LTE Call Flows

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Introduction to LTE 

LTE is a high-speed, packet-based mobile communication standard. It uses the “open access” principle, inherited from GSM, to allow any subscriber to communicate with any other subscriber that is not their home operator. LTE can be described as being an evolution of third-generation (3G) wireless data communications technologies such as UMTS and HSPA+. LTE is a highly efficient, all-IP data-based mobile communication technology that provides one of the most robust, reliable, and dynamic networks in the world. LTE allows service providers to use bandwidth more efficiently and create enhanced user experiences for users. LTE is a wireless communication standard that uses a cellular architecture. It is based on the GSM/EDGE and UMTS/HSPA technologies, increasing the capacity and data rate using a different radio interface together with core network improvements. It provides enhanced support for multiple input multiple output (MIMO) antennas, higher-order modulation (256QAM), and frequency division duplexing (FDD). LTE call flows are protocols that govern how signals are transferred and devices are connected. 

All LTE base stations, mobile devices, and smartphones must comply with these protocols in order to ensure a seamless process when connecting users. The LTE call flow begins with a UE and an eNodeB, which perform the centralized MME functions of authenticating the subscriber, obtaining real-time location information on the subscriber, and performing authentication and authorization operations including PTAI, forwarding session start requests and other messages. In LTE, the user equipment (UE) is any device that uses LTE to communicate with other entities in its wireless communication network. For example, such a device could be a laptop computer, or it could be an information appliance (also known as a "mobile broadband stick" or "laptop dongle"), or a smartphone. The UE communicates with an evolved Node B (eNB), a radio base station that covers a small region. The eNodeB provides access to other networks through inter-cell handover and inter-RAT mobility. Users can roam between cells but only if their UEs are equipped with tracking capability and can report their location; thus UEs can potentially move between eNBs operated by different operators. IMS (IP Multimedia Subsystem) is an architecture that supports a service-based architecture in which all the elements necessary to deliver multimedia services are grouped into a single IMS domain. 

The domain can be served by an SBC, a collection of one or more BSCs, an MME, and an HSS or by any other networks that may be associated with LTE. LTE is a technology designed to provide wireless communications to mobile devices. LTE is based on GSM but differs in the frequencies used and other aspects such as latency and transmission power. LTE is a wireless telecommunication technology and the name of the ITU's fourth generation of mobile cellular standards. It is based on GSM/EDGE and UMTS/HSPA technologies, increasing the capacity and speed using a different radio interface together with core network improvements. The standard is described in three parts: the physical layer (LTE-PHY), the Medium Access Control Layer (LTE-MAC), and the Radio Link Control Layer (RLC).

LTE call flows

LTE call flows are a set of parameters and configurations used when configuring Voice over LTE (VoLTE) calls over EPC. These parameters include QPSK, 16QAM, and 64QAM, which represent different modulation codecs for VoLTE calls. LTE call flows also specify cell re-selection procedures, mobility handling, and call routing between the CS domain and PS domain. LTE call flows are used to establish, maintain, and release the connection between two parties that wish to communicate. The LTE call flow is typically organized into five basic steps: Establishment, Session, Release, Re-establishment, and Re-Session. 

LTE call flows with wireshark

The LTE call flow specification is the formal description of how an LTE call is made, and how it is routed. The LTE call flow specification effectively allows an LTE user to roam on other networks and still make calls. LTE calls are initiated from a UE and are similar to those of UMTS. Outgoing calls may be established on either the E-DCH or a 1xRTT PS handover may be initiated by the network when it determines that the UE is in a poor coverage area. Incoming calls are mainly connected on E-DCH for both CS fallback and supplementary service request, but LTE can also establish VoLTE calls over 1xRTT radio access technology (RAT).

Website link for LTE call flows Certification:

https://telcomaglobal.com/p/lte-call-flow-with-wireshark