TejVox

Network Simulator

Step through LTE and 5G signalling procedures message by message. Every message shows its information elements, timers and the 3GPP clause it comes from.

SpecsTS 23.401 §5.3.2.1TS 24.301TS 36.331TS 36.413TS 29.272TS 29.274Rel-15
Click any box or line to see what it does and which messages cross it.
Uu — Radio interface, UE ↔ RAN · 7 messages hereUuS1-MME — S1AP control plane, eNB ↔ MME (SCTP) · 8 messages hereS1-MMES6a — Diameter, MME ↔ HSS (subscription + AVs) · 4 messages hereS6aS11 — GTP-C, MME ↔ SGW (session management) · 4 messages hereS11S1-U — GTP-U user plane, eNB ↔ SGW · 1 message hereS1-US5 — GTP-C / GTP-U, SGW ↔ PGW · 2 messages hereS5SGi — PGW ↔ packet data networkSGiGx — Diameter policy, PGW ↔ PCRF · 1 message hereGxUser Equipment · involved in 14 messagesUEEvolved NodeB (E-UTRAN) · involved in 16 messageseNBMobility Management Entity · involved in 16 messagesMMEHome Subscriber Server (with AuC) · involved in 4 messagesHSSPolicy and Charging Rules FunctionPCRFServing Gateway · involved in 7 messagesSGWPDN Gateway · involved in 4 messagesPGWPacket Data Network / APNInternet

Uu — Radio interface, UE ↔ RAN

1 / 27
Layers
UERRC_IDLE — RA in progress
MMEEMM-DEREGISTERED
UEeNBMMEHSSSGWPGW
Random access & RRC connection1Msg1 — Random Access PreamblePHYUu2Msg2 — Random Access ResponseMACUu3Msg3 — RRCConnectionRequestRRCUu4Msg4 — RRCConnectionSetupRRCUu5Msg5 — RRCConnectionSetupCompleteRRCUuEMM attach & EPS-AKA6Attach Request (in S1AP Initial UE Message)NAS-EMMS1-MME7Authentication-Information-Request (AIR)DiameterS6a8Authentication-Information-Answer (AIA)DiameterS6a9Authentication RequestNAS-EMMS1-MME10Authentication ResponseNAS-EMMS1-MME11Security Mode CommandNAS-EMMS1-MME12Security Mode CompleteNAS-EMMS1-MMESubscription & default bearer13Update-Location-Request (ULR)DiameterS6a14Update-Location-Answer (ULA)DiameterS6a15Create Session RequestGTP-CS1116Create Session RequestGTP-CS517Gx CCR-I / CCA-I with PCRF (optional)DiameterGx18Create Session ResponseGTP-CS519Create Session ResponseGTP-CS11Context setup & completion20Initial Context Setup Request (+ Attach Accept)S1APS1-MME21SecurityModeCommand + RRCConnectionReconfigurationRRCUu22RRCConnectionReconfigurationCompleteRRCUu23Initial Context Setup ResponseS1APS1-MME24Attach Complete (+ Activate Default EPS Bearer Context Accept)NAS-EMMS1-MME25Modify Bearer RequestGTP-CS1126Modify Bearer ResponseGTP-CS1127User plane active — GTP-U data flowsUser-PlaneS1-U
PHYStep 1 of 27

Msg1 — Random Access Preamble

UE → eNB · over Uu

TS 36.321clause 5.1.2PRACH

UE has already read MIB/SIB1/SIB2, so it knows the PRACH configuration. It picks a random preamble from the contention-based group and transmits it on the PRACH occasion. RA-RNTI is derived from the time/frequency of that occasion.

Information elements

IEPFmt / lenValue
Random Access Preamble ID (RAPID)36.321 5.1.2Group A/B chosen by Msg3 size and pathlossM—23
PRACH preamble format36.211 5.7.1Format 0 → up to ~14 km cell radiusM—0
RA-RNTI36.321 5.1.41 + t_id + 10 × f_idM—0x0002

State after this message

UERRC_IDLE — RA in progress

Values shown are illustrative and internally consistent, not captured from a live network — the point is to make the structure of each message legible. Clause references are the authoritative part; check them against the specification release you are working to.