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BSS overview (Review)RG20(BSS)
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Objectives
After this module the participants should be able to:
Label a diagram of the elements and interfacesused within the BSS
Describe the functions of the BSS elements
Describe RG20 transport features
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GSM subsystems
Control flow
User data flow
PSTN
PLMN
PSPDN
CSPDN
ISDN
PSTN Public Switched Telephone NetworkPSPDN Packet Switched Public Data Network
PLMN Public Land Mobile Network
CSPDN Circuit-Switched Public Data Network
ISDN Integrated Services Digital Network
OSS
NSS BSS Mobile Station
The GSM network is functionally divided into four elements. Base Station Subsystem
(BSS) is one of the main functional elements of the GSM network. The other elements
in the GSM network are the network switching subsystem (NSS), GPRS core networkto SGSN and network service and management subsystem (provided by NetAct).
The main function of the BSS is to connect the mobile subscriber's mobile station (MS)
to the GSM network and provide connections to the mobile switching centre (MSC), and
to GPRS core network, serving GPRS support node (SGSN). The BSS also takes care
of the mobility management of the cellular network including, for example, handover
management and various measurements.
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GSM subsystems
Network Switching Subsystem
Switching
Mobility Management
Connection
OSS
NSS
BSS
Base Station Subsystem
Radio Resource Management
Radio Link Management
Operation and Support System
Fault Management
Configuration Management
Performance Management
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Circuit-switched/Packet-switched services
Control flow
User data flow
PSTN
PLMN
SCN Switching Core Network
PCN Packet Core Network
OSS
SCNBSS
Mobile Station
PCNInternet
The Switching Core Network (SCN) comprises network elements that implement CSservices (e.g. voice calls), like Multimedia Gateway (MGW), Mobile switching centreserver (MSS).
Packet Core Network (PCN), on the other hand, supports PS data connections toexternal networks (e.g. Internet).
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BSS Network Elements
OSS
MSC orMGW/MSS
SGSN
BSCTCSM
BTS
BTS
BTS
MS
BSS
Transcoder, TCSM2
- considered as part of the BSC
- normally at the MSC site- used for converting the bit rate of
traffic channels between 64 and 16
kbit/s
- speech activity detection
- framing and synchronisation of the
vocoder block
- interfaces to the MSC / BSC
Base Station Controller, BSC
- terrestrial channel management
- configuration and management of traffic
channels
- frequency hopping control
- paging
- BTS and MS power control
- idle channel quality monitor
- quality and field strength control for active
channels
- handover control
- maintenance of BTS / BSC / TC
- interfaces to the NMS / BTS / TC / SGSN
Base Transceiver Station, BTS
- timing Broadcast Control Channels (BCCH) and Common Control Channels
(CCCH)
- forwarding MS and BTS measurements to the BSC
- detecting RACHs (Random Access Channels) from the MS
- channel coding and decoding on the radio path
- interleaving and deinterleaving on the radio path
- encryption and decryption on the radio path
- performing frequency hopping
- GMSK modulation, demodulation, up / down conversion and power amplifying
- transmitter RF signal combining
- receiver RF signal filtering, amplifying and multicoupling
- reporting idle traffic channel quality to the BSCTransmission Unit TRU
- provides Abis interface
- reallocates the Traffic and signalling channels in the BTS
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BSS interfaces
MSC
A Ater Abis Um
Gb
TCSM BSC BTS
SGSN
MS
MGW
AoIP(TC in MGW)
A interface
The interface between the mobile switching centre (MSC) or Multimedia Gateway
(MGW) and the base station controller (BSC) is implemented according to the GSMspecifications.
