Patent Description:
As used herein, the terms "user agent" and "UA" might in some cases refer to mobile devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices that have telecommunications capabilities. Such a UA might be part of a UE (User Equipment). A UE may have multiple UAs. A UE may have removable memory module associated, such as but not limited to a Universal Integrated Circuit Card (UICC) that includes a Subscriber Identity Module (SIM) application, a Universal Subscriber Identity Module (USIM) application, a IP Multimedia Services Identity Module (ISIM) application, or a Removable User Identity Module (R-UIM) application, etc. Examples of such modules could include, but are not limited to, PC Card, CompactFlash I, CompactFlash II, SmartMedia, Memory Stick, Memory Stick Duo, Memory Stick PRO Duo, Memory Stick PRO-HG Duo, Memory Stick Micro M2, Multimedia Card, Reduced Size Multimedia Card, MMCmicro Card, Secure Digital card, SxS, Universal Flash Storage, miniSD card, microSD card, xD-Picture Card, Intelligent Stick, Serial Flash Module, µ card, and NT Card. When the information is stored on a removable memory module, the contents of the module may be imaged into the UE.

Alternatively, such a UA might consist of the device itself without such a module. In other cases, the term "UA" might refer to devices that have similar capabilities but that are not transportable, such as fixed line telephones, desktop computers, set-top boxes, or network nodes. When one or more UAs are part of a network node, the network node could act on behalf of another function such as a UA or a fixed line device and simulate or emulate the UA or fixed line device. For example, for some UAs, the IMS SIP client that would typically reside on the device actually resides in the network and relays SIP message information to the device using optimized protocols. In other words, some functions that were traditionally carried out by a UA can be distributed in the form of a remote UA, where the remote UA represents the UA in the network. The term "UA" can also refer to any hardware or software component that can terminate a communication session that could include, but is not limited to, a SIP session. Also, the terms "user agent", "UA", "user equipment", "UE", and "node" might be used synonymously herein. Also, the terms "header" and "header field" might be used synonymously herein. Also, a SIP message is SIP request or a SIP response.

A UA might connect to a SIP-based network that includes a plurality of other components such as a P-CSCF (Proxy Call Session Control Function), an S-CSCF (Serving CSCF), an IBCF (Interconnect Border Control Function), an Application Server (AS), and other components, any of which could be referred to as network nodes. A trust relationship might exist between nodes in a SIP network. That is, a group of nodes within a network might regard all messages received from other nodes in the group as legitimate. Such a group can be said to form a trust domain or one or more trusted networks. IETF RFC <NUM> titled "Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Networks" discusses this subject further.

It should be understood at the outset that although illustrative implementations of one or more embodiments of the present disclosure are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence.

A node within a trust domain in an IMS network might receive a message from a node outside the trust domain. In some cases, such a message might direct the node in the trust domain to perform one or more actions that may not be desirable for that node to perform. For example, a message may maliciously be sent to a plurality of UAs falsely informing the UAs that a server timeout has occurred. A UA receiving such a message might attempt to re-register with a SIP registrar even though re-registration is not actually necessary. If a large number of the UAs attempt to re-register, the registrar might become overloaded and fail. This could lead to major problems in the network since other UAs might then be unable to register.

In an embodiment, a message sent to a network node from outside the network node's trust domain can include a trust indicator that indicates the trustworthiness of the message. A trust indicator can also be a trust token, trust identifier or trust flag. Trust indicators can be one of two types. The presence of one type of trust indicator in a message indicates that the network node that sent the message can be trusted. The recipient of a message containing such a trust indicator need not perform any verification of the trust indicator. When the other type of trust indicator is present in a message, the recipient of the message compares the trust indicator with internally stored trust information/database. If the trust indicator matches the stored trust information, the trust indicator is verified, and the recipient/receiver knows that the network node that sent the message can be trusted.

If the first type of trust indicator is present in a message or if the second type is present and is verified, the network node that receives the message performs the actions that are typically associated with receipt of the message or the message and its contents. If no trust indicator is present or if the trust indicator is not verified, the network node that receives the message might not perform one or more of the actions that are typically associated with receipt of the message or the message and its contents.

