Transports¶

Transports connect module streams across process boundaries and/or networks.

• Module: a running component (e.g., camera, mapping, nav).
• Stream: a unidirectional flow of messages owned by a module (one broadcaster → many receivers).
• Topic: the name/identifier used by a transport or pubsub backend.
• Message: payload carried on a stream (often dimos.msgs.*, but can be bytes / images / pointclouds / etc.).

Each edge in the graph is a transported stream (potentially different protocols). Each node is a module:

What the transport layer guarantees (and what it doesn’t)¶

Modules don’t know or care how data moves. They just:

• emit messages (broadcast)
• subscribe to messages (receive)

A transport is responsible for the mechanics of delivery (IPC, sockets, Redis, ROS 2, etc.).

Important: delivery semantics depend on the backend:

• Some are best-effort (e.g., UDP multicast / LCM): loss can happen.
• Some can be reliable (e.g., TCP-backed, Redis, some DDS configs) but may add latency/backpressure.

So: treat the API as uniform, but pick a backend whose semantics match the task.

Choosing a backend¶

• zenoh: is our default. Reliable delivery and the same typed message model through LCM binary encoding of messages
• lcm: the legacy path, opt-in. Fast and simple, but UDP multicast is best-effort.

At the CLI level, you can select the stream transport globally with:

dimos --transport=lcm run unitree-go2
dimos --transport=zenoh run unitree-go2

Generally LCM is legacy and we suggest using zenoh (the default) going forward

Zenoh¶

What the default talks to¶

A stock zenoh session is pinned to localhost. It listens on tcp/127.0.0.1:0 and scouts for peers over loopback only, so sibling dimOS processes on this machine find each other and nothing on the LAN can link to them.

Peers on this machine carry their data through shared memory, not the socket. Zenoh negotiates it per link at handshake, a remote peer keeps getting the payload over TCP.

Reaching off the machine is opt-in

Every one of these unpins the listener back to zenoh's all-interfaces default.

Two ways to override for one run or for your shell:

1. CLI: dimos --transport=zenoh ... or dimos --transport=lcm ... (see CLI for precedence with .env and blueprints).
2. Environment: DIMOS_TRANSPORT=zenoh or DIMOS_TRANSPORT=lcm.

Architecture notes (Rerun bridge) live under Zenoh in PubSub transports below.

Per-topic QoS¶

Zenoh publisher QoS lives on the Zenoh Topic object (see zenohpubsub.py):

from dimos.core.transport import ZenohTransport
from dimos.protocol.pubsub.impl.zenohpubsub import Topic, ZenohQoS

blueprint = blueprint.transports(
    {("image", CameraModule): ZenohTransport(Topic("dimos/image", Image, qos=ZenohQoS(reliability="best_effort", congestion_control="drop")))}
)

When the factory builds transports from the global switch, it applies defaults (default_zenoh_qos in transport_factory.py):

• The agent channels (human_input, agent, agent_idle): reliable, block under congestion (never drop).
• Image/PointCloud2 streams: best-effort, drop under congestion (latest wins).
• Everything else: zenoh defaults (reliable, drop under congestion).

Benchmarks¶

Quick view on performance of our pubsub backends:

python -m pytest -sv -k "not bytes" dimos/protocol/pubsub/benchmark/tool_benchmark.py

Abstraction layers¶

color = white
fill = none
linewid = 0.5in
boxwid = 1.0in
boxht = 0.4in

# Boxes with labels
B: box "Blueprints" rad 10px
arrow
M: box "Modules" rad 5px
arrow
T: box "Transports" rad 5px
arrow
P: box "PubSub" rad 5px

# Descriptions below
text "robot configs" at B.s + (0.1, -0.2in)
text "camera, nav" at M.s + (0, -0.2in)
text "LCM, SHM, ROS" at T.s + (0, -0.2in)
text "pub/sub API" at P.s + (0, -0.2in)

We’ll go through these layers top-down.

Using transports with blueprints¶

See Blueprints for the blueprint API.

From unitree/go2/blueprints/smart/unitree_go2.py.

Example: rebind a few streams from the default LCMTransport to ROSTransport (defined at transport.py) so you can visualize in rviz2.

nav = autoconnect(
    basic,
    voxel_mapper(voxel_size=0.1),
    cost_mapper(),
    replanning_a_star_planner(),
    wavefront_frontier_explorer(),
).global_config(n_workers=6, robot_model="unitree_go2")

ros = nav.transports(
    {
        ("lidar", PointCloud2): ROSTransport("lidar", PointCloud2),
        ("global_map", PointCloud2): ROSTransport("global_map", PointCloud2),
        ("odom", PoseStamped): ROSTransport("odom", PoseStamped),
        ("color_image", Image): ROSTransport("color_image", Image),
    }
)

Using transports with modules¶

Each stream on a module can use a different transport. Set .transport on the stream before starting modules.

