Internet DRAFT - draft-mjsraman-rtgwg-bgp-power-path
draft-mjsraman-rtgwg-bgp-power-path
RTGWG Working Group Shankar Raman
Internet-Draft Balaji Venkat Venkataswami
Intended Status: Experimental RFC Gaurav Raina
Expires: October 30, 2013 Vasan Srini
IIT Madras
April 28, 2013
Reducing Power Consumption using BGP path selection
draft-mjsraman-rtgwg-bgp-power-path-04
Abstract
In this paper, we propose a framework to reduce the aggregate power
consumption of the Internet using a collaborative approach between
Autonomous Systems (AS). We identify the low-power paths among the AS
and then use suitable modifications to the BGP path selection
algorithm to route the packets along the paths. Such low-power paths
can be identified by using the consumed-power-to-available-bandwidth
(PWR) ratio as an additional parameter in the BGP Path Selection
Algorithm. For re-routing the data traffic through these low-power
paths, the power based best path is selected and advertised as per
the modified algorithm proposed in this document. Extensions to the
Border Gateway Protocol (BGP) can be used to disseminate the PWR
ratio metric among the AS thereby creating a collaborative approach
to reduce the power consumption. The feasibility of our approaches is
illustrated by applying our algorithm to a subset of the Internet.
The techniques proposed in this paper for the Inter-AS power
reduction require minimal modifications to the existing features of
the Internet. The proposed techniques can be extended to other levels
of Internet hierarchy, such as Intra-AS paths, through suitable
modifications. A recent addition is the use of this method in AIGP
domains and also the use of power source data in the calculation of
low power paths using the BGP path selection algorithm.
Status of this Memo
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Low-power routers and switches . . . . . . . . . . . . . . . 4
1.2 Power reduction using routing and traffic engineering . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Methodology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Pre-requisites for the Proposed Method . . . . . . . . . . . 5
2.1.1 PWR ratio calculation . . . . . . . . . . . . . . . . . 5
2.1.1.1 Power Sources as additional factor . . . . . . . . . 7
2.1.1.2 Earlier method of computing numerator of PWR
ratio. . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 LOW-POWER PATHS . . . . . . . . . . . . . . . . . . . . . . 9
2.2.0.1 Current BGP Best Path Selection Algorithm . . . . . 10
2.2.0.2 Algorithm 1 on ASBR . . . . . . . . . . . . . . . . 12
2.2.0.3 Modified Algorithm 0 on all BGP routers . . . . . . 13
2.3 Implementation notes and Discussion . . . . . . . . . . . . 14
2.4 Applicability within ASes within a single Admin Domain . . . 16
2.4.1 PWR_SESSION . . . . . . . . . . . . . . . . . . . . . . 16
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2.4.2 Power profiles of Routers and Switches . . . . . . . . . 17
2.4.2.1 Concave and Convex power curves . . . . . . . . . . 19
2.4.2.3 Need to advertise both available power and
consumed power . . . . . . . . . . . . . . . . . . . 20
2.4.3 Conclusion and Future Work . . . . . . . . . . . . . . . 21
2.5 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 23
4 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 23
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.1 Normative References . . . . . . . . . . . . . . . . . . . 23
5.2 Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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1 Introduction
Estimates of power consumption for the Internet predict a 300%
increase, as access speeds increase from 10 Mbps to 100 Mbps [3],
[8]. Access speeds are likely to increase as new video, voice and
gaming devices get added to the Internet. Various approaches have
been proposed to reduce the power consumption of the Internet such as
designing low-power routers and switches, and optimizing the network
topology using traffic engineering methods [2].
1.1 Low-power routers and switches
Low-power router and switch design aim at reducing the power consumed
by hardware architectural components such as transmission link,
lookup tables and memory. In [4] it is shown that the router's link
power consumption can vary by 20 Watts between idle and traffic
scenarios. Hence the authors suggest having more line cards and
running them to capacity: operating the router at full throughput
will lead to less power per bit, and hence larger packet lengths will
consume lower power. The two important components in routers that
have received attention for high power consumption are buffers and
TCAMs. Buffers are built using dynamic RAM (DRAM) or static RAM
(SRAM). SRAMs are limited in size and consume more power, but have
low access times. Guido [1] states that a 40Gb/s line card would
require more than 300 SRAM chips and consume 2:5kW. DRAM access times
prevent them from being used on high speed line cards. Sometimes the
buffering of packets in DRAM is done at the back end, while SRAM is
used at the front end for fast data access. But these schemes cannot
scale with increasing line speeds. Some variants of TCAMs have been
proposed for increasing line speeds and for reduced power consumption
[7].
