Patent Publication Number: US-2023155838-A1

Title: Offloading Authentication to an Authenticator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application Ser. No. 63/280,182, “Offloading Authentication to an Authenticator,” filed on Nov. 17, 2021, by Yuzhou Chen, et al., the contents of which are herein incorporated by reference. 
    
    
     FIELD 
     The described embodiments relate to techniques for offloading authenticating from an authentication computer to an authenticator. 
     BACKGROUND 
     Many electronic devices are capable of wirelessly communicating with other electronic devices. In particular, these electronic devices can include a networking subsystem that implements a network interface for: a cellular network (UMTS, LTE, etc.), a wireless local area network (e.g., a wireless network such as described in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard or Bluetooth from the Bluetooth Special Interest Group of Kirkland, Washington), and/or another type of wireless network. For example, many electronic devices communicate with each other via wireless local area networks (WLANs) using an IEEE 802.11-compatible communication protocol (which is sometimes collectively referred to as ‘Wi-Fi’). In a typical deployment, a Wi-Fi-based WLAN includes one or more access points (or basic service sets or BSSs) that communicate wirelessly with each other and with other electronic devices using Wi-Fi, and that provide access to another network (such as the Internet) via IEEE 802.3 (which is sometimes referred to as ‘Ethernet’). 
     One challenge is managing a network is how to authenticate users to confirm their identity and to authorize their access to the network. In enterprise wireless networks (such as an enterprise wireless local area network or WLAN), IEEE 802.1x authentication is widely used when a user accesses a WEAN. Moreover, in a large-scale WLAN deployment, IEEE 802.1x authentication message are typically forwarded to a remote authentication dial-in user service (RADIUS) server for processing. 
     However, the architecture can result in a variety of problems. For example, the RADIUS server may become overload, which result in IEEE 802.1x failure or delayed authentication. Alternatively or additionally, when the RADIUS server is unavailable for an extended period of time, then clients may be unable to join the FLAN until the RADIUS server is back in service or available. These delays or barriers to network access are frustrating to users and network administrators. 
     SUMMARY 
     An electronic device that selectively performs authentication to a network is described. This electronic device may include: one or more interface circuits that communicate with a second electronic device and an authentication computer; a processor; 
     and a memory that stores program instructions, where, when executed by the processor, the program instructions cause the electronic device to perform operations. Notably, during operation, the electronic device provides an identity request addressed to the second electronic device. Then, the electronic device receives, associated with the second electronic device, an identity response. In response, when the authentication computer is unavailable, the electronic device accesses, in the memory, a predefined hash function and associated authentication parameters for an authentication technique. Next, the electronic device performs authentication with the second electronic device based at least in part on the predefined hash function, where the authentication is compatible with the authentication technique. Moreover, the electronic device generates an encryption key, and establishes secure communication with the second electronic device by performing a four-way handshake with the second electronic device based at least in part on the encryption key. 
     Note that the electronic device may include an access point. 
     Moreover, the authentication computer may include a RADIUS server or an authentication, authorization, and accounting (AAA) server. 
     Furthermore, the second electronic device may have previously been authenticated by the authentication computer and then may have disconnected from the electronic device. After the authentication computer authenticated the second electronic device, the electronic device may have: received, associated with the authentication computer, the predefined hash function and the authentication parameters, where the predefined hash function and the authentication parameters are associated with the second electronic device; and stored, in the memory, the predefined hash function and the authentication parameters. 
     Additionally, the authentication parameters may specify a time interval for the predefined hash function. After the time interval has elapsed, the electronic device may delete the predefined hash function. 
     Note that the authentication technique may include a type of Extensible Authentication Protocol (EAP). 
     In some embodiments, prior to providing the identity request, the electronic device may associate with (or establish a connection with) the second electronic device. 
     Moreover, the encryption key may include a pairwise master key (PMK). 
     Furthermore, the electronic device may provide, addressed to the authentication computer, a renewal request prior to the time interval elapsing. In response, the electronic device may receive, associated with the authentication computer, a second predefined hash function and second authentication parameters. Then, the electronic device may store, in the memory, the second predefined hash function and the second authentication parameters. 
     Additionally, the four-way handshake may include or may be compatible with EAP over local area network (EAPol). 
     Moreover, the network may include a virtual network associated with a location. For example, the virtual network may include: a virtual local area network (VLAN) or a virtual extensible local area network (VXLAN). 
     Another embodiment provides the second electronic device that performs counterpart operations to at least some of the aforementioned operations of the electronic device. 
     Another embodiment provides the authentication computer that performs counterpart operations to at least some of the aforementioned operations of the electronic device. 
     Another embodiment provides a system that includes the electronic device and/or the authentication computer. 
     Another embodiment provides a computer-readable storage medium with program instructions for use with one of the aforementioned components. When executed by the component, the program instructions cause the component to perform at least some of the aforementioned operations in one or more of the preceding embodiments. 
     Another embodiment provides a method, which may be performed by one of the aforementioned components. This method includes at least some of the aforementioned operations in one or more of the preceding embodiments. 
     This Summary is provided for purposes of illustrating some exemplary embodiments, so as to provide a basic understanding of some aspects of the subject matter described herein. Accordingly, it will be appreciated that the above-described features are examples and should not be construed to narrow the scope or spirit of the subject matter described herein in any way. Other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a block diagram illustrating an example of communication among electronic devices in accordance with an embodiment of the present disclosure. 
         FIG.  2    is a flow diagram illustrating an example of a method for performing authentication to a network using an electronic device in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  3    is a drawing illustrating an example of communication among the electronic devices in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  4    is a drawing illustrating an example of communication among the electronic devices in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  5    is a drawing illustrating an example of communication among the electronic devices in  FIG.  1    in accordance with an embodiment of the present disclosure. 
         FIG.  6    is a block diagram illustrating an example of an electronic device in accordance with an embodiment of the present disclosure. 
     
    
    
     Note that like reference numerals refer to corresponding parts throughout the drawings. Moreover, multiple instances of the same part are designated by a common prefix separated from an instance number by a dash. 
     DETAILED DESCRIPTION 
     An electronic device (such as an access point) that selectively performs authentication to a network is described. During operation, the electronic device provides an identity request addressed to the second electronic device. Then, the electronic device receives, associated with the second electronic device, an identity response. In response, when the authentication computer is unavailable, the electronic device accesses, in memory, a predefined hash function and authentication parameters for an authentication technique. Next, the electronic device performs authentication with the second electronic device based at least in part on the predefined hash function, where the authentication is compatible with the authentication technique (a type of EAP). Moreover, the electronic device generates an encryption key, and establishes secure communication with the second electronic device by performing a four-way handshake with the second electronic device based at least in part on the encryption key. 
