Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L63/00—Network architectures or network communication protocols for network security
  • H04L63/04—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks
  • H04L63/0428—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks wherein the data content is protected, e.g. by encrypting or encapsulating the payload
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W12/00—Security arrangements; Authentication; Protecting privacy or anonymity
  • H04W12/03—Protecting confidentiality, e.g. by encryption
  • H04W12/033—Protecting confidentiality, e.g. by encryption of the user plane, e.g. user's traffic
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W56/00—Synchronisation arrangements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W76/00—Connection management
  • H04W76/10—Connection setup

Definitions

• the invention relates to a method for synchronizing in a mobile communication system a counter in a mobile station with a counter in a network element of a mobile communication network, wherein the respective value of the counters is employed as a parameter for ciphering and deciphering data transmitted between the mobile station and the network element.
• the invention relates equally to a corresponding mobile station and to a corresponding network element .
• GERAN GSM (Global System for Mobile communications)
• EDGE Enhanced Data Rates for GSM evolution
• Radio Access Network Iu mode
• ciphering is performed in RRC-Connected mode using the Kasumi f8 algorithm.
• GERAN Iu mode is a mode of operation of the mobile station when connected to the Core Network via GERAN and the Iu interface
• the Iu interface that comprises Iu-cs and Iu-ps interfaces
• the Iu interface that comprises Iu-cs and Iu-ps interfaces
• the Iu interface that comprises Iu-cs and Iu-ps interfaces
• the Iu interface that comprises Iu-cs and Iu-ps interfaces
• the Iu interface that comprises Iu-cs and Iu-ps interfaces
• the Iu interface that comprises Iu-cs and Iu-ps interfaces
• the Iu interface that comprises Iu-cs and Iu-ps interfaces
• the Iu interface that comprises Iu-cs and
• RRC Radio Resource Control plane protocol for radio resource management that is used when a mobile station is operating in Iu mode.
• RRC-Connected mode the mobile station has an established RRC connection, which is a point-to-point bi-directional connection between RRC peer entities in the mobile station and the GERAN.
• the Kasumi f8 algorithm is a 3GPP (3rd Generation Partnership Project) Confidentiality Algorithm described for example in 3GPP TS 35.201.
• Ciphering in the GERAN Iu mode is done on a radio bearer basis.
• the ciphering function is located within the protocol layer 2, namely within the RLC/MAC (Radio Link Control / Medium Access Control) protocol.
• RLC/MAC Radio Link Control / Medium Access Control
• T-RLC transparent RLC mode
• N-RLC non-transparent RLC mode
• the layer 2 control signaling may be ciphered, which is performed at the MAC sublayer.
• RLC and MAC protocols are described for instance in the technical specifications 3GPP TS 44.060 V5.1.1 (2002-05): "Technical Specification Group GSM/EDGE Radio Access Network; General Packet Radio Service (GPRS) ; Mobile Station (MS) - Base Station System (BSS) interface; Radio Link Control/Medium Access Control (RLC/MAC) protocol
• a variety of input parameters is used in the algorithm for ciphering, more specifically a 32 -bit counter value, a 1 bit direction value, a 5-bit bearer value RB Id, which identifies the radio bearer for which the ciphering is to be carried out, and the length of the plain data that is to be ciphered.
• these parameters must be synchronized in transmitter and receiver.
• the structure of the 32 bit counter is illustrated in figure 1. It comprises a BSN (Block Sequence Number) of b bits, an RB Id (Radio Bearer Identity) indicator of 1 bit and an HFN (Hyper Frame Number) of 31-b bits.
• the BSN is the sequence number of the respective RLC data block that is to be ciphered and deciphered.
• the BSN numbering is made in-sequence and modulo the Sequence Number Space (SNS) .
• the BSN thus constitutes a cyclic state variable.
• the HFN is a counter that increments by one at every cycle of the BSN, more specifically each time when the BSN reaches 0.