1.2 Power reduction using routing and traffic engineering
At the Internet level, creating a topology that allows route
adaptation, capacity scaling and power-aware service rate tuning,
will reduce power consumption. In [8] the author has proposed a
technique to traffic engineer the data packets in such a way that the
link capacity between routers is optimized. Links which are not
utilized are moved to the idle state. Power consumption can be
reduced by trading off performance related measures like latency. For
example, power savings while switching from 1 Gbps to 100 Mbps is
approximately 4 W and from 100 Mbps to 10 Mbps around 0.1 Watts.
Hence instead of operating at 1 Gbps the link speed could be reduced
to a lower bandwidth under certain conditions for reduced power
consumption.
Multi layer traffic engineering based methods make use of parameters
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such as resource usage, bandwidth, throughput and QoS measures, for
power reduction. In [6] an approach for reducing Intra-AS power
consumption for optical networks that uses Djikstra's shortest path
algorithm is proposed. The input to this method assumes the existence
of a network topology using which an auxiliary graph is constructed.
Power optimization is done on the auxiliary graph and traffic is
routed through the low-power links. However, the algorithm expects
the topology to be available for getting the auxiliary graph. This
topology is easy to obtain for Intra-AS scenario, but not for Inter-
AS cases. In our approach, we propose a collaborative approach by AS
in power reduction. The core of the Internet at the Inter-AS level,
uses the BGP best path selection algorithm. The AS use the Border
Gateway Protocol (BGP) for exchanging routing related information.
One of the attributes of BGP namely, AS-PATH-INFO is used to derive
the topology of the Internet at the AS level. In this document we
propose that the BGP best path selection algorithm is run in each AS
at an appropriate BGP router with the consumed-power-to-available-
bandwidth (PWR) ratio as a parameter, to determine the low-power
paths from the head-end to the tail-end AS in order to reach a prefix
or a set of prefixes. The PWR ratio can be exchanged among the
collaborating AS using BGP attributes.
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Methodology
<Document text>
2.1 Pre-requisites for the Proposed Method
In this section we discuss the pre-requisites for the implementation
of the proposed scheme.
2.1.1 PWR ratio calculation
In this proposal each AS is expected to share its PWR ratio from as
many ASBRs (Autonomous System Border Routers) that it has.
Intuitively in order to calculate this ratio we need to calculate the
consumed power representative of the AS and the maximum bandwidth
available with an ASBR on its egress links into the AS. The entry
point to the AS is through the ASBRs that advertise the prefixes
reachable through the AS. Hence the numerator of the PWR ratio is
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calculated for the AS at each ingress ASBR. We first obtain the
summation of power consumed at the Provider (P) and the Provider Edge
(PE) routers within an AS. The numerator of the PWR ratio is
calculated by summing up the consumed power of all the routers to be
taken into account and then dividing this sum by the number of
routers. A more intuitive approach would be to use a weighted average
method by assigning routers to categories and having appropriate co-
efficients for each of these categories, thus arriving at a weighted
average which is more accurate. One of these alternatives can be used
to arrive at the numerator of the PWR ratio. Yet another alternative
would have been to sum up the total consumed power of all routers in
the AS and represent that as the numerator of the PWR ratio.
This average consumed power is divided by the maximum bandwidth
available at each of the ASBR's egress link. This step is necessary
as the requested bandwidth for any path from the head-end to the
tail-end using the ASBR is limited by the bandwidth available in the
ASBR's egress links. The highest available bandwidth amongst the
egress links of the ASBR is used as the denominator in the PWR ratio
computation. If the entry point to the AS is through a different ASBR
then the PWR ratio assigned to the ingress link of the ASBR might
vary. Hence, an head-end AS might see different PWR ratios for an
intermediate AS, if the intermediate AS has different ASBRs as its
entry point.
We now illustrate the PWR ratio calculation. Consider an AS X which
is one of the AS in the vicinity of another AS Y . Let this ASBR of X
have 3 egress links into X denoted as E(1), E(2) and E(3), and 2
ingress links labeled I(1) and I(2). We now calculate the PWR ratio
for I(1) and I(2). Assume that the routers in X have average consumed
power of 200K Watts per hour. From figure 4 we can calculate the PWR
ratio for I(1) and I(2) as 200K Watts / (60 * 60 * 1.5 Gigb = 3.7037
* (10 raised to -8) We could scale this to 0.37087 by multiplying
with a base value of 10 raised to the 7th power.
