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Network-Based Mobility Management in the Evolved 3GPP Core Network

Irfan Ali, Motorola Inc.Alessio Casati, Alcatel-Lucent

Kuntal Chowdhury, Starent NetworksKatsutoshi Nishida, NTT DoCoMo Inc.

Eric Parsons, Nortel NetworksStefan Schmid, NEC Europe Ltd.

Rahul Vaidya, Samsung India Software Operations

IEEE Communications Magazine, vol. 47, no. 2, pp. 58-66, 2009.

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Outline • Introduction• Network-Based IP Mobility Management• Network-Based Mobility Architecture of the EPC (evolved

packet core)• Inter-Access System Mobility Flows– Non-Optimized Handovers– Optimized Handovers

• Summary and Future Work

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Introduction • The Evolved Packet Core (EPC) of 3GPP system– supports multiple access networks– one common packet core network for 3GPP radio accesses (E-

UTRAN, UTRAN, and GERAN), as well as other wireless and wireline access networks (e.g., eHRPD, WLAN, WIMAX, and DSL/Cable), • providing the operator with a common set of services and capabilities

across the networks.

• A key requirement of the EPC is to provide seamless mobility at the IP layer – as the user moves within and between accesses.– maintaining QoS is an important facet

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• This article provides an overview of the EPC specifications – a network-based mobility mechanism based on Proxy Mobile

IPv6 to enable mobility between access networks.– An overview of the “off-path” QoS model to supplement

PMIPv6 is also provided.

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Network-Based IP Mobility Management

• IP-based mobility management – enables the UE (user equipment) to preserve IP address (referred

to as home address), even when the UE changes its point of attachment.

• Two basic approaches – Network-based mobility management and – client-based mobility management.

• The UE obtains a new local-IP address (referred to as care-of-address) when it moves to a new point of attachment.

• It is then the responsibility of the UE to update its home agent, – which maintains a binding between the care-of-address and the home

address of the UE.

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• Network-based mobility management– the network (e.g., access gateway), on detecting that the UE has changed

its point of attachment, provides the UE with the same IP address that it had at its previous point of attachment.

– The network entity providing the IP address to the UE also handles updating the mobility anchor

– The UE is not aware of the mobility management signaling.

• network-based mobility management fulfills these requirements well:– provide handover capability– Efficient use of wireless resources – minimize UE involvement

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Network-Based IP Mobility Management (cont.)

• PMIPv6 was adopted as the IP mobility protocol for mobility between 3GPP and non-3GPP accesses – and as an option for intra-3GPP access mobility.

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Proxy Mobile IPv6 (PMIPv6)

• Mobile IPv6 requires client functionality in the IPv6 stack of a mobile node.– Host-based

• Network-based mobility is another approach to solving the IP mobility challenge.

• Per-MN-Prefix model – an addressing model where there is a unique network prefix or

prefixes assigned for each node.

S. Gundavelli, K. Leung, V. Devarapalli, K. Chowdhury, and B. Patil, "Proxy Mobile IPv6," IETF, RFC 5213, 2008.

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• Local Mobility Anchor (LMA)– has the functional capabilities of a MIPv6 home agent as with

the additional capabilities– the topological anchor point for the MN’s “home network”

prefix(es) in a PMIPv6 domain

• Mobile Access Gateway (MAG)– a function on an access router– tracks the MN’s movements– manages the mobility signaling on behalf of an MN

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homedomain

wide area network

correspondent node

MAG2MAG1

AP1 AP2

Initiation

LMA

home domain(e.g., 1400:0112::0/40)

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L2 access authenticationwith MN-ID

2Proxy Binding Update:

with MN-ID and the address of MAG1

(e.g., proxy-CoA1)

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Proxy Binding Ack.: with a home prefix

for the MN(e.g., 1400:0112::1/64)

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1) Unicast Router Advertisement2) Configure “home address”

(e.g., 1400:0112::1::30)

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homedomain

wide area network

correspondent node

MAG2MAG1

AP1 AP2

LMA

home domain(e.g., 1400:0112::0/40)

CommunicationCommunicate with the MN using the MN’s “home address” (1400:0112::1::30::MN_MAC)

Downlink : LMA tunnels packets that

destined to the MN’s “home address”

to Proxy-CoA1Uplink:

MAG1 tunnels packets from the MN to the LMA

data

packets

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homedomain

wide area network

correspondent node

MAG2MAG1

AP1 AP2

Handover within the Home Domain

LMA

home domain(e.g., 1400:0112::0/40)

1

L2 access authentication

2Proxy Binding Update:

with MN-ID and the address of MAG2

(e.g., proxy-CoA2)

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Proxy Binding Ack.: with the same home prefix

for the MN(i.e., 1400:0112::1/64)

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1) Unicast Router Advertisement2) use the same “home address”

(e.g., 1400:0112::1::30)

data

packets

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homedomain

wide area network

correspondent node

MAG2MAG1

AP1 AP2

LMA

home domain(e.g., 1400:0112::0/40)

Communication-2Communicate with the MN using the MN’s “home address” (1400:0112::1::30::MN_MAC)

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Network-Based Mobility Architecture of the Evolved Packet Core (EPC) - PMIP

Home Public Land Mobile Network

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Key requirements and impacts

• Support of IPv4 UE: – The EPC requires support for IPv4 only, IPv6 only, and dual stack hosts.