     By selectively performing the authentication technique, these communication techniques may facilitate authentication and secure access to the network. Notably, the communication techniques may provide reliable authentication and secure access to the network, even when the authentication computer is unavailable. In the process, the communication techniques may eliminate delays in authenticating users. Consequently, the communication techniques may reduce frustration of the users and network operators or network administrators, and may improve the user experience when using in the network. 
     In the discussion that follows, electronic devices or components in a system communicate packets in accordance with a wireless communication protocol, such as: a wireless communication protocol that is compatible with an IEEE 802.11 standard (which is sometimes referred to as Wi-Fi®, from the Wi-Fi Alliance of Austin, Tex.), Bluetooth, a cellular-telephone network or data network communication protocol (such as a third generation or 3G communication protocol, a fourth generation or 4G communication protocol, e.g., Long Term Evolution or LTE (from the 3rd Generation Partnership Project of Sophia Antipolis, Valbonne, France), LTE Advanced or LTE-A, a fifth generation or 5G communication protocol, or other present or future developed advanced cellular communication protocol), and/or another type of wireless interface (such as another wireless-local-area-network interface). For example, an IEEE 802.11 standard may include one or more of: IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.11-2007, IEEE 802.11n, IEEE 802.11-2012, IEEE 802.11-2016, IEEE 802.11ac, IEEE 802.11ax, IEEE 802.11ba, IEEE 802.11be, or other present or future developed IEEE 802.11 technologies. Moreover, an access point, a radio node, a base station or a switch in the wireless network may communicate with a local or remotely located computer (such as a controller) using a wired communication protocol, such as a wired communication protocol that is compatible with an IEEE 802.3 standard (which is sometimes referred to as ‘Ethernet’), e.g., an Ethernet II standard. However, a wide variety of communication protocols may be used in the system, including wired and/or wireless communication. In the discussion that follows, Wi-Fi, LTE and Ethernet are used as illustrative examples. 
     We now describe some embodiments of the communication techniques.  FIG.  1    presents a block diagram illustrating an example of communication in an environment  106  with one or more electronic devices  110  (such as cellular telephones, portable electronic devices, stations or clients, another type of electronic device, etc., which are sometimes referred to as ‘end devices’) via a cellular-telephone network  114  (which may include a base station  108 ), one or more access points  116  (which may communicate using Wi-Fi) in a WLAN and/or one or more radio nodes  118  (which may communicate using LTE) in a small-scale network (such as a small cell). For example, the one or more radio nodes  118  may include: an Evolved Node B (eNodeB), a Universal Mobile Telecommunications System (UMTS) NodeB and radio network controller (RNC), a New Radio (NR) gNB or gNodeB (which communicates with a network with a cellular-telephone communication protocol that is other than LTE), etc. In the discussion that follows, an access point, a radio node or a base station are sometimes referred to generically as a ‘communication device.’ Moreover, as noted previously, one or more base stations (such as base station  108 ), access points  116 , and/or radio nodes  118  may be included in one or more wireless networks, such as: a WLAN, a small cell, and/or a cellular-telephone network. In some embodiments, access points  116  may include a physical access point and/or a virtual access point that is implemented in software in an environment of an electronic device or a computer. 
     Note that access points  116  and/or radio nodes  118  may communicate with each other, computer  112  (which may be a cloud-based controller that manages and/or configures access points  116 , radio nodes  118  and/or switch  128 , or that provides cloud-based storage and/or analytical services) and/or authentication computer  130  (such as a RADIUS server and/or an AAA server) using a wired communication protocol (such as Ethernet) via network  120  and/or  122 . Note that networks  120  and  122  may be the same or different networks. For example, networks  120  and/or  122  may an LAN, an intra-net or the Internet. In some embodiments, network  120  may include one or more routers and/or switches (such as switch  128 ). 
     As described further below with reference to  FIG.  6   , electronic devices  110 , computer  112 , access points  116 , radio nodes  118 , switch  128  and authentication computer  130  may include subsystems, such as a networking subsystem, a memory subsystem and a processor subsystem. In addition, electronic devices  110 , access points  116  and radio nodes  118  may include radios  124  in the networking subsystems. More generally, electronic devices  110 , access points  116  and radio nodes  118  can include (or can be included within) any electronic devices with the networking subsystems that enable electronic devices  110 , access points  116  and radio nodes  118  to wirelessly communicate with one or more other electronic devices. This wireless communication can comprise transmitting access on wireless channels to enable electronic devices to make initial contact with or detect each other, followed by exchanging subsequent data/management frames (such as connection requests and responses) to establish a connection, configure security options, transmit and receive frames or packets via the connection, etc. 
     During the communication in  FIG.  1   , access points  116  and/or radio nodes  118  and electronic devices  110  may wired or wirelessly communicate while: transmitting access requests and receiving access responses on wireless channels, detecting one another by scanning wireless channels, establishing connections (for example, by transmitting connection requests and receiving connection responses), and/or transmitting and receiving frames or packets (which may include information as payloads). 
     As can be seen in  FIG.  1   , wireless signals  126  (represented by a jagged line) may be transmitted by radios  124  in, e.g., access points  116  and/or radio nodes  118  and electronic devices  110 . For example, radio  124 - 1  in access point  116 - 1  may transmit information (such as one or more packets or frames) using wireless signals  126 . These wireless signals are received by radios  124  in one or more other electronic devices (such as radio  124 - 2  in electronic device  110 - 1 ). This may allow access point  116 - 1  to communicate information to other access points  116  and/or electronic device  110 - 1 . Note that wireless signals  126  may convey one or more packets or frames. 
     In the described embodiments, processing a packet or a frame in access points  116  and/or radio nodes  118  and electronic devices  110  may include: receiving the wireless signals with the packet or the frame; decoding/extracting the packet or the frame from the received wireless signals to acquire the packet or the frame; and processing the packet or the frame to determine information contained in the payload of the packet or the frame. 
