Call flows
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Transcript of Call flows
MSC Innovation Configuration
SN B
LTG
LTG
SSNC
MB D
CPAMPC IOP:MB
Trunks and
SS7 Links
High Speed
SS7 Links
207Mb/s
PCM30/24
NetM
207Mb/s
SSNC: Signaling SystemNetworkControl
LTG: Line TrunkGroup
SN: SwitchingNetwork
MB: MessageBuffer Typ D
IOP: Input/OutputProcessor
AMP: ATM BridgeProcessor
CP: CoordinationProcessor
NetM: Net Manager
MSC structure
SNDLU LTG
LTG
Access
SSNC
SignalingSystem
Network
Control
SYP
Switching
Coordination
MB
CCG
CP
Switching
Exchange
4
Switching
Exchange
5
Switching
Exchange
2
Switching
Exchange
1
Switching
Exchange
3
Some terms of the Circuit Switched Exchange Telephony
Transit
Exchange
Originating
Exchange Terminating
Exchange
Incoming
Traffic
Transit Call and
Outgoing Traffic
Originating
Call
Lines Trunks
Busy
Idle
Calling Party
(A Subscriber)
Called Party
(B Subscriber)Note: The network shown here is only an example.
Routing
Routing in general is the method, how to find a way through a network
for a given Routing Information.
Whithin a Switch, Routing is to find an outgoing trunk, according to the
evaluation results of the Routing Information
Some typical elements of the Routing Information whithin a Switch:
Called Party Number (= dialed number, the most classical element)
Originating Trunk (where the call comes from, see Origin. Depend.
Routing)
Category of the Calling Subscriber (Ordinary, Priority, Operator,..)
Calling Party Number
Transmission Medium Required (Any, Only Digital, Analog,..)
….
During the evaluation of the of the Routing Information, one, some or
all elements can be considered.
Authentication and Ciphering
Authentication and ciphering execution
In the personalization center (PCS), the SIM cards are produced on the one hand and the
database for the subscriber are generated in the authentication center on the other.
The following parameters are necessary on the SIM card along with the IMSI for
authentication and ciphering:
Ki General key
A3 Algorithm 3. Used for generating the authentication code
A8 Algorithm 8. Used for generating the ciphering key
The following parameters are necessary in the database commands along with theIMSI for
authentication and ciphering:
KiA4 General key, however enciphered with algorithm A4 and additional key K4
A3 version Version of the algorithm 3 stored in the AC and to be used.
A8 Version Version of the algorithm 8 stored in the AC and to be used.
The KiA4 is deciphered in the AC with the help of algorithm A4 and key K4 (Ki=A4(K4,KiA4))
and is stored, enciphered again (KiA2=A2(K2,Ki)), in the subscriber database as KiA2 with
A2 and K2.
As soon as the subscriber is set up in the HLR, the AC begins with the generation of the
security parameters. These consist of three values: the rand (a random value), the Sres or
signed response (electronic signature for authentication) and the kc (key for the ciphering on
the radio interface). These three values are designated "triples". A reserve of 6 "triples" are
provisioned.
Authentication and ciphering execution (part2)
Authentication• The Rand is relayed to the mobile station. This generates the Sres with
the help of the parameter Ki stored on the SIM card and A3 (Sres=A3(ki ,rand)). The Sres is sent back to the MSC/VLR and there compared with the Sres of the triple. If both Sres are the same, the authentication is successful. If they are different, the SIM card is rejected, and only emergency calls are possible depending on theproject.
Ciphering• For the ciphering, the Rand is also used in the MS. The key Kc is
generated (Kc=A8(Ki, Rand)) with the help of the parameter Ki stored on the SIM card and A8. The ciphering is thereupon carried out with the algorithm 5 stored in the mobile equipment and the key Kc. The key Kccontained in the triple is meanwhile relayed to the BSS. The algorithm A5 is also available here, so that the ciphering can be carried out here as well.
Location Registration
Since subscribers can change their locations in the PLMN any number of times, it is absolutely necessary to log the current site to a central position for the availability of the subscriber. This central position is the HLR of the respective subscriber. Therefore the routing label of the visited MSC/VLR is entered there.
