10 Interworking to the ISDN

09.073GPPGeneral Requirements on Interworking between the Public Land Mobile Network (PLMN) and the Intergrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN)TS

The interworking to the ISDN is specified on the principle of the network supporting standardized associated signalling protocol as outlined in clause 2, i.e. DSS1 and ISUP. An ISDN not complying with this definition differs ‑ for the purpose of this ETS ‑ in that it does not support the compatibility information to that degree necessary for deducing a GSM Basic Service. These networks will find their reflection in the following where those implications are to be set out.

The calling address sent in a mobile originated call to the ISDN is always the basic MSISDN even if the ISDN user has to use a different MSISDN (multi numbering scheme, see 9.2.2 case a) for a mobile terminated call (call back) as only the basic MSISDN is available at the VLR (see GSM 09.02).

The scope of this clause is to describe the handling of the content of the Information Elements where "content" is understood to be the value of the parameter fields of the Information Elements, namely BC‑IE, HLC and LLC, after the length indicator. For the transport of these Information Elements within the PLMN refer to GSM 09.02.

The handling of multislot or 14.4kbit/s-related parameter of the call control signalling and the applicability of single- or multislot configurations (refer to GSM 08.20 and GSM 04.21) is the same as for the PSTN interworking cases. For multislot or 14.4kbit/s-operations, the MS may also propose to the network to modify the Fixed Network User Rate and Other Modem Type parameters (see GSM 07.01).In case a CE:T is used, the call shall be released. For a CE:NT with flow control, the MSC/IWF shall use towards the fixed network the unmodified "fixed network user rate" and shall use the "wanted air interface user rate" towards the mobile station.

10.1 Speech Calls

Since at the interworking point the transcoder provides for A law PCM at 64 kbit/s, no particular interworking is required. It is anticipated that the ISDN Teleservice Telephony and ISDN Bearer Service speech, respectively would be used. Transmission aspects are covered in GSM 03.50. Any further requirements are a national matter.

10.2 Data Calls

In this case it is assumed that the ISDN bearer service 3,1 kHz audio shall only be interworked by means of a modem pool in the PLMN. If a network operator provides this facility, then the MSC/IWF operation will be similar to that described for interworking to the PSTN.

10.2.1 Network interworking mobile originated

Low layer compatibility checking of the mobile originated call is carried out by the MSC/IWF to determine the appropriate bearer service selection in the ISDN. This will entail the MSC/IWF in mapping appropriately the GSM BC‑IE to the ISDN BC‑IE (bearer capability information element). If it is not possible for the MSC/IWF to provide a bearer service match, then the MSC/IWF shall fail the call and indicate the reason to the user.

The MS shall provide further compatibility information (LLC/HLC‑IEs) if required for defining end‑to‑end compatibility.

As well as compatibility checking, subscription checking should be performed.

10.2.1.1 Circuit switched calls

Where the bearer capability information indicates that the call is a circuit switched unrestricted digital call, then the MSC/IWF shall select the appropriate rate adapted ISDN bearer service.

The selection of the MSC/IWF will be by means of the bearer capability information within the call set up message. The mobile subscriber shall be able to select the unrestricted digital capability, which the MSC/IWF will map to the same capability in the ISDN call set up message. If an interworking point is encountered within the ISDN which does not support this service request, then either a call release message including an appropriate error cause or progress message is returned to the PLMN, indicating that the ISDN network is unable to support the service requested. In the case of a call release message the network shall release the call. In the case of progress message the network releases the call or forwards it (see GSM 04.08) to the mobile which will release the call.

10.2.1.2 Packet calls

The mobile network offers only Bm channel access for the packet mode service. The ISDN offers both B and D channel access for the packet mode service. The interworking of mobile packet service calls is described in GSM 09.06.

10.2.2 Network interworking mobile terminated

This subclause describes the interworking of calls where the calling subscriber can communicate ISDN compatibility information with exhaustive contents for deducing a GSM Basic Service to a PLMN (gateway MSC/interrogating node) i.e. by means of ISDN signalling.

The GMSC has to perform a mapping of the received Basic Service Information for the transport to the HLR, for details of this transport refer to GSM 09.02.

Compatibility checking of the low layers of the ISDN originated call is carried out by the MSC/IWF to determine the appropriate bearer service selection in the PLMN. This will entail the MSC/IWF in mapping appropriately the ISDN BC/LLC‑IE to the GSM BC‑IE.

As well as compatibility checking, subscription checking should be performed. If either the subscription check or the compatibility check fails then the call will be rejected.

For ISDN originated calls it will not be possible to signal mobile specific requirements e.g. transparent/non transparent, full/half rate channel. Therefore the MSC/IWF shall select a default setting appropriate to the visited PLMN’s network capabilities. In general it will be beneficial, where a network supports both full and half rate channels and transparent/non transparent capabilities, to indicate so in the appropriate GSM BC field of GSM 04.08. The mobile subscriber has the option to indicate in the call confirmation message a change to this default setting according to the rules specified in GSM 07.01. The appropriate MSC/IWF shall be selected on the basis of this requirement.

At call Set‑up, the interrogating node passes in the "send routing information" to the HLR, the ISDN BC, LLC and HLC received in the initial address message. The coding of these parameters must comply with ETS 300 102‑1 edition 1, with one exception: for the mapping of the parameter modem type to/from the ISDN BC‑IE, refer to tables 6A and 6B.

According to the contents of the Compatibility Information, i.e. the ISDN BC, LLC and HLC received, the HLR applies one of the following alternatives:

1) No ISDN BC is received, or one from which a GSM Basic Service cannot be deduced with the information Transfer Capability field set to "3,1 kHz audio" but without any associated modem type[1]1 in the ISDN BC and LLC, or without HLC indication of group 3 facsimile. Two cases have to be considered:

a) The called MSISDN has one or two corresponding GSM BC‑IE(s) stored in the HLR (see option a) of 9.2.2); then the service attached to this number in the HLR tables is applicable and the corresponding GSM BC‑IE(s) is passed to the VLR in "provide roaming number". See figure 6.

If two GSM BC‑IE have to be sent to the VLR they are preceded by a repeat indicator information element according to 04.08. These three information elements shall be included within the MAP parameter "GSM Bearer Capability" of the message "Provide Roaming Number".

NOTE: For the case of two GSM BC‑IEs see subclause 10.3.

b) The called MSISDN has no corresponding GSM BC‑IE(s) stored in the HLR (see option b in 9.2.2). In this case no GSM BC is passed to the VLR in the "provide roaming number" message.

2) Compatibility Information is received from which a GSM Basic Service can be deduced, i.e. the ITC field in the ISDN BC received is "unrestricted digital" and the fields for the applicable user layer 1 protocol and user rate are available (either in the ISDN BC or LLC), or the ITC field is "3,1 kHz audio", and a modem type, user rate, etc. is indicated but the HLC does not indicate "facsimile group 3". The received ISDN BC (and possibly LLC plus HLC) is then considered applicable regardless of the kind of MSISDN received (GSM BC associated or not) and either the equivalent GSM BC or the original ISDN BC/LLC is sent to the VLR. Additionally in both cases the originally received HLC may also be sent to the VLR, see figure 7.

When the HLR interworks with a phase 1 VPLMN (VLR/VMSC), then the HLR shall convert the ISDN BC to the equivalent GSM BC, and forward to the VLR. In this case however no LLC can be forwarded.

3) Compatibility Information is received from which the GSM Teleservice category Facsimile transmission can be deduced i.e. the ITC field in the ISDN BC received is "3,1kHz audio" and the HLC indicates "facsimile group 3" (see figure 7), the following two cases have to be considered:

a) The called MSISDN has a corresponding GSM BC stored in the HLR (either stating TS 61 or TS 62). In this case the service attached to the MSISDN in the HLR tables is applicable and the corresponding GSM BC is passed to the VLR in the "provide roaming number" message, see also subclause 10.3.1.3.

b) The called MSISDN has no corresponding GSM BC stored in the HLR. In this case the HLR shall forward the appropriate GSM BC to the VLR in line with the subscribers subscription to teleservice 61 or 62.

For TS 61 the value of the GSM BC‑IE parameter "Information Transfer Capability" shall be set to "alternate speech/facsimile group 3, starting with speech"

In both cases the HLC IE should be passed to the VLR in the "provide roaming number" message.

Alternatively the HLR may forward the originally received ISDN/LLC/HLC, when interworking with a phase 2 VLR.

4) In the case where Compatibility Information received does not allow for deducing a GSM Bearer Service but an ISDN BC is received with the ITC field indicating "unrestricted digital", but without the fields indicating applicable "user layer 1 protocol", user rate, etc., neither in the ISDN BC or the ISDN LLC then the following shall apply. The call is managed as for an udi call according to section 9.2.2, i.e either the "multi numbering" or "single numbering" scenario is applied depending on which capability is provided by home PLMN/HLR.

