Cs c n overview

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Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
Core-CS Network Overview

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Page1
Content
1. WCDMA Core Network Overview
2. MSC pool network
3. AOIP and AOTDM

Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved. Page 2
Release Evolution of WCDMA
R4
R5
R99
 Inherit all the services and
functions of 2G ( GSM
and GPRS )
 CN is composed of CS
domain and PS domain
 Adopt WCDMA UTRAN
 Iu interface between RAN
and CN is based on ATM
 Inherit all the services and
functions of R99
 CS domain change: control is
separated from bearer, the
function of MSC can be fulfilled
by MSC SERVER and MGW.
 Packet voice supported by CS
domain, supporting ATM, IP,
TDM bearer
 Inherit all the services
and functions of R4
 IM domain is adopted
 RAN evolved to IP
 Enhanced IP QoS ability ,
supporting end to end IP
multimedia service
2000 2001 2002 function frozen time

R99 Network Architecture
GSM /GPRS BSS
BTS
BSC
NodeB
RNC
PCU
UTRAN
SCP
SMS
SCE
PSTN
ISDN
Internet,
Intranet
MSC/VLR GMSC
HLR/AUC
SGSN
CG BG
GGSN
GPRS骨干网/
Other PLMN
SS7

SCP
SMS-C
GMLC/SMLC
HLR/EIR
CAP
MAP
MAP
MAP
SIGTRAN
SS7
UTRAN
BSS
TDM
MGW
MGW
RTP(AAL2)/AMR
IP(ATM)
BackBone IP network
GSM/R99PLMN
PSTN/ISDNVMSC Server
RANAP
BSSAP
AAL2
H.248
MAP
BICC
GMSC Server
TDM/G.711
TDM/G.711
R4 Network
Architecture

R4 Core Network－Interface and
Protocol (1)
MGW
Mc Mc
Nb
Nc
MSC
Server
MGW
GMSC
Server
/ISUP/TUP
MTP3 MTP3B M3UA
MTP2 SSCF/SSCOP SCTP
MTP1 AAL5/ATM IP
H.248
SCTP UDP MTP3B
IP SSCF/SSCOP/AAL5
RTP AAL2 Voice
UDP/IP ATM PCM

Bearer and Control Separated
Control
Layer
Bearer
Layer
MSC
H.248

Distributed Architecture－Flexible
networking
Traditional network
Inter-working mode.
 The advantage of distributed networking：
 Traffic route is the best, network performance is the
best.
 Mostly suitable for the operators with wide coverage.
Distributed network
inter-working mode.

GSM /GPRS BSS
BTS
BSC
NodeB
RNC
PCU
UTRAN
SCP
SMS
SCE
PSTN/PLMN
Internet,
Intranet
HLR/AUC/HSS
SGSN
CG BG
GGSN
GPRS
backbone
MGW MGW
VMSC Server GMSC Server
IP/ATM BackboneCS domain
PS
domain
Iu-CS
Iu-PS
IP backbone
MRFP
IMS domain
MGW
P-CSCF S-CSCF
MGCF
MRFC
SS7
R5 Network Architecture

Content
2. MSC pool network
3. AOIP and AOTDM

 MSC Pool is a network scheme that adopts the Iu/A-Flex technology. In an
MSC Pool network, one RNC/BSC can be connected to multiple MSCs that
form an MSC resource pool to share the resources of the core network.
What is MSC Pool?
Iu-flex/A-flex
RNC
MSC 2MSC 1
RNC BSC BSC
MSC 3
MSC Pool

MSC Pool Network Architecture
Legacy network MSC Pool network
 In an MSC Pool network, one RNC/BSC can be connected to multiple MSCs. In this way, the
MSCs in the MSC Pool as a whole provide services as a single MSC with a large capacity for
the radio network side.

