N.2 IMS VoIP
33.1083G Security3GPPHandover interface for Lawful Interception (LI)Release 17TS
N.2.0 General
IMS-VoIP-Correlation used to carry the correlation information for IMS VoIP may consists of one or more set of the following:
IRI-to-IRI-Correlation
IRI-to-CC-Correlation (optional).
IRI-to-IRI-Correlation contains the correlation number related to the IRI messages and the IRI-to-CC-Correlation contains correlation numbers related to the CC. Since not all intercepts may have the associated CC, the presence of IRI-to-CC-Correlation is optional. With being a SET, the above structure allows to have multiple ICE points for the IRI and multiple CC Intercept Functions for the CC. The IRI-to-CC-Correlation is defined as a combination of the following two:
One or more Correlation Number used for the CC
Present only when more than one Correlation Numbers are used for CC.
The ASN.1 defined in B.3 and B.9 show the following:
IMS-VoIP-Correlation ::= SET OF SEQUENCE {
ims-iri [0] IRI-to-IRI-Correlation,
ims-cc [1] IRI-to-CC-Correlation OPTIONAL
}
IRI-to-CC-Correlation ::= SEQUENCE { — correlates IRI to Content
cc [0] SET OF OCTET STRING,– correlates IRI to multiple CCs
iri [1] OCTET STRING OPTIONAL
— correlates IRI to CC with signaling
}
IRI-to-IRI-Correlation ::= OCTET STRING — correlates IRI to IRI
Some of the fields present in the above definition may not be used at all and their presence is only for historical reasons (in other words, they were present in the early versions of the TS 33.108 and retained to avoid an impacts on to early implementations).
For easy understanding, the above definition is shown in a tabular form in Table N-1 below:
Table N-1: Structure of IMS-VoIP-Correlation
|
IMS-VoIP-Correlation |
||||||||||
|
SET 1 |
… |
SET m |
||||||||
|
ims-iri |
ims-cc |
… |
ims-iri |
ims-cc |
||||||
|
cc |
iri |
… |
cc |
iri |
||||||
|
SET 1 |
… |
SET n |
… |
SET 1 |
… |
SET p |
||||
It may be difficult to grasp the structure of the IRI-to-CC-Correlation correlation number. The idea is perhaps to allow the possibility of a change in the CC Intercept Function during a call. This annex assumes that a for a VoIP call, only one instance of cc within the ims-cc (i.e. IRI-to-CC-Correlation) is required.
N.2.1 One Correlation Number Value
The IMS nodes involved in the setting up of a session, exchange the correlation number values used for an IMS session and the same correlation number is used for the CC as well. In this case, the usage of the correlation information in IRI and CC can be as shown in Table N-2 below:
Table N-2: An example to show the use of IMS-VoIP-Correlation with single value
|
IMS-VoIP-Correlation |
||||||||||
|
SET 1 |
… |
SET m |
||||||||
|
ims-iri |
ims-cc |
… |
ims-iri |
ims-cc |
||||||
|
cc |
iri |
… |
cc |
Iri |
||||||
|
SET 1 |
… |
SET n |
… |
SET 1 |
… |
SET p |
||||
|
100 |
100 |
— |
||||||||
In Table N-2, a value of 100 is used as the correlation number. All IRI messages will have the correlation number value of 100 and the associated CC will have use the same correlation number value of 100. In this example, there is only one set of {ims-iri, ims-cc} and there is only one set of {cc} within the ims-cc and {iri} in ims-cc is not used.
A typical example use-case for the usage of Table N-2 could be: P-CSCF is the CC Intercept Triggering Function, IMS-AGW as the CC Intercept Function and S-CSCF as the IRI ICE. P-CSCF and S-CSCF coordinate to use the value 100 and P-CSCF supplies the value 100 to the IMS-AGW.
N.2.2 Multiple Correlation Number Values
N.2.2.0 General
Here, the IMS nodes do not exchange the correlation number values. In this case, correlation numbers may be delivered in multiple ways. The Table N-3, Table N-4 and Table N-5 illustrate the usages.