At the VMSC, when the incoming call arrives, the LLC/HLC and the GSM or ISDN BC associated with the MSRN is retrieved from the VLR. LLC and HLC are sent with the GSM BC in general to the MS at call set‑up. In particular, however the following rules apply:

1) If the Initial Address Message (IAM) contains no ISDN BC and there is no GSM or ISDN BC/LLC/HLC retrieved from the VLR, the call is handled as subclause 9.2.2 case b.

2) If there is no ISDN BC in the IAM but a GSM or ISDN BC/LLC/HLC was signalled in the "provide roaming number" message, the retrieved GSM or ISDN BC/LLC/HLC applies.

3) If there is an ISDN BC in the IAM with the ITC field set to "3,1 kHz audio" but without any associated modem type or indication of facsimile group 3 in the HLC, the GSM or ISDN BC/LLC/HLC retrieved from the VLR is considered as applicable when it exists. If no GSM or ISDN BC is retrieved from the VLR, the call is handled as in subclause 9.2.2 case b.

4) If the ISDN BC received in the IAM has the ITC field set to the value "unrestricted digital information" and the fields for the applicable "user layer 1 protocol" and "user rate" are available (either in the ISDN BC or ISDN LLC), or if 3,1 kHz audio and a modem type is indicated, this ISDN BC is applicable regardless of what has been retrieved from the VLR. In this case the ISDN BC has to be mapped to an appropriate GSM BC (refer to table 6B).

5) If the ISDN BC received in the IAM has the ITC field set to the value "3,1kHz audio" and a HLC "facsimile group 3" is indicated, the GSM BC retrieved from the VLR is applicable when it exists. If a GSM BC‑IE with the parameter "information transfer capability" set to "alternate speech/facsimile group 3, starting with speech" (stating TS61) is retrieved from the VLR, this shall be mapped to two GSM BC‑IE preceded by a repeat indicator, one representing speech, the other representing facsimile group 3.

When no GSM BC is retrieved from the VLR, either two GSM BCs preceded by a repeat indicator (stating teleservice 61), or a single GSM BC‑IE (stating TS 62), are sent in the setup message, depending whether TS 61 or TS 62 is subscribed (see also subclause 10.3.1.3).

In case of TS 61, the order in which the two GSM BC‑IEs are sent towards the MS, in the setup message, is a network option.

6) If the ISDN BC received in the IAM has a ITC value "unrestricted digital information" but without applicable "user layer 1 protocol" and "user rate", etc. fields, neither in the ISDN BC nor ISDN LLC, then the GSM or ISDN BC/LLC retrieved from the VLR is applicable, if available otherwise subclause 9.2.2 case b applies.

In case of an ISDN BC/LLC/HLC was attached to the MSRN this has to be mapped to an appropriate GSM BC (refer to table 6B). However in both cases (GSM or ISDN BC attached) the PLMN specific parameters of the GSM BC‑IEs may be added/modified in line with procedures identified in subclause 9.2.2.

In all cases when no GSM or ISDN BC is retrieved from the VLR and no ISDN Compatibility information allowing deduction of a GSM Bearer Service is available, then no GSM BC is inserted by the VMSC and subclause 9.2.2 case b applies.

The mapping between GSM and ISDN BCs is shown in table 6.

Mobile terminated, ISDN originated call compatibility Information provided not exhaustive for deducing a GSM Bearer Service, but Information Transfer Capability = 3,1 kHz audio, no modem type and no HLC IE indicating facsimile group 3. HLR stores GSM BC against MSISDN number multi‑numbering scheme.

Abbreviations: see figure 2.

NOTE: (1) Some parameters of BCgk may be provided/modified according to the MSC’s capabilities/preferences. See subclause 9.2.2

(2) In the "Call Confirm" message, the MS may modify some parameters of the GSM BC. See subclause 9.2.2.

Figure 6

Mobile terminated, ISDN originated call compatibility Information provides sufficient information to deduce:

‑ a GSM Bearer Service, or

‑ Information Transfer Capability = 3,1 kHz audio with HLC IE indicating facsimile group 3.

NOTES: (1) BCij denotes ISDN ETS 300 102‑1 BC*; BCgj is the corresponding GSM BC.

(2) Assumes signalling capabilities permit the transfer of BC between IN and VMSC. If this is not the case, the VLR uses the stored BC/LLC/HLC.

(3) BC’ij denotes BCij as maybe modified by intervening networks.

(4) Some parameters of BCgk may be provided/modified according to the MSC’s capabilities/preferences. See subclause 9.2.2.

(5) In the "Call Confirm" message, the MS may modify some parameters of the BC. See subclause 9.2.2.

(6) For details on how the BC, HLC, and LLC are transported, refer to GSM 09.02.

* HLC and LLC refers to ISDN values.

Abbreviations: see figure 2.

Figure 7

The following tables (6A + 6B) show that only the ISDN BC is used for mapping (exceptions are indicated).

NOTE: The ISDN/GSM BC‑IE mapping shall be performed as specified in tables 6A and 6B. This must be done to allow setup of a compatible end‑to‑end connection between two MSs or one MS and an ISDN terminal.

It has been acknowledged that octets 5a, 5b, 5c and 5d or a combination of them may also be sent and received in 3,1 kHz audio calls. Follow‑up versions of ETS 300 102‑1 (i.e. ETS 300 403‑1), confirm this interpretation. This is especially important for MOC‑ISDN terminating calls, where early Customer Premise Equipment (e.g. PABXs), may reject these calls.

In the following table the comparison is drawn between parameters in the GSM call set up request message and that of the ISDN call set up request message. In some cases no comparable values are available and these will be marked as such. In these cases reference will need to be made to the table of network interworking in GSM 09.07 to identify the appropriate choice. In some cases it is not necessary to support a particular option, and in this case those parameters will be annotated appropriately.

Table 6A: Comparable setting of parameters in GSM 04.08 and ETS 300 102‑1
(ETSI ISDN user to network signalling) Mobile Originated

Octet

GSM 04.08 parameter value as in GSM 07.01

Octet

ETS 300 102‑1 parameter value

1

Bearer Capability IEI

1

Bearer Capability IEI

2

Length of BC contents

2

Length of BC contents

3
#7..6

Radio channel requirement
half rate channel
full rate channel
dual, full, rate preferred
dual, half rate preferred

No comparable field

3
#4

Coding Standard
GSM standard coding

3
#7..6

Coding Standard
CCITT standardized coding

3
#4

Transfer mode
circuit mode
packet mode (note7)

4
#7..6

Transfer mode
circuit mode
packet mode

3
#3..1

Information transfer capability
speech
unrestricted digital
3,1 kHz audio ex PLMN
facsimile group 3 (note 1)
other ITC (see octet 5a)

3
#5..1

Information transfer capability
speech
unrestricted digital
3,1 kHz audio
see table 4 in GSM 09.07
no comparable value

5a
#7..6

Other ITC
restricted digital


(note 18)

4
#7

Compression (note 14)
data compression allowed
data compression not allowed

No comparable field

4
#6..5

Structure
SDU integrity
unstructured

4a
#7..5

Structure (note 4)

4
#4

Duplex mode
half duplex
full duplex

5d
#7

Duplex mode
half duplex
full duplex

(continued)

Table 6A (continued): Comparable setting of parameters in GSM 04.08 and ETS 300 102‑1 (ETSI ISDN user to network signalling) Mobile Originated

Octet

GSM 04.08 parameter value as in GSM 07.01

Octet

ETS 300 102‑1 parameter value

4
#3

Configuration
point to point

4a
#4..3

Configuration (note 4)
point to point

4
#1

Establishment
demand

4a
#2..1

Establishment (note 4) demand

4

NIRR (note 12)
meaning
Data  4.8kbit/s, FR nt,
6kbit/s radio interface is requested

No comparable field

5
#5..4

Rate adaptation
no rate adaptation (note 2)
V.110/X.30 rate adaptation

CCITT X.31 flag stuffing

No comparable value (note 11)
No comparable value (note 11)

No comparable value (note 11)

other rate adaptation (see octet 5a)

5
#5..1

User information layer 1 protocol
no comparable value
CCITT standardized rate adaption V.110/X.30
CCITT standardized rate adaption X.31 flag stuffing
Recommendation G.711 µ law
Recommendation G.711 A law (note 3)
Recommendation G.721 32 kbit/s
ADPCM and I.460
No comparable value

5a
#5..4

Other rate adaptation
V.120 (note 17)

No comparable value

5
#3..1

Signalling access protocol
I.440/I.450
X.21
X.28, ded.PAD, indiv.NUI
X.28, ded PAD, univ.NUI
X.28, non‑ded PAD
X.32

No comparable field

6
#1

Synchronous/asynchronous
synchronous
asynchronous

5a
#7

Synchronous/asynchronous
synchronous
asynchronous

6
#5..2

User info. layer 1 protocol
default layer 1 protocol

5
#5..1

User info. layer 1 protocol
see section under rate adaptation for GSM 04.08 above

6a
#7

Number of stop bits
1 bit
2 bits

5c
#7..6

Number of stop bits
1 bit
2 bits

6a
#6

Negotiation
In band neg. not possible
no comparable value

5a
#6

Negotiation
In band neg. not possible
In band neg. possible (note 10)