• the RB Id indicator indicates whether the RB Id field in the ciphering parameters is valid.
• the RB Id indicator indicates that the RB Id field is "valid" when in NT-RLC mode.
• BSN and RB Id, or a corresponding identifier providing a one-to-one mapping with the RB Id are transmitted in the RLC data block comprising the respective RLC data, while the HFN is determined with an individual HFN counter at the transmitter and the receiver.
• the HFN at the receiver for this radio bearer in this direction can be updated based on the BSN of this data block. If the BSN of the current data block is smaller than the BSN of the most recently received RLC data block for the same radio bearer in the same direction, i.e. if the BSN has gone through 0, the current HFN is incremented by one and used for deciphering the newly received RLC data block. If the BSN of the current data block is larger than the BSN of the most recently received RLC data block for the same radio bearer in the same direction, i.e. if the BSN has not gone through 0, the current HFN is maintained and used for deciphering the newly received RLC data block.
• ciphering of a given RLC data block is independent of the preceding RLC data blocks.
• deciphering of a given RLC data block is independent of whether or not the previously transmitted RLC data blocks were received, as it is always possible, in normal operation, to recover the required HFN based on the BSN of the received RLC data block.
• a temporary layer 2 link is established on a SBPSCH (Shared Basic Physical Sub-Channel) or on a DBPSCH (Dedicated Basic Physical Sub-CHannel) , respectively, between the RLC transmitter and RLC receiver comprising the RLC instance and the peer RLC instance.
• SBPSCH Shared Basic Physical Sub-Channel
• DBPSCH Dedicated Basic Physical Sub-CHannel
• SFACCH Shared Fast Associated Control CHannel
• a TBF on SBPSCH is established for at least as long as there is data to send for the RLC instance for which the TBF was established.
• a release of the TBF is carried out depending on the data transfer occurring on the TBF.
• a TBF release is fully controlled by the network, which may order through peer-to-peer signaling the release of a TBF at any time.
• a TBF on DBPSCH is established until the DBPSCH is released or until the corresponding radio bearer is released.
• an abnormal release of a TBF i.e. a release without any peer-to-peer signaling, may occur for uplink and downlink TBFs as well on the receiver side as on the transmitter side, as defined in the above cited specification 3GPP TS 44.060 and 3GPP TS 44.160.
• a mobile station will proceed with an abnormal release of a downlink TBF on SBPSCH without access retry, in case it has not received any valid RLC data block for this TBF for a predetermined duration of time, more specifically for the duration of 5 seconds measured by timer T3190.
• the network will release a downlink TBF on SBPSCH abnormally, in case it has not received any acknowledgement in an RLC/MAC control message from the mobile station, in spite of having polled a predetermined number of times. This predetermined number of times is defined by the variable N3105max.
• the mobile station will proceed with an abnormal release of an uplink TBF on SBPSCH with access retry, in case it has not been granted any uplink resources for a predetermined duration of time after the most recently sent RLC/MAC block, more specifically for a duration of 5 seconds measured by timer T3180.
• the network will release an uplink TBF on SBPSCH abnormally, in case it has not received any RLC/MAC block from the mobile station in any of a predetermined number of the last allocated uplink radio blocks to this mobile station.
• This predetermined number of blocks is defined by the variable N3101max. Similar situations may occur for TBF on DBPSCH for instance in case of a handover.
• Cases of abnormal release of a TBF thus occur when the RLC transmitter has not received any response from the RLC receiver for some time, or when the RLC receiver has not received any RLC data block from the RLC transmitter for some time, or more generally, when no peer-to-peer signaling is involved in releasing the TBF. It is important to note that before the establishment of a new TBF for a given RLC instance, this RLC instance is reestablished unless otherwise ordered. This implies in particular that the transmitter resets all state variables, hence also the current BSN value.
• the RLC transmitter will continue transmitting RLC data blocks, even if the RLC receiver might not be able any more to receive the data blocks correctly or to receive the data blocks at all.
