LTE-A Mobile Relay Handling: Architecture Aspectseshare.stust.edu.tw/EshareFile/2017_1/2017_1_fbeae8bd.pdf · A USER AND CONTROL PLANE ASPECTS OF DIFFERENT ARCHITECTURE ALTERNATIVES

LTE-A MOBILE RELAY HANDLING:

ARCHITECTURE ASPECTS報告者：洪偉晉

班級：碩研資管一甲

學號：MA590203

課程：南台科大資管所無線網路與行動計算

授課老師：陳偉業

報告出處：Wireless Conference (EW), Proceedings of the 2013 19th European

INTRODUCTION

INTRODUCTION

• Support for fixed cellular relays was introduced in 3GPP Rel’ 10 (LTE-Advanced

• coverage of high data rates

• the cell-edge throughput

• temporary network deployment

• In the 3GPP Technical Report [1] different architecture alternatives have been

analyzed.

• proxy S1/X2 has more benefits in compare with other three alternatives

• This alternative was selected as the baseline architecture for Rel’ 10

INTRODUCTION

• This paper is devoted to architecture issues concerning mobile relay handling that

imposes additional network requirements

• persistent IP connectivity during relay mobility

• group mobility for mobile terminals attached to the mobile relay

• Other architecture alternatives could have more advantages

• review the 3GPP fixed relay architecture alternatives

• select the most appropriate one for enabling mobile relay (MR)

• compare control and user planes of different architecture alternatives

• consider network scenarios based

• latency budget analysis

A USER AND CONTROL PLANE ASPECTS OF DIFFERENT ARCHITECTURE

ALTERNATIVES

A USER AND CONTROL PLANE ASPECTS OF DIFFERENT ARCHITECTURE ALTERNATIVES

• Compare the architecture Alt 2 (Proxy S1/X2) and Alt1 (Full-L3 relay)

• they present two different philosophies

• Alt 2 (Proxy S1/X2)

• the S-GW/P-GW functionality serving the relay is embedded in the DeNB

• the relay S1/X2 interfaces in the architecture are terminated in the DeNB

• Alt 1 (Full-L3 relay)

• the S-GW/P-GW entity serving the relay is separated from the DeNB

• the relay is transparent for DeNB


• User plane aspects

• Alt 2(Proxy S1/X2)

• the S-GW/P-GW functionality related to the relay is located within the DeNB

• allows avoiding situations when packets traverse via two S-GW/P-GWs

• the home eNB GW functionality is added into the DeNB

• results in the “ProxyS1/X2” architecture

• a GTP tunnel establishment per User Equipment (UE) bearer

• Alt 1(Full-L3 relay)

• the S-GW/P-GW functionality serving the relay is out of the DeNB

• the user plane packets are delivered to/from a UE via two gateways

• this architecture was not selected as the baseline one for the fixed relay

• the packet forwarding path is longer in this architecture that can lead to large latency


• User plane aspects

• Alt 1(Full-L3 relay)

• the separation of the S-GW/P-GW from the DeNB can bring some benefits

• this S-GW/P-GW can be considered as a stable “IP anchor point” to support mobility of the relay

• One more specific feature of the Alt 1

• transparence of the DeNB for the full L3 relay

• a GTP tunnel per UE bearer is entire without any switching in the DeNB and goes from the S-

GW/P-GW serving the UE directly to the relay


• Control plane aspects

• Alt 2

• the S1-AP messages are sent in two steps:

• between the MME serving the UE and the DeNB

• between the DeNB and the relay

• The messages are encapsulated by SCTP/IP in the MME serving the UE

• transferred over an EPS data bearer of the relay

• the S-GW/P-GW functionality for the relay’s EPS bearers is incorporated into the DeNB

• Alt 1

• the S1-AP signalling messages are sent in one step directly between the MME serving the UE and the relay

• the S1 signalling messages sent between the relay and the MME serving the UE are mapped on user plane EPS

bearers of the relay



• Alt 2

• In the architecture Alt 2 there is a single S1 interface relation between the relay and the DeNB

• there is one S1 interface relation between the DeNB and each MME (serving the UEs) in the MME

pool

• the relay has to maintain only one S1 interface (to the DeNB)

