Patent ID: 12212426

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

The present disclosure relates generally to providing the ability to have mixed Internet Group Management Protocol (IGMP) querier versions in a network such as an Ethernet Virtual Private Network (EVPN). EVPN is a network technology for carrying layer2Ethernet traffic as a virtual private network using wide area network protocols. IGMP is a communications protocol used by network devices (e.g., routers) to establish multicast group memberships and allows networks such as EVPNs to deliver multicast transmissions from a source to one or more receivers. There are currently three versions of IGMP: IGMPv1 (defined by RFC 1112), IGMPv2 (defined by RFC 2236), and IGMPv3 (defined by RFC 3376).

According to some embodiments, an Ethernet Virtual Private Network (EVPN) includes a first router configured as an Internet Group Management Protocol (IGMP) version 3 querier and a second router configured as an IGMP version 2 querier. The second router is configured to receive a Selective Multicast Ethernet (SMET) route message generated by the first router. The SMET route message includes an IGMP version 3 join request from a receiver, and the IGMP version 3 join request includes an address of a multicast source device. The second router is further configured to convert the IGMP version 3 join request of the SMET route message to an IGMP version 2 join request. The second router is further configured to send multicast traffic from the multicast source device to the receiver via the first router.

According to another embodiment, a method performed by a network device in an EVPN includes receiving an IGMP version 3 join request generated by a receiver. The IGMP version 3 join request includes an address of a multicast source device. The method further includes converting the IGMP version 3 join request to an IGMP version 2 join request. The method further includes sending multicast traffic from the multicast source device to the receiver.

Technical advantages of certain embodiments of this disclosure may include one or more of the following. Certain systems and methods described provide network devices such as routers that are configured as IGMPv2 devices to process IGMP join requests from other network devices that are configured as IGMPv3 devices. Unlike existing networks where a first network device that is configured as an IGMPv2 querier is unable to process IGMP join requests from a second network device that is configured as an IGMPv3 querier, embodiments of this disclosure provide an enhanced join handling procedure for IGMPv2 queriers that allows such queriers to convert IGMPv3 join requests to IGMPv2 join requests. By converting IGMPv3 join requests to IGMPv2 join requests by a network device that is configured as an IGMPv2 querier, the IGMPv2 querier device may be able to provide multicast traffic to a receiver that would otherwise not be able to receive the desired multicast traffic. Furthermore, by converting IGMPv3 join requests to IGMPv2 join requests by a network device that is configured as an IGMPv2 querier, network bandwidth and computer resources (e.g., computer memory and processing power) may be optimized by not having to process a dropped route that would otherwise occur in current networks. Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages.

Example Embodiments

The present disclosure relates generally to providing the ability to have mixed IGMP querier versions in a network such as an EVPN. Generally, network devices such as routers that are configured as IGMPv2 devices are not able to process requests for multicast transmissions (e.g., IGMP join requests) from other network devices that are configured as IGMPv3 devices. That is, if an IGMPv2 querier receives an IGMPv3 join request, the IGMPv2 querier will not process the IGMPv3 join request and multicast traffic will not be forwarded to the requesting receiver. More specifically, IGMP queries are local to hosts behind each EVPN leaf and IGMP queries are not flooded into the EVPN fabric. In order to maintain IGMP membership reports, each leaf of the EVPN should have a local querier. However, IGMPv2 queriers are not be able to process IGMPv3 membership reports. In some scenarios such as when a source node in the EVPN fabric is a IGMPv2 querier and a receiver node is a IGMPv3 querier, multicast transmission will not be possible from the source to the receiver.

To address these and other problems with networks that have mixed IGMP querier versions, the enclosed embodiments provide system and methods that allow network devices such as routers that are configured as IGMPv2 queriers to process IGMPv3 join requests. To do so, embodiments of the disclosure provide an enhanced join handling procedure for IGMPv2 queriers that allows such queriers to convert IGMPv3 join requests to IGMPv2 join requests. For example, a router configured as an IGMPv2 querier may receive a Selective Multicast Ethernet (SMET) route message that includes an IGMPv3 join request from a receiver. The IGMPv2 querier device may then convert the IGMPv3 join request of the SMET route message to an IGMPv2 join request. Finally, the IGMPv2 querier may send multicast traffic to the receiver according to the converted IGMPv2 join request. As a result, a receiver behind an IGMPv3 querier may be able to receive multicast traffic from a source behind an IGMPv2 querier where it would otherwise be unable to do so.

