Abstract:
A method is disclosed that enables mitigating at least some of the problems caused by a packet attack. When a first Internet Protocol (IP)-capable device is subjected to a packet attack, it indicates periodically to a second IP-capable device that certain communications with the first device are to be suspended. The periodic transmitting of the indication is performed at a slower rate than the keep-alive mechanism that is normally used to detect loss of connectivity. When the second device receives the transmitted indication, it refrains from transmitting keep-alive messages to the first device for a predetermined interval. Meanwhile, the first device also refrains from transmitting keep-alive messages to the second device for a similar interval. In transmitting the suspend indication, the illustrative embodiment seeks to prevent pairs of communicating devices that are experiencing packet attacks from continuing their operation under the erroneous assumption that each device is unavailable.

Description:
FIELD OF THE INVENTION 
     The present invention relates to telecommunications in general, and, more particularly, to maintaining communication between two network nodes when one or both nodes are subjected to a packet attack. 
     BACKGROUND OF THE INVENTION 
     Voice over Internet Protocol (or “VoIP”) features the routing of voice conversations over the Internet or through another type of Internet Protocol-based network. Voice signals from the voice conversations to be routed are digitized and formatted into data packets, which are then transmitted through the network. A telecommunications network that is based on VoIP is able to transmit voice conversations between devices that are able to access the network.  FIG. 1  depicts a schematic diagram of telecommunications system  100  in the prior art, which is able to transmit voice conversations between end-user devices such as telephones. Telecommunications system  100  comprises:
         i. backbone packet network  101 ;   ii. local area network (LAN)  102 ;   iii. Internet Protocol-capable endpoints  103 - 1  through  103 -R, wherein R is a positive integer;   iv. gateways  104 - 1  through  104 -S, wherein S is a positive integer;   v. Public Switched Telephone Network (PSTN)  105 ;   vi. PSTN telecommunications terminal  106 ; and   vii. gatekeeper  107 .
 
All of the elements depicted in  FIG. 1  are interconnected as shown.
       

     System  100  comprises a plurality of different types of networks, including backbone packet network  101 , local area network  102 , and Public Switched Telephone Network  105 . Backbone packet network  101  comprises one or more transmission-related nodes such as routers that are used to direct data packets, in this case voice packets, from one or more sources to the correct destinations of those packets. Network  101  is capable of handling Internet Protocol-based messages that are transmitted between Internet Protocol-capable devices, such as endpoints  103 - 1  through  103 -R, and gateways, such as gateways  104 - 1  through  104 -S. Local area network (or “LAN”)  102  provides for the local distribution of signals, such as in an enterprise system, and comprises networking equipment such as hubs, bridges, and switches between backbone packet network  101  and Internet Protocol-capable endpoints  103 - 1  through  103 -R. LAN  102  operates in accordance with a networking protocol such as Ethernet or IEEE 802.3. Public Switched Telephone Network  105  comprises one or more transmission-related nodes such as switches that are used to direct call-related signals from one or more sources to the correct destinations of those signals. Network  105  is capable of handling either analog or digital bearer information in circuit-switched calls between devices such as PSTN terminal  106  and gateway  104 - 1 . 
     Backbone network  101 , as well as some of the depicted nodes, is governed by the H.323 protocol standard specified by the International Telecommunication Union. Nodes depicted in  FIG. 1  that are governed by the H.323 standard include endpoints  103 - 1  through  103 -R, gateways  104 - 1  through  104 -S, and gatekeeper  107 , which are described below. Some VoIP systems other than system  100  are governed by the Session Initiation Protocol (or “SIP”) or a proprietary protocol. 
     Internet Protocol-capable endpoint  103 - r , for r=1 through R, is a communication appliance such as a deskset, a conferencing unit, a wireless terminal, a desktop or portable computer (i.e., “softphone”), an Internet phone, and so forth. As depicted, endpoint  103 - r  operates in a local area network. Endpoint  103 - r  is capable of digitizing voice signals from its user and formatting the digitized signals into transmittable data packets through an audio compressor/decompressor (or “CODEC”) circuit. Similarly, the CODEC circuit of endpoint  103 - r  is also capable of receiving data packets and converting the information contained within those packets into voice signals that are understandable by the endpoint&#39;s user. 