• the DeNB maintains one S1 interface to each MME in the respective MME pool

• All S1 signalling connections between relay and MMEs are processed by the DeNB for all UE-

dedicated procedures

• All non-UE-dedicated S1-AP procedures are terminated at the DeNB, and handled locally

between the relay and the DeNB, and between the DeNB and the MME



• Alt 1

• there is one S1 signalling relation for each connected UE on the given S1 interface between the

relay and the MME serving the UE

• the relay has to maintain one S1 interface relation to each MME in the respective MME pool

• The S1 interface and the signalling connections go through the DeNB transparently



RELAY MOBILITY SCENARIOS BASED ON DIFFERENT ARCHITECTURES


• The mobility scenarios to support Mobile Relay (MR) when it moves from Source-

DeNB (S-DeNB) to Target-DeNB (T-DeNB)

• Alt 2

• The S-GW/P-GW functionality serving the relay (or MR in case of mobility) is in the DeNB

• The S-GW/P-GW (MR) entity handles the IP packets flowing to/from the relay and the

attached UEs

• When the MR changes its backhaul from S-DeNB to T-DeNB, the user plane IP connectivity

that was established between the MR and S-DeNB is missed




• Alt 2

• The group mobility for the attached UEs is not supported.

• The MR needs to obtain a new IP address and establish the IP connectivity with T-DeNB.

• This phase of the attach procedure includes

• relay backhaul reconfiguration that is completed by OAM (Operations, Administration and

Maintenance)

• relay-initiated S1/X2 setup

• S1/X2 eNB configuration update

• one more problem because of the IP connectivity is lost when the MR


• Alt 2

• When the MR goes from the S-DeNB to the T-DeNB the connection between the MR and its

OAM is interrupted

• Alarms in the MR generate bursts of high-priority traffic and have to be transported in real

time

• Not appropriate at it is to support these requirements and some enhancements are

needed.


• Alt 1

• When the MR moves from the S-DeNB to the T-DeNB, the S-GW/P-GW of the MR serves as

anchor

• IP connectivity is handled through retaining a stable “IP anchor point” in the network

• The IP address of the MR is not changed during the movement.

• As a result group mobility for the attached UEs is supported

• It is not required also to perform the network re-entry at the T-DeNB

MOBILE RELAY HANDOVER PROCEDURE FOR DIFFERENT ARCHITECTURE

ALTERNATIVES

MOBILE RELAY HANDOVER PROCEDURE FOR DIFFERENT ARCHITECTURE ALTERNATIVES

• Concentrate on the handover procedure when the mobile relay moves between S-DeNB

and T-DeNB

• the relay supports a subset of the UE functionality in order to be wirelessly connected to

the DeNB

• the legacy UE handover procedure can be re-used as a basis for the mobile relay handover

procedure

• like the legacy UE handover procedure includes three phases

• handover preparation

• handover execution

• handover preparation


• Mobile relay handover procedure for Alternative 2

• Handover preparation phase

• S-DeNB makes handover decision based on measurement reports received from the MR

• The S-DeNB sends a Handover Request to the selected T-DeNB

• The T-DeNB performs the Admission Control procedure based on the received E-RAB QoS

information to increase the likelihood of a successful handover




• Handover execution phase

• The RRC message contains RRC Connection Reconfiguration information to be sent by the S-

DeNB towards the MR for the relay backhaul reconfiguration specified for the Un interface

• The S-DeNB sends the SN Status Transfer to the T-DeNB taking into account the Un interface

specific functionality

• After receiving the RRC Connection Reconfiguration message

• the MR completes synchronization and reconfiguration of the relay backhaul to T-DeNB

• The T-DeNB performs uplink allocation towards the MR.

• The MR sends the RRC Connection Reconfiguration Complete message to the T-DeNB to confirm the

handover



• Handover execution phase

• The MR configuration is downloaded from the OAM system through the T-DeNB

• The S1/X2 setup is initiated between the MR and the T-DeNB

• T-DeNB updates its configuration on the S1/X2 interfaces



• Handover completion phase

• The mobile relay sends a Path Switch Request

• The S-GW/P-GW of the UEs switches downlink path and sends packet data to the T-DeNB sends

one or more "end marker" packets on the old path to the S-DeNB

• The S-GW/P-GW of the UEs issues a User Plane Response to the MME (UEs) which sends a Path

Switch Acknowledge message towards the mobile relay

• if the UEs attached to the mobile relay are served by different S-GWs/MMEs, the above items of the

handover completion phase are completed for each S-GW/MME serving the UEs

• the S-DeNB can release related resources associated to the MR context




• The handover preparation phase is similar to one for the Alternative 2

• Handover execution phase is also similar excepting last three items

• there is no need in this case for the MR to download configuration from the OAM