In an embodiment, the network node that receives the message is a UA that maintains trust information related to network nodes outside the UA's trust domain. Upon receiving a message from outside its trust domain, the UA can compare the trust indicator that might be included with the message with the trust information that the UA maintains. If the UA verifies that the trust indicator matches the trust information that it maintains, the UA performs the actions that are typically associated with receipt of the message or the message and its contents. If the UA cannot verify that the trust indicator matches the trust information that it maintains, the UA does not perform at least one action that is typically associated with receipt of the message or the message and its contents.

These embodiments are illustrated in <FIG>, where a UA <NUM> is capable of communicating with a network node B <NUM>, which is capable of communicating with a network node A <NUM>. The UA <NUM>, network node A <NUM>, and network node B <NUM> might be components in an IMS-based network, and network node A <NUM> and network node B <NUM> might be outside the UA's trust domain. While only two other network nodes are shown, other numbers could be present. In this embodiment, network node A <NUM> generates a message A <NUM> and includes a trust indicator A <NUM> in the message A <NUM>. Network node <NUM> then sends the message A <NUM> to network node B <NUM>. Receipt of message A <NUM> causes network node B <NUM> to generate a message B <NUM> containing a trust indicator B <NUM>, and message B <NUM> is then sent to the UA <NUM>. Message A <NUM> may or may not be the same as message B <NUM>, and trust indicator A <NUM> may or may not be the same as trust indicator B <NUM>. In other words, network node B <NUM> might simply pass on the trust indicator A <NUM> that is received from network node A <NUM>, or network node B <NUM> might generate a new trust indicator B <NUM> based on the trust indicator A <NUM> or other information received from the network node A <NUM> and/or other network nodes.

In other embodiments, network node A <NUM> does not include the trust indicator A <NUM> in the message A <NUM>. Instead, network node B <NUM> generates the trust indicator B <NUM> without regard to any information included in message A <NUM>, and network node B <NUM> then includes trust indicator B <NUM> in the message B <NUM> sent to the UA <NUM>. In other words, the trust indicator that the UA <NUM> receives might have been generated by the network node with which the UA <NUM> is in direct communication, might have been generated by another network node and then passed on without modification by the network node which the UA <NUM> is in direct communication, or might have been generated by another network node and then passed on with modification by the network node which the UA <NUM> is in direct communication.

In some embodiments, upon receiving a message that contains a trust indicator, the UA <NUM> performs the actions that are typically associated with receipt of the message. In other embodiments, upon receiving a message that contains a trust indicator, the UA <NUM> compares the trust indicator to trust information <NUM> that the UA <NUM> has previously received and stored. When a match is found between the trust indicator in the message and the stored trust information <NUM>, the UA <NUM> performs the actions that are typically associated with receipt of the message. When a match is not found between the trust indicator and the stored trust information <NUM>, the UA <NUM> does not perform at least one action that is typically associated with receipt of the message.

In an embodiment, the trust indicator and/or the trust information <NUM> might be a Uniform Resource Identifier (URI), or some other type of identifier, of a trusted network node. A network node might include its URI in a message sent to the UA <NUM>. The UA <NUM> might have previously received trust information <NUM> in the form of a list of trusted URIs. Upon receiving a message with a trust indicator in the form of a URI, the UA <NUM> might compare the URI in the message with the URIs in the list of URIs. If a match is found, the UA <NUM> might trust the network node that sent the message.

The UA <NUM> might not be capable of identifying whether a URI belongs to a P-CSCF, an S-SCSF, an IBCF, or some other type of network node. Some network nodes (such as an IBCF) may or may not include their URI information. Hence, the UA may not be sure which URI represents which network node. In order to determine this, some conventions might be followed or an additional indicator may be added. A SIP REGISTER request and its response (and the header field values included in the response or request) typically should not leave the trusted domain. A third party REGISTER request triggered by the original REGISTER request may leave the trusted domain. In an embodiment, measures are set up to prevent contamination of the information in the responses to the REGISTER in such a case. For example, the fact that a URI represents a known network node could be indicated by a URI parameter to a SIP message. For instance, for an S-CSCF, the URI parameter scscf could be added. Alternatively, a URI parameter such as "fe" could be set to a value or a list of values such as fe ="scscf" or fe-'pcscf,scscf". Here, a network node is referred to as a functional element, or "fe". When the SIP Service-Route header is used, the message might take a form such as the following:
Service-Route: sip:orig@scscf1. com;Ir;scscf
or
Service-Route: sip:orig@pcscf1. com;Ir;fe="pcscf,scscf'
in deployments where the P-CSCF and S-CSCF (and possibly other) functional elements are collocated on one physical equipment.