     Note that the wireless communication in  FIG.  1    may be characterized by a variety of performance metrics, such as: a data rate for successful communication (which is sometimes referred to as ‘throughput’), an error rate (such as a retry or resend rate), a mean-square error of equalized signals relative to an equalization target, intersymbol interference, multipath interference, a signal-to-noise ratio, a width of an eye pattern, a ratio of number of bytes successfully communicated during a time interval (such as 1-10 s) to an estimated maximum number of bytes that can be communicated in the time interval (the latter of which is sometimes referred to as the ‘capacity’ of a communication channel or link), and/or a ratio of an actual data rate to an estimated data rate (which is sometimes referred to as ‘utilization’). While instances of radios  124  are shown in components in  FIG.  1   , one or more of these instances may be different from the other instances of radios  124 . 
     In some embodiments, wireless communication between components in  FIG.  1    uses one or more bands of frequencies, such as: 900 MHz, 2.4 GHz, 5 GHz, 6 GHz, 60 GHz, the Citizens Broadband Radio Spectrum or CBRS (e.g., a frequency band near 3.5 GHz), and/or a band of frequencies used by LTE or another cellular-telephone communication protocol or a data communication protocol. Note that the communication between electronic devices may use multi-user transmission (such as orthogonal frequency division multiple access or OFDMA). 
     Although we describe the network environment shown in  FIG.  1    as an example, in alternative embodiments, different numbers or types of electronic devices may be present. For example, some embodiments comprise more or fewer electronic devices. As another example, in another embodiment, different electronic devices are transmitting and/or receiving packets or frames. 
     As discussed previously, when authentication computer  130  is unavailable, it can be difficult for electronic devices  110  to authenticate and obtain secure access to networks  120  and/or  122 . Moreover, as described further below with reference to  FIGS.  2 - 5   , in order to address these problems, an electronic device (such as access point  116 - 1 , radio node  118 - 1  or switch  128 , and more generally a computer network device) may perform the disclosed communication techniques. In the discussion that follows, access point  116 - 1  is used to illustrate the communication techniques. 
     During operation, an electronic device  110 - 1  may discover and associate with (or establish a connection with) access point  116 - 1  (and, thus, with a network, such as a WLAN and/or network  120 , provided by access point  116 - 1 ). For example, electronic device  110 - 1  may provide an authentication request to access point  116 - 1 . Then, access point  116 - 1  may provide a user-equipment context request to computer  112 . Computer  112  may subsequently provide a user-equipment context response to access point  116 - 1 , which may confirm that there is not an existing context or association for electronic device  110 - 1  in the WLAN. 
     Moreover, access point  116 - 1  may provide an authentication response to electronic device  110 - 1 . Next, electronic device  110 - 1  may provide an association request to access point  116 - 1 , which may respond by providing an association response to electronic device  110 - 1 . Note that, at this point there is a connection between electronic device  110 - 1  and access point  116 - 1 , but the communication is not encrypted. Furthermore, computer  112  may provide the user-equipment context response to access point  116 - 1 , such as a negative acknowledgment or NACK. 
     After associating with electronic device  110 - 1 , access point  116 - 1  may provide an identity request to electronic device  110 - 1 . Then, electronic device  110 - 1  may provide an identity response to access point  116 - 1 . 
     In order to address circumstances in which authentication computer  130  is unavailable, access point  116 - 1  may be configured to perform authentication of electronic device  110 - 1  to network  120  and/or network  122 . Notably, electronic device  110 - 1  may have previously been authenticated by authentication computer  130  and then electronic device  110 - 1  may have disconnected from access point  116 - 1 . After authentication computer  130  authenticated electronic device  110 - 1 , access point  116 - 1  may have: received, from authentication computer  130 , a predefined hash function and associated authentication parameters, where the predefined hash function and the authentication parameters are associated with electronic device  110 - 1 ; and stored, in memory in or associated with access point  116 - 1 , the predefined hash function and the authentication parameters. 
     Therefore, after receiving the identity response and when authentication computer  130  is unavailable, access point  116 - 1  may access, in the memory in or associated with access point  116 - 1 , the predefined hash function and the authentication parameters for an authentication technique (such as a type of EAP). Next, access point  116 - 1  may perform authentication with electronic device  110 - 1  based at least in part on the predefined hash function, where the authentication is compatible with the authentication technique. Moreover, access point  116 - 1  may generate an encryption key (such as a PMIS), and may establish secure communication with electronic device  110 - 1  by performing a four-way handshake with electronic device  110 - 1  based at least in part on the encryption key. For example, the four-way handshake may include or may be compatible with EAPol. As discussed further below, note that in some authentication techniques the authentication is performed by access point  116 - 1  during the four-way handshake with electronic device  110 - 1 . 
     In some embodiments, the authentication parameters may specify a time interval for the predefined hash function. Consequently, after the time interval has elapsed, access point  116 - 1  may delete the predefined hash function, e.g., in the memory. Alternatively, when authentication computer  130  is available, access point  116 - 1  may provide, to authentication computer  130 , a renewal request prior to the time interval elapsing. In response, access point  116 - 1  may receive, from authentication computer  130 , a second predefined hash function and second authentication parameters. Then, access point  116 - 1  may store, in the memory, the second predefined hash function and the second authentication parameters. 
     In these ways, the communication techniques may offload authentication to an authenticator, such as access point  116 - 1 . Notably, the communication techniques may allow access point  116 - 1  to selectively authenticate and provide secure access by electronic device  110 - 1  to a network. This capability may allow dynamic secure access to the network (such as access at one or more locations and/or at different times), even when authentication computer  130  is unavailable. Consequently, the communication techniques may improve the user experience when using electronic device  110 - 1 , access point  116 - 1  and communicating via the network. 
     We now discuss embodiments in which the authentication is performed by access point  116 - 1  during the four-way handshake with electronic device  110 - 1 . Notably, after receiving the identification response and generating the encryption key, access point  116 - 1  may provide, to electronic device  110 - 1 , a first message in a four-way handshake with electronic device  110 - 1 . This first message may include a random number associated with access point  116 - 1  (which is sometimes referred to as an ‘ANonce’). In response, electronic device  110 - 1  may construct, derive or generate a pairwise transient key (PTK). For example, the PTK may be constructed or generated using a cryptographic calculation (such as a pseudo-random function) and optionally a pre-shared key (such as a passphrase, e.g., a dynamic pre-shared key or DPSK or another type of digital certificate), the ANonce, a second random number associated with electronic device  110 - 1  (which is sometimes referred to as an ‘SNonce’), an identifier of access point  116 - 1  (such as a media access control or MAC address of access point  116 - 1 ), and/or an identifier of electronic device  110 - 1  (such as a MAC address of electronic device  110 - 1 ). Note that the passphrase may be preinstalled or preconfigured on electronic device  110 - 1  and may be stored in memory that is accessible by access point  116 - 1 . In some embodiments, a user of electronic device  110 - 1  may receive the passphrase and install it on electronic device  110 - 1  using a portal (such as website or web page), an email, an SMS message, etc. 
