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NG_L2CAP(4)		 BSD Kernel Interfaces Manual		   NG_L2CAP(4)

NAME
     l2cap -- Netgraph node type that implements Bluetooth Logical Link	Con-
     trol and Adaptation Protocol (L2CAP)

SYNOPSIS
     #include <sys/types.h>
     #include <netgraph/ng_message.h>
     #include <netgraph/netgraph.h>
     #include <netgraph/ng_hci.h>
     #include <netgraph/ng_l2cap.h>

DESCRIPTION
     The l2cap node type is a Netgraph node type that implements Bluetooth
     Logical Link Control and Adaptation Protocol as per chapter D of the
     Bluetooth Specification Book v1.1.

     L2CAP provides connection-oriented	and connectionless data	services to
     upper layer protocols with	protocol multiplexing capability, segmentation
     and reassembly operation, and group abstractions. L2CAP permits higher
     level protocols and applications to transmit and receive L2CAP data pack-
     ets up to 64 kilobytes in length.

   L2CAP assumptions
	   1.	The ACL	link between two units is set up. The Baseband pro-
		vides orderly delivery of data packets,	although there might
		be individual packet corruption	and duplicates.	No more	than 1
		ACL link exists	between	any two	devices.

	   2.	The Baseband always provides the impression of full-duplex
		communication channels.	This does not imply that all L2CAP
		communications are bi-directional.  Multicasts and unidirec-
		tional traffic (e.g., video) do	not require duplex channels.

	   3.	L2CAP provides a reliable channel using	the mechanisms avail-
		able at	the Baseband layer. The	Baseband always	performs data
		integrity checks when requested	and resends data until it has
		been successfully acknowledged or a timeout occurs. Because
		acknowledgements may be	lost, timeouts may occur even after
		the data has been successfully sent.

L2CAP GENERAL OPERATION
     The Logical Link Control and Adaptation Protocol (L2CAP) is based around
     the concept of channels.  Each channel is bound to	a single protocol in a
     many-to-one fashion. Multiple channels can	be bound to the	same protocol,
     but a channel cannot be bound to multiple protocols. Each L2CAP packet
     received on a channel is directed to the appropriate higher level proto-
     col.

     Each one of the end-points	of an L2CAP channel is referred	to by a	chan-
     nel identifier. Channel identifiers (CIDs)	are local names	representing a
     logical channel end-point on the device. Identifiers from 0x0001 to
     0x003F are	reserved for specific L2CAP functions. The null	identifier
     (0x0000) is defined as an illegal identifier and must never be used as a
     destination end-point.  All L2CAP signalling commands are sent to CID
     0x0001. CID 0x0002	is reserved for	group-oriented channel.	The same CID
     must not be reused	as a local L2CAP channel endpoint for multiple simul-
     taneous L2CAP channels between a local device and some remote device.

     CID assignment is relative	to a particular	device and a device can	assign
     CIDs independently	from other devices. Thus, even if the same CID value
     has been assigned to (remote) channel endpoints by	several	remote devices
     connected to a single local device, the local device can still uniquely
     associate each remote CID with a different	device.

   Channel operational states
     NG_L2CAP_CLOSED
	     In	this state, there is no	channel	associated with	this CID. This
	     is	the only state when a link level connection (Baseband) may not
	     exist. Link disconnection forces all other	states into the
	     NG_L2CAP_CLOSED state.

     NG_L2CAP_W4_L2CAP_CON_RSP
	     In	this state, the	CID represents a local end-point and an	L2CAP
	     Connect Request message has been sent referencing this endpoint
	     and it is now waiting for the corresponding L2CAP Connect Re-
	     sponse message.

     NG_L2CAP_W4_L2CA_CON_RSP
	     In	this state, the	remote end-point exists	and an L2CAP Connect
	     Request has been received by the local L2CAP entity. An L2CA Con-
	     nect Indication has been sent to the upper	layer and the part of
	     the local L2CAP entity processing the received L2CAP Connect Re-
	     quest waits for the corresponding response. The response may re-
	     quire a security check to be performed.