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.__________________
(
( E(1)
\ ( +--------->(Core router)
\ +-------+ / 1Gb
+------>| |/ E(2)
200KW / (60*60*1.5Gb) | ASBR |------------>(Core router)
+------>| of |\ 1Gb
/ | AS 100| \
/ +-------+ \ E(3)
( +-------->(Core router)
( 1.5Gb
.__________________
Figure 1:Calculation of PWR ratio by an ASBR associated with an AS.
The I represents ingress links and E represents egress links. 200KW
is the average consumed power in the AS. 1.5Gb is the maximum
available bandwidth of the egress link in an ASBR.
Note that this ratio is actually a mapping function that is defined
for each of the ingress links of the ASBR associated with an AS. For
the head-end which is the BGP Path selection running AS this mapping
function does not exist as there is no ingress link. The PWR ratio
can then be advertised to the other neighboring AS using the control
plane through BGP extensions. BGP ensures that the information is
percolated to other AS beyond the immediate neighbors. On receipt of
these power metrics to the AS at the far-ends of the Internet, the
overall AS level PWR ratio based Internet topology can be
constructed. This view of the Internet is available with each of the
routers without using any other complex discovery mechanism. Some
sample link weights shown in Figure 1 is obtained by using such a
mapping function on the ingress links.
2.1.1.1 Power Sources as additional factor
It is envisaged that the power sources of the Autonomous system using
which the routers in the AS are powered should be declared as a
metric which is further incorporated in the PWR ratio.
A suitable weight is provided to each type of source and the
following table which is not claimed as totally exhaustive can be
used to add this metric in the equation to compute the PWR ratio.
A formal classification of power sources and their weights is a topic
to be considered later. For now we will deal with 2 main categories.
Renewable sources of energy and non-renewable sources. There would be
multiple categories under each of these major categories. Each such
power source is assigned a weight.
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Renewable Sources of Energy :
Wind - HighWeightOne
Solar - HighWeightTwo
Hydro - HighWeightThree
etc...
Non-renewable Sources of Energy :
Natural Gas - LowWeightOne
Petroleum and Diesel - LowWeightTwo
Nuclear - LowWeightThree
etc...
The PWR-SOURCE ratio is calculated in the proportion of how the above
sources are combined to power the routers and its coolant systems and
ancillary facilities in the AS.
Thus PWR-RATIO = ( Consumed-Power / Available-Bandwidth)
* (1 / Weighted Average of Power Sources)
This compound metric could be used as the PWR metric in the
calculations specified in this draft.
2.1.1.2 Earlier method of computing numerator of PWR ratio.
Earlier in the previous versions of this document in order to
calculate this PWR ratio we needed to calculate the available power
and the maximum bandwidth available with an ASBR. The entry point to
the AS is through ASBRs that advertise the prefixes reachable through
the AS. Hence, the numerator of the PWR ratio is calculated for the
AS at each ingress ASBR. We first obtained the summation of power
consumed at the major Provider (P) and Provider Edge (PE) routers
within an AS. The average available power is obtained by subtracting
the consumed power from the maximum power rating and summing the
values for all the routers and then dividing the result by the number
of routers. As an alternative, one could use a weighted average for
more accuracy depending on the category of the router advertising the
consumed power. Yet another alternative is to take the average or sum
of the maximum power rating of all the routers within an AS without
taking into account the consumed power. One of these alternatives was
chosen to calculate the numerator of the PWR ratio.
Intuition however drives us towards consumed power as a better
numerator since the lesser the power consumed the lesser the
numerator and hence lesser the ratio if enough bandwidth is available
at the ingress ASBR. The amount of consumed power per bit of
information ought to be low for the shortest path to work out
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properly. One more aspect is that lesser the power consumed per
available bit of bandwidth it could be a sign that routers are more
optimal in their power consumption as they take on more traffic. This
is a very crucial point to be considered.
However additional research seems to indicate that both Available and
Consumed Power for a router be advertised. The need that arises for
such a proposition is that there exist power profiles of routers
which is dealt in later sections (section 2.4.2). Please refer
section 2.4.2.1 onwards for more analysis and research on this
subject.
