Documentation/networking/rmnet.txt

   1 1. Introduction
   2
   3 rmnet driver is used for supporting the Multiplexing and aggregation
   4 Protocol (MAP). This protocol is used by all recent chipsets using Qualcomm
   5 Technologies, Inc. modems.
   6
   7 This driver can be used to register onto any physical network device in
   8 IP mode. Physical transports include USB, HSIC, PCIe and IP accelerator.
   9
  10 Multiplexing allows for creation of logical netdevices (rmnet devices) to
  11 handle multiple private data networks (PDN) like a default internet, tethering,
  12 multimedia messaging service (MMS) or IP media subsystem (IMS). Hardware sends
  13 packets with MAP headers to rmnet. Based on the multiplexer id, rmnet
  14 routes to the appropriate PDN after removing the MAP header.
  15
  16 Aggregation is required to achieve high data rates. This involves hardware
  17 sending aggregated bunch of MAP frames. rmnet driver will de-aggregate
  18 these MAP frames and send them to appropriate PDN's.
  19
  20 2. Packet format
  21
  22 a. MAP packet (data / control)
  23
  24 MAP header has the same endianness of the IP packet.
  25
  26 Packet format -
  27
  28 Bit             0             1           2-7      8 - 15           16 - 31
  29 Function   Command / Data   Reserved     Pad   Multiplexer ID    Payload length
  30 Bit            32 - x
  31 Function     Raw  Bytes
  32
  33 Command (1)/ Data (0) bit value is to indicate if the packet is a MAP command
  34 or data packet. Control packet is used for transport level flow control. Data
  35 packets are standard IP packets.
  36
  37 Reserved bits are usually zeroed out and to be ignored by receiver.
  38
  39 Padding is number of bytes to be added for 4 byte alignment if required by
  40 hardware.
  41
  42 Multiplexer ID is to indicate the PDN on which data has to be sent.
  43
  44 Payload length includes the padding length but does not include MAP header
  45 length.
  46
  47 b. MAP packet (command specific)
  48
  49 Bit             0             1           2-7      8 - 15           16 - 31
  50 Function   Command         Reserved     Pad   Multiplexer ID    Payload length
  51 Bit          32 - 39        40 - 45    46 - 47       48 - 63
  52 Function   Command name    Reserved   Command Type   Reserved
  53 Bit          64 - 95
  54 Function   Transaction ID
  55 Bit          96 - 127
  56 Function   Command data
  57
  58 Command 1 indicates disabling flow while 2 is enabling flow
  59
  60 Command types -
  61 0 for MAP command request
  62 1 is to acknowledge the receipt of a command
  63 2 is for unsupported commands
  64 3 is for error during processing of commands
  65
  66 c. Aggregation
  67
  68 Aggregation is multiple MAP packets (can be data or command) delivered to
  69 rmnet in a single linear skb. rmnet will process the individual
  70 packets and either ACK the MAP command or deliver the IP packet to the
  71 network stack as needed
  72
  73 MAP header|IP Packet|Optional padding|MAP header|IP Packet|Optional padding....
  74 MAP header|IP Packet|Optional padding|MAP header|Command Packet|Optional pad...
  75
  76 3. Userspace configuration
  77
  78 rmnet userspace configuration is done through netlink library librmnetctl
  79 and command line utility rmnetcli. Utility is hosted in codeaurora forum git.
  80 The driver uses rtnl_link_ops for communication.
  81
  82 https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/dataservices/tree/rmnetctl