6a
#5

Number of data bits

7 bits
8 bits

5c
#5..4

Number of data bits excluding parity if present
7 bits
8 bits

(continued)

Table 6A (continued): Comparable setting of parameters in GSM 04.08 and ETS 300 102‑1 (ETSI ISDN user to network signalling) Mobile Originated

Octet

GSM 04.08 parameter value as in GSM 07.01

Octet

ETS 300 102‑1 parameter value

6a
#4..1

User rate
0.3 kbit/s
1.2 kbit/s
2.4 kbit/s
4.8 kbit/s
9.6 kbit/s
12 kbit/s (note 7)
1.2 kbit/s / 75 bit/s
any value
no comparable value

5a
#5..1

User rate
0.3 kbit/s
1.2 kbit/s
2.4 kbit/s
4.8 kbit/s
9.6 kbit/s
12 kbit/s
75 bit/s / 1.2 kbit/s
19.2 kbit/s (note 14)
Ebits or inband negotiation
(note 10)

6b
#7..6

Intermediate rate
8 kbit/s
16 kbit/s
any value

5b
#7..6

Intermediate rate (note 13)
8 kbit/s or not used
16 kbit/s or not used 32 kbit/s or not used (note 14)

6b
#5

NIC on Tx
does not require
requires (note7)

5b
#5b

NIC on Tx
does not require
requires (note 8)

6b
#4

NIC on Rx
cannot accept
can accept (note 7)

5b
#4

NIC on Rx
cannot accept
can accept (note 8)

6b
#3..1

Parity information
odd
even
none
forced to 0
forced to 1

5c
#3..1

Parity information
odd
even
none
forced to 0
forced to 1

6c
#7..6

Connection element
transparent
non‑transparent (RLP)
both, transp. preferred
both, non‑transp. preferred

No comparable field

6c
#5..1

Modem type
none
V.21
V.22
V.22bis
V.23
V.26ter
V.32
modem for undef. interface
autobauding type 1

5d
#6..1

Modem type (note 9)
no comparable value (note 5)
V.21
V.22
V.22bis
V.23
V.26ter
V.32
No comparable value (note 5)
No comparable value (note 5, note 10)

7
#5..1

User info. layer 2 protocol
X.25 link level
ISO 6429, codeset 0
COPnoFlCt
videotex profile 1 (note 7)
X.75 layer 2 modified (CAPI)

6

User info.layer 2 prot. (note 6)
X.25 link level
no comparable value
no comparable value
no comparable value
X.25 link level

Table 6A (concluded): Comparable setting of parameters in GSM 04.08 and ETS 300 102‑1 (ETSI ISDN user to network signalling) Mobile Originated

6d
#5..1

Fixed network user rate (note 15)

FNUR not applicable (note 7)
9,6 kbit/s
12 kbit/s (note 7)
14,4 kbit/s
19,2 kbit/s
28,8 kbit/s
38,4 kbit/s
48,0 kbit/s
56,0 kbit/s
64,0 kbit/s

5a
#5..1

User rate

no comparable value
9,6 kbit/s
12 kbit/s
14,4 kbit/s
19,2 kbit/s
28,8 kbit/s
38,4 kbit/s
48,0 kbit/s
56,0 kbit/s
no comparable value (note 16)

6e
#3..1

Maximum number of traffic channels

1 TCH
2 TCH
3 TCH
4 TCH
5 TCH
6 TCH
7 TCH (note 7)
8 TCH (note 7)

No comparable field

6f
#4..1

Wanted air interface user rate

air interface user rate not applicable (note 7)
9,6 kbit/s
14,4 kbit/s
19,2 kbit/s
28,8 kbit/s
38,4 kbit/s
43,2 kbit/s

57,6 kbit/s

interpreted by the network as 38.4 kbit/s (note 7)

No comparable field

6d
#7..6

Other modem type (note 15)

No other modem type
V.34

5d

#6..1

Modem type

no comparable value
V.34

6e
#7..4

Acceptable channel coding(s)

TCH/F4.8 acceptable (note 19)
TCH/F9.6 acceptable
TCH/F14.4 acceptable

No comparable field

6f
#7..5

User initiated modification indicator

User initiated modification not
required
User initiated modification upto 1
TCH/F may be requested
User initiated modification upto 2
TCH/F may be requested
User initiated modification upto 3
TCH/F may be requested
User initiated modification upto 4
TCH/F may be requested

No comparable field

The application rules for coding the information elements ISDN‑BC/LLC/HLC as set out in ETR 018 and ETS 300 102‑1 shall apply.

Other field values in the ISDN BC‑IE of ETS 300 102‑1 not supported in GSM 04.08 are:

Information transfer rate: In this case default 64 kbit/s is selected.

Symmetry: In this case default bi‑directional symmetric is selected for all user data rates (note 5).

Flow control on transmission: This shall be selected if outband flow control applies.

Flow control on reception: This shall be selected if outband flow control applies.

NOTE: Outband flow control is indicated by the absence of the UIL2P parameter for non‑transparent connections.

User information layer 3 protocol: Octet 7 shall not be sent unless specific application rules are given for particular cases (to be defined by GSM). End‑to‑end significant User Information layer 3 protocol shall be sent by LLC.

NOTE 1: In the case where GSM BC "Information Transfer Capability" indicates "Facsimile group 3" and only a single GSM BC is contained in the call set‑up request then this shall be mapped to an ISDN BC with:

Coding standard: CCITT

Information Transfer capability 3,1 kHz audio

Transfer mode circuit

Information transfer rate 64 kbit/s

User layer 1 protocol G711 A Law

and

‑ If an HLC is not present, the network will insert a "Facsimile group 2/3" HLC.

‑ If an HLC element is present, the network will pass it through unmodified.

In the case where GSM BC "Information Transfer Capability" indicates "Facsimile group 3" and two GSM BCs are contained in the call set‑up request, then the same ISDN BC as mentioned above is created. If the first GSM BC indicates "facsimile group 3" an HLC "facsimile group 2/3" will be inserted by the network (if not received from the MS). However if the first GSM BC indicates "speech", the network will not send a HLC, irrespective where a HLC was received from the MS or not.

NOTE 2: This value is present in combination with information transfer capability parameter value "3,1 kHz audio Ex PLMN" or "facsimile group 3" and will therefore be mapped to the value "CCITT Recommendation G.711 A Law" of the ETS 300 102‑1 parameter user layer 1 protocol (see note 3).

NOTE 3: The value "CCITT Recommendation G.711 A Law" applies only when the ETS 300 102‑1 parameter information transfer capability indicates "3,1 kHz audio" or "speech".

NOTE 4: Octets 4a and 4b shall not be included because default values apply.

NOTE 5: In this case octet 5d shall not be included.

NOTE 6: Octet 6 shall not be sent unless specific application rules are given for a particular case (GSM specified). End‑to‑end significant user information layer 2 protocol shall be sent by LLC.

NOTE 7: Not used for currently defined Bearer Services and Teleservices.

NOTE 8: These values will only be set if the "Information Transfer Capability" indicates "3,1 kHz audio", synchronous data transmission is used and octet 5b of the ISDN BC is present.

NOTE 9: The mapping of the modem type shall be according to Draft ETS 300 102‑1/prA1.

NOTE 10: The GSM BC‑IE parameter value "autobauding modem type 1" will be mapped to the ISDN BC‑IE parameter values "inband negotiation possible" and "user rate indicated by E‑bits specified in CCITT Rec I.460 or may be negotiated inband" (octet 5a of ISDN BC‑IE). In case of data compression high speed modems, like V.32bis and/or V.34 may be used in the IWF.

NOTE 11: The ITC value of the GSM BC‑IE "speech", "3,1 kHz audio Ex PLMN" will indicate these requirements.

NOTE 12: For the use of NIRR see GSM 07.01.

NOTE 13: The value of the Intermediate Rate field of the ISDN Bearer Capability information element shall only depend on the values of the User Rate and the Information Transfer Capability in the same information element. The correspondence is:

Intermediate Rate = not used if User Rate > than 19.2 kbit/s

Intermediate Rate = 32 kbit/s if User Rate = 19,2 kbit/s or 14.4 kbit/s

Intermediate Rate = 16 kbit/s if User Rate = 9,6 kbit/s

Intermediate Rate = 8 kbit/s otherwise.

In case of Audio calls the value of the Intermediate Rate may be set to "not used".

NOTE 14: If compression is supported by the MSC and "data compression allowed" is indicated, then the ISDN user rate for UDI calls shall be set as follows. If the parameter "FNUR" is present the ISDN user rate shall be set to this value. Otherwise the GSM user rate shall be mapped to an equal or any higher ISDN user rate value (in case of V.110 the highest ISDN user rate shall be 19.2 kbit/s). The Intermediate Rate shall be set to an appropriate value.(see subclause 10.2.4.11).

In case of "3,1 kHz audio" the modem must try to negotiate data compression and flow control (see subclause 9.2.4.11). In case of "autobauding type 1" high speed modems may be used (see note 10).