The runnable example below uses a tiny synthetic image publisher instead of CameraModule so it works without a webcam and in CI; the wiring is the same as with a real camera.

import time

import numpy as np
import reactivex as rx

from dimos.core.core import rpc
from dimos.core.coordination.module_coordinator import ModuleCoordinator
from dimos.core.module import Module, ModuleConfig
from dimos.core.stream import In, Out
from dimos.core.transport import LCMTransport
from dimos.msgs.sensor_msgs.Image import Image, ImageFormat

class TickerCameraConfig(ModuleConfig):
    frequency_hz: float = 2.0

class TickerCameraModule(Module):
    """Publish synthetic frames so this example runs without a webcam."""

    config: TickerCameraConfig
    color_image: Out[Image]

    @rpc
    def start(self) -> None:
        super().start()

        def emit(_: int) -> None:
            img = Image.from_numpy(
                np.zeros((480, 640, 3), dtype=np.uint8),
                format=ImageFormat.RGB,
                frame_id="synthetic",
            )
            self.color_image.publish(img)

        period = 1.0 / max(self.config.frequency_hz, 0.1)
        self.register_disposable(rx.interval(period).subscribe(emit))

class ImageListener(Module):
    image: In[Image]

    async def handle_image(self, img: Image) -> None:
        print(f"Received: {img.shape}")

if __name__ == "__main__":
    # Start local cluster and deploy modules to separate processes
    dimos = ModuleCoordinator()
    dimos.start()

    camera = dimos.deploy(TickerCameraModule, frequency_hz=2.0)
    listener = dimos.deploy(ImageListener)

    # Choose a transport for the stream (example: LCM typed channel)
    camera.color_image.transport = LCMTransport("/camera/rgb", Image)

    # Connect listener input to camera output
    listener.image.connect(camera.color_image)

    dimos.start_all_modules()

    time.sleep(2)
    dimos.stop()

12:36:05.648 [inf][ation/worker_manager_python.py] Worker pool started. n_workers=2
12:36:06.053 [inf][/coordination/python_worker.py] Deployed module. module=TickerCameraModule module_id=0 worker_id=0
12:36:06.159 [inf][/coordination/python_worker.py] Deployed module. module=ImageListener module_id=1 worker_id=1
12:36:08.283 [inf][dination/module_coordinator.py] Stopping module... module=imagelistener
12:36:08.284 [inf][dination/module_coordinator.py] Module stopped. module=imagelistener
12:36:08.285 [inf][dination/module_coordinator.py] Stopping module... module=tickercameramodule
12:36:08.334 [inf][dination/module_coordinator.py] Module stopped. module=tickercameramodule
12:36:08.335 [inf][ation/worker_manager_python.py] Shutting down all workers...
Received: (480, 640, 3)
Received: (480, 640, 3)
Received: (480, 640, 3)
Received: (480, 640, 3)
12:36:08.336 [inf][/coordination/python_worker.py] Worker stopping module... module=ImageListener module_id=1 worker_id=1
12:36:08.336 [inf][/coordination/python_worker.py] Worker module stopped. module=ImageListener module_id=1 worker_id=1
12:36:08.388 [inf][/coordination/python_worker.py] Worker stopping module... module=TickerCameraModule module_id=0 worker_id=0
12:36:08.388 [inf][/coordination/python_worker.py] Worker module stopped. module=TickerCameraModule module_id=0 worker_id=0
12:36:08.394 [inf][ation/worker_manager_python.py] All workers shut down

See Modules for more on module architecture.

Inspecting traffic (CLI)¶

dimos spy is the universal transport spy: one live view of every topic moving on every dimOS pubsub transport (names, message rates, bandwidth, sizes, and liveness), whether the system runs on LCM, Zenoh, or both.

dimos spy                     # everything, all transports
dimos spy --transport zenoh   # filter to one transport (repeatable flag)
dimos lcmspy                  # deprecated alias for: dimos spy --transport lcm

dimos topic echo /topic listens on typed channels like /topic#pkg.Msg and decodes automatically:

Listening on /camera/rgb (inferring from typed LCM channels like '/camera/rgb#pkg.Msg')... (Ctrl+C to stop)
Image(shape=(480, 640, 3), format=RGB, dtype=uint8, dev=cpu, ts=2026-01-24 20:28:59)

Implementing a transport¶

At the stream layer, a transport is implemented by subclassing Transport (see core/stream.py) and implementing:

• broadcast(...)
• subscribe(...)

Your Transport.__init__ args can be anything meaningful for your backend:

• (ip, port)
• a shared-memory segment name
• a filesystem path
• a Redis channel

Encoding is an implementation detail, but we encourage using LCM-compatible message types when possible.

Encoding helpers¶

Many of our message types provide lcm_encode / lcm_decode for compact, language-agnostic binary encoding (often faster than pickle). For details, see LCM.

PubSub transports¶

Even though transport can be anything (TCP connection, unix socket) for now all our transport backends implement the PubSub interface.

• publish(topic, message)
• subscribe(topic, callback) -> unsubscribe

from dimos.protocol.pubsub.spec import PubSub
import inspect

print(inspect.getsource(PubSub.publish))
print(inspect.getsource(PubSub.subscribe))

    @abstractmethod
    def publish(self, topic: TopicT, message: MsgT) -> None:
        """Publish a message to a topic."""
        ...

