Local Switching for Packet Abis
Short Description
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Description
RG25 (BSS) Network Engineering Information Local Switching for Packet Abis BSS21327 Andrzej Maciołek Network Engineering NWS LTE RA E2E Mgmt SA NE GSM<E Migration February 2011
Please always use the latest version of the materials which can be found under the link: https://sharenet-ims.inside.nokiasiemensnetworks.com/Open/410495798 For internal use only 2 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis BSS21327
Table of Contents • • • • • • •
Background Information Feature Details Impact on Planning and Dimensioning Feature Dependencies Database Parameters Performance Measurements Feature Impact Analysis and Verification
For internal use only 3 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis BSS21327
Dependency Table GSM800
GSM900
GSM1800
GSM1900
MSS
MGW
NetAct
-
-
-
-
-
-
OSS5.3 CD Set 3
BSC
SGSN
BTS Talk Family
BTS MetroSite
BTS UltraSite
BTS FlexiEDGE
BTS Flexi MultiRadio
BTSplus
S15 BSC3i (1000/2000 ) FlexiBSC
-
N
N
N
Y EX4.1
Y EX4.1
-
For internal use only 5 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Background Information
For internal use only 6 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Background Information
• Normally, MS-to-MS calls are always transferred through all network elements of the GERAN network, i.e. BTSs, BSCs, trans-coders and a core network Speech and signalling
Abis
MS1
BTS1
E1/T1
BSC1
TRAU1
MSC1
MSC2
TRAU2
BSC2
BTS2
MS2
• This is also the case for calls established between terminals served by the same cell, co-sited cells or cells served by a common BSC
Calls and related signalling are transferred through all network entities Speech and signalling
Abis
MS2
MS1
BTS1
E1/T1
BSC1
For internal use only 7 © Nokia Siemens Networks
TRAU1
MSC1
Local Switching for Packet Abis / A. Maciołek / April 2010
MSC2
TRAU2
BSC2
BTS2
Local Switching for Packet Abis Background Information
• According to statistics, in ‘isolated areas’, e.g. in remote towns and villages, even up to 95% of calls is established locally • As a result, it can be imagined that such calls would not be transferred to the network elements beyond the BTS thus saving Abis resources • Such the concept, known as local switching, is valid for speech data only => signalling data would be transferred ’traditionally’ to allow using existing features => otherwise, a completely new control plane concept had to be invented • Local switching does not apply to PS calls as well because normally a PS call is established ’non-locally’ between MS and a server (GGSN) and not between two MSs
Abis
MS2 Speech
MS1
BTS1
E1/T1
Signalling
BSC1
For internal use only 8 © Nokia Siemens Networks
TRAU1
MSC1
Local Switching for Packet Abis / A. Maciołek / April 2010
MSC2
TRAU2
BSC2
BTS2
Local Switching for Packet Abis Background Information
Up to BSS13 ED
• No solutions supporting local switching
BSS13 ED
• Solutions operating with the legacy E1/T1 Abis interface => new dedicated HW
(RGW, CGW) must be installed to support local switching: – BSS21436/BSS30370 Local Switching for Satellite Abis/Terrestrial Abis – Up to 8 E1/T1 links (16 E1/T1 links) or up to 60 TRXs (16 RGW) supported by RGW (CGW)
For locally switched calls only signalling is conveyed to BSC
Aggregating and switching local traffic IP over Ethernet IP over Ethernet for satellite Abis for satellite Abis IP over TDM for IP over TDM for terrestrial Abis terrestrial Abis
E1 /T
1 Abis
RGW
1 /T E1
For internal use only 9 © Nokia Siemens Networks
Abis
E1/T1
CGW BSC
Local Switching for Packet Abis / A. Maciołek / April 2010
TRAU
MSC
PSTN
Local Switching for Packet Abis Background Information
RG25 (BSS) • A completely new implementation fully relying on the packet Abis is introduced without involving equipment of external vendors: – BSS21327 ”Local Switching for Packet Abis”
For internal use only 10 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Feature Details
For internal use only 11 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
• In RG25 local switching means a possibility to transfer MS-to-MS voice calls originated and terminated by the same BSC directly between involved BTSs without going through the controlling BSC: – Speech data is directly switched between the involved BTSs – Signalling/PS data is transmitted through all network entities => there is no
impact of the local switching on conveying signalling/PS data – Packet Abis is a must => legacy E1/T1 between BTS and BSC is not allowed with the RG25 local switching
• There are two main configurations of the local switching: – Intra-BCF local switching => two terminals are served by the same BTS (BCF)
=> the call can be switched internally by the BTS (BCF) – Inter-BCF local switching => two terminals are served by different BCFs belonging to the same BSS and to the same local switching area => the voice call is directly transferred from one BTS (BCF) to another BTS (BCF) without involving the BSC
For internal use only 12 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
• Intra-BCF local switching with the packet Abis over TDM Switching local traffic
Speech and signalling
For locally switched calls only signalling is conveyed to BSC
Packet Abis over TDM
BSC
TRAU
MSC
• Intra-BCF local switching with the packet Abis over Ethernet Switching local traffic
For locally switched calls only signalling is conveyed to BSC
Speech and signalling
IP network Packet Abis over Ethernet
Packet Abis over Ethernet
BSC For internal use only 13 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
TRAU
MSC
Local Switching for Packet Abis Feature Details
• Inter-BCF local switching with the packet Abis over Ethernet For locally switched calls only signalling is conveyed to BSC
Switching local traffic
Speech and signalling
IP network Packet Abis over Ethernet
Packet Abis over Ethernet
BSC
TRAU
MSC
• Inter-BCF local switching with the packet Abis over TDM Switching local traffic and aggregating nonlocally switched traffic
For locally switched calls only signalling is conveyed to BSC
Speech and signalling
Packet Abis over TDM Packet Abis over TDM
hub-BTS For internal use only 14 © Nokia Siemens Networks
BSC
Local Switching for Packet Abis / A. Maciołek / April 2010
TRAU
MSC
Local Switching for Packet Abis Feature Details • • • • •
Local Switching Area (1/2) A locally switched voice call can be established in a so-called local switching area The local switching area is built up of up to 16 sites including a hub-BTS (packet Abis over TDM) and is identified by the packet Abis BCF group ID (PABGID) Any two local switching areas must not overlap with each other, i.e. a site cannot belong to any two local switching areas Speech data of locally switched calls is transported between the involved sites without engaging a BSC Signalling/PS data is managed in a ‘traditional way’ irrespectively of the local switching functionality
For internal use only 15 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Local Switching Area (2/2) • In case of the intra-BCF local switching the area consists of a single BCF only • In case of the inter-BCF local switching the area consists of few BCFs, out of which one must operate as a hub-BTS (packet Abis over TDM) Each BCF creates a LS area
PABGID = 0
Local switching areas with inter-BCF local switching
PABGID = 0 PABGID = 0 PABGID = 0