NOTE 15: User rate of the GSM-BC is overriden by the fixed network user rate of the GSM BC-IE if available. When the MT indicates „autobauding", „modem for undefined interface" or „none", the other modem type shall be set to „no other modem type"; any other value of the modem type is overridden by the other modem type value (see GSM 07.01).

NOTE 16: The ISDN-BC will consist of the octets 1 to 4 only, coded:

Coding standard: CCITT
Information Transfer capability UDI
Transfer mode circuit Information transfer rate 64 kbit/s

NOTE 17: V.120 interworking is selected.

If an LLC element is not present, the network will insert an LLC. If an LLC is present it may be modified. The GSM-BC parameters negotiated with the MS shall be mapped to the LLC parameters. The LLC parameter Rate Adaptation will be set to "V.120".

When interworking with unrestricted 64 kbit/s networks the ISDN BC shall be coded according to note 16.

NOTE 18: When the MSC is directly connected to a restricted 64 kbit/s network, the ISDN BC-IE is coded with an ITC = RDI (not applicable to ISDNs conforming to ETS 300 102-1).
When indirectly interworking with a restricted 64 kbit/s network the ISDN BC-IE shall be coded according to ETR 018, as shown below:

Coding standard: CCITT
Information Transfer capability: UDI
Transfer mode: circuit
Information transfer rate: 64 kbit/s
User information layer 1 protocol: V.110/X.30
Synchronous/Asynchronous: synchronous
Negotiation: In-band negotiation not possible
User rate: 56 kbit/s

If an LLC element is not present, the network will insert an LLC. If an LLC is present it may be modified. The GSM-BC parameters negotiated with the MS shall be mapped to the LLC parameters according to the rules in this table. The LLC parameter Information Transfer Capability will be set to „restricted digital"

NOTE 19: In case the MS signals an ACC containing TCH/F4.8 only and the network does not support TCH/F4.8 channel coding, then the MSC may act as if TCH/F9.6 were included in the ACC.

Table 6B: Comparability and Mapping of bearer capability parameter values according to ETS 300 102‑1 and GSM 04.08 within the HLR for a mobile terminated Call

Octet

ETS 300 102‑1 parameter value

Octet

GSM 04.08 parameter value

1

Bearer Capability IEI

1

Bearer Capability IEI

2

Length of BC contents

2

Length of BC contents

no comparable field

3
#7..6

Radio channel requirement (note 1)
half rate channel
full rate channel
both, half rate preferred
both, full rate preferred

3
#7..6

Coding standard
CCITT standardized coding

3
#5

Coding standard
GSM standardized coding

3
#5..1

Information transfer capability
speech
unrestricted digital
3,1 kHz audio
no comparable value
no comparable value
7 kHz audio
video

3
#3..1

Information transfer capability
speech
unrestricted digital
3,1 kHz audio ex PLMN (note2)
facsimile group 3 (note 3)
other ITC (see octet 5a)
not supported
not supported

(note 23)

5a
#7..6

Other ITC
restricted digital

4
#7..6

Transfer mode
circuit mode
packet mode

3
#4

Transfer mode
circuit mode
circuit mode

(continued)

Table 6B (continued): Comparability and Mapping of bearer capability parameter values according to ETS 300 102‑1 and GSM 04.08 within the HLR for a mobile terminated Call

Octet

ETS 300 102‑1 parameter value

Octet

GSM 04.08 parameter value

4
#5..1

Information transfer rate
64 kbit/s

no comparable field

No comparable field

4
#7

Compression (note 18)
data compression possible
data compression not possible

4a
#7..5

Structure
default
8 kHz integrity
SDU integrity
unstructured

(4) 4
#6..5

Structure
no comparable value
no comparable value
SDU integrity (note 9)
unstructured (note 5)

4a
#4..3

Configuration
point‑to‑point

4
#3

Configuration
point‑to‑point (*)


No comparable field

4
#2

NIRR (note 17)
No meaning
Data  4.8 kbit/s, FR nt,
6 kbit/s radio interface requested

4a
#2..1

Establishment
demand

4
#1

Establishment
demand (*)

4b
#7..6

Symmetry
bi‑directional symmetric

no comparable field

4b
#5..1

Information transfer rate (dest‑>orig.)
64 kbit/s

no comparable field

5
#5..1

User information layer 1 protocol
no comparable value
CCITT V.110 / X.30
CCITT G.711 A‑law
CCITT X.31 flag stuffing
no comparable value

5
#5..4

Rate adaption no rate adaption (note 11)
V.110/X.30 rate adaption
no comparable value
CCITT X.31 flag stuffing
other rate adaption (see octet 5a)

No comparable value

5a
#5..4

Other rate adaptation
V.120 (note 24)

no comparable field

5
#3..1

Signalling access protocol
I.440/I.450
X.21
X.28, ded.PAD, indiv.NUI
X.28, ded.PAD, univ.NUI
X.28, non‑ded.PAD
X.32

see above

6
#5..2

User information layer 1 protocol
default layer 1 protocol

5a
#7

Synchronous / asynchronous
synchronous
asynchronous

6
#1

Synchronous/asynchronous
synchronous
asynchronous

(continued)

Table 6B (continued): Comparability and Mapping of bearer capability parameter values according to ETS 300 102‑1 and GSM 04.08 within the HLR for a mobile terminated Call

Octet

ETS 300 102‑1 parameter value

Octet

GSM 04.08 parameter value

5a
#6

Negotiation
not possible
inband neg, possible (note 16)

6a
#6

Negotiation
not possible
no comparable value

5a
#5..1

User rate
0,3 kbit/s
1,2 kbit/s
2,4 kbit/s
4,8 kbit/s
9,6 kbit/s
12 kbit/s
rate is indicated by Ebit as specified in CCITT rec. I.460
0,6 kbit/s
3,6 kbit/s
7,2 kbit/s
8 kbit/s
14,4 kbit/s
16 kbit/s
28.8 kbit/s
32 kbit/s
38.4 kbit/s
48 kbit/s
56 kbit/s
64 kbit/s
0,1345 kbit/s
0,1 kbit/s
75 bit/s / 1,2 kbit/s
1,2 kbit/s / 75 bit/s
0,110 kbit/s
0,115 kbit/s
0,2 kbit/s

6a
#4..1

User rate (note 18)
0,3 kbit/s
1,2 kbit/s
2,4 kbit/s
4,8 kbit/s
9,6 kbit/s
12 kbit/s (note 13)
(note 16)

not supported
not supported
not supported
not supported
(note 20)
not supported
(note 20)
not supported
(note 20)
(note 20)
(note 20)
not supported

5b
#7..6

Intermediate rate
not used (note 19)
8 kbit/s
16 kbit/s

32 kbit/s

6b
#7..6

Intermediate rate (note 6) (note 18)
8 or 16 kbit/s
8 kbit/s 16 kbit/s

5b
#5

NIC on Tx (note 14)
does not require
requires

6b
#5

NIC on Tx
does not require
requires (note 13)

5b
#4

NIC on Rx (note 14)
cannot accept
can accept

6b
#4

NIC on Rx
cannot accept
can accept (note 13)

5b
#3

Flow control on Tx (note 15)
Not Required
Required

no comparable field

5b
#2

Flow control on Rx (note 15)
Cannot Accept
Accept

no comparable field

(continued)

Table 6B (continued): Comparability and Mapping of bearer capability parameter values according to ETS 300 102‑1 and GSM 04.08 within the HLR for a mobile terminated Call

Octet

ETS 300 102‑1 parameter value

Octet

GSM 04.08 parameter value

5c
#7..6

Number of stop bits
1 bit
2 bits
not used
1.5 bits

6a
#7

Number of stop bits
1 bit
2 bits
no comparable value
not supported

5c
#5..4

Number of data bits
7 bits
8 bits
not used
5 bits

6a
#5

Number of data bits
7 bits
8 bits
no comparable value
not supported

5c
#3..1

Parity information
odd
even
none
forced to 0
forced to 1

6b
#3..1

Parity information
odd
even
none
forced to 0
forced to 1

no comparable field

6c
#7..6

Connection element (note 1)
transparent
non‑transparent (RLP)
both, transp. preferred
both, non‑transp preferred

5d
#7

Duplex mode
half duplex
full duplex

4
#4

Duplex mode half duplex (note 13)
full duplex (*)

5d
#6..1

Modem type
reserved
V.21
V.22
V.22bis
V.23
V.26ter
V.32
V.26
V.26bis
V.27
V.27bis
V.29
V.35
no comparable value

6c
#5..1

Modem type (note 12)
none (note 7)
V.21
V.22
V.22bis V.23
V.26ter V.32
not supported

autobauding type 1 (note 16)

(continued)

Table 6B (concluded): Comparability and Mapping of bearer capability parameter values according to ETS 300 102‑1 and GSM 04.08 within the HLR for a mobile terminated Call

Octet

ETS 300 102‑1 parameter value

Octet

GSM 04.08 parameter value

5a
#5..1

User rate

no comparable value
9,6 kbit/s
14,4 kbit/s
19,2 kbit/s
28,8 kbit/s
38,4 kbit/s
48 kbit/s
56 kbit/s
no comparable value

6d
#5..1

Fixed network user rate (note 20)

FNUR not applicable 9,6 kbit/s
14,4 kbit/s
19,2 kbit/s
28,8 kbit/s
38,4 kbit/s
48,0 kbit/s
56,0 kbit/s
64,0 kbit/s (note 22)

Modem type

no comparable value (note 21)
V.34

6d
#7..6

Other modem type

No other modem type
V.34

No comparable field

6f
#7..5

User initiated modification indicator (note 1)

User initiated modification not
required
User initiated modification upto 1
TCH/F may be requested
User initiated modification upto 2
TCH/F may be requested
User initiated modification upto 3
TCH/F may be requested
User initiated modification upto 4
TCH/F may be requested

6

#5..1

User information layer 2 protocol
(note 10)
Q.921 (I.441)
X.25, link level
no comparable value

7

User information layer 2 protocol (note 8)
no comparable value
X.25, link level
ISO 6429, codeset 0

7

User information layer 3 protocol
(note 10)
Q.931 (I.451)
X.25, packet level

not supported

General notes:

1) Other ETS 300 102‑1 parameter values than those listed in the table, if indicated in the BC‑IE, will be rejected by clearing the call.