     Gateway  104 - s , for s=1 through S, is a data-processing system that acts as a translator between two types of networks; for example, gateway  104 - 1  interconnects and acts as a translator between backbone packet network  101  and Public Switched Telephone Network  105 . Because gateway  104 - s  connects two different types of networks together, one of its main functions is to convert between the different transmission and coding techniques used across the two networks. Gateway  104 - 1  is a Voice over Internet Protocol (VoIP)-capable gateway that performs the conversion between time division multiplexed voice signals that originate at a switched telephone network telecommunications terminal, such as terminal  106 , and VoIP signals that are intended for an Internet Protocol network endpoint, such as one of IP-capable endpoints  103 - 1  through  103 -R, as part of a telephone conversation between two parties. Gateway  104 - 1  performs the conversion in the reverse direction as well (i.e., from an IP terminal to a PSTN terminal) and is able to perform bidirectional conversion for multiple calls concurrently. 
     Gatekeeper  107  is a data-processing system that manages each collection of IP-capable endpoint devices that belong to a particular zone. Gatekeeper  107  provides address translation and routing for the IP-capable devices in their zone. In addition, gatekeeper  107  provides the call admission control, in terms of specifying which of IP-capable devices  103 - 1  through  103 -R may call which other devices in telecommunications system  100 . 
     Gatekeeper  107  receives one or more registration messages from each Internet Protocol-capable endpoint  103 - r  when the endpoint first connects to the network. The registration message indicates the current IP address of the endpoint and enables endpoint  103 - r  to use the network, such as to make a call. When the user of endpoint  103 - r  desires to make a call, the endpoint transmits a message that includes the destination telephone number. After network  101  determines which gateway the destination telephone number corresponds to, gatekeeper  107  transmits the address of the destination gateway to the calling endpoint  103 - r . The endpoint then can send packets directly to the gateway (e.g., gateway  104 - 1 , etc.), and the gateway initiates a local call to the destination telephone (e.g., terminal  106 , etc.). 
     As can be seen from the call-control scenario just described, it is crucial for each endpoint  103 - r  and gatekeeper  107  to maintain an ongoing awareness of each other and an ongoing ability to communicate with each other. To maintain this ongoing relationship with each other, each endpoint  103 - r  exchanges a “heartbeat” message with gatekeeper  107 . A loss of the heartbeat would prompt the affected endpoint to rediscover a gatekeeper or would prompt the affected gatekeeper to deregister the endpoint, or both. 
       FIG. 2  depicts such a heartbeat mechanism in the prior art, in which endpoint  103 - 1  is the instigator of the heartbeat sequence and gatekeeper  107  responds to each heartbeat message that it receives from endpoint  103 - 1 . Note that gatekeeper  107  can also be the instigator of a heartbeat sequence with endpoint  103 - 1 , or with a different endpoint, but that is not shown here. As depicted, endpoint  103 - 1  has been transmitting a series of normal “keep-alive” packets, such as packet  201 , and in response to each keep-alive packet, gatekeeper  107  has transmitted an acknowledgment packet, such as packet  202 . Endpoint  103 - 1  transmits the keep-alive packets at regular, predetermined intervals. If endpoint  103 - 1  does not receive an acknowledgment packet in response to a keep-alive packet, such as with keep-alive packet  203 , the endpoint commences transmitting retry keep-alive packets, such as packets  204  through  207 , but at a faster rate than before. If the retry keep-alive packets go unanswered, endpoint  103 - 1  eventually deregisters and goes into a discovery mode at event  208 , in which it attempts to find and reregister with a gatekeeper. 
     The heartbeat-based reliability technique described above works well under ordinary conditions. However, in a non-ordinary condition endpoint  103 - r  or gatekeeper  107 , or both, can be subjected to what is known as a “packet attack,” sometimes referred to as a “Denial-of-Service attack,” in which an intruder can target one or more devices and continuously transmit, at a high rate, packets that are addressed to the targeted device. If a device, such as endpoint  103 - r  or gatekeeper  107 , is under a packet attack, the device might not have enough processing power to continue to generate or process heartbeats. If endpoint  103 - r  is targeted, gatekeeper  107  will eventually deregister endpoint  103 - r , which will then go into discovery mode to reregister with a gatekeeper. As implied above, the absence of a heartbeat leads to additional message traffic in the network and increases the processing load on gatekeeper  107 , which possibly degrades its performance and reduces its overall availability to the other nodes in system  100 . Furthermore, if a large number of endpoints were to reregister concurrently, a flood of registration-related messages would occur, creating an even higher load on gatekeeper  107  and ultimately leading to degraded performance across system  100 . 
