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25 .\" $Id: ng_l2cap.4,v 1.4 2003/09/14 23:37:52 max Exp $
33 .Nd Netgraph node type that implements Bluetooth Logical Link Control and
34 Adaptation Protocol (L2CAP)
37 .In netgraph/bluetooth/include/ng_hci.h
38 .In netgraph/bluetooth/include/ng_l2cap.h
42 node type is a Netgraph node type that implements Bluetooth Logical Link
43 Control and Adaptation Protocol as per chapter D of the Bluetooth Specification
46 L2CAP provides connection-oriented and connectionless data services to upper
47 layer protocols with protocol multiplexing capability, segmentation and
48 reassembly operation, and group abstractions.
49 L2CAP permits higher level
50 protocols and applications to transmit and receive L2CAP data packets up to
51 64 kilobytes in length.
53 .Bl -enum -offset indent
55 The ACL link between two units is set up.
56 The Baseband provides orderly
57 delivery of data packets, although there might be individual packet corruption
59 No more than one ACL link exists between any two devices.
61 The Baseband always provides the impression of full-duplex communication
63 This does not imply that all L2CAP communications are bi-directional.
64 Multicasts and unidirectional traffic (e.g., video) do not require duplex
67 L2CAP provides a reliable channel using the mechanisms available at the
69 The Baseband always performs data integrity checks when
70 requested and resends data until it has been successfully acknowledged or
72 As acknowledgements may be lost, timeouts may
73 occur even after the data has been successfully sent.
75 .Sh L2CAP GENERAL OPERATION
76 The Logical Link Control and Adaptation Protocol (L2CAP) is based around the
79 Each channel is bound to a single protocol in a many-to-one fashion.
81 channels can be bound to the same protocol, but a channel cannot be bound to
83 Each L2CAP packet received on a channel is directed to
84 the appropriate higher level protocol.
86 Each one of the end-points of an L2CAP channel is referred to by a channel
88 Channel identifiers (CIDs) are local names representing a logical
89 channel end-point on the device.
90 Identifiers from 0x0001 to 0x003F are reserved
91 for specific L2CAP functions.
92 The null identifier (0x0000) is defined as an
93 illegal identifier and must never be used as a destination end-point.
94 All L2CAP signalling commands are sent to CID 0x0001.
95 CID 0x0002 is reserved for group-oriented channel.
96 The same CID must not be reused as a local L2CAP
97 channel endpoint for multiple simultaneous L2CAP channels between a local
98 device and some remote device.
100 CID assignment is relative to a particular device and a device can assign CIDs
101 independently from other devices.
102 Thus, even if the same CID value has been
103 assigned to (remote) channel endpoints by several remote devices connected
104 to a single local device, the local device can still uniquely associate each
105 remote CID with a different device.
106 .Ss Channel Operational States
108 .It Dv NG_L2CAP_CLOSED
109 In this state, there is no channel associated with this CID.
111 state when a link level connection (Baseband) may not exist.
113 forces all other states into the
116 .It Dv NG_L2CAP_W4_L2CAP_CON_RSP
117 In this state, the CID represents a local end-point and an L2CAP Connect
118 Request message has been sent referencing this endpoint and it is now waiting
119 for the corresponding L2CAP Connect Response message.
120 .It Dv NG_L2CAP_W4_L2CA_CON_RSP
121 In this state, the remote end-point exists and an L2CAP Connect Request has
122 been received by the local L2CAP entity.
123 An L2CA Connect Indication has been
124 sent to the upper layer and the part of the local L2CAP entity processing the
125 received L2CAP Connect Request waits for the corresponding response.
126 The response may require a security check to be performed.
127 .It Dv NG_L2CAP_CONFIG
128 In this state, the connection has been established but both sides are still
129 negotiating the channel parameters.
130 The Configuration state may also be
131 entered when the channel parameters are being renegotiated.
132 Prior to entering the
134 state, all outgoing data traffic is suspended since
135 the traffic parameters of the data traffic are to be renegotiated.
137 data traffic is accepted until the remote channel endpoint has entered
143 state, both sides will issue
144 L2CAP Configuration Request messages if only defaults are being used, a null
145 message will be sent.
146 If a large amount of parameters need to be negotiated,
147 multiple messages will be sent to avoid any MTU limitations and negotiate
153 state requires both sides to be ready.
154 An L2CAP entity is ready when it has received
155 a positive response to its final request and it has positively responded to
156 the final request from the remote device.
158 In this state, the connection has been established and configured, and data
160 .It Dv NG_L2CAP_W4_L2CAP_DISCON_RSP
161 In this state, the connection is shutting down and an L2CAP Disconnect Request
162 message has been sent.
163 This state is now waiting for the corresponding response.
164 .It Dv NG_L2CAP_W4_L2CA_DISCON_RSP
165 In this state, the connection on the remote endpoint is shutting down and an
166 L2CAP Disconnect Request message has been received.
168 Indication has been sent to the upper layer to notify the owner of the CID
169 that the remote endpoint is being closed.
