path: root/share/man/man4/ng_l2cap.4

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.\" $Id: ng_l2cap.4,v 1.4 2002/11/12 17:16:19 max Exp $
.\" $FreeBSD$
.Dd July 4, 2002
.Dt NG_L2CAP 4
.Os
.Sh NAME
.Nm l2cap
.Nd Netgraph node type that implements Bluetooth Logical Link Control and
Adaptation Protocol (L2CAP)
.Sh SYNOPSIS
.In sys/types.h
.In netgraph/ng_message.h
.In netgraph/netgraph.h
.In netgraph/ng_hci.h
.In netgraph/ng_l2cap.h
.Sh DESCRIPTION
The
.Nm
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.
.Pp
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 packets up to
64 kilobytes in length.
.Ss L2CAP assumptions
.Bl -enum -offset indent 
.It
The ACL link between two units is set up. The Baseband provides 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.
.It
The Baseband always provides the impression of full-duplex communication
channels. This does not imply that all L2CAP communications are bi-directional.
Multicasts and unidirectional traffic (e.g., video) do not require duplex
channels.
.It
L2CAP provides a reliable channel using the mechanisms available 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.
.El
.Sh L2CAP GENERAL OPERATION
The Logical Link Control and Adaptation Protocol (L2CAP) is based around the
concept of
.Em 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 protocol.
.Pp
Each one of the end-points of an L2CAP channel is referred to by a channel 
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 simultaneous L2CAP channels between a local 
device and some remote device.
.Pp
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.
.Ss Channel operational states
.Bl -tag -width foobar
.It Dv 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.
.It Dv 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 Response message.
.It Dv 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 Connect Indication has been
sent to the upper layer and the part of the local L2CAP entity processing the
received L2CAP Connect Request waits for the corresponding response. The
response may require a security check to be performed.
.It Dv 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
requires 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.
.It Dv NG_L2CAP_OPEN
In this state, the connection has been established and configured, and data
flow may proceed.
.It Dv NG_L2CAP_W4_L2CAP_DISCON_RSP
In this state, the connection is shutting down and an L2CAP Disconnect Request
message has been sent. This state is now waiting for the corresponding response.
.It Dv 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.
.El
.Ss Protocol Multiplexing
L2CAP supports protocol multiplexing because the Baseband Protocol does not 
support any 
.Dq 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.
.Ss 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 received Baseband 
packets may be reassembled into a single larger L2CAP packet. 
.Ss Quality of Service
The L2CAP connection establishment process allows the exchange of information
regarding the quality of service (QoS) expected between two Bluetooth units. 
.Ss Groups
The Baseband Protocol supports the concept of a piconet, a group of devices 
synchronously hopping together using the same clock. The L2CAP group 
abstraction permits implementations to efficiently map protocol groups on to
piconets. 
.Pp
The following features are outside the scope of L2CAP responsibilities:
.Bl -dash -offset indent
.It
L2CAP does not transport audio designated for SCO links.
.It
L2CAP does not enforce a reliable channel or ensure data integrity,
that is, L2CAP performs no retransmissions or checksum calculations.
.It
L2CAP does not support a reliable multicast channel.
.It
L2CAP does not support the concept of a global group name.
.El
.Sh HOOKS
This node type supports the following hooks:
.Pp
.Bl -tag -width foobar
.It Dv hci
Bluetooth Host Controller Interface downstream hook.
.It Dv l2c
Upper layer protocol upstream hook. Usually Bluetooth L2CAP sockets layer
is connected to the hook.
.It Dv ctl
Control hook. Usually Bluetooth raw L2CAP sockets layer is connected 
to the hook.
.El
.Sh INTERFACE TO THE UPPER LAYER PROTOCOLS (L2CA CONTROL MESSAGES)
Bluetooth specification says that L2CA request must block until response 
is ready. L2CAP node uses 
.Dq token 
field from Netgraph message header to match L2CA request and response. The
upper layer protocol must populate 
.Dq token . 