PABGID = 0
Local switching areas with intra-BCF local switching only
Local switching area with intra-BCF locally switched calls only
Up to 16 BTSs in the LS area including hub-BTS
Local switching area with inter-BCF locally switched calls PABGID = 2 PABGID = 1 PABGID = 3
For internal use only 16 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Hub-BTS (1/3) • Hub-BTS is a mandatory network element of the local switching with the inter-BTS local switching and packet Abis over TDM • The hub-BTS is a fully equipped BTS acting also as a site of the local switching area with the IP forwarding functionalities • The following IP forwarding functionalities are supported by the hub-BTS: – Aggregating IP packets arriving from BTSs of the local switching area and
forwarding them outside to a BSC (non-locally switched calls) or inside to other BTSs of the local switching area (locally switched calls) – Receiving IP packets from the BSC and forwarding them to the BTSs of the local switching area (non-locally switched calls) – Handling IP packets from the BSC if they are dedicated for the hub-BTS
• The hub-BTS is not required in a configuration for the intra-BTS local switching or with the packet Abis over Ethernet
For internal use only 17 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Hub-BTS (2/3) • A hub-BTS is connected to a BSC with the packet Abis over TDM
• The same interface type, i.e. TDM, must be used between BTSs of a given local switching area and the hub-BTS => mixture of the Ethernet/TDM links is not allowed
• The hub-BTS connected to the BSC/BTSs stores a routing table, i.e. a list of IP addresses assigned to BCFs of the local switching area and their corresponding ML-PPP bundles => the routing table is created according to the content of the SCF (Site Commissioning File) file sent by a BSC to the hub-BTS
For internal use only 18 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details Hub-BTS (3/3) • Hub-BTS configuration with the packet Abis over TDM • Up to 8 HDLC links can be configured in a single ML-PPP bundle
Synchronisation recovery
ML-PPP(2)
HDLC(1)
HDLC(1)
ML-PPP (3) HDLC(3)
HDLC(3)
BSC 192.168.0.y
Packet Abis over TDM
TSLy
hub-BTS
Grooming @ BTS2 => BTS2 and BTS3 connected to the hub-BTS on a single E1/T1 interface, but with direct ML-PPP bundles
192.168.0.102
TSLx …
TSLy
Local Switching for Packet Abis / A. Maciołek / April 2010
192.168.0.101
ML-PPP bundle
ML-PPP HDLC(6) (4) HDLC(6)
6) C(
call 1
… HDLC(2)
BTS1 Packet Abis over TDM
L HD
TSLx
HDLC(3)
) (6
Few HDLC links are bundled in a single MLPPP bundle
HDLC(1)
le nd bu PP -PPP -P L M (4) ML
Each E1/T1 line is mapped to a HDLC link
SCF file loaded to the hub-BTS by the BSC
ML-PPP bundle
2) C( DL
For internal use only 19 © Nokia Siemens Networks
192.168.0.100
ML-PPP HDLC(2) HDLC(5) (1)
• Up to 8 E1/T1 lines terminated at a hubBTS
ML-PPP(3)
LC HD
bundles can be served by the hub-BTS
192.168.0.101
P H PP LM M (2) TD ) er (2 ov LC is HD Ab et ck Pa
• Up to 16 ML-PPP
ML-PPP(4)
ML-PPP bundle
• Up to 68 HDLC links (due to memory limitations) can be configured in total for all ML-PPP bundles (in a hub-BTS)
192.168.0.103
BTS2 192.168.0.100
BTS3 192.168.0.103
Local Switching for Packet Abis Feature Details
Local Switching with Packet Abis over Ethernet • In case of the packet Abis over Ethernet each BTS (BCF) of the local switching area has a list of other BCFs located in the same local switching area and IP addresses associated with the particular BCFs • The hub-BTS is not needed as each local BCF is aware of other local BCFs belonging to the same local switching area according to the list
For internal use only 20 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Local Switching with Packet Abis over Ethernet • Local switching area configuration with the packet Abis over Ethernet BTS2
Packet Abis over Ethernet
Packet Abis over Ethernet
IP network
call 2
192.168.0.100*
call 1 call 2 call 3
BTS1
call 3
192.168.0.101 cal l1
BSC
Pac ket A Eth bis o er n v et er
192.168.0.y
White-list of BCF IDs and IP addresses exchanged inside LSA BTS1
192.168.0.101 *
BTS2 192.168.0.100 Synchronisation recovery
* - CS U-plane IP addresses
For internal use only 21 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details • • • •
Lawful Interception The operator may request to intercept also locally switched calls A BSC contains a database with up to 150 000 records with MSISDN numbers of subscribers to be intercepted During the local call detection procedure the BSC sniffs the MSISDN of the MS originating or terminating the call from the DTAP signalling messages If the match is found in the database the locally switched call is to be intercepted: – The local switching is disabled for the call being established or… – … the call is locally switched (to maintain the same user perception in terms of
the end-to-end speech delay), but copies of the locally switched speech frames are sent to MSC via BSC and TCSM/MGW
• => the behaviour depends on the BSS database parameter settings (see slide 55)
For internal use only 22 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
TrFO with Local Switching (1/4)
• In general, TrFO (Trans-coder Free Operation) is a functionality allowing for
transmission of speech frames between MSs without trans-coding at MGW when the same codec type is used by MSs at both connection ends • The differences between the TrFO and TFO* (Tandem Free Operation) are: – TrFO employs an out-of-band signalling whereas the TFO operates with an in-band signalling (some bits in speech frames are stolen to convey signalling) – TrFO is executed with the A over IP and trans-coding done at MGW (core side) whereas TFO runs when trans-coding is done at TCSM (BSS side) – A call setup is completed after the codec negotiation by TrFO is finished => extra delay (to be measured in tests) in a call setup procedure is expected; the codec negotiation by TFO is started just after the call setup is completed => no extra delays – With TrFO only radio codec + header bits are transmitted => bandwidth savings; with TFO also G.711 bits are transmitted on the MSB (Most Significant Bits) bits => no bandwidth savings
• For more details please refer to NEI BSS21341 ”A over IP” * - see BSS14 NEI slides ”AMR Wideband & TFO” (BSS20960, BSS21118) https://sharenet-ims.inside.nokiasiemensnetworks.com/Download/409226619 For internal use only 23 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details •
• • • • •
TrFO with Local Switching (2/4) Due to the fact that local switching calls are established directly between the BTSs without involving trans-coders the TrFO operation is the only option for the locally switched calls, i.e. there is no room for trans-coding functionalities in the local switching transmission chain TrFO negotiation is done between the involved BCSUs (not in MGW) Therefore, the same speech codec type and the same active codec set (in case of AMR) must be applied to both connection ends to successfully establish a locally switched call The following speech codec types are supported with the local switching: EFR, FR, HR, AMR-NB FR, AMR-NB HR and AMR-WB The same codec type must be used in DL and UL directions Link adaptation (in case of AMR) is done considering radio conditions at both connection ends => the worse radio conditions forces the use of more robust codec mode
For internal use only 24 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
