a technique of optimizing signaling overhead in the...

A Technique of Optimizing Signaling Overhead

in the 3GPP C-IoT Network

Kisoon Sung and Jaeseung Shin

Mobile Terminal Control Research Section, 5G Giga Communication Research Lab

Electronics and Telecommunications Research Institute

218 Gajeongro, Yuseonggu, Daejeon, 305-700, KOREA

{kssung, sjs}@etri.re.kr

Abstract. The control plane CIoT EPS optimization of the 3GPP CIoT standard

enables to support of efficient transport of user data (IP, non-IP) or SMS

messages over control plane via the MME without triggering data radio bearer

establishment, so reduces the total number of message when handling a short

data transaction. However, it is not sufficient to reduce signal transmission

significantly because the 3GPP maintains signal flows of existing LTE system.

The signal reduction is an important issue in CIoT system because of the

battery and network resource saving issues. In this paper, we propose a

signaling reduction technique to overcome this restriction.

Keywords: 3GPP, NB-IoT, C-IoT, EMM, ESM, CP CIoT EPS optimization

1 Introduction

IoT services are characterized by intermittent transmission and reception of a small

amount of data. The 3GPP defines a new standard CIoT to support these services.

CIoT is the Cellular network supporting low complexity and low throughput devices

for a network of Things. NB-IoT is a new cellular radio access technology that forms

part of Cellular IoT.

CIoT provides a new architecture for IoT and CIoT EPS optimizations for

optimizing signalling to minimize the power consumption of the terminals that send

and receive sporadic small data. CIoT EPS optimizations that can be requested

include control plane CIoT EPS optimization, user plane CIoT EPS optimization,

EMM-REGISTERED without PDN connection, SMS transfer without combined

procedure, non-IP PDN type, S1-U data transfer.

The control plane CIoT EPS optimization of the 3GPP CIoT standard enables to

support of efficient transport of user data (IP, non-IP) or SMS messages over control

plane via the MME without triggering data radio bearer establishment, so reduces the

total number of message when handling a short data transaction. However, it is not

sufficient to reduce signal transmission significantly because the 3GPP maintains

signal flows of existing LTE system. The signal reduction is an important issue in

CIoT system because of the battery and network resource saving issues.

Advanced Science and Technology Letters Vol.146 (FGCN 2017), pp.6-11

http://dx.doi.org/10.14257/astl.2017.146.02

ISSN: 2287-1233 ASTL Copyright © 2017 SERSC

In this paper, we propose a signalling reduction technique to overcome this

restriction.

2 Overview of CP CIoT EPS optimization in the 3GPP CIoT

The control plane CIoT EPS optimization enables to support of efficient transport of

user data (IP, non-IP) or SMS messages over control plane via the MME without

triggering data radio bearer establishment. The support of control plane CIoT EPS

optimization is mandatory for the NB-IoT network. The 3GPP defines two messages

to transmit user data via the control plane. The first is CONTROL PLANE SERVICE

REQUEST message. The purpose of this message is to transfer the EMM mode from

EMM-IDLE to EMM-CONNECTED mode and to carry an ESM message in an

encapsulated format. The second is ESM DATA TRANSPORT message. This

message is used to transport of user data via the control plane when UE is in EMM-

CONNECTED mode or UE in EMM-IDLE mode by piggyback in a CONTROL

PLANE SERVICE REQUEST message.

ESM Data Transport

:Control Plane Service Request

:initial UE Messages

DL data

UL data

ESM DATA transport

:Downlink NAS transport

UE eNB MME GW/HSS

S11-U connection establishment

SWG-PGW bearer modification

RRC Connection Request

RRC Connection Setup

ESM DATA transport

:DL Information Transfer

S1 release procedure

If downlink user data are available

No data

Fig. 1. Mobile Originated Data Transport in CP CIoT EPS opt. with PGW connectivity

Fig 1 describes the mobile originated data transport in idle mode UE with control

plane CIoT EPS optimization. CONTROL PLANE SERVICE REQUEST that is an

Advanced Science and Technology Letters Vol.146 (FGCN 2017)

Copyright © 2017 SERSC 7

initial NAS message can piggyback ESM DATA TRANSPORT that delivers user

data. It is a meaningful mechanism in respect of the signaling reduction because a

signaling message performs its own function as well as data delivery. However, it is

applied only CONTROL PLANE SERVICE REQUEST so an effect of the signaling

reduction is insignificant. The signaling reduction is very important in view of battery

consumption and radio resource utilization in CIoT networks.

