Local Switching for Packet Abis

(1)

(2)

Andrzej Maciołek

Network Engineering

NWS LTE RA E2E Mgmt SA NE GSM&LTE Migration

February 2011

RG25 (BSS) Network Engineering Information

Local Switching for Packet Abis

BSS21327

Please always use the latest version of the materials which can be found under the link:

(3)

Local Switching for Packet Abis

BSS21327

• Background Information

• Feature Details

• Impact on Planning and Dimensioning

• Feature Dependencies

• Database Parameters

• Performance Measurements

• Feature Impact Analysis and Verification

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

MetroSite

BTS

UltraSite

BTS

FlexiEDGE

BTS

MultiRadio

BTS Flexi

BTSplus

S15

BSC3i

(1000/2000

)

FlexiBSC

-

N

Y

EX4.1

Y

(5)

-Background Information

(6)

• 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

• 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

Local Switching for Packet Abis

Background Information

BSC1

BTS1

TRAU1

MSC1

MSC2

TRAU2

BSC2

BTS2

MS1

MS2

Speech and signalling

BSC1

BTS1

TRAU1

MSC1

MSC2

TRAU2

BSC2

BTS2

MS1

MS2

E1/T1 Abis E1/T1

Abis

Calls and related signalling are transferred through all network entities

(7)

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

BSC1

BTS1

TRAU1

MSC1

MSC2

TRAU2

BSC2

BTS2

MS1

MS2

Speech Signalling E1/T1 Abis

(8)

Local Switching for Packet Abis

Background Information

• No solutions supporting local switching

• 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)

Up to BSS13

ED

BSS13

ED

RGW

BSC

CGW

TRAU

MSC

PSTN

IP over Ethernet

for satellite Abis

IP over TDM for

terrestrial Abis IP over Ethernet

for satellite Abis

IP over TDM for terrestrial Abis Aggregating and switching local traffic E1/T1 E1/T₁ E1/T 1 Abis Abis

For locally switched calls only signalling is

(9)

• A completely new implementation fully relying on

the packet

Abis

is introduced without involving equipment of external

vendors:

–

BSS21327 ”Local Switching for Packet Abis”

Local Switching for Packet Abis

Background Information

RG25

(BSS)

(10)

Feature Details

(11)

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

(12)

• Intra-BCF

local switching with the

packet Abis over TDM

• Intra-BCF

local switching with the

packet Abis over Ethernet

Local Switching for Packet Abis

Feature Details

BSC

TRAU

MSC

Switching local traffic

Packet Abis over TDM

conveyed to BSC

BSC

TRAU

MSC

Packet Abis over Ethernet

conveyed to BSC

IP network

Switching local traffic

(13)

• Inter-BCF

local switching with the

packet Abis over Ethernet

• Inter-BCF

local switching with the

packet Abis over TDM

Local Switching for Packet Abis

Feature Details

Switching local traffic and aggregating non-locally switched traffic

conveyed to BSC

BSC

TRAU

MSC

conveyed to BSC

Packet Abis over Ethernet Switching

local traffic

(14)

Local Switching for Packet Abis

Feature Details

• 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

Local Switching Area

(1/2)

(15)

Local Switching for Packet Abis

Feature Details

• 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)

PABGID = 2

Local Switching Area

(2/2)

Up to 16 BTSs in the LS area including hub-BTS

Local switching area with inter-BCF locally

switched calls Local switching area

with intra-BCF locally switched calls only Each BCF creates a LS area PABGID = 1 PABGID = 0 PABGID = 0 PABGID = 0 PABGID = 0

Local switching areas with

intra-BCF local switching only

Local switching areas with

inter-BCF local switching

(16)

Local Switching for Packet Abis

Feature Details

• 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

Hub-BTS

(1/3)

(17)

Local Switching for Packet Abis

Feature Details

• 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

Hub-BTS

(2/3)

(18)

M L-P PP (4₎ H_D LC (6₎ H_D LC (6₎

• Hub-BTS configuration with the

packet Abis over TDM

hub-BTS

BTS1

BSC

ML-PPP (1) HDLC(2) HDLC(5) ML-PPP bundle M L-P PP bu nd_le M L-P PP (2₎ H_D LC (2₎ H_D LC (2₎ Pa ck et A bis ov er _TD M