Advantages of the MSC Pool
solution
Improved
resource
utilization
Enhance
d
network
reliability
Reduced
signaling
traffic
What are the advantages of the MSC Pool solution?
DHD JGDJ
D J
Better
quality of
service

Improved Resource Utilization
 The multiple MSCs in the MSC Pool share the load in the whole Pool area. This
networking mode improves resource utilization in the core network and saves
investment on equipment.
Residential area Commercial area
HLR
BSC/RNC
MGW
Residential area Commercial area
HLR
BSC/RNC
MGW
900 K
Location update Only intra-MSC location
update is required.
Non-MSC Pool network MSC Pool network
Total resource
Occupied
resource
800 K200 K
Occupied
resource
Total
resource
900 K200 K800 K
Total
resourceOccupied
resource
600 K500 K
Total
resourceOccupied
resource
600 K500 K
Inter-MSC
handover
Inter-MSC
handover is
unnecessary.

Enhanced Network Reliability
…
MSC server
 Data can be backed up on multiple MSCs in the MSC Pool to implement disaster tolerance and
improve network reliability.

Reduced Signaling Traffic and Better
QoS
MSC 2MSC 1
HLR
BSS 1 BSS 2 BSS 3
No inter-MSC
handover is
required.
The serving MSC
is not changed
when an MS/UE
roams within the
MSC Pool area.
 No inter-MSC location update is
performed in the MSC Pool area,
which reduces signaling traffic
over the C/D interface.
 No inter-MSC handover is performed in
the MSC Pool area, which improve the
QoS.

Content
1. Overview
2. Basic Concepts
3. Principle

Content
2. Basic Concepts
2.1 MSC Pool and MSC Pool Area
2.2 Iu-Flex and A-Flex
2.3 NNSF
2.4 TMSI and NRI
2.5 Null-NRI and Non-broadcast LAI
2.6 CN-ID
2.7 Default MSC
2.8 Index of MSC in the MSC Pool
2.9 Virtual MGW

MSC Pool and MSC Pool Area
 MSC Pool: a group of MSCs sharing
traffic in parallel.
 MSC Pool Area: the area served by
an MSC Pool.
 If one or more RNCs/BSCs are
connected to an MSC Pool, all the
service areas of the RNCs/BSCs
comprise an MSC Pool area, and all
subscribers in the Pool area are
served by the MSCs in parallel in the
MSC Pool.
 Subscribers located in the MSC Pool
area need not to change the serving
core network node for roaming.

Iu-Flex and A-Flex
 Iu-Flex, short for intra-domain connection of RAN nodes to multiple CN nodes,
enables one RNC to connect to multiple CN nodes in the same CS/PS domain.
 A-Flex enables one BSC to connect to multiple CN nodes in the same CS/PS
domain.
MSC 2MSC 1
CN-CS
Iu-CS A
RAN
RNC RNC BSC BSC

NNSF
 NNSF : non-access stratum (NAS) node selection function.
 The NNSF enables the selection of a serving MSC from an MSC Pool for an MS.
 The entity that has the NNSF function is called an NNSF entity. The NNSF entity may
be BSC/RNC and MGW.
BSC/RNC
MGW
MSC server
An NNSF entity can be the
BSC, RNC, or MGW.
Select a serving
MSC for the MS/UE

TMSI and NRI
 A temporary mobile subscriber identifier (TMSI) is a temporary identifier that is
assigned to an MS/UE when the MS/UE is registered with an MSC. The TMSI is
used to increase the security of subscriber data.
 A network resource identifier (NRI) is used to identify an MSC serving a specific
MS/UE.
 One NRI defines a unique MSC in an MSC Pool.
 An MSC in one MSC Pool can be assigned with more than one NRI.
 Each NRI must be unique in an individual MSC Pool and between neighboring
MSC Pools. Otherwise, the NNSF entity cannot balance the load when routing
traffic to the MSCs.
31 30 29 28 … 24 23 22 21 20 19 18 17 16 15 14 13 … 0
CS/PS VLR restart
User ID
range
NRI range
User ID
range

Relationship Between NRI and User
ID
 In an MSC Pool network, the total number of bits used for NRI and user
ID is fixed.
 If the NRI is longer, the user ID becomes shorter. Consequently, the
MSC/VLR serves less subscribers. If the user ID is longer, the NRI
becomes shorter. In this case, less MSCs can be included in the MSC
Pool.
NRI Length
Number of MSCs in the MSC
Pool
Number of Subscribers
Served by the MSCs
5 25 = 32 2(29-5) = 16,777,216
6 26 = 64 2(29-6) = 8,388,608
7 27 = 128 2(29-7) = 4,194,304
8 28 = 256 2(29-8) = 2,097,152

