text: #!/usr/bin/env python3
  #
  #  Copyright (c) 2018, The OpenThread Authors.
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  #     derived from this software without specific prior written permission.
  #
  #  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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  #  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
  #  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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  #  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  #  POSSIBILITY OF SUCH DAMAGE.
  
  import wpan
  from wpan import verify
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Test description:
  #
  # Traffic over multi-hop in a network with chain topology
  #
  #       r1 ----- r2 ---- r3 ----- r4
  #       /\       |       |        /\
  #      /  \      |       |       /  \
  #    fed1 sed1  sed2    sed3   sed4 fed4
  #
  #
  # Traffic flow:
  #  - From first router to last router
  #  - From SED child of last router to SED child of first router
  #  - From FED child of first router to FED child of last router
  #
  # The test verifies the following:
  # - Verifies Address Query process to routers and FEDs.
  # - Verifies Mesh Header frame forwarding over multiple routers.
  # - Verifies forwarding of large IPv6 messages (1000 bytes) requiring lowpan fragmentation.
  
  test_name = __file__[:-3] if __file__.endswith('.py') else __file__
  print('-' * 120)
  print('Starting \'{}\''.format(test_name))
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Creating `wpan.Nodes` instances
  
  speedup = 4
  wpan.Node.set_time_speedup_factor(speedup)
  
  NUM_ROUTERS = 4
  
  routers = []
  sed_children = []
  fed_children = []
  
  for index in range(NUM_ROUTERS):
      routers.append(wpan.Node())
      sed_children.append(wpan.Node())
  
  fed_children.append(wpan.Node())
  fed_children.append(wpan.Node())
  
  all_nodes = routers + sed_children + fed_children
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Init all nodes
  
  wpan.Node.init_all_nodes()
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Build network topology
  #
  #       r1 ----- r2 ---- r3 ----- r4
  #       /\       |       |        /\
  #      /  \      |       |       /  \
  #    fed1 sed1  sed2    sed3   sed4 fed4
  
  # Allowlist routers with their corresponding sleepy children
  
  for index in range(0, NUM_ROUTERS):
      routers[index].allowlist_node(sed_children[index])
      sed_children[index].allowlist_node(routers[index])
  
  # Allowlist a FED child for the first and last routers
  
  routers[0].allowlist_node(fed_children[0])
  fed_children[0].allowlist_node(routers[0])
  
  routers[-1].allowlist_node(fed_children[-1])
  fed_children[-1].allowlist_node(routers[-1])
  
  # While list routers at [index-1] and [index]
  
  for index in range(1, NUM_ROUTERS):
      routers[index - 1].allowlist_node(routers[index])
      routers[index].allowlist_node(routers[index - 1])
  
  routers[0].form("multi-hop")
  sed_children[0].join_node(routers[0], wpan.JOIN_TYPE_SLEEPY_END_DEVICE)
  sed_children[0].set(wpan.WPAN_POLL_INTERVAL, '500')
  
  for index in range(1, NUM_ROUTERS):
      routers[index].join_node(routers[index - 1], wpan.JOIN_TYPE_ROUTER)
      sed_children[index].join_node(routers[index], wpan.JOIN_TYPE_SLEEPY_END_DEVICE)
      sed_children[index].set(wpan.WPAN_POLL_INTERVAL, '500')
  
  fed_children[0].join_node(routers[0], wpan.JOIN_TYPE_END_DEVICE)
  fed_children[-1].join_node(routers[-1], wpan.JOIN_TYPE_END_DEVICE)
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Test implementation
  
  NUM_MSGS = 3
  MSG_LENS = [40, 100, 400, 800, 1000]
  
  # Wait till first router has either established a link or
  # has a valid "next hop" towards all other routers.
  
  ROUTER_TABLE_WAIT_TIME = 60 / speedup + 5
  INVALID_ROUTER_ID = 63
  
  r1_rloc = int(routers[0].get(wpan.WPAN_THREAD_RLOC16), 16)
  
  
  def check_r1_router_table():
      router_table = wpan.parse_router_table_result(routers[0].get(wpan.WPAN_THREAD_ROUTER_TABLE))
      verify(len(router_table) == NUM_ROUTERS)
      for entry in router_table:
          verify(entry.rloc16 == r1_rloc or entry.is_link_established() or entry.next_hop != INVALID_ROUTER_ID)
  
  
  wpan.verify_within(check_r1_router_table, ROUTER_TABLE_WAIT_TIME)
  
  # Send from the first router in the chain to the last one.
  
  src = routers[0].get(wpan.WPAN_IP6_MESH_LOCAL_ADDRESS)[1:-1]
  dst = routers[-1].get(wpan.WPAN_IP6_MESH_LOCAL_ADDRESS)[1:-1]
  
  for msg_length in MSG_LENS:
      sender = routers[0].prepare_tx(src, dst, msg_length, NUM_MSGS)
      recver = routers[-1].prepare_rx(sender)
      wpan.Node.perform_async_tx_rx()
      verify(sender.was_successful)
      verify(recver.was_successful)
  
  # Send from the SED child of the last router to the SED child of the first
  # router.
  
  src = sed_children[-1].get(wpan.WPAN_IP6_MESH_LOCAL_ADDRESS)[1:-1]
  dst = sed_children[0].get(wpan.WPAN_IP6_MESH_LOCAL_ADDRESS)[1:-1]
  
  for msg_length in MSG_LENS:
      sender = sed_children[-1].prepare_tx(src, dst, msg_length, NUM_MSGS)
      recver = sed_children[0].prepare_rx(sender)
      wpan.Node.perform_async_tx_rx()
      verify(sender.was_successful)
      verify(recver.was_successful)
  
  # Send from the FED child of the first router to the FED child of the last
  # router.
  
  src = fed_children[0].get(wpan.WPAN_IP6_MESH_LOCAL_ADDRESS)[1:-1]
  dst = fed_children[-1].get(wpan.WPAN_IP6_MESH_LOCAL_ADDRESS)[1:-1]
  
  for msg_length in MSG_LENS:
      sender = fed_children[0].prepare_tx(src, dst, msg_length, NUM_MSGS)
      recver = fed_children[-1].prepare_rx(sender)
      wpan.Node.perform_async_tx_rx()
      verify(sender.was_successful)
      verify(recver.was_successful)
  
  # -----------------------------------------------------------------------------------------------------------------------
  # Test finished
  
  wpan.Node.finalize_all_nodes()
  
  print('\'{}\' passed.'.format(test_name))
  