Source: http://www.google.com/patents/US7966409?dq=5726663
Timestamp: 2015-04-19 09:06:39
Document Index: 220469051

Matched Legal Cases: ['Application No. 200480021154', 'Application No. 200480021154', 'Application No. 200480021154', 'Application No. 04755658', 'Application No. 04755658', 'Application No. 200480021154']

Patent US7966409 - Routing protocol based redundancy design for shared-access networks - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA protection CMTS is available to immediately service a cable modem should that modem's service from a working CMTS fail for any reason. To speed the service transfer (cutover) from the working CMTS to the protection CMTS, the cable modem may preregister with the protection CMTS well before the cutover...http://www.google.com/patents/US7966409?utm_source=gb-gplus-sharePatent US7966409 - Routing protocol based redundancy design for shared-access networksAdvanced Patent SearchPublication numberUS7966409 B1Publication typeGrantApplication numberUS 10/899,668Publication dateJun 21, 2011Filing dateJul 26, 2004Priority dateJan 18, 2000Fee statusPaidAlso published asUS6839829Publication number10899668, 899668, US 7966409 B1, US 7966409B1, US-B1-7966409, US7966409 B1, US7966409B1InventorsFeisal Daruwalla, James R. Forster, Guenter E. Roeck, Richard M. Woundy, Michael A. ThomasOriginal AssigneeCisco Technology, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (122), Non-Patent Citations (145), Referenced by (6), Classifications (31), Legal Events (1) External Links: USPTO, USPTO Assignment, EspacenetRouting protocol based redundancy design for shared-access networks
US 7966409 B1Abstract
1. A method implemented on a working CMTS for providing redundancy to a cable network in which the working CMTS provides normal service to a cable modem via a first channel and a protection CMTS provides protection service, by taking over service to the cable modem should normal service from the working CMTS become unavailable, via a second channel, the method comprising:
receiving, by the working CMTS, a registration request from the cable modem;
obtaining an IP address by the working CMTS for the cable modem, the IP address being obtained from an address space outside a first subnet of IP addresses;
wherein the first subnet of IP addresses is dedicated to the working CMTS for assignment to its cable modems;
informing the cable modem of the obtained IP address;
informing the cable modem of at least one registration parameter specific to the first channel;
wherein the cable modem is informed of the second channel;
wherein the cable modem pre-registers, in response to being informed of the second channel, with the protection CMTS via the second channel;
wherein the cable modem is informed of at least one registration parameter specific to the second channel;
wherein the cable modem stores the at least one registration parameter specific to the second channel in preparation for a failover event;
wherein the cable modem loads, in response to the determining of the failure, the at least one registration parameter specific to the second channel;
wherein the cable modem connects with the protection CMTS via the second channel using the loaded at least one registration parameter specific to the second channel;
wherein the obtained IP address is used in communications with both the working CMTS and the protection CMTS;
wherein the protection CMTS takes over service to the cable modem without obtaining a new IP address for the cable modem.
3. The method of claim 1, wherein the address space is outside a second subnet of IP addresses, the second subnet of IP addresses being dedicated to the protection CMTS for assignment to its cable modems.
4. The method of claim 1, further comprising communicating the obtained IP address for the cable modem to the protection CMTS.
7. The method of claim 1, wherein the at least one registration parameter specific to the first channel comprises a transmission power, a transmission frequency, or transmission time slots at which the cable modem is to communicate with the working CMTS via the first channel.
8. The method of claim 1, wherein the at least one registration parameter specific to the second channel comprises a transmission power, a transmission frequency, or transmission time slots at which the cable modem is to communicate with the protection CMTS via the second channel.
9. The method of claim 1, wherein the cable modem sends a ranging request message to the protection CMTS after the determining of a failure of the working CMTS's service to the cable modem.
10. The method of claim 1, wherein obtaining an IP address by the working CMTS for the cable modem comprises:
requesting, by the working CMTS, an IP address for the cable modem from a provisioning server; and
receiving, by the working CMTS, an IP address assigned to the cable modem from the provisioning server.
11. The method of claim 10, wherein the provisioning server assigns an IP address for the cable modem using DHCP; and
wherein the working CMTS performs a DHCP relay function.