2) Only the GSM 04.08 parameter values listed in the table may be generated (comparable values) during a mobile‑terminated call by mapping the ETS 300 102‑1 parameter values, exception see (10).

3) According to ETS 300 102‑1 and GSM 04.08, respectively, the octets are counted from 1 to n onwards; the bit position in a particular octet is indicated by #x..y, with {x,y} = 1..8 (bit 1 is the least and bit 8 the most significant bit).

4) If octets 5 to 5d of the ISDN BC are absent but present in the LLC, the LLC octets should apply for the mapping as indicated above. In the case of V.120 interworking (see note 24) these LLC octets shall apply.

5) If within the ISDN BC the parameters information transfer capability indicates "3,1 kHz audio" and user layer 1 protocol indicates "G711 A Law" but no modem type is available and the HLC does not indicate "facsimile group 3", octets 5 to 5d of the LLC, if available, apply for the above mapping procedure.

6) The number of octets which shall be encoded for the GSM BC‑IE must comply to encoding rules in GSM 04.08 and the combination of the different parameter values shall be in accordance to GSM 07.01.

Notes regarding the mapping:

(*) This GSM 04.08 parameter value is inserted, if the comparable ETS 300 102‑1 parameter value is missing.

1) This GSM 04.08 parameter value is inserted according to user rate requirements and network capabilities / preferences.

2) This GSM 04.08 parameter value is inserted, if the information transfer capability in ISDN BC is "3,1kHz audio" and a comparable modem type is specified.

3) This GSM 04.08 parameter value is inserted, if the information transfer capability is "3,1 kHz audio" and the content of the HLC‑IE, if any, indicates "facsimile group 2/3", (for details refer to subclause 10.2.2 case 3 for HLR action and case 5 for VMSC action). Note that via MAP the value "alternate speech/facsimile group 3 ‑ starting with speech" shall be used, when TS 61 applies.

4) If octet 4a is omitted the default condition according to ETS 300 102‑1 applies.

5) The GSM 04.08 parameter value shall be set to "unstructured" where the network indicates connection element "transparent".

6) The value of the Intermediate Rate field of the GSM Bearer Capability information element shall only depend on the values of the user rate or the radio channel requirement in the same information element. If the connection element is "transparent", the value is 16 kbit/s, if the user rate is 9.6 or 12 kbit/s, and 8 kbit/s otherwise. For any other connection element setting the value is 16 kbit/s, if the radio channel requirements are "full rate" or "dual, full rate preferred", or "dual, half rate preferred", and 8 kbit/s, if the radio channel requirements is "half rate".

7) This GSM 04.08 parameter value is inserted, if the GSM BC parameter "Information Transfer Capability" indicates "Unrestricted digital information", "facsimile group 3" or "alternate speech/facsimile group 3, starting with speech".

8) Where the network indicates "asynchronous" and connection elements "non‑transparent", "both, transparent preferred" or "both, non‑transparent preferred" , then the GSM BC should be forwarded without parameter user information layer 2 protocol, see also (10).

9) Where the network indicates connection elements "non transparent" "both, transparent preferred" or "both, non transparent preferred" the value of the parameter structure shall be set to "SDU Integrity".

10) Mapping of parameter values of this octet to GSM BC parameters and values are subject to specific application rules, i.e. unless otherwise explicitly stated in an appropriate TS mapping to GSM BC parameters shall not take place.

11) This value shall be used when the value of the GSM BC parameter "Information Transfer Capability" indicates the value "3,1 kHz audio ex PLMN", "facsimile group 3" or "alternate speech/facsimile group 3, starting with speech" which is reserved for MAP operations.

12) The modem encoding of both Draft ETS 300 102‑1/prA1 and ETS 300 102‑1 version 1 shall be accepted and mapped according to GSM 04.08.

13) Value not used for currently defined bearer services and Teleservices.

14) NIC is only supported for "3,1 kHz Ex PLMN audio" interworking with synchronous data transmission.

15) Because the required flow control mechanism can not be indicated to the MS (refer to GSM 07.01), the network shall check if the flow control mechanism selected by the MS and indicated in the CALL CONFIRMED message suits to the requirements requested by the ISDN terminal adaptor. In case of a mismatch the call shall be released in the IWF.

Because an asymmetric flow control mechanism (with respect to transmitting and receiving side) is not supported in GSM PLMNs, the different values of the ISDN BC‑IE parameters "flow control on Tx" and "flow control on Rx" shall be interpreted in the following way:

‑ "Flow control on Rx" set to "accepted" matches with "outband flow control", irrespective of the value of the parameter "flow control on Tx"

‑ "Flow control on Rx" set to "not accepted" and "flow control on Tx" set to "not required" matches with "inband flow control" and "no flow control"

‑ where "Flow control on Rx" is set to "not accepted" and "flow control on Tx" to "required" the call shall be released by the IWF

16) If in case of 3,1 kHz audio interworking "inband negotiation possible" is indicated and the parameter user rate is set to "rate is indicated by E bits specified in Recommendation I.460 or may be negotiated inband" the user rate in the GSM BC‑IE shall be set according to a network preferred value, whereas the preferred value of the Radio Channel Requirement shall be considered. If parameter ISDN‑BC modem type is present, its value shall be ignored. The parameter GSM‑BC modem shall be set according to the user rate in case of connection element "transparent" and to "autobauding type 1" in case of connection element "non transparent", "both, transparent preferred" or "both, non transparent preferred". In case of data compression high speed modems, like V.32bis and/or V.34 may be used in the IWF.

For unrestricted digital interworking the call shall be rejected if these values are indicated.

17) For the use of NIRR see GSM 07.01. The VMSC shall set this parameter dependent upon its capabilities and preferences.

18) If compression is supported by the MSC, the value "data compression possible" may be set. Depending on the capabilities of the MSC, the user rate value and the intermediate rate value is set to an appropriate value.

19) Only applicable if the parameter ISDN-BC ITC indicates "3.1 kHz audio" and for "UDI" calls if User Rate > "19.2 kbit/s".

20) The user rate of the GSM BC is set to the value for the fall-back bearer service. In case the mobile station does not support the fixed network user rate (i.e. the call confirmation message does not contain the fixed network user rate parameter), the network may release the call for a transparent connection element.

21) The modem type parameter of the GSM-BC is taken into account, only.

22) In case no LLC is received and the ISDN-BC received consists of octets 1 to 4 only, coded:

Coding standard: CCITT

Information Transfer capability UDI

Transfer mode circuit

Information transfer rate 64kbit/s,

the following GSM-BC parameters, indicating a 64 kbit/s bit transparent service, shall be set to:

fixed network user rate 64 kbit/s

connection element transparent

The other parameters of the GSM-BC shall be set to values indicating a fall-back service.

(23) When the MSC is directly connected to a restricted 64 kbit/s network, the ISDN BC-IE is coded with an ITC = RDI (not applicable to ISDNs conforming to ETS 300 102-1).
An ISDN BC-IE, as specified in ETR 018 and shown below, shall be taken to indicate that interworking with an indirectly connected restricted 64 kbit/s network is required

Coding standard: CCITT
Information Transfer capability: UDI
Transfer mode: circuit
Information transfer rate: 64 kbit/s
User information layer 1 protocol: V.110/X.30
Synchronous/Asynchronous: synchronous
Negotiation: In-band negotiation not possible
User rate: 56 kbit/s

In this case the GSM BC parameter Information Transfer Capability is set to „Other ITC" and Other ITC parameter is set to „restricted digital". All the corresponding fields in the GSM BC shall be derived from the ISDN LLC.

24) V.120 interworking is required if the ISDN LLC parameter User Information Layer 1 Protocol is set to „V.120". In this case the GSM BC parameter Rate Adaptation is set to „Other rate adaptation" and Other Rate Adaptation parameter is set to „V.120". All the corresponding fields in the GSM BC shall be derived from the ISDN LLC.

