LTE

The call flows below are sequence diagrams of the LTE control-plane procedures. Working from your own captures? VisualEther renders an LTE PCAP as exactly this kind of sequence diagram — attach, bearer setup, handover, and security — so you can line a real trace up against the reference flow.

Control plane signaling flows

LTE eNodeB S1 startup, MIB-SIB broadcast and RRC connection

Learn about eNodeB startup: (1) eNodeB performs an S1 setup (2) MIB and SIB broadcast (3) eNodeB sends UE specific configuration information via the RRC Connection Setup message.

LTE Random Access Procedure and Contention Resolution

This sequence diagram explains with an example how LTE UEs connect to the eNodeB. Contention resolution between UEs also explored in this flow.

LTE Attach and Default Bearer Setup Flow

LTE attach and default bearer signaling flow describe the attach to a new MME followed by a default bearer setup.

S1AP View of LTE Attach and EPS Bearer Setup for Two PDNs

Explore the S1AP handling of: (1) LTE Attach (2) PDN Setup and Default Bearer Setup for two PDNs (3) UE context release (4) Service Request.

Tracking Area Update Signaling Flow

The flow describes a tracking area update that results in MME change.

Voice over LTE (VoLTE) Call Flow

An iPhone setting up a VoLTE call with IMS signaling.

Security

LTE Security Keys and Procedures

Presentation and signaling flow that describe the key exchange and signaling in LTE security procedures.

LTE Security Presentation

Authentication, Integrity Protection and Encryption. Generation of keys during LTE signaling procedures.

Handover

LTE X2 Handover Sequence Diagrams

X2 interface connects eNodeBs in LTE. Explore the inter eNodeB handover procedures over the X2 interface.

LTE S1 Handover Sequence Diagrams

S1 interface connects eNodeBs to the MME. S1 handover is used when the direct X2 interface is not available.

LTE S1AP View of an Inter-MME S1 Handover

Examine the S1AP messages involved in an S1 Handover at full message level detail. In this scenario, the source and target eNodeBs are served by different MMEs.

X2 Handover Messaging Presentation

Explore contents of messages exchanged during an X2 handover between two eNodeBs.

Inter-working with 3G and 5G

LTE to 3G Circuit Switched Fallback (CSFB) Call Flow

A 4G LTE subscriber initiates a voice call in an LTE network that does not support VoLTE. In such cases, the UE falls back to 3G networks to establish a voice call.

LTE 5G-NR Non-standalone access

LTE support for 5G dual connectivity will enable 4G network operators to introduce 5G services with a minimal upgrade to support 5G data plane. This is achieved with the support for 4G eNB and 5G gNB dual connectivity (EN-DC).

Presentations and Tutorials

LTE Tutorial Presentation

LTE presentation with audio narration. OFDM basics, LTE channels, signaling procedures and MIMO are covered.

OFDM and SC-FDMA Video Lectures

LTE is built over OFDM and SC-FDMA foundation. The video lectures build a conceptual understanding of OFDM and SC-FDMA.

LTE Medium Access Control (MAC) Presentation

Learn about the MAC layer. The logical, transport and physical channels are described. Signaling flows for random access and data transfer are also covered.

LTE Radio Link Control (RLC) Presentation

Covers Transparent Mode (TMD), Unacknowledged Mode (UMD) and Acknowledged Mode (AMD). RLC state variables and PDU formats are also described.

LTE Packet Data Convergence Protocol (PDCP) Presentation

Robust Header Compression (ROHC) and PDCP PDU formats are covered.

LTE RRC Connection Setup Messaging Presentation

Describes the RRC connection signaling procedure with detailed description of the RRC message contents.

Attach and Default Bearer Setup Messaging Presentation

Messages involved in LTE attach and default bearer setup are described in detail.

LTE Identifiers Presentation

LTE signaling protocol define a large number of identifiers for UEs, RABs and signaling endpoints. The presentation covers the IMSI, GUTI, GUMMEI, IMEISV, RNTI, TAI and APN.

Medium blog posts

Moving 4G EPC to the Cloud

CUPS — Control and User Plane Separation