     What is needed is a technique to mitigate the problems that a packet attack causes, without some of the disadvantages in the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention enables mitigating at least some of the problems caused by a packet attack, without some of the disadvantages in the prior art. In particular, when a first Internet Protocol (IP)-capable device is subjected to a packet attack, it indicates periodically to a second IP-capable device that certain communications with the first device are to be suspended. In accordance with the illustrative embodiment of the present invention, the periodic transmitting of the indication is performed at a slower rate than the keep-alive mechanism that is normally used to detect loss of connectivity. When the second device receives the transmitted indication, it refrains from transmitting keep-alive messages to the first device for a predetermined interval. Meanwhile, the first device also refrains from transmitting keep-alive messages to the second device for a similar interval. By transmitting each suspend packet, which acts as a directive to the second device to preserve its awareness of the first device&#39;s operational state, the illustrative embodiment seeks to prevent pairs of communicating devices that are experiencing packet attacks from continuing their operation under the erroneous assumption that each device is unavailable. 
     The tasks that are part of mitigating the packet attack problem are described here. First, a device in the telecommunications system of the illustrative embodiment detects a packet attack. A secure, reliable channel is then opened between the first device, such as an endpoint, and the second device, such as a gatekeeper. Periodically, the first device transmits a suspend packet to keep the operational state of the first device preserved (i.e., “frozen”) at the second device, where the state of the first device can indicate, for example, whether the first device is registered at the second device. The second device sends an acknowledgment packet back to the first device and suspends the transmission of keep-alive packets to the first device. When the first device receives the acknowledgment packet, it too can refrain from transmitting keep-alive packets to the second device for a predetermined duration, referred to as the “back-off period.” Each device will stop transmitting keep-alive messages to the other device and wait for the packet attack to finish. If the packet attack continues past the current back-off period, the first device will send additional suspend packets as needed. Once the first device detects, or is notified, that the attack is over, it sends a resume packet to the second device. At this point, the normal heartbeat state machine resumes at the first device, and the second device can also choose to resume its heartbeat state machine. 
     In some embodiments, the IP-capable device of the illustrative embodiment can blunt the immediate effect of the packet attack by using mechanisms in addition to those of the technique of the illustrative embodiment. For example, the device can disable the local area network interface through which the packet attack stream arrives; this has the effect of conserving processing cycles instead of expending processing cycles to deal with the attack stream. 
     The illustrative embodiment of the present invention comprises: detecting a packet attack that affects a first Internet Protocol-capable device; and transmitting, based on the detection of the packet attack, a first packet from the first Internet Protocol-capable device to a second Internet Protocol-capable device with which the first Internet Protocol-capable device has been exchanging a plurality of heartbeat-related packets that comprises a series of keep-alive packets; wherein the first packet indicates that the second Internet Protocol-capable device is to suspend the transmission of additional heartbeat-related packets to the first Internet Protocol-capable device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a schematic diagram of telecommunications system  100  in the prior art. 
         FIG. 2  depicts a heartbeat mechanism in the prior art. 
         FIG. 3  depicts a schematic diagram of telecommunications system  300  in accordance with the illustrative embodiment of the present invention. 
         FIG. 4  depicts the salient components of enhanced Internet Protocol-capable endpoint  303 - q  of system  300 . 
         FIG. 5  depicts the salient components of enhanced gatekeeper  307  of system  300 . 
         FIG. 6  depicts a flowchart of the salient tasks that are executed by a first Internet Protocol-capable device, in accordance with the illustrative embodiment of the present invention. 
         FIG. 7  depicts a flowchart of the salient tasks that are executed by a second Internet Protocol-capable device, in accordance with the illustrative embodiment of the present invention. 
         FIG. 8  depicts a message flow diagram of the combination of some of the messages and events that are depicted in  FIGS. 6 and 7 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 3  depicts a schematic diagram of telecommunications system  300  in accordance with the illustrative embodiment of the present invention. Telecommunications system  300  comprises:
         i. backbone packet network  101 ;   ii. local area network  102 ;   iii. enhanced Internet Protocol-capable endpoints  303 - 1  through  303 -Q, wherein Q is a positive integer; and   iv. enhanced gatekeeper  307 .
