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
Advanced Science and Technology Letters Vol.146 (FGCN 2017)
8 Copyright © 2017 SERSC
- TAU update response piggyback ESM Data Transfer, receive two
signals simultaneously
Fig. 2 (2) Legacy TAU and Data transmission procedure:
# of transmitted signal of UE : 2
- 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:
# of transmitted signal of UE : 2
- 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
Advanced Science and Technology Letters Vol.146 (FGCN 2017)
Copyright © 2017 SERSC 9
Fig. 3 (2) Legacy PDN connection and Data transmission procedure:
# of transmitted signal of UE : 3
- 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
Advanced Science and Technology Letters Vol.146 (FGCN 2017)
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
Advanced Science and Technology Letters Vol.146 (FGCN 2017)
Copyright © 2017 SERSC 11