The Ultimate Cheat Sheet for LTE Identifiers

By Azar

There is a term for too much known as information overload, which means when you have too much to learn and understand in short time. Too much information to remember is not only challenging it can cause confusion and frustration as well. 

4G LTE or any other cellular technology is no exception and is not free from acronyms and information overload.

In order to make your lives easier. I decided to elaborate a number of LTE identifiers for you. 


  • Firstly we will have a visual breakdown
  • Secondly, we will explain each of the identifier as well


This list of identifiers is not an exhaustive list of all LTE identifiers. However, it covers a lot of LTE identifiers you may encounter in your LTE everyday work. 


In case if you want any identifier to be covered, please list them in the comments below.  



Visual cheat sheet for lte identifiers


The overview of major LTE identifiers are given below.

LTE Acronyms Cheat Sheet



As you may have observed, there are a lot of acronyms listed in the cheat sheet above. In order to unpack the list of acronyms, let's take a look at the details of these acronyms below. 



List of Acronyms and their meaning 


The acronyms list is divided into two portions to explain the meaning (description) of each acronym

LTE Acronyms Part 1





LTE Acronyms Part 2

Dictionary for these acronyms 


It is important to understand each and every acronym listed above. Therefore, I will explain briefly each of the acronym below. Continue reading below 


MSIN

This is Mobile Subscriber Identification Number,assigned by operator. It is 9 or 10 bits long

MCC

The MCC identifies uniquely the country of domicile of a mobile subscriber. It consists of three digits. In LTE it is used in the con-
struction of network entity related identities such as the E-UTRAN Cell Global Identifier (ECGI), the Global eNodeB Identifier and the Tracking Area Identity. It is 12 bits long

MNC

Mobile Network Code. In conjunction with the Mobile Country Code (MCC), the MNC uniquely identifies a mobile network operator/carrier. In LTE it is used in the construction of network entity related identities such as the E-UTRAN Cell Global Identifier (ECGI), the Global eNodeB Identifier, and the Tracking Area Identity (TAI).

IMSI

International Mobile Subscriber Identity. A unique number associated with each mobile phone user. It is stored in the SIM inside the phone and is sent by the phone to the network. It is primarily intended for obtaining information on the use of the Public Land Mobile Network (PLMN) by subscribers. It is
also used for other functions such as to compute the Paging Occasions (PO) in
LTE.

PLMN

Public Land Mobile Network. Typically the mobile network run by one network operator in one country.

MMEGI

Mobility Management Entity Group Identifier Identifies MME group within a PLMN. It is Unique within a PLMN. It is 16 bits long

MMEC

Mobility Management Entity Code. Identifies a Mobility Management Entity (MME) within the scope of an MME Group within a Public Land Mobile Network (PLMN). It is 8 bits long

MMEI

It is an MME Identifier, to identify an MME uniquely within a PLMN. It is 24 bits long. MMEI = MMEGI + MMEC

GUMMEI

Globally Unique Mobility Management Entity Identifier. This consists of a Public Land Mobile Network (PLMN) identity, a Mobility Management Entity (MME) group identity and an MME code. The MME code is used in the
eNodeB by the Non-Access Stratum (NAS) node selection function to select the MME. It is  up to 48 bits long. GUMMEI = PLMN + MMEI 

M-TMSI

M Temporary Mobile Subscriber Identity. A temporary identity used to preserve subscriber confidentiality. It identifies a user between the UE and the Mobility Management Entity (MME). The relationship between M-TMSI and
International Mobile Subscriber Identity (IMSI) is known only in the UE and in the MME. It is 32 bits long and unique within an MME

S-TMSI

System Architecture Evolution (SAE) - Temporary Mobile Subscriber Identity. The
S-TMSI is a unique identifier assigned to the UE by the Mobility Management Entity (MME) in order to identify the UE context while supporting subscriber identity confidentiality. It is used to locally identify a UE within an MME group (Unique within a MME Pool). It is 40 bits long. S-TMSI = MMEC + M-TMSI 

GUTI

Globally Unique Temporary Identity (GUTI). This is an unambiguous identification
of the UE that does not reveal the UE or the user’s permanent identity in the Evolved Packet System (EPS). It also allows the identification of the Mobility Management Entity (MME) and network. It can be used by the network and the UE to establish the UE’s identity during signalling between them in the EPS. In short, GUTI is used to identify a UE between the UE and the MME on behalf of IMSI for security reason. It is no longer than 80 bits. GUTI = GUMMEI + M-TMSI

Value of GUTI you can see in your network


TAC


Tracking Area Code. The TAC is part of the Tracking Area Identity (TAI). It is a 16-bit integer. It is used to indicate eNodeB to which Tracking Area the eNodeB belongs (per Cell). It is unique within a PLMN

TAI

Tracking Area Identity (TAI). This is the identity used to identify tracking areas. It is composed of a Tracking Area Code (TAC), a Mobile Network Code (MNC) and a Mobile Country Code (MCC). It is up to 32 bits.

TAI = PLMN + TAC

Anatomy of Tracking Area Identity

How can you find the value of Tracking Area Identity in System Information?


Enodeb-id


evolved NodeB IDentifier. Used to identify an eNodeB uniquely within a Public Land Mobile Network (PLMN). The eNB-ID can have either 20 bits or 28 bits. It is also comprised within the Global eNB-ID, which uniquely identifies an eNodeB globally. The Global eNB-ID is constructed from the Mobile Country Code (MCC), Mobile Network Code (MNC) and eNB-ID.