     Note that the passphrase may be independent of an identifier associated with electronic device  110 - 1 , such as the MAC address of electronic device  110 - 1 . More generally, the passphrase may be independent of electronic device  110 - 1  or hardware in electronic device  110 - 1 . The passphrase may be associated with a location, such as a room, a building, a communication port (such as a particular Ethernet port), etc. (In general, in the present discussion a ‘location’ may not be restricted to a physical location, but may be abstracted to include an object or entity associated with a physical location, such as a particular room or building.) Alternatively or additionally, the passphrase may be associated with one or more users, such as a guest or family in a hotel. Thus, in some embodiments, the passphrase includes a common passphrase that is shared by a group of electronic devices (e.g., the common passphrase may be a group DPSK). 
     Furthermore, electronic device  110 - 1  may provide a second message in the four-way handshake to access point  116 - 1 . The second message may include the SNonce and a message integrity check (MIC) to access point  116 - 1 . In some embodiments, the second message includes: the inputs to the cryptographic calculation and an output of the cryptographic calculation. 
     Additionally, instead of providing an access request to authentication computer  130 , access point  116 - 1  may perform authentication and authorization of electronic device  110 - 1 , including comparing cryptographic information specified by passphrase parameters (which may be included in the authentication parameters) with stored information in or associated with access point  116 - 1  (such as the DPSK or the other type of digital certificate) for electronic device  110 - 1 . More generally, access point  116 - 1  may use information specified by the passphrase parameters to determine whether electronic device  110 - 1  is authorized to access network  120  and/or network  122 . Note that the passphrase parameters may include: the inputs to the cryptographic calculation and an output of the cryptographic calculation. For example, the passphrase parameters may include: the ANonce, the SNonce, the MIC, the MAC address of electronic device  110 - 1 , and/or the MAC address of access point  116 - 1 . In addition, the passphrase parameters may include other information, such as: a cluster name, a zone name, a service set identifier (SSID) of the WLAN, a basic service set identifier (BSSID) of access point  116 - 1 , and a username of the user. 
     Notably, access point  116 - 1  may perform brute-force calculations of outputs of the cryptographic calculation based at least in part on the inputs to the cryptographic calculation and different stored passphrases. When there is a match between one of these calculated outputs and the output received from electronic device  110 - 1 , it may confirm that access point  116 - 1  is able to construct, derive or generate the same PTK as electronic device  110 - 1 , so that electronic device  110 - 1  and access point  116 - 1  will be able to encrypt and decrypt their communication with each other. (Alternatively, instead of performing the brute-force calculations, authentication computer  130  may provide the output of the cryptographic calculation to access point  116 - 1 , so access point  116 - 1  can directly confirm that there is match with the output received from electronic device  110 - 1 .) 
     Then, access point  116 - 1  may optionally access a policy associated with the user (which may be included in the authentication parameters and/or by performing a look up based at least in part on an identifier of the user, such as a username of the user) that governs the access to W LAN (and, more generally, to network  120  and/or network  122 ). For example, the policy may include the policy may include a time interval when the passphrase is valid. Moreover, the policy may include a location where the passphrase is valid (such as a location of access point  116 - 1 ) or the network that the user is allowed to access. In some embodiments, access point  116 - 1  may communicate with a property management (PM) server (not shown), which is associated with an organization, to determine whether electronic device  110 - 1  is associated with the location (such as whether a user of electronic device  110 - 1  is checked into or associated with a room where access point  116 - 1  is located). Note that the location may include: a room, a building, a communication port, a facility associated with the organization (such as a hotel or an education institution), etc. More generally, access point  116 - 1  may optionally communicate with the PM server to determine whether one or more criteria associated with the policy are met. 
     Then, when there is match of the outputs of the cryptographic calculation and/or one or more criteria associated with the policy are met, access point  116 - 1  may selectively provide access acceptance information in a third message in the four-way handshake to electronic device  110 - 1 . This third message may include information for establishing secure access of electronic device  110 - 1 . For example, the access acceptance information may include: an identifier of electronic device  110 - 1 , a tunnel type, a tunnel medium type, a tunnel privilege group identifier, a filter identifier, and the username. 
     Furthermore, electronic device  110 - 1  may provide a fourth message in the four-way handshake to access point  116 - 1 , such as an acknowledgment. At this point, access point  116 - 1  may establish secure access to the WLAN for electronic device  110 - 1  (and, more generally, secure access to network  120  and/or network  122 , such as an intranet or the Internet). Notably, the secure access may be in a personal area network (PAN) in the WLAN, which is independent of traffic associated with other PANs in the WLAN. 
     In some embodiments, the secure access may be implemented using a virtual network associated with the location (such as a virtual network for the PAN), and the information in the access acceptance information may allow electronic device  110 - 1  to establish secure communication with the virtual network. This secure communication may be independent of traffic associated with other users of the WLAN. For example, access point  116 - 1  may bridge traffic between electronic device  110 - 1  and another member of a group of electronic devices (such as electronic device  110 - 2 ) in the virtual network in the WLAN, where the traffic in the virtual network is independent of other traffic associated with one or more different virtual networks in the network. Note that the virtual network may include a VLAN. Alternatively, when the aforementioned operations of access point  116 - 1  are performed by switch  128 , the virtual network may include a VXLAN. In these embodiments, switch  128  may bridge wired traffic (such as Ethernet frames) associated with electronic device  110 - 1  in virtual network. 
     Moreover, the virtual network may be specified by an identifier that is included in the access acceptance information. For example, the identifier may include a VLANID (for use with access point  116 - 1 ) or a VNI (for use with switch  128 ). Moreover, the identifier may include information that is capable of specifying more than 4,096 virtual networks. In some embodiments, the identifier may include 24 bits, which can be used to specify up to 16 million virtual networks. 
