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Transports

Overview

A Simulation Transport specifies how data-exchange between Models is facilitated by a simulation environment. Each transport has its own specific properties and the selection of a transport will be determined by the planned operational deployment of a simulation.

Transport Latency Status
Loopback Fastest Available, stacked simulations (single process).
Stream (TCP/UDS) Fastest Available, new development.
Redis Faster Recommended.
Redis PubSub Fast Available, stable.
RESP Fast Under consideration, for cloud connectivity (tunnelling).
gPPC Fast Under consideration, for cloud connectivity (HTTP).
Redis Async Slower Available, experimental.

Usage

A simulation transport can be specified in a number of ways, however typically a transport will be configured in a Stack Configuration (YAML) or via an Environment Variable.

Stack Configuration

Example Simulation Stack

simulation.yaml 
---
kind: Stack
metadata:
  name: example
spec:
  connection:
    transport:
      redis:
        uri: redis://localhost:6379
        timeout: 60

Environment Variables

Variable CLI Option (ModelC/Simer) Default
SIMBUS_TRANSPORT --transport redispubsub
SIMBUS_URI --uri redis://localhost:6379
N/A --timeout 60 (seconds)

Note: Simer parameters have only a single - prefix (i.e. -transport). Environment variables can be specified with the -env parameter.

Transports

Loopback

loopback

The loopback transport implements a limited SimBus algorithm which makes it possible to run a model, or a stack of models, without connecting to a SimBus. Because the messaging associated with connecting to a SimBus is removed (or internalised) by the loopback, this is the fastest transport available when building simulations, however it is only suitable for particular deployment scenarios and when developing models.

Note: The loopback transport is only suitable for stacked simulations (i.e. models are arranged within single process).

Configuration Parameters

Parameter Example
transport (name) loopback
uri loopback
timeout (seconds) 60

Stream (TCP/UDS)

redis

The stream transport is a new development for connecting models in a simulation. Models connect directly to the SimBus via TCP or UDS (Unix Domain Sockets). This transport offers very low latency performance.

Configuration Parameters

Parameter Example
transport (name) stream
uri tcp://127.0.0.1, tcp://127.0.0.1:5001, unix:///tmp/simbus.sock
timeout (seconds) 60

Redis

redis

The redis transport is recommended for connecting models in a simulation. It uses blocking Redis commands and simple data types to implement a message exchange mechanism.

Configuration Parameters

Parameter Example
transport (name) redis
uri redis://localhost:6379
timeout (seconds) 60

Redis Async

redisasync

An experimental transport which uses and asynchronous Redis library. The performance was slower than expected; its still fast, however the redis transport is faster; and development has stopped.

Configuration Parameters

Parameter Example
transport (name) redis
uri redisasync://localhost:6379
timeout (seconds) 60

Redis PUB/SUB

redispubsub

The redispubsub transport is the original, and reference, implementaion. Migration to the newer redis transport is recommended.

Note: In some deployment scenarios, particularly clould environments, the redispubsub transport might not work. In such cases the newer redis transport will operate correctly.

Configuration Parameters

Parameter Example
transport (name) redispubsub
uri redis://localhost:6379
timeout (seconds) 60