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2G/GSM |
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LLC
LLC (Logical Link Control) layer protocol is a procedure for packet data transfer between a MS and SGSN(Serving GPRS Support Node). This layer is specified in 3GPP 44.064. LLC is intended for use with both acknowledged and unacknowledged data transfer.
< 44.064 - Figure 3: LLC frame format >
< 44.064 - Figure 7: Address field format >
< 44.064 - Table 1: C/R field bit usage >
< 44.064 - Table 2: Allocation of SAPI values >
< 44.064 - Figure 8: Control field format >
< 44.064 - 6.3.5.1 Poll/Final bit (P/F) > All U frames contain the Poll/Final (P/F) bit. The P/F bit serves a function in both command frames and response frames. In command frames the P/F bit is referred to as the P bit. In response frames it is referred to as the F bit. The P bit set to 1 is used by an LLE to solicit (poll) a response frame from the peer LLE. The F bit set to 1 is used by an LLE to indicate the response frame transmitted as a result of a soliciting (poll) command.
< 44.064 - 6.3.5.2 Acknowledgement request bit (A) > All I and S frames contain the Acknowledgement Request (A) bit. The A bit set to 1 is used by an LLE to solicit an acknowledgement (i.e., an I+S or S frame) from the peer LLE. The A bit set to 0 is used by an LLE to indicate that the peer LLE is not requested to send an acknowledgement.
< 44.064 - Figure 9: SACK I and S frame control field format >
L3 -> LLC (LL_UNIDATA_REQ) : 08 12 00 10 21 36 36 33 35 36 32 38 37 33 36 36 33 35 36 32 38 80 28 10 36 32 37 3E 30 3B 00 00 36 37 31 36 32 37 3E 30
LLC -> R/M (GRR_DATA_REQ): 41 C0 01 08 12 00 10 21 36 36 33 35 36 32 38 37 33 36 36 33 35 36 32 38 80 28 10 36 32 37 3E 30 3B 00 00 36 37 31 36 32 37 3E 30 2C 18 61
RM -> PHY (PH_DATA_REQ - Seg 1) : 00 00 01 41 C0 01 08 12 00 10 21 36 36 33 35 36 32 38 37 33 36 36 33 35 36 32 38 80 28 10 36 32 37 3E 30 3B 00 00 36 00
RM -> PHY (PH_DATA_REQ - Seg 2) : 08 01 02 29 37 31 36 32 37 3E 30 2C 18 61 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 00
Let's decode following LLC frame :
LLC -> R/M (GRR_DATA_REQ): 41 C0 01 08 12 00 10 21 36 36 33 35 36 32 38 37 33 36 36 33 35 36 32 38 80 28 10 36 32 37 3E 30 3B 00 00 36 37 31 36 32 37 3E 30 2C 18 61
DLT: 147, Payload: llcgprs (Logical Link Control GPRS) MS-SGSN LLC (Mobile Station - Serving GPRS Support Node Logical Link Control) SAPI: GPRS Mobility Management FCS: 0x61182c (correct) Address field SAPI: LLGMM 0... .... = Protocol Discriminator_bit: OK .1.. .... = Command/Response bit: DownLink/UpLink = Command/Response .... 0001 = SAPI: GPRS Mobility Management (1) Unconfirmed Information format - UI, N(U) = 0 110. .... .... .... = UI format: 0x0006 ...0 0... .... .... = Spare bits: 0x0000 .... .000 0000 00.. = N(U): 0 .... .... .... ..0. = E bit: non encrypted frame .... .... .... ...1 = PM bit: FCS covers the frame header and information fields GSM A-I/F DTAP - Authentication and Ciphering Req Protocol Discriminator: GPRS mobility management messages .... 1000 = Protocol discriminator: GPRS mobility management messages (0x08) 0000 .... = Skip Indicator: No indication of selected PLMN (0) DTAP GPRS Mobility Management Message Type: Authentication and Ciphering Req (0x12) IMEISV Request 0... .... = Spare bit(s): 0 .000 .... = IMEISV request: IMEISV not requested (0) Cipher Algorithm .... 