4 Layer 1 specification

08.143GPPBase Station System (BSS) - Serving GPRS Support Node (SGSN) interfaceGb interface Layer 1General Packet Radio Service (GPRS)Release 1999TS

Since Frame Relay shall be used on the Gb interface for phase 1 of GPRS, see TS 3GPP TS 03.60 [3], this version of this Technical Specification refers to "The Frame Relay Forum User-to-Network Implementation Agreement (UNI)" [5] which recommends physical layer interfaces to be used in conjunction with Frame Relay.

4.1 Physical configuration of the Gb interface

The detailed physical configuration of the Gb interface is subject to negociation between operators and equipment providers and is out of the scope of this Technical Specification.

For example, 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.

4.2 Physical layer interface

Each of the physical layer of the Gb interface shall conform to one of the following FRF 1.1 [5] 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 1.1 [5].

a) clause 2.1.1: ANSI T1.403.
b) clause 2.1.2: V.35, physical circuit and DTE/DCE interface clauses.
c) clause 2.1.3: G.703.
d) clause 2.1.4: G.704.
e) clause 2.1.5: X.21.
f) clause 2.1.6: ANSI‑530‑A‑1992.
g) 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, CCITT Recommendation G.704 [6] shall be applied according to FRF 1.1 [5] and 3GPP TS 08.04 [4] as appropriate, and in case of T1 interface ANSI Recommendation T1.403 [7] shall be applied according to FRF 1.1 [5] and 3GPP TS 08.04 [4] 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 CCITT Recommendation G.704 [6], clause 5 and included sub-clauses. In case where multiple 64kbit/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 [8]. 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.

4.3 Error rate

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

4.4 Provision of physical channels

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

Annex A (informative):
Change History

Date / Meeting




New ver

Creation of R99 version


May 2002

Updated to 3GPP TS style format. Reference clause cleaned up