request arrives and leaves dynamically, which makes
it impossible to know all the SFC requests in
advance. Therefore, it is difficult to provision the
online SFC requests just like offline requests.
In this paper, we analyse the power consumption
for provisioning SFC requests in substrate network
and formulate the problem of energy-efficient
provisioning of online SFC requests across multiple
domains by using integer linear programming (ILP).
The model’s objective is to minimize the power
consumption and we also give the constraints which
must be met during mapping an SFC such as
resource constraints and VNF order constraints.
Since the problem of provisioning SFC requests
across multiple domains is NP-hard (Wang Y et al.,
2017), we also propose a heuristic algorithm named
EE-SFCO-MD to efficiently solve the problem. The
EE-SFCO-MD algorithm firstly extends node
aggregation (Hong S et al., 2014) to build a domain-
level function graph of the physical network. Then
the algorithm generates all domain-level reachable
paths between the source and destination of SFC
request. For each domain-level reachable path, EE-
SFCO-MD will build a local candidate graph based
on the path and select a candidate provisioning
solution with minimum energy consumption as the
online SFC request partitioning result on the
domain-level reachable path. And then the bidding
mechanism is used for select the minimal energy
consumption segment solution among various
domain-level reachable paths as the final SFC
partitioning scheme. Finally, EE-SFCO-MD maps
each sub-SFC of the final partitioning result into
corresponding domain.
The remainder of this paper is organizes as
follows. Section 2 describes the problem of energy-
efficiently provisioning for online SFC requests
across multiple domains and formulates the problem
as an ILP optimization problem. In Section 3, we
propose a heuristic algorithm for efficiently mapping
online SFC request. Section 4 gives the simulation
result and analysis. And we conclude this paper in
Section 5.
2 PROBLEM STATEMENT AND
FORMULATION
We research the problem of how to reduce energy
consumption for provisioning an online SFC request
in multiple domains network, which is different
from the single domain network is that the VNFs of
SFC request may be deployed to several different
domains and the virtual link need to be embedded on
an inter-domain physical path if the two endpoints of
SFC are hosted in two different domains.
Unlike offline SFC request, the online SFC
requests arrive dynamically and uncertainly and thus
cannot be accurately predicted, and the number of
SFC requests need to be processed cannot be known
in advance. Therefore, the energy-efficient online
SFC request provisioning problem is not suitable for
the purpose of saving energy by merging VNFs on
the SFC requests as an offline problem.
To save energy, it’s best for the mapping scheme
to share the demand-meet active physical server as
much as possible for activating fewer servers.
However, in multi-domain environment, the biggest
challenge of provisioning an online SFC request is
the provisioning decision makers do not have all the
information in each domain of substrate network. In
addition, the correct order of VNFs in the SFC
request should be kept in the provisioning result.
Moreover, the energy cost (e.g. server computation
power cost and network transmission power cost)
and the response time of requests are expected to be
reduced while all of the resource and function
constraints are satisfied.
2.1 Primary Definitions
2.1.1 SFC Request
We model an SFC request as a directed weighted
graph
=(
,
,,), where
represents
the set of VNFs and
denotes the set of VNFs-
connected virtual links on an online SFC request.
and denote the source and destination of the
SFC request, respectively. For each VNF node
, (
) indicates its computing resource
demand, and (
) denotes the function demand
of
. For each virtual link
, (
)
represents the amount of link bandwidth resource
demanded. We consider a scenario in which each
virtual link on an SFC request has the same
bandwidth resource demand but the computing
resource demand and function demand of each VNF
node are different.
2.1.2 Physical Network
The physical network can be modelled as an
undirected weighted graph
=(
,
), where
indicates the set of physical noes and
represents
the set of substrate edges in physical network. For
each physical node
, the available computing
resource on
can be denoted by (
), and (
)