Location update is carried out for the following situations:
• When first checking into a network.
– The subscriber checks into a network for the first time.
• Upon change of location.
– The subscriber changes to another MSC area.
• Periodical location update (only in the VLR)
– A time provider in the mobile station runs out and a location update is carried out in the VLR.
• After failure of the HLR
– After a HLR failure, all affected VLRs are informed of the possible data loss. After subsequent originating traffic (mobile originating call), for instance, a location update is carried out in the HLR.
MS BS/MSC/VLR
old LAI & old TMSI
Acknowledgement
ciphered(new TMSI)
Allocate
new TMSI
Location up-date
• While staying in the old MSC area, the identification code of the location area (LAI location area ID) is noted on the SIM card (subscriber identity Module)• If the subscriber now moves to a new MSC area and thus also to a new location area, the mobile subscriber receives a new LAI from the MSC/VLR.• Since the new LAI is different from the old LAI, the mobile subscriber sends both LAIs back to the MSC.• If the new MSC knows the old LAI or the corresponding old MSC/VLR, it requests from there the security parameters not used (triples) and the subscriber identification IMSI (international mobile subscriber identity).• Hereupon the new location area is transmitted to the HLR from the new VLR/MSC.• The HLR thereupon informs the old MSC/VLR that the subscriber is to be deletedin the VLR.
MSold LAI & old TMSI
Acknowledgement
ciphered(new TMSI)
Allocate
new TMSI
old TMSI
unknown
IMSI
ID request
BS/MSC/VLR
Location up-date –TMSI unknown
Location Update with Location Change to anUnknown MSC/VLR
• While staying in the old MSC area, the identification code of the location area
• (LAI location area ID) is noted on the SIM card (subscriber identity Module)
• If the subscriber now moves to a new MSC area and thus also to a new location
• area, the mobile subscriber receives a new LAI from the MSC/VLR.
• Since the new LAI is different from the old LAI, the mobile subscriber sends both
• LAIs back to the MSC.
• Since in this case the old MSC/VLR is unknown in the new MSC/VLR, the MSC/
• VLR requests the subscriber identification number (IMSI international subscriber
• identity) from the mobile subscriber and transmits the new location to the HLR.
• The HLR thereupon informs the old MSC/VLR that the subscriber is to be deleted
• in the VLR.
Mobile Originated Call (MOC) in D900
Visited
MSC
Transit
switch
Transit
switch
Terminating
exchange
MOC
Outgoing Traffic
Transit Call
Outgoing Traffic
Transit Call
Outgoing Traffic
Terminating Call
Terminating Traffic
A-sideMobile Station
Signalling
e g by ISUP, TUP, MFCR2
BSC
BTS
VLR
A-interfaceBSSAP
based on SCCP
Air interface
B-sideterminal
equipment
Bnumber
Bnumber
Bnumber
Bnumber
•The dialing information is received via BSSAP in the MSC.
•An audit of possible subscriber restrictions takes place in the MSC/VLR.
•The dialing information is converted in the MSC and via the routing a route into
the PSTN is determined.
MOC macro
Message 1 MSC <- BSS CR(Complete L3 info(CM service request))
Message 2 MSC -> BSS CC(Authentication Request)
Message 3 MSC <- BSS DT1(Authentication Response)
Message 4 MSC -> BSS DT1(Cipher Mode Command)
Message 5 MSC <- BSS DT1(Cipher Mode Complete)
Message 6 MSC -> BSS DT1(ID Request (IMEI))
Message 7 MSC <- BSS DT1(Setup)
Message 8 MSC -> BSS DT1(Call Proceeding)
Message 9 MSC -> BSS DT1(Assignment Request)
Message 10 MSC <- BSS DT1(ID Response (IMEI))
Message 11 MSC <- BSS DT1(Assignment Complete)
Message 12 MSC -> BSS DT1(TMSI Reallocation Command)
Message 13 MSC <- BSS DT1(TMSI Reallocation Complete)
Message 14 PSTN <- MSC IAM
Message 15 PSTN -> MSC ACM
Message 16 MSC -> BSS DT1(Alerting)
Message 17 PSTN -> MSC ANM
Message 18 MSC -> BSS DT1(Connect)
Message 19 MSC <- BSS DT1(Connect Acknowledge
Mobile Originated Call (MOC) in D900 with MNP (QoD – query on digits)
Visited
MSC
Transit
switch
Transit
switch
Terminating
exchange
MOC
Outgoing Traffic
Transit Call
Outgoing Traffic
Transit Call
Outgoing Traffic
Terminating Call
Terminating Traffic
A-sideMobile Station
Signalling
e g by ISUP, TUP, MFCR2
BSC
BTS
VLR
A-interfaceBSSAP
based on SCCP
Air interface
B-sideterminal
equipment
Bnumber
Bnumber
Bnumber
Bnumber
•The dialing information is received via BSSAP in the MSC.