TrFO with Local Switching (3/4)
• The only supported AMR-NB codec modes are 4.75, 5.9, 7.4 and 12.2 kbps (the ”Config-NB-Code-1” codec modes configuration): – If other codec modes are configured at the connection ends the TrFO is not
possible => the establishment of the locally switched call is not possible – TrFO is possible on a locally switched call with AMR-NB codec modes operating in FR at one connection end and in HR mode at another connection end as long as 4.75, 5.9 and 7.4 kbps codec modes are on-air => AMR packing/unpacking can work with the locally switched calls
• Before a locally switched call is established between two MSs served by
BTS(s) of the local switching area, BCSUs serving the involved BTSs exchange information on supported speech codec types based on MS preference and BTS capability: – If a common codec type is found, then the local switching is possible – If a common codec type is not found, then the call is established without local switching
For internal use only 25 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
TrFO with Local Switching (4/4)
MS1BTS1 (AMR FR)
MS2BTS2 (AMR HR) ACS: 4.75, 5.9, 7.4
ACS: 4.75, 5.9, 7.4, 12.2
MS1MS2
encoding
common ACS: 4.75, 5.9, 7.4
local switching ok MS1 BTS1 decoding
FR-HR matching
MS1BTS1 (EFR)
MS2BTS2 (AMR FR, EFR)
EFR
ACS: 4.75, 5.9, 7.4, 12.2
IP network
MS1MS2 EFR
BSC
MS2 BTS2
local switching ok
max. 12.65* kbps + IP overhead
* - AMR-WB source bit rate of the least robust codec mode
An operator must configure the same AMR codec mode sets in all BTSs of the local switching area For internal use only 26 © Nokia Siemens Networks
Codec type optimisation with the channel mode modify procedure, i.e. AMR changed to EFR
Local Switching for Packet Abis / A. Maciołek / April 2010
MS1BTS1 (EFR)
MS2BTS2 (AMR HR)
EFR
ACS: 4.75, 5.9, 7.4
MS1 does not support AMR
MS1MS2
local switching nok
not found
Load conditions forces use of AMR-HR
Local Switching for Packet Abis Feature Details Congestion Control • In principle, the congestion control mechanisms for the local switching act in the
same way as in a ‘classical’ packet Abis network as described in the NEI for Packet Abis • The BTSBSC connections are monitored for the congestion => locally switched calls are not taken into account in BU (Bandwidth Utilisation)/PL (Packet Loss) evaluation • PL evaluation is done based on PS/CS traffic exchanged with the BSC • Local switching with the packet Abis over TDM: a hub-BTS can indicate a congestion situation to a BSC on the hub-BTSBSC interface: – The BSC replies to all local BTSs => the congestion control mechanisms affect all the local BTSs even if some of them do not really experience a congestion situation => voice quality is compromised in the whole local switching area
• Local switching with the packet Abis over Ethernet: any local BTS can indicate a
congestion situation • The TX queues handling is done as described in the NEI for Packet Abis with the only difference: – C- and M-plane packets forwarded to the local BTSs are never dropped For internal use only 27 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details Handovers (1/3)
• Intra-cell HO => 3 cases are distinguished: – Between TRXs belonging to the same cell represented by the BTS object =>
local switching is supported after the HO – Between TRXs represented by different BTS objects, but belonging to the same cell represented by the SEG and BCF object => local switching is supported after the HO – Between TRXs represented by different BTS and BCF objects, but belonging to the same cell represented by the SEG object (multi-BCF) => local switching is supported after the HO if the BCFs belong to the same local switching area intra-cell HO inside BTS
intra-cell HO inside BCF
intra-cell HO between BCFs
local switching NOT released
local switching NOT released
local switching NOT released if BCFs are in the same LS area
BTS-1 BCF-1
SEG-1
BTS-1 BCF-1 BTS-2 BCF-1
For internal use only 28 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
SEG-1
BTS-1 BCF-1 BTS-2 BCF-2
Local Switching for Packet Abis Feature Details
Handovers (2/3) • Inter-cell internal BSC HO: – Local switching is supported after the HO if the cells belong to the same local switching area
• Inter-cell external HO: – Local switching is released after the HO
inter-cell HO between BCFs inter-cell HO between BCFs
local switching NOT released if BCFs are in the same LS area
SEG-1
BTS-1 BCF-2
local switching released
BTS-1 BCF-1
BTS-2 BCF-3
For internal use only 29 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
BCF-1
BCF-1
Local Switching for Packet Abis Feature Details
Handovers (3/3) • When selecting a target channel, if possible, a BSC selects a channel of the same type and codec (in case of AMR) as used in a source channel • Local switching is signalled to the target cell by sending the new local switching IE in the CHANNEL ACTIVATION message • Also the new IP address and the UDP port number of the target cell are signalled in the CHANNEL ACTIVATION message
For internal use only 30 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Local Switching Release • Local switching is released in the following cases: – External inter-cell HO (inter-cell HO between cells belonging to different BCSs) – Internal inter-cell HO to a cell configured in a different local switching area – Intra-cell HO to a BCF configured in a different local switching area (multi-BCF) – Supplementary services are activated during an on-going call (call holding, multi-party connection, explicit call transfer and cellular text telephone modem) even if the services refer to subscribers from the same local switching area – Codec mismatch after any handover was completed
• => the call continues with speech frames transferred to MSC via BSC and TCSM/MGW • => the call never becomes locally switched again if local switching once released Local switching release may cause audible effects on voice quality due to an additional delay, especially in the case with the satellite backhaul For internal use only 31 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Application Scenarios (1/3) • Connection of small/medium and isolated towns/villages to a GSM network, which
Isolated area – small/medium town
Savings on satellite links due to lower Abis utilisation
Lower load on Ethernet link towards BSC
BTS
BTS
IP network
BTS
BTS BTS
hub-BTS
BSC
BTS
BTS Packet Abis over TDM BTS
Local switching area
For internal use only 32 © Nokia Siemens Networks
Packet Abis over Ethernet
BTS
Local switching area
Local Switching for Packet Abis / A. Maciołek / April 2010
BTS
Isolated area – small/medium town
are not reachable with landline transmission (microwave link difficult or not possible at all) and the only alternative is a satellite Abis • Voice traffic is a dominant service and majority of calls is established locally
Local Switching for Packet Abis Feature Details
Application Scenarios (2/3) • Serving large traffic generated mostly among subscribers located, e.g. in the same office, campus or area • Local switching areas typically consisting of a single site Local switching area Traffic switched locally in a site
Lower load on Ethernet link towards BSC
Lower load on TDM link towards BSC
Traffic switched locally in a site
IP network
BTS The case is justified if it leads to a reduction of PCM lines!