170 This state is now waiting for the
171 corresponding response from the upper layer before responding to the remote
174 .Ss Protocol Multiplexing
175 L2CAP supports protocol multiplexing because the Baseband Protocol does not
178 field identifying the higher layer protocol being multiplexed above it.
179 L2CAP is able to distinguish between upper layer protocols such as the Service
180 Discovery Protocol, RFCOMM and Telephony Control.
181 .Ss Segmentation and Reassembly
182 The data packets defined by the Baseband Protocol are limited in size.
184 L2CAP packets must be segmented into multiple smaller Baseband packets prior
185 to their transmission over the air.
186 Similarly, multiple received Baseband
187 packets may be reassembled into a single larger L2CAP packet.
188 .Ss Quality of Service
189 The L2CAP connection establishment process allows the exchange of information
190 regarding the quality of service (QoS) expected between two Bluetooth units.
192 The Baseband Protocol supports the concept of a piconet, a group of devices
193 synchronously hopping together using the same clock.
195 abstraction permits implementations to efficiently map protocol groups on to
198 The following features are outside the scope of L2CAP responsibilities:
199 .Bl -dash -offset indent
201 L2CAP does not transport audio designated for SCO links.
203 L2CAP does not enforce a reliable channel or ensure data integrity,
204 that is, L2CAP performs no retransmissions or checksum calculations.
206 L2CAP does not support a reliable multicast channel.
208 L2CAP does not support the concept of a global group name.
211 This node type supports the following hooks:
212 .Bl -tag -width ".Va hci"
214 Bluetooth Host Controller Interface downstream hook.
216 Upper layer protocol upstream hook.
217 Usually the Bluetooth L2CAP socket layer is connected to the hook.
220 Usually the Bluetooth raw L2CAP sockets layer is connected to the hook.
222 .Sh INTERFACE TO THE UPPER LAYER PROTOCOLS (L2CA CONTROL MESSAGES)
223 Bluetooth specification says that L2CA request must block until response
227 field from Netgraph message header to match L2CA request and response.
228 The upper layer protocol must populate
230 L2CAP node will queue request and start processing.
231 Later, when response is
232 ready or timeout has occurred, L2CAP node will create new Netgraph message, set
236 flag and send message to the upper layer.
237 Note that L2CA indication messages
243 There is no reason for this, because they are just notifications and do
244 not require acknowledgment.
246 .It Dv NGM_L2CAP_L2CA_CON
247 Requests the creation of a channel representing a logical connection to a
249 Input parameters are the target protocol (PSM) and remote
250 device's 48-bit address (BD_ADDR).
251 Output parameters are the local CID (LCID)
252 allocated by the local L2CAP entity, and Result of the request.
254 indicates a pending notification, the Status value may contain more information
255 of what processing is delaying the establishment of the connection.
256 .It Dv NGM_L2CAP_L2CA_CON_IND
257 This message includes the parameters for the address of the remote device that
258 issued the connection request, the local CID representing the channel being
259 requested, the Identifier contained in the request, and the PSM value the
260 request is targeting.
261 .It Dv NGM_L2CAP_L2CA_CON_RSP
262 Issues a response to a connection request event indication.
264 are the remote device's 48-bit address, Identifier sent in the request, local
265 CID, the Response code, and the Status attached to the Response code.
266 The output parameter is the Result of the service request.
267 This primitive must be
268 called no more than once after receiving the indication.
269 .It Dv NGM_L2CAP_L2CA_CFG
270 Requests the initial configuration (or reconfiguration) of a channel to a new
271 set of channel parameters.
272 Input parameters are the local CID endpoint, new
273 incoming receivable MTU (InMTU), new outgoing flow spec-ification, and flush
275 Output parameters are the Result, accepted incoming MTU
276 (InMTU), the remote side's flow requests, and flush and link timeouts.
277 .It Dv NGM_L2CAP_L2CA_CFG_IND
278 This message includes the parameters indicating the local CID of the channel
279 the request has been sent to, the outgoing MTU size (maximum packet that can
280 be sent across the channel) and the flowspec describing the characteristics of
282 All other channel parameters are set to their default values
283 if not provided by the remote device.
284 .It Dv NGM_L2CAP_L2CA_CFG_RSP
285 Issues a response to a configuration request event indication.
287 include the local CID of the endpoint being configured, outgoing transmit MTU
288 (which may be equal or less to the OutMTU parameter in the configuration
289 indication event) and the accepted flowspec for incoming traffic.