     In some embodiments, the virtual network is implemented in a virtual dataplane in access point  116 - 1  (such as using a generic routing encapsulation or GRE tunnel). Note that a dataplane is generally responsible for moving data around transmit paths, while a control plane is generally responsible for determining and setting up those transmit paths. The dataplane may be implemented using virtual machines that are executed by multiple cores in one or more processors (which is sometimes referred to as a ‘virtual dataplane’), which allows the dataplane to be flexibly scaled and dynamically reconfigured. In the present discussion, a virtual machine is an operating system or application environment that is implemented using software that imitates or emulates dedicated hardware or particular functionality of the dedicated hardware. 
     Additionally, in some embodiments, the policy allows the user to access multiple networks at different locations (such as different geographic locations, e.g., different hotels in a hotel brand or chain). In these embodiments, the inputs used to calculate the one or more second outputs of the cryptographic calculation may include a given identifier of a given network (such as a given SSID). Moreover, one or more stored passphrases may be organized based at least in part on identifiers of different networks. In these embodiments, related stored passphrases may be grouped based at least in part on a given network that a user is asking to join, which may reduce the computational time need by access point  116 - 1  to calculate the outputs for the different stored passphrases. 
     While the preceding discussion illustrated the communication techniques with communication between access point  116 - 1  (and, more generally, a computer network device) and electronic device  110 - 1 , in other embodiments this communication may be mediated by one or more other components and/or may involve communication with the one or more other components. 
     We now describe embodiments of the method.  FIG.  2    presents a flow diagram illustrating an example of a method  200  for selectively performing authentication to a network, which may be performed by an electronic device, such as one of access points  116 , one of radio nodes  118  or switch  128  in  FIG.  1   . During operation, the electronic device may provide an identity request (operation  210 ) addressed to a second electronic device. For example, the identity request may include an EAPol identity request. 
     Then, the electronic device may receive, associated with the second electronic device, an identity response (operation  212 ). For example, the identity request may include an EAPol identity response with a username of a user. 
     In response, when an authentication computer is unavailable (operation  214 ), the electronic device may access, in a memory in or associated with the electronic device, information, including a predefined hash function and associated authentication parameters (operation  216 ) for an authentication technique (such as a type of EAP). 
     Next, the electronic device may perform the authentication (operation  218 ) with the second electronic device based at least in part on the predefined hash function, where the authentication is compatible with the authentication technique. For example, during the authentication (operation  218 ), the electronic device may provide one or more challenges to the second electronic device and may receive one or more responses from the second electronic device. 
     Moreover, the electronic device may generate an encryption key (operation  220 ), and may establish secure communication with the second electronic device by performing a four-way handshake (operation  222 ) with the second electronic device based at least in part on the encryption key (e.g., using a PTK derived from the PMK to encrypt data). 
     Alternatively, when the authentication computer is available (operation  210 ), the electronic device may optionally communicate with the authentication computer to initiate the authentication (operation  224 ). 
     Note that the authentication computer may include a RADIUS server and/or a AAA server. 
     Moreover, the encryption key may include a pairwise master key (PMK). 
     Furthermore, the four-way handshake may include or may be compatible with EAPol. 
     Additionally, the network may include a virtual network associated with a location. For example, the virtual network may include: a VLAN or a VXLAN. 
     Note that the type of EAP may include: Protected EAP (PEAP), a password-based and one-way authentication protocol (such as EAP-MD5), EAP-Transport Layer Security (EAP-TLS), EAP-Tunnel TLS (EAP-TTLS), EAP-Encrypted Key Exchange (EKE), Lightweight EAP (LEAP), etc. For PEAP, generating the encryption key (operation  220 ) may involve: performing a hash (e.g., using the predefined hash function) of a password of a user, and then using the hash result to generate the encryption key. 
     In some embodiments, the authentication may include a MAC-level authentication implemented, at least in part, using software. 
     In some embodiments, the electronic device may optionally perform one or more additional operations (operation  226 ). Notably, prior to providing the identity request (operation  210 ), the electronic device may associate with (or establish a connection with) the second electronic device. 
     Moreover, the second electronic device may have previously been authenticated by the authentication computer and then may have disconnected from the electronic device. After the authentication computer authenticated the second electronic device, the electronic device may have: received, associated with the authentication computer, the predefined hash function and the authentication parameters, where the predefined hash function and the authentication parameters are associated with the second electronic device; and stored, in the memory, the predefined hash function and the authentication parameters. 
     Additionally, the authentication parameters may specify a time interval for the predefined hash function. After the time interval has elapsed, the electronic device may delete the predefined hash function. Alternatively, the electronic device may provide, addressed to the authentication computer, a renewal request prior to the time interval elapsing. In response, the electronic device may receive, associated with the authentication computer, a second predefined hash function and second authentication parameters. Then, the electronic device may store, in the memory, the second predefined hash function and the second authentication parameters. 
     In some embodiments of method  200 , there may be additional or fewer operations. Furthermore, the order of the operations may be changed, and/or two or more operations may be combined into a single operation. 
     Embodiments of the communication techniques are further illustrated in  FIG.  3   , which presents a drawing illustrating an example of communication among electronic device  110 - 1 , access point  116 - 1 , and authentication computer  130 . In  FIG.  3   , electronic device  110 - 1  may discover and associate  312  with access point  116 - 1  via an interface circuit (IC)  310  in access point  116 - 1 . 
     Moreover, electronic device  110 - 1  may authenticate  314  with authentication computer  130  via communication with interface circuit  310 . After this occurs, authentication computer  130  may provide to interface circuit  310  a predefined hash function or PHF (such as a key hash)  316  and associated authentication parameters (APs)  318 , which are associated with an authentication technique (such as a type of EAP). After receiving the predefined hash function  316  and the authentication parameters  318 , interface circuit  310  may store the predefined hash function  316  and the authentication parameters  318  in memory  320  in access point  116 - 1 . Then, interface circuit  310  may perform a four-way handshake (4WH)  322  with electronic device  110 - 1 . 
     Subsequently, electronic device  110 - 1  may de-associate  324  from access point  116 - 1 . Furthermore, electronic device  110 - 1  may subsequently associate  326  again with access point  116 - 1  via interface circuit  310 . When this occurs, interface circuit  310  may provide an identity request (IR)  328  to electronic device  110 - 1 . After receiving identity request  328 , electronic device  110 - 1  may provide an identity response (IRS)  330  to access point  110 - 1 , e.g., with a password of a user of electronic device  110 - 1 . This identity response may be received by interface circuit  310 . 
     Next, when authentication computer  130  is unavailable, interface circuit  310  may access  332  predefined hash function  316  and the authentication parameters  318  in memory  320 . Additionally, interface circuit  310  may perform authentication  334  with electronic device  110 - 1  based at least in part on the predefined hash function  316 , where the authentication is compatible with the authentication technique. 