12. The method of claim 1, wherein obtaining an IP address by the working CMTS for the cable modem comprises:
gleaning, by the working CMTS, an IP address assigned to the cable modem.
recording, by the working CMTS, the obtained IP address.
14. A computer program product comprising a non-transitory machine readable medium containing program instructions which, when executed by a working CMTS, perform a method for providing redundancy to a cable network in which the working CMTS provides normal service to a cable modem via a first channel and a protection CMTS provides protection service, by taking over service to the cable modem should normal service from the working CMTS become unavailable, via a second channel, the method comprising:
wherein the cable modem is informed of at least one registration parameter specific to the second channel in preparation for a failover event;
wherein the cable modem loads, in response to determination of a failure of the working CMTS's service to the cable mode, the at least one registration parameter specific to the second channel;
wherein the obtained IP address is used for communications with both the working CMTS and the protection CMTS,
15. The computer program product of claim 14, wherein the working CMTS is a routing CMTS.
16. The computer program product of claim 14, wherein the address space is outside a second subnet of IP addresses, the second subnet of IP addresses being dedicated to the protection CMTS for assignment to its cable modems.
17. The computer program product of claim 14, wherein the method further comprises communicating the obtained IP address for the cable modem to the protection CMTS.
18. The computer program product of claim 14, wherein the method further comprises injecting a host route to the cable modem into a routing protocol.
19. The computer program product of claim 18, wherein injecting the host route comprises providing the host route to one or more aggregation routers servicing the cable network.
20. The computer program product of claim 14, wherein the at least one registration parameter specific to the first channel comprises a transmission power, a transmission frequency, or transmission time slots at which the cable modem is to communicate with the working CMTS via the first channel.
21. The computer program product of claim 14, wherein the at least one registration parameter specific to the second channel comprises a transmission power, a transmission frequency, or transmission time slots at which the cable modem is to communicate with the protection CMTS via the second channel.
22. The computer program product of claim 14, wherein the cable modem sends a ranging request message to the protection CMTS after the determination of a failure of the working CMTS's service to the cable modem.
23. The computer program product of claim 14, wherein obtaining an IP address by the working CMTS for the cable modem comprises:
24. The computer program product of claim 23, wherein the provisioning server assigns an IP address for the cable modem using DHCP; and
25. The computer program product of claim 14, wherein obtaining an IP address by the working CMTS for the cable modem comprises:
26. The computer program product of claim 14, wherein the method further comprises:
27. A working CMTS for providing redundancy to a cable network in which a working CMTS provides normal service to a cable modem via a first channel and a protection CMTS provides protection service, by taking over service to the cable modem should normal service from the working CMTS become unavailable, via a second channel, the working CMTS comprising:
receive a registration request from the cable modem;
obtain an IP address for the cable modem, the IP address being obtained from an address space outside a first subnet of IP addresses;
inform the cable modem of the obtained IP address; and
inform the cable modem of at least one registration parameter specific to the first channel; and
wherein the protection CMTS is configured to:
inform the cable modem of at least one registration parameter specific to the second channel;
take over service to the cable modem without obtaining a new IP address for the cable modem; and
wherein the cable modem is configured to:
pre-register, in response to being informed of the second channel, with the protection CMTS via the second channel;
store the at least one registration parameter specific to the second channel in preparation for a failover event;
load, in response to a determination of a failure of the working CMTS's service to the cable modem, the at least one registration parameter specific to the second channel;
connect with the protection CMTS via the second channel using the loaded at least one registration parameter specific to the second channel;
wherein the first subnet of IP addresses is dedicated to the working CMTS for assignment to its cable modems; and
wherein the obtained IP address is used in communications with both the working CMTS and the protection CMTS.
28. The working CMTS of claim 27, wherein the working CMTS is a routing CMTS.
29. The working CMTS of claim 27, wherein the address space is outside a second subnet of IP addresses, the second subnet of IP addresses being dedicated to the protection CMTS for assignment to its cable modems.
30. The working CMTS of claim 27, wherein the working CMTS is further configured to communicate the obtained IP address for the cable modem to the protection CMTS.
31. The working CMTS of claim 27, wherein the working CMTS is further configured to inject a host route to the cable modem into a routing protocol.
32. The working CMTS of claim 31, wherein the injection of the host route comprises providing the host route to one or more aggregation routers servicing the cable network.