2.2 LOW-POWER PATHS
In this section we present the low-power path BGP best path selection
algorithm. The algorithm consists of two sub-algorithms: the first
algorithm is executed by all the ASBRs in the network and the second
by all the BGP routers in their respective AS. The algorithms for the
ASBRs and BGP routers are given as Algorithm 1 and 2. The algorithm
in 2.2.0.1 is the current BGP best path algorithm and is titled
Algorithm 0.
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2.2.0.1 Current BGP Best Path Selection Algorithm
As taken from [11] the following is the current BGP Best Path
Selection Algorithm.
Algorithm 0 : BEGIN
BGP assigns the first valid path as the current best path. BGP then
compares the best path with the next path in the list, until BGP
reaches the end of the list of valid paths. This list provides the
rules that are used to determine the best path:
1) Prefer the path with the highest WEIGHT.
2) Prefer the path with the highest LOCAL_PREF.
3) Prefer the path that was locally originated via a network or
aggregate BGP subcommand or through redistribution from an IGP.
Local paths that are sourced by the network or redistribute commands
are preferred over local aggregates that are sourced by the
aggregate-address command.
4) Prefer the path with the shortest AS_PATH.
An AS_SET counts as 1, no matter how many ASs are in the set.
The AS_CONFED_SEQUENCE and AS_CONFED_SET are not included in the
AS_PATH length.
5) Prefer the path with the lowest origin type.
Note: IGP is lower than Exterior Gateway Protocol (EGP), and EGP is
lower than INCOMPLETE.
6) Prefer the path with the lowest multi-exit discriminator (MED).
7) Prefer eBGP over iBGP paths.
If bestpath is selected, go to Step 9 (multipath).
Note: Paths that contain AS_CONFED_SEQUENCE and AS_CONFED_SET are
local to the confederation. Therefore, these paths are treated as
internal paths. There is no distinction between Confederation
External and Confederation Internal.
8) Prefer the path with the lowest IGP metric to the BGP next hop.
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Continue, even if bestpath is already selected.
9) Determine if multiple paths require installation in the routing
table for BGP Multipath.
Continue, if bestpath is not yet selected.
10) When both paths are external, prefer the path that was received
first (the oldest one).
This step minimizes route-flap because a newer path does not displace
an older one, even if the newer path would be the preferred route
based on the next decision criteria (Steps 11, 12, and 13).
Skip this step if any of these items is true:
You have enabled the bgp best path compare-routerid command.
The router ID is the same for multiple paths because the routes were
received from the same router.
There is no current best path.
The current best path can be lost when, for example, the neighbor
that offers the path goes down.
11) Prefer the route that comes from the BGP router with the lowest
router ID.
The router ID is the highest IP address on the router, with
preference given to loopback addresses. Also, you can use the bgp
router-id command to manually set the router ID.
Note: If a path contains route reflector (RR) attributes, the
originator ID is substituted for the router ID in the path selection
process.
12) If the originator or router ID is the same for multiple paths,
prefer the path with the minimum cluster list length.
This is only present in BGP RR environments. It allows clients to
peer with RRs or clients in other clusters. In this scenario, the
client must be aware of the RR-specific BGP attribute.
13) Prefer the path that comes from the lowest neighbor address.
This address is the IP address that is used in the BGP neighbor
configuration. The address corresponds to the remote peer that is
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used in the TCP connection with the local router.
Algorithm 0: END
2.2.0.2 Algorithm 1 on ASBR
1: Begin
2: if ROUTER == ASBR then
3: /* As part of IGP-TE */
4: Trigger exchange of available bandwidth on bandwidth change,
to the AS internal neighbors;
5: BEGIN PROCESS 1
6: while PWR ratio changes do
7: Assign the PWR ratio to the Ingress links;
8: Exchange the PWR ratio with its external neighbors;
9: Exchange the PWR ratio with AS's (internal) ASBRs;
10: end while
11: END PROCESS 1
12: End
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2.2.0.3 Modified Algorithm 0 on all BGP routers
1: Begin
2: If ROUTER is Configured with BGP then
3: Run all steps from 1 to 3 in BGP regular path selection algorithm;
/* when comparing AS_PATHS (MODIFICATION HERE) */
4: Check if there are no multiple AS_PATHS then goto regular step
(4);
5: if PWR metric based path selection is configured then
6: For each AS_PATH(1..n) in this set in step (4)
7: if there exists a PWR metric for all
elements in AS_PATH then
8: PWR_SUM[i] = sum the PWR
metrices for that AS_PATH;
9: else
10: ignore the AS_PATH;
11: endif
12: endFor
13: If there exists multiple PWR_SUM[i] then
14: Choose the AS_PATH / AS_PATHS with
least PWR_SUM;
15: if multiple least PWR_SUMs (equal valued)
exist then
16: Take up the set of such
AS_PATHS and goto step 5;
17: endif
18: else
19: if there exist no PWR_SUM because of
exclusion then
20: do regular step(4)
to select best paths;
21: endif
22: endif
23: else
24: Do regular step(4);
25: endif
26: Run all steps from 5 to 13 in BGP regular path selection
algorithm;
27: endif
28: End
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It is to be noted that the PWR metric based path selection will ensue
only if the modified steps are activated as a result of specific user
configuration.