FIG.1illustrates a network diagram illustrating a mixed IGMP querier network100. Mixed IGMP querier network100includes an EVPN fabric110that includes multiple instances130. For example, EVPN fabric110may include a first instance130A, a second instance130B, a third instance130C, and a fourth instance130D. Each instance130may include a network device120(e.g., network devices120A-D). Network devices120are communicatively coupled within EVPN fabric110using any appropriate communication protocol.

In general, mixed IGMP querier network100permits instances130that are IGMPv2 to send multicast traffic to instances130that are IGMPv3 where they would typically be unable to do so. More specifically, network devices120that are configured as IGMPv2 queriers are modified in order to allow them to process IGMPv3 join requests, thereby enabling IGMPv2 network devices120to send multicast traffic to a receiver in an IGMPv3 instance130. To do so, network devices120include an enhanced join handling procedure that converts IGMPv3 join requests to IGMPv2 join requests when the network device120is configured as an IGMPv2 querier. For example, network device120D, which is configured as an IGMPv2 querier in the illustrated example ofFIG.1, may receive a Selective Multicast Ethernet (SMET) route message170B that includes an IGMPv3 join request160B from a receiver140B that wishes to receive multicast traffic from a source150. Network device120D may then convert IGMPv3 join request160B to an IGMPv2 join request. Finally, network device120D may send multicast traffic from source150to receiver140B according to the converted IGMPv2 join request. As a result, receiver150that is located in an IGMPv3 instance130C may be able to receive multicast traffic from source150that is in an IGMPv2 instance130D where it would otherwise be unable to do so.

In general, instances130are physical locations in mixed IGMP querier network100where one or more network devices120(e.g., an edge router) may reside. For example, a branch office of an enterprise may be an instance130of router110and may include multiple network devices120. Each network device120provides an entry point into an enterprise or service provider network. Examples of network devices120include routers, routing switches, integrated access devices (IADs), and wide area network (WAN) access devices. Network devices120may be either hardware devices or software (e.g., a cloud-based router) that runs as a virtual machine. InFIG.1, each instance130site includes a single network device120(i.e., network device120A in instance130A, network device120B in instance130B, network device120C in instance130C, and network device120D in instance130D). However, it is to be understood that a given instance130may have multiple network devices120.

In the example ofFIG.1, instances130A-D are multicast sites and network devices120A-D are configured with IGMPv2 or IGMPv3 multicast routing. More specifically network devices120A and120D (i.e., “R1” and “R4”) are configured as IGMPv2 queriers, and network devices120B and120C (i.e., “R2” and “R3”) are configured as IGMPv3 queriers. Additionally, instance130A includes a multicast receiver140A that sits behind network device120A and instance130C includes a multicast receiver140B that sits behind network device120C. Finally, instance130D includes a multicast source150) that is located behind network device120D.

Join request160is an IGMP Membership Report that is generated by a receiver140. Join request160may be an IGMPv2 join request (i.e., a (*, G) request) or an IGMPv3 join request (i.e., a (S, G) request). In both cases, the G represents the multicast address for receiving the multicast stream. The S indicates that the multicast stream is to be received from a particular source, such as an IP address of source150. The * is a wildcard indicating that the multicast stream can be received from any source. Using the example ofFIG.1, receiver140A may generate an IGMPv2 join request160A of “(*, 233.1.1.1)” and receiver140B may generate an IGMPv3 join request160B of “(10.1.1.1, 233.1.1.1).” In these examples, 10.1.1.1 is the IP address of source150and 233.1.1.1 is the multicast address.