33. The working CMTS of claim 27, wherein the at least one registration parameter specific to the first channel comprises a transmission power, a transmission frequency, or transmission time slots at which the cable modem is to communicate with the working CMTS via the first channel.
34. The working CMTS of claim 27, wherein the at least one registration parameter specific to the second channel comprises a transmission power, a transmission frequency, or transmission time slots at which the cable modem is to communicate with the protection CMTS via the second channel.
35. The working CMTS of claim 27, wherein the cable modem is further configured to send a ranging request message to the protection CMTS after determining a failure of the working CMTS's service to the cable modem.
36. The working CMTS of claim 27, wherein obtaining an IP address by the working CMTS for the cable modem comprises:
37. The working CMTS of claim 36, wherein the provisioning server assigns an IP address for the cable modem using DHCP; and
wherein the working CMTS is further configured to perform a DHCP relay function.
38. The working CMTS of claim 27, wherein obtaining an IP address by the working CMTS for the cable modem comprises:
39. The working CMTS of claim 27, wherein the working CMTS is further configured to:
record the obtained IP address.
This application is a continuation of U.S. patent application Ser. No. 09/484,189 filed Jan. 18, 2000 now U.S. Pat. No. 6,839,829 in the name of F. Daruwalla, J. Forster, G. Roeck, R. Woundy, and M. Thomas, and entitled �ROUTING PROTOCOL BASED REDUNDANCY DESIGN FOR SHARED-ACCESS NETWORKS,� which is incorporated herein by reference in its entirety and for all purposes.
This invention is related to U.S. patent application Ser. No. 09/484,611, filed on Jan. 18, 2000, naming J. Chapman, J. Zang, and Y. Lu as inventors, and titled �METHOD FOR A CABLE MODEM TO RAPIDLY SWITCH TO A BACKUP CMTS.� This application is incorporated herein by reference in its entirety and for all purposes.
A cable modem network or �cable plant� employs cable modems, which are an improvement of conventional PC data modems and provide high speed connectivity. Cable modems are therefore instrumental in transforming the cable system into a full service provider of video, voice and data telecommunications services. Digital data on upstream and downstream channels of the cable network is carried over radio frequency (�RF�) carrier signals. Cable modems convert digital data to a modulated RF signal for upstream transmission and convert a downstream RF signal to digital form. The conversion is done at a subscriber's home. At a cable modem termination system (�CMTS�) located at a head end of the cable network, the conversions are reversed. The CMTS converts downstream digital data to a modulated RF signal, which is carried over the fiber and coaxial lines to the subscriber premises. The cable modem then demodulates the RF signal and feeds the digital data to a computer. On the return path, the digital data is fed to the cable modem (from an associated PC for example), which converts it to a modulated RF signal. Once the CMTS receives the upstream RF signal, it demodulates it and transmits the digital data to an external source.
According to a current standard for transmission of data over cable networks (termed �DOCSIS�), there is no provision for any redundancy at the CMTS of the cable system. Therefore, a failure of the CMTS will result in a service disruption or service outage of the cable modems relying upon the failed element. If a CMTS fails, for example, it may have to be repaired or replaced before service can resume. This means that service can be out for an extended period. From the perspective of the service provider and the end user, any type of disruption or delay in service is extremely undesirable.
This problem becomes particularly acute as broadband access technologies, including cable, move toward digital telephony (e.g., Voice over IP or �VoIP�). For these applications, rapid reliable cutover from a failed component becomes critical. If such technologies are to compete with analog telephony, a greatly improved protection/cutover technology is necessary.
FIGS. 2A-2E present various cable network topologies that may be used in implementing the present invention. FIG. 2A depicts a network topology deemed �1:1� in which the network includes two CMTSs. Both are working CMTSs and both provide protection for the other. Thus, if one of the two CMTSs fails, the other one assumes the functions of the failed CMTS, while maintaining its own functions.