2.3 Implementation notes and Discussion
We propose addition of some BGP attributes with no change to the
protocol implementation. There may be a time lag when the far ends of
the Internet receive the attribute and the time it originated. This
however cannot be avoided as with other attributes and metrics.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-------------------------------------------------------------+
| Owning 32 bit Autonomous System Number |
+-------------------------------------------------------------+
| Other 32 bit Autonomous System Number |
+-------------------------------------------------------------+
| PWR Ratio for the AS (Consumed PWR) |
+-------------------------------------------------------------+
| PWR Ratio for the AS (Available PWR) |
+-------------------------------------------------------------+
| Advertising ASBR's IP router ID |
+-------------------------------------------------------------+
| Peer ASBR's IP router ID |
+-------------------------------------------------------------+
| 64 bit sequence number for restarts, aging |
| and comparison of current PWR Ratio. |
+-------------------------------------------------------------+
Figure 2: Proposed PDU format with an added attribute for AS-PATH-
POWER-METRIC
The additions to the above Attribute have been added to optimize and
correctly correlate the connecting ASes and the inter-AS links among
them. For the traffic direction into the Advertising AS the above
information will be easier to correlate than the previous version
which did not advertise the peer AS which had the ingress links into
the advertising Router.
In MPLS-TE for example, when the TE metrics are modified, there is a
reliable flooding process within an Interior Gateway Protocol (IGP).
Such triggered updates apply to the PWR ratio in BGP as well. The
proposed PWR ratio is advertised to the neighboring AS and the
information percolated to all the AS, in a AS-PATH-POWER-METRIC
attribute. This attribute can be implemented as shown in Figure 2.
The frequency of the updates for this attribute should be fixed to
avoid network flooding.
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The AS-PATH-POWER-METRIC for each ASBR is calculated, and advertised
as the PWR ratio for the AS. This AS-PATH-POWER-METRIC is filled into
the appropriate transitive non-discretionary attribute and inserted
into a unique vector for a set of prefixes advertised from the AS.
Such advertised prefixes may have originated from the AS or be the
transit prefixes. The filled vector is sent to the ASBR of the
neighboring AS and the information propagates to all the ASBRs. If
the elements denoting AS in a vector of AS-PATH-INFO is not the same
as the ones that need to be advertised in a AS-PATH-POWER-METRIC,
then a suitable subset of AS-PATH-POWER-METRIC is identified and sent
in the BGP updates. A vector of size 1 also can be employed if the AS
in question is the only one for which PWR ratio has changed in the
originating AS. The collation can be done depending on availability
of such metrics and their mapping to a valid AS-PATH-INFO metric.
The power consumed by each router may fluctuate over short time
intervals. In order to dampen these fluctuations which can cause
unnecessary updates, power can be measured when falling within
intervals of suitable size (say a range of values). This is as
opposed to measuring power as a discrete quantity. This method of
power measurement reduces the frequency of triggered updates from the
routers due to power change.
0.1 0.2 0.1
(A) ---> (B) ---> (D)
0.1 0.2 0.02 0.2
(A) ---> (C) ---> (E) ---> (D)
0.1 0.2
(D) ---> (X)
Figure 4: Example of strands where more than one PWR ratio is
advertised by "D"
0.2 0.1 0.2
(A).....>(B).....>(D).....>(X)
| ^
|0.2 0.02 | 0.2
+--->(C)-------->(E)
Figure 5:Choice of low-power path derived using the algorithm which
uses lower value of the ingress link but through the same AS
A use case of multiple ASBRs advertising differing PWR ratio shows
that an AS may be seen as green through one ingress link and not
through the other. Consider the case of multiple ASBRs that belong to
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the same AS, advertising PWR ratios that differ. This could lead to
power values that belong to different classes of ratios with many
intervening classes in between. These advertised PWR ratios could
lead to one ASBR being preferred over the other thus taking a
different path from head-end to tail-end. This also entails that
there may be multiple paths to the AS through these different ASBRs.
