The Type Frame field of F frames along with the subclass field determines the function of the package that has been sent or received.They are the control signaling messages.

The Type Frame field is a set of 8 bits (1 byte) and the main values that can take are shown in the following table:

Table 1. Main values of the "Type Frame" field of F frames or Full Frame

"type frame" value	Description	Details
00000001	DTMF	To send DTMF digits
00000002	Voice Data	Subclass field show the audio codec used. See table 2.
00000003	Video	Subclass field show the video codec used.
00000004	Control	Provide session control. They refer to control of the devices connected to the IAX endpoint. Subclass field show the specific control message. See table 3.
00000005	No usado
00000006	IAX Control	Provide IAX protocol specific endpoint management. They are used to manage IAX protocol interactions that are generally independent of the type of endpoints. Subclass field show the specific IAX control message. See table 4.
00000007	Text
00000008	Image
00000009	HTML

Table 2. Meaning of the subclass values for Frame Type = "0x02" (voice data)

Subclass Value (Type Frame =0x02)	Description (codec used in the convesation)
0x0001	G.723.1
0x0002	GSM
0x0004	G.711 u (u-law)
0x0008	G.711 a (a-law)
0x0080	LPC10
0x0100	G.729
0x0200	Speex
0x0400	iLBC

Table 3. Meaning of the subclass values for Frame Type = "0x04" (control)

Subclass Value (Type Frame =0x04)	Description
0x01	Hangup
0x02	Ring
0x03	Ringing (ringback)
0x04	Answer
0x05	Busy Condition
0x08	Congestion Condition
0x0e	Call Progress

Table 4. Meaning of the subclass values for Frame Type = "0x06" (IAX control)

Subclass Value (Type Frame =0x05)	Description	Details
0x01	NEW	Initiate a new call		0x10	REGREJ	Registration reject
0x02	PING	Ping request		0x11	REGREL	Registration release
0x03	PONG	Ping reply		0x12	VNAK	Video/Voice retransmit request
0x04	ACK	Acknowledgement		0x13	DPREQ	Dialplan request
0x05	HANGUP	Initiate call teardown		0x14	DPREP	Dialplan response
0x06	REJECT	Reject		0x15	DIAL	Dial
0x07	ACCEPT	Accepted		0x16	TXREQ	Transfer request
0x08	AUTHREQ	Authentication request		0x17	TXCNT	Transfer connect
0x09	AUTHREP	Authentication reply		0x18	TXACC	Transfer accept
0x0a	INVAL	Invalid call		0x19	TXREADY	Transfer ready
0x0b	LAGRQ	Lag request		0x1a	TXREL	Transfer release
0x0c	LAGRP	Lag reply		0x1b	TXREJ	Transfer reject
0x0d	REGREQ	Registration request		0x1c	QUELCH	Halt audio/video transmission
0x0e	REGAUTH	Registration authenticate		0x1d	UNQUELCH	Resume audio/video transmission
0x0f	REGACK	Registration acknowledgement		0x20	MWI	Message waiting indication
				0x21	UNSUPPORT	Unsupported message