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