In this paper, we propose expanding initial NAS message that can piggyback ESM

DATA TRANSPORT to minimize the signal transmission.

3 Optimization Technique for Reduction of the Signal Overhead

A NAS message is considered as an initial NAS message, if this NAS message can

trigger the establishment of a NAS signaling connection. For instance, the ATTACH

REQUEST, TRACKING AREA UPDATE REQUEST, DETACH REQUEST,

SERVICE REQUEST, EXTENDED SERVICE REQUEST, and CONTROL PLANE

SERVICE REQUEST message are initial NAS messages.

Attach without PDN connection is a new capability that has been introduced in the

3GPP rel.13 to allow UEs supporting CIoT optimizations to remain attached without

PDN connection, in other words if Attach without PDN connection is supported, the

UE needs not establish a PDN connection as part of the Attach procedure and the UE

and MME may release all the PDN connections at any time and remain EPS attached.

In this case, the procedure is used to establish the default bearer to a PDN by sending

the PDN CONNECTIVITY REQUEST message stand-alone. It may be useful for

cases where huge numbers of devices would keep a connection inactive for very long

period of time and seldom transmit data over it. Therefore, it can also be said that

PDN CONNECTIVITY REQUEST message operates as an initial NAS message.

CONTROL PLANE SERVICE REQUEST is initial NAS message and can carry

ESM data simultaneously. It can reduce signalling overhead so we think that it’s very

useful if other initial NAS message can carry ESM data too.

We propose that TRACKING AREA UPDATE REQUEST and PDN

CONNECTIVITY REQUEST message that are initial NAS messages can carry ESM

DATA TRANSPORT message.

The normal tracking area update process is to update the registration of the actual

tracking area of a UE in the network. If TAU period is adjusted to be equal to the time

of data generation, TAU and data transfer can be done simultaneously. Fig. 2

describes the signal count comparison between legacy TAU and simultaneous TAU

and data transmission procedure. In case 1 Tracking Area Update and 1 Data

Transfer, transmitted and received signals of UE are as follows:

Fig. 2 (1) Simultaneous TAU and Data transmission procedure:

# of transmitted signal of UE : 1

- TAU update request piggyback ESM Data Transfer, send two signals

simultaneously

# of received signal of UE : 1


8 Copyright © 2017 SERSC

- TAU update response piggyback ESM Data Transfer, receive two

signals simultaneously

Fig. 2 (2) Legacy TAU and Data transmission procedure:


- send TAU update request and ESM Data Transfer separately

# of received signal of UE: 2

- receive TAU update response and ESM Data Transfer separately

It can reduce the number of signal transmission by up to 50%.

Esm Data Transfer

:Tracking Area Update Request

Esm Data Transfer

:Tracking Area Update Accept

T3412 or

T3412Ext

T3412 or

T3412Ext

Tracking Area Update Request

Tracking Area Update Accept

T3412 or

T3412Ext

T3412 or

T3412Ext

App.

Generates

data

Esm Data Transfer

Esm Data Tranfer

UE MME UE MME

Separation timer between

data generation & transmissionApp.

Generates

data

Esm Data Transfer

:Tracking Area Update Request

Esm Data Transfer

:Tracking Area Update Accept

App.

Generates

dataTracking Area Update Request

Tracking Area Update Accept

Esm Data Transfer

Esm Data Tranfer

App.