• a transmitted RLC data block is considered not to be received, if the RLC/MAC header and the payload of an RLC data block are corrupted. In this case, any identification of the RLC data block is impossible, and the BSN cannot be decoded in the RLC/MAC header.
• a transmitted RLC data block is considered not be received correctly, if only the payload is corrupted. In this case, an identification of the RLC data block is possible, and the BSN can be decoded in the RLC/MAC header.
• the respective RLC transmitter When the respective RLC transmitter is unable to know which RLC data blocks were received, it will continue to increment its HFN counter normally until an abnormal release.
• the RLC receiver When at the same time, the RLC receiver is unable to receive any RLC data blocks triggering an HFN increase, i.e. all RLC data blocks that would trigger an HFN increase in the RLC receiver are not received, it cannot increase its HFN counter. As a result, an HFN desynchronization may occur between transmitter and receiver.
• the transmitter does not reset the state variables between subsequent TBFs belonging to a single radio bearer in the same direction.
• the BSN which represents the next in- sequence RLC data block to be sent for this radio bearer in this direction would start for the new TBF from the value it had at the release of the previous TBF.
• the receiver would then be able to update the HFN as described above for normal operation.
• this solution is not compatible with the current principles of TBF operation on SBPSCH and would therefore require significant changes to the current specifications.
• the BSNs are not compatible between different TBF modes, i.e. GPRS (general packet radio system) and EGPRS (Enhanced GPRS) , therefore this solution would only be feasible for the case that all TBFs of a radio bearer are in the same TBF mode.
• This object is reached according to the invention with a method for synchronizing in a mobile communication system such counters, which method comprises as a first step transmitting at least the least significant bit (LSB) of the current value of such a counter in the mobile station or of such a counter in the network element to the respective other entity during an establishment of a temporary data connection between the mobile station and the network element.
• the proposed method comprises synchronizing the counter at the respective other entity based at least on the transmitted least significant bit.
• the object of the invention is moreover reached with a mobile station comprising means for establishing a temporary data connection to a network element, means for ciphering and/or deciphering data transmitted via an established connection, and a counter for providing a parameter for the ciphering and/or deciphering.
• the mobile station comprises means for carrying out the proposed method, i.e. means for transmitting at least the least significant bit of its counter value and/or for synchronizing its counter based on a received least significant bit.
• the object of the invention is equally reached with a network element comprising corresponding means.
• the invention proceeds from the consideration that a synchronization of the counters can be regained after a desynchronization, in case a sufficient portion of the current counter value at the mobile station or the network element is known to the respective other entity. It is therefore proposed that such a sufficient portion is transmitted from one of the entities to the respective other entity.
• the entire counter value of one of the entities might have to be transmitted.
• a desynchronization of such counters will be restricted to a maximum possible amount.
• the counter value in the transmitter is at the most one counter value higher than the counter value in the receiver.
• the least significant bit by itself may be a clear indication of a possible desynchronization between the counter in the transmitter and the counter in the receiver, and can be used as a basis for a required synchronization.
• a maximum desynchronization of more than one unit can be dealt with correspondingly by extending the transmitted information by the required number of additional bits adjacent to the least significant bit of the counter.
• the invention has the advantage that it allows in any situation a synchronization of a counter value between a mobile station and a network element. More specifically, any desynchronization that may occur in abnormal operation may be automatically caught up with the invention.
• either the mobile station or the network element operates as transmitter of the data, while the respective other entity operates as receiver of the data.
• the least significant bit is preferably transmitted from the transmitter to the receiver of the data, while the counter is synchronized in the receiver of the data.
• the counters can be desynchronized at the maximum by one counter increment between the mobile station and the network element, and in case the transmitter transmits the least significant bit of the value of its counter to the receiver, the counter can be synchronized at the receiver simply by incrementing the counter value by one in case the least significant bit received differs from the least significant bit of the current value of the counter at the receiver.