As an alternative, after receiving trust information <NUM> in the form of a list of URIs, the UA <NUM> could query a database or other data repository to determine the network nodes and/or trust indicator and/or the trust information that correspond to the listed URIs. The database could be a network node in the network or a database on the device stored in memory that is either internal or in a removable memory module.

In another embodiment, the SIP Config Framework, the SIP Policy Framework, an EAP based policy retrieval mechanism, an XCAP/HTTP based server, or an Open Mobile Alliance (OMA) device management (DM) object could be used to convey trust indicators and/or the trust information and/or the network nodes that correspond to the listed URIs to the UA <NUM>.

The UA <NUM> might receive the trust information <NUM> in one or more of several different ways. In some embodiments, the trust information <NUM> might be provided to the UA <NUM> in response to a SIP REGISTER request submitted by the UA <NUM>. In some variations of these embodiments, the response might be a SIP <NUM> OK response, and the trust information <NUM> might be included directly in the <NUM> OK response. The trust information <NUM> could be included in the <NUM> OK response by a network node, such as an application server, that received the REGISTER request because the request was routed through it. Alternatively, the application server might have received a third party registration request as configured by initial Filter Criteria on an S-CSCF.

In other variations of these embodiments, the <NUM> OK response that the UA <NUM> receives in response to a REGISTER request might contain information that informs the UA <NUM> how the trust information <NUM> can be obtained. Such an embodiment is illustrated in <FIG>. At event <NUM>, the UA <NUM> registers with an IMS network by sending a REGISTER request to network node B <NUM>, which might be an S-CSCF. As part of the registration procedure <NUM>, a home subscriber server (HSS) <NUM>, or a similar component, might download to network node B <NUM> the trust information <NUM> that is to be used by the UA <NUM>. At event <NUM>, the registration is complete, and network node B <NUM> sends the UA <NUM> a <NUM> OK response. In the embodiment of <FIG>, the <NUM> OK response might contain a URI, or some other type of identifier, that identifies a location where the trust information <NUM> can be obtained. In other embodiments, as mentioned above, the <NUM> OK response might directly include the trust information <NUM>.

Alternatively, as shown at event <NUM>, as part of the SIP registration, the UA <NUM> might subscribe to the SIP Reg Event package, which can deliver information back to the UA <NUM>. In response to the Subscribe message at event <NUM>, network node B <NUM>, at event <NUM>, might return a message such as a Notify message. The Notify message might contain the location of the trust information <NUM> that was downloaded from the HSS <NUM> as described above.

When the UA <NUM> has received the location of the trust information <NUM>, either via the <NUM> OK message at event <NUM>, via the Notify message at event <NUM>, or via another SIP method, the UA <NUM> can retrieve the trust information <NUM> from the specified location. In this case, the specified location is network node A <NUM>, but in other cases, the trust information <NUM> could be retrieved from other network nodes. At event <NUM>, the UA <NUM> sends a message, such as an HTTP GET message, to retrieve the trust information <NUM> from network node A <NUM>. At event <NUM>, network node A <NUM> sends the trust information <NUM> to the UA <NUM>. The UA <NUM> can then store the trust information <NUM> in internal or removable memory, where the trust information <NUM> will be available for future use by the UA <NUM> in determining whether a network node is trusted.

In an alternative embodiment, the trust information <NUM> might be provided during the registration of the UA <NUM> in one or more fields in the SIP Path header or the SIP Service-Route header. For example, a SIP REGISTER request originated by the UA <NUM> might be routed through at least a P-CSCF and an S-CSCF, where the S-CSCF performs the role of REGISTRAR. The response (such as a <NUM> OK response) that the UA <NUM> receives to its REGISTER request might include an indicator (such as a new P-header, an existing header, or embedded XML) conveying information about the network nodes (such as a P-CSCF and an S-SCSF) on the path the REGISTER request was routed over. In addition, one or more fields in the SIP Service-Route header might contain at least the addresses of the P-CSCF or S-CSCF that actually perform any services. The address of the S-CSCF on the Service-Route header field and the S-CSCF on the Path header field are not necessarily the same.

