Sysmocom is in the process of adding 3G support to OpenBSC. This is done in the nature of using an existing hNodeB Femtocell that exposes the Iuh interface. The binary protocol for Iuh (and related protocols) is defined using the Abstract Syntax Notation One (ASN.1) and the aligned packed encoding rules (APER) are used to encode/decode the data.

After exploring several options LaForge picked the one that adds APER support to Lev Walkin’s ASN1 compiler, simplifies the 3GPP ASN.1 input files and then have a python script to post-process the result.

The next issue comes that we have two protocol suites, HNBAP and RANAP, and want to use them inside the same codebase. To avoid having conflicting types LaForge extended the asn1c compiler to add a prefix to generated types and we are using this patched compiler.

At this point we had an encoder/decoder for the HNBAP and RANAP protocols and could begin on writing our own Free Software HNB-GW. After working with the HNB-GW code Daniel noticed several crashes. The crashes were related to making deep copies of the decoded data and it took several iterations to not leak and not double free.

We have not had crashes, leaks or other issues in this part of the code for quite a bit and it seems time for a formal release. To build the osmo-iuh module you will need:

• master of libosmocore
• master of libosmo-abis
• master of libosmo-netif
• sysmocom/iu of libosmo-sccp
• aper-prefix of asn1c
• master of libasn1c
• master of osmo-iuh