Increasing the Utilization of A-Interface Circuits
 Example: Assume that there are 100 people in a company and 10 cars are exactly enough for
use. The company is divided into 10 affiliate companies, each with 10 people and one car. In
this case, people in some affiliate companies will always find that cars are always unavailable,
whereas people in other affiliate companies may find that cars are always left unused.
 How to use the limited resources efficiently?
BSC
MSC server
MGW
Mc
BSC
MSC server
MGW
Mc

Facilitating Planning, Operation and
Maintenance of A-Interface Circuits
 Capacity expansion of the MSC
Pool
 All the TDM resources of the A-
interface circuits must be planned
again and redistributed after an
MSC server is added to the MSC
Pool.
 Operation and Maintenance of A-
Interface Circuits in the MSC Pool
 Before performing the BLOCK
CIRCUIT operation for A-interface
circuits, check the MSC servers that
manage the A-interface circuits. If
these A-interface circuits are
managed by different MSC servers,
perform the BLOCK CIRCUIT
operation on the different MSC
servers.
BSC
MSC server 1
MGW
MSC server 2 MSC server 3 MSC server 4

Ensuring Effective Utilization of A-Interface
Circuits
 A-interface circuits are managed
by the MSC servers. If the MSC
server fails, the management
becomes invalid. In this case, the
A-interface circuits served by the
faulty MSC server cannot be
used again, even though the
circuits are not faulty. The A-
interface circuits are wasted.
 Managing A-interface circuits on
the MGW can prevent such
waste of A-interface circuits.BSC
MSC server 1
MGW
BLOCK

Managing A-Interface Circuits on the MGW
 TDM circuits are shared
between multiple virtual MGWs
to prevent resource waste if an
MSC server fails, and therefore
increase the reuse ratio of A-
interface circuits.
 Managing A-interface circuits on
the MGW facilitates the
operation and maintenance of
the MSC Pool. A-interface
circuits do not need to be
redistributed after an MSC
server is added to the MSC
Pool.
BSC1 BSC2 BSC3
Shared
A-
interface
circuits
Shared
A-
interface
circuits
Shared
A-
interface
circuits
A-interface
circuit
management

Content
2. MSC pool network
3. AOIP and AOTDM

Page 28
Application Scenarios of the AoIP Feature —
Background Information
 The A interface is an interface between
the Base Station Controller (BSC) and the
Core Network (CN). A-interface over IP
(AoIP) refers to the adoption of the IP
transmission mode over the A interface.
After implementation of the AoIP feature,
the BSC and the CN communicate with
each other over IP on both the signaling
plane and the user plane.

Page 29
Application Scenarios of the AoIP Feature —
Background Information
 In the 3GPP GERAN R7, the IP-based Signaling Transport (SIGTRAN) is added
over the A interface on the basis of the existing TDM signaling transmission, as
shown in the preceding figure. On the user plane, however, only the TDM
transmission is used. In addition, the transcoder is located in the BSS. Only the
PCM (G.711) codec is defined for the A interface over TDM (AoTDM).
 In the 3GPP GERAN R8, the IP transmission protocol is introduced to the A
interface so that the low-cost intermediate IP network can be used for
transmission on the user plane of the A interface.
MSC-S
MGW
BSS
A (IP or
TDM)
Mc/IP
MSC-S
MGW
Mc/IP
Nb
Nc
A/TDM A/TDM
= Signalling
= User plane
A (IP or
TDM)
TRAU
BSS
TRAU
= Transcoder