SMET route message170) is a message that contains a join request160from a receiver140. In general, SMET route message170) is communicated by a particular network device120to other network devices120. For example, SMET route message170A that is sent from network device120A to network device120D may be “(V2, *, 233.1.1.1)” and SMET route message170B that is sent from network device120C to network device120D may be “(V3, 10.1.1.1, 233.1.1.1).” As illustrated in these examples, each SMET route message170may include an IGMP version number (i.e., “V2” or “V3”) in addition to the join request160from receiver140.

In operation, network devices120include an enhanced join handling procedure that converts IGMPv3 join requests160to IGMPv2 join requests160when the network device120is configured as an IGMPv2 querier. In the illustrated example ofFIG.1, for example, network device120D, which is configured as an IGMPv2 querier and is configured to perform IGMP snooping, may receive SMET route message170B that includes IGMPv3 join request160B from receiver140B that wishes to receive multicast traffic from source150. Network device120D may then convert IGMPv3 join request160B to an IGMPv2 join request. Finally, network device120D may send multicast traffic from source150to receiver140B according to the converted IGMPv2 join request. As a result, receiver150that is located in an IGMPv3 instance130C may be able to receive multicast traffic from source150that is in an IGMPv2 instance130D where it would otherwise be unable to do so.

In some embodiments, each network device120includes a locally-stored database that may be used to store mapping states for the network device120. For example, if network device120D converts IGMPv3 join request160B to an IGMPv2 join request, network device120D may update a mapping state in its local database to include the conversion of the IGMPv3 join request160B to the IGMPv2 join request. Using the example ofFIG.1, once SMET route message170B is received at network device120D from network device120C, network device120D may convert join request160B of SMET route message170B to an IGMPv2 join request and record the final state in its database as “(*, G), outgoing port: network device120C.”

As illustrated inFIG.1, mixed IGMP querier network100may include network device120A of instance130A that is configured as an IGMPv2 querier. If receiver140A in instance130A also wants to receive multicast traffic from source150, it will send join request160A of (*, 233.1.1.1) to network device120A. In turn, network device120A will send SMET route message170A of (V2, *, 233.1.1.1) to network device120D. Once SMET route message170A is received by network device120D, network device120D will not be required to convert join request160A of SMET route message170A to an IGMPv2 join request since it is already an IGMPv2 join request (i.e., join request160A was generated by a receiver140A in an IGMP instance130A). Network device120D may then send multicast traffic from source150to receiver140A and may record the final state in is database as “(*, G), outgoing port: network device120C, network device120A.”

In some embodiments, instead of a receiving IGMPv2 network device120converting a received IGMPv3 join request to an IGMPv2 join request, a transmitting IGMPv3 network device120may perform the conversion from IGMPv3 to IGMPv2. In these embodiments, network devices120may each advertise their IGMP querier capability along with a proxy feature. For example, each network device120, when originating an IMET route with a proxy support bit, would include an additional flag which would indicate whether it is operating in IGMPv2 mode. In some embodiments, this flag would be enabled only if the querier version is V2. Once routes have been exchanged, each network device120will keep track of what version of querier are present in the network. For example, each network device120may maintain a table of peers and each of their associated querier versions. In the example ofFIG.1, for example, each network device120may maintain a table with information such as: “network device120A: querier version 2: network device120B: querier version 3; network device120C: querier version 3: network device120D: querier version 2.” Then, when an IGMPv3 network device120such as network device120C receives a join request160B from receiver140B, the network device120would consult the table to determine whether there are any network devices120operating in IGMPv2 mode. In the example ofFIG.1, network device120C would determine that there are two peers (i.e., network devices120A and120D) that are operating in IGMPv2 mode and would therefore convert IGMPv3 join request160B of (10.1.1.1, 233.1.1.1) to an IGMPv2 join request of (*, 233.1.1.1). SMET route message170would then become “(V2, *, 233.1.1.1).”