Packet Abis over TDM Packet Abis over TDM

BTS2

192.168.0.100 192.168.0.101 192.168.0.102 192.168.0.y Synchronisation recovery ML-PPP (3) _HDLC(3) HDLC(1) HDLC(3) HDLC(1) ML-PPP bundle

Each E1/T1 line is mapped to a HDLC link

Few HDLC links are bundled in a single ML-PPP bundle HDLC(3) HDLC(1) HDLC(2) TSLx … TSLy TSLx … TSLy call 1 SCF file loaded to the hub-BTS by the BSC

Local Switching for Packet Abis

Feature Details

Hub-BTS

(3/3)

192.168.0.103 ML-PPP(4) 192.168.0.101 ML-PPP(3) 192.168.0.100 ML-PPP(2)

• Up to 8 HDLC links can

be configured in a

single 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)

• Up to 16 ML-PPP

bundles can be served

by the hub-BTS

• Up to 8 E1/T1 lines

terminated at a

hub-BTS

192.168.0.103

BTS3

ML-PPP (4) HDLC(6) HDLC(6) ML-PPP bundle Grooming @ BTS2 => BTS2 and BTS3 connected to the hub-BTS on a single E1/T1 interface, but

(19)

Local Switching for Packet Abis

Feature Details

• 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

Local Switching with Packet Abis over

Ethernet

(20)

BTS1

BSC

call 1 call 3 call 2

BTS2

Packet Abis over Ethernet Packet Abis over

Ethernet call 2 call 3 call 1 Packe t Abis_over Ethern_et Synchronisation recovery 192.168.0.101 192.168.0.100 192.168.0.y White-list of BCF IDs and IP addresses exchanged inside LSA

IP network

• Local switching area configuration with the

packet Abis over Ethernet

* - CS U-plane IP addresses

Local Switching for Packet Abis

Feature Details

BTS2 192.168.0.100*

BTS1 192.168.0.101 *

Local Switching with Packet Abis over

Ethernet

(21)

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

(22)

Local Switching for Packet Abis

Feature Details

• 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”

TrFO with Local Switching

(1/4)

* - see BSS14 NEI slides ”AMR Wideband & TFO” (BSS20960, BSS21118)

(23)

Local Switching for Packet Abis

Feature Details

• 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

TrFO with Local Switching

(2/4)

(24)

Local Switching for Packet Abis

Feature Details

• 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

TrFO with Local Switching

(3/4)

(25)

Local Switching for Packet Abis

Feature Details

TrFO with Local Switching

(4/4)

BSC

BTS1

BTS2

encoding decoding max. 12.65* kbps + IP overhead

* - AMR-WB source bit rate of the least robust codec mode

MS1

MS2

ACS: 4.75, 5.9, 7.4, 12.2 ACS: 4.75, 5.9, 7.4

MS1MS2

common ACS: 4.75, 5.9, 7.4

MS1BTS1 (EFR)

EFR ACS: 4.75, 5.9, 7.4, 12.2

MS1MS2

EFR

Codec type optimisation with the channel mode modify procedure, i.e.

AMR changed to EFR FR-HR matching

local switching ok

MS1BTS1 (EFR)

EFR ACS: 4.75, 5.9, 7.4

MS1MS2

not found

local switching nok

An operator must configure the same

AMR codec mode sets in all BTSs of the

local switching area

IP network

MS2BTS2 (AMR

HR)

MS1BTS1 (AMR

FR)

MS2BTS2 (AMR

FR, EFR)

MS2BTS2 (AMR

HR)

Load conditions forces MS1 does not

(26)

Local Switching for Packet Abis

Feature Details

• 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 BTSBSC 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-BTSBSC 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

Congestion

Control

(27)

Local Switching for Packet Abis

Feature Details

• 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

Handovers

(1/

3

3 )

)

BTS-1

intra-cell HO inside BTS

local switching NOT released

BTS-1

SEG-1

BCF-1

SEG-1

BTS-1

BCF-1

intra-cell HO inside BCF

local switching NOT released

intra-cell HO between BCFs

local switching NOT released if BCFs are in the same LS area

(28)

Local Switching for Packet Abis

Feature Details

• 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

Handovers

(

2

2 /

/

3

3 )

)