CMTS 207 is given the designation �W1� for working group 1. This means that it is responsible for handling communications with modem 203 and its peers. Similarly, CMTS 209 is designated �W2,� as it serves needs of cable modem 205 and possibly many other modems. In accordance with this invention, the CMTSs serve additional roles. CMTS 207 provides a protection path for CMTS 209, while CMTS 209 provides a protection path for CMTS 207. Thus, if CMTS 207 fails or otherwise goes out of service, CMTS 209 will take over responsibility for servicing cable modem 203 and its peers. Likewise, if CMTS 209 fails, CMTS 207 will take over responsibility for cable modem 205 and its peers. Note that this invention is not limited to cases in which a working CMTS �fails.� It is also useful for cases where the user simply wants the modems to move to the protection CMTS while the user upgrades or services the working CMTS software, hardware, etc.
In another topology, deemed �1 for 1 sparing,� the network uses two CMTSs: one is a normal working CMTS intended to carry on the normally working functions of a CMTS and another is dedicated to providing protection. In this topology, the protection CMTS does not provide service until the working CMTS fails. It then takes over that machine's functions. FIG. 2B depicts a 1 for 1 sparing topology. As shown, a cable network 201′ includes a working CMTS 213 and a protection CMTS 215. Working CMTS provides service to cable modem 203 and cable modem 205, both over channel 56. This is depicted by the connection paths through HFC plant 211. Note that protection CMTS 215 does not normally provide service to any cable modems. It remains available to take over in the case of a failure.
In another embodiment, �1 for N sparing,� multiple working CMTSs are protected by a single protection CMTS. The protection CMTS does not provide cable service until one of the N working CMTSs fails. This network topology is depicted in FIG. 2C. As shown, a network 201″ includes three working CMTSs: a CMTS 213, a CMTS 217, and a CMTS 219. CMTS 213 provides service to cable modem 203 over channel 56, CMTS 217 provides service to cable modem 205 over channel 57, and CMTS 219 provides service to a cable modem 222 over channel 58. A protection CMTS 221 does not normally service any cable modems but is available to service any cable modem in case it needs to take over for a failed peer. Note that in the depicted topology, protection CMTS 221 is assigned downstream channel 59.
In yet another topology, deemed �1:N� service, the cable network includes N+1 working CMTSs, and at least one of these working machines can provide protection for some or all of the other N machines. These approaches have the benefit of making use of all resources during normal operation. That is, the protection CMTS does not sit idle as it must in the �sparing� embodiments. Normally it provides a working path for some of the network modems. However, when a protection/working CMTS is filling in for a failed CMTS, it may have a rather heavy load.
FIGS. 2D and 2E present detailed examples of head-end topologies employing a 1:1 service. The invention is by no means limited to these topologies. As shown in FIG. 2D, the cable network head-end 230 includes a first CMTS interface 232 and a second CMTS interface 234. These CMTS interfaces may be provided on a single CMTS chassis or on separate CMTSs. In this specific embodiment, each interface has one downstream port, labeled �DS,� and six upstream ports labeled �U0�-�U5.� Downstream signals from CMTS 232 are provided at an intermediate frequency. When the signal reaches an upconverter 236, its frequency is increased to a level associated with cable channel 64.
Considering now the upstream signal, cable modems provide data on a specified upstream frequency band to fiber nodes 248 and 250. Normally, upstream data passing through fiber node 248 passes to CMTS interface 232 (via port �U0�). If the upstream path to CMTS interface 232 is disrupted for any reason (e.g., CMTS interface 232 fails), that upstream data is provided to CMTS interface 234. To this end, a splitter 252 allows data from fiber node 248 to pass through to either interface 232 or interface 234. Similarly, a splitter 254 allows upstream date from fiber node 250 to pass to either of interfaces 232 or 234.
1. Stage 1�Establishing a Cutover Path
One approach to speeding up the cutover process involves using cable modem IP addresses that are not part of any particular CMTS's interface subnet. Preferably, a registering cable modem obtains its IP address from an address block that is not part of a CMTS interface IP subnet, but is typically on an IP �supernet� shared among various CMTSs. Then when a cutover is required, the cable modem need not obtain a new IP address from a different address space. Various protocols may be used to assign the CMTS-independent IP addresses. In one embodiment, a registering cable modem obtains its IP address from a Dynamic Host Configuration Protocol (DHCP) server configured to provide IP addresses from outside the address space of any CMTS interface. DHCP is described in RFC 2131, incorporated herein by reference for all purposes. Generally, in this protocol, the computer is told to ask the network�according to prescribed rules�for a temporary network address.