N.2.2.1 Method 1
Table N-3: An example to show the use of IMS-VoIP-Correlation with multiple values (method 1)
|
IMS-VoIP-Correlation |
||||||||||
|
SET 1 |
… |
SET m |
||||||||
|
ims-iri |
ims-cc |
… |
ims-iri |
ims-cc |
||||||
|
cc |
iri |
… |
cc |
Iri |
||||||
|
SET 1 |
… |
SET n |
… |
SET 1 |
… |
SET p |
||||
|
100 |
250 |
— |
||||||||
In Table N-3, the values of 100 and 250 are used as the correlation number values. All IRI messages will have the correlation number value of 100 and the associated CC will have use the correlation number value of 250. In this example, there is only one set of {ims-iri, ims-cc} and there is only one set of {cc} within the ims-cc. The {iri} in ims-cc is not used.
A typical example use-case for the usage of Table N-3 could be: P-CSCF is the CC Intercept Triggering Function, IMS-AGW as the CC Intercept Function and S-CSCF as the IRI ICE. P-CSCF tells the IMS-AGW to use the correlation number value of 250 and S-CSCF uses the value of 100 for IRI.
N.2.2.2 Method 2
Table N-4: An example to show the use of IMS-VoIP-Correlation with multiple IRI ICEs (method 2)
|
IMS-VoIP-Correlation |
||||||||||
|
SET 1 |
… |
SET m |
||||||||
|
ims-iri |
ims-cc |
… |
ims-iri |
ims-cc |
||||||
|
cc |
iri |
… |
cc |
Iri |
||||||
|
SET 1 |
… |
SET n |
… |
SET 1 |
… |
SET p |
||||
|
100 |
250 |
200 |
||||||||
In Table N-4, the values of 100, 200 and 250 are used as the correlation number values. The IRI messages will have the correlation number values of 100 and 200 and the associated CC will have use the correlation number value of 250. In this example, there is only one set of {ims-iri, ims-cc} and there is only one set of {cc} within the ims-cc. The {iri} in ims-cc is used.
A typical example use-case for the usage of Table N-4 could be: P-CSCF is the CC Intercept Triggering Function, IMS-AGW as the CC Intercept Function and S-CSCF as the IRI ICE. P-CSCF tells the IMS-AGW to use the correlation number value of 250 and S-CSCF uses the value of 100 for IRI. P-CSCF may additionally provide the IRI ICE functions and when it does, the related IRI messages use the correlation number 200.
As an alternative example, the iri (in ims-cc) and cc (in ims-cc) may use the same value (e.g. 200) instead of two values 200 and 250.
N.2.2.3 Method 3
Table N-5: An example to show the use of IMS-VoIP-Correlation with multiple values (method 3)
|
IMS-VoIP-Correlation (# of SETs = 2) |
||||||||||
|
SET 1 |
… |
SET 2 |
||||||||
|
ims-iri |
ims-cc |
… |
ims-iri |
ims-cc |
||||||
|
cc |
iri |
… |
cc |
iri |
||||||
|
SET 1 |
… |
SET n |
… |
SET 1 |
… |
SET p |
||||
|
100 |
– |
– |
200 |
250 |
– |
|||||
In Table N-3, the values of 100, 200 and 250 are used as the correlation number values. The IRI messages will have the correlation number value of 100, 200 and the associated CC will have use the correlation number value of 250. In this example, there are two sets of {ims-iri, ims-cc} and there is only one set of {cc} within each of the ims-cc and {iri} in ims-cc is not used.
A typical example use-case for the usage of Table N-5 could be: P-CSCF is the CC Intercept Triggering Function, IMS-AGW as the CC Intercept Function and S-CSCF as the IRI ICE. P-CSCF tells the IMS-AGW to use the correlation number value of 250 and S-CSCF uses the value of 100 for IRI. P-CSCF may additionally provide the IRI ICE functions and when it does, the related IRI messages use the correlation number 200.
