A chain and a star

More than two nodes means routers. A node with role: router forwards packets; a host does not. The routes are computed by the shortest path, and you can list your own.

A chain

A client and a server with two routers between them, each hop with its own values. The chain shortcut writes the nodes and the links for you:

# file: chain.yaml
version: 0
name: chain
seed: 1
duration: 4s
topology:
  chain:
    nodes: [client, edge, core, server]
    links:
      - both: { delay: 5ms, rate: 50mbit }        # client - edge
      - both: { delay: 15ms, rate: 10mbit }       # edge - core
      - both: { delay: 5ms }                      # core - server
workloads:
  - { id: stream, kind: udp-cbr, from: client, to: server, rate: 2mbit, packet-size: 1000b }

The delay of the stream is the sum of the three hops, 25 ms, and its rate is held to the smallest rate on the path. netscenario show chain.yaml prints the nodes, the links, the routes and the path the stream takes; netscenario expand chain.yaml prints the long form.

A star

Three hosts around a hub with their own values, and a call from one of them to another through the hub:

# file: star.yaml
version: 0
name: star
seed: 2
duration: 4s
topology:
  star:
    hub: hub
    leaves: [phone, laptop, server]
    links:
      - both: { delay: 30ms, jitter: { amount: 5ms, distribution: normal }, rate: 20mbit }
      - both: { delay: 3ms, rate: 100mbit }
      - both: { delay: 1ms }
workloads:
  - { id: call, kind: udp-cbr, from: phone, to: server, rate: 1mbit, packet-size: 800b }

The call crosses two links, the phone’s and the server’s, so its delay is near 31 ms. The laptop is in the network but carries nothing; add a workload from it and both flows share the hub.

By hand

The shortcuts are only a way to write nodes and links. Any network of hosts and routers can be written in the long form, with routes to set a route by hand over the computed ones (routing: manual turns the computed ones off). The files scenarios/three-hops.yaml and scenarios/manual-routes.yaml show both, and scenarios/ipv6.yaml the same with IPv6 addresses.