10.2.2.1 Circuit switched calls

Where the bearer capability information indicated that the call is a circuit switched unrestricted digital call, then the MSC/IWF shall select the appropriate rate adapted PLMN bearer service.

10.2.2.2 Packet calls

The mobile network offers only Bm channel access for the packet mode service. The ISDN offers both B and D channel access for the packet mode service. The interworking of mobile packet calls is described in GSM 09.06.

10.2.3 Transparent service support (see GSM 03.10)

GSM 08.20 identifies the rate adaptation scheme to be utilized on the BS to MSC link. The transcoding function will generate the 64 kbit/s rate adapted format utilizing the 8 and 16 kbit/s intermediate data rates. The MSC ‑ MSC/IWF will utilize the same rate adaptation scheme as that indicated in GSM 08.20, i.e. adapted to 64 kbit/s.

10.2.3.1 MSC ‑ IWF rate adaptation scheme

This link consists of a 64 kbit/s channel with the information, both user data and in band parameter information (where provided) rate adapted in conformance to GSM 08.20.

10.2.3.2 Rate adaptation process in MSC/IWF

When interworking to the unrestricted digital bearer service then no further rate adaptation will be necessary within the MSC/IWF. For multislot or TCH/F14.4 operations MSC/IWF shall adapt the data stream as defined in GSM 04.21 and GSM 08.20.

When interworking to the 3,1 kHz audio service, then the same process as for the PSTN case is necessary.

10.2.3.3 Mapping of signalling MS/MSC/IWF to modem interface requirements

Only necessary for the 3’1 kHz audio interworking case (see subclause 9.2.3.3). For a multislot configuration refer to GSM 03.10.

Figure 8: Protocol structure in the MSC/IWF (transparent)

10.2.3.4 Establishment of end‑to‑end terminal synchronizations

Prior to exposing the traffic channel of a PLMN connection to transmission of user data, the controlling entities of the connection have to assure of the availability of the traffic channel. This is done by a so called synchronizations process:

‑ starting on the indication of "physical connection established" resulting from the PLMN‑inherent outband signalling procedure This indication is given on sending the message CONNECT in case of MOC, CONNECT ACKNOWLEDGEMENT in case of MTC and MODIFY COMPLETE (which is sent after reception of the ASSIGN COMPLETE message) in case of in‑call modification.

‑ ending by indicating the successful execution of this process to the controlling entity, which then takes care of the further use of the inband information (data, status).

Network interworking within an MSC/IWF is concerned with the terminating side (to the MS) and the transit side (to the fixed network) of a connection. Both sides have to be treated individually related to the synchronizations process.

With respect to the terminating side the procedure for all traffic channel types except TCH/F14.4 is as follows:

‑ sending of synchronizations pattern 1/OFF (all data bits "1"/all status bits "OFF") to the MS using the RA1/RA2 rate adaptation function. In multislot transparent operation, the synchronisation pattern sent is 1/OFF with the exception of the bit positions S1, first X, S3, and S4 which contain the substream number and multiframe alignment pattern (Ref. GSM TS 04.21);

‑ searching for detection of the synchronizations pattern from the MS within valid V.110 frames, and in multislot operation, also searching for the multiframe alignment pattern "0000 1001 0110 0111 1100 0110 1110 101" (Ref. to GSM 04.21) in bit position S4 and substream numbers in bit positions S1, first X, and S3. This implies that the E1, E2 and E3 bit of the V.110 frame shall be checked for the appropriate user rate in order to distinguish the synchronization pattern from the BSS idle data frame.

With respect to the terminating side the procedure for TCH/F14.4 is as follows:

‑ Searching for detection of the A-TRAU frame alignment pattern (TS 08.20) from the BSS.

‑ After the detection of the A-TRAU frame alignment pattern, sending A-TRAU frames with the data rate set in the bits C1-C4 (TS 08.20) and data bits set to one, sending the multiframe structure with the alignment pattern (bit M1) and with the status bits OFF (bit M2) and, in a multislot case, sending substream numbers (bit M2).

– Searching for the detection of the multiframe alignment pattern „0000 1001 0110 0111 1100 0110 1110 101" (TS 04.21) in the bit M1 and, in a multislot case, searching for substream numbers in the bit M2. (Any 5 bit sequence in the multiframe alignment pattern is unique, i.e. the multiframe alignment can take place by recognition of five successive M1 bits.)

In case of interworking to the ISDN "3,1 kHz audio" bearer service the synchronization process is as for the PSTN interworking case (see subclause 9.2.3.4). In case of interworking to the ISDN unrestricted digital bearer service the following synchronization process has to be performed.

When the frame alignment pattern and, in case of multislot operation or TCH/F14,4, the multiframe alignment pattern have been recognised as a steady state, the MSC/IWF continues sending the synchronizations patterns to the MS unless a timer T expires. From this time, after the expiration of the timer T of each allocated traffic channel, the information on the receiving lines from the MS and from the fixed network are directly mapped to the respective sending lines.

During the synchronizations process described above, i.e. while the synchronizations pattern is being sent by the MSC/IWF, the MSC/IWF will not send the V110 frame structure to the ISDN transit network. Once timer "T" for each of the allocated traffic channel(s) of the call expires the synchronizations pattern will continue to be transmitted from the MSC/IWF to the MS, and the MSC/IWF will start sending the V110 frames received from the MS to the ISDN transit network, possibly having set their S and X bits to ON. The MSC/IWF will start looking for the ISDN frame alignment to be received from the ISDN. On recognising frame alignment the MSC/IWF will cease sending its synchronizations pattern to the MS and connect the ISDN through to the MS. In case of multislot operation or TCH/14.4 the IWF shall adapt the data stream as defined in GSM TS 04.21 and 08.20.

It should be noted that in a GSM PLMN V.‑series and X.‑series interfaces are only supported in full duplex mode. Thus the call control phase can be mapped almost completely to the signalling procedure (the S‑bits during the call control phase are irrelevant). However, the "ready for data" condition (i.e. CT106/109, in case of V.‑series interface, and I‑circuit, in case of X.‑series interface) is derived directly from the traffic channel (see also filtering of channel control information).

10.2.3.5 Network independent Clocking (NIC)

Due to the incompatibility between the ISDN and the GSM requirements for NIC interworking is not provided between these two formats. As such no NIC function is required in providing interworking to the ISDN. In this case, the IWF shall disregard the value of bits E4, E5, E6 and E7 in the data transmission phase.

10.2.4 Non‑transparent service support (See GSM 03.10)

GSM 08.20 identifies the corresponding necessary support concerning the rate adaptation scheme to be utilized on the BS‑MSC link.

10.2.4.1 MSC ‑ IWF Rate adaptation scheme

This will be the same as for the transparent case.

10.2.4.2 Protocol layer structure in the MSC/IWF

GSM 03.10 identifies the protocol layer structure for the non-transparent case, the MSC/IWF provides the inverse of the action in the terminal adaptation function. For a multislot configuration refer to GSM 03.10.

Figure 9: Protocol structure in the MSC/IWF (non‑transparent)

10.2.4.3 Re‑constitution of user data

GSM 04.22 refers to the frame of user data in the radio link protocol. The layer 2 relay functions in the MS and the MSC/IWF (identified in GSM 03.10) contain the mechanism for packing and unpacking the user data into the L2R protocol data units.

10.2.4.4 Layer 2 relay functionality

Specific functionality is required on the L2R dependant upon the service which is being requested to be supported. The selection of the appropriate L2R function will be determined by the MSC/IWF on the basis of the bearer capability information signalled in the call set‑up request, or call confirmation message. The prime information element being transparent or non transparent service indication. In addition the particular L2R function ‑ type of protocol to be terminated and mode of flow control to be applied (see appropriate subclauses in 07 series) ‑ will be selected on the basis of the user’s layer 2 indication.

The specific interaction between the L2R function and the RLP function and the L2R frame structure will be the same as that detailed in the Annex to the appropriate GSM 07 series.

10.2.4.5 In band signalling mapping flow control

This entails the L2R function providing the means of controlling and responding to flow control function of the modem (or in the rate adapted frame) plus any synchronizations requirements related to flow control. for synchronous services flow control is covered by the protocol indicated whereas for asynchronous services a specific rule applies for flow control (see GSM 07.01).

In case of interworking to the ISDN "3,1kHz audio" bearer service the flow control process is as for the PSTN interworking case (see subclause 9.2.4.5). In case of interworking to the ISDN unrestricted digital bearer service the following procedures apply:

The flow control function chosen will be dependent upon the availability of the "user information layer 2" information element of the GSM BC and if available its value.

For V.110 interworking, outband flow control will be by means of the "X" bit in the V.110 frame to the ISDN.

For V.120 interworking, outband flow control shall be as follows. In Multiple frame acknowledged mode the functions of the data link control sublayer (send RNR or withhold update of the sequence state variable V(R)) shall be used. In Unacknowledged mode the RR bit in the Control State octet shall be used.

If flow control is provided irrespective of the type used, the L2R function must:

a) provide immediate indication of flow control to the fixed network on receipt of flow control request from the MS.

and/or

b) provide immediate indication of flow control to the MS on receipt of flow control request from the fixed network i.e. in the next available L2R status octet to be transmitted.