The Transcoder Submultiplexer (TCSM) is located normally at the MSC site, because
of the superior transmission savings possible with submultiplexing between the TCSM
and the BSC. A physical A interface used to consist of PCM lines or optical lines
between network elements. But with the introduction of the AoIP feature in RG20(BSS),
the A-interface between BSS and MGW can also be based on IP/Ethernet. There are
two scenarios for AoIP functionality:
1. AoIP Transcoder in BSSThe transcoder function is located in the BSS. The transcoder is the A over IP termination
point. The G.711/RTP/IP protocol is employed
The benefit for this configuration is that it utilizes existing transcoder capacity when
IP-connections in A-interface are used.
2. AoIP Transcoder in Core Network (MGW)
The transcoder function is located in the core network (that is, the 3G network architecture).
The BSC is the A over IP termination point. At the same time, the BSC
hides the mobility from the core network. The CODECx/RTP/IP protocol is
employed
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IP/Eth E2E Connectivity - Evolution OverviewBefore BSS13 RG20
BTS
BSC
TCSM /TRAU
NetActTM
Abis
Ater
A
GbO&M
SMLC
Lb+
Sigtran
MGWMSCHLR
RG10
Integrated IP/ETH interfaces for Gb, BSC-BSC, LB+, Sigtran and O&M available today
Abis IP available today
Ater /Abis IP integrated for BSC3i and TCSM3i available today; external for legacy Standardized AoIP with RG20
All interfaces are capable for IP/ETH connectivity with todays plans
Packet Abis coming on TOP offering additional advantages
BSC
BSC-BSC
SGSN
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Abis/A/Ater over IP/Ethernet for Installed Base
2G BTS
Packet SwitchedNetwork
Packet transport convenience and cost
A-1200
Legacy BSC
A-2200
BSC3i 1000/2000
Flexi BSC
ETIP
IP /
Ethernet
IP /
Ethernet
Note: See alternative IP / Ethernet evolution in RG20:using Flexi EDGE System module (BSS21443)
Supports CESoPSN (PWE3) functionality
Multiple synchronization methods available
Media conversion from TDM to IP/Eth
A-2200 can also be applied to A/Ater-interface
E1/T1
E1/T1
RG10EP
Feature ID(s): BSS21481
A-1200 and A-2200 supports Synchronous Ethernet, Timing Over Packet IEEE 1588-2008
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A over IP
Feature ID(s): BSS21341, BSS30380
Simplified Multipoint A configurationGreater transport efficiency
The A-interface between BSS and MGW will be based on IP / Ethernet
Several scenarios are under discussion in 3GPP standardisation:
Transcoder in the BSS (G.711 / RTP / IP protocol)
Transcoder in MGW (CODECx / RTP / IP protocol)
Simplifies the system configuration in Multipoint A / Flexible A scenarios
Improved transport efficiency for the Transcoder in the MGW scenario throughstandardising TrFO for GSM/EDGE
A over IP introduces new interface plug-in unit in the BSC and TCSM ETP-A Exchange Terminal for Packet transport over A interface ETP-A is responsible for IP processing and packet-PCM conversion for interfacing with
the BSC switching network
Available for Flexi BSC, BSC3i 1000/2000 and TCSM3i Flexi BSC and BSC3i 2000 (two cabinets): 4 ETP-A cards
BSC3i 1000 (one cabinet): 2 ETP-A cards
TCSM3i RG20: 5 cards per cabinet, TCSM3i RG10 or older: 3 cards per cabinet When ETP-A is used for A over IP in stand alone TCSM3i, IP/Ethernet connection is needed between BSC and
TCSM3i for control functions
RG20
Benefits for the Operator: The key benefit arises from the CAPEX / OPEX savingsthat can be derived through employing IP networking. The flexibility of the solution isalso increased. Further, configuration is also simpler in Multipoint A type network
scenarios.With Transcoder in the BSS, the existing transcoder capacity can be used along withthe new IP-connectivity at the A-interface.
With Transcoder in the Core Network, voice quality is enhanced since tandem codingis no longer necessary and latency is also improved. A reduced transcoding capacityis required in the BSS (realised in the Core Network).
