diff options
Diffstat (limited to 'Documentation/networking')
| -rw-r--r-- | Documentation/networking/phonet.txt | 32 |
1 files changed, 21 insertions, 11 deletions
diff --git a/Documentation/networking/phonet.txt b/Documentation/networking/phonet.txt index f3c72e0ca8d..57d3e59edb1 100644 --- a/Documentation/networking/phonet.txt +++ b/Documentation/networking/phonet.txt @@ -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. |