Where in band (X‑on/X‑off) flow control is in use, then the X‑on/X‑off characters will not be passed across the radio interface.

If no flow control is provided the involved end systems are responsible for performing in‑band flow control on their own by taking into account the buffer capacity of the MSC/IWF as stated below.

10.2.4.5.1 Conditions requiring flow control ‑ if flow control is provided ‑towards the fixed network

The L2R function will initiate flow control in the following circumstances:

1) The transmit buffer reaches a preset threshold (BACK PRESSURE).

2) The L2R function receives a "flow control active" indication.

On removal of buffer congestion or receipt of L2R "flow control inactive" the flow control will be removed.

No flow initiation/removal will take place at the L2R function and loss of data may occur, if no flow control is provided.

10.2.4.5.2 Conditions requiring flow control towards the MS

The L2R function will transmit to the MS a "flow control active indication", if flow control is provided, in the following circumstances:

1) If the receive buffer from the radio side reaches a preset threshold (BACK PRESSURE).

2) If a flow control indication is received from the fixed network customer. On receipt of this flow control indication, transmission of data from the receive buffers towards the fixed network terminal is halted.

On removal of the buffer congestion or fixed network flow control indication, the L2R function will send a "flow control inactive" indication towards the MS. In addition, for the fixed network indication, transmission of data from the receive buffers will be restarted.

If no flow control is provided at the L2R function, no flow control initiation/removal will take place by the MSC/IWF. Data might be lost without any indication by the MSC/IWF to the end systems involved.

10.2.4.6 Data buffers

10.2.4.6.1 Transmit buffers (towards MS)

Incoming data from the fixed network customer shall be buffered such that if the MSC/IWF is unable to transfer data over the radio path the data is not lost.

The buffer shall be capable of holding the data. Its size is up to the implementers. When the buffer is half full flow control towards the fixed network shall be initiated if flow control is provided as per subclause 10.2.4.5.1.

10.2.4.6.2 Receive buffers (from MS)

Incoming data from the MS is buffered such that if the fixed network terminal is unable to accept the data then it is not lost.

The buffer shall be capable of holding the data. Its size is up to the implementers. When the buffer becomes half full, the L2R function will send a "flow control active" indication towards the MS if flow control is provided at the L2R function, as per subclause 10.2.4.5.2.

10.2.4.7 BREAK Indication

The BREAK indication is managed as detailed in subclause 9.2.4.7.

When V.120 rate adaptation is being used in protocol sensitive asynchronous mode on the ISDN, the L2R break condition shall map on to the BR bit of the V.120 header octet.

10.2.4.8 Signalling mapping modem status information or in band rate adapted frame information

Status information from the modem, V.120 rate adaption function, or within the V.110 rate adapted frame, will be carried by the L2R function, in the MSC/IWF, to the L2R function in the terminal adaptation function. Status information carried from the L2R function in the terminal adaptation function to the L2R function in the MSC/IWF may be discarded in which case CT 108 and CT 105 (in case of modem and V.120 interworking) or the SA and SB bits in the rate adapted frames (in case of V.110 interworking) are clamped to ON. The MSC/IWF is not intended to utilize status information for any purpose. The use of "Data carrier detect" or "clear to send" by the terminal adaptation function to determine ISDN link establishment or failure is not utilized by the MSC/IWF. For example, call clearing, in event of line failure, will be generated normally by the MS not the MSC/IWF.

10.2.4.9 Support of out‑band flow control

Out‑band flow control in the case of V.110 rate adaption requires V.110 TA to TA "end‑to‑end flow control" as defined therein. If this functionality is requested by MS but cannot be supported by the MSC/IWF for any reason (refer also to note 15 of table 6B) the call pending shall be released.

For V.120 interworking, outband flow control shall be as follows. In Multiple frame acknowledged mode the functions of the data link control sublayer (send RNR or withhold update of the sequence state variable V(R)) shall be used. In Unacknowledged mode the RR bit in the Control State octet shall be used.

10.2.4.10 Synchronizations

In case of interworking to the ISDN "3,1kHz audio" bearer service the synchronization process is as for the PSTN interworking case (see subclause 9.2.3.4). In case of interworking to the ISDN unrestricted digital bearer service the following synchronization process has to be performed:

10.2.4.10.1 V.110 and V.120 Frame synchronizations

The ISDN frame synchronizations will need to be mapped to the frame synchronizations utilized on the MSC/IWF to MSC link.

10.2.4.10.2 RLP Frame start indication

The frame start indication is defined in GSM 08.20. Link establishment and frame error recovery are defined in GSM 04.22.

10.2.4.10.3 L2R Frame synchronizations

The synchronizations of user data and its interaction between the L2R function and RLP function are defined in GSM 07 series .

10.2.4.10.4 Establishment of end‑to‑end terminal synchronizations

Prior to exposing the traffic channel of a PLMN connection to transmission of user data, the controlling entities of the connection have to assure of the availability of the traffic channel. This is done by a so called synchronization process:

‑ starting on the indication of "physical connection established" resulting from the PLMN‑inherent outband signalling procedure This indication is given on sending the message CONNECT in case of MOC, CONNECT ACKNOWLEDGEMENT in case of MTC and MODIFY COMPLETE (which is sent after reception of the ASSIGN COMPLETE message) in case of in‑call modification;

‑ ending by indicating the successful execution of this process to the controlling entity, which then takes care of the further use of the in‑band information (data, status).

Network interworking within an MSC/IWF is concerned with the terminating side (to the MS) and the transit side (to the fixed network) of a connection. Both sides have to be treated individually related to the synchronization process.

With respect to the terminating side the procedure is as follows:

– reception of V.110 or A-TRAU frames on all allocated traffic channels for the call is required before the MSC/IWF shall reply with an RLP-UA frame to the MT’s RLP link establishment request (if the MSC/IWF initiates the RLP link establishment, reception of V.110 or A-TRAU frames on all allocated traffic channels for the call must be detected first)

‑ waiting for RLP link establishment by the MT (in addition the MSC/IWF may initiate the RLP link establishment).

Depending upon implementation, the synchronization of the V.110 or V.120 rate adaptation protocol on the ISDN transit network may be performed either after RLP establishment or in parallel to the RLP establishment. In case of the parallel establishment, data received from the transit side during RLP establishment shall be stored within the L2R buffers until the RLP establishment at the terminating side has been finished. When the RLP has been established and on recognizing frame alignment the information from/to the RLP is mapped by the L2R entity applicable to this particular bearer capability.

For V.110 rate adaptation on the ISDN, the synchronization process consists of sending the V.110 frame structure and looking for incoming frame synchronization. For V.120 rate adaptation the following applies. In Multiple frame acknowledged mode, data (I frames) may be sent following an exchange of SABME and UA in the traffic channel. In Unacknowledged mode, data (UI frames) may be sent immediately after an ISUP CONNECT or CONNECT COMPLETE message has been received on the ISDN signalling channel. Optionally, an XID exchange may take place in the traffic channel to verify link integrity.

NOTE; UI frames may be sent in Multiple frame acknowledged mode at any time in addition to I frames. Although not specified in V.120, it is recommended that the recipient should deliver to the user the sequence of I and UI frames in the order in which they are received.

It should be noted that in a GSM/PLMN, V.‑series and X.‑series interfaces are only supported in full duplex mode. Thus the call control phase can be mapped almost completely to the signalling procedure (the S‑bits during the call control phase are irrelevant). However, the "ready for data" condition (i.e. CT106/109, in case of V.‑series interface, and I‑circuit, in case of X.‑series interface) is derived directly from the traffic channel (see also filtering of channel control information).

10.2.4.11 Data compression

When data compression is invoked within a non‑transparent bearer service, interworking to the ISDN is realized by mapping the GSM user rate to at least the same user rate in the ISDN. When the ISDN user rate is the same flow control will ensure data integrity, but the overall performance will be slow. When the ISDN user rate is higher the overall performance may be faster.

10.2.4.12 Additional aspects of V.120 Interworking

V.120 rate adaptation applies on the ISDN, whereas between the MS and IWF V.110 applies. The interworking between V.110 and V.120 shall be performed in the MSC/IWF. V.120 rate adaptation may be invoked with either synchronous or asynchronous services. V.120 is applicable to both UDI and RDI connections.

10.2.4.12.1 V.120 Signalling parameters

The signalling parameters relevant to V.120 will be carried in the ISDN LLC and GSM BC and GSM LLC information elements. The mapping of the parameter values takes place in the MSC/IWF.

For mobile terminated calls both single-numbering and multi-numbering scenarios may apply, as defined in subclause 9.2.2. The HLR shall not store an ISDN LLC with the MSISDN.

10.2.4.12.2 V.120 Protocol parameters

The following restrictions apply for the parameters relevant for V.120:

– BS 2x NT will use the protocol sensitive asynchronous mode,. BS 3x NT will use the protocol sensitive synchronous mode. As a consequence, the rate adaption header shall always be present.