Functional Description: There are two architecture options:
1. The Transcoder function is located in the BSS (that is, the standard GSMarchitecture). The Transcoder is the A over IP termination point.
The G.711 / RTP / IP protocol is employed.
2. The Transcoder function is located in the Core Network (that is, the 3Gnetwork architecture). The BSC is the A over IP termination point. At thesame time, the BSC hides the mobility from the Core Network.
The CODECx / RTP / IP protocol is employed.
For the Transcoding in BSS scenario, the ETP-A module is required for the TCSM3i,which is managed from the BSC via Ethernet. For this configuration both A over TDMand A over IP are supported within the same TCSM3i. The Abis interface may beeither Packet Abis (requiring both the ETS2 and ETP modules) or Legacy Abis.
When transcoding is performed within the Core Network, then the Abis interfacemust be a Packet Abis type. Calls to Handsets on Packet Abis are routed on A overIP directly to the Core Network transcoder. Calls to Handsets on a Legacy Abis arerouted via the TCSM3i to the Core Network (as normal). A handover between aPacket Abis BTS and a Legacy Abis BTS is managed by the Core Network as anInternal Handover.
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A over IP implementation scenarios- Transcoder in BSS
Feature ID(s): BSS21341
Note:
UltraSite, BTSplus, MetroSite support legacy Abis
Flexi EDGE supports both legacy Abis and Packet Abis
1) Support availability needs to be confirmed from MGW-supplier
RG20
Packet / TDM conversion
TDMIPoTDM
IPoTDMBSC
Packet Abis
TDM TDM
Ater
Eth IPoEthIPoEth
Packet Abis
Eth/ETP
TDM/ETS2+ETP
Alternative interface
AoIP
(G.711)
TC in BSS
Eth/ETP-APWE PWE
TCSM
MGW 1)
Flexi EDGE
Flexi EDGE
Flexi BSC
BSC3i 1000/2000
TCSM3iTDM
TDMTDM
TDMLegacy AbisAvailablewithRG20
MGW
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A over IP implementation scenarios- Transcoder in MGW
Note:
BTS must be connected via Packet Abis to BSC
BTS connected through legacy Abis to BSC is not supported until RG30. Prioravailability of Legacy Abis support with AoIP and TC in MGW following options exist:
Parallel use of AoIP (TC in MGW) for Packet Abis traffic and Ater/AoIP (TC in BSS) for legacyAbis. Ater can utilize TDM or integrated IP/Ethernet (PWE3 CESoPSN).
Feature ID(s): BSS30380
RG20
TDMTDMTDM
TDMIPoTDM
IPoTDM
TDM
BSC
Packet Abis
Legacy Abis
Eth IPoEthIPoEth
Packet Abis
AoIP
(CodecX )
TC in MGW
AvailablewithRG20
Flexi EDGE
Flexi EDGE
Flexi BSC
BSC3i 1000/2000
RG30
candidate
BSS101407
Any vendors
MGW
MGW
TC
TDM/ETS2+ETP
Eth/ETPEth/ETP-A
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Packet Abis over IP/Ethernet
Significant OPEX Savingscombining optimized Abis and low cost Transport Media
Feature ID(s): BSS21454
Full BSS integrated Abis Optimization
Cost efficient transport media (Ethernet)
EDGE Phase II and OSC optimized
BSC
Eth Eth
RG20
Packet SwitchedNetwork
IP
Packet Abis
Ethernet
IP
Packet Abis
Ethernet
Flexi EDGE
Compared to traditional TDM Abis(for typical traffic scenario)
Bandwidth savings
up to ~50%
Summary:
This fully integrated feature enables the transport of Abis information using native IPover Packet Switched Networks (via Ethernet).