BTS-1

BTS-2

BTS-1

SEG-1

BCF-2

BCF-3

BCF-1

inter-cell HO between BCFs

local switching NOT released if BCFs are in the same LS area

BCF-1

inter-cell HO between BCFs local switching released

(29)

Local Switching for Packet Abis

Feature Details

• 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

Handovers

(

(30)

Local Switching for Packet Abis

Feature Details

• 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

Local switching release may cause audible effects on voice quality due to an

additional delay, especially in the case with the satellite backhaul

(31)

Local Switching for Packet Abis

Feature Details

• Connection of small/medium and isolated towns/villages to a GSM network, which

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

Application Scenarios

(1/

3

3 )

)

hub-BTS BTS BTS BTS BTS BTS BSC

Local switching area

Is ol at e d a re a – s m al l/m ed iu m to w n Savings on satellite links due to lower

Abis utilisation BTS BTS BTS BTS BTS

IP network

Lower load on Ethernet link towards BSC

Packet Abis over Ethernet Isol

at e d a re a – s m al l/m ed iu m to w n

(32)

Local Switching for Packet Abis

Feature Details

• 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

Application Scenarios

(

2

2 /

/

3

3 )

)

BTS BSC

BTS BTS

IP network

Lower load on Ethernet link towards BSC

BTS

Traffic switched locally in a site

The case is justified if it leads to a reduction of PCM lines!

Lower load on TDM link towards BSC

(33)

Local Switching for Packet Abis

Feature Details

• 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

Application Scenarios

(

3

3 /

/

3

3 )

)

hub-BTS BTS BTS BTS BTS BSC Is o la te d a re a – sm al l/m ed iu m to w n Locally established calls are switched

by the hub-BTS PS traffic generated by

subscribers increases

Locally switched calls are not put to Abis => more room for PS calls

(34)

Local Switching for Packet Abis

Feature Details

• 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 coding due to removal of coders from the transmission path =>

trans-coder 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)

Benefit

s

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

(35)

Impact on Planning and Dimensioning

(36)

Local Switching for Packet Abis

Impact on Planning and Dimensioning (1/11)

Summary

Interfac

e

Realisation

Connection

Savings

Abis

Packet Abis

_{over TDM/Eth}

BTSBSC

There

are savings

– see the next slides

Ater

TDM

BSCTCSM

”Empty” speech frames are transmitted to keep the connection

alive =>

no savings

BSCMGW

A

over IP

BSCMGW

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

TCSMMGW

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

TDM

TCSMMGW

”Empty” speech frames are transmitted to keep the connection

_{alive =>}

_{no 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!

(37)

Local Switching for Packet Abis

Impact on Planning and Dimensioning (2/11)

• 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)

Packet Abis Calculator for Local

Switching

(38)

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)

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 hard-coded); 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

8) Specify the voice and

codec distribution

9) Press Calculate

Inputs

(39)

Local Switching for Packet Abis

Impact on Planning and Dimensioning (4/11)

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)

3) Total bandwidth

required towards BSC 4) The required number of E1 lines 4) Total bandwidth 5) The required number of E1 lines

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

Outputs –

Inter-Site Local

Site Local

Switching

(40)

Local Switching for Packet Abis

Impact on Planning and Dimensioning (5/11)

towards a BSC and the required number of E1s (in case of packet Abis over TDM) towards the BSC without intra-site local switching

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

Outputs –

Intra-Site Local

Site Local

Switching

(41)

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)

(42)

Local Switching for Packet Abis

Impact on Planning and Dimensioning (7/11)

Inter-Site Local Switching with Packet Abis over

Ethernet

Edge node Edge node

IP network

L2 switch L2 switch L2 switch L2 switch L2 switch

ISP

Local BTS Local BTS Local BTS Local BTS

Local switching area

Edge node

BSC 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 €

Only non-locally switched calls are transferred by the IP

network provided by the ISP

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

IP network

ISP

Edge node Local BTS Local BTS Local BTS Local BTS

Local switching area

1GB Ethernet switch supporting fibre optic Locally switched calls are switched between ports of the switch without affecting the IP network provided by the ISP

Examples of network architecture for local switching

SFP* link in FIYA/FIQA

SFP link in FIYA/FIQA

(43)

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

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

(44)

Local Switching for Packet Abis

Impact on Planning and Dimensioning (9/11)

Intr

a

-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

(45)

Local Switching for Packet Abis

Impact on Planning and Dimensioning (10/11)

Intr

a

-Site Local Switching with Packet Abis over

TDM

- without local switching

- 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.