FIGS. 3A, 3B, and 4 illustrate one set of procedures for registering a cable modem in accordance with an embodiment of this invention. Referring first to FIG. 3A, a flow chart is presented depicting generally the steps that a cable modem (and associated CMTSs) may go through to register on both the working CMTS a protection CMTS. As illustrated, a process 301 begins at 303 with the cable modem submitting a registration request to a working CMTS. In a specific embodiment, the registration complies with the procedures required by the DOCSIS standard. Normally, this involves obtaining an IP address for the cable modem, obtaining �ranging� parameters such as upstream frequency, power and timing, etc.
After pre-registration, but before cutover, the protection CMTS remains in a �protection state� ready to take over service to the cable modem when it determines that the modem's working route has failed. While in the protection state, the protection CMTS may periodically ensure that it is ready to take over service to the cable modem. This may entail that the protection CMTS determine that the protection path still works. If communication can take place over the path, the protection CMTS may request that the cable modem change certain parameters to optimize communication if a cutover becomes necessary. As indicated, the transmission characteristics of a cable network path vary with temperature, load, mechanical conditions, etc. Thus, what were optimal transmission settings one day, may be far from optimal the next day.
As mentioned, associated with the registration process, the cable network head-end injects the relevant host route into an appropriate routing protocol. FIG. 4 illustrates this process schematically. Normally, a CMTS advertises routes to its cable modems by identifying its interface subnet(s) via the appropriate routing protocol. In an embodiment of this invention, the CMTS advertises only a very small chunk of address space, not normally associated with its interfaces. These addresses provide host routes or small chunks of address space including IP addresses assigned to the cable modems during registration. Note that when the advertised address space is so small as to identify only a single cable modem, that �chunk� of address space, as used in a routing protocol, is referred to as a �host route.�
2. Stage 2�The Cutover Process
After failure detection, the cable modem loads, at 606, its previously stored protection path parameters. These include, for example, the upstream and downstream frequency bands for communicating with the protection CMTS, the appropriate cable modem transmission power to the protection CMTS, the communications time slots allotted for the protection CMTS, etc. Then, at 608, the cable modem connects to the protection CMTS and trims its parameters. Note that signal transmission properties vary nearly continually within a cable network. As a consequence, the parameters obtained during the pre-registration stage may no longer be optimal for communication with the protection CMTS. Trimming simply refers to the process of reoptimizing the transmission frequency, power, timing, etc. in light of current network conditions. In accordance with the DOCSIS protocol, trimming may be accomplished by the �ranging� process.
In normal operation (according to a standard such as DOCSIS), there should be continual �chit chat� between the CMTS and its modems. These messages are often sent at the link or MAC level. In DOCSIS, the messages take the form of pings and/or ranging requests. These messages, which are sent at least about every 30 seconds, confirm that the upstream and downstream paths between cable modem and CMTS are operational. If the CMTS should go down or some part of the path between it and the cable should become inoperational, then the cable modem will recognize that it can no longer communicate. At that point, it may begin the cutover procedure. In another scenario, the downstream path is operational, the cable modem is operational, and the CMTS is operational. The upstream path, however, is inoperational. The CMTS will recognize that it is not receiving messages from the cable modem. It may then infer that the upstream path has a problem and initiate the cutover to its protection CMTS. These examples illustrate that either the head end or the cable modems can initiate the cutover from a working to a protection path. This capability provides high system reliability.
Upstream optical data signals (packets) arriving via an optical fiber node 810 are converted to electrical signals by a receiver 812. Next, the upstream information packet (RF electrical signals) is demodulated by the demodulator/receiver 814 and then passed to MAC layer block 830. A primary purpose of MAC layer 830 is to encapsulate, with MAC headers, downstream packets and decapsulate, of MAC headers, upstream packets. In one embodiment, the encapsulation and decapsulation proceed as dictated by the above-mentioned DOCSIS standard for transmission of data or other information. Note that at the time when this document was filed, the DOCSIS standard was described in the �Data-Over-Cable Service Interface Specifications�Radio Interface Specifications� SP-RFIv1.1-I02-990731, Interim Specification Jul. 31, 1999. That document is incorporated herein by reference for all purposes. The MAC headers include addresses to specific modems or to a hub (if sent upstream) by a MAC layer block 830 in CMTS 804. Note that the cable modems also include MAC addressing components. In the cable modems, these components encapsulate upstream data with a header containing the MAC address of the hub.
