networking/caif/linux_caif.rst

1 .. SPDX-License-Identifier: GPL-2.0
8 Copyright |copy| ST-Ericsson AB 2010
17 CAIF is a MUX protocol used by ST-Ericsson cellular modems for
22 ST-Ericsson modems support a number of transports between modem
31 * CAIF Socket Layer and GPRS IP Interface.
32 * CAIF Core Protocol Implementation
39    !	      +------+	 +------+
40    !	     +------+!	+------+!
41    !	     !	IP  !!	!Socket!!
42    +-------> !interf!+	! API  !+	<- CAIF Client APIs
43    !	     +------+	+------!
45    !		+-----------+
47    !		   +------+		<- CAIF Core Protocol
49    !		   ! Core !
50    !		   +------+
51    !	   +----------!---------+
53    !	+------+   +-----+   +------+
54    +--> ! HSI  !   ! TTY !   ! USB  !	<- Link Layer (Net Devices)
55 	+------+   +-----+   +------+
63 CAIF Core Protocol Layer
64 ------------------------
66 CAIF Core layer implements the CAIF protocol as defined by ST-Ericsson.
75 The Core CAIF implementation contains:
77       -	Simple implementation of CAIF.
78       -	Layered architecture (a la Streams), each layer in the CAIF
79 	specification is implemented in a separate c-file.
80       -	Clients must call configuration function to add PHY layer.
81       -	Clients must implement CAIF layer to consume/produce
83       -	Clients must call configuration function to add and connect the
85       - When receiving / transmitting CAIF Packets (cfpkt), ownership is passed
94       - CFPKT CAIF Packet. Implementation of CAIF Protocol Packet. The
100       - CFCNFG CAIF Configuration layer. Configures the CAIF Protocol
101 	Stack and provides a Client interface for adding Link-Layer and
104       - CFCTRL CAIF Control layer. Encodes and Decodes control messages
108       - CFSERVL General CAIF Service Layer functionality; handles flow
111       - CFVEI CAIF VEI layer. Handles CAIF AT Channels on VEI (Virtual
114       - CFDGML CAIF Datagram layer. Handles CAIF Datagram layer (IP
117       - CFMUX CAIF Mux layer. Handles multiplexing between multiple
121 	on Channel-Id and Physical-ID.
123       - CFFRML CAIF Framing layer. Handles Framing i.e. Frame length
126       - CFSERL CAIF Serial layer. Handles concatenation/split of frames
131 		    +---------+
134 		    +---------+
136     +---------+	    +---------+	    +---------+
139     +---------+	    +---------+	    +---------+
142 		    +---------+
145 		    +---------+
148 	    +---------+	    +---------+
151 	    +---------+	    +---------+
153 	    +---------+	    +---------+
156 	    +---------+	    +---------+
161       - All layers embed the same structure "struct cflayer"
162       - A layer does not depend on any other layer's private data.
163       - Layers are stacked by setting the pointers::
165 		  layer->up , layer->dn
167       -	In order to send data upwards, each layer should do::
169 		 layer->up->receive(layer->up, packet);
171       - In order to send data downwards, each layer should do::
173 		 layer->dn->transmit(layer->dn, packet);
176 CAIF Socket and IP interface
179 The IP interface and CAIF socket API are implemented on top of the
180 CAIF Core protocol. The IP Interface and CAIF socket have an instance of
181 'struct cflayer', just like the CAIF Core protocol stack.
184 receive of packets is handled as by the rest of the layers: the 'dn->transmit()'
188 ---------------------------
192 The CAIF Protocol relies on a loss-less link layer without implementing
194 Therefore a flow-control mechanism is implemented where the physical