A.2 Introduction

24.1093GPPBootstrapping interface (Ub) and network application function interface (Ua)Protocol detailsRelease 17TS

A.2.1 General

Bootstrapping procedure is executed in order to establish bootstrapped security association, i.e. bootstrapping session between an UE and the BSF.

The bootstrapping session is used between a UE and a NAF. An example usage of it is described in annex B.

A.2.2 Key required to interpret signalling flows

3GPP TS 24.228 [13], clause 4.1.1, specifies the key required to interpret the contents of the SIP methods. This key is used with HTTP based messages (cf. RFC 7231 [31]) as well since SIP and HTTP messages resemble each other in structure. The following key rules are used in addition to those specified in 3GPP TS 24.228 [13]:

a) The HTTP based messaging is always initiated by the client:

– HTTP request is generated by the client (i.e. UE);

– HTTP response is generated by the server as a response to the HTTP request;

– HTTP proxies may be between the client and the server.

b) There is only one single HTTP response to the HTTP request.

c) In order to differentiate between HTTP messages and other protocol messages, the HTTP messages are marked with simple arrow line, and all non-HTTP messages with block arrows.

d) The flows show the signalling exchanges between the following functional entities in addition to those specified in 3GPP TS 24.228 [13]:

– Bootstrapping Server Function (BSF);

– Network Application Function (NAF);

– PKI portal (PKI portal).

e) The "(B-TID)" sequence of characters is used to indicate that the bootstrapping transaction identifier (B-TID) needs to be filled in.