SU et al.: ENERGY-AWARE VIRTUAL NETWORK EMBEDDING 1609
Fig. 1. Example of VN embedding. (a) VN request. (b) Substrate network.
Fig. 2. Hourly electricity price of five locations in one week.
,where denotes t he set of routers and
denotes the set of hosts. Similar ly, the substrate links can also
be classified into two categories: the backbone link and the local
link, denoted by
and , respectively. Fig. 1(b) shows an
SN exam ple where circles and rectangles denote router and host
nodes, respectively.
For router nodes, we consider the following th ree attributes.
The first attribute is the number of virtual rou ters t hat t he
physical router can suppo rt fo r deploying and runn ing different
personalized network protocols. In Fig. 1(b), the numbers that
are in parentheses and b eside each circle are such num bers.
The second attribute is the location that the router is located as
routers are generally geo grap hically distribu ted. For example,
in Fig. 1(b),
may be located in Los Angeles, CA, USA;
in Chicago, IL, USA; in New York, NY, USA; and
in New Jersey, USA. We use a two-dimensional coordin ate
to denote the location of nod e . The third
attribute is electricity price. The power markets of different lo-
cations are managed by different independen t system operators
(ISOs), and the ISOs are under competitive electricity mark et
structure. Therefore, different locations often have different
electricity prices. Even for the sam e location, the electricity
price m ay vary frequently over time [9], [12]. Fig. 2 show s the
hourly electricity price of the first week of Septem ber 2011
available at [14] for five regions in the day-ahead market, in-
cluding the Eastern Hub of PJM (Pennsylvania–Maryland–New
Jersey), NP-15 Hub of CA I SO (Cali for nia), Capital Hub of
NYISO (New York), Mass Hub of ISO-NE (New England),
and Illinois Hub of MISO (Midwest). We observe that the elec-
tricity price varies over both location and time. To characterize
the spot price dynamics, in this paper, we use a discrete-time
model, which has a time window (e.g., an hour) of interest
.Weuse to denote the electricity price
for node
at time-slot , to denote th e arriving time of a VN
request, and
to denote the duration of the VN request being
served in the SN. Thus, the expiration time
of the VN request
is
.
For host nod es, we consider three attributes: CPU speed,
memory size, and storage capacity. In Fig. 1 (b), the triple
beside each host node denotes the values of these attributes.
For links, we consider bandwidth. In Fig. 1(b), the number
beside each link is the bandwidth. Note that t he modeling,
analysis, and algorithms in this paper can be easily extended
to incorporate o ther attributes, such as latency and jitter con-
straints, as well.
A VN is represented as a weighted graph
.
Here,
,where and denote
the set of virtual router and host nodes, respectively; and
,where denotes the set of virtual links
between any two virtual routers and
denotes the set of
virtual links between host nodes and routers. Fig. 1(a) shows
the VN requested by a user on the SN in Fig. 1(b).
We now formally define th e VN embedding problem. Given
a VN request
with a set of virtual n odes
and a set of virtual links ,andanSN
with a set of physical nodes and a set of
physical links
,embed on ,which
means to fi nd two one-to-one mappin gs:
and . Here,
is a one-to-one mapping from to a s ubset of .Th
is
mapping includes tw o submappings,
and ,where
is from to a subset of ,and is from
to a subset of . For each virtual router node a
nd the
physical node
that it maps to, satisfies
both virtual router quan tity and location requirements of
.
For each virtual host node
and the physical n
ode
that i t maps to, satisfies the node requirements on
CPU speed, mem ory size, and storage capacity of
. Here,
is from to a subset of , which denotes a
ll loop-free
paths composed by the physical links in
. This mappin g
also includes two subm app ings,
and ,where
is from to a subset of , denoting a ll lo
op-free paths
between any two routers, and
is from to a subset of
, denoting all loop-free paths between hosts and routers.
For each virtual link
and the ph ys
ical path
that it
maps to, the bandwidth of each physical link in
is no
less than the bandw idth requirement of
. Take the em bed-
ding in Fig. 1 as an example. The no
de mapping solution is
and the link m apping solution is
.
Note that we focus on consideringoneISPinthispaper.
When multiple IS Ps collabora
te to provided VN services, as
each ISP knows only the characteristics of his own infrastruc-
ture, there are many technical challenges to address this issue.
The readers can refer to [15
] for more discussion on this topic.
B. Energy Co st Modeling
1) Node Energy Cost: Let
denote the additional
power consumption for mapp ing a virtual router
to
asubstraterouter
,and denote the additional
power for mapp ing a virtual host node
to a substrate