     Moreover, interface circuit  310  may generate an encryption key (EK)  336 , and may establish secure communication with electronic device  110 - 1  by performing a four-way handshake (4WH)  338  with electronic device  110 - 1  based at least in part on the encryption key  336 . 
     Furthermore, the authentication parameters  318  may specify a time interval or a timeout for the predefined hash function  316 . After the time interval has elapsed, interface circuit  310  may optionally delete  340  the predefined hash function  316 . Alternatively, when authentication computer  130  is available, interface circuit  310  may provide, to authentication computer  130 , a renewal request (RR)  342  prior to the time interval elapsing. In response, authentication computer  130  may provide to interface circuit  310  a second predefined hash function  344  and second authentication parameters  346 , which are associated with the authentication technique. After receiving the second predefined hash function  344  and the second authentication parameters  346 , interface circuit  310  may store the second predefined hash function  344  and the second authentication parameters  346  in memory  320 . 
     While  FIG.  3    illustrates communication between components using unidirectional or bidirectional communication with lines having single arrows or double arrows, in general the communication in a given operation in this figure may involve unidirectional or bidirectional communication. Moreover, while  FIG.  3    illustrates operations being performed sequentially or at different times, in other embodiments at least some of these operations may, at least in part, be performed concurrently or in parallel. 
     We now further describe the communication techniques. In order to mitigate a load of an authentication computer and to provide survivability of an IEEE 802.1x-based WLAN service when the authentication computer is out of service for some time, the authentication computer may pass a key hash and related authentication parameters to an access point. Notably, after a first successful IEEE 802.1x authentication of an electronic device (or client), the authentication computer may pass a key hash and related authentication parameters and information specifying a type of EAP technique to the access point. Note that the authentication parameters may be associated with the client and may be used to generate a PMK. In some embodiments, the authentication parameters may include a hash timeout value. The access point may store the key hash and the authentication parameters until its timeout. 
     Then, the client may disconnect from the access point. When the client subsequently reconnects and associates with the access point, the access point may start IEEE 802.1x authentication by sending an identity request to the client. After receiving an identity response from the client, instead of initiating the type EAP technique with the authentication computer, the access point may use the stored key hash to start the IEEE 802.1x EAP technique with client. For example, the access point may perform the authentication with the client when the authentication computer is unavailable. However, in other embodiments, the access point may perform the authentication with the client for a variety of reasons (such as loading of the authentication computer or an authorization latency or delay), even when the authentication computer is available. Thus, the type of EAP authentication may happens internally between the client and the access point. Note that the access point may generate or derive a PMK, and the access point may perform a four-way handshake with the client. In some embodiments, after the key hash has timed out, the access point may delete the key hash. 
     Note that in some embodiments, a master key (MK) may be used to generate a PMK. For example, the PMK may be generated using a pseudorandom function hash (such as a TLS pseudorandom function or TLS-PRF) based at least in part on: the master key, a type of EAP authentication, a client random number and/or an access point random number. The PMK may be used to generate a PTK using a second pseudorandom function hash (such as an EAPol-PRF) based at least in part on: the master key, an access point nonce, a client nonce, an access point MAC address and/or a client MAC address. Moreover, the PTK may be used to determine or generate: a key confirmation key (KCK), e.g., using PTK bits  0 - 127 ; a key encryption key (KEK), e.g., using PTK bits  128 - 255 ; and/or a temporal key, e.g., using PTK bits  256 -n (where n is a non-zero integer greater than 256). Note that the temporal key may have a cipher-suite specific structure. 
     As shown in  FIG.  3   , during the communication techniques, after the first successful IEEE 802.1x authentication, the authentication computer may pass a key hash with related authentication parameters and information specifying the type of EAP technique to the access point. The authentication parameters may be the ones from the client and may be used to generate the PMK. In some embodiments, the authentication parameters may include the hash timeout value. The access point may store or cache the key hash (which is sometimes referred to as a ‘hash key’) or function and the authentication parameters until the timeout has expired. 
     Subsequently, the client may disconnect and then may reconnect. After IEEE 802.11 association, the access point may start IEEE 802.1x authentication by sending an identity request to the client. Upon receiving an identity response, instead of initiating the EAP authentication with the authentication computer, the access point may uses the stored hash function to start the IEEE 802.1x EAP authentication with the client. This EAP authentication may happen internally between the client and the access point. During this process, the access point may derive a new PMK and may perform the four-way handshake with the client. After the key hash timeout, the access point can delete the key hash. Alternatively, before the timeout, the access point may trigger a renew request to refresh the stored information. Upon receiving the renew request, the authentication computer may generate a new key hash by using new authentication parameters and may include them in the response to the access point. 
     The hash key and the authentication parameters derivation techniques may be different depending on the authentication technique.  FIG.  4    presents a block diagram of an example of communication between authentication computer  130 , access point  116 - 1  and electronic device  110 - 1  for PEAP Microsoft Challenge Handshake Authentication Protocol version 2 (MS-CHAPv2) authentication, including EAP-MSCHAPv2, EAP-PEAP-MSCHAPv2 and/or EAP-TTLS-MSCHAPv2. In  FIG.  4   , authentication computer  130  generates a hash function (NT_password_hash) and access point  116 - 1  exchanges the challenges with electronic device  110 - 1  and calculates if the challenge_response is as expected. Notably, authentication server  130  may provide the NT_password_hash and a timeout. Note that NT_password_hash may be defined in RFC 2759 (from the Internet Engineering Task Force of Fremont, Calif.). Moreover, the peer_challenge and the server_challenge may be random numbers. A challenge_hash may be a secure hash algorithm 1 (SHA-1) cryptographic hash function of the peer challenge, the server challenge and a username of the user. Furthermore, the challenge_response may be a data encryption standard (des_encrypt) 56-bit symmetric encryption of the NT_password_hash and the challenge_hash. 
       FIG.  5    presents a block diagram of an example of communication between authentication computer  130 , access point  116 - 1  and electronic device  110 - 1  for a message digest algorithm hash function (such as MD5), including EAP-MD5 and/or EAP-PEAP-MD5. In  FIG.  5   , authentication computer  130  generates the key_hash and passes it along with an identifier and a challenge to access point  116 - 1 . Access point  116 - 1  may exchange the identifier and challenge with electronic device  110 - 1 , and may verify the response hash. Note that the key_hash may be an md5 hash of the identifier, the password, and the challenge. In some embodiments, the identifier may be a username of the user. 