L2CAP node will queue request and start processing. Later, when response is 
ready or timeout has occur L2CAP node will create new Netgraph message, set 
.Dq token 
and 
.Dv NFG_RESP 
flag and send message to the upper layer. Note that L2CA indication messages 
will not populate 
.Dq token 
and will not set 
.Dv NGF_RESP 
flag. There is no reason for this, because they are just notifications and do 
not require acknowledgment.
.Pp
.Bl -tag -width foo
.It Dv 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 parameters are the local CID (LCID) 
allocated by the local L2CAP entity, and Result of the request. If Result 
indicates a pending notification, the Status value may contain more information
of what processing is delaying the establishment of the connection.
.It Dv 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 representing the channel being 
requested, the Identifier contained in the request, and the PSM value the 
request is targeting.
.It Dv 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 attached 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. 
.It Dv 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.
.It Dv 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 describing the characteristics of 
the incoming data. All other channel parameters are set to their default values if not provided by the remote device.
.It Dv 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 parameter in the configuration 
indication event) and the accepted flowspec for incoming traffic. The output 
parameter is the Result value.
.It Dv 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.
.It Dv NGM_L2CAP_L2CA_DISCON
Requests the disconnection of the channel. Input parameter is the CID 
representing the local channel endpoint. Output parameter is Result. 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. 
.It Dv NGM_L2CAP_L2CA_DISCON_IND
This message includes the parameter indicating the local CID the request has 
been sent to.
.It Dv 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 defined as follows.
.Pp
.Bd -literal -offset indent
/* 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;
.Ed
.Pp
The output parameters are Result and Length of data written.
.It Dv 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 incoming traffic. Output 
parameter is the CID representing the local endpoint. On creation, the group 
is empty but incoming traffic destined for the PSM value is readable.
.Em This request has not been implemented .
.It Dv NGM_L2CAP_L2CA_GRP_CLOSE
The use of this message closes down a Group.
.Em This request has not been implemented .
.It Dv 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 success or failure of the request.
.Em This request has not been implemented .
.It Dv 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 member to be removed. 
The output parameter Result confirms the success or failure of the request.
.Em This request has not been implemented .
.It Dv 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 confirms the success or 
failure of the operation. If the Result is successful, BD_ADDR_Lst is a list 
of the Bluetooth addresses of the N members of the group.
.Em This request has not been implemented .
.It Dv NGM_L2CAP_L2CA_PING
Initiates a L2CA Echo Request message and the reception of the corresponding
L2CAP Echo Response message. The input parameters are remote 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.
.It Dv 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.
.It Dv 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. 
.El
.Sh NETGRAPH CONTROL MESSAGES
This node type supports the generic control messages, plus the following:
.Bl -tag -width foo
.It Dv NGM_L2CAP_NODE_GET_FLAGS
Returns current state for the node.
.It Dv NGM_L2CAP_NODE_GET_DEBUG
Returns an integer containing the current debug level for the node.
.It Dv NGM_L2CAP_NODE_SET_DEBUG
This command takes an integer argument and sets current debug level
for the node.
.It Dv NGM_L2CAP_NODE_GET_CON_LIST
Returns list of active baseband connections (i.e. ACL links).
.It Dv NGM_L2CAP_NODE_GET_CHAN_LIST
Returns list of active L2CAP channels.
.El
.Sh SHUTDOWN
This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
when all hooks have been disconnected.
.Sh BUGS
Most likely. Please report if found.
.Sh SEE ALSO
.Xr netgraph 4 ,
.Xr ngctl 8 ,
.Xr l2control 8 ,
.Xr l2ping 8
.Sh HISTORY
The
.Nm
node type was implemented in
.Fx 5.0 .
.Sh AUTHORS
.An Maksim Yevmenkin Aq m_evmenkin@yahoo.com