In some cases, an S-CSCF acting as a REGISTRAR may not be the S-CSCF that replies to other requests from the UA <NUM>. More generally, not all network nodes that are capable of transmitting a trusted message may be included on the path over which the REGISTER request or its response is routed. However, if a network node transmits a trusted message, it may be advantageous to populate a header field (such as a SIP P-Asserted-Identity header field) or a URI parameter or a SIP body part with a value representative of the originator. Several means exist to enable the UA <NUM> to determine that some value representative of the originator could only be known or only be inserted by the originator. For example, a value in the P-Asserted-Identity header field could be compared against a value on the Service-Route header field.

When a trust indicator is not present in a message received by the UA <NUM> from a network node outside the UA's trust domain, or when a trust indicator is present but does not match the UA's stored trust information <NUM>, the UA <NUM> could react in several different ways. In some cases the UA <NUM> might deny, discard, or terminate the message. In other cases, the UA <NUM> might return an error message to the network node that sent the message. In still other cases, the UA <NUM> might remove portions of the message that might cause undesirable actions to be taken and might process the remainder of the message. In some cases, various combinations of these actions could be taken.

<FIG> illustrates an embodiment of a method <NUM> for determining if a node outside a trust domain in an IMS network can be trusted. At block <NUM>, a UA receives from the network node a message containing a trust indicator. At block <NUM>, the UA determines whether the trust indicator matches trust information stored in the UA. At block <NUM>, when the trust indicator matches trust information stored in the UA, the UA performs all actions typically associated with receipt of the message. At block <NUM>, when the trust indicator does not match trust information stored in UA, the UA refrains from performing at least one action typically associated with receipt of the message.

<FIG> illustrates an alternative embodiment of a method <NUM> for determining if a node outside a trust domain in an IMS network can be trusted. At block <NUM>, a UA receives a message from the network node. At block <NUM>, the UA determines whether a trust indicator is present in message. At block <NUM>, when the trust indicator is present in the message, the UA performs all actions typically associated with receipt of the message. At block <NUM>, when the trust indicator is not present in the message, the UA refrains from performing at least one action typically associated with receipt of the message.

Returning to the example mentioned above where a message is maliciously sent to a plurality of UAs falsely informing the UAs that a server timeout has occurred, the embodiments described herein might prevent the UAs from unnecessarily attempting to re-register with the network. When one of the UAs receives the malicious message, the UA might use a technique described herein to determine whether the sender of the message can be trusted. Since, in this case, the sender would not be trusted, the UA would not perform one or more actions typically associated with receipt of the message. In this case, the UA would not re-register.

One possible reflection for the UE could be as follows in <NPL>":
In the event the UE receives a <NUM> (Server Time-out) response containing:.

One possible reflection for the P-CSCF could be as follows in<NPL>":
When the P-CSCF is unable to forward an initial request for a dialog or a request for a standalone transaction to the next hop in the Service-Route header, as determined by one of the following:.

NOTE: These procedures do not prevent the usage of unspecified reliability or recovery techniques above and beyond those specified in this subclause.

One possible reflection for the S-CSCF could be as follows in <NPL>":
When the S-CSCF receives a request initiated by the served user for which the S-CSCF does not have the user profile or does not trust the data that it has (e.g. due to restart), the S-CSCF shall attempt to retrieve the user profile from the HSS. If the S-CSCF fails to retrieve the user profile and the S-CSCF supports restoration procedures, then the S-CSCF shall:.

In addition, the following modifications might be made to <NPL>":
NOTE <NUM>: THIG functionality is performed in LCSCF in Release-<NUM> and Release-<NUM> and is compatible with the procedures specified in this subclause.

The following procedures shall only be applied if network topology hiding is required by the network. The network requiring network topology hiding is called the hiding network. NOTE <NUM>: Requests and responses are handled independently therefore no state information is needed for that purpose within an IBCF.

