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Commit ac2dc8ca authored by Rémi Denis-Courmont's avatar Rémi Denis-Courmont Committed by David S. Miller
Browse files

Phonet: improve documentation 



Fix grammar errors spotted by Randy Dunlap,
and adds some more details.

Signed-off-by: default avatarRemi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8980713b

Documentation/networking/phonet.txt

+21 −11
Original line number Diff line number Diff line
@@ -21,7 +21,7 @@ depending on the device, such as: 
Packets format

--------------



Phonet packet have a common header as follow:

Phonet packets have a common header as follows:



  struct phonethdr {

    uint8_t  pn_media;  /* Media type (link-layer identifier) */
@@ -33,14 +33,17 @@ Phonet packet have a common header as follow: 
    uint8_t  pn_sobj;   /* Sender object ID */

  };



The device ID is split: the 6 higher order bits consitutes the device

address, while the 2 lower order bits are used for multiplexing, as are

the 8-bits object identifiers. As such, Phonet can be considered as a

On Linux, the link-layer header includes the pn_media byte (see below).

The next 7 bytes are part of the network-layer header.



The device ID is split: the 6 higher-order bits consitute the device

address, while the 2 lower-order bits are used for multiplexing, as are

the 8-bit object identifiers. As such, Phonet can be considered as a

network layer with 6 bits of address space and 10 bits for transport

protocol (much like port numbers in IP world).



The modem always has address number zero. Each other device has a its

own 6-bits address.

The modem always has address number zero. All other device have a their

own 6-bit address.





Link layer
@@ -49,11 +52,18 @@ Link layer 
Phonet links are always point-to-point links. The link layer header

consists of a single Phonet media type byte. It uniquely identifies the

link through which the packet is transmitted, from the modem's

perspective.



Linux Phonet network interfaces use a dedicated link layer type

(ETH_P_PHONET) which is out of the Ethernet type range. They can only

send and receive Phonet packets.

perspective. Each Phonet network device shall prepend and set the media

type byte as appropriate. For convenience, a common phonet_header_ops

link-layer header operations structure is provided. It sets the

media type according to the network device hardware address.



Linux Phonet network interfaces support a dedicated link layer packets

type (ETH_P_PHONET) which is out of the Ethernet type range. They can

only send and receive Phonet packets.



The virtual TUN tunnel device driver can also be used for Phonet. This

requires IFF_TUN mode, _without_ the IFF_NO_PI flag. In this case,

there is no link-layer header, so there is no Phonet media type byte.



Note that Phonet interfaces are not allowed to re-order packets, so

only the (default) Linux FIFO qdisc should be used with them.