BTS
Packet Abis over TDM
BSC
Packet Abis over Ethernet Local switching area
Local switching area
For internal use only 33 © Nokia Siemens Networks
BTS
Local Switching for Packet Abis / A. Maciołek / April 2010
BTS
Local Switching for Packet Abis Feature Details
Application Scenarios (3/3) • Increasing PS capacity on the Abis interface serving an isolated area, especially
over satellite, without the need to extend Abis capacity => locally switched traffic does not require Abis resources => the released Abis resources can be utilised in a different way, e.g. to increase bandwidth for PS services • The majority of calls is established locally
Isolated area – small/medium town
PS traffic generated by subscribers increases
Locally established calls are switched by the hub-BTS
Locally switched calls are not put to Abis => more room for PS calls
BTS BTS
BTS
hub-BTS BTS
BTS
Local switching area
For internal use only 34 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
BSC
Local Switching for Packet Abis Feature Details Benefit s • Reduction of Abis transmission costs (OPEX) in an operator’s network: – Potential savings particularly significant in case of satellite links, which are very
expensive – Possibility of deploying coverage for remote communities with low ARPU at a reasonable price where the only option is to use the Abis satellite links – Option to introduce new features or expand capacity of base stations without expanding the backhaul
• Improved speech quality by: – Shorter transmission delays, especially in case of a satellite backhaul – No trans-coding due to removal of trans-coders from the transmission path => transcoder free operation (TrFO) is applied
• Bandwidth savings on A interface, but only with the A over IP with trans-coder (TC) in media gateway (MGW)
Transmission is the main priority for operators in emerging markets. Transmission costs from a BTS to a BSC, either over satellite or terrestrial leased line, makes up a large percentage of the Total Cost of Ownership (TCO) of a GSM site. For internal use only 36 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Impact on Planning and Dimensioning
For internal use only 37 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (1/11) Summary Interfac e
Realisation
Connection
Abis
Packet Abis over TDM/Eth
BTSBSC
Ater
TDM
BSCTCSM BSCMGW
TDM
There are savings – see the next slides ”Empty” speech frames are transmitted to keep the connection alive => no savings
BSCMGW
Only SID frames are sent to MGW every 160 ms for AMR-NB and AMR-WB and every 480 ms for remaining codec types to keep the connection alive => there are savings – see slide 49
TCSMMGW
IP flows are transmitted to keep the connection alive => no savings: SID frames are sent to MGW every 160 ms for AMR-NB and AMR-WB and every 480 ms for remaining codec types NoData frames for AMR-NB and AMR-WB and speech frames with the BFI (Bad Frame Indicator) set are sent for the remaining codec types
TCSMMGW
”Empty” speech frames are transmitted to keep the connection alive => no savings
over IP A
Savings
Local switching aims at bandwidth savings on Abis! The savings on other interfaces should be considered as a nice side-effect, but not as a reason for the feature introduction! For internal use only 38 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (2/11) Packet Abis Calculator for Local Switching
• The Packet Abis Calculator (the Local Switching sheet) can be used to
evaluate the local switching in terms of: – the Abis bandwidth utilisation – the required number of E1 lines (packet Abis over TDM variant) between a hub-
BTS and BSC (inter-site local switching).. – …or between BTS and BSC (intra-site local switching) for different percentages of locally switched calls
• The next slides contain work instructions, i.e. step-by-step description how to use the tool, and examples of calculation results for different modes of local switching and packet Abis realisations (over Ethernet or TDM)
For internal use only 39 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (3/11) 1) Select the LS mode: inter-site with packet Abis over Eth (LS over Eth), over TDM (LS over TDM), intra-site with packet Abis over Eth (ISS over Eth), over TDM (ISS over TDM)
9) Press Calculate
2) Decide on the number of site configurations that are foreseen for the LS area – they are created immediately for providing further input 3) Select the configuration representing the hub-BTS (only in case of inter-site LS over TDM) 4) Specify the percentage of locally switched calls 5) Specify the number of sites for each configuration; for the configuration representing the hub-BTS only a single site can be specified (the value is hardcoded); the number of sites over all configurations cannot exceed 16 6) Specify the number of TRXs for each site configuration 7) Specify other parameters for each site configuration, in the load mode a user can type in directly the amount of traffic in Erlangs irrespective the voice distribution input For internal use only 40 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Inputs 8) Specify the voice and codec distribution
Local Switching for Packet Abis
Impact on Planning and Dimensioning (4/11)
Outputs – InterSite Local Switching 1) Total amount of traffic served per site and by all sites of the given site configuration 2) Required bandwidth per site of a local switching area towards BSC and the required number of E1s (in case of packet Abis over TDM) towards the hub-BTS (inter-site local switching)
6) If the required number of E1 lines in the hub-BTS (packet Abis over TDM) exceeds 8 a warning is issued – such the configuration of the inter-site local switching is not feasible
3) Total bandwidth required towards BSC from all sites without inter-site local switching For internal use only 41 © Nokia Siemens Networks
4) The required number of E1 lines towards BSC for all sites without inter-site local switching (in case of packet Abis over TDM)
4) Total bandwidth required towards BSC from all sites with intersite local switching
Local Switching for Packet Abis / A. Maciołek / April 2010
5) The required number of E1 lines towards BSC for all sites with inter-site local switching (in case of packet Abis over TDM)
Local Switching for Packet Abis
Impact on Planning and Dimensioning (5/11)
Outputs – IntraSite Local Switching
1) Required bandwidth per site towards a BSC and the required number of E1s (in case of packet Abis over TDM) towards the BSC without intra-site local switching 2) Required bandwidth per site towards a BSC and the required number of E1s (in case of packet Abis over TDM) towards the BSC with intra-site local switching 3) Application of intra-site local switching is recommended if the number of E1 lines towards BSC is reduced (in case of packet Abis over TDM) 4) With a single E1 line towards BSC (in case of packet Abis over TDM) application of the intra-site local switching makes no sense
For internal use only 42 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (6/11) Inter-Site Local Switching with Packet Abis over Ethernet
- without local switching - with local switching
Assumptions: • Estimated bandwidth refers to required bandwidth between BTSs and a BSC • For 2/2/2 and 4/4/4 16 BTSs in a local switching area, for 8/8/8 8 BTSs in a local switching area (to save computation time) • Up to 30% HR, no PS data For internal use only 43 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (7/11) Inter-Site Local Switching with Packet Abis over Ethernet L2 switch L2 switch
Local BTS
Locally switched calls are switched outside the IP network managed by an ISP => bandwidth savings seen in the IP network provided by the ISP => savings in €
SFP link in FIYA/FIQA
ISP
ISP
IP network Edge node
L2 switch Edge node
Edge node BSC
Local switching area
Only non-locally switched calls are transferred by the IP network provided by the ISP
SFP link in FIYA/FIQA
1GB Ethernet switch supporting fibre optic
Local BTS
SFP link in FIYA/FIQA
L2 switch Local BTS
Local BTS
IP network
L2 switch
Local BTS
SFP* link in FIYA/FIQA
Local BTS Edge node
Local BTS
Locally switched calls are switched between ports of the switch without affecting the IP network provided by the ISP
Local BTS Examples of network architecture for local switching
Local switching area
To achieve bandwidth and OPEX savings in Ethernet network provided by an ISP locally switched calls must be switched outside the network managed by the ISP * - the small form-factor pluggable (SFP) is a hot-pluggable transceiver; it can be used in L2/L3 equipment to support fibre optic links For internal use only 44 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (8/10) Inter-Site Local Switching with Packet Abis over TDM
- without local switching - with local switching - max number of sites in a LS area
Assumptions: • Up to 30% HR, no PS data With the increasing penetration of LS calls the size of the local switching area can be increased to the upper limit of 8 E1 lines served by the hub-BTS For internal use only 45 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (9/11) Intra-Site Local Switching with Packet Abis over Ethernet
- without local switching - with local switching
Assumptions: • Estimated bandwidth refers to required bandwidth between a BTS and a BSC • Up to 30% HR, no PS data
For internal use only 46 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (10/11) Intra-Site Local Switching with Packet Abis over TDM intra-site local switching not applicable – there is no room for E1 lines reduction
intra-site local switching not applicable – there is no room for E1 lines reduction
- without local switching Application of intra-site local switching (TDM) makes sense for certain LS calls penetrations and site configurations
- with local switching
Assumptions: • Up to 30% HR, no PS data With the increasing penetration of LS calls the number of E1 lines between a BTS and a BSC can be reduced from, e.g. 2 to 1. For the taken assumptions this is possible starting with the 7/7/7 TRX configuration in a site.
