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129 lines
4.8 KiB
Markdown
129 lines
4.8 KiB
Markdown
# Berkely BSD Sockets {#socket}
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The socket node-type is the most comprehensive and complex one.
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It allows to send and receive simulation data over the network.
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Internally it uses the well known BSD socket API.
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Please note that only datagram / packet, connection-less based network protocols are supported.
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This means that there's currently no support for TCP!
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The implementation supports multiple protocols / OSI layers:
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- Layer 1: Raw Ethernet Frames (no routing!)
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- Layer 2: Raw IP (internet / VPN routing possible)
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- Layer 3: UDP encapsulation
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## Configuration
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Every `socket` node supports the following special settings:
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#### `local` *("ip:port" | "mac:protocol")*
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#### `remote` *("ip:port" | "mac:protocol")*
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#### `netem` *(dictionary)*
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Enables and configures the network emulation qeueing discipline.
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See below for a more detailed description of this feature.
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netem = { # Network emulation settings
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# Those settings can be specified for each node invidually!
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delay = 100000, # Additional latency in microseconds
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jitter = 30000, # Jitter in uS
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distribution = "normal", # Distribution of delay: uniform, normal, pareto, paretonormal
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loss = 10 # Packet loss in percent
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duplicate = 10, # Duplication in percent
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corrupt = 10 # Corruption in percent
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}
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#### `layer` *("udp" | "ip" | "eth")*
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### Example
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nodes = {
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udp_node = { # The dictionary is indexed by the name of the node.
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type = "socket", # Type can be one of: socket, opal, file, gtfpga, ngsi
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# Start the server without arguments for a list of supported node types.
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### The following settings are specific to the socket node-type!! ###
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layer = "udp" # Layer can be one of:
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# udp Send / recv UDP packets
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# ip Send / recv IP packets
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# eth Send / recv raw Ethernet frames (IEEE802.3)
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local = "127.0.0.1:12001", # This node only received messages on this IP:Port pair
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remote = "127.0.0.1:12000" # This node sents outgoing messages to this IP:Port pair
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vectorize = 30 # Receive and sent 30 samples per message (multiplexing).
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}
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}
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## Packet Format
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The on-wire format of the network packets is not subject to a standardization process.
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It's a very simple packet-based format which includes:
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- 32bit floating-point or integer values
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- 32bit timestamp (integral seconds)
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- 32bit timestamp (integral nanoseconds)
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- 16bit sequence number
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- 4bit version identified
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- and several flags...
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## Message
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A message contains a variable number of values.
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Usually a a simulator sends one message per timestep.
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Simulation data is encapsulated in UDP packages in sent over IP networks like the internet.
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We designed a lightweight message format (or protocol) to facilitate a fast transmission.
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@diafile msg_format.dia
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For now, only the first message type (`data`) is used.
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Therefore the complete protocol is **stateless**.
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Later we might want to support more complex simulation scenarios which require some kind of controlling.
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Except for the simulation data, all values are sent in **network byte order** (big endian)!
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The endianess of the simulation data is indicated by a single bit in the message header.
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This allows us to reduce the amount of conversions during one transfer.
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@see msg for implementation details.
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### Example
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@todo add screenshot of wireshark dump
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## Network Emulation {#netem}
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VILLASnode supports the emulation of wide-area network characterisics.
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This emulation can be configured on a per-node basis for **outgoing** (egress) data only.
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Incoming data is not processed by the network emulation!
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This network emulation is handled by Linux' [netem queuing discipline](http://www.linuxfoundation.org/collaborate/workgroups/networking/netem) which is part of the traffic control subsystem.
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Take a look at the following manual page for supported metrics: [tc-netem(8)](http://man7.org/linux/man-pages/man8/tc-netem.8.html).
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VILLASnode only takes care of setup and initalizing the netem queuing discipline inside the kernel.
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For this the iproute2 software package (`ip` & `tc` commands) must be installed.
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The configuration is done via the config file.
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Look at `etc/example.conf` for a section called `netem` or `tc-netem(8)` for more details.
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### Custom delay distribution
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Netem supports loading custom delay distributions.
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1. Load and compile the netem tools from:
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https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/tree/netem
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2. Create a custom distribution by following the steps described here:
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https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/tree/README.distribution
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3. Put the generated distrubtion with the suffix `.dist` in the `tc` lib directory: `/usr/lib/tc/`.
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4. Load the distribution specifying the basename in the server config.
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### Further information
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- https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/tree/README.iproute2+tc
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- https://github.com/stv0g/netem
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