Generates

data

(1) Simultaneous TAU and Data transmission procedure (2) Legacy TAU and Data transmission procedure

Fig. 2. Signal count comparison between legacy TAU and simultaneous TAU + Data

transmission procedures

Fig 3 is the signal flow of PDN connection procedure after attach without PDN

connection. When PDN CONNECTIVITY REQUEST message carries the user data,

it can be seen that the number of signal transmission has decreased. For PDN

connection establishment procedure and 1 data transmission, transmitted and received

signals of UE are as follows:

Fig. 3 (1) Simultaneous PDN connection and Data transmission procedure:


- ESM Connectivity request piggyback ESM Data Transfer, send two

signals simultaneously

- Send Activate Default EPS Context Accept

# of received signal of UE : 1

- Receive Activate Default EPS Context Request



Fig. 3 (2) Legacy PDN connection and Data transmission procedure:


- send ESM Connectivity request

- send Activate Default EPS Context Accept

- send ESM Data Transfer

# of received signal of UE: 2

- receive Activate Default EPS Context Request

- receive ESM Data Transfer

In this case, it can reduce the number of signal transmission by up to 40%.

ESM DUMMY MESSAGE

:Attach Complete

ESM DUMMY MESSAGE

:Attach Accept

Identification/Authentication/Security procedure

ESM DATA TRANSFER

:ACTIVATE DEFAULT EPS BEARER

CONTEXT REQUEST

UE MME

App.

Generates

data

ESM DUMMY MESSAGE

:Attach Complete

ESM DUMMY MESSAGE

:Attach Accept

Identification/Authentication/Security procedure

ACTIVATE DEFAULT EPS BEARER

CONTEXT REQUEST

UE MME

App.

Generates

data

(1) Simultaneous PDN connection and Data transmission

procedure

(2) Legacy PDN connection and Data transmission

procedure

ESM DATA TRANSFER

Fig. 3. Signal count comparison between legacy PDN connection and simultaneous PDN

connection + Data transmission procedures

According to the 3GPP traffic model, the number of devices per cell site sector is

calculated to be about 52547. Four different application traffic models are defined to

reflect the traffic characteristics of applications expected to be supported using

Cellular IoT. They are Exception reports (Ex smoke alarm), Periodic Reports (Ex

gas/water metering), network command (switch on the light) and SW update. Most of

these applications generate a small amount of data from about 20 bytes to 200bytes

with a generation cycle of 1hour to 2hour. These application data can be delivered in

one two ESM DATA TRANSGER MESSAGE. Fig2 and Fig3 shows this situation

and it can reduce the number of signal transmission by up to 50% as mentions earlier.

This figure shows that efficient use of radio resources is possible in an environment


10 Copyright © 2017 SERSC

where many terminals are concentrated, and the battery consumption of the terminal

can be greatly reduced.

4 Conclusion

Reducing the terminal scheduling load of the eNB, saving resources, and reducing the

battery consumption of the UE are the biggest challenges in NB-IoT systems, and

therefore it is absolutely necessary to keep the number of signaling transmissions to a

minimum. In this paper, we propose expanding initial NAS message that can

piggyback ESM DATA TRANSPORT. It is a very efficient technique to minimize the

signal transmission because C-IoT application generate a small amount of data with

very long period similar to the occasional signaling cycle.

Acknowledgement: This work was supported by Institute for Information &

communications Technology Promotion (IITP) grant funded by the Korea

government (MSIT) (No. 2014-0-00282, Development of 5G Mobile Communication

Technologies for Hyper-connected smart services).

References

1. 3GPP TS 24.301 Technical Specification Group Core Network and Terminals; Non-

Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3

2. 3GPP TS 23.401 Technical Specification Group Services and System Aspects; General

Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio

Access Network (E-UTRAN) access

3. 3GPP TR 45.820 Technical Specification Group GSM/EDGE Radio Access Network;

Cellular system support for ultra-low complexity and low throughput Internet of Things

(CIoT)

4. NB-IoT Deployment Guide to Basic Feature set Requirements, http://www.gsma.com/IoT



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