• the least significant bit of a counter value can be transmitted in particular from the network element to the mobile station within a downlink message used, e.g., for establishing a downlink connection.
• the least significant bit of a counter value can be transmitted in particular from the mobile station to the network element within an uplink message used, e.g., for requesting radio resources, or within data blocks employed for a data transfer from the mobile station to the network element until contention resolution is completed.
• the value of a counter that is to be synchronized with another counter might equally be included in other suitable messages transmitted between the mobile station and the network element .
• the invention can be employed in particular, though not exclusively, for synchronizing HFN counter values used in GERAN Iu mode in RRC connected mode in a non-transparent RLC operation for ciphering and deciphering RLC data blocks for a given radio bearer and in a given direction.
• Fig. 1 shows a counter input to a ciphering algorithm
• Fig. 2 illustrates a signaling flow in an embodiment of the invention for an uplink TBF establishment
• Fig. 3 illustrates a signaling flow in the embodiment of the invention for a downlink TBF establishment in non MAC-idle mode
• Fig. 4 illustrates a signaling flow in the embodiment of the invention for a downlink TBF establishment in a MAC-idle mode using a one-phase packet access
• Fig. 1 shows a counter input to a ciphering algorithm
• Fig. 2 illustrates a signaling flow in an embodiment of the invention for an uplink TBF establishment
• Fig. 3 illustrates a signaling flow in the embodiment of the invention for a downlink TBF establishment in non MAC-idle mode
• Fig. 4 illustrates a signaling flow in the embodiment of the invention for a downlink TBF establishment in a MAC-idle mode using a one-phase packet access
• FIG. 5 illustrates a signaling flow in the embodiment of the invention for a downlink TBF establishment in a MAC-idle mode using a two-phase packet access
• Fig. 6 shows an uplink RLC data block for GPRS TBF mode to be used for the embodiment of the invention
• Fig. 7 shows an uplink RLC data block for EGPRS TBF mode to be used for the embodiment of the invention.
• FIGS 2 to 7 illustrate an embodiment of the method according to the invention, which is implemented in a mobile communication system comprising a mobile station and a communication network with at least one GERAN.
• the . mobile station is assumed to be able to access the communication network in GERAN Iu mode.
• the presented embodiment ensures that the HFN parameter used in GERAN Iu mode in RRC-Connected mode in a non-transparent RLC operation for ciphering and deciphering RLC data blocks transmitted on a given radio bearer and in a given direction between the mobile station and the GERAN can always be synchronized.
• either the mobile station or a base station system of the GERAN can be the RLC transmitter, while the respective other entity constitutes the RLC receiver.
• Figures 2 to 5 show signaling flows for four different situations.
• the signaling flows are used for establishing a new TBF corresponding to a given radio bearer in a given direction, a preceding TBF for the same radio bearer in the same direction having been released abnormally.
• two vertical line are depicted.
• the respective vertical line on the left hand side represents the mobile station MS, while the respective vertical line on the right hand side represents the base station system BSS of the GERAN.
• the horizontal arrows between the vertical lines represent the signaling flow between the mobile station MS and the BSS.
• FIG. 2 shows a signal flow for a downlink TBF establishment, i.e. the BSS operates currently as RLC transmitter and the mobile station as RLC receiver.
• an HFN counter in the BSS has a value of "HFN”.
• An HFN counter in the mobile station MS in contrast, has a value of "HFN-1", since the mobile station MS did not receive any indication to increment the counter correctly.
• a PACKET DOWNLINK ASSIGNMENT message is transmitted by the BSS to the mobile station MS on a PACCH/PAGCH for assigning allocated radio resource to the mobile station MS.