•An audit of possible subscriber restrictions takes place in the MSC/VLR.
•Based on the dialled digits, MNP query is started; MNP server is triggered
•The information from MNP server is converted in the MSC and via the routing a
route into the PSTN is determined.
MNP server
Mobile Terminating Call e.g. from PSTN
• The dialing information is received by PSTN e.g. via ISUP in the PLMN gateway MSC
• The dialing information is converted in the gateway MSC.• A so-called "interrogation" is started as a response; i.e. a MAP message
is sent to the HLR in order to obtain location-specific routing information. The HLR knows the location routing label i.e. the MSC/VLR by the"location update" and relays the query there.
• The MSC/VLR makes a temporary directory number available and sends it back via the HLR to the gateway MSC.
• The gateway MSC converts this temporary directory number and sets up a circuit connection (ISUP) to the visited MSC. The location area is specified in the MSC/VLR owing to the cross-connection between temporary directory number and mobile subscriber.
• The visited MSC now sends a "paging" to all BSCs situated in the location area.
• The BSC in which the subscriber is currently situated answers with a "paging response".
• The MSC makes the connection to the called subscriber.
Mobile Terminating Call
VLR
Transit
switch
Transit
switchlocal
exchange
Mobile
Terminating
Traffic
Transit Call
Outgoing
Traffic
Outgoing
Traffic
Originating Call
Outgoing Traffic
B-sideMobile Station
Signalling
e g by ISUP (TUP, MFCR2)
BSC
BTS
Visited
MSC
A-interfaceBSSAP
based on SCCP
Air interface
A-sideterminal
equipment
Gateway
MSC
Interrogation
HLR
MSRN MSRNMSISDN
MSISDN
MAP signalling
based on SCCP and TCAP
MSRN MSRN
SendRoutingInfo
ProvideRoamingNr
MSRN
MTC macro
Message 1 PSTN -> MSC IAM
Message 2 MSC -> BSS UDT(paging)
Message 3 MSC <- BSS CR(ComL3Inf (Paging response)
Message 4 MSC -> BSS CC(Authentication Request)
Message 5 MSC <- BSS DT1(Authentication Response)
Message 6 MSC -> BSS DT1(Cipher Mode Command)
Message 7 MSC <- BSS DT1(Cipher Mode Complete)
Message 8 MSC -> BSS DT1(ID Request)
Message 9 MSC -> BSS DT1(Setup)
Message 10 MSC <- BSS DT1(ID Response)
Message 11 MSC -> BSS DT1(TMSI Reallocation Command)
Message 12 MSC <- BSS DT1(Call Confirmed)
Message 13 MSC -> BSS DT1(Assignment Request)
Message 14 MSC <- BSS DT1(Assignment Complete)
Message 15 MSC <- BSS DT1(TMSI Reallocation Complete)
Message 16 MSC <- BSS DT1(Alerting)
Message 17 PSTN <- MSC ACM
Message 18 MSC <- BSS DT1(Connect)
Message 19 MSC -> BSS DT1(Connect Acknowledge)
Message 20 PSTN <- MSC ANM
Mobile Terminating Call with MNP (QoHLR – query on HLR)
Transit
switchTransit
switchlocal
exchange Transit Call
Outgoing
Traffic
Outgoing
Traffic
Originating Call
Outgoing Traffic
Signalling
e g by ISUP (TUP, MFCR2)
A-sideterminal
equipment
Gateway
MSC
Interrogation
HLR
MSISDNMSISDN
MAP signalling
based on SCCP and TCAP
Unknown subscriber
SendRoutingInfo
Transit
switch
Call Forwarding Unconditional
Transit
switch
Transit
switchlocal
exchange Transit Call
Outgoing
Traffic
Transit Call
Outgoing Traffic
Originating Call
Outgoing Traffic
Signalling
e g by ISUP (TUP, MFCR2)
terminating
exchange
A-sideterminal
equipment
Gateway
MSC
Transit Call
Interrogation
HLR