For internal use only 47 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Impact on Planning and Dimensioning (11/11) A Interface
• The maximum bandwidth saving on the A interface over IP (BSCMGW) is a sum of bandwidth savings of local switching areas connected to a MGW:
BWsavings A BWsavings lsa lsa
• •
lsa – local switching area => BW(lsa) – bandwidth saving of the local switching area lsa connected to the MGW A – A interface => BW(A) – bandwidth saving on the A interface
The maximum bandwidth savings on the A interface are reached when traffic distributions in local switching areas are identical. In practice, this assumption may not be satisfied, so the actual savings may be lower. For internal use only 48 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Feature Dependencies
For internal use only 49 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Dependencies Packet Abis (RG20, BSS21321) • Packet Abis over Ethernet or Packet Abis over TDM is a prerequisite for the local switching feature
DTM • If an MS with an on-going locally switched call requests a DTM connection, an
intra-cell HO is done to a packet territory (both CS and PS parts), but the local switching is maintained on the CS part after the handover • The same holds for the DTM connection requested by SGSN to the MS with the on-going locally switched call => the local switching is maintained • The local switching is also maintained in case of BSC or PCU initiated intra-cell and internal inter-cell HOs causing the DTM reallocation • The local switching is also maintained when the DTM is released => an intra-cell HO is done to the CS territory
For internal use only 50 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Dependencies
Other Dependencies • For the capability of the local call detection the User-User Signalling (UUS) core feature (TS 22.087) must be activated
For internal use only 51 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Database Parameters
For internal use only 52 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Database Parameters New New parameters parameters (1/2) packetAbisBcfGroupId
Packet Abis BCF Group ID
object: BCF unit: none range: 0..3000 step: 1 default: 65535 MML commands: EFC, EFM, EFO MML abbreviated name: PABGID
The parameter defines the identifier of the BCF group. The BCF group delimits a group of BTSs (BCFs) among which local switching is possible, i.e. among all BTSs (BCFs) having the same value of the identifier assigned. The maximum number of BTSs (BCFs) in the BCF group is 16. There are two special settings: PABGID = 65535 to indicate that local switching is not in use for the BCF and PABGID = 0 to indicate that only intra-BCF local switching is possible for the BCF, i.e. the LS area contains that specific BCF only. The first valid BCF group value indicating a real LS area, i.e. a group of BCFs among which local switching is possible, is 1. Note: If more BCFs are configured with the PABGID set to the special values 0 or 65535, this does not mean that they belong to the same LS area. The parameter is valid only if the Abis interface connection type (AICT) is other than Legacy Abis.
N/A
List of Subscribers to Intercept
object: N/A unit: none range: N/A step: N/A default: N/A MML commands: N/A MML abbreviated name: N/A
A list containing MSISDN numbers of subscribers to be intercepted in a core network is provided to a BSC by an operator. Up to 150000 numbers can be saved to the BSC.
MML commands (examples):
For internal use only 53 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Database Parameters New parameters (2/2) lsEnabledInterceptedCalls
Local Switching Enabled for Intercepted Calls
object: BSC unit: none range: [true, false] step: none default: false MML commands: EEM, EEO MML abbreviated name: LSEIC
The parameter defines whether the local switching should be disabled or enabled for calls under the lawful interception. If the parameter is set to false, the calls to be intercepted are not locally switched even if possible, i.e. they go through the whole transmission path via BSC, TRAU/MGW and MSC. If the parameter is set true, the calls to be intercepted are locally switched (if possible), but copies of locally switched speech frames are sent to the MSC via BSC and TRAU/MGW.
abisInterfaceConnectionType
Abis Interface Connection Type
object: BCF unit: none range: [Packet Abis Over TDM, Packet Abis Over Ethernet, Legacy Abis, Packet Abis over TDM (Hub BTS)] step: none default: Legacy Abis MML commands: EFC, EFM, EFO MML abbreviated name: AICT
The new setting is used for a BTS (BCF) connected through the packet Abis over TDM to a BSC. The BTS acts in this case as a hub-BTS for the inter-BTS local switching for the packet Abis over TDM. The new setting is applicable to the hub-BTSBSC connection only. If the local switching area is defined for a group of BTSs (BCFs) connected through the packet Abis over TDM, the Abis interface connection type parameter should be set to “Packet Abis over TDM (Hub BTS)” for the BTS acting as the hub-BTS. In this case the PABGID parameter must be specified for the hub-BTS. If only the intra-BTS (intra-BCF) local switching is enabled for a BTS connected through the packet Abis over TDM, there is no need to configure a hub-BTS and the Abis interface connection type parameter should be set to “Packet Abis over TDM”. If the Abis Interface Connection Type parameter is set either to Packet Abis over TDM or to Packet Abis over TDM (Hub BTS) the HDLC parameters must be specified
MML commands (examples): For internal use only 54 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Performance Measurements
For internal use only 55 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Performance Measurements New counters (1/9) Counter name
Description
001274: MO_LS_CALL_SUCC (1 Traffic Measurement)
Number of successful mobile originated speech calls, which have established a locally switched speech path. Trigger event: When local switching establishment is successful for mobile originated calls.