Page 30
Application Scenarios of the AoIP Feature — Benefits
 The end-to-end Transcoder Free Operation (TrFO) is implemented for 2G calls, which is consistent
with the TrFO implemented for 3G calls.
 Transmission resources are saved. The IP network adopts the statistical multiplexing technology.
During network access, the bandwidth is allocated according to the requirements. The bandwidth
allocation is not subject to limitations such as the granularity limitation of the TDM network. When a
compressed codec is transmitted, the AoIP feature can effectively reduce the bandwidth usage and the
Capital Expenditure (CAPEX).
 The maintenance cost is reduced. When IP transformation of the core network, A interface, and BSS is
complete, various types of networks are maintained as a single type of network. This lowers the
requirements on the technical capability of maintenance personnel and reduces the Operating
Expenditure (OPEX).
Beneficiary Description
Carriers
The AoIP feature reduces investment on the TC resources of BSCs,
enables sharing of the IP bearer network, reduces the 2G maintenance
costs, and saves transmission resources. It also facilitates deployment of
the MSC Pool solution.
Subscribers
The AoIP feature helps implement the TrFO throughout the call process,
improve the voice quality, and thus improve satisfaction of subscribers.

Page 31
Chapter 2 Implementation Principles of the
AoIP Feature
1.1 Comparison Between AoIP and AoTDM
1.2 Basic Call Scenario
1.3 Handover Scenario
1.4 Intra-BSC Handover Scenario
1.5 Data Service Scenario
1.6 Performance Measurement
Contents

Implementation Principles — Comparison Between
AoIP and AoTDM
Item AoTDM AoIP
Signaling plane: applying for the
termination at the access side
through the Mc interface
The MSC server sends a request to the MGW to
apply for the TDM termination.
The MSC server sends a request to the MGW to apply
for the IP termination with the specified codec. It also
obtains the IP address and port number of the
termination.
Signaling plane: sending the
Assignment Request message
through the interface at the access
side
The MSC server allocates and sends the CIC to
the BSC.
The MSC server sends the codec, IP address, and port
number of the termination allocated by the MGW to the
BSC.
Signaling plane: receiving the
Assignment Complete message
through the interface at the access
side
The BSC directly selects a circuit based on the
CIC. Therefore, the BSC sends the Assignment
Complete message the MSC server, informing the
MSC server that assignment is complete.
The BSC allocates and sends the IP address and port
number to the MSC server through the Assignment
Complete message.
Signaling plane: confirming the
termination at the access side
through the Mc interface
This step is not required. The MSC server sends the IP address and port number
allocated by the BSC to the MGW. The MGW then
establishes the user plane between the MGW and the
BSC.
Signaling plane: intra-BSC
handover
The MSC need not take part in this step. The MSC must take part in this step.
User plane: transcoder The transcoder is located on the BSC. The transcoder is located on the MGW.
TFO and TrFO: speech codec Only the G.711 uncompressed codec is
transferred.
Compressed codecs, such as FR, EFR, HR, and AMR
are transferred. This saves the bandwidth of the A
interface.
Data service codec When the bearer is being prepared, the MSC
server does not send any codec, but sends a
message that contains the information element
PLMNBC.
The MSC server sends the data service code.
User experience The subscribers do not notice any difference between the AoTDM and the AoIP. They are not aware of whether
the A interface is TDM or IP based.

Page 33
1. The BSC sends a CM SERVICE REQUEST
message to the MSC. This message contains the
speech codecs supported by the BSC.
2. The UE sends a Setup message to the MSC. This
message contains the speech codecs supported by
the UE.
3. The MSC server sends an Add Req message to the
MGW to establish an IP termination.
4. The MGW sends the allocated IP address,
PayloadType, PTime, and ClockRate to the MSC
server through the Add Reply message.
5. The MSC server sends an Assignment Request
message to the BSC.
6. On receiving the Assignment Request message, the
BSC selects a codec and allocates the IP address
and port number used on the user plane. The BSC
then sends an Assignment Complete message that
contains the codec selected by the BSS and the
codec list supported by the BSS.
7. The MSC server sends a Mod Req message to the
MGW.
Implementation Principles — Basic Call Scenario (MO Call)
BSC MSC Server MGW
CM Service Request
Classmark Request
Classmark Update
CM Service Accept
Setup
Call Proceeding
Add Req
Add Reply
Assignment Request
Assignment Complete
Mod Req
Mod Reply
Alert Mod Req
Mod Reply
Connect Mod Req
Mod Reply
Disconnect
Release
Release Complete
Clear Command
Cleare Complete
Sub Req
Sub Reply
Establishment of the user plane is completed.

