a test result of overload in a common channel signaling link system
to which the present invention is not applied;
Fig. 5 is a diagram showing a test result of overload in a common channel signaling link system
to which the present invention is applied.
DETAILED DESCRIPTION OF EMBODIMENTS
The present invention now will be described more fully hereinafter with reference to the
accompanying drawings, in which preferred embodiments of the invention are shown.
Fig. 1 is a structural schematic diagram of a system in which a method of overload control in a
common channel signaling link system according to an embodiment of the present invention can be
implemented. As shown in Fig. 1, the common channel signaling link system in the embodiment
includes a link control process 101 and a service processing process 103. Both processes transmit
communication messages between each other through a communication platform 105. In the
common signaling link system, service processing process 103 is in a service layer for controlling
access of new services and generating corresponding signaling messages. The link control process
101 is in a transmission layer for controlling the transmission of local signaling messages to a link
layer of an opposite end system 109 over a singling link 107. The link layer of the opposite end
system 109 performs an acknowledgement process for the received signaling messages and then

transmits these messages to the service layer for processing. After a number of signaling messages
are sent to the opposite end system by the transmission layer of the local system, other signaling
messages cannot continue to be sent until an acknowledgement message is received from the
opposite end system 109. When the service traffic of the local system is very large, the signaling
messages tend to be accumulated at the transmission layer of the local system because the speed of
generating the signaling messages by the local system is always faster than that of acknowledging
the signaling messages at the opposite end. Therefore, the overload in the signaling link system is
needed to be controlled to rationally control an amount of accessed services of the system in the
case that the system is overloaded, so that the load of the signaling link is ensured to be in relative
steady and controllable state and the system can operate normally with large call traffic.
Fig. 2 shows a flow diagram of a method of overload control in a common channel signaling link
system according to the present invention. As shown in Fig. 2, first at Step 201, the link control
process monitors an amount of unprocessed signaling messages.
Then, at Step 203, the link control process determines whether the amount of unprocessed
signaling messages exceeds an overload start threshold. If so, an overload controlling message will
be sent to the service processing process. Specifically, since a message buffer for storing the
unprocessed signaling messages in the system usually has large size and extremely goes beyond the
capabilities of signaling processing and link transmission of the system, the overload control should
be performed as early as possible on the basis of the capabilities of signaling processing and link
transmission of the system, such that the system is able to control the link state and service access
sufficiently. If the overload control is enabled late and a great number of services have accessed to
the system, the services would generate a great number of signaling messages, which leads the link
control process to lose the control capability of signaling link and thus the signaling link would be
blocked. In this embodiment, the overload start threshold is set to 60%, representing ratio of an
amount of current signaling messages in the queue of messages and the size of storage area for the
queue of messages. When the link control process detects that the amount of unprocessed signaling
messages in the current queue of messages exceeds 60% of the size of storage area for the queue of
messages, the overload controlling message is sent to the service processing process to start the
overload control. After receiving the overload controlling message from the link control process, the
service processing process decreases the amount of new accessed services. In this embodiment, the
service processing process decreases 2 new accessed services each time receiving the overload
controlling message. In this embodiment, the overload control is implemented in a manner of
refusing certain new services to access randomly, rather than discarding the generated signaling
messages or releasing the established services.

At Step 205, the link control process dynamically controls the amount of new services accessed
by the service processing process. Specifically, the process of the link control process dynamically
controlling the amount of new services accessed by the service processing process is shown as Fig.
3.
Fig. 3 shows a flow diagram of the process of dynamically controlling the amount of new
accessed services in the method of overload control in a common channel signaling link system
according to an embodiment of the present invention As shown in Fig. 3, the link control process
dynamically controls the amount of new services accessed by the service processing process by
performing all the steps in Fig. 3 repeatedly at a particular time interval, until the amount of
signaling message in the queue of messages is lower than or equal to an overload retrieval threshold.
At first, At Step 301, the link control process initiates an overload monitor timer to set the time
interval for detecting the queue of messages regularly. When the singling link is overloaded, the
signaling traffic is very large and more signaling messages would be generated in a short time, thus
the time interval should be set as short as possible to prevent from generating more new signaling
messages due to such a long time interval. Moreover, the time interval is depended on the time
interval of a scheduling process of an operation system. Generally, the time interval is set to 20 ms.
At Step 302, when the overload monitor timer is up, the link control process detects the amount
of signaling messages in the queue of messages and determines whether the amount of signaling
messages in the queue of messages is lower than or equal to the overload retrieval threshold. If the
amount of signaling messages in the queue of messages is lower than or equal to the overload
retrieval threshold, the process is advanced to Step 303; otherwise Step 305 will be performed. In
this embodiment, in order to early and dynamically control the overload of the signaling link of the
system to make the system still has great control capability under overload state, the overload
retrieval threshold is set to approximate to and be lower than the overload start threshold so that the
system can detect new overload state as soon as possible and control it if the traffic of signaling
messages is large after the system is relieved of overload state.
At Step 303, the link control process informs the service processing process of entering into the
overload retrieval phase. The service processing process begins to retrieve the services and sets a
service retrieval timer, by which the amount of the accessed services is gradually increased until the
system retrieves normal state (Step 304). In this embodiment, the service retrieval timer can be used
to control a time interval, such as 2 seconds, for the service processing process to retrieve the
amount of new accessed services. Slight adjustment may be adopted to make the increment of the
new accessed services each time not too big to prevent the system from fluctuating greatly, for
example, the increment of the new accessed services each time is one. The service retrieval phase is

