MBSF: HTTP Server for MBS User Service Announcement propagation

[davidjwbbc]

Introduction

When an MBS User Service Announcement is delivered using the VIA_MBS_DISTRIBUTION_SESSION Service Announcement Mode, the multipart MIME document, including the MBS User Service Announcement document, is pulled by the MBSTF for transmission in a special service announcement Object Distribution Session.

This necessitates the MBSF being able to serve the multipart MIME document to the MBSTF for inclusion in the service announcement Object Distribution Session.

Server

The HTTP Server shall be capable of serving multiple User Service Descriptions Bundles as multipart/related objects which contains the application/3gpp-mbs-user-service-description+json;‌profiles="urn:3GPP:26517:17:baseline";‌version="Rel17" type MBS User Service Announcement document as the first part of the multipart. The path will be used to discriminate between User Service Descriptions Bundles for different MBS User Services by using the mbsUserServId as a path element. See TS 26.517 Clause 5.3 for more details of the User Service Descriptions Bundle.

So that this can be multiplexed, if required, with other API services we will also use a distinct path prefix.

Therefore the User Service Descriptions Bundles shall be served using the following URL path:

/x-5gmag-service-announcements/v1/user-service/{mbsUserServId}

...for all User Service Descriptions for an MBS User Service

/x-5gmag-service-announcements/v1/user-data-ingest-session/{mbsUserDataIngSessId}

...for the User Service Description related to a single MBS User Data Ingest Session

There is also a need to fetch individual documents for a PASSED_BACK User Service Description, this will use the following paths:

/x-5gmag-service-announcements/v1/user-data-ingest-session/{mbsUserDataIngSessId}/announcement.json
/x-5gmag-service-announcements/v1/user-data-ingest-session/{mbsUserDataIngSessId}/{distributionSessionId}.sdp

The standard If-Modified-Since and/or If-None-Match headers may be provided in the client request to detect if the User Service Descriptions Bundle has changed.

The MBSF will respond with one of the following:

Status Code	Headers	Body	Notes
200	Content-Type: multipart/related ETag: "<Hash of the User Service Descriptions Bundle>" Last-Modified: <Date of the last change to the MBS User Service or one of the attached MBS User Data Ingest Sessions, whichever is later>	multipart/related document with the first part being the MBS User Service Announcement	When {mbsUserServId} indicates a valid MBS User Service which has a VIA_MBS_DISTRIBUTION_SESSION Service Announcement Mode
304			When the If-None-Match header value in the request matches the hash of the current User Service Descriptions Bundle or when the If-Modified-Since header value is a date-time on or after the last change to the MBS User Service or one of the attached MBS User Data Ingest Sessions, whichever is later. Not for initial implementation.
307/308	Location: <URL of alternative server>		When service is being redirected to another MBSF, either temporarily or permanently. Not to be implemented in this initial version and is only here for future expansion if and when service migration is implemented in the MBSF.
404			When the {mbsUserServId} does not match any known MBS User Service
500			Unexpected internal error

Configuration Variables

Key			Description	Example
mbsf
	userServiceAnnouncement
		addr	IP address for the User Service Announcement HTTP server. The addr and port pair may be repeated to provide multiple listening addresses. The should be at least one address for Nmb2 and one for MBS-1 reference points, these may be the same entry if Nmb2 and MBS-1 share the same network interface.	127.0.0.80
		port	TCP port for the User Service Announcement HTTP server. The addr and port pair may be repeated to provide multiple listening addresses. The should be at least one address for Nmb2 and one for MBS-1 reference points, these may be the same entry if Nmb2 and MBS-1 share the same network interface.	8000

[davidjwbbc]

Supporting If-None-Match and If-Modified-Since will make the operation of the MBSTF more efficient when it has to refresh its cache of objects to transmit via the FLUTE session.

We can live without this (and the 304 response) in an initial implementation of this server.

The 307 or 308 redirection responses are only included here for future implementation and to match the operation of other RESTful API interfaces on the MBSF when migrating services to an alternative instance.

[davidjwbbc]

After a discussion with @devbbc this morning we realised that we cannot implement this using the ogs_sbi_server_t server object in Open5GS as that only provides an HTTP 2 prior knowledge interface and we need a more general web server.

In order to accomplish this we would have to either:

1. Write an HTTP server class to handle microhttpd and upgrade to nghttp2 server.
   • This is extra development, but something we've wanted to do in other NFs and so could be written as shared code.
2. Use an external web server process such as nginx or Apache HTTPd.
   • We would either have to:
     1. Write out the bundles to the filesystem to be served (may have a problem with the multipart separator).
     2. Write a PHP or LUA script to build the bundles on demand.
   • Also need to consider how we disable serving User Service Announcements that are no longer active.
     • Do we delete all the files or just rename the directory to disable it?

[davidjwbbc]

Got the basic server working from configuration in the mbsf.yaml file.

At the moment the announcement bundle is generated if files exist within a directory, this needs changing to interrogate an internal UserServiceAnnouncement object for the files to include and do a 404 if the object doesn't exist for the given UserDataIngSessionId.

The document root directory for serving the bundles also needs to be set to match the root directory used for outputting the UserServiceAnnouncement compiled files to disk.