In the above example, since the same SMET route message170B of “(V2, *, 233.1.1.1)” is sent to all peer network devices120, all the multicast traffic for 233.1.1.1 would be sent to network device120C if there are multiple sources150behind network device120B. This is undesirable since network device120C is interested only in one source (i.e., source150). To eliminate this undesirable traffic, any IGMPv3 network device120that converts an IGMPv3 join request160to an IGMPv2 join request may indicate the conversion with an extra flag. This may allow other IGMPv3 network devices120to ignore the route and wait for an actual route to arrive. For example, when network device120B receives the above SMET route message170of “(V2, *, 233.1.1.1)” (i.e., the IGMPv3 join request160that network device120C converted to an IGMPv2 join request), network device120B will know it was an auto generated route that can be ignored and therefore would not forward any traffic to the EVPN fabric.

FIG.2is a flow diagram illustrating an example method200by a network device in an EVPN to support mixed IGMP querier versions. For example, method200may be performed by an IGMPv2 network device such as network device120D of mixed IGMP querier network100. Method200may begin in step210where method200receives an IGMP join request generated by a receiver. In some embodiments, the IGMP join request is join request160. In some embodiments, the IGMP join request is in an SMET route message170. In some embodiments the IGMP join request includes an address (e.g., an IP address) of a multicast source device such as source150.

In step220, method200determines whether the IGMP join request of step210is an IGMP version 3 join request. In some embodiments, step220may include comparing the information or format of the IGMP join request to standardized IGMPv2 and IGMPv3 join requests. (i.e., whether the IGMP join request includes a “*” that indicates an IGMPv2 join request). If method200in step220determines that the IGMP join request is an IGMP version 3 join request, method200proceeds to step240. Otherwise, method200proceeds to step230.

In step230, method200sends multicast traffic from the multicast source device to the receiver according to the IGMP join request received in step210. After step230, method200may end.

In step240, method200converts the IGMP join request received in step210to an IGMPv2 join request and proceeds to step250. In step250, method200sends multicast traffic from the multicast source device to the receiver according to the converted IGMP join request of step240. After step240, method200may end.

FIG.3illustrates an example computer system300. In particular embodiments, one or more computer systems300perform one or more steps of one or more methods described or illustrated herein. In particular embodiments, one or more computer systems300provide functionality described or illustrated herein. In particular embodiments, software running on one or more computer systems300performs one or more steps of one or more methods described or illustrated herein or provides functionality described or illustrated herein. Particular embodiments include one or more portions of one or more computer systems300. Herein, reference to a computer system may encompass a computing device, and vice versa, where appropriate. Moreover, reference to a computer system may encompass one or more computer systems, where appropriate.

This disclosure contemplates any suitable number of computer systems300. This disclosure contemplates computer system300taking any suitable physical form. As example and not by way of limitation, computer system300may be an embedded computer system, a system-on-chip (SOC), a single-board computer system (SBC) (such as, for example, a computer-on-module (COM) or system-on-module (SOM)), a desktop computer system, a laptop or notebook computer system, an interactive kiosk, a mainframe, a mesh of computer systems, a mobile telephone, a personal digital assistant (PDA), a server, a tablet computer system, an augmented/virtual reality device, or a combination of two or more of these. Where appropriate, computer system300may include one or more computer systems300: be unitary or distributed: span multiple locations: span multiple machines: span multiple data centers: or reside in a cloud, which may include one or more cloud components in one or more networks. Where appropriate, one or more computer systems300may perform without substantial spatial or temporal limitation one or more steps of one or more methods described or illustrated herein. As an example and not by way of limitation, one or more computer systems300may perform in real time or in batch mode one or more steps of one or more methods described or illustrated herein. One or more computer systems300may perform at different times or at different locations one or more steps of one or more methods described or illustrated herein, where appropriate.

In particular embodiments, computer system300includes a processor302, memory304, storage306, an input/output (I/O) interface308, a communication interface310, and a bus312. Although this disclosure describes and illustrates a particular computer system having a particular number of particular components in a particular arrangement, this disclosure contemplates any suitable computer system having any suitable number of any suitable components in any suitable arrangement.