     In other embodiments, EAP-EKE or EAP-LEAP may be used. For example, in EAP-EKE, a hash function may be derived using a pseudorandom function hash of a password of the user. Consequently, authentication server  130  may only need to send this pseudorandom function hash of the password to access point  116 - 1 . Then, access point  116 - 1  may perform the authentication with electronic device  110 - 1 . Moreover, in EAP-LEAP, authentication computer  130  may first generate an NT_password_hash first and provide it to access point  116 - 1 . 
     While the preceding discussion illustrated the communication techniques with a variety of authentication techniques, in other embodiments the communication techniques may be extended for use with additional authentication techniques. For example, the communication techniques may be extended to be compatible with some types of EAP techniques (such as EAP-TTLS-Challenge Handshake Authentication Protocol or CHAP and EAP-generalized Pre-Shared Key or GPSK) that exchange parameters with the client to generate its hash key. Alternatively, the communication techniques may be extended to be compatible with other types of EAP techniques (such as EAP-TTLS-Password Authentication Protocol or PAP and EAP-Generic Token Card or GTC) that verify a password without a hash derivation. In these embodiments, the authentication computer may provide the necessary information to the access point needed to support any of these authentication techniques, thereby offloading the authentication to the access point. 
     We now describe embodiments of an electronic device, which may perform at least some of the operations in the communication techniques.  FIG.  6    presents a block diagram illustrating an example of an electronic device  600  in accordance with some embodiments, such as one of: base station  108 , one of electronic devices  110 , computer  112 , one of access points  116 , one of radio nodes  118 , switch  128 , or authentication computer  130 . This electronic device includes processing subsystem  610 , memory subsystem  612 , and networking subsystem  614 . Processing subsystem  610  includes one or more devices configured to perform computational operations. For example, processing subsystem  610  can include one or more microprocessors, graphics processing units (GPUs), ASICs, microcontrollers, programmable-logic devices, and/or one or more digital signal processors (DSPs). 
     Memory subsystem  612  includes one or more devices for storing data and/or instructions for processing subsystem  610  and networking subsystem  614 . For example, memory subsystem  612  can include DRAM, static random access memory (SRAM), and/or other types of memory. In some embodiments, instructions for processing subsystem  610  in memory subsystem  612  include: one or more program modules or sets of instructions (such as program instructions  622  or operating system  624 , such as Linux, UNIX, Windows Server, or another customized and proprietary operating system), which may be executed by processing subsystem  610 . Note that the one or more computer programs, program modules or instructions may constitute a computer-program mechanism. Moreover, instructions in the various modules in memory subsystem  612  may be implemented in: a high-level procedural language, an object-oriented programming language, and/or in an assembly or machine language. Furthermore, the programming language may be compiled or interpreted, e.g., configurable or configured (which may be used interchangeably in this discussion), to be executed by processing subsystem  610 . 
     In addition, memory subsystem  612  can include mechanisms for controlling access to the memory. In some embodiments, memory subsystem  612  includes a memory hierarchy that comprises one or more caches coupled to a memory in electronic device  600 . In some of these embodiments, one or more of the caches is located in processing subsystem  610 . 
     In some embodiments, memory subsystem  612  is coupled to one or more high-capacity mass-storage devices (not shown). For example, memory subsystem  612  can be coupled to a magnetic or optical drive, a solid-state drive, or another type of mass-storage device. In these embodiments, memory subsystem  612  can be used by electronic device  600  as fast-access storage for often-used data, while the mass-storage device is used to store less frequently used data. 
     Networking subsystem  614  includes one or more devices configured to couple to and communicate on a wired and/or wireless network (i.e., to perform network operations), including: control logic  616 , an interface circuit  618  and one or more antennas  620  (or antenna elements). (While  FIG.  6    includes one or more antennas  620 , in some embodiments electronic device  600  includes one or more nodes, such as antenna nodes  608 , e.g., a metal pad or a connector, which can be coupled to the one or more antennas  620 , or nodes  606 , which can be coupled to a wired or optical connection or link. Thus, electronic device  600  may or may not include the one or more antennas  620 . Note that the one or more nodes  606  and/or antenna nodes  608  may constitute input(s) to and/or output(s) from electronic device  600 .) For example, networking subsystem  614  can include a Bluetooth™ networking system, a cellular networking system (e.g., a 3G/4G/5G network such as UMTS, LTE, etc.), a universal serial bus (USB) networking system, a coaxial interface, a High-Definition Multimedia Interface (HDMI) interface, a networking system based on the standards described in IEEE 802.11 (e.g., a Wi-Fi® networking system), an Ethernet networking system, and/or another networking system. 
     Note that a transmit or receive antenna pattern (or antenna radiation pattern) of electronic device  600  may be adapted or changed using pattern shapers (such as directors or reflectors) and/or one or more antennas  620  (or antenna elements), which can be independently and selectively electrically coupled to ground to steer the transmit antenna pattern in different directions. Thus, if one or more antennas  620  include N antenna pattern shapers, the one or more antennas may have 2 N  different antenna pattern configurations. More generally, a given antenna pattern may include amplitudes and/or phases of signals that specify a direction of the main or primary lobe of the given antenna pattern, as well as so-called ‘exclusion regions’ or ‘exclusion zones’ (which are sometimes referred to as ‘notches’ or ‘nulls’). Note that an exclusion zone of the given antenna pattern includes a low-intensity region of the given antenna pattern. While the intensity is not necessarily zero in the exclusion zone, it may be below a threshold, such as 3 dB or lower than the peak gain of the given antenna pattern. Thus, the given antenna pattern may include a local maximum (e.g., a primary beam) that directs gain in the direction of electronic device  600  that is of interest, and one or more local minima that reduce gain in the direction of other electronic devices that are not of interest. In this way, the given antenna pattern may be selected so that communication that is undesirable (such as with the other electronic devices) is avoided to reduce or eliminate adverse effects, such as interference or crosstalk. 
     Networking subsystem  614  includes processors, controllers, radios/antennas, sockets/plugs, and/or other devices used for coupling to, communicating on, and handling data and events for each supported networking system. Note that mechanisms used for coupling to, communicating on, and handling data and events on the network for each network system are sometimes collectively referred to as a ‘network interface’ for the network system. Moreover, in some embodiments a ‘network’ or a ‘connection’ between the electronic devices does not yet exist. Therefore, electronic device  600  may use the mechanisms in networking subsystem  614  for performing simple wireless communication between the electronic devices, e.g., transmitting advertising or beacon frames and/or scanning for advertising frames transmitted by other electronic devices as described previously. 
