question on USSD messages

Hi all, I'm looking at USSD message generation in openbsc, and would like to move a bit of msg generation to libosmocore. However, in libosmocore's gsm0480.c I already find an implementation that seems to do the same, yet with some differences I'm not sure how to deal with. The function originally in openbsc: gsm0480_send_releaseComplete() On the iu branch, I've moved the msg generation to gsm0480_gen_releaseComplete() This should rather go to libosmocore. There I already find gsm0480_create_ussd_resp() The openbsc variants are rather shorter. Is it incomplete/incorrect?? Is the libosmocore gsm0480_create_ussd_resp() just bloat for this case?? For convenience, let me paste the code: openbsc's Release Complete, very lean: struct msgb *gsm0480_gen_releaseComplete(void) { struct msgb *msg; msg = gsm48_msgb_alloc_name("GSM 04.08 USSD REL COMPL"); if (!msg) return NULL; gsm0480_l3hdr_push(msg, GSM48_PDISC_NC_SS, GSM0480_MTYPE_RELEASE_COMPLETE); return msg; } Note that the above does not set a direction flag nor trans_id in the proto_discr, like libosmocore's gsm0480_create_ussd_resp() does; neither do I understand the purpose of all the constant "code/id" TLs and wrapping: struct msgb *gsm0480_create_ussd_resp(uint8_t invoke_id, uint8_t trans_id, const char *text) { struct msgb *msg; uint8_t *ptr8; int response_len; msg = msgb_alloc_headroom(1024, 128, "GSM 04.80"); if (!msg) return NULL; /* First put the payload text into the message */ ptr8 = msgb_put(msg, 0); gsm_7bit_encode_n_ussd(ptr8, msgb_tailroom(msg), text, &response_len); msgb_put(msg, response_len); /* Then wrap it as an Octet String */ msgb_wrap_with_TL(msg, ASN1_OCTET_STRING_TAG); /* Pre-pend the DCS octet string */ msgb_push_TLV1(msg, ASN1_OCTET_STRING_TAG, 0x0F); /* Then wrap these as a Sequence */ msgb_wrap_with_TL(msg, GSM_0480_SEQUENCE_TAG); /* Pre-pend the operation code */ msgb_push_TLV1(msg, GSM0480_OPERATION_CODE, GSM0480_OP_CODE_PROCESS_USS_REQ); /* Wrap the operation code and IA5 string as a sequence */ msgb_wrap_with_TL(msg, GSM_0480_SEQUENCE_TAG); /* Pre-pend the invoke ID */ msgb_push_TLV1(msg, GSM0480_COMPIDTAG_INVOKE_ID, invoke_id); /* Wrap this up as a Return Result component */ msgb_wrap_with_TL(msg, GSM0480_CTYPE_RETURN_RESULT); /* Wrap the component in a Facility message */ msgb_wrap_with_TL(msg, GSM0480_IE_FACILITY); /* And finally pre-pend the L3 header */ gsm0480_l3hdr_push(msg, GSM48_PDISC_NC_SS | trans_id | (1<<7) /* TI direction = 1 */, GSM0480_MTYPE_RELEASE_COMPLETE); return msg; } Thanks for any insights! ~N -- - Neels Hofmeyr &lt;nhofmeyr(a)sysmocom.de&gt; http://www.sysmocom.de/ ======================================================================= * sysmocom - systems for mobile communications GmbH * Alt-Moabit 93 * 10559 Berlin, Germany * Sitz / Registered office: Berlin, HRB 134158 B * Geschäftsführer / Managing Directors: Harald Welte