Found no support for HSS provided charging characteristics. Following TS32.251 A.4:
- Use PDN level CC, if one wasn't provided then use subscription level CC
- Don't send CC in S11 if it wasn't included
These will be further needed in PFCP in the future, as well as in other
Diameter based interfaces (such as Gy).
Let's put all implementation details in APIs so that devs don't need to
care about those details every time.
* [CORE] tlv: Store mode in ogs_tlv_t
This allows specifying the format of the IE for each individual IE,
hence allowing messages containing IEs formatted in different ways.
This is needed in order to support parsing GTPv1-C, since messages
contain IEs with different structure (TLV vs TV). Hence, this is a
preparation patch to add support for parsing TVs in ogs-tlv.c/.h.
* [CORE] tlv: Support parsing msg with both TLV and TV in it
IEs of type TV are sometimes used in GTPv1-C. Current tlv parser/builder
doesn't provide with ways to parse messages which contain TV formatted
IEs. This patch adds the relevant types and ways to encode/decode them.
Furthermore, the current parser/builder allows parsing/building messages
containing the exact same format in all its IEs. A new parser function
is added which allows parsing messages of different types (TV, TLV)
mixed in the same message. In order to be able to do so, it uses the
general msg_mode passed to it in order to know the general TLV format
(in essence, the length of the Tag field, and also the length of the
Length field if applicable each IE).
Looking up the instance in the TLV description is left undone and
hadcoded to 0, since the only user so far requiring this API is GTPv1-C,
which has no instances.
* [CORE] tlv: Support repeated tag+instance parsing TLV message
In GTPv2C, repeated IEs (same tag) are easily differentiated by the
Instance byte, which provides info to match different decoded
structures. In GTPv1C though, there's no Instance byte, and we still
encounter repeated IEs (like GSN Address in Create PDP Context Request).
Hence, the TLV decoder needs to be updated to track count of IEs found
(identified by tag+instance, where instance is always 0 in GTPv1C) and
get the proper description index + offset into the decoded structure.
* [GTP]: Move GTPv2-C specifics to its own libgtp subdir
This will allow adding GTPv1-C code by the side. Most GTPv2 code is left
in this patch as "gtp" instead of renaming it to "gtp2" in order to
avoid massive changes. It can be done at a later stage if wanted.
* [GTP] Support generating GTPv1-C messages
* [SMF] Add Gn interface support
This patch introduces GTPv1C support to open5gs-smfd. With it,
open5gs-becomes a GGSN too, where SGSN can connect to, hence supporting
GERAN and UTRAN networks.
