Vo
LT
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Anchor
An anchor application server (AS) provides IMS services to an LTE subscriber who
roams onto a CS network by allocating an IMS routing number (IMRN) to anchor
the LTE subscriber to the IMS network.
Anchor AS
IMS network
CS network
LTE subscriber
Benefits
Improves customer satisfaction
IMS subscribers who roam onto CS networks can still access
IMS services.
Reduces cost
Contributes to smooth network evolution from CS to IMS
networks. During network evolution, devices used on live
networks do not require any changes.
Acquires potential IMS subscribers
Enables CS subscribers to use IMS services.
Application Scenario
1
A VoLTE subscriber roaming onto a CS network
initiates a call and triggers an IMS service.
MO anchoring flow
VoLTE subscriber
CS network
2
IMS network
A CS subscriber attempts to use an IMS service.
CS subscriber
CS network
3
IMS network
A CS subscriber calls a VoLTE subscriber
using an irregular number
MT anchoring flow
CS subscriber
VoLTE subscriber
IMS network
CS network
Anchor Solution
The Anchoring solution includes IMRN segment-based anchoring and IMRN
prefix-based anchoring, depending on the different ways that the IMRN can
be obtained.
This solution is only used in the
MT anchoring flow.
IMRN prefix-based anchoring: The Anchor AS adds a prefix at
the beginning of the original called number to obtain an IMRN.
CS
IMS
Convergent
HLR/HSS
Anchor AS
he
1 Obtains
t
ins
RN
IM
Removes the prefix to
restore the called number
a
Anchor
service
data.
2
t
Ob
4
Routes the call to
3 the MGCF based
5
on the IMRN
VMSC/GMSC
MGCF
IMRN segment-based anchoring solution: The Anchor
AS obtains an IMRN from the planned IMRN segment and
stores the call information with the IMRN as an index.
I/S-CSCF
This solution can be used in
the MO and MT anchoring flow.
CS
IMS
Convergent
HLR/HSS
Convergent
HLR/HSS
Anchor AS
e
th ber
es m
or u
st d n
Re alle
c
1 Obtains
6
he
t
ins
RN
IM
a
Anchor
subscriptio
n data
2
t
Ob
Routes the call to
3 the MGCF based
on the IMRN
5
Obtains
the Anchor
AS address
4
VMSC/GMSC
MGCF
I/S-CSCF
Compared to the IMRN segment-based anchoring solution, the IMRN prefix-based
anchoring solution enables the Anchor AS not to consume live network resources
or maintain dynamical call data. In addition, this solution improves call routing
efficiency. Therefore, the IMRN prefix-based anchoring solution is recommended
to apply to the MT anchoring flow.
Key Operations in Anchoring Flows
An ATS, as an anchor AS on the IMS
network, allocates IMRNs to implement
Anchor services.
LTE subscribers need to subscribe to
anchoring data on the HSS before
using the Anchor service. In the
Anchor subscription data, the SCP
address is set to the Anchor AS.
CS IN services of
anchored subscribers
need to be triggered on
the IMS network.
In the MT anchoring flow, if
the CS
domain is selected to connec
t a call,
the Anchor AS is required to
suppress repeated MT anch
oring.
Charging
Charging on the originating side: In the MO
anchoring flow, the AS generates ACRs for the Anchor
service and sends them to the CCF, and the SCP
generates CDRs for IN services.
Charging on the terminating side: The AS generates
ACRs for a called party, regardless of whether the AS
selects the CS or IMS domain to connect a call to the
called party.
Domain Selection
LTE terminals may attach to LTE networks or CS networks based on signaling
strength. Therefore, an AS needs to use the terminating access domain selection
(T-ADS) function to select a domain to connect calls to LTE terminals.
Application scenario: In a call placed to an IMS subscriber, an MMTel AS
triggers the subscriber's IMS services, and then a service centralization and
continuity (SCC) AS determines whether the IMS subscriber is on an IMS or a
CS network.
Selects a domain to connect
the call to the called party.
SCC AS
LTE
2G/3G
Technical Principles
MO
MT
6 Determines the domain for UE_B
based on the information responded
by the convergent HSS/HLR
The processing flow
after domain selection
is the same as the
processing flow of
basic calls.
IMS
3
1
or
tf
es
qu
re DS
s a T-A
nd ’s on
Se _B ati
UE form
in
ATS
2 Triggers
UE_B's
services based
on the iFC
5
4
Receives an
INVITE
message
Sends requests to the
MME and SGSN for
domain selection
information
Convergent
HLR/HSS
I/S-CSCF
EPC
PS
MME
SGSN
LTE
2G/3G
Key Operations in Domain Selection
Queries the convergent
HSS/HLR for T-ADS
data.
1
SCC AS
Selects a domain based
on the T-ADS data
response, sent by the
convergent HSS/HLR.
3
Sh
Queries the MME and
SGSN for T-ADS data.
2
Convergent
HLR/HSS
MME
SGSN
An ATS functions as an SCC AS to implement domain selection.
Next issue
DRA Networking
Brief introduction
An SPS as a DRA converges and distributes Diameter signaling
messages, and works as a gateway between networks.
Prepared by: Li Xiaonan (content), Tang Suwen (figure)
Core Network Documentation Dept.
Copyright © Huawei Technologies Co., Ltd. 2015. All rights reserved.
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ow