 
All of the elements depicted in  FIG. 3  are interconnected as shown. In addition, system  300  comprises gateways  104 - 1  through  104 -S, Public Switched Telephone Network (PSTN)  105 , and PSTN telecommunications terminal  106 , all of which are described above and with respect to  FIG. 1 , as are backbone packet network  101  and local area network  102 .
       

     System  300  is similar to system  100  in that it is able to transmit voice conversations between end-user devices. However, as those who are skilled in the art will appreciate, in some alternative embodiments of the present invention, the present invention is also well-suited for telecommunications systems that transmit other types of bearer information than voice, such as video. 
     Furthermore, as those who are skilled in the art will appreciate, telecommunications system  300  is capable in some alternative embodiments of handling other types of networks and other combinations of networks than depicted. In some alternative embodiments, each network might in turn comprise additional networks, such as cellular telephone networks and local area networks that are either wired or wireless. 
     In accordance with the illustrative embodiment, backbone network  101  is governed by the H.323 protocol standard specified by the International Telecommunication Union. Enhanced endpoints  303 - 1  through  303 -Q and enhanced gatekeeper  307 , which are described below, are also governed by the H.323 standard. As those who are skilled in the art will appreciate, in some alternative embodiments, some or all of system  300  can be governed by a different protocol such as the Session Initiation Protocol (or “SIP”), either proprietary or standardized. 
     Enhanced Internet Protocol-capable endpoint  303 - q , for q=1 through Q, is a communication appliance such as a deskset, a conferencing unit, a cellular telephone, a desktop or portable computer (i.e., “softphone”), and so forth. The salient components of endpoint  303 - q  are described below and with respect to  FIG. 4 . As depicted, endpoint  303 - q  operates in a local area network, but in some alternative embodiments the endpoint operates in a different type of network. Endpoint  303 - q  is capable of digitizing voice signals from its user and formatting the digitized signals into transmittable data packets through an audio compressor/decompressor (or “CODEC”) circuit. Similarly, the CODEC circuit of endpoint  303 - q  is also capable of receiving data packets and converting the information contained within those packets into voice signals that are understandable by the endpoint&#39;s user. 
     In addition, endpoint  303 - q  is capable of performing the tasks described below and with respect to  FIGS. 6 through 8 , in accordance with the illustrative embodiment of the present invention. It will be clear to those skilled in the art, after reading this specification, how to make and use enhanced Internet Protocol-capable endpoint  303 - q.    
     Enhanced gatekeeper  307  is a data-processing system that manages each collection of IP-capable endpoint devices that belong to a particular zone. The salient components of gatekeeper  307  are described below and with respect to  FIG. 5 . Gatekeeper  307  provides address translation and routing for the IP-capable devices in their zone. In addition, gatekeeper  307  provides the call admission control, in terms of specifying which of enhanced Internet Protocol-capable devices  303 - 1  through  303 -Q may call which other devices in telecommunications system  300 . Although one gatekeeper is depicted, additional gatekeepers can be present, as those who are skilled in the art will appreciate. 
     In addition, endpoint  303   q  is capable of performing the tasks described below and with respect to  FIGS. 6 through 8 , in accordance with the illustrative embodiment of the present invention. It will be clear to those skilled in the art, after reading this specification, how to make and use enhanced Internet Protocol-capable endpoint  303 - q.    
     To maintain the ability to communicate with each other during periods of ordinary packet traffic, each endpoint  303 - q  exchanges a “heartbeat” message with its gatekeeper (e.g., gatekeeper  307 , etc.), as described above and with respect to  FIG. 2  for endpoint  103 - r  and gatekeeper  107 . In accordance with the illustrative embodiment, endpoint  303 - q  and gatekeeper  307  exchange heartbeat-related packets and execute the tasks of the illustrative embodiment. However, as those who are skilled in the art will appreciate, in some alternative embodiments, other packet-based devices can exchange heartbeat-related signals, as well as execute the tasks described below and with respect to  FIGS. 6 through 8 . 
