9 Dedicated packet mode service


9.1 General

The "dedicated packet mode service" shall provide to the mobile subscriber the shortest possible connection from the GSM PLMN to the PH for both subscribers staying in the HPLMN as well as for roaming foreign subscribers staying in the VPLMN. Interworking with the PH through the ISDN or directly may be used in the GSM PLMN to satisfy this requirement (see figures 2, 3, and 6/GSM 09.06).

Only mobile originated calls are supported.

Figure 6/GSM 09.06: Dedicated packet mode service; mobile originated call for roaming MS

NOTE: The support of mobile terminated calls for roaming subscribers would require the PSPDN to provide redirection functionality at the GMSC of home PLMNs does for routing circuit switched calls for their roaming subscribers. This is currently not the case. Thus the support cannot be provided.

In the dedicated packet mode service, the MT or TA does not use the E.164 address of the PH. A common access procedure as described below shall be applied by all GSM PLMNs supporting this type of service hiding the differences of existing PSPDNs in GSM countries for GSM PLMN subscribers. The mobile subscriber has only a subscription to his HPLMN for the use of packet mode service. The applicable bearer services are those of the 50‑series in GSM 02.02. No special E.164 number for addressing the PH or performing the registration with the PSPDN in satisfying the identification needs is necessary for the mobile subscriber in this case.

The advantage of this procedure to the mobile subscriber is that the service offered by the GSM PLMN is completely compatible irrespective of the nature of the packet service in any transit or terminating network, which the GSM PLMN is working to. Additionally the mobile subscriber may receive all billing information for this service, the charges of GSM PLMN and PSPDN from the home GSM PLMN operator/retailer. If this is required, it may be necessary for the GSM PLMN to generate both volume and duration related charging parameters.

User access to the PSPDN at the user/network interface of GSMN PLMN is the same for any type of implementation. Uniform functionality is assumed in the obligatory set‑up of the "dedicated packet mode service". Standard procedures are supported over the air interface to support this service.

Concerning the aspects of transparent/non‑transparent mode the PH scenario part of subclause 8.7 ‑ in essence only non‑transparent mode ‑ applies.

Three distinct areas of this service ‑ being realized according to the PH interface (X.31 Case A) of the pan‑European ISDN ‑ impact upon the overall GSM PLMN interworking requirements:

‑ general application rules;

‑ specific application rules for this service;

‑ connection establishment procedures for this service.

9.2 General application rules

The dedicated packet mode service supports the X.31 Case A with a default service profile which is applicable for non‑registered subscribers. This X.31 Case A default service profile is set up as defined for the GSM profile in table 3/GSM 09.06.

X.31 Case A customized service profiles are not supported.

Support of the OSI Network Layer Service by this service is a general requirement.

9.3 Specific application of rules for dedicated packet mode service

Particularly, the following rules apply for the PH interface (X.31 Case A) in support of the dedicated packet mode service:

‑ The calling party number IE of the SETUP message towards the PH is mandatory to provide the PH with the basic MSisdn of the calling mobile subscriber as stored in the VLR. The insertion of the value of the calling party number is an act of the network, thus the PH can take this entry as a verified E.164 number (MSisdn) of the MS.

‑ The calling party number may be used by the packet handler for charging purposes.

‑ In cases where the available PH only supports the ISDN X.31 Case B, the PH is required to perform a GSM specific function, i.e. to substitute in the X.25 "call request" packet the PH port address in place of a foreign subscribers calling address.

‑ There is no need for administration of the DTE identity at the PH because of the MS has only subscription with the PLMN operator.

‑ Mobile originated calls arriving at the PH shall be accepted as a result of a respective pre‑arrangement with the PLMN operator.

‑ Mobile terminated calls are not supported in its purity according to the dedicated packet mode services. However, the support of mobile terminated calls for home subscribers according to the basic packet mode service may be provided by the same PH equipment, which performs the dedicated packet mode service.

Table 3/GSM 09.06: GSM profile for layer 3 and layer 2 attributes and parameters, respectively



DTE identity


Verified E.164 number of MS (MSisdn).

Packet sequence numbering

Modulo 8.

Logical channel assignment

n = 2 (outgoing virtual circuits).

Packet length

128 octets.

Window size


Fast select and fast select acceptance


Default throughput class

Half of user rate.

Throughput class negotiation


Transit delay

Negotiable, if applicable (exclusive of inherent GSM PLMN delay budget).

RPOA selection

Provided, if required and supported by the accessed PSPDN.

UIL2P (note)

X.25 link level

X.75 layer 2 modified (CAPI)

Link procedure

Single link procedure.

Link Layer Address Assignment

as for LAPB X.25.

Frame sequence numbering

Modulo 8.

Window size

k = 7.

k = 2.

Max. frame length

N1 = 2 104 bit.

N1 = 16 440 bit.

Retransmission attempts

N2 = 10.

Acknowledge timer

T1 = [3] s (both directions).

T1 = [10] s (both directions).

NOTE: The link layer parameter values depend on the value of the UIL2P parameter of the GSM‑BC. The value "X.75 layer 2 modified (CAPI)" is restricted to the direct DTE‑DTE‑interworking.

9.4 Mobile originated calls

9.4.1 General

Within the GSM PLMN a subscription to the bearer services BS 51, 52 and/or 53 is required. In addition either the GSM PLMN or the PH ensures that only calls from subscribers of GSM PLMNs for which roaming agreement exists are progressed. The MS indicates in the call set‑up the appropriate bearer capability IE according to GSM 07.01 for 50‑series Bearer Services.

In the called party number IE of the setup message the following parameters are included to select the dedicated packet mode service:

‑ Type Of Number (TON) = "dedicated access, short code".

‑ Numbering Plan Identification (NPI) = "Private Numbering Plan".

‑ number digits = "short code" (see subclause 9.4.2).

The connection shall be established in line with GSM 09.07 and 07.03.

The MSC/IWF uses the short code number to select, if applicable, the PH and routes the connection to the appropriate PH.

The interworking function (MSC/IWF) would need to determine the following points:

‑ User rate from the call set‑up request.

‑ Selection of the RLP function and rate for the non‑transparent service.

‑ Routing information for PH.

9.4.2 Short code

The value "0000" of the short code is used for the case of one PH operator "visible" to the mobile subscriber and the single GSM profile according to table 3/GSM 09.06, thus serving currently as the "dedicated indicator" only. The individual PLMN operator may arrange for establishing the connections to the PSPDN through networks of different PSPDN operators, but this is currently not at the disposal of the mobile subscribers.

All other values of the short code are reserved for future enhancements, e.g. introduction of a selection procedure for selecting a particular PSPDN operator and/or a particular profile.

9.5 Particular packet access functionality

A number of particular capabilities may be necessary for the support of dedicated packet mode service:

‑ Charging

It may be necessary to generate both volume and duration related charging information. This shall be done within the PH.

‑ Supplementary services interworking

Interworking of GSM PLMN supplementary services with PSPDN optional user facilities is not provided. The following SS apply: call barring of all outgoing calls and advice of charge. The advice of charge shall be applied for the circuit switched portion only.