As an alternative example, in SET2, the ims-iri (in ims-cc) and cc (in ims-cc) may use the same value (e.g. 200) instead of two values 200 and 250.
N.2.3 Complex Example – Use of one Correlation Number
Multiple IMS nodes are providing the IRI functions (e.g. S-CSCF and AS/MRFC) and two media streams (IMS-AGW and MRFP) are delivered to the LEMF as separate CC. When IMS nodes exchange the correlation numbers used, it is possible to use the same correlation number for all IRI messages and the CC. This is illustrated in Figure N-6.
Table N-6: Complex Example, but one value for the correlation number
|
IMS-VoIP-Correlation (# of SETs = 2) |
||||||||||
|
SET 1 |
… |
SET 2 |
||||||||
|
ims-iri |
ims-cc |
… |
ims-iri |
ims-cc |
||||||
|
cc |
iri |
… |
cc |
iri |
||||||
|
SET 1 |
… |
SET n |
… |
SET 1 |
… |
SET p |
||||
|
100 |
100 |
– |
100 |
100 |
– |
|||||
In Table N-6, correlation number value 100 is used. In the example, two sets of {ims-iri, ims-cc} and only one set of {cc} within each of the ims-cc is used. The {iri} in ims-cc is not used.
A typical example use-case for the usage of Table N-6 could be: S-CSCF provides the IRI ICE functions and the P-CSCF provides the CC Intercept Triggering Function, IMS-AGW as the CC Intercept Function. For the conference side of the call, AS provides the IRI ICE functions, MRFC provides the CC Intercept Trigger Function and the MRFP is the CC Intercept Function. In set 1, the P-CSCF tells the IMS-AGW to use the correlation number 100 for the CC and S-CSCF uses the correlation number 100. In set 2, the MRFC tells the MRFP to use the correlation number 100 and AS uses the correlation number 100 for the IRI.
N.2.4 Complex Example – Use of Multiple Correlation Numbers
N.2.4.0 General
Multple IMS nodes are providing the IRI functions (e.g. S-CSCF and AS/MRFC) and two media streams (IMS-AGW and MRFP) are delivered to the LEMF as separate CC. Here, the IMS nodes do not exchange the correlation number information.
In this case, correlation numbers may be delivered in multiple ways. The Table N-7, Table N-8 and Table N-9 illustrate the usages.
N.2.4.1 Method 1
Table N-7: Complex example to show the use of IMS-VoIP-Correlation with multiple values (method 1)
|
IMS-VoIP-Correlation |
||||||||||
|
SET 1 |
… |
SET m |
||||||||
|
ims-iri |
ims-cc |
… |
ims-iri |
ims-cc |
||||||
|
cc |
iri |
… |
cc |
Iri |
||||||
|
SET 1 |
… |
SET n |
… |
SET 1 |
… |
SET p |
||||
|
100 |
250 |
— |
1000 |
2500 |
||||||
In Table N-7, the values of 100, 250, 1000 and 2500 are used as the correlation number values. The IRI messages will have the correlation number value of 100 and 1000. The associated CC will have the correlation number values 250 and 2500. In this example, there are two sets of {ims-iri, ims-cc} and there is only one set of {cc} within the ims-cc. The {iri} in ims-cc is not used.
A typical example use-case for the usage of Table N-7 could be: S-CSCF provides the IRI ICE functions and the P-CSCF provides the CC Intercept Triggering Function, IMS-AGW as the CC Intercept Function. For the conference side of the call, AS provides the IRI ICE functions, MRFC provides the CC Intercept Trigger Function and the MRFP is the CC Intercept Function. In set 1, the P-CSCF tells the IMS-AGW to use the correlation number 250 for the CC and S-CSCF uses the correlation number 100. In set 2, the MRFC tells the MRFP to use the correlation number 2500 and AS uses the correlation number 1000 for the IRI.
As an alternative example, in SET2, the ims-iri and cc (in ims-cc) may use the same value (e.g. 1000) instead of two values 1000 and 2500.
