Core-CS Network Overview
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Content 1. WCDM WCDMA A Cor Core e Net Netwo work rk Over Overvi view ew 2. MSC pool network 3. AOIP and AOTDM
Release Evolution of WCDMA
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
R5 R4
R99
2000
2001
2002
function frozen time
R99 Network Architecture
GSM /GPRS BSS
MSC/VLR
PSTN ISDN
GMSC
BSC HLR/AUC
BTS PCU
SCE
SS7
RNC SMS NodeB
SCP GPRS
UTRAN
SGSN CG
Internet, Intranet
/
GGSN BG Other PLMN
R4 Network Architecture
HLR/EIR
GMLC/SMLC
SMS-C
MAP
MAP MAP SCP CAP
SIGTRAN SS7
BICC
GMSC Server
PSTN/ISDN
VMSC Server MAP
RANAP
UTRAN
BSSAP
AAL2 TDM
BSS
TDM/G.711
H.248
GSM/R99PLMN
MGW
MGW RTP(AAL2)/AMR IP(ATM) BackBone
TDM/G.711
IP network
R4 Core Network－Interface and Protocol (1) /ISUP/TUP MTP3
MTP3B
M3UA
MTP2
SSCF/SSCOP
SCTP
MTP1
AAL5/ATM
IP
MSC Server
Nc
GMSC Server H.248
Mc
Mc
SCTP
Nb
MGW
UDP IP
MGW
RTP
AAL2
Voice
UDP/IP
ATM
PCM
MTP3B SSCF/SSCOP/AAL5
Bearer and Control Separated MSC
Control Layer
H.248
Bearer Layer
Distributed Architecture－Flexible networking
The advantage of distributed networking：
Traffic route is the best, network performance is the best.
Mostly suitable for the operators with wide coverage. Traditional network Distributed network Inter-working mode. inter-working mode.
R5 Network Architecture CS domain
IP/ATM Backbone
MGW
GSM /GPRS BSS
PSTN/PLMN
MGW
VMSC Server GMSC Server
BSC
HLR/AUC/HSS
BTS
Iu-CS PCU
SCE
SS7
RNC
SMS
SCP NodeB
Iu-PS SGSN
UTRAN
PS domain
Internet, Intranet
GPRS backbone
GGSN MGW
CG
MGCF
BG IP backbone
S-CSCF
P-CSCF MRFC MRFP
IMS domain
Content 1. WCDMA Core Network Overview 2. MSC pool network 3. AOIP and AOTDM
What is MSC Pool?
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. MSC Pool MSC 1
MSC 2
MSC 3
RNC
BSC
Iu-flex/A-flex
RNC
BSC
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.
What are the advantages of the MSC Pool solution?
Advantages of the MSC Pool solution
Improved resource utilization
Enhance d network reliability
Reduced signaling traffic
Better DHD JGDJ quality D J of service
Improved Resource Utilization HLR
Location update
Occupied resource Total resource
Occupied Total resource resource Inter-MSC handover
800 K 900 K 200
800 200 K 900 K
500 K 600 K
HLR
Only intra-MSC location update is required.
Inter-MSC handover is unnecessary.
Total Occupied resource resource
500 K
MGW
MGW
BSC/RNC Residential area
BSC/RNC Commercial area
Non-MSC Pool network
Total Occupied resource resource
Residential area
Commercial area
MSC Pool network
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.
600 K
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
No inter-MSC location update is performed in the MSC Pool area,
HLR
which reduces signaling traffic
The serving MSC is not changed when an MS/UE roams within the MSC Pool area.
over the C/D interface.
No inter-MSC handover is performed in the MSC Pool area, which improve the QoS.
MSC 1
MSC 2
No inter-MSC handover is required.
BSS 1
BSS 2
BSS 3
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 2
MSC 1
CN-CS RAN Iu-CS
RNC
RNC
A
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. MSC server
MGW An NNSF entity can be the BSC, RNC, or M GW.
BSC/RNC
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 M SC. 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
CS/PS
29
VLR restart
28
…
User ID range
24
23
22
21
20
19
18
NRI range
17
16
15
14
13
…
User ID range
0
Relationship Between NRI and User ID
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
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.