The IBCF shall apply network topology hiding to all header fields which reveal topology information, such as Via, Route, Record-Route, Service-Route, and Path.

Upon receiving an incoming REGISTER request for which network topology hiding has to be applied and which includes a Path header field, the IBCF shall add the routable SIP URI of the IBCF to the top of the Path header field. The IBCF may include in the inserted SIP URI an indicator that identifies the direction of subsequent requests received by the IBCF i.e., from the S-CSCF towards the P-CSCF, to identify the UE-terminating case. The IBCF may encode this indicator in different ways, such as, e.g., a unique parameter in the URI, a character string in the username part of the URI, or a dedicated port number in the URI. NOTE <NUM>: Any subsequent request that includes the direction indicator (in the Route, header field) or arrives at the dedicated port number, indicates that the request was sent by the S-CSCF towards the P-CSCF.

Upon receiving an incoming initial request for which network topology hiding has to be applied a SIP request or SIP response with a P-Asserted-Identity header field set the SIP URI of a functional element within its trust domain, the IBCF shall apply network topology hiding to the P-Asserted-Identity header field.

Upon receiving an incoming initial request for which network topology hiding has to be applied and which includes a Record-Route header field, the IBCF shall add its own routable SIP URI to the top of the Record-Route header field.

The UE may receive a different value than the value stored by the network node as the IBCF may perform location hiding and replace the URIs in the SIP message (such as the Path or Service-Route header fields) with, for example, at least one of the values of the SIP URI of the IBCF. The IBCF would have to consistently perform this location hiding or replacing of URIs in order not to break the trust that is indicated.

When the SIP UA receives a SIP message, it will analyze a table within the function to see if any actions need to be performed for that SIP message, e.g., an INVITE request. The table or data structure identifies the indicators. These indicators could be, but are not limited to, SIP header fields, SIP specific values to look for, etc. For each field, there might also be an action or group of actions that could be performed but are not limited to:.

For the latter two items, "Trust mess" and "Trustnomess", all items in the SIP method have to be trusted. The method for identifying the message as trusted could be conveyed as:.

An example embodiment of the data structure is below.

The UA <NUM> and other components described above might include a processing component that is capable of executing instructions related to the actions described above. <FIG> illustrates an example of a system <NUM> that includes a processing component <NUM> suitable for implementing one or more embodiments disclosed herein. In addition to the processor <NUM> (which may be referred to as a central processor unit or CPU), the system <NUM> might include network connectivity devices <NUM>, random access memory (RAM) <NUM>, read only memory (ROM) <NUM>, secondary storage <NUM>, and input/output (I/O) devices <NUM>. These components might communicate with one another via a bus <NUM>. In some cases, some of these components may not be present or may be combined in various combinations with one another or with other components not shown. These components might be located in a single physical entity or in more than one physical entity. Any actions described herein as being taken by the processor <NUM> might be taken by the processor <NUM> alone or by the processor <NUM> in conjunction with one or more components shown or not shown in the drawing, such as a digital signal processor (DSP) <NUM>. Although the DSP <NUM> is shown as a separate component, the DSP <NUM> might be incorporated into the processor <NUM>.

The processor <NUM> executes instructions, codes, computer programs, or scripts that it might access from the network connectivity devices <NUM>, RAM <NUM>, ROM <NUM>, or secondary storage <NUM> (which might include various disk-based systems such as hard disk, floppy disk, or optical disk). While only one CPU <NUM> is shown, multiple processors may be present. Thus, while instructions may be discussed as being executed by a processor, the instructions may be executed simultaneously, serially, or otherwise by one or multiple processors. The processor <NUM> may be implemented as one or more CPU chips.

The network connectivity devices <NUM> may take the form of modems, modem banks, Ethernet devices, universal serial bus (USB) interface devices, serial interfaces, token ring devices, fiber distributed data interface (FDDI) devices, wireless local area network (WLAN) devices, radio transceiver devices such as code division multiple access (CDMA) devices, global system for mobile communications (GSM) radio transceiver devices, worldwide interoperability for microwave access (WiMAX) devices, and/or other well-known devices for connecting to networks. These network connectivity devices <NUM> may enable the processor <NUM> to communicate with the Internet or one or more telecommunications networks or other networks from which the processor <NUM> might receive information or to which the processor <NUM> might output information. The network connectivity devices <NUM> might also include one or more transceiver components <NUM> capable of transmitting and/or receiving data wirelessly.