• Simultaneous access to multiple Packet Data Networks:– An access point name (APN) is used to identify a PDN.

• Included in the PMIPv6 proxy binding update (PBU)• the PDN GW (LMA) assign an IP address to the UE from the appropriate PDN.

• Support for overlapping address spaces of different PDNs:– for example, the use of private address spaces. – the generic routing encapsulation (GRE) key extensions for tunneling

packets between the LMA and MAG PMIPv6 are employed. • enables the network to disambiguate traffic related to different PDNs based on

the GRE.

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• Unique UE identification across accesses on EPC PMIPv6 interfaces:– an international mobile subscriber identity (IMSI)-based network-

access identifier (NAI), • the IMSI is the identity that currently is used to identify the UE in GSM/UMTS

networks– non-3GPP accesses must obtain the IMSI of the UE during access

authentication (either from the UE or from the HSS/AAA) and use the IMSI-based NAI on the PMIPv6 interfaces.

• Providing a PDN GW address to the target access:– The EPC support multiple PDN GWs serving the same PDN– the PDN GW identity along with the corresponding APN is stored in

the HSS/AAA• provided to the MAG in the target access during authentication.

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Network-Based Mobility Architecture of the Evolved Packet Core (EPC) - PCC

• The objective of the Policy and Charging Control (PCC) architecture – to provide QoS for IP-based service data flows – to charge for the resources

• provided based on the user’s subscription and other policy related to the access, network, and service.

• To not overload PMIPv6 signaling with QoS and PCC aspects, an “off-path” PCC model was developed

18Policy and Charging Control

Policy and Charging Rules Function :makes policy decisions for a UEand provides charging and QoS rules to the Policy and Charging Enforcement Function and QoS rules to the Bearer Binding and Event Reporting Function for enforcement.

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Network-Based Mobility Architecture of the Evolved Packet Core (EPC) - AAA

Authentication, Authorization and Accounting

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• The QoS information with the associated IP-flow description also must be provided to the access network– through the S-GW or A-GW node

• the off-path paradigm relies on the signaling of QoS information off-the-bearer-path from the PCRF directly to the access network.– the PMIPv6 protocol is used only for mobility management and

has no notion of QoS tunnels.

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Inter-Access System Mobility• Non-optimized handovers – cover a situation where the source network is not involved in

preparing resources in the target network.

• Optimized handovers– typically used when the UE is UNABLE to transmit and receive in

both the source and target networks simultaneously.

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Non-Optimized HandoversU

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Call

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Non-Optimized HandoversU

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scov

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d ha

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• For dual-radio-capable UEs, where the radios of both access

technologies can transmit and receive packets simultaneously, non-optimized handovers can provide a seamless handover experience to the end user. – A “make-before-break” can be achieved

• for single-radio terminals it would lead to substantial interruption time during inter-technology handovers.

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Optimized Handovers

LTE

CDMA2000

evolved-High Rate Packet Data

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Optimized HandoversPr

e-re

gist

ratio

n

‧The purpose of pre-registration is to avoid lengthy delays‧pre-registration can take several seconds

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Optimized HandoversPr

epar

ation

Exee

cura

tion

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• Release 8 of the EPC standard only defines optimized handover between eHRPD and E-UTRAN.

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Summary and Future Work• This article presented the motivation, design, and

realization of inter-access system mobility support based on Proxy Mobile IPv6 for the 3GPP EPC, – enabling a common packet core to be used for access

technologies. • The document also addresses the issues of QoS

provisioning and seamless handover support. • Detailed flows illustrating the use of PMIPv6 to achieve– non-optimized handovers between 3GPP accesses and other

non-3GPP accesses, as well as – optimized handovers between E-UTRAN and eHRPD were

provided.

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• Release 8 is the first release of the EPC specification• additional work is required to enhance and adapt the

new system – For instance, further study is required to determine

• how to support the UE to access the EPC through multiple-access networks simultaneously

• while providing mobility management and controlling the routing of individual IP flows between the different radio interfaces.