Increasing the Utilization of A-Interface Circuits MSC server
MSC server
Mc Mc
MGW
MGW
BSC
BSC
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 ar e always unavailable, whereas people in other affiliate companies may find that cars are always left unused.
How to use the limited resources efficiently?
Facilitating Planning, Operation and Maintenance of A-Interface Circuits MSC server 1 MSC server 2 MSC server 3 MSC server 4
Capacity expansion of the MSC Pool
All the TDM resources of the Ainterface circuits must be planned again and redistributed after an MSC server is added to the MSC Pool.
Operation and Maintenance of AInterface Circuits in the MSC Pool
MGW
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
BSC
operation on the different MSC servers.
Ensuring Effective Utilization of A-Interface Circuits MSC server 1 MSC server 2 MSC server 3 MSC server 4
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
MGW
faulty MSC server cannot be used again, even though the circuits are not faulty. The A-
BLOCK
interface circuits are wasted.
Managing A-interface circuits on the MGW can prevent such
BSC
waste of A-interface circuits.
Managing A-Interface Circuits on the MGW MSC server 1 MSC server 2 MSC server 3 A-interface circuit management
TDM circuits are shared between multiple virtual MGWs to prevent resource waste if an MSC server fails, and therefore
increase the reuse ratio of Ainterface circuits .
Managing A-interface circuits on the MGW facilitates the
operation and maintenance of
Shared Ainterface circuits
Shared Ainterface circuits
Shared Ainterface circuits
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
Content 1. WCDMA Core Network Overview 2. MSC pool network 3. AOIP and AOTDM
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.
Application Scenarios of the AoIP Feature — Background Information BSS
BSS MSC-S
Nc
MSC-S A (IP or TDM)
A (IP or TDM) Mc/IP
Mc/IP
TRAU MGW A/TDM
= Signalling
Nb
TRAU
MGW A/TDM
= Transcoder
= User plane
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.
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 interf ace, 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 The AoIP feature reduces investment on the TC resources of BSCs,
Carriers
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.
Contents 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
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 t o 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.
Implementation Principles — Basic Call Scenario (MO Call) 1.
2.
3.
4.
5.
6.
7.
The BSC sends a CM SERVICE REQUEST message to the MSC. This message contains the speech codecs supported by the BSC. The UE sends a Setup message to the MSC. This message contains the speech codecs supported by the UE. The MSC server sends an Add Req message to the MGW to establish an IP termination. The MGW sends the allocated IP address, PayloadType, PTime, and ClockRate to the MSC server through the Add Reply message. The MSC server sends an Assignment Request message to the BSC. 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. The MSC server sends a Mod Req message to the MGW.
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 Establishment of the user plane is completed. Alert
Mod Req Mod Reply
Connect
Mod Req Mod Reply
Disconnect Release Release Complete Clear Command
Sub Req
Cleare Complete
Sub Reply
Implementation Principles — Basic Call Scenario (MO Call) 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
Implementation Principles — Basic Call Scenario (MO Call) 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 AMR codec description Current termination type
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.
Implementation Principles — Basic Call Scenario (MO Call) The Assignment Request message contains the major information elements, such as the IP address, call identifier, and codec. Speech Codec List (MSC Preferred) Transport Layer Address
Call Identifier
Implementation Principles — Basic Call Scenario (MO Call) The Assignment Complete message contains major information elements, such as the IP address of the BSC, selected codec, and supported codec (optional). Transport Layer Address
Speech Codec
Speech Codec List (BSS Supported)
Implementation Principles — Basic Call Scenario (MO Call) 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.
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 Handover Request Handover Request Ack Mod Req Mod Reply Handover Command Handover Complete Sub Req Sub Reply
Target BSC
Implementation Principles — Handover Scenario Handover Request
Handover Request ACK
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 c an 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
MSC Server Internal Handover Required
MGW
Add Req Add Reply Internal Handover Command Handover Detect Handover Complete
Mod Req Mod Reply Sub Req Sub Reply
Implementation Principles — Intra-MSC Handover Scenario Information elements in the Internal Handover Required message
Information elements in the Internal Handover Command message
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 t ype 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 , t he 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