In particular embodiments, processor302includes hardware for executing instructions, such as those making up a computer program. As an example and not by way of limitation, to execute instructions, processor302may retrieve (or fetch) the instructions from an internal register, an internal cache, memory304, or storage306; decode and execute them; and then write one or more results to an internal register, an internal cache, memory304, or storage306. In particular embodiments, processor302may include one or more internal caches for data, instructions, or addresses. This disclosure contemplates processor302including any suitable number of any suitable internal caches, where appropriate. As an example and not by way of limitation, processor302may include one or more instruction caches, one or more data caches, and one or more translation lookaside buffers (TLBs). Instructions in the instruction caches may be copies of instructions in memory304or storage306, and the instruction caches may speed up retrieval of those instructions by processor302. Data in the data caches may be copies of data in memory304or storage306for instructions executing at processor302to operate on: the results of previous instructions executed at processor302for access by subsequent instructions executing at processor302or for writing to memory304or storage306: or other suitable data. The data caches may speed up read or write operations by processor302. The TLBs may speed up virtual-address translation for processor302. In particular embodiments, processor302may include one or more internal registers for data, instructions, or addresses. This disclosure contemplates processor302including any suitable number of any suitable internal registers, where appropriate. Where appropriate, processor302may include one or more arithmetic logic units (ALUs): be a multi-core processor: or include one or more processors302. Although this disclosure describes and illustrates a particular processor, this disclosure contemplates any suitable processor.

In particular embodiments, memory304includes main memory for storing instructions for processor302to execute or data for processor302to operate on. As an example and not by way of limitation, computer system300may load instructions from storage306or another source (such as, for example, another computer system300) to memory304. Processor302may then load the instructions from memory304to an internal register or internal cache. To execute the instructions, processor302may retrieve the instructions from the internal register or internal cache and decode them. During or after execution of the instructions, processor302may write one or more results (which may be intermediate or final results) to the internal register or internal cache. Processor302may then write one or more of those results to memory304. In particular embodiments, processor302executes only instructions in one or more internal registers or internal caches or in memory304(as opposed to storage306or elsewhere) and operates only on data in one or more internal registers or internal caches or in memory304(as opposed to storage306or elsewhere). One or more memory buses (which may each include an address bus and a data bus) may couple processor302to memory304. Bus312may include one or more memory buses, as described below. In particular embodiments, one or more memory management units (MMUs) reside between processor302and memory304and facilitate accesses to memory304requested by processor302. In particular embodiments, memory304includes random access memory (RAM). This RAM may be volatile memory, where appropriate. Where appropriate, this RAM may be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, where appropriate, this RAM may be single-ported or multi-ported RAM. This disclosure contemplates any suitable RAM. Memory304may include one or more memories304, where appropriate. Although this disclosure describes and illustrates particular memory, this disclosure contemplates any suitable memory.

In particular embodiments, storage306includes mass storage for data or instructions. As an example and not by way of limitation, storage306may include a hard disk drive (HDD), a floppy disk drive, flash memory, an optical disc, a magneto-optical disc, magnetic tape, or a Universal Serial Bus (USB) drive or a combination of two or more of these. Storage306may include removable or non-removable (or fixed) media, where appropriate. Storage306may be internal or external to computer system300, where appropriate. In particular embodiments, storage306is non-volatile, solid-state memory. In particular embodiments, storage306includes read-only memory (ROM). Where appropriate, this ROM may be mask-programmed ROM, programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), electrically alterable ROM (EAROM), or flash memory or a combination of two or more of these. This disclosure contemplates mass storage306taking any suitable physical form. Storage306may include one or more storage control units facilitating communication between processor302and storage306, where appropriate. Where appropriate, storage306may include one or more storages306. Although this disclosure describes and illustrates particular storage, this disclosure contemplates any suitable storage.

In particular embodiments, I/O interface308includes hardware, software, or both, providing one or more interfaces for communication between computer system300and one or more I/O devices. Computer system300may include one or more of these I/O devices, where appropriate. One or more of these I/O devices may enable communication between a person and computer system300. As an example and not by way of limitation, an I/O device may include a keyboard, keypad, microphone, monitor, mouse, printer, scanner, speaker, still camera, stylus, tablet, touch screen, trackball, video camera, another suitable I/O device or a combination of two or more of these. An I/O device may include one or more sensors. This disclosure contemplates any suitable I/O devices and any suitable I/O interfaces308for them. Where appropriate, I/O interface308may include one or more device or software drivers enabling processor302to drive one or more of these I/O devices. I/O interface308may include one or more I/O interfaces308, where appropriate. Although this disclosure describes and illustrates a particular I/O interface, this disclosure contemplates any suitable I/O interface.