       FIG. 4  depicts the salient components of enhanced Internet Protocol-capable endpoint  303 - q  in accordance with the illustrative embodiment of the present invention. Endpoint  303 - q  comprises local area network (LAN) interface  401 , processor  402 , and memory  403 , interconnected as shown. 
     LAN interface  401  is capable of receiving packet signals from local area network  102 , such as incoming packets from other Internet Protocol-capable devices, and of forwarding the information encoded in the signals to processor  402 , in well-known fashion. LAN interface  401  is also capable of receiving information from processor  402  and of transmitting signals that encode this information to other Internet Protocol-capable devices via local area network  102 , in well-known fashion. It will be clear to those skilled in the art, after reading this specification, how to make and use LAN interface  401 . 
     Processor  402  is a general-purpose processor that is capable of receiving information from interface  401 , executing instructions stored in memory  403 , reading data from and writing data into memory  403 , executing the tasks described below and with respect to  FIGS. 6 through 8 , and transmitting information to interface  401 . In some alternative embodiments of the present invention, processor  402  might be a special-purpose processor. In either case, it will be clear to those skilled in the art, after reading this specification, how to make and use processor  402 . 
     Memory  403  stores the instructions and data used by processor  402 . Memory  403  might be any combination of dynamic random-access memory (RAM), flash memory, disk drive memory, and so forth. It will be clear to those skilled in the art, after reading this specification, how to make and use memory  403 . 
       FIG. 5  depicts the salient components of enhanced gatekeeper  307  in accordance with the illustrative embodiment of the present invention. Gatekeeper  307  comprises Internet Protocol network interface  501 , processor  502 , and memory  503 , interconnected as shown. 
     Internet Protocol network interface  501  is capable of receiving packet signals from backbone network  101 , such as incoming packets from other Internet Protocol-capable devices, and of forwarding the information encoded in the signals to processor  502 , in well-known fashion. Internet Protocol interface  501  is also capable of receiving information from processor  502  and of transmitting signals that encode this information to other Internet Protocol-capable devices via backbone packet network  101 , in well-known fashion. It will be clear to those skilled in the art, after reading this specification, how to make and use Internet Protocol network interface  501 . 
     Processor  502  is a general-purpose processor that is capable of receiving information from interface  501 , executing instructions stored in memory  503 , reading data from and writing data into memory  503 , executing the tasks described below and with respect to  FIGS. 6 through 8 , and transmitting information to interface  501 . In some alternative embodiments of the present invention, processor  502  might be a special-purpose processor. In either case, it will be clear to those skilled in the art, after reading this specification, how to make and use processor  502 . 
     Memory  503  stores the instructions and data used by processor  502 . Memory  503  might be any combination of dynamic random-access memory (RAM), flash memory, disk drive memory, and so forth. It will be clear to those skilled in the art, after reading this specification, how to make and use memory  503 . 
       FIGS. 6 and 7  depict flowcharts of salient tasks performed in responding to a packet attack on one of both of enhanced Internet Protocol-capable endpoint  303 - q  and enhanced gatekeeper  307 . In particular, the tasks in  FIG. 6  are associated with transmitting one or more packets that indicate that the device receiving those packets is to suspend transmitting keep-alive packets. The tasks in  FIG. 7  are associated with receiving one or more packets that indicate suspending the transmission of keep-alive packets. In addition,  FIG. 8  depicts a message flow diagram of the combination of some of the messages and events that are depicted in  FIGS. 6 and 7 . 
     As those who are skilled in the art will appreciate, some of the tasks that appear in  FIGS. 6 and 7  can be performed in parallel or in a different order than that depicted. Furthermore, as those who are skilled in the art will appreciate, multiple pairs of Internet Protocol-capable devices throughout telecommunications system  300  that exchange heartbeat packets with each other can concurrently perform the tasks described with respect to  FIGS. 6 and 7 . For example, endpoint  303 - 1  can perform the tasks in  FIG. 6  while its gatekeeper can perform the tasks in  FIG. 7 ; concurrently, endpoint  303 - 2  can also perform the tasks in  FIG. 6  while its gatekeeper, possibly the same one as for endpoint  303 - 1  or a different one, can perform the tasks in  FIG. 7 . In addition, each device in a particular pair of devices might perform the tasks in both  FIGS. 6 and 7 ; for example, endpoint  303 - 3  might perform the tasks in  FIG. 6  while gatekeeper  307  performs the corresponding tasks in  FIG. 7 , and gatekeeper  307  might perform the tasks in  FIG. 6  while endpoint  303 - 3  performs the corresponding tasks in  FIG. 7 . Finally, a single device such as gatekeeper  307  might perform the tasks in  FIG. 6  or  FIG. 7 , or both, with more than one other device, such as with multiple endpoints. 