Page 34
The CM SERVICE REQUEST message contains the information
element Speech Codec List (BSS Supported), indicating the
bearer types and codec types supported by the BSC.
Structure of the information element Speech Codec List
Structure of the information element Speech Codec Element

Page 35
Current termination type
AMR codec description
The ADD REQ message contains the following information:
Codec list used for the call
Parameters of each codec, such as PayloadType, PTime, and ClockRate
Rate indicators such as ACS/SCS if the multi-rate codec (such as 2G AMR) is
used

Page 36
Implementation Principles — Basic Call Scenario (MO
Call)
Through the Add Reply message, information such as the allocated IP address,
PayloadType, PTime, and ClockRate are sent to the MSC server.

Page 37
The Assignment Request message contains the major information
elements, such as the IP address, call identifier, and codec.
Transport Layer Address
Call Identifier
Speech Codec List (MSC Preferred)

Page 38
The Assignment Complete message contains major information elements, such as
the IP address of the BSC, selected codec, and supported codec (optional).
Speech Codec
Speech Codec List (BSS Supported)Transport Layer Address

Page 39
The MSC server sends a Mod Req message to the MGW. This message contains the IP
address and port number of the BSC. If the MSC server requires modification of the
codec type on the MGW, this message also contains the corresponding codec,
Payloadtype, PTime, ClockRate, and ACS.

Page 40
Implementation Principles — Handover Scenario
During handover, the messages exchanged between the MSC server and the MGW are
modified in the same way as those in the basic call scenario. The Handover Request
and Handover Request Ack messages are modified in the similar way as the
Assignment Request、Assignment Complete message. Note the following difference:
In the basic call scenario, the MSC server can obtain the BSC bearer type through the
CM Service Request and Paging Response messages.
In the handover scenario, the MSC server can obtain the bearer type of the target BSC
by querying the relevant table.
Source BSC MSC Server MGW
Handover Required
Add Req
Add Reply
Mod Req
Mod Reply
Handover Complete
Handover Request
Handover Command
Sub Req
Sub Reply
Target BSC
Handover Request Ack

Page 41
Implementation Principles — Handover Scenario
Handover Request
Handover Request ACK

Page 42
Implementation Principles — Intra-MSC Handover Scenario
The intra-BSC flow is added after the AoIP feature is implemented. Through
frequent handovers, the general voice quality of the network can be improved.
According to the 3GPP AoIP specifications, the BSSAP
signaling supports sending of the information about the
change in the codec if the codecs used before and after
the handover are compatible with each other. The BSC
sends the Handover Performed message containing the
latest codec information to the MSC server only after
the handover is complete. If the codecs used before
and after the handover are not compatible with each
other, the BSC sends a Handover Request message to
the MSC server and the MSC server takes part in the
intra-BSC handover. The MSC server sends the new IP
address, port number, and codec information of the
BSS to the MGW, instructing the MGW to use the
information to establish a termination. In this way, the
codec is modified.
BSC MGW
Add Req
Add Reply
Mod Req
Mod Reply
Sub Req
Sub Reply
Internal Handover Required
Internal Handover Command
Handover Complete
Handover Detect
MSC Server

Page 43
Implementation Principles — Intra-MSC Handover
Scenario
Information elements in the Internal Handover
Required message
Information elements in the Internal Handover
Command message

Page 44
Implementation Principles — Data Service Scenario
According to the definition in 3GPP 43903, rate adaptation is implemented by the BSC during the data
service. The rate between the BSC and the UMG is fixed to 64 kbit/s. The packet time is 20 ms. The
RTP is encapsulated in compliance with RFC4040. The UMG needs to convert the bearer type of the
data. Only the PLMNBC and GSM channel coding need to be sent over the A interface. The UP
packets are not sent over the A interface. Based on the PLMNBC and GSM channel coding , the UMG
adds the IWF resource.
Like the codec negotiation during the voice call, the data service also has a redundancy negotiation
process.
Assignment Request
Assignment Complete

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