     Within electronic device  600 , processing subsystem  610 , memory subsystem  612 , and networking subsystem  614  are coupled together using bus  628 . Bus  628  may include an electrical, optical, and/or electro-optical connection that the subsystems can use to communicate commands and data among one another. Although only one bus  628  is shown for clarity, different embodiments can include a different number or configuration of electrical, optical, and/or electro-optical connections among the subsystems. 
     In some embodiments, electronic device  600  includes a display subsystem  626  for displaying information on a display, which may include a display driver and the display, such as a liquid-crystal display, a multi-touch touchscreen, etc. 
     Moreover, electronic device  600  may include a user-interface subsystem  630 , such as: a mouse, a keyboard, a trackpad, a stylus, a voice-recognition interface, and/or another human-machine interface. In some embodiments, user-interface subsystem  630  may include or may interact with a touch-sensitive display in display subsystem  626 . 
     Electronic device  600  can be (or can be included in) any electronic device with at least one network interface. For example, electronic device  600  can be (or can be included in): a desktop computer, a laptop computer, a subnotebook/netbook, a server, a tablet computer, a cloud-based computing system, a smartphone, a cellular telephone, a smartwatch, a wearable electronic device, a consumer-electronic device, a portable computing device, an access point, a transceiver, a router, a switch, communication equipment, an eNodeB, a controller, test equipment, and/or another electronic device. 
     Although specific components are used to describe electronic device  600 , in alternative embodiments, different components and/or subsystems may be present in electronic device  600 . For example, electronic device  600  may include one or more additional processing subsystems, memory subsystems, networking subsystems, and/or display subsystems. Additionally, one or more of the subsystems may not be present in electronic device  600 . Moreover, in some embodiments, electronic device  600  may include one or more additional subsystems that are not shown in  FIG.  6   . Also, although separate subsystems are shown in  FIG.  6   , in some embodiments some or all of a given subsystem or component can be integrated into one or more of the other subsystems or component(s) in electronic device  600 . For example, in some embodiments instructions  622  is included in operating system  624  and/or control logic  616  is included in interface circuit  618 . 
     Moreover, the circuits and components in electronic device  600  may be implemented using any combination of analog and/or digital circuitry, including: bipolar, PMOS and/or NMOS gates or transistors. Furthermore, signals in these embodiments may include digital signals that have approximately discrete values and/or analog signals that have continuous values. Additionally, components and circuits may be single-ended or differential, and power supplies may be unipolar or bipolar. 
     An integrated circuit (which is sometimes referred to as a ‘communication circuit’) may implement some or all of the functionality of networking subsystem  614  and/or of electronic device  600 . The integrated circuit may include hardware and/or software mechanisms that are used for transmitting wireless signals from electronic device  600  and receiving signals at electronic device  600  from other electronic devices. Aside from the mechanisms herein described, radios are generally known in the art and hence are not described in detail. In general, networking subsystem  614  and/or the integrated circuit can include any number of radios. Note that the radios in multiple-radio embodiments function in a similar way to the described single-radio embodiments. 
     In some embodiments, networking subsystem  614  and/or the integrated circuit include a configuration mechanism (such as one or more hardware and/or software mechanisms) that configures the radio(s) to transmit and/or receive on a given communication channel (e.g., a given carrier frequency). For example, in some embodiments, the configuration mechanism can be used to switch the radio from monitoring and/or transmitting on a given communication channel to monitoring and/or transmitting on a different communication channel. (Note that ‘monitoring’ as used herein comprises receiving signals from other electronic devices and possibly performing one or more processing operations on the received signals). 
     In some embodiments, an output of a process for designing the integrated circuit, or a portion of the integrated circuit, which includes one or more of the circuits described herein may be a computer-readable medium such as, for example, a magnetic tape or an optical or magnetic disk. The computer-readable medium may be encoded with data structures or other information describing circuitry that may be physically instantiated as the integrated circuit or the portion of the integrated circuit. Although various formats may be used for such encoding, these data structures are commonly written in: Caltech Intermediate Format (CIF), Calma GDS II Stream Format (GDSII) or Electronic Design 
     Interchange Format (EDIF), OpenAccess (OA), or Open Artwork System Interchange Standard (OASIS). Those of skill in the art of integrated circuit design can develop such data structures from schematics of the type detailed above and the corresponding descriptions and encode the data structures on the computer-readable medium. Those of skill in the art of integrated circuit fabrication can use such encoded data to fabricate integrated circuits that include one or more of the circuits described herein. 
     While the preceding discussion used Wi-Fi, LTE and/or Ethernet communication protocols as illustrative examples, in other embodiments a wide variety of communication protocols and, more generally, communication techniques may be used. Thus, the communication techniques may be used in a variety of network interfaces. Furthermore, while some of the operations in the preceding embodiments were implemented in hardware or software, in general the operations in the preceding embodiments can be implemented in a wide variety of configurations and architectures. Therefore, some or all of the operations in the preceding embodiments may be performed in hardware, in software or both. For example, at least some of the operations in the communication techniques may be implemented using program instructions  622 , operating system  624  (such as a driver for interface circuit  618 ) or in firmware in interface circuit  618 . Alternatively or additionally, at least some of the operations in the communication techniques may be implemented in a physical layer, such as hardware in interface circuit  618 . 
     Note that the use of the phrases ‘capable of,’ ‘capable to,’ ‘operable to,’ or ‘configured to’ in one or more embodiments, refers to some apparatus, logic, hardware, and/or element designed in such a way to enable use of the apparatus, logic, hardware, and/or element in a specified manner. 
     While examples of numerical values are provided in the preceding discussion, in other embodiments different numerical values are used. Consequently, the numerical values provided are not intended to be limiting. 
     In the preceding description, we refer to ‘some embodiments.’ Note that ‘some embodiments’ describes a subset of all of the possible embodiments, but does not always specify the same subset of embodiments. 
     The foregoing description is intended to enable any person skilled in the art to make and use the disclosure, and is provided in the context of a particular application and its requirements. Moreover, the foregoing descriptions of embodiments of the present disclosure have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present disclosure to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Additionally, the discussion of the preceding embodiments is not intended to limit the present disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.