not stopped until the system retrieves normal state or the service processing process receives the
overload controlling message again.
At Step 305, the link control process initiates the overload monitor timer again and then, at Step
306, the link control process determines whether the amount of signaling messages in the queue of
messages is more than the overload start threshold and determines whether the length of the current
queue of messages is shorter than that of the queue of messages detected when the overload monitor
timer is up last time. If yes, the process is advanced to Step 307; otherwise Step 309 will be
performed.
At Step 307, the link control process further determines whether the decrement of the signaling
messages in the queue of messages is more than a predetermined overload decrement threshold
during the period defined by the overload monitor timer. If yes, the process is advanced to Step 308
in which the amount of the new accessed services is increased; otherwise Step 311 will be
performed. The overload decrement threshold is determined based on the size of storage area for the
queue of messages as well as capabilities of service access and link control of the system. The
overload decrement threshold is set to 45 in this embodiment.
At Step 308, the link control process sends an overload relieving message. After the service
processing process receives the message, the amount of the new accessed service is increased and
the overload retrieval timer is reset. In this embodiment, after the service processing process
receives the overload relieving message, the amount of the new accessed service is increased by
one. Then, the process is advanced to Step 311.
At Step 309, the link control process further determines whether the increment of the signaling
messages in the queue of messages is more than a predetermined overload increment threshold
during the period defined by the overload monitor timer. If yes, the process is advanced to Step 310
in which the amount of the new accessed services is further decreased and the overload retrieval
timer is reset; otherwise Step 311 would be performed. The overload increment threshold is
determined based on the size of storage area for the queue of messages as well as capabilities of
service access and link control of the system. The overload increment threshold is set to 40 in this
embodiment.
At Step 310, the link control process sends the overload controlling message to the service
processing process. After the service processing process receives the message, the amount of the
new accessed services is further decreased. In this embodiment, after receiving the overload
controlling message, the service processing process decreases 2 new accessed services. Then the
process is advanced to Step 311. In this embodiment, in order to prevent the system from fluctuating
greatly, slight adjustment for overload is used to ensure that the changed service traffic each time is

not very large, thus the speed of decreasing the new accessed services of the system is faster than
that of increasing the new accessed services.
At Step 311, the process returns to Step 302 and repeats above steps to continue the regular
detection of the amount of signaling messages in the queue of messages and dynamical control of
the amount of the new services accessed by the service processing process, until the system retrieves
normal state.
In this embodiment, the service processing process limits the access of new calls equally
according to the overload controlling message and overload relieving message sent from the link
control process. The control of the access of new calls by the service processing process is as
follows: the service processing process sets the number of statistical windows in accordance with
the ratio of overload control service access. Generally, the number of statistical windows is set to
32, i.e. the amount of accessed calls is counted with a cycle of every 32 calls. The amount of calls
allowed by the current statistical window to be accessed is set and it is determined that whether the
newly accessed call numbers are allowed to be accessed. The call numbers allowed to be accessed
are equally distributed into the statistical windows. When a new service is accessed, if its call
number is the one allowed to be accessed, the new service is allowed to be accessed; otherwise, if
its call number is the one rejected to be accessed, the new service is rejected.
Moreover, Fig. 4 shows a test result of overload in a common channel signaling link system to
which the present invention is not applied. In the common channel signaling link system, a program
for simulating large call traffic is used for call test. A front end controls continual calls and
simulates initiation of calls in 240 lines (total 480 lines including lines for initiating calls and lines
for receiving calls). The duration of a call is 6 seconds and the interval between calls is 4 seconds. It
can be seen that the call traffic is fluctuated greatly in the common channel signaling link system
when the embodiment of the present invention is not applied. The interface tends to be interrupted
due to the overload of the system
Fig. 5 is a diagram showing a test result of overload in a common channel signaling link system
to which the present invention is applied. In this embodiment, the program for simulating large call
traffic is used for call test. A front end controls continual calls and simulates initiation of calls in
240 lines (total 480 lines including lines for initiating calls and lines for receiving calls). The
duration of a call is 6 seconds and the interval between calls is 4 seconds. It can be seen that the call
traffic is fluctuated slightly in the common channel signaling link system to which the embodiment
of the present invention is applied. The traffic of the system is steady.
While the present invention has been described in detail with reference to the preferred
embodiments, those skilled in the art will appreciate that various modifications and substitutions

can be made thereto without departing from the spirit and scope of the present invention as set forth
in the appended claims.