001275: MT_LS_CALL_SUCC (1 Traffic Measurement)
Number of successful mobile terminated speech calls, which have established a locally switched speech path. Trigger event: When local switching establishment is successful for mobile terminated calls. Use case: To observe ratio of calls established locally – aggregated over the local switching area (trf_1002)
trf_1002
MO _ LS _ CALL _ SUCC MT _ LS _ CALL _ SUCC 100 SUCC_TCH_SEIZ_CALL_ATTEMPT
BTS ( lsa )
BTS ( lsa )
BTS ( lsa )
…or per BTS (with the distinction of MOC (moc_1000) and MTC (mtc_1000) calls established locally):
For internal use only 56 © Nokia Siemens Networks
moc_1000
MO _ LS _ CALL _ SUCC 100 SUCC_TCH_SEIZ_CALL_ATTEMPT
mtc_1000
MT _ LS _ CALL _ SUCC 100 SUCC_TCH_SEIZ_CALL_ATTEMPT
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Performance Measurements New counters (2/9) Counter name 001276: LS_ESTAB_UNSUCC_DUE_ CODEC (1 Traffic Measurement)
Description
Number of unsuccessful establishments of locally switched calls due to different speech codec types on local call peers Trigger event: Updated after a TCH allocation, when local switching cannot be established because of mismatch between chosen codec and codec used by peer. Use case: To observe ratio of calls not established locally due to codec mismatch between the involved terminals localised in the local switching area – aggregated over the local switching area:
Calls _ not _ est _ locally _ codec _ mismatch[%]
LS_ESTAB_U NSUCC_DUE_CODEC 100 SUCC_TCH_SEIZ_CALL_ATTEMPT
BTS ( lsa )
BTS ( lsa )
…or per BTS (csf_1000):
csf_1000
For internal use only 57 © Nokia Siemens Networks
LS_ESTAB_U NSUCC_DUE_CODEC 100 SUCC_TCH_SEIZ_CALL_ATTEMPT
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Performance Measurements New counters (3/9) Counter name
Description
001277: Number of releases of local switching due to an inter-cell handover outside a LS Area LS_REL_DUE_INTER_HO_OUT_LS Trigger event: (1 Traffic Measurement) When the inter-cell handover is triggered outside the LS area for a locally switched call. This is updated before a handover command is sent to mobile. Use case: To observe ratio of local switching releases due to inter-cell HO outside the local switching area – aggregated over the local switching area (dcr_1000):
dcr_1000
LS_REL _ DUE_INTER_HO_OUT_LS 100 MO _ LS _ CALL _ SUCC MT _ LS _ CALL _ SUCC BTS ( lsa )
BTS ( lsa )
BTS ( lsa )
…or per BTS
LS _ released_i nternal_HO _ BTS [%]
For internal use only 58 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
LS_REL _ DUE_INTER_HO_OUT_LS 100 MO _ LS _ CALL _ SUCC MT _ LS _ CALL _ SUCC
Local Switching for Packet Abis Performance Measurements New counters (4/9) Counter name 001278: LS_REL_DUE_EXTERNAL_HO (1 Traffic Measurement)
Description Number of releases of local switching due to an external handover Trigger event: When an inter-BSC handover is triggered for a locally switched call. This is updated before a handover command is sent to mobile. Use case: To observe ratio of local switching releases due to external HO (to another BSC) – aggregated over the local switching area (dcr_1001)
dcr_1001
LS_REL _ DUE_EXTERNAL_HO 100 MO _ LS _ CALL _ SUCC MT _ LS _ CALL _ SUCC BTS ( lsa )
BTS ( lsa )
BTS ( lsa )
…or per BTS
LS_release d_external_HO _ BTS [%]
For internal use only 59 © Nokia Siemens Networks
LS_REL _ DUE_EXTERNAL _ HO 100 MO _ LS _ CALL _ SUCC MT _ LS _ CALL _ SUCC
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Performance Measurements New counters (5/9) Counter name
Description
001279: LS_REL_DUE_SUPPL_SERV_ESTAB (1 Traffic Measurement)
Number of releases of local switching due to establishment of supplementary services, which require speech path control of an MSC Trigger event: When local-switching is released due to the start of supplementary services. Use case: To observe ratio of local switching releases due to establishment of supplementary services – aggregated over the local switching area (dcr_1002):
dcr_1002
LS_REL _ DUE_SUPPL _ SERV_ESTAB 100 MO _ LS _ CALL _ SUCC MT _ LS _ CALL _ SUCC BTS ( lsa )
BTS ( lsa )
For internal use only 60 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
BTS ( lsa )
Local Switching for Packet Abis Performance Measurements New counters (6/9)
The new measurement ‘132 Local Switching Traffic’ monitors CS U-plane RTP and UDP packets for each BTS configured in a LS area. The object level is a LS peer BCF.
Counter name
Description
132000: CS_U_PLN_RTP_PACKT_REC_LSBTS (132 Local Switching Traffic)
Number of DL RTP packets containing TRAU frames of the CS U-plane, which have been successfully received from a LS peer BCF, including packets received on time, too late and too early. Trigger event: Each time the DL RTP packet containing the TRAU frame of the CS U-plane from the LS peer BCF is received at a base station regardless it is received on time, too early or too late.
132001: CS_U_PLN_RTP_PACKT_LOST_LSBTS (132 Local Switching Traffic)
Number of DL RTP packets containing TRAU frames of the CS U-plane, which are missing or lost. Trigger event: Each time the next sequence number is missing from the RTP packet received from a peer BTS. If the gap in the RTP sequence numbers is smaller than a threshold value (100), then the counter is incremented by the amount of missing RTP packets. If the gap in the RTP sequence numbers is greater than or equal to the threshold value (100), then it is interpreted as a jump in the RTP sequence number. Use case: To measure packet loss rate of locally switched calls in DL from a peer BTS
LS _ DL _ packet _ loss _ rate [%] CS_U_PLN_RTP_PACKT_L OST_LSBTS 100 CS_U_PLN_RTP_PACKT_R EC_LSBTS CS_U_PLN_RTP_PACKT_L OST_LSBTS
For internal use only 61 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Performance Measurements New counters (7/9)
The new measurement ‘132 Local Switching Traffic’ monitors CS U-plane RTP and UDP packets for each BTS configured in a LS area. The object level is a LS peer BCF.
Counter name
Description
132002: CS_U_PLN_RTP_TOO_LATE_LSBTS (132 Local Switching Traffic)
Number of DL RTP packets containing TRAU frames of the CS U-plane received from a LS peer BCF too late according to the timestamp of the RTP packet. Trigger event: Updated when the RTP packet arrives but a processing window of the packet already elapsed.
132003: CS_U_PLN_RTP_TOO_EARLY_LSBTS (132 Local Switching Traffic)
Number of DL RTP packets containing TRAU frames of the CS U-plane received from a LS peer BCF too early according to the timestamp of the RTP packet. Trigger event: Updated when the RTP packet arrives but there is no room in the de-jitter buffer to process the packet. Use case: To measure packet loss rate for locally switched calls from a peer BTS due to improper configuration a de-jitter buffer in DL
LS _ DL _ packet _ loss _ rate _ due _ to _ dejitter [%] CS_U_PLN_RTP_TOO_LAT E_LSBTS CS_U_PLN_RTP_TOO_EARLY_LSBTS 100 CS_U_PLN_RTP_PACKT_R EC_LSBTS
For internal use only 62 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Performance Measurements New counters (8/9)
The new measurement ‘132 Local Switching Traffic’ monitors CS U-plane RTP and UDP packets for each BTS configured in a LS area. The object level is a LS peer BCF.
Counter name
Description
132004: CS_U_PLN_RTP_PACKT_SENT_LSBTS (132 Local Switching Traffic)
Number of UL RTP packets containing TRAU frames of the CS U-plane sent to a LS peer BCF Trigger event: Each time the UL RTP packet containing the TRAU frame of the CS U-plane is sent to another LS peer BCF.
132005: CS_U_PLN_UDP_PACKT_REC_LSBTS (132 Local Switching Traffic)
Number of DL UDP packets containing NSN (a proprietary format) multiplexed RTP packets (p-RTP) of the CS U-plane successfully received at a BCF from a LS peer BCF. Trigger event: Each time the DL p-RTP packet of the CS U-plane from the LS peer BCF is received at a base station.
