LTE vs 5G NR Signaling — RRC & NAS Compared
A side-by-side comparison of LTE and 5G NR signaling protocols covering RRC, NAS, logical channels, state machines and network architecture differences with 3GPP specification references.
Key Facts — LTE vs 5G NR Signaling
- LTE RRC spec
- 3GPP TS 36.331 (E-UTRA RRC)
- LTE NAS spec
- 3GPP TS 24.301 (EPS NAS — EMM / ESM)
- NR RRC spec
- 3GPP TS 38.331 (NR RRC)
- NR NAS spec
- 3GPP TS 24.501 (5GS NAS — 5GMM / 5GSM)
- Encoding
- ASN.1 UPER for both LTE and NR RRC; TLV binary for NAS
- Key difference
- NR adds RRC_INACTIVE state, separates AMF/SMF, introduces 5GMM/5GSM NAS
RRC protocol comparison
| Aspect | LTE RRC (TS 36.331) | 5G NR RRC (TS 38.331) |
|---|---|---|
| 3GPP specification | TS 36.331 | TS 38.331 |
| RRC states | RRC_IDLE, RRC_CONNECTED | RRC_IDLE, RRC_INACTIVE, RRC_CONNECTED |
| Reconfiguration message | RRCConnectionReconfiguration | RRCReconfiguration |
| Cell config structure | RadioResourceConfigDedicated | CellGroupConfig (MCG / SCG) |
| Measurement framework | measObjectEUTRA, reportConfigEUTRA | measObjectNR, reportConfigNR, condReconfiguration |
| Handover command | mobilityControlInfo in RRCConnectionReconfiguration | reconfigurationWithSync in RRCReconfiguration |
| Signaling radio bearers | SRB0, SRB1, SRB2 | SRB0, SRB1, SRB2, SRB3 (for SCG) |
| Encoding | ASN.1 UPER | ASN.1 UPER |
NAS protocol comparison
| Aspect | EPS NAS (TS 24.301) | 5GS NAS (TS 24.501) |
|---|---|---|
| 3GPP specification | TS 24.301 | TS 24.501 |
| Sub-protocols | EMM (Mobility Mgmt) + ESM (Session Mgmt) | 5GMM (Mobility Mgmt) + 5GSM (Session Mgmt) |
| Registration procedure | Attach Request / Attach Accept | Registration Request / Registration Accept |
| Session establishment | PDN Connectivity Request / ESM Information Request | PDU Session Establishment Request / Accept |
| Security | EIA / EEA algorithms, KASME-based key hierarchy | NIA / NEA algorithms, KAUSF / KSEAF key hierarchy |
| Core network peer | MME (combined mobility + session) | AMF (mobility) + SMF (session) — separated |
| Cause codes | EMM cause / ESM cause (TS 24.301 Annex A) | 5GMM cause / 5GSM cause (TS 24.501 Annex A) |
Logical channel differences
| Channel | LTE | 5G NR |
|---|---|---|
| BCCH-BCH | MasterInformationBlock | MasterInformationBlock (MIB) |
| BCCH-DL-SCH | SIB1 – SIB19+ | SIB1 – SIB14+ (restructured content) |
| DL-CCCH | RRCConnectionSetup, RRCConnectionReject | RRCSetup, RRCReject |
| UL-CCCH | RRCConnectionRequest, RRCConnectionReestablishmentRequest | RRCSetupRequest, RRCReestablishmentRequest, RRCResumeRequest |
| DL-DCCH | RRCConnectionReconfiguration, RRCConnectionRelease | RRCReconfiguration, RRCRelease |
| UL-DCCH | MeasurementReport, UECapabilityInformation | MeasurementReport, UECapabilityInformation |
| PCCH | Paging | Paging |
Architecture differences
In LTE (EPC architecture), the protocol stack flows from the UE through the eNB to the core network elements: MME for control plane (NAS signaling, mobility, authentication) and S-GW/P-GW for user plane (bearer transport, IP allocation). The MME handles both mobility management (EMM) and session management (ESM) in a single entity.
In 5G NR (5GC architecture), the base station is the gNB and the core network is decomposed into service-based functions: AMF handles mobility and registration (5GMM), SMF handles session management (5GSM), and UPF handles user plane forwarding. This separation enables independent scaling and flexible network slicing.