WE CLAIM:
1. A method of overload control in a common channel signaling link system, said
method comprising the steps of
a link control process detecting an amount of unprocessed signaling messages in
a queue of messages regularly (201) and determining whether the amount of
unprocessed signaling messages is more than an overload start threshold (203); and
if the amount of unprocessed signaling messages is more than the overload start
threshold, by sending a message to a service processing process, the link control
process also dynamically controlling an amount of new services accessed by the service
processing process (205);
wherein the step of the link control process dynamically controlling an amount of
new services accessed by a service processing process comprises:
performing the following steps of (i) and (ii) repeatedly at a predetermined time
interval until an amount of signaling messages in the queue of messages is less than
an overload retrieval threshold:
(i) determining whether the amount of signaling message in the queue of messages
is less than the overload retrieval threshold (302);
(ii) if the amount of signaling message in the queue of messages is more than the
overload retrieval threshold, comparing a length of current queue of messages with a
length of a queue of messages previous to the predetermined time interval, and
decreasing or increasing the amount of new accessed services according to the
comparing result.
2. The method as claimed in claim 1, wherein in steps (i) and (ii):
determining whether a length of current queue of messages is longer than that
of a queue of messages previous to the predetermined time interval (306),
if the length of current queue of messages is longer than that of the queue of
messages previous to the predetermined time interval, determining whether an
increment of the signaling messages in the queue of messages is more than an
overload increment threshold (309),

if the increment of the signaling messages in the queue of messages is more
than the overload increment threshold, the link control process sends an overload
controlling message to the service processing process,
if the length of current queue of messages is less than or equal to that of the
queue of messages previous to the predetermined time interval, determining whether
the decrement of the signaling messages in the queue of messages is more than an
overload decrement threshold (307), and
if the decrement of the signaling messages in the queue of messages is more
than the overload decrement threshold, the link control process sends an overload
relieving message to the service processing process.
3. The method as claimed in claim 1 or 2, wherein, if the amount of signaling
message in the queue of messages is less than the overload retrieval threshold,
informing the service processing process that the system has retrieved normal state.
4. The method as claimed in claim 1, wherein the step of the link control
process dynamically controlling an amount of new services accessed by a service
processing process comprises:
the service processing process receiving the message from the link control
process, decreasing or increasing a predetermined amount in the amount of new
accessed services and equally distributing calls allowed to be accessed into statistical
windows for call accessing.
5. The method as claimed in claim 3, wherein the step of informing the service
processing process that the system has retrieved normal state of the system comprises:
the service processing process gradually increasing the amount of new accessed
services at a predetermined time interval (303).
6. The method as claimed in claim 2, wherein the step of the link control process
dynamically controlling an amount of new services accessed by a service processing
process comprises:

the service processing process receiving the message from the link control process,
if the message is the overload controlling message, the service processing process
decreasing the amount of new accessed services by m (310),
if the message is the overload relieving message, the service processing process
increasing the amount of new accessed services by n (308),
wherein both m and n are natural numbers and m>n.
7. The method as claimed in claim 1, wherein the overload start threshold is set
to 50% ~ 70% of a size of storage area for the queue of messages occupied by an
amount of current signaling messages in the queue of messages.
8. The method as claimed in claim 7, wherein the overload start threshold is set
to 60% of the size of storage area for the queue of messages occupied by the amount of
current signaling messages in the queue of messages.
9. The method as claimed in claim 7, wherein the overload retrieval threshold
approximates to and is less than the overload start threshold.

ABSTRACT

A METHOD OF OVERLOAD CONTROL IN A COMMON CHANNEL
SIGNALING LINK SYSTEM
The invention relates to a method of overload control in a common channel signaling link system,
comprising the steps of: a link control process detecting an amount of unprocessed signaling
messages in a queue of messages regularly (201) and determining whether the amount of
unprocessed signaling messages is more than an overload start threshold (203), if the amount of
unprocessed signaling messages is more than the overload start threshold, the link control process
dynamically controlling an amount of new services accessed by a service processing process by
sending a message to the service processing process (205).

A METHOD OF OVERLOAD CONTROL IN A COMMON CHANNEL SIGNALING LINK SYSTEM

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