0... = Spare bit(s): 0 .... .000 = Type of ciphering algorithm: ciphering not used (0) A&C Reference Number 0001 .... = A&C reference number: 1 Force to Standby .... 0... = Spare bit(s): 0 .... .000 = Force to standby: Force to standby not indicated (0) Authentication Parameter RAND Element ID: 0x21 RAND value: 36363335363238373336363335363238 Ciphering key sequence number: 0x00 (0) Authentication Parameter AUTN (UMTS and EPS authentication challenge) Element ID: 0x28 Length: 16 AUTN value: 3632373e303b00003637313632373e30 SQN xor AK: 3632373e303b AMF: 0000 MAC: 3637313632373e30
L3 -> LLC (LL_UNIDATA_REQ) : 08 12 00 10 21 31 39 35 39 37 30 33 34 33 31 39 35 39 37 30 33 80 28 10 0A 73 65 55 43 BB 00 00 31 28 17 0A 73 65 55 43
LLC -> R/M (GRR_DATA_REQ): 41 C0 01 08 12 00 10 21 31 39 35 39 37 30 33 34 33 31 39 35 39 37 30 33 80 28 10 0A 73 65 55 43 BB 00 00 31 28 17 0A 73 65 55 43 FA 4B F2
RM -> PHY (PH_DATA_REQ - Seg 1) : 00 00 01 41 C0 01 08 12 00 10 21 31 39 35 39 37 30 33 34 33 31 39 35 39 37 30 33 80 28 10 0A 73 65 55 43 BB 00 00 31 00
RM -> PHY (PH_DATA_REQ - Seg 2) : 08 01 02 29 28 17 0A 73 65 55 43 FA 4B F2 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 2B 00
Let's decode following LLC frame :
LLC -> R/M (GRR_DATA_REQ): 41 C0 01 08 12 00 10 21 31 39 35 39 37 30 33 34 33 31 39 35 39 37 30 33 80 28 10 0A 73 65 55 43 BB 00 00 31 28 17 0A 73 65 55 43 FA 4B F2
DLT: 147, Payload: llcgprs (Logical Link Control GPRS) MS-SGSN LLC (Mobile Station - Serving GPRS Support Node Logical Link Control) SAPI: GPRS Mobility Management FCS: 0xf24bfa (correct) Address field SAPI: LLGMM 0... .... = Protocol Discriminator_bit: OK .1.. .... = Command/Response bit: DownLink/UpLink = Command/Response .... 0001 = SAPI: GPRS Mobility Management (1) Unconfirmed Information format - UI, N(U) = 0 110. .... .... .... = UI format: 0x0006 ...0 0... .... .... = Spare bits: 0x0000 .... .000 0000 00.. = N(U): 0 .... .... .... ..0. = E bit: non encrypted frame .... .... .... ...1 = PM bit: FCS covers the frame header and information fields GSM A-I/F DTAP - Authentication and Ciphering Req Protocol Discriminator: GPRS mobility management messages .... 1000 = Protocol discriminator: GPRS mobility management messages (0x08) 0000 .... = Skip Indicator: No indication of selected PLMN (0) DTAP GPRS Mobility Management Message Type: Authentication and Ciphering Req (0x12) IMEISV Request 0... .... = Spare bit(s): 0 .000 .... = IMEISV request: IMEISV not requested (0) Cipher Algorithm .... 0... = Spare bit(s): 0 .... .000 = Type of ciphering algorithm: ciphering not used (0) A&C Reference Number 0001 .... = A&C reference number: 1 Force to Standby .... 0... = Spare bit(s): 0 .... .000 = Force to standby: Force to standby not indicated (0) Authentication Parameter RAND Element ID: 0x21 RAND value: 31393539373033343331393539373033 Ciphering key sequence number: 0x00 (0) Authentication Parameter AUTN (UMTS and EPS authentication challenge) Element ID: 0x28 Length: 16 AUTN value: 0a73655543bb00003128170a73655543 SQN xor AK: 0a73655543bb AMF: 0000 MAC: 3128170a73655543
3GPP Decoder Tip
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