FTNO FTNOMSISDN
MSISDN
MAP signalling
based on SCCP and TCAP
FTNOSendRoutingInfo
C-sideterminal
equipment
Terminating Call
Terminating Traffic
B side (mobile) to
C side
Mobile to Mobile Call (Mobile Subscribers indifferent MSC/VLRs)
• The dialing information is received via BSSAP in the MSC
• An audit of possible subscriber restrictions takes place in the MSC/VLR
• The dialing information is converted in the visited MSC of the calling subscriber.
• A so-called "interrogation" is started as a response; i.e. a message is sent to the HLR in order to obtain location-specific routing information. The HLR knows the location routing label i.e. the MSC/VLR by the"location update" and relays the query there.
• The MSC/VLR makes a temporary directory number available and sends it back via the HLR to the MSC of the calling subscriber.
• The MSC of the calling subscriber converts this temporary directory number and sets up a circuit connection (ISUP) to the visited MSC. The location area is specified in the MSC/VLR owing to the cross-connection between temporary directory number and mobile subscriber.
• The visited MSC now sends a "paging" to all BSCs situated in the location area. The BSC in which the subscriber is currently situated answers with a "paging response".
• The MSC makes the connection to the called subscriber.
MIC LOOP: (Mobile Internal Call Loop)
CP
CP
BSSAP - LTG
BSSAP - LTG
MS
MS
LOOP - LTG
MOC
MTC
MIC-Code would be
neccesary
The ORIG1 Story
When we need to perform different actions in differnet callsetup-states with the
same digits, then we use the ORIG1 parameter in command CR CPT
The ORIG1 can be imagined as an additional digit suffix. It is copied into the CPB
and is together with the digits an additional input for the digittranslator.
There are two kinds, how an ORIG1 can be assigned to a call (and copied to the
CPB):
a) assignment via incoming trunk group
b) assignment within specific callsetup
An incoming trunkgroup can be forced to assign an ORIG1 by the ORIG1
parameter in CR TGRP. (see Origination Dependent Routing in the EWSD).
This method is used in D900 MIC/PBX-loop treatment to distinguish between
BSSAP, Trunk or PBX call origination
In specific cases during call setup, the assignement occurs with a procedural
access to preadministered ORIG1 values for MSRN, CF, IN Loop, NP,...
(see MML command ENTRMPRDDAT)
Quiz• Q1: Does the HLR know the respective location of the subscriber?
• Q2: Does the AC generate the mobile station roaming number?
• Q3: Does the MSC serve to through connect the call from the BSC to other MSCs?
• Q4: Which number serves to identify the subscriber and is stored onthe SIM card?
• Q5: With which number can the subscriber be internationally dialed?
• Q6: Which number is transmitted to the equipment identification register for auditing?
• Q7: Which number is used instead of the IMSI in order to avoid unnecessary interchange of the IMSI via the radio interface?
• Q8: Which three components does a so-called triple comprise?
• Q9: Which parameter of the triple compares the MSC/VLR for the authentication test?
• Q10: Did you find this course interesting/usefull?
Answers
• A1: Yes
• A2: No
• A3: Yes
• A4: IMSI
• A5: MSISDN
• A6: IMEI
• A7: TMSI
• A8: Sres, rand, kc
• A9: Sres
• A10: Of course