This is the server output when asked for a (faked) user service announcement bundle:

< HTTP/1.1 200 OK
< Date: Thu, 23 Apr 2026 13:38:54 GMT
< Connection: close
< Content-Type: multipart/related;boundary=4iL2i7NKM8ikGNC7VPoh7Uzn6p=!ygeBT!SRigw?8kagvl\t/qaP:pqWqzc?dL1:
< Server: 5G-MAG-HTTP-Server/0.1.0 (microhttpd/1.0.3)
< Content-Length: 2782
< 
--4iL2i7NKM8ikGNC7VPoh7Uzn6p=!ygeBT!SRigw?8kagvl\t/qaP:pqWqzc?dL1:
Content-Length: 1358
Content-Transfer-Encoding: binary
Content-Type: application/3gpp-mbs-user-service-descriptions+json;version="Rel17"
ETag: "74c42d99be090883bf6a15660ec4fb106606e8a1abbc9070e5e2003ca2718e19"
Last-Modified: Thu, 23 Apr 2026 13:15:49 GMT
Content-Disposition: inline;filename=announcement.json

{
  "serviceIds": [
    "https://example.com/service1",
    "https://example.com/service2",
    "https://example.com/service3"
  ],
  "class": "urn:oma:bcast:oma_bsc:st:1.0",
  "names": [
    {
      "name": "Example Service",
      "lang": "eng"
    },
    {
      "name": "Exemple de service 2",
      "lang": "fra"
    }
  ],
  "descriptions": [
    {
      "description": "This is an example service",
      "lang": "eng"
    },
    {
      "description": "Voici un exemple de service 2",
      "lang": "fra"
    }
  ],
  "distributionSessionDescriptions": [
    {
      "distributionMethod": "OBJECT",
      "sessionDescriptionLocator": "5d74b1bc-3e61-41f1-bc31-3df76a42d897/AP_MBS_SESSION_1.sdp",
      "applicationServiceDescriptions": [
        {
          "entryPointLocator": "https://livesim2.dashif.org/livesim2/WAVE/vectors/cfhd_sets/12.5_25_50/t1/2022-10-17/stream.mpd",
          "contentType": "application/dash+xml"
        }
      ]
    },
    {
      "distributionMethod": "OBJECT",
      "sessionDescriptionLocator": "5d74b1bc-3e61-41f1-bc31-3df76a42d897/AP_MBS_SESSION_2.sdp",
      "applicationServiceDescriptions": [
        {
          "entryPointLocator": "https://livesim2.dashif.org/livesim2/WAVE/vectors/cfhd_sets/12.5_25_50/t1/2022-10-17/stream.mpd",
          "contentType": "application/dash+xml"
        }
      ]
    }
  ]
}

--4iL2i7NKM8ikGNC7VPoh7Uzn6p=!ygeBT!SRigw?8kagvl\t/qaP:pqWqzc?dL1:
Content-Length: 127
Content-Transfer-Encoding: binary
Content-Type: application/octet-stream
ETag: "d7518334afa1ceafee8d9d241ad1314931a3035eccf50bc40ec4eaf4740b3bb8"
Last-Modified: Thu, 23 Apr 2026 13:19:56 GMT
Content-Disposition: attachment;filename=AP_MBS_SESSION_1.sdp

v=0
o=User Data Ingest dummy
s=AP_MBS_SESSION_1
i=Example Service
m=something
i=media info
c=connection info
a=media attribute

--4iL2i7NKM8ikGNC7VPoh7Uzn6p=!ygeBT!SRigw?8kagvl\t/qaP:pqWqzc?dL1:
Content-Length: 137
Content-Transfer-Encoding: binary
Content-Type: application/octet-stream
ETag: "7964dcf467f66f56e60f72456937597aa347a6da1fe2e0a3eff92312ad5f97af"
Last-Modified: Thu, 23 Apr 2026 13:20:36 GMT
Content-Disposition: attachment;filename=AP_MBS_SESSION_2.sdp

v=0
o=User Data Ingest dummy
s=AP_MBS_SESSION_2
i=Example Service
m=something
i=media info 2
c=connection info for 2
a=media 2 attribute

--4iL2i7NKM8ikGNC7VPoh7Uzn6p=!ygeBT!SRigw?8kagvl\t/qaP:pqWqzc?dL1:--

Please note that this example uses manually created files in a directory on the disk and just demonstrates that dynamic bundling of the files upon request. These files will not be representative of the final files output for a bundle when #32 has been completed.

[davidjwbbc]

Todo on the HTTP server:

• Fix the document root directory
• Use internal UsesServiceAnnouncement objects to check the availability of the announcement bundle and for the list of files to include if the bundle is available.
• Replace the Server header value with an MBSF specific value.
• Add handler for the MBSUserService bundle (multiple description documents based on the UserDataIngSessions attached to the MBSUserService in a combined bundle).

Todo for the multipart mime bundle:

• Check the format and headers used

[davidjwbbc]

Integrated the HTTP server with the User Service Announcement Bundle compiler object, i.e.:

• Both the HTTP Server and Bundle compiler use the same docroot directory for bundle files.
• The HTTP Server asks the Bundle compiler for the list of files that are part of the bundle instead of scanning the directory.

Also added MBSF server name instead of the default generic server name. So the Server header looks like:

Server: MBSF (5G-MAG-HTTP-Server/0.1.0; microhttpd/1.0.3)

Which indicates the version of the HTTP server library and the version of microhttpd that underlies it in the server comment and uses "MBSF" as the server name as specified in TS 29.580.

The Content-Disposition header (from the previous example output) has been changed to Content-Location as per the TS 26.517 specification.

The only thing left to do is the MBS User Service bundle of multiple User Service Description documents and their ancillary files.