     NG_L2CAP_CONFIG
	     In	this state, the	connection has been established	but both sides
	     are still negotiating the channel parameters. The Configuration
	     state may also be entered when the	channel	parameters are being
	     renegotiated. Prior to entering the NG_L2CAP_CONFIG state,	all
	     outgoing data traffic is suspended	since the traffic parameters
	     of	the data traffic are to	be renegotiated. Incoming data traffic
	     is	accepted until the remote channel endpoint has entered the
	     NG_L2CAP_CONFIG state. In the NG_L2CAP_CONFIG state, both sides
	     will issue	L2CAP Configuration Request messages if	only defaults
	     are being used, a null message will be sent. If a large amount of
	     parameters	need to	be negotiated, multiple	messages will be sent
	     to	avoid any MTU limitations and negotiate	incrementally. Moving
	     from the NG_L2CAP_CONFIG state to the NG_L2CAP_OPEN state re-
	     quires both sides to be ready. An L2CAP entity is ready when it
	     has received a positive response to its final request and it has
	     positively	responded to the final request from the	remote device.

     NG_L2CAP_OPEN
	     In	this state, the	connection has been established	and config-
	     ured, and data flow may proceed.

     NG_L2CAP_W4_L2CAP_DISCON_RSP
	     In	this state, the	connection is shutting down and	an L2CAP Dis-
	     connect Request message has been sent. This state is now waiting
	     for the corresponding response.

     NG_L2CAP_W4_L2CA_DISCON_RSP
	     In	this state, the	connection on the remote endpoint is shutting
	     down and an L2CAP Disconnect Request message has been received.
	     An	L2CA Disconnect	Indication has been sent to the	upper layer to
	     notify the	owner of the CID that the remote endpoint is being
	     closed. This state	is now waiting for the corresponding response
	     from the upper layer before responding to the remote endpoint.

   Protocol Multiplexing
     L2CAP supports protocol multiplexing because the Baseband Protocol	does
     not support any "type" field identifying the higher layer protocol	being
     multiplexed above it.  L2CAP is able to distinguish between upper layer
     protocols such as the Service Discovery Protocol, RFCOMM and Telephony
     Control.

   Segmentation	and Reassembly
     The data packets defined by the Baseband Protocol are limited in size.
     Large L2CAP packets must be segmented into	multiple smaller Baseband
     packets prior to their transmission over the air. Similarly, multiple re-
     ceived Baseband packets may be reassembled	into a single larger L2CAP
     packet.

   Quality of Service
     The L2CAP connection establishment	process	allows the exchange of infor-
     mation regarding the quality of service (QoS) expected between two	Blue-
     tooth units.

   Groups
     The Baseband Protocol supports the	concept	of a piconet, a	group of de-
     vices synchronously hopping together using	the same clock.	The L2CAP
     group abstraction permits implementations to efficiently map protocol
     groups on to piconets.

     The following features are	outside	the scope of L2CAP responsibilities:

	   -   L2CAP does not transport	audio designated for SCO links.

	   -   L2CAP does not enforce a	reliable channel or ensure data	integ-
	       rity, that is, L2CAP performs no	retransmissions	or checksum
	       calculations.

	   -   L2CAP does not support a	reliable multicast channel.

	   -   L2CAP does not support the concept of a global group name.

HOOKS
     This node type supports the following hooks:

     hci     Bluetooth Host Controller Interface downstream hook.

     l2c     Upper layer protocol upstream hook. Usually Bluetooth L2CAP sock-
	     ets layer is connected to the hook.

     ctl     Control hook. Usually Bluetooth raw L2CAP sockets layer is	con-
	     nected to the hook.