In particular embodiments, communication interface310includes hardware, software, or both providing one or more interfaces for communication (such as, for example, packet-based communication) between computer system300and one or more other computer systems300or one or more networks. As an example and not by way of limitation, communication interface310may include a network interface controller (NIC) or network adapter for communicating with an Ethernet or other wire-based network or a wireless NIC (WNIC) or wireless adapter for communicating with a wireless network, such as a WI-FI network. This disclosure contemplates any suitable network and any suitable communication interface310for it. As an example and not by way of limitation, computer system300may communicate with an ad hoc network, a personal area network (PAN), a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), or one or more portions of the Internet or a combination of two or more of these. One or more portions of one or more of these networks may be wired or wireless. As an example, computer system300may communicate with a wireless PAN (WPAN) (such as, for example, a BLUETOOTH WPAN), a WI-FI network, a WI-MAX network, a cellular telephone network (such as, for example, a Global System for Mobile Communications (GSM) network, a Long-Term Evolution (LTE) network, or a 5G network), or other suitable wireless network or a combination of two or more of these. Computer system300may include any suitable communication interface310for any of these networks, where appropriate. Communication interface310may include one or more communication interfaces310, where appropriate. Although this disclosure describes and illustrates a particular communication interface, this disclosure contemplates any suitable communication interface.

In particular embodiments, bus312includes hardware, software, or both coupling components of computer system300to each other. As an example and not by way of limitation, bus312may include an Accelerated Graphics Port (AGP) or other graphics bus, an Enhanced Industry Standard Architecture (EISA) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an Industry Standard Architecture (ISA) bus, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCIe) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus, or another suitable bus or a combination of two or more of these. Bus312may include one or more buses312, where appropriate. Although this disclosure describes and illustrates a particular bus, this disclosure contemplates any suitable bus or interconnect.

Herein, a computer-readable non-transitory storage medium or media may include one or more semiconductor-based or other integrated circuits (ICs) (such, as for example, field-programmable gate arrays (FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs), hybrid hard drives (HHDs), optical discs, optical disc drives (ODDs), magneto-optical discs, magneto-optical drives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes, solid-state drives (SSDs), RAM-drives, SECURE DIGITAL cards or drives, any other suitable computer-readable non-transitory storage media, or any suitable combination of two or more of these, where appropriate. A computer-readable non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate.

Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context.

The scope of this disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that a person having ordinary skill in the art would comprehend. The scope of this disclosure is not limited to the example embodiments described or illustrated herein. Moreover, although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, feature, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, features, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Additionally, although this disclosure describes or illustrates particular embodiments as providing particular advantages, particular embodiments may provide none, some, or all of these advantages.

The embodiments disclosed herein are only examples, and the scope of this disclosure is not limited to them. Particular embodiments may include all, some, or none of the components, elements, features, functions, operations, or steps of the embodiments disclosed herein. Certain embodiments are in particular disclosed in the attached claims directed to a method, a storage medium, a system and a computer program product, wherein any feature mentioned in one claim category, e.g. method, can be claimed in another claim category, e.g. system, as well. The dependencies or references back in the attached claims are chosen for formal reasons only. However, any subject matter resulting from a deliberate reference back to any previous claims (in particular multiple dependencies) can be claimed as well, so that any combination of claims and the features thereof are disclosed and can be claimed regardless of the dependencies chosen in the attached claims. The subject-matter which can be claimed comprises not only the combinations of features as set out in the attached claims but also any other combination of features in the claims, wherein each feature mentioned in the claims can be combined with any other feature or combination of other features in the claims. Furthermore, any of the embodiments and features described or depicted herein can be claimed in a separate claim and/or in any combination with any embodiment or feature described or depicted herein or with any of the features of the attached claims.