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TS 48.014
GPRS – BSS-SGSN Interface –
Gb Interface Layer 1

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Mr. Andersen, Niels Peter Skov
Anemone Technology

Content for  TS 48.014  Word version:  18.0.0

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1  Scopep. 5

The present document specifies the physical layer on the Base Station System (BSS) to Serving GPRS Support Node (SGSN) interface (Gb interface) and references layer 1 standards to be used on this interface.
The protocol stack on the Gb interface is defined in the stage 2 TS 23.060.

2  Referencesp. 5

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
TR 21.905: "Vocabulary for 3GPP Specifications".
TS 22.060: "General Packet Radio Service (GPRS); Service description; Stage 1".
TS 23.060: "General Packet Radio Service (GPRS); Service description; Stage 2".
TS 48.004: "Base Station System - Mobile-services Switching Centre (BSS-MSC) interface; Layer 1 specification".
FRF.1.2 (July 2000): "User-to-Network Interface (UNI) Implementation Agreement".
ITU-T Recommendation G.704 (Blue Book): "Synchronous frame structures used at 1 544, 6 312, 2 048, 8 488 and 44 736 kbit/s hierarchical levels".
ANSI T1.403-1999: "Network and Customer Installation Interfaces - DS1 - Electrical Interface".
Bellcore TR-NWT-001203 Issue 2 (December 1992): "Generic Requirements for the Switched DS1/Switched Fractional DS1 Service Capability From an ISDN Interface (SWF-DS1/ISDN)".
ITU-T Recommendation V.35: "Data transmission at 48 kilobits per second using 60-108 kHz group band circuits".
ITU-T Recommendation G.703: "Physical/electrical characteristics of hierarchical digital interfaces".
ITU-T Recommendation X.21: "Interface between Data Terminal Equipment and Data Circuit terminating Equipment for synchronous operation on public data networks".
TIA/EIA-530-A: "High Speed 25-Position Interface for Data Terminal Equipment and Data Circuit-Terminating Equipment, Including Alternative 26-Position Connector (ANSI/TIA/EIA 530-A-92) (R98)".

3  Abbreviationsp. 6

For the purposes of the present document, the abbreviations given in TR 21.905 and TS 23.060, and the following apply:
Data Circuit-terminating Equipment
Data Terminal Equipment
Frame Relay Forum

4  Definitionsp. 6

4.1  Definitionsp. 6

For the purposes of the present document, the terms and definitions given in TS 22.060 and the following apply:
a four wire symmetrical digital transmission path carrying PCM signal at 2048 kbit/s.
a four wire symetrical digital transmission path carrying PCM signal at 1544 kbit/s.

4.2  Symbolsp. 6

For the purposes of the present document, the symbols given in TS 23.060 apply.

5  Layer 1 specificationp. 6

Since Frame Relay shall be used on the Gb interface for phase 1 of GPRS, see TS 23.060, the present document refers to "The Frame Relay Forum User-to-Network Implementation Agreement (UNI)" which recommends physical layer interfaces to be used in conjunction with Frame Relay.

5.1  Physical configuration of the Gb interfacep. 6

The detailed physical configuration of the Gb interface is subject to negociation between operators and equipment providers and is out of the scope of the present document.
Point-to-point physical lines or an intermediate Frame Relay network may be used. In the latter case, the two ends of the Gb interface may use different types of physical interfaces.

5.2  Physical layer interfacep. 6

Each of the physical layer of the Gb interface shall conform to one of the following FRF 1.2 clauses. This does not mean that each BSS and SGSN equipment has to support all of these physical interfaces, it means that the supported physical interfaces shall be compliant with the corresponding clause of FRF 1.2.
  1. clause 2.1.1: ANSI T1.403.
  2. clause 2.1.2: V.35, physical circuit and DTE/DCE interface clauses.
  3. clause 2.1.3: G.703.
  4. clause 2.1.4: G.704.
  5. clause 2.1.5: X.21.
  6. clause 2.1.6: TIA/EIA-530-A.
  7. clause 2.1.7: HSSI.
The Gb interface may be multiplexed with the A interface on the same E1 (2048 kbit/s), or T1 (1544 kbit/s) digital path. In case of E1 interface, ITU-T Recommendation G.704 shall be applied according to FRF 1.2 and TS 48.004 as appropriate, and in case of T1 interface ANSI T1.403 shall be applied according to FRF 1.1 and TS 48.004 as appropriate.
In the case where multiple 64 kbit/s channels are used on an E1 (2048 kbit/s), digital path on the Gb interface, it is recommended to aggregate them into one nx64 kbit/s channel, see ITU-T Recommendation G.704, clause 5 and included clauses. In case where multiple 64 kbit/s channels are used on a T1 (1544 kbit/s) digital path on the Gb interface, it is recommended to aggregate them into nx64kbit/s (where 2 ≤ n ≤ 24) channel, see Bellcore TR NWT 1203. This approach optimises the use of the available bandwidth by taking advantage of the statistical multiplexing at the upper layer. However, this approach requires that no slipping occurs between individual 64 kbit/s channels e.g. when passing through intermediate equipment between BSS and SGSN.

5.3  Error ratep. 7

The error rate experienced at the physical layer between the BSS and the SGSN shall be compatible with the operation of the upper layers.

5.4  Provision of physical channelsp. 7

The physical channels on the Gb interface shall be permanently reserved by means of administrative procedures.

$  Change Historyp. 8

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