       FIG. 6  depicts a flowchart of the salient tasks that are executed by a first Internet Protocol-capable device, in accordance with the illustrative embodiment of the present invention. For pedagogical purposes, the tasks associated with  FIG. 6  are described below as being performed by enhanced Internet Protocol-capable endpoint  303 - 1 ; however, as those who are skilled in the art will appreciate, a different device can perform the tasks as shown. 
     At task  601 , endpoint  303 - 1  transmits a series of keep-alive packets to another Internet Protocol-capable device in well-known fashion; in the illustrative example, endpoint  303 - 1  transmits the series to gatekeeper  307 . In  FIG. 8 , packet  801  is one such keep-alive packet that endpoint  303 - 1  transmits and is acknowledged by packet  802 . 
     At task  602 , a device in telecommunications system  300  detects a packet attack that affects at least endpoint  303 - 1 . For example, the packet attack prevents endpoint  303 - 1  from receiving an acknowledgment packet in response to keep-alive packet  803 . In some embodiments, endpoint  303 - 1  detects the attack, at event  804 , while in some other embodiments a different device than endpoint  303 - 1 , such as a separate intrusion detection system, detects the attack and reports the attack to endpoint  303 - 1 . 
     At task  603 , endpoint  303 - 1  establishes a secure reliable channel (i.e., a separate channel than the one used to exchange heartbeat-related packets) with gatekeeper  307 , in well-known fashion. The channel can be direct or through a third Internet Protocol-capable device, such as the intrusion detection system. 
     At task  604 , a device in system  300  attempts to mitigate the effects of the packet attack on endpoint  303 - 1 . For example, if endpoint  303 - 1  itself attempts to mitigate the attack, it can do so by disabling local area network interface  401  over which the attacking packets are being received so that few processor cycles are used in dealing with the attack. 
     At task  605 , endpoint  303 - 1  transmits packet  805  to gatekeeper  307 , which packet indicates that gatekeeper  307  is to suspend the transmission of additional heartbeat-related packets (keep-alive packets) to endpoint  303 - 1 . In some embodiments, the suspend packet indicates that gatekeeper  307  is to suspend the transmission of the additional packets for a predetermined length of time; this length of time is longer than the time between two consecutive non-retry packets in the series of keep-alive packets ordinarily sent. The length of time, in some embodiments, is based on the type of packet attack being experienced. In some other embodiments, the length of time is based on the severity of the packet attack. As those who are skilled in the art will appreciate, in still some other embodiments, the length of time can be based on yet another characteristic of the packet attack or on something else within system  300 . 
     At task  606 , endpoint  303 - 1  receives acknowledgment packet  806  from gatekeeper  307 , in response to having transmitted the suspending packet at task  605 . 
     At task  607 , endpoint  303 - 1  refrains from transmitting additional keep-alive packets to gatekeeper  307  for a particular back-off interval. The back-off interval is based on the predetermined length of time that is longer than the time between two consecutive non-retry packets in the series of keep-alive packets that are ordinarily transmitted to maintain the heartbeat with gatekeeper  307 . The predetermined length of time can be based on one or more characteristics, as described above and with respect to task  605 . 
     At task  608 , a device in telecommunications system  300  monitors the packet attack to detect if the attack is mitigating. In accordance with the illustrative embodiment endpoint  303 - 1  monitors the attack, while in some alternative embodiments a different device monitors the attack. 
     At task  609 , endpoint  303 - 1  checks if the back-off interval has expired. If the interval has expired, task execution proceeds to task  610 . If the interval has not expired, task execution proceeds back to task  607 . 
     At task  610 , endpoint  303 - 1  checks (at event  807  or  810 ) if the packet attack is over—that is, if there has been a sufficient mitigation in the packet attack to allow for normal heartbeat-related transmissions to resume. Endpoint  303 - 1  is aware of the packet attack&#39;s status, based on the monitoring performed at task  608 . If the attack has mitigated sufficiently, task execution proceeds to task  611 . Otherwise, task execution proceeds back to task  605 , to transmit another suspend packet such as packet  808  and to receive the corresponding acknowledgment packet such as packet  809 . 