INTERFACE TO THE UPPER LAYER PROTOCOLS (L2CA CONTROL MESSAGES)
     Bluetooth specification says that L2CA request must block until response
     is	ready. L2CAP node uses "token" field from Netgraph message header to
     match L2CA	request	and response. The upper	layer protocol must populate
     "token".  L2CAP node will queue request and start processing. Later, when
     response is ready or timeout has occur L2CAP node will create new Net-
     graph message, set	"token"	and NFG_RESP flag and send message to the up-
     per layer.	Note that L2CA indication messages will	not populate "token"
     and will not set NGF_RESP flag. There is no reason	for this, because they
     are just notifications and	do not require acknowledgment.

     NGM_L2CAP_L2CA_CON
	  Requests the creation	of a channel representing a logical connection
	  to a physical	address. Input parameters are the target protocol
	  (PSM)	and remote device's 48-bit address (BD_ADDR). Output parame-
	  ters are the local CID (LCID)	allocated by the local L2CAP entity,
	  and Result of	the request. If	Result indicates a pending notifica-
	  tion,	the Status value may contain more information of what process-
	  ing is delaying the establishment of the connection.

     NGM_L2CAP_L2CA_CON_IND
	  This message includes	the parameters for the address of the remote
	  device that issued the connection request, the local CID represent-
	  ing the channel being	requested, the Identifier contained in the re-
	  quest, and the PSM value the request is targeting.

     NGM_L2CAP_L2CA_CON_RSP
	  Issues a response to a connection request event indication. Input
	  parameters are the remote device's 48-bit address, Identifier	sent
	  in the request, local	CID, the Response code,	and the	Status at-
	  tached to the	Response code. The output parameter is the Result of
	  the service request. This primitive must be called no	more than once
	  after	receiving the indication.

     NGM_L2CAP_L2CA_CFG
	  Requests the initial configuration (or reconfiguration) of a channel
	  to a new set of channel parameters. Input parameters are the local
	  CID endpoint,	new incoming receivable	MTU (InMTU), new outgoing flow
	  spec-ification, and flush and	link timeouts. Output parameters are
	  the Result, accepted incoming	MTU (InMTU), the remote	side's flow
	  requests, and	flush and link timeouts.

     NGM_L2CAP_L2CA_CFG_IND
	  This message includes	the parameters indicating the local CID	of the
	  channel the request has been sent to,	the outgoing MTU size (maximum
	  packet that can be sent across the channel) and the flowspec de-
	  scribing the characteristics of the incoming data. All other channel
	  parameters are set to	their default values if	not provided by	the
	  remote device.

     NGM_L2CAP_L2CA_CFG_RSP
	  Issues a response to a configuration request event indication. Input
	  parameters include the local CID of the endpoint being configured,
	  outgoing transmit MTU	(which may be equal or less to the OutMTU pa-
	  rameter in the configuration indication event) and the accepted
	  flowspec for incoming	traffic. The output parameter is the Result
	  value.

     NGM_L2CAP_L2CA_QOS_IND
	  This message includes	the parameter indicating the address of	the
	  remote Bluetooth device where	the QoS	contract has been violated.

     NGM_L2CAP_L2CA_DISCON
	  Requests the disconnection of	the channel. Input parameter is	the
	  CID representing the local channel endpoint. Output parameter	is Re-
	  sult.	Result is zero if a L2CAP Disconnect Response is received,
	  otherwise a non-zero value is	returned. Once disconnection has been
	  requested, no	process	will be	able to	successfully read or write
	  from the CID.

     NGM_L2CAP_L2CA_DISCON_IND
	  This message includes	the parameter indicating the local CID the re-
	  quest	has been sent to.

     NGM_L2CAP_L2CA_WRITE
	  Response to transfer of data request.	Actual data must be received
	  from appropriate upstream hook and must be prepended with header de-
	  fined	as follows.

		/* L2CA	data packet header */
		typedef	struct {
			u_int32_t token;  /* token to use in L2CAP_L2CA_WRITE */
			u_int16_t length; /* length of the data	*/
			u_int16_t lcid;	  /* local channel ID */
		} __attribute__	((packed)) ng_l2cap_l2ca_hdr_t;

	  The output parameters	are Result and Length of data written.