– Only the default logical link will be established, i.e. the LLI negotiation value is "Default, LLI=256 only".

– V.120 recommends the use of the multiple frame acknowledged information transfer procedure for the protocol sensitive mode of operation.

– The IWF shall use the default value for the V.120 window size and the default value for the maximum transmit information field size. It shall be able to receive frames with the default maximum size.

Note. V.120 does not specify the values for these and other HDLC-related parameters directly. They are specified in Q.922 (1992) section 5.9. The information field includes the V.120 terminal adaption data field, the rate adaption header and the header extension (Control State octet), if present.

10.2.4.12.3 Data compression on the ISDN

Whilst V.110 rate adaptation does not support standardized data compression, V.42bis data compression may be used with V.120 protocol sensitive asynchronous mode. This is described in V.120 (10/96) annex C.

10.2.4.13 Interworking with restricted 64 kbit/s networks

10.2.4.13.1 Rate adaptation

Both V.110 and V.120 rate adaption protocols may be used on a restricted 64 kbit/s network.

For V.110 rate adaption, the procedure is described in CCITT Rec. I.464. The RA2 function shall set the 8th bit of each octet in the 64 kbit/s stream to binary 1. A consequence of this is that the highest permitted intermediate rate is 32 kbit/s. At the receiver, the 8th bit shall be ignored.

Rec. V.120 states that the user data shall be rate adapted to 56 kbit/s by using only the first 7 bits of each octet in the 64 kbit/s stream. The 8th bit shall be set to binary 1. At the receiver, the 8th bit shall be ignored.

10.2.4.13.2 MSC – ISDN signalling

When interworking indirectly with restricted 64 kbit/s networks the ISDN BC information element shall be coded according to ETR 018 (as shown in the notes to tables 6A and 6B). The information corresponding to the GSM BC-IE shall be communicated in the ISDN LLC-IE which shall be provided by the MS for mobile originated calls.

In the case of direct interworking, an ITC = RDI in the GSM BC-IE maps on to an ITC = RDI in the ISDN BC-IE for both MO and MT calls (not applicable to ISDNs conforming to ETS 300 102-1).

10.2.5 DTE/Modem interface (Filtering)

The DTEs taken into account for the PLMN at the MS side conform to CCITT’s DTE/Modem interface specifications, which assume basically an error‑free environment, i.e.:

‑ limited distance, point‑to‑point local interconnection of the interface circuits for data and status;

‑ steady state signalling.

The envisaged use of these DTE’s in the PLMN environment leads to the exposure of these "interconnections" ‑ which may, in the ISDN case, lead to the ISDN Rate Adaptation rather than to a Modem in the MSC/IWF ‑ to the PLMN Radio Channel. To assure proper operation even under these conditions appropriate measures have to be taken. In the "non‑transparent case" the RLP satisfies the requirement for both data and status lines. In the "transparent" case, the:

‑ data line aspects have to be dealt with end‑to‑end between the users, while

‑ status line aspects are of concern to the network which are dealt with in the following.

The use of the channel control information for the remote control of the DTE/Modem control interchange‑circuits between the MS and the MSC/IWF (the conveyance of which is supported by the rate adaptation scheme adopted for PLMN application) requires alignment to the particular transmission occurrences in the traffic channel to be taken into account within the PLMN. In principle this can be best achieved by:

‑ relying only on the PLMN outband signalling as far as connection control is concerned;

‑ eliminating the dependence upon the transmission of channel control information via the radio link.

Support for this strategy is given to a certain extent by the confinement of PLMN data connections to:

‑ full duplex operation;

‑ switched service (demand access);

‑ mapping of connection‑control relevant conditions of the DTE/DCE control interchange‑circuits to/from outband PLMN signalling according to GSM 04.08 after successful traffic channel synchronization (refer to subclause 10.2.3.4);

‑ flow control by a network entity supported only in non‑transparent mode;

‑ support of connections with the same user data rate only (no TA to TA end‑to‑end flow control in case of transparent mode).

The only DTE/Modem control interchange‑circuit conditions, which actually are not covered by the above confinements, are the indications of readiness for data transmission, i.e. CT106/109 in case of V.‑series interface and I‑circuit of X.‑series interface. As the effect of a condition change of the afore‑mentioned DTE/Modem interchange‑circuits depends on the:

‑ phase within the course of the connection;

‑ direction of change (ON‑OFF or OFF‑ON).

The required precaution to be applied (Filtering) must be determined individually in view of:

‑ function deduced from the change;

‑ resilience of the connection needed;

‑ error condition possibly invoked due to a delay in performing the condition change of the control interchange circuit;

‑ potential loss of performance in connection usage.

The details of the filtering function are laid down in GSM 07‑ series.

10.3 Interworking Alternate speech data calls

Alternation between speech and unrestricted digital (BS61) and speech followed by unrestricted digital (BS 81) are not applicable for interworking with the ISDN, since the alternate speech/unrestricted bearer service is currently not specified in the ISDN.

A BS 61 or BS 81 call where one of the two bearer capability information elements indicates the ITC value "unrestricted digital information" shall therefore be rejected.

10.3.1 Alternate speech data bearer interworking

10.3.1.1 General

The procedure for the alternate speech/data service is invoked at the MS‑MSC link during the call set‑up phase. This service is invoked by indication of repeated bearer capability information elements in the setup message and/or call confirmed message, respectively (preceded by a repeat indicator "circular"), one indicating speech and the other indicating the specific data service with the ITC, "3,1 kHz audio Ex PLMN" or "facsimile group 3" plus user rate etc., as for normal data calls. The bearer capability first indicated i.e. speech or 3,1 kHz Ex PLMN, etc. determines the first selection required of the network by the subscriber. Depending on the type of service requested and direction of call establishment (M0/MT, see relevant clauses of the 07 series) low layer and high layer capabilities may also be included. The MSC/IWF will perform both compatibility checking and subscription checking for mobile originated calls and optionally for mobile terminated calls (single numbering scheme) on both sets of capabilities as for normal data calls. If either the subscription check or the compatibility check fails then the call shall be rejected. The only exception to this is when TS61/TS62 negotiation takes place, see GSM 07.01.

As regards the supplementary services the application rules are laid down in GSM 02.04.

The speech phase of the call, when invoked, is handled by the transcoder and will utilize the normal telephony teleservice interworking requirements and mobile network capabilities. The 3,1 kHz audio Ex PLMN and Facsimile group 3 phase of the call, when invoked, will utilize the appropriate data interworking capability (e.g. IWF) and may use either the transparent or non‑transparent mobile network capability.

The network shall provide, for service and operational reasons, a rapid and reliable changeover of capability upon request from the mobile user. This changeover may involve the disabling, by‑passing or introduction of particular network functions (e.g. speech coder, modem etc.) and change of the channel configuration on the radio interface. This changeover is initiated on the receipt of the "MODIFY" message (see GSM 04.08) from the MS. The network itself will not initiate a changeover.

10.3.1.2 Mobile originated ISDN terminated

If one bearer capability information element indicates the ITC value "3,1 kHz audio Ex PLMN" or "facsimile group 3", the call set up is as for the PSTN case. Interworking is provided to the ISDN bearer service 3,1 kHz audio for the whole connection, including the speech phase. The MODIFY message (see GSM 04.08) will be generated by the mobile subscriber. This message is not transmitted to the ISDN, i.e no outband correlation between the user on the fixed network and the mobile user will be possible. In this instance it is necessary for change of network capabilities to be carried out in the mobile network.

10.3.1.3 ISDN originated mobile terminated

In principle this is handled as for normal ISDN originated call. In the following however, the different cases are described in more detail:

a) When the calling user indicates an ISDN BC‑IE with an ITC value "3,1 kHz audio" with no other ISDN BC information such as modem type, etc. and the HLC is not "facsimile group 3", i.e. the calls arrive at the GMSC with compatibility information not exhaustive to deduce a GSM Bearer Service the call setup is as for the PSTN case described in subclause 9.2.1.3.

b) When the calling user however indicates an ISDN BC‑IE with an ITC value "3,1 kHz audio" and a HLC "facsimile group 3", i.e. the call arrives at the GSM with compatibility information allowing for deducing the Teleservice "Facsimile transmission", the call setup is as described in subclause 10.2.2 (case 3 in HLR, case 5 in VMSC).

In the information transfer phase the call is dealt with as indicated in the previous paragraph.

10.3.2 Speech followed by data interworking

10.3.2.1 General

The set up and selection of interworking function for this service is the same as that indicated for the alternate speech/data service. The service will be indicated by repeated BC‑IEs (the first indicating speech and the second indicating the appropriate data service with the ITC "3,1 kHz audio Ex PLMN") and the specific data user rate, etc. as for normal data calls, preceded by a repeat indicator "sequential". The only difference in this service is that speech will always be the first bearer capability selection and once the MODIFY message, see GSM 04.08, is received from the MS then all network resources associated with the handling of the speech call may be released for reallocation to other calls, i.e. they will not be required again in the handling of this call. Both mobile originated and terminated are dealt with as detailed in subclauses 10.3.1.2 and 10.3.1.3.