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

Application of intra-site local switching (TDM) makes sense for certain LS calls

(46)

Local Switching for Packet Abis

Impact on Planning and Dimensioning (11/11)

• The maximum bandwidth saving on the A interface over IP (BSCMGW)

is a sum of bandwidth savings of local switching areas connected to a

MGW:

• 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

A

Interface

 



_

 

lsa

savings

A

BW

lsa

BW

The maximum bandwidth savings on the A interface are reached when traffic

distributions in local switching areas are identical. In practice, this assumption may

(47)

Feature Dependencies

(48)

• Packet Abis over Ethernet or Packet Abis over TDM is a prerequisite for the local

switching feature

• 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

Local Switching for Packet Abis

Feature Dependencies

Packet Abis (RG20,

BSS21321)

DTM

(49)

• For the capability of the local call detection the User-User Signalling

(UUS) core feature (TS 22.087) must be activated

Local Switching for Packet Abis

Feature Dependencies

Other

Dependencies

(50)

Database Parameters

(51)

Local Switching for Packet Abis

Database Parameters

Packet Abis BCF Group ID packetAbisBcfGroupId

New

parameters

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.

object: BCF unit: none range: 0..3000 step: 1

default: 65535

MML commands: EFC, EFM, EFO MML abbreviated name: PABGID

MML commands (examples):

New parameters

(1/2)

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.

object: N/A unit: none range: N/A step: N/A default: N/A MML commands: N/A MML abbreviated name: N/A

List of Subscribers to Intercept N/A

(52)

Local Switching for Packet Abis

Database Parameters

Local Switching Enabled for Intercepted Calls lsEnabledInterceptedCalls

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.

object: BSC unit: none

range: [true, false] step: none

default: false

MML commands: EEM, EEO MML abbreviated name: LSEIC

MML commands (examples):

New parameters

(2/2)

Abis Interface Connection Type abisInterfaceConnectionType

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-BTSBSC 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

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

(53)

Performance Measurements

(54)

Local Switching for Packet Abis

Performance Measurements

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.

001274: MO_LS_CALL_SUCC (1 Traffic Measurement) Description Counter name

New counters

(1

/9

)

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)

…or per BTS (with the distinction of MOC (moc_1000) and MTC (mtc_1000) calls established locally):

001275: MT_LS_CALL_SUCC (1 Traffic Measurement)

100 _

_

) ( ) ( ) (

_







lsa BTS lsa BTS lsa BTS

TTEMPT

EIZ_CALL_A

SUCC_TCH_S

SUCC

CALL

LS

MT

SUCC

CALL

LS

MO

trf_1002

100 _

_

_



TTEMPT

EIZ_CALL_A

SUCC_TCH_S

SUCC

CALL

LS

MO

moc_1000

100 _

_

_



TTEMPT

EIZ_CALL_A

SUCC_TCH_S

SUCC

CALL

LS

MT

mtc_1000

(55)

Local Switching for Packet Abis

Performance Measurements

Description Counter name

New counters

(

2/9

)

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:

…or per BTS (csf_1000): 001276: LS_ESTAB_UNSUCC_DUE_ CODEC (1 Traffic Measurement)

100 [%]

_

) ( ) (

_





lsa BTS lsa BTS

TTEMPT

EIZ_CALL_A

SUCC_TCH_S

CODEC

NSUCC_DUE_

LS_ESTAB_U

mismatch

codec

locally

est

not

Calls

100 



TTEMPT

EIZ_CALL_A

SUCC_TCH_S

CODEC

NSUCC_DUE_

LS_ESTAB_U

csf_1000

(56)

Local Switching for Packet Abis

Performance Measurements

Number of releases of local switching due to an inter-cell handover outside a LS Area

Trigger event:

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):

…or per BTS 001277: LS_REL_DUE_INTER_HO_OUT_LS (1 Traffic Measurement) Description Counter name

New counters

(

3/9

)

100 _

_

) ( ) ( ) (

_







SUCC

CALL

LS

MT

SUCC

CALL

LS

MO

HO_OUT_LS

DUE_INTER_

LS_REL

dcr_1000

100 _

_

[%]