The ENB ID is part of the globally unique E-UTRAN Cell Global Identity (ECGI), together with the PLMN and the Cell ID. 

cell-id

An internal descriptor for the cell.
The range is 0-255

ECI

E-UTRAN Cell Identifier (ECI). Used to identify a cell uniquely within a Public Land
Mobile Network (PLMN). The ECI has a length of 28 bits and contains the eNodeB-IDentifier (eNB-ID). The ECI can address either 1 or up to 256 cells per eNodeB, depending on the length of the eNB-ID.

In short, it is used to identify a cell within a PLMN

ECI = eNodeB-ID + Cell-ID

GENodeb-id

Global eNodeB Identity (GENB-ID) is used to identify the eNodeB over the S1-interface. 

GENB-ID = PLMN-ID + ENB-ID

ECGI 

E-UTRAN Cell Global Identifier (ECGI). The globally unique identity of a cell in E-UTRA.

ECGI = PLMN-ID + ECI

Explanation of ECGI , Cell ID and Global eNodeB ID



radio network temporary identifiers (RNTI)

When a UE is trying to get connected to the eNodeB or already connected to the eNodeB, RNTI identities are specified by the scheduler to indicate various types of information for the UE.


 The MAC schedular uses the PDCCH to indicate radio resource allocation, the RNTI that is mapped on the PDCCH depends on the Logical Channel Type  

In order to understand how many RNTI exist in the downlink. Take a look at the diagram below.

Different RNTIs used in Downlink portion of LTE



RNTI in the downlink

Radio Network Temporary Identifier. RNTIs are used to identify UEs within E-UTRAN, in particular in signalling messages between the UE and E-UTRAN. Several types of RNTI exist, including Cell-RNTI (C-RNTI), Paging-RNTI (P-RNTI), Random Access-RNTI (RA-RNTI) and System Information-RNTI (SI-RNTI).


The details about these different RNTIs are given below.



C-RNTI

Cell Radio Network Temporary Identifier. A UE identifier allocated by an eNodeB and unique within one cell controlled by that eNodeB. The C-RNTI can be reallocated when a UE moves to a new cell.

The range is 0x0001 ~ 0xFFF3 (16 bits)

TC-RNTI

A temporary identity, when the UE terminal has not been assigned a final identity. The TC-RNTI is used for further communication between the terminal and the network. Cell Radio Network Temporary Identifier. A UE identifier allocated by an eNodeB and unique within one cell controlled by that eNodeB. The C-RNTI can be reallocated when a UE moves to a new cell.

SPS-C-RNTI

Semi-Persistent Scheduling Cell- Radio Network Temporary Identifier. An identifier of the scheduling messages transmitted on the Physical Downlink Control CHannel (PDCCH) for semi-persistently scheduled Physical Downlink Shared CHannel (PDSCH) data transmissions. It allows the UE to differentiate
these messages from those used for dynamic scheduling messages identified by Cell- Radio Network Temporary Identifier (C-RNTI). It is transmitted as a scrambling code applied to the Cyclic Redundancy Check (CRC) of the PD-
CCH transmission.

P-RNTI

Paging-Radio Network Temporary Identifier. A fixed identifier used on the Physical Downlink Control CHannel (PDCCH) to indicate paging messages on the Physical Downlink Shared CHannel (PDSCH). It is transmitted as a scram-
bling code applied to the Cyclic Redundancy Check (CRC) of the PDCCH transmission.

RA-RNTI

Random Access Radio Network Temporary Identifier. The RA-RNTI is used to identify a message sent on the Physical Downlink Control CHannel (PDCCH) as a Random Access Response (RAR). It also indicates the time-frequency slot of the preamble to which the RAR corresponds.

SI-RNTI

System Information Radio Network Temporary Identifier (RNTI). A fixed identifier used on the Physical Downlink Control CHannel (PDCCH) to indicate broadcast System Information Blocks (SIBs) transmitted on the Physical
Downlink Shared CHannel (PDSCH). The SI-RNTI is known a priori to all UEs and thus allows SIBs to be distinguished from UEs’ data transmitted on the same channel. It is transmitted as a scrambling code applied to the Cyclic Redundancy Check (CRC) of the PDCCH transmission.

RA-RNTI

System Information Radio Network Temporary Identifier (RNTI). A fixed identifier used on the Physical Downlink Control CHannel (PDCCH) to indicate broadcast System Information Blocks (SIBs) transmitted on the Physical
Downlink Shared CHannel (PDSCH). The SI-RNTI is known a priori to all UEs and thus allows SIBs to be distinguished from UEs’ data transmitted on the same channel. It is transmitted as a scrambling code applied to the Cyclic Redundancy Check (CRC) of the PDCCH transmission.

RNTI in the uplink


In the Uplink we have two channels Physical Uplink Shared Channel (PUSCH) and Physical Uplink Control Channel (PUCCH). There are RNTIs assigned in case of uplink as well which are shown below. 


Before you read about RNTIs in the Uplink. Please take a look at TPC. TPC stands for Transmitter Power Control. The process of setting the transmission power, by
either open-loop or closed-loop means. It can be used to counteract propagation
effects such as path-loss, shadowing or fast fading, or to control interference to
neighbouring cells.

TPC-PUCCH-RNTI

The Radio Network Temporary Identifier (RNTI) used for sending Transmitter Power Control (TPC) commands applicable to the Physical Uplink Control CHannel (PUCCH).

TPC-PUSCH-RNTI

The Radio Network Temporary Identifier (RNTI) used for sending Transmitter Power Control (TPC) commands applicable to the Physical Uplink Shared CHannel (PUSCH).


I tried to cover a lot of identifiers you can encounter in your LTE journey. If you feel something has been missed or needs more elaboration. Post in your comments below with questions and critiques.


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