290 The output parameter is the Result value.
291 .It Dv NGM_L2CAP_L2CA_QOS_IND
292 This message includes the parameter indicating the address of the remote
293 Bluetooth device where the QoS contract has been violated.
294 .It Dv NGM_L2CAP_L2CA_DISCON
295 Requests the disconnection of the channel.
296 Input parameter is the CID representing the local channel endpoint.
297 Output parameter is Result.
299 is zero if an L2CAP Disconnect Response is received, otherwise a non-zero value
301 Once disconnection has been requested, no process will be able to
302 successfully read or write from the CID.
303 .It Dv NGM_L2CAP_L2CA_DISCON_IND
304 This message includes the parameter indicating the local CID the request has
306 .It Dv NGM_L2CAP_L2CA_WRITE
307 Response to transfer of data request.
308 Actual data must be received from
309 appropriate upstream hook and must be prepended with header defined as follows.
310 .Bd -literal -offset indent
311 /* L2CA data packet header */
313 uint32_t token; /* token to use in L2CAP_L2CA_WRITE */
314 uint16_t length; /* length of the data */
315 uint16_t lcid; /* local channel ID */
316 } __attribute__ ((packed)) ng_l2cap_l2ca_hdr_t;
319 The output parameters are Result and Length of data written.
320 .It Dv NGM_L2CAP_L2CA_GRP_CREATE
321 Requests the creation of a CID to represent a logical connection to multiple
323 Input parameter is the PSM value that the outgoing connectionless
324 traffic is labelled with, and the filter used for incoming traffic.
325 Output parameter is the CID representing the local endpoint.
326 On creation, the group
327 is empty but incoming traffic destined for the PSM value is readable.
329 This request has not been implemented.
331 .It Dv NGM_L2CAP_L2CA_GRP_CLOSE
332 The use of this message closes down a Group.
334 This request has not been implemented.
336 .It Dv NGM_L2CAP_L2CA_GRP_ADD_MEMBER
337 Requests the addition of a member to a group.
338 The input parameter includes the
339 CID representing the group and the BD_ADDR of the group member to be added.
340 The output parameter Result confirms the success or failure of the request.
342 This request has not been implemented.
344 .It Dv NGM_L2CAP_L2CA_GRP_REM_MEMBER
345 Requests the removal of a member from a group.
346 The input parameters include
347 the CID representing the group and BD_ADDR of the group member to be removed.
348 The output parameter Result confirms the success or failure of the request.
350 This request has not been implemented.
352 .It Dv NGM_L2CAP_L2CA_GRP_MEMBERSHIP
353 Requests a report of the members of a group.
354 The input parameter CID represents the group being queried.
355 The output parameter Result confirms the success or
356 failure of the operation.
357 If the Result is successful, BD_ADDR_Lst is a list
358 of the Bluetooth addresses of the N members of the group.
360 This request has not been implemented.
362 .It Dv NGM_L2CAP_L2CA_PING
363 Initiates an L2CA Echo Request message and the reception of the corresponding
364 L2CAP Echo Response message.
365 The input parameters are remote Bluetooth device
366 BD_ADDR, Echo Data and Length of the echo data.
367 The output parameters are
368 Result, Echo Data and Length of the echo data.
369 .It Dv NGM_L2CAP_L2CA_GET_INFO
370 Initiates an L2CA Information Request message and the reception of the
371 corresponding L2CAP Info Response message.
372 The input parameters are remote Bluetooth device BD_ADDR and Information Type.
373 The output parameters are
374 Result, Information Data and Size of the information data.
375 .It Dv NGM_L2CAP_L2CA_ENABLE_CLT
376 Request to disable (enable) the reception of connectionless packets.
378 parameter is the PSM value indicating service that should be blocked
379 (unblocked) and Enable flag.
381 .Sh NETGRAPH CONTROL MESSAGES
382 This node type supports the generic control messages, plus the following:
384 .It Dv NGM_L2CAP_NODE_GET_FLAGS
385 Returns current state for the node.
386 .It Dv NGM_L2CAP_NODE_GET_DEBUG
387 Returns an integer containing the current debug level for the node.
388 .It Dv NGM_L2CAP_NODE_SET_DEBUG
389 This command takes an integer argument and sets current debug level
391 .It Dv NGM_L2CAP_NODE_GET_CON_LIST
392 Returns list of active baseband connections (i.e., ACL links).
393 .It Dv NGM_L2CAP_NODE_GET_CHAN_LIST
394 Returns list of active L2CAP channels.
395 .It Dv NGM_L2CAP_NODE_GET_AUTO_DISCON_TIMO
396 Returns an integer containing the current value of the auto disconnect
398 .It Dv NGM_L2CAP_NODE_SET_AUTO_DISCON_TIMO
399 This command accepts an integer and sets the value of the auto disconnect
401 The special value of 0 (zero) disables auto disconnect timeout.
404 This node shuts down upon receipt of an
407 when all hooks have been disconnected.
416 node type was implemented in
419 .An Maksim Yevmenkin Aq m_evmenkin@yahoo.com
422 Please report if found.