132007: CS_U_PLN_UDP_OCTET_REC_LSBTS (132 Local Switching Traffic)
Number of DL octets received at a BCF from a LS peer BCF within UDP packets containing NSN multiplexed RTP packets (p-RTP) of the CS U-plane. Framing characters are included. Unit is kB. Trigger event: Each time the DL octet of the CS U-plane from the LS peer BCF is received at a base station. Use case: To measure the average UDP packet size in DL of locally switched calls in kB
LS _ DL _ UDP _ packet _ size [ kB]
For internal use only 63 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
CS_U_PLN_UDP_OCTET_REC_LSBTS CS_U_PLN_UDP_PACKT_R EC_LSBTS
Local Switching for Packet Abis Performance Measurements New counters (9/9)
The new measurement ‘132 Local Switching Traffic’ monitors CS U-plane RTP and UDP packets for each BTS configured in a LS area. The object level is a LS peer BCF.
Counter name
Description
132006: CS_U_PLN_UDP_PACKT_SENT_LSBTS (132 Local Switching Traffic)
Number of UL UDP packets containing NSN (a proprietary format) multiplexed RTP packets (p-RTP) of CS U-plane sent from a BCF to a LS peer BCF. Trigger event: Each time the UL p-RTP packet of the CS U-plane is sent to another LS peer BCF.
132008: CS_U_PLN_UDP_OCTET_SENT_LSBTS (132 Local Switching Traffic)
Number of UL octets sent from a BCF to a LS peer BCF within UDP packets containing NSN multiplexed RTP packets (p-RTP) of the CS U-plane. Framing characters are included. Unit is kB Trigger event: Each time the UL octet of the CS U-plane is sent from a BCF to another LS peer BCF. Use case: To measure the average UDP packet size in UL of locally switched calls in kB
LS _ DL _ UDP _ packet _ size [ kB]
For internal use only 64 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
CS_U_PLN_UDP_OCTET_SENT_LSBTS CS_U_PLN_UDP_PACKT_S ENT_LSBTS
Feature Impact Analysis & Verification
For internal use only 65 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Feature Impact Analysis & Verification (1/6) Feature impact Feature works on a configured local switching area. Local switching area includes cells, among which the locally switched calls are frequently established. In each cell a significant portion of calls (incoming and outgoing) should be established locally.
How to measure? Counters: 001274 (MO_LS_CALL_SUCC) and 001275 (MT_LS_CALL_SUCC) Both counters should have non-zero values after a sufficiently long observation period, e.g. one day. These are absolute values not giving information on rate of calls established locally. This disadvantage is reconciled by the KPI shown below. KPIs: Percentage of calls established locally (aggregated over the local switching area):
trf_1002 Percentage of incoming (MTC) and outgoing (MOC) calls established locally (measured on the level of the BTS belonging to the local switching area)
mtc_1000 moc_1000 The low percentage of locally switched calls may indicate that the local switching area is incorrectly designed, i.e. it may not include cells between which locally switched calls are frequently established.
For internal use only 66 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Feature Impact Analysis & Verification (2/6) Feature impact
How to measure?
Codec types/modes are aligned in cells of a local switching area, so TrFO can work efficiently, i.e. a common codec type can be found between to MSs establishing a locally switched call.
Counters: 001276 (LS_ESTAB_UNSUCC_DUE_CODEC) If codec types are aligned among cells of the local switching area, the counter should have a small value. This is an absolute value not giving information on rate of calls not established locally due to codec type mismatch. This disadvantage is reconciled by the KPI shown below. KPIs: Percentage of calls not established locally due to codec mismatch (aggregated over the local switching area):
If the common codec type is not found the call is established normally without local switching.
Calls _ not _ est _ locally _ codec _ mismatch [%] Percentage of calls not established locally due to codec mismatch (measured on the level of the BTS belonging to the local switching area):
Also the KPIs presented on the previous slide demonstrates a lower rate of calls established locally, although the local switching area is correctly designed.
For internal use only 67 © Nokia Siemens Networks
csf_1000
The high percentage may indicate that codec types in cells of the local switching area are
not aligned and, as a result, TrFO works inefficiently. In an ideal case the percentage should be low (near zero). This KPI may also indicate the need for corrections in ACSs of BTSs belonging to the local switching area if AMR codec type is in use and the percentage is high.
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Feature Impact Analysis & Verification (3/6) Feature impact During internal HOs within a local switching area a locally switched call is maintained. If a local switching area is incorrectly designed, i.e. it does not contain cells between which handovers are frequently done, a local switching is released The local switching can also be released during the internal HO if TrFO cannot be established, i.e. supported codec types in cells of a local switching area mismatch
How to measure? Counters: 001277 (LS_REL_DUE_INTER_HO_OUT_LS) 001278 (LS_REL_DUE_EXTERNAL_HO) If internal HOs are mostly done between cells of the same local switching area, the counter should have a small value. This is an absolute value not giving information on rate of local switching releases due to an internal HO to a cell outside the local switching area. This disadvantage is reconciled by the KPI shown below. KPIs: Percentage of local switching releases during internal/external HOs (aggregated over the local switching area):
dcr_1000
dcr_1001
Percentage of local switching releases during internal/external HOs (measured on the level of the local switching area):
LS _ released_i nternal_HO _ BTS [%]
LS _ released_external_HO _ BTS [%]
The high percentage indicates that the local switching area is not properly designed, i.e. it does not contain cells between which HOs are frequently performed. These KPIs are inputs for re-planning of the local switching area. If a local switching area is correctly designed the percentages should be low.
For internal use only 68 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Feature Impact Analysis & Verification (4/6) Feature impact If during a locally switched call a supplementary service is established the local switching is released. The local switching feature is designated for basic peer-topeer voice calls without supplementary services.
For internal use only 69 © Nokia Siemens Networks
How to measure? Counters: 001279 (LS_REL_DUE_SUPPL_SERV_ESTAB) KPIs: Percentage of local switching releases due to a supplementary service setup (measured on the level of the local switching area):
Calls_rele ased_supl [%]
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Feature Impact Analysis & Verification (5/6) Feature impact
How to measure?
Quality of locally switched calls should be monitored. The high packet loss rate may indicate network congestion in its part serving a local switching area. However, the network congestion may not necessarily take place on a route to a BSC at the same time.
Counters: 132000 (CS_U_PLN_RTP_PACKT_REC_LSBTS) 132001 (CS_U_PLN_RTP_PACKT_LOST_LSBTS) KPIs: Packet loss rate in DL for locally switched calls
Length of a de-jitter buffer impacts PDV (Packet Delay Variation). If the buffer is too short, the PDV goes down, but the incoming packets may be rejected, because there is no room in the buffer. If it is too long, then all incoming packets can be served, but the PDV increases. Both cases lead to quality degradation.