• a PACCH Packet Associated Control Channel
• PAGCH Packet Access Grant Channel
• the PACKET DOWNLINK ASSIGNMENT message contains the least significant bit HFN_LSB of the current value of the HFN counter in the BSS . Based on this LSB, the mobile station MS performs an update of its own HFN counter. It recognizes that the received LSB does not correspond to the LSB of the current value of its own HFN counter, and therefore it increments its counter by one, which thereby changes its value from "HFN-1" to "HFN". As a result, the HFN counters in the BSS and in the mobile station MS are synchronized, and thus a ciphering and deciphering of downlink RLC data blocks is enabled.
• the mobile station MS in the RRC-Connected mode may be in a MAC-idle state or not.
• the MAC-idle state is a MAC-control-entity state in the Iu mode, in which no basic physical subchannels are assigned.
• FIG. 3 shows a signal flow for an uplink TBF establishment for the case that the mobile station MS is not in the MAC-idle state.
• an HFN counter in the mobile station MS has a value of "HFN”.
• An HFN counter in the BSS has a value of "HFN-1", since the BSS did not receive any indication to increment the counter correctly.
• a PACKET RESOURCE REQUEST message is transmitted by the mobile station MS to the BSS on a PACCH, in order to request a change in the assigned uplink resources.
• the PACKET RESOURCE REQUEST message contains the least significant bit HFN_LSB of the current value of the HFN counter in the mobile station MS.
• the BSS Based on this LSB, the BSS performs an update of its own HFN counter. It recognizes that the received LSB does not correspond to the LSB of the current value of its own HFN counter, and therefore it increments the counter by one to have a value of "HFN" as well. As a result, the HFN counters in the BSS and in the mobile station MS are synchronized. Then, the BSS transmits a PACKET UPLINK ASSIGNMENT message to the mobile station MS on a PACCH, which message assigns radio resources to be used by the mobile station MS. Due to the synchronization of the HFN counters, the subsequent uplink RLC data blocks can be ciphered and deciphered correctly.
• a packet access can be achieved either in one phase or in two phases .
• Figure 4 shows a signal flow for an uplink TBF establishment for the case that the mobile station MS is in the MAC-idle state and that the TBF is to be established with a one-phase packet access.
• an HFN counter in the mobile station MS has again a value of "HFN”
• an HFN counter in the BSS has again a value of "HFN-1” since the BSS did not receive any indication to increment the counter correctly.
• the mobile station MS now sends a PACKET CHANNEL REQUEST message to the BSS on a PRACH for initiating the packet access procedure.
• the PRACH Packet Random Access Channel
• the PRACH is an uplink channel used to request GPRS resources .
• the BSS Upon receipt of the PACKET CHANNEL REQUEST message, the BSS sends a PACKET UPLINK ASSIGNMENT to the mobile station MS on a PAGCH.
• the mobile station MS transmits the least significant bit HFN_LSB of the current value of its HFN counter within RLC/MAC blocks employed for an uplink data transfer to the BSS, until contention resolution is completed.
• the BSS is now able to update its HFN counter based on the received LSB, as described with reference to figure 3.
• the BSS further transmits a PACKET UPLINK ACK/NACK message to the mobile station MS on a PAGCH, for indicating the status of the received RLC data blocks and hence completing contention resolution.
• the subsequent RLC data blocks transmitted on the established TBF can then be ciphered and deciphered correctly based on the values of the synchronized HFN counters.
• Figure 5 shows a signal flow for an uplink TBF establishment for the case that the mobile station MS is in the MAC-idle state and that the TBF is to be established with a two-phase packet access.
• an HFN counter in the mobile station MS has again a value of "HFN”
• an HFN counter in the BSS has again a value of "HFN-1” since the BSS did not receive any indication to increment the counter correctly.
• the mobile station MS now sends a PACKET CHANNEL REQUEST message to the BSS on a PRACH.
• the BSS sends again a PACKET UPLINK ASSIGNMENT message to the mobile station MS on a PAGCH.
• the mobile station MS transmits the least significant bit HFN_LSB of the current value of its HFN counter within a PACKET RESOURCE REQUEST message on a PACCH to the BSS.