Benefits for the Operator:
The operator is able to employ Packet Switched Networks in order to provide thetransport backhaul for the Abis traffic, offering significant OPEX savings due to themore cost effective physical media (Ethernet) and the simplified operation andmaintenance of the network that can then be derived. In addition to the physicalmedia benefit, Packet Abis also offers significant bandwidth savings in comparisonwith traditional TDM- or PWE-based packet transport since it introduces a veryefficient and fully integrated Abis Optimization capability. The integrated AbisOptimization also facilitates the introduction of high bandwidth features such asEDGE Evolution and OSC without necessarily increasing the backhaul bandwidthcapacity requirement. Bandwidth can be shared by CS, PS and Signalling traffic.There are no predefined limitations except the total available bandwidth provided bythe physical link.
Functional Description:
The Packet Abis solution removes the traditional TDM Abis structure, where thestatic relationship between the Air and the Abis Interfaces is eliminated. Further, AbisOptimization through the removal of silence and idle frames, multiplexing andbandwidth sharing for the CS-Userplane; PS-Userplane; Control-Plane andManagement-Plane achieves significant bandwidth savings. If no data needs to besent then no capacity is occupied/utilised.
The Packet Abis U-Plane is transported over UDP/IP and the C-Plane/M-Plane istransported over SCTP/IP. The physical interface supported is Ethernet.
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Packet Abis over TDM
Feature ID(s): BSS21440, BSS21539 (related)
Full BSS integrated Abis Optimization
Packet Transport Efficiency on TDM
EDGE PhaseII and OSC optimized
BSC
RG20
TDM Network
MLPPP
IP
E1/T1/SDH
MLPPP
IP
E1/T1/FB
Flexi EDGE
Significant OPEX SavingsOptimized Abis while keeping the existing transport infrastructure
Bandwidth savings
up to ~55%
Compared to traditional TDM Abis(for typical traffic scenario)
TDM TDM
Packet Abis Packet Abis
Summary:
This fully integrated feature enables the transport of Abis information using native IP overTime Division Multiplexed (TDM) Networks.
Benefits for the Operator:The operator can utilise the existing installed TDM Infrastructure, easing the introduction ofthe Packet Abis solution.
Packet Abis over TDM offers significant bandwidth savings in comparison with traditional TDMtransport since it introduces a very efficient and fully integrated Abis Optimization capability.Bandwidth can be shared by CS, PS and Signalling traffic as transmission resources are usedas pools. Pooling results as reduced number of TDM lines or reduced bandwidth withMicrowave radios/SDH transmission. Resource overbooking is possible: TRX number canexceed transmission line nominal capacity. There are no predefined limitations except thetotal available bandwidth provided by the physical links. The integrated Abis Optimization alsofacilitates the introduction of high bandwidth features such as EDGE Evolution and OSCwithout necessarily increasing the backhaul bandwidth capacity requirement.
Functional Description:
The Packet Abis solution removes the traditional TDM Abis structure, where the static
relationship between the Air and the Abis Interfaces is eliminated. Further, Abis Optimizationthrough the removal of silence and idle frames, multiplexing and bandwidth sharing for theCS-Userplane; PS-Userplane; Control-Plane and Management-Plane achieves significantbandwidth savings. That is, if no data needs to be sent then no capacity occupied/utilised.
The Packet Abis U-Plane is transported over UDP/IP/MLPPP and the C-Plane/M-Planetransported over SCTP/IP/MLPPP. The physical interface supported is TDM.
Multiple E1 or T1 interfaces effectively provide virtual common bandwidth (larger pool) usingMLPPP. Packet Abis over TDM is supported by all existing Flexi EDGE BTS transport units,including e.g. FIFA and FIYA/FIQA units. As Packet Abis over TDM allows to reducetransmission capacity of individual BTS site this allows overbooking. Overbooking meansadding TRXs beyond transmission line nominal capacity.
Packet Abis IP/TDM Aggregation feature (BSS21539) allows to chain multiple BTS-sites andperform transmission aggregation/optimization (=reduction) at every chained site. This uniqueMultistage aggregation technique provides the most cost efficient TDM transmission option
on the market.
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Exercise: Network Elements and interfaces
BSS