• initiate the S1/X2 setup

• it is not required for the T-DeNB to update its configuration on the S1/X2 interfaces



• Handover completion phase

• The T-DeNB sends a Path Switch Request to the MME serving the MR to inform that the MR was

detached from the S-DeNB

• The MME serving the MR issues a User Plane Update Request to the S-GW/P-GW serving the MR

to switch downlink path. Now packet data are sent to the T-DeNB

• The S-GW/P-GW of the MR sends one or more "end marker" packets on the old path to the S-

DeNB to release resources related to the user plane

• It also issues a User Plane Update Response to the MME of the MR which sends a Path Switch

Request Acknowledge to the T-DeNB.


• The handover procedure for the MR moving between S-DeNB and T-DeNB based in the

architecture Alt 1 looks more simplified than one based on the architecture Alt 2

• it does not include the network re-entry procedure for the MR at T-DeNB

• the separated S-GW/P-GW (MR) acting as the MR stable IP anchor point

• architecture Alt 2

• the user plane is handled by the S-GW/P-GW of a UE

• The UEs attached to the MR can be connected to different the S-GW/P-GWs (UE) that can be under

control of different MMEs (UE)

• It can lead to more complex and time-consuming procedure because of multiple data path switching

COMPARATIVE ANALYSIS WITH OTHERALTERNATIVES

COMPARATIVE ANALYSIS WITH OTHERALTERNATIVES

• We briefly re-analyze the other architectural solutions, Alt 3 and Alt 4

• Alt 3

• that relay bearers are terminated in the DeNB

• Alt 4

• that the user plane of the S1 interface is terminated in the DeNB

• These alternatives have the same crucial problems as the architecture Alt 2

• the S-GW/P-GW functionality serving the relay in the architectures Alt 3 and Alt 4 is embedded into the

DeNB

• no “IP anchor point” handling IP connectivity for the mobile relay performing the handover procedure

• Some enhancements can be done to support the relay mobility in the Alternatives 2, 3, and 4

PERFORMANCE EVALUATION OF BASIC RELAY ARCHITECTURE SCENARIOS

(LATENCY ANALYSIS)

PERFORMANCE EVALUATION OF BASIC RELAYARCHITECTURE SCENARIOS (LATENCY

ANALYSIS)


ANALYSIS)


ANALYSIS)

• the handover procedure duration when the MR moves from S-DeNB to T-DeNB is

analyzed for the Alt 1 and Alt 2.

• Assumed that one-way transmission time between the relay and the DeNB (2 ms) is the

same as the transmission time between a UE and a relay/Enb

• OAM configuration downloading for the MR takes 7 ms

• S1/X2 setup initiation between the MR and the T-DeNB is around 17 ms

• The T-DeNB configuration update takes 2 ms.


ANALYSIS)

• As seen from Table I

• the latency to perform the MR handover procedure from S-DeNB to T-DeNB for the Alt 1 is

about 1.5 times less than for the Alt 2

• The handover procedure for the Alt 2 requires additional operations when MR performs the

network re-entry at the TDeNB

• Alt 2, it is supposed in Table I that all UEs attached to the MR are under the same S-

GW/MME serving the UEs

• If they are connected to different S-GWs/MMEs it can lead to multiple downlink data path

switching

• The architecture Alt 1 shows better performance in a mobile relay network.

CONCLUSIONS

CONCLUSIONS

• In the study we have reviewed the basic 3GPP fixed relay architecture alternatives

• That for mobile relay changing its backhaul link (Un interface) from Source-DeNB to

Target-DeNB

• Alt 1 (a full L3 relay) has more benefits than other architecture alternatives

• The architecture Alt 1 supposes the stable IP anchor point supporting continuous IP

connectivity for the mobile relay.

• does not require the time-consuming relay re-attach procedure when backhaul link is re-

established to TDeNB

• it handles interworking between the mobile relay and OAM without connectivity interruption

• the handover procedure does not require some downlink data path switches related to different

S-GWs/MMEs serving UEs.

Documents

LTE-A Mobile Relay Handling: Architecture Aspectseshare.stust.edu.tw/EshareFile/2017_1/2017_1_fbeae8bd.pdf · A USER AND CONTROL PLANE ASPECTS OF DIFFERENT ARCHITECTURE ALTERNATIVES