• the BSS is able to update its HFN counter based on the received LSB, as described with reference to figure 3.
• the BSS transmits a PACKET UPLINK ASSIGNMENT message on a PACCH to the mobile station MS.
• the RLC data blocks transmitted on the established TBF can then be ciphered and deciphered correctly due to the synchronized HFN counters .
• 3GPP TS 44.160 defines different RLC/MAC block structures for data transfers for GPRS and EGPRS .
• Figure 6 shows an uplink RLC data block with an RLC/MAC header for a GPRS TBF mode.
• the figure shows more specifically a first row representing the MAC header and further rows representing different octets, Octet 1 to Octet N.
• the MAC header and each of the octets is subdivided into 8 bits, the numbering of the bits 1-8 being indicated on top of the rows.
• the presentation proceeds from the corresponding RLC data block defined in specification TS 44.060, and for the details of the block structure, it is referred to this specification.
• a BSN may be inserted for example to bits 2 to 8 of Octet 2, RLC data to Octets M+7 to N, and a length indicator indicating the length of the comprised RLC data to optional Octets 4 to M.
• an RB Id may be distributed to bits 2 to 4 of optional Octet M+5 and to bits 7 and 8 of optional Octet M+6.
• a further field was defined in the data block presented in figure 6, in order to enable its use in the signal flow of figure 4. More specifically, it is provided that the LSB of the current HFN counter value in the involved mobile station may be inserted to bit 6 of optional Octet M+6. This bit reserved for the LSB is shaded in gray in figure 6.
• FIG. 7 shows an uplink RLC data block for an EGPRS TBF mode. Also this block is composed of Octets 1 to N with bits 1 to 8. The presentation proceeds again from the corresponding RLC data block defined in specification TS 44.060, and it is referred again to this specification for the details of the block structure.
• a BSN may be inserted to a combined downlink RLC/MAC header, which is not depicted in figure 7.
• RLC data may be inserted as in the case of GPRS to Octets M+7 to N, while a length indicator indicating the length of the comprised RLC data may be inserted to optional Octets 1 to M.
• An RB Id may be distributed again to bits 2 to 4 of optional Octet M+5 and to bits 7 and 8 of optional Octet M+6.
• a further field was defined in the data block presented in figure 7 compared to the specified RLC data block, in order to enable its use in the signal flow of figure 4.
• This further field which is associated to bit 6 of optional Octet M+6, is provided as in figure 6 for the LSB of the current HFN counter value in the involved mobile station. The bit reserved for the LSB is shaded again in gray in figure 7.
• a field for another identifier that uniquely identifies the radio bearer to which the respective RLC data block belongs could be included in the uplink RLC data blocks .
• all or part of the following messages have to be adapted to include the LSB of an HFN counter value, in order to ensure an HFN synchronization between the network and the mobile station according to the presented embodiment of the invention: PACKET DOWNLINK ASSIGNMENT, MULTIPLE TBF DOWNLINK ASSIGNMENT and PACKET RESOURCE REQUEST.
• the MULTIPLE TBF DOWNLINK ASSIGNMENT message is a message which has been proposed for assigning multiple TBFs between the network and a mobile station.
• a field for the LSB should be included in a suitable message for every possible TBF.
• the HFN_LSB field contains the least significant bit of the value of an HFN counter associated to the radio bearer for which the TBF is established.

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• Engineering & Computer Science (AREA)
• Computer Security & Cryptography (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Computer Hardware Design (AREA)
• Computing Systems (AREA)
• General Engineering & Computer Science (AREA)
• Mobile Radio Communication Systems (AREA)

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Citations (3)

• 2002
  • 2002-06-12 WO PCT/IB2002/002156 patent/WO2003107706A1/en not_active Application Discontinuation
  • 2002-06-12 AU AU2002309126A patent/AU2002309126A1/en not_active Abandoned
• 2003
  • 2003-05-22 TW TW092113793A patent/TW200402212A/zh unknown

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