N.2.4.2 Method 2
Table N-8: Complex Example to show the use of IMS-VoIP-Correlation
with multiple IRI ICEs (method 2)
|
IMS-VoIP-Correlation |
||||||||||
|
SET 1 |
… |
SET m |
||||||||
|
ims-iri |
ims-cc |
… |
ims-iri |
ims-cc |
||||||
|
cc |
iri |
… |
cc |
iri |
||||||
|
SET 1 |
… |
SET n |
… |
SET 1 |
… |
SET p |
||||
|
100 |
250 |
200 |
1000 |
2500 |
||||||
In Table N-8, the values of 100, 200, 250, 1000 and 2500 are used as the correlation number values. The IRI messages will have the correlation number values of 100, 200 and 1000, and the associated CC will have to use the correlation number value of 250 and 2500. In this example, there are two sets of {ims-iri, ims-cc} and there is only one set of {cc} within the ims-cc. The {iri} in ims-cc is used in one set.
A typical example use-case for the usage of Table N-8 could be: S-CSCF provides the IRI ICE functions and the P-CSCF provides the CC Intercept Triggering Function, IMS-AGW as the CC Intercept Function. For the conference side of the call, AS provides the IRI ICE functions, MRFC provides the CC Intercept Trigger Function and the MRFP is the CC Intercept Function. In set 1, the P-CSCF tells the IMS-AGW to use the correlation number 250 for the CC and S-CSCF uses the correlation number 100. P-CSCF may additionally provide the IRI ICE functions, and when it does, it uses the correlation number 200. In set 2, the MRFC tells the MRFP to use the correlation number 2500 and AS uses the correlation number 1000 for the IRI.
As an alternative example, in SET2, the ims-iri and cc (in ims-cc) may use the same value (e.g. 1000) instead of two values 1000 and 2500. Also, in SET 1, the iri and cc (in ims-cc) may use the same value (e.g. 200) instead of two values 200 and 250.
N.2.4.3 Method 3
Table N-9: Complex example to show the use of IMS-VoIP-Correlation with multiple values (method 3)
|
IMS-VoIP-Correlation |
||||||||||||||
|
SET 1 |
SET 2 |
SET 3 |
||||||||||||
|
ims-iri |
ims-cc |
ims-iri |
ims-cc |
ims-iri |
ims-cc |
|||||||||
|
cc |
iri |
cc |
iri |
cc |
iri |
|||||||||
|
SET 1 |
.. |
SET n |
SET 1 |
… |
SET p |
SET 1 |
… |
SET q |
||||||
|
100 |
200 |
250 |
1000 |
2500 |
||||||||||
In Table N-9, the values of 100, 200, 250, 1000 and 2500 are used as the correlation number values. The IRI messages will have the correlation number values of 100, 200 and 1000 and the associated CC will have to use the correlation number value of 250 and 2500. In this example, there is one set of {ims-iri}, two sets of {ims-iri, ims-cc} with one set of {cc} in each of the {ims-cc} and {iri} in {ims-cc} is not used.
A typical example use-case for the usage of Table N-9 could be: S-CSCF provides the IRI ICE functions and the P-CSCF provides the CC Intercept Triggering Function, IMS-AGW as the CC Intercept Function. For the conference side of the call, AS provides the IRI ICE functions, MRFC provides the CC Intercept Trigger Function and the MRFP is the CC Intercept Function. In set 1, S-CSCF uses the correlation number 100. In set 2, the P-CSCF tells the IMS-AGW to use the correlation number 250 for the CC and P-CSCF may provide the IRI ICE functions with the correlation number 200. In set 3, the MRFC tells the MRFP to use the correlation number 2500 and AS uses the correlation number 1000 for the IRI.
As an alternative example, in SET3, the ims-iri and cc (in ims-cc) may use the same value (e.g. 1000) instead of two values 1000 and 2500. Also, in SET 2, the ims-iri and cc (in ims-cc) may use the same value (e.g. 200) instead of two values 200 and 250.