     At task  611 , endpoint  303 - 1  transmits packet  811  to gatekeeper  307 , which packet indicates that gatekeeper  307  is to resume sending keep-alive packets to endpoint  303 - 1 . 
     At task  612 , endpoint  303 - 1  receives acknowledgment packet  812  from gatekeeper  307 , in response to having transmitted the resume packet at task  611 . Endpoint  303 - 1  itself resumes its own transmission of keep-alive packets to gatekeeper  307  and expects to receive an acknowledgment packet for each keep-alive packet transmitted. Task execution then ends. 
       FIG. 7  depicts a flowchart of the salient tasks that are executed by a second Internet Protocol-capable device, in accordance with the illustrative embodiment of the present invention. For pedagogical purposes, the tasks associated with  FIG. 7  are described below as being performed by enhanced gatekeeper  307 ; however, as those who are skilled in the art will appreciate, a different device can perform the tasks as shown. 
     At task  701 , gatekeeper  307  transmits a series of keep-alive packets to another Internet Protocol-capable device in well-known fashion; in the illustrative example, gatekeeper  307  transmits the series to endpoint  303 - 1 . 
     At task  702 , gatekeeper receives packet  805  from endpoint  303 - 1 , which packet indicates that gatekeeper  307  is to suspend the transmission of additional heartbeat-related packets (keep-alive packets) to endpoint  303 - 1 . In some embodiments, the suspend packet indicates that gatekeeper  307  is to suspend the transmission of the additional packets for a predetermined amount of time that is longer than the time between two consecutive non-retry packets in the series of keep-alive packets ordinarily sent. The length of time, in some embodiments, is based on the type of packet attack being experienced. In some other embodiments, the length of time is based on the severity of the packet attack. As those who are skilled in the art will appreciate, in still some other embodiments, the length of time can be based on yet another characteristic of the packet attack or on something else within system  300 . 
     At task  703 , gatekeeper  307  transmits acknowledgment packet  806  to endpoint  303 - 1 , in response to having received the suspending packet at task  702 . 
     At task  704 , gatekeeper  307  refrains from transmitting additional keep-alive packets, based on having received the suspend packet from endpoint  303 - 1 , for a particular back-off interval. The back-off interval is based on a predetermined length of time that is longer than the time between two consecutive non-retry packets in the series of keep-alive packets that are ordinarily transmitted to maintain the heartbeat with endpoint  303 - 1 . The predetermined length of time can be based on one or more characteristics, as described above and with respect to task  605 . 
     At task  705 , gatekeeper  307  monitors for an indication to resume the transmission of keep-alive packets. 
     At task  706 , gatekeeper  307  checks if a resume packet has been received. If a packet that indicates resumption of keep-alive transmissions has been received, task execution proceeds to task  709 . Otherwise, task execution proceeds to task  707 . 
     At task  707 , gatekeeper  307  checks if another suspend packet has been received, in contrast to a resume packet. If another packet that indicates suspension of keep-alive transmissions has been received (such as packet  808 ), task execution proceeds to task  703 . Otherwise, task execution proceeds to task  708 . 
     At task  708 , gatekeeper  307  checks if the back-off interval has expired. If the interval has expired, task execution proceeds to task  709 . If the interval has not expired, task execution proceeds back to task  704 . 
     At task  709 , gatekeeper  307  resumes transmitting keep-alive packets to endpoint  303 - 1 . Task execution then ends. 
     It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. For example, in this Specification, numerous specific details are provided in order to provide a thorough description and understanding of the illustrative embodiments of the present invention. Those skilled in the art will recognize, however, that the invention can be practiced without one or more of those details, or with other methods, materials, components, etc. 
     Furthermore, in some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the illustrative embodiments. It is understood that the various embodiments shown in the Figures are illustrative, and are not necessarily drawn to scale. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that a particular feature, structure, material, or characteristic described in connection with the embodiment(s) is included in at least one embodiment of the present invention, but not necessarily all embodiments. Consequently, the appearances of the phrase “in one embodiment,” “in an embodiment,” or “in some embodiments” in various places throughout the Specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.