The RAM <NUM> might be used to store volatile data and perhaps to store instructions that are executed by the processor <NUM>. The ROM <NUM> is a non-volatile memory device that typically has a smaller memory capacity than the memory capacity of the secondary storage <NUM>. ROM <NUM> might be used to store instructions and perhaps data that are read during execution of the instructions. Access to both RAM <NUM> and ROM <NUM> is typically faster than to secondary storage <NUM>. The secondary storage <NUM> is typically comprised of one or more disk drives or tape drives and might be used for non-volatile storage of data or as an over-flow data storage device if RAM <NUM> is not large enough to hold all working data. Secondary storage <NUM> may be used to store programs that are loaded into RAM <NUM> when such programs are selected for execution.

The I/O devices <NUM> may include liquid crystal displays (LCDs), touch screen displays, keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, printers, video monitors, or other well-known input or output devices. Also, the transceiver <NUM> might be considered to be a component of the I/O devices <NUM> instead of or in addition to being a component of the network connectivity devices <NUM>.

In an embodiment, a method is provided for determining if a node outside a trust domain in an IMS network can be trusted. The method includes a UA receiving from the network node a message that contains a trust indicator. The method further includes the UA determining whether the trust indicator matches trust information stored in the UA. The method further includes, when the trust indicator matches trust information stored in the UA, the UA performing all actions typically associated with receipt of the message. The method further includes, when the trust indicator does not match trust information stored in the UA, the UA refraining from performing at least one action typically associated with receipt of the message.

In another embodiment, a UA is provided. The UA includes a processor configured to receive from a node outside a trust domain in an IMS network a message containing a trust indicator. The processor is further configured to determine whether the trust indicator matches trust information stored in the UA. The processor is further configured, when the trust indicator matches trust information stored in the UA, to perform all actions typically associated with receipt of the message. The processor is further configured, when the trust indicator does not match trust information stored in the UA, to refrain from performing at least one action typically associated with receipt of the message.

In another embodiment, an alternative method is provided for determining if a node outside a trust domain in an IMS network can be trusted. The method includes a UA receiving a message from the network node. The method further includes the UA determining whether a trust indicator is present in the message. The method further includes, when the trust indicator is present in the message, the UA performing all actions typically associated with receipt of the message. The method further includes, when the trust indicator is not present in the message, the UA refraining from performing at least one action typically associated with receipt of the message.

In another embodiment, a UA is provided. The UA includes a processor configured to receive a message from a node outside a trust domain in an IMS network. The processor is further configured to determine whether a trust indicator is present in the message. The processor is further configured, when the trust indicator is present in the message, to perform all actions typically associated with receipt of the message. The processor is further configured, when the trust indicator is not present in the message, to refrain from performing at least one action typically associated with receipt of the message.

In another embodiment, a method is provided for performing registration. The method includes receiving a server timeout message, the server timeout message including at least a first field set to a value equal to a value received in a second field during a first registration. The method further includes initiating restoration procedures by performing a second registration in response to receiving the server timeout message.

In another embodiment, a UA is provided. The UA includes one or more processors configured such that the UA receives a server timeout message that includes at least a first field set to a value equal to a value received in a second field during a first registration, and configured such that the UA initiates restoration procedures by performing a second registration in response to receiving the server timeout message.

The following 3rd Generation Partnership Project (3GPP) Technical Specification (TS) is incorporated herein by reference: TS <NUM>.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

Claim 1:
A method in a user agent, UA, (<NUM>), the method comprising:
sending a Session Initiation Protocol, SIP, register request; and
receiving (<NUM>) a SIP response to the SIP register request, the SIP response indicating a server timeout and including a trust indicator (<NUM>) consisting of a Uniform Resource identifier, URI, the URI including a parameter "fe", wherein one of a plurality of types of network nodes is assigned to the parameter "fe";
determining whether the trust indicator is present in the SIP response;
when the trust indicator is not present in the message, refraining from attempting to re-register.