_







SUCC

CALL

LS

MT

SUCC

CALL

LS

MO

HO_OUT_LS

DUE_INTER_

LS_REL

BTS

nternal_HO

released_i

LS

(57)

001278:

LS_REL_DUE_EXTERNAL_HO

(1 Traffic Measurement)

Local Switching for Packet Abis

Performance Measurements

New counters

(

4/9

)

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)

…or per BTS

100 _

_

) ( ) ( ) (

_







SUCC

CALL

LS

MT

SUCC

CALL

LS

MO

AL_HO

DUE_EXTERN

LS_REL

dcr_1001

100 _

_

[%]

_







SUCC

CALL

LS

MT

SUCC

CALL

LS

MO

HO

AL

DUE_EXTERN

LS_REL

BTS

_HO

d_external

LS_release

(58)

001279:

LS_REL_DUE_SUPPL_SERV_ESTAB

(1 Traffic Measurement)

Local Switching for Packet Abis

Performance Measurements

New counters

(

5/9

)

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):

100 _

_

) ( ) ( ) (

_







SUCC

CALL

LS

MT

SUCC

CALL

LS

MO

SERV_ESTAB

DUE_SUPPL

LS_REL

dcr_1002

(59)

132000:

CS_U_PLN_RTP_PACKT_REC_LSBTS

(132 Local Switching Traffic)

Local Switching for Packet Abis

Performance Measurements

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.

New counters

(

6/9

)

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

132001:

CS_U_PLN_RTP_PACKT_LOST_LSBTS

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.

100 [%]

_







OST_LSBTS

TP_PACKT_L

CS_U_PLN_R

EC_LSBTS

TP_PACKT_R

CS_U_PLN_R

OST_LSBTS

TP_PACKT_L

CS_U_PLN_R

rate

loss

packet

DL

LS

(60)

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

132003:

CS_U_PLN_RTP_TOO_EARLY_LSBTS

Local Switching for Packet Abis

Performance Measurements

New counters

(

7/9

)

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.

132002:

CS_U_PLN_RTP_TOO_LATE_LSBTS

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.

100 [%]

_







EC_LSBTS

TP_PACKT_R

CS_U_PLN_R

LY_LSBTS

TP_TOO_EAR

CS_U_PLN_R

E_LSBTS

TP_TOO_LAT

CS_U_PLN_R

dejitter

to

due

rate

loss

packet

DL

LS

(61)

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

132007:

CS_U_PLN_UDP_OCTET_REC_LSBTS

Local Switching for Packet Abis

Performance Measurements

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.

132004:

CS_U_PLN_RTP_PACKT_SENT_LSBTS

New counters

(

8/9

)

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.

132005:

CS_U_PLN_UDP_PACKT_REC_LSBTS

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.

EC_LSBTS

DP_PACKT_R

CS_U_PLN_U

EC_LSBTS

DP_OCTET_R

CS_U_PLN_U

kB

size

packet

UDP

DL

LS

_

[

]



(62)

Local Switching for Packet Abis

Performance Measurements

New counters

(

9/9

)

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.

132006:

CS_U_PLN_UDP_PACKT_SENT_LSBTS

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.

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

Local Switching for Packet Abis

Andrzej Maciołek

Network Engineering

NWS LTE RA E2E Mgmt SA NE GSM&LTE Migration

February 2011

RG25 (BSS) Network Engineering Information

Local Switching for Packet Abis

BSS21327

BSS21327

Please always use the latest version of the materials which can be found under the link:

Local Switching for Packet Abis

BSS21327

•

Background Information

•

Feature Details

•

Impact on Planning and Dimensioning

•

Feature Dependencies

•

Database Parameters

•

Performance Measurements

•

Feature Impact Analysis and Verification

Table of Contents

Local Switching for Packet Abis

BSS21327

Dependency

Dependency

Table

Table

GSM800

GSM900

GSM1800

GSM1900

MSS

MGW

NetAct

-

-

-

-

-

-

OSS5.3

CD Set 3

BSC

SGSN

BTS Talk

Family

MetroSite

BTS

UltraSite

BTS

FlexiEDGE

BTS

MultiRadio

BTS Flexi

BTSplus

S15

BSC3i

(1000/2000

)

FlexiBSC

-

N

N

N

Y

EX4.1

EX4.1

Y

-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

•

This is also the case for calls established between terminals served by the same