    @abstractmethod
    def subscribe(
        self, topic: TopicT, callback: Callable[[MsgT, TopicT], None]
    ) -> Callable[[], None]:
        """Subscribe to a topic with a callback. returns unsubscribe function

        The unsubscribe function must not block waiting for an in-flight
        callback (callers may hold an event loop the backend needs for
        progress), must be callable from within the callback itself, and once
        it returns no further deliveries start (a callback already executing
        may still complete).
        """
        ...

Topic/message types are flexible: bytes, JSON, or our ROS-compatible LCM types. We also have pickle-based transports for arbitrary Python objects.

LCM (UDP multicast)¶

LCM is UDP multicast. It’s very fast on a robot LAN, but it’s best-effort (packets can drop). For local emission it autoconfigures system in a way in which it's more robust and faster then other more common protocols like ROS, DDS

from dimos.msgs.geometry_msgs.Vector3 import Vector3
from dimos.protocol.pubsub.impl.lcmpubsub import LCM, Topic

lcm = LCM()
lcm.start()

received = []
topic = Topic("/robot/velocity", Vector3)

lcm.subscribe(topic, lambda msg, t: received.append(msg))
lcm.publish(topic, Vector3(1.0, 0.0, 0.5))

import time
time.sleep(0.1)

print(f"Received velocity: x={received[0].x}, y={received[0].y}, z={received[0].z}")
lcm.stop()

Received velocity: x=1.0, y=0.0, z=0.5

Zenoh¶

Shared memory (IPC)¶

Shared memory is highest performance, but only works on the same machine.

from dimos.protocol.pubsub.impl.shmpubsub import PickleSharedMemory

shm = PickleSharedMemory(prefer="cpu")
shm.start()

received = []
shm.subscribe("test/topic", lambda msg, topic: received.append(msg))
shm.publish("test/topic", {"data": [1, 2, 3]})

import time
time.sleep(0.1)

print(f"Received: {received}")
shm.stop()

Received: [{'data': [1, 2, 3]}]

DDS Transport¶

For network communication, DDS uses the Data Distribution Service (DDS) protocol:

from dataclasses import dataclass
from cyclonedds.idl import IdlStruct

from dimos.protocol.pubsub.impl.ddspubsub import DDS, Topic

@dataclass
class SensorReading(IdlStruct):
    value: float

dds = DDS()
dds.start()

received = []
sensor_topic = Topic(name="sensors/temperature", data_type=SensorReading)

dds.subscribe(sensor_topic, lambda msg, t: received.append(msg))
dds.publish(sensor_topic, SensorReading(value=22.5))

import time
time.sleep(0.1)

print(f"Received: {received}")
dds.stop()

Received: [SensorReading(value=22.5)]

A minimal transport: Memory¶

The simplest toy backend is Memory (single process). Start from there when implementing a new pubsub backend.

from dimos.protocol.pubsub.impl.memory import Memory

bus = Memory()
received = []

unsubscribe = bus.subscribe("sensor/data", lambda msg, topic: received.append(msg))

bus.publish("sensor/data", {"temperature": 22.5})
bus.publish("sensor/data", {"temperature": 23.0})

print(f"Received {len(received)} messages:")
for msg in received:
    print(f"  {msg}")

unsubscribe()

Received 2 messages:
  {'temperature': 22.5}
  {'temperature': 23.0}

See pubsub/impl/memory.py for the complete source.

Encode/decode mixins¶

Transports often need to serialize messages before sending and deserialize after receiving.

PubSubEncoderMixin at pubsub/encoders.py provides a clean way to add encoding/decoding to any pubsub implementation.

Available mixins¶

LCMEncoderMixin is especially useful: you can use LCM message definitions with any transport (not just UDP multicast). See LCM for details.

Creating a custom mixin¶

import json

from dimos.protocol.pubsub.encoders import PubSubEncoderMixin

class JsonEncoderMixin(PubSubEncoderMixin[str, dict, bytes]):
    def encode(self, msg: dict, topic: str) -> bytes:
        return json.dumps(msg).encode("utf-8")

    def decode(self, msg: bytes, topic: str) -> dict:
        return json.loads(msg.decode("utf-8"))

Combine with a pubsub implementation via multiple inheritance:

from dimos.protocol.pubsub.impl.memory import Memory

class MyJsonPubSub(JsonEncoderMixin, Memory):
    pass

Swap serialization by changing the mixin:

from dimos.protocol.pubsub.encoders import PickleEncoderMixin
from dimos.protocol.pubsub.impl.memory import Memory

class MyPicklePubSub(PickleEncoderMixin, Memory):
    pass

Testing and benchmarks¶

Spec tests¶

See pubsub/test_spec.py for the grid tests your new backend should pass.

Benchmarks¶

Add your backend to benchmarks to compare in context:

python -m pytest -sv -k "not bytes" dimos/protocol/pubsub/benchmark/tool_benchmark.py

Available transports¶