For Non-Standalone (NSA / EN-DC) deployments, LTE acts as the master node (MN) and NR acts as the secondary node (SN). The LTE eNB anchors the control plane while NR provides additional user-plane capacity. The NR secondary cell group configuration is carried inside the LTE RRCConnectionReconfiguration message via the nr-SecondaryCellGroupConfig information element.
When to use each
Legacy LTE networks
Use LTE RRC (TS 36.331) and EPS NAS (TS 24.301) for analyzing signaling on standalone 4G deployments. This covers Attach, Detach, TAU, handover, bearer setup and all traditional LTE procedures.
NSA dual connectivity (EN-DC)
In EN-DC deployments, you need both LTE and NR decoders. The LTE eNB is the master node, so control-plane signaling uses LTE RRC. The NR CellGroupConfig for the secondary node is embedded inside the LTE RRCConnectionReconfiguration. NAS remains EPS-based (TS 24.301) since the core is still EPC.
SA standalone 5G
Use NR RRC (TS 38.331) and 5GS NAS (TS 24.501) for standalone 5G networks. The gNB is the sole RAN node and the 5G Core (AMF, SMF, UPF) handles all control and user plane functions. Registration Request/Accept, PDU Session Establishment and all 5GMM/5GSM procedures apply here.
How to decode both LTE and NR
Select technology
Open the HiCellTek L3 Decoder and choose 4G LTE or 5G NR. Pick the logical channel (DL-DCCH, UL-DCCH, BCCH-DL-SCH, etc.).
Paste hex frame
Paste the hexadecimal RRC or NAS frame from QCAT, Wireshark, PCAP or DIAG log. The decoder auto-detects the message type within the selected channel.
Compare side by side
Decode LTE and NR frames in separate tabs to compare message structures, IEs and parameter differences. Export to JSON for automated analysis.
Frequently Asked Questions
What is the main difference between LTE and 5G NR signaling?
The main difference is the addition of the RRC_INACTIVE state in 5G NR, the split between AMF and SMF in the core network (replacing the single MME), and the introduction of new NAS protocols (5GMM/5GSM) replacing EMM/ESM. On the RRC side, NR uses simplified message names (e.g. RRCReconfiguration instead of RRCConnectionReconfiguration) and introduces CellGroupConfig as the primary cell configuration structure.
Can I decode both LTE and 5G NR frames with the same tool?
Yes. The HiCellTek online decoder supports both LTE (TS 36.331 / TS 24.301) and 5G NR (TS 38.331 / TS 24.501) RRC and NAS messages. Select the technology and logical channel, paste the hex frame, and decode instantly. Both use ASN.1 UPER encoding and the decoder handles the grammar differences automatically.
What are 5GMM and 5GSM in 5G NAS?
5GMM (5G Mobility Management) and 5GSM (5G Session Management) are the two NAS sub-protocols defined in TS 24.501 for 5G standalone networks. 5GMM handles UE registration, authentication, security mode and deregistration, replacing the EMM protocol in LTE. 5GSM manages PDU session establishment, modification and release, replacing the ESM protocol in LTE.
Which 3GPP specifications define LTE and NR signaling?
LTE RRC is defined in TS 36.331 and LTE NAS (EPS) in TS 24.301. 5G NR RRC is defined in TS 38.331 and 5G NAS (5GS) in TS 24.501. Both RRC specs use ASN.1 for message encoding, while NAS messages use a TLV (Tag-Length-Value) binary format. These specs are maintained by 3GPP and updated with each release.
Related resources
L3 Protocol Decoder
Online RRC and NAS decoder for 2G/3G/4G/5G. Free, no signup.
What is RRC Protocol?
Full guide to Radio Resource Control: states, messages, channels and decoding.
RRC vs NAS — Comparison
Key differences between RRC and NAS protocols in LTE and 5G NR.
ASN.1 Telecom Guide
How ASN.1 encoding works in 3GPP RRC and NAS signaling.
Telecom Glossary
RRC, NAS, RSRP, SINR, ASN.1, UPER and more terms explained.