MAC layer block 830 includes a MAC hardware portion 803 and a MAC software portion 884, which together serve the above-described functions. In a preferred embodiment, MAC hardware portion 803 is distinct from the router's general-purpose microprocessor and is dedicated to performing some MAC layer functions.
After MAC layer block 830 has processed the upstream information, it is then passed to network layer block 834. Network layer block 834 includes switching software 882 for causing the upstream information packet to be switched to an appropriate data network interface on data network interface 802. When a packet is received at the data network interface 802 from an external source, the switching software within network layer 834 passes the packet to MAC layer 830. MAC block 803 then transmits information via a one-way communication medium to downstream modulator and transmitter 806. Downstream modulator and transmitter 806 takes the data (or other information) in a packet structure and converts it to modulated downstream frames, such as MPEG or ATM frames, on the downstream carrier using, for example, QAM 64 modulation (other methods of modulation can be used such as CDMA (Code Division Multiple Access) OFDM (Orthogonal Frequency Division Multiplexing), FSK (FREQ Shift Keying)). The return data is likewise modulated using, for example, QAM 16 or QSPK. Data from other services (e.g. television) is added at a combiner 807. An optical converter 808 converts the modulated RF electrical signals to optical signals that can be received and transmitted via Fiber Node 810 to the cable modem hub.
Cable Modem�CMTS Interaction Cable Modem Initialization
step2: For Failure Ranging, the CM must send the RNG-REQ using the Failure Ranging SID. The Protect CMTS must send the RNG-RSP message with the Ranging Status=�success� and with the a Primary SID for use with the Protect CMTS.
Type Length Value: 29.1 10-7
Downstream Frequency The receive frequency to be used by the CM. This is the center frequency of the downstream channel in Hz stored as a 32-bit binary number. Downstream Frequency is the unique index of the Backup Downstream Channel Set.
Valid Range The receive frequency must be a multiple of 62599 Hz
Modem Primary SID for Protect CMTS: This is a 16-bit field of which the lower 14 bits define the SID with bits 14 and 15 defined to be 0. During initialization with Protect CMTS, the CM must send REG-REQ message containing this TLV with an Initialization SID 0. Protect CMTS must send REG-RSP message containing this TLV with an assigned Primary SID if provided now or Initialization SID of 0 if provided later when a failure occurs. During failure switchover, the Protect CMTS must send RNG-RSP message with Ranging Status=�success�, containing this TLV with the assigned primary SID.
Modem Failure Ranging SID for Protect CMTS: The SID is a 16-bit field of which the lower 14 bits define the SID with bits 14 and 15 defined to be 0. During the initialization with Protect CMTS, the Protect CMTS must send a REG-RSP message containing this TLV. During failure switch-over, when the CM does Failure Ranging with the Protect CMTS, the CM must send the RNG-REQ using this Failure Ranging SID. The Protect CMTS must send a RNG-RSP with Ranging Status=�success� message and containing the Modem Primary SID for Protect CMTS TLV with the assigned Primary SID. The Protect CMTS must allocate a contention ranging opportunity with a region large enough to account for the variation in delays between any two CMs.
Type Length Value: 29.8 4 HD,
Occasional Ranging The CM will perform occasional ranging with the Protect CMTS
The solution is to allocate a much more quicker contention ranging opportunity to Modem Failure Ranging SID for Protect CMTS. This is similar in concept to the Initial Maintenance IE. The CM gets a Primary SID assigned in RNG-RSP with Ranging Status=success message. The CM must invoke DHCP mechanisms to obtain an IP address and must initialize Baseline Privacy operations if the CM is provisioned to run Baseline Privacy.
While the discussion to this point has focused on a redundancy technology for cable networks, the technology of the present invention may be applied to any shared-access network having a plurality of hosts or nodes which share at least one channel for communicating with at least one �head-end� in the network. Examples of shared-access networks include, in addition to cable networks, wireless networks, Ethernet, etc. In the cable network, the plurality of nodes represents a plurality of cable modems that communicate with at least one CMTS at the centralized termination system using at least one shared-access upstream and downstream channel.
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