     NGM_L2CAP_L2CA_GRP_CREATE
	  Requests the creation	of a CID to represent a	logical	connection to
	  multiple devices. Input parameter is the PSM value that the outgoing
	  connectionless traffic is labelled with, and the filter used for in-
	  coming traffic. Output parameter is the CID representing the local
	  endpoint. On creation, the group is empty but	incoming traffic des-
	  tined	for the	PSM value is readable.	This request has not been
	  implemented.

     NGM_L2CAP_L2CA_GRP_CLOSE
	  The use of this message closes down a	Group.	This request has not
	  been implemented.

     NGM_L2CAP_L2CA_GRP_ADD_MEMBER
	  Requests the addition	of a member to a group.	The input parameter
	  includes the CID representing	the group and the BD_ADDR of the group
	  member to be added.  The output parameter Result confirms the	suc-
	  cess or failure of the request.  This	request	has not	been
	  implemented.

     NGM_L2CAP_L2CA_GRP_REM_MEMBER
	  Requests the removal of a member from	a group. The input parameters
	  include the CID representing the group and BD_ADDR of	the group mem-
	  ber to be removed.  The output parameter Result confirms the success
	  or failure of	the request.  This request has not been	implemented.

     NGM_L2CAP_L2CA_GRP_MEMBERSHIP
	  Requests a report of the members of a	group. The input parameter CID
	  represents the group being queried. The output parameter Result con-
	  firms	the success or failure of the operation. If the	Result is suc-
	  cessful, BD_ADDR_Lst is a list of the	Bluetooth addresses of the N
	  members of the group.	 This request has not been implemented.

     NGM_L2CAP_L2CA_PING
	  Initiates a L2CA Echo	Request	message	and the	reception of the cor-
	  responding L2CAP Echo	Response message. The input parameters are re-
	  mote Bluetooth device	BD_ADDR, Echo Data and Length of the echo
	  data.	The output parameters are Result, Echo Data and	Length of the
	  echo data.

     NGM_L2CAP_L2CA_GET_INFO
	  Initiates a L2CA Information Request message and the reception of
	  the corresponding L2CAP Info Response	message. The input parameters
	  are remote Bluetooth device BD_ADDR and Information Type. The	output
	  parameters are Result, Information Data and Size of the information
	  data.

     NGM_L2CAP_L2CA_ENABLE_CLT
	  Request to disable (enable) the reception of connectionless packets.
	  The input parameter is the PSM value indicating service that should
	  be blocked (unblocked) and Enable flag.

NETGRAPH CONTROL MESSAGES
     This node type supports the generic control messages, plus	the following:

     NGM_L2CAP_NODE_GET_FLAGS
	  Returns current state	for the	node.

     NGM_L2CAP_NODE_GET_DEBUG
	  Returns an integer containing	the current debug level	for the	node.

     NGM_L2CAP_NODE_SET_DEBUG
	  This command takes an	integer	argument and sets current debug	level
	  for the node.

     NGM_L2CAP_NODE_GET_CON_LIST
	  Returns list of active baseband connections (i.e. ACL	links).

     NGM_L2CAP_NODE_GET_CHAN_LIST
	  Returns list of active L2CAP channels.

SHUTDOWN
     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
     when all hooks have been disconnected.

BUGS
     Most likely. Please report	if found.

SEE ALSO
     netgraph(4), ngctl(8), l2control(8), l2ping(8)

HISTORY
     The l2cap node type was implemented in FreeBSD 5.0.

AUTHORS
     Maksim Yevmenkin <m_evmenkin@yahoo.com>

BSD				 July 4, 2002				   BSD

NAME | SYNOPSIS | DESCRIPTION | L2CAP GENERAL OPERATION | HOOKS | INTERFACE TO THE UPPER LAYER PROTOCOLS (L2CA CONTROL MESSAGES) | NETGRAPH CONTROL MESSAGES | SHUTDOWN | BUGS | SEE ALSO | HISTORY | AUTHORS

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