Counters: 132002 (CS_U_PLN_RTP_TOO_LATE_LSBTS) 132003 (CS_U_PLN_RTP_TOO_EARLY_LSBTS) KPIs: Packet loss rate in DL for locally switched calls due to de-jitter buffer
For internal use only 70 © Nokia Siemens Networks
LS _ DL _ packet _ loss _ rate [%]
LS _ DL _ packet _ loss _ rate _ due _ to _ dejitter [%] The KPI may be useful to optimise the length of the de-jitter buffer to minimise the PDV.
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis
Feature Impact Analysis & Verification (6/6) Feature impact Locally switched calls are multiplexed (if originated and terminated by the same local BTSs) in a part of a network serving a local switching area. The higher is the multiplexing factor (the larger is a packet size), the greater are bandwidth savings.
For internal use only 71 © Nokia Siemens Networks
How to measure? KPIs: Average UDP packet size in DL of locally switched calls in kB
LS _ DL _ UDP _ packet _ size [kB ] Average UDP packet size in UL in the local switching area in kB
LS _ UL _ UDP _ packet _ size [kB ]
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis References
• Local Switching for Packet Abis, BSS21327, BSC S15, Requirements • • • •
Specification, v.1.0.1, Timo Olkkonen, Outi Rissanen, Jarno Filipoff, Hannu Makkonen Local Switching for Packet Abis, BSS21327, System Feature Specification, v.1.2.1, Sergio Parolari Local Switching for Packet Abis, BSS21327, BSC S15, Implementation Specification, v.0.0.1, Manoj R Nair, Sharath K Feature Description: BSS21436 Local Switching for Satellite Abis, BSS30370 Local Switching for Terrestrial Abis 3GPP TS 48.008 version 8.7.0 Release 8 – Digital cellular telecommunications system (Phase 2+); Mobile Switching Centre - Base Station system (MSC-BSS) interface; Layer 3 specification
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Local Switching for Packet Abis / A. Maciołek / April 2010
Backup
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Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
ML-PPP in Local Switching with Packet Abis over TDM • ML-PPP (Multi-Link Point-to-Point) layer 2 protocol is used to transport speech
data in the packet Abis over TDM variant: – Inside a local switching area between two BTSs of a local switching area through a hubBTS for locally switched calls (inter-site local switching) => BTS1hub-BTSBTS2 – Between a BTS and a BSC through a hub-BTS for non-locally switched calls (intra-site local switching) => BTS1hub-BTSBSC – Between a BTS and a BSC for non-locally switched calls (intra-site local switching) => BTS1BSC
• Signalling data and PS traffic is always transmitted by the ML-PPP protocol to/from the BSC irrespective of the local switching functionality • As the maximum number of BTSs connected to the hub-BTS is 15 the maximum number of ML-PPP bundles going through the hub-BTS is 16: – Maximum 15 ML-PPP bundles to connect the hub-BTS with the local BTSs – … + 1 ML-PPP bundle to connect the hub-BTS to the BSC • There is a constant mapping between destination IP addresses contained in the IP packets arriving at the hub-BTS and the ML-PPP bundles connecting the hub-BTS with BTSs For internal use only 74 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Local Call Detection & Setup – Phase 1 • Detection of a local call is based on sniffing/manipulation of the DTAP (Direct Transfer Application Part) messages by a BSC: – DTAP is used to transfer call control and mobility management messages between the MSC and the MS at call setup – Normally, the DTAP information in these messages is not interpreted by the BSS
• To check whether a call being established is a candidate for the local switching the
following steps are performed: – BSC inserts a call identifier of an MS originating a call to the User-User IE (part of the DTAP – – – –
signalling) The call identifier is saved to the BSC lookup table The manipulated DTAP signalling is forwarded to MSC If the MS originating the call tries to establish the call with an MS served by the same BSC the manipulated DTAP signalling containing the call identifier arrives back from the MSC at the BSC BSC sniffs the call identifier from the manipulated DTAP signalling and compares it with call identifiers saved to the BSC lookup table to check the connection being established was started through the same BSC => if so, the local switching is possible
• At this point the call is not yet established => the local switching is to be tried out For internal use only 75 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Local Call Detection & Setup – Phase 2
• The MSs may be served by the same or different BCSUs • The BCSUs serving the MSs make an exchange of lists of codec types they support (FR, EFR, HR, AMR HR, AMR FR, AMR WB): – RRM tries to allocate a common codec type to both connection ends, e.g. AMR
HRAMR HR, AMR HRAMR FR with the same source bit rate => the local switching is possible – Common codec type not found by the RRM => the local switching is not possible and both connection ends operate with their preferred codec types – The TrFO (Transcoder Free Operation) mechanism is responsible for the selection of the common codec type (see the next slides)
• The BCSUs serving the MSs make an exchange of IP addresses of BTSs and
radio channel UDP ports, on which the TCH channel should be established: – At this moment it is checked if the BTSs belong to the same local switching area => if this is a case, then the call is finally established with the local switching, otherwise the call is connected without the local switching
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Local Switching for Packet Abis / A. Maciołek / April 2010
Local Switching for Packet Abis Feature Details
Local Call Detection & Setup – Summary BSC id
BCSU index
counter*
insert MS1 call identifier to User-User IE of DTAP protocol and save the call identifier to BSC lookup table
call identifier
BSC lookup table
call setup
MS1
BTS1
BSC
forward the manipulated DTAP to MSC
TRAU
BCSU1 BCSU2
call setup
MS2 BTS2
Local switching area ID
if the match is found it means MS1 tries to connect with the MS2 served by the same BSC BCSU1 and BCSU2 start establishment of local switching…
sniff the call identifier from DTAP and, if present, compare it with the call identifiers stored in the BSC lookup table remove the call identifier from User-User IE (DTAP)
* - counter is incremented each time a new call is established to distinguish the calls established in the same BSC For internal use only 77 © Nokia Siemens Networks
Local Switching for Packet Abis / A. Maciołek / April 2010
if the terminating MS is to be served by the same BSC as the originating MS the MSC sends the manipulated DTAP back to the same BSC
MSC
Local Switching for Packet Abis Feature Details
Local Call Detection & Setup – Summary BCSUs exchange information on the supported codec types and try to find a common codec type
BSC lookup table
MS1 BTS1
BSC
the BCSUs exchange the IP addresses and radio channel UDP port numbers
TRAU
BCSU1 BCSU2
MS2 BTS2
Local switching area ID
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if the common codec type is found and both BTSs belong to the same local switching area the call is finally switched locally
Local Switching for Packet Abis / A. Maciołek / April 2010
MSC
Local Switching for Packet Abis Feature Details
Local Switching Area (3/3) • In case of the packet Abis over Ethernet all BTSs of the local switching area must belong to the same VLAN (Virtual LAN) network (apart from belonging to the same local switching area) • C/U-plane and M-plane can be handled by the same VLAN ID (no separation between C/U- and M-planes) or separate VLAN IDs (general restriction of the packet Abis feature)
192.168.0.108 192.168.0.106 PABGID = 2
IP network
192.168.0.102
Packet Abis over Ethernet
VLAN id = 11 VLAN id = 12 Packet Abis over Ethernet
192.168.0.107
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BSC 192.168.0.101 C/U-plane M-plane
Local Switching for Packet Abis / A. Maciołek / April 2010
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