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protocol for task distribution. Any agent currently holding a container, e.g. a ship, initi-
ates a call for proposals (CFP) to other suitable agents, e.g. cranes. They respond with
a REFUSE or PROPOSE message, in the latter case containing the possible time of
pick-up. The initiating agent then decides on one of the proposals and sends an AC-
CEPT message to that agent; all other agents get a REJECT message. Through this
message exchange, the issuing agent and the determined contractor established a time
and place to meet physically to hand over the container in question. Both agents move
independently and can also negotiate with other agents about more containers in the
meantime, thus building up a local plan. When the agreed upon time is reached, both
agents should have moved to their negotiated position and the initiating agent issues
a REQUEST to execute the appointment, i.e. to hand over the container. The contrac-
tor will acknowledge with an INFORM message. At this point, the administration over
the container changes from the initiating agent to the contractor, which can itself be-
come an initiator and issue a CFP for the next step of transportation, e.g. from crane to
apron, adding a new
TransportOrder
to the
TransportOrderChain
. The communication
between very different types of handling devices and other agents therefore is homoge-
neous and the
TransportOrderChain
builds up during negotiation. The set of all TOCs
reaching the yard in one run contains a complete record of all container transfers and
the corresponding time represents a trace or resulting global plan for a given setup.
Additional Features:
In
ContMAS
, it is also possible to import
TOC
s with varying
amounts of detail to determine the level of freedom the agents have. This allows the
simulation to be used for several purposes, such as testing pre-planned runs against
plans that have been produced just-in-time through negotiation or “replay” data from a
real port, as was done in our project.
5
Optimisation of Allocation of Moves to Straddle Carriers
As mentioned in Section 2, Straddle Carrier management is an important sub-problem.
We have therefore developed a negotiation-based optimisation strategy to allocate con-
tainer moves to Straddle Carriers.
A key feature that distinguishes this mechanism from the process used by
ContMAS
is that we develop a schedule of planned moves ahead of time, whereas in
ContMAS
until now container moves are put up for bids when the machine is ready to dispose of
the container. Planning ahead and therefore negotiating over containers not yet held by
a machine is a feature likely to be included in one of the next versions of
ContMAS
.
In our approach each machine agent, Quay Crane or Straddle Carrier, maintains a
schedule
of container moves. In essence this is a timeline: a list of container moves
(each with associated source and destination locations) with associated timing infor-
mation. The timing information is defined in terms of
processing
time and
setup
time.
Processing time is the time taken to move a given container from its source location
to its destination location. The processing time depends only on the container and the
machine. The setup time is the time between finishing one container and being ready to
pick up the next container. It depends on both containers.
The container move allocation problem is how to assign the needed container moves
to machines (QCs and SCs) in a way that meets all constraints, while attempting to