Consider Figure 4 which shows a set of strands that derive a topology
as in Figure 5. Here D is reachable via two paths but the PWR ratios
differ. This illustrates the case where the better metric wins out.
The average power consumed would not have an effect but the bandwidth
available on these ASBR egress links would definitely influence the
path.
2.4 Applicability within ASes within a single Admin Domain
As per [draft-ietf-idr-aigp] there are deployments in which a single
administration runs a network which has been sub-divided into
multiple, contiguous ASes, each running BGP. There are several
reasons why a single administrative domain may be broken into several
ASes (which, in this case, are not really "autonomous".) It may be
that the existing IGPs do not scale well in the particular
environment; it may be that a more generalized topology is desired
than could be obtained by use of a single IGP domain; it may be that
a more finely grained routing policy is desired than can be supported
by an IGP. In such deployments, it can be useful to allow BGP to
make its routing decisions based on the IGP metric, so that BGP
chooses the "shortest" path between two nodes, even if the nodes are
in two different ASes within that same administrative domain. The
authors refer to the set of ASes in a common administrative domain as
an "AIGP Administrative Domain".
A combination of the AIGP administrative metric and the Path
selection algorithm could be combined to arrive at a set of a
suitable number of equal k power-shortest paths and then use a tie-
break amongst such k power-shortest-paths with the least AIGP metric.
This is provided the set of ASes where the decision is being made all
fall under a AIGP Administrative domain. This provides a trade-off of
power shortest paths and least number of hops (link wise) to get from
source to destination across these ASes.
2.4.1 PWR_SESSION
An implementation that supports the PWR attribute CAN support a per-
session configuration item, PWR_SESSION, that indicates whether the
PWR attribute is enabled or disabled for use on that session.
- The default value of PWR_SESSION, for EBGP sessions, between
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providers (distinct operators) CAN be "disabled".
- The default value of PWR_SESSION, for IBGP and confederation-
EBGP sessions, MUST be "enabled."
The PWR attribute MUST NOT be sent on any BGP session for which
PWR_SESSION is disabled.
If an PWR attribute is received on a BGP session for which
PWR_SESSION is disabled, the attribute MUST be treated exactly as if
it were an unrecognized transitive attribute. That is, " The
handling of an unrecognized optional attribute is determined by the
setting of the Transitive bit in the attribute flags octet. Paths
with unrecognized transitive optional attributes SHOULD be accepted.
If a path with an unrecognized transitive optional attribute is
accepted and passed to other BGP peers, then the unrecognized
transitive optional attribute of that path MUST be passed, along with
the path, to other BGP peers with the Partial bit in the Attribute
Flags octet set to 1. If a path with a recognized, transitive
optional attribute is accepted and passed along to other BGP peers
and the Partial bit in the Attribute Flags octet is set to 1 by some
previous AS, it MUST NOT be set back to 0 by the current AS".
This helps in confining the distribution of the attribute and use in
calculation of the power shortest paths only amongst ASes that have
trust relationships with other ASes. Of course, this includes and
promotes the use of PWR attribute within a AIGP administrative
domain.
2.4.2 Power profiles of Routers and Switches
It has been experimented and from several sources found that there
exist routers which have different power profiles. The power profile
of a router is the curve of power consumption to available bandwidth.
Mentioned below are a few of these prominent ones that have to be
taken into consideration.
The first profile that we will consider is the flattening curve. The
power consumed to available bandwidth curve takes the shape of a
steep one initially and then tapers off to a plateau. The point at
which it begins to give a delta-C (delta in Power Consumed) to delta-
B (Available Bandwidth exhausted) is the inflection point that tapers
off to a plateau. Here the delta-C/delta-B begins to slow down or
decrease rapidly. The more the traffic that is added onto the device
the lesser it draws power.
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^
|
P | .
o | .
w | .
e | .
r | .
| .
c | .
o | .
n | .
s | .
u.| .
------------------------------------>
| Available Bandwidth exhausted
The second profile that we will consider is the exponential curve.
The power consumed to available bandwidth curve takes the shape of an
ever increasing steep curve as shown below. Here the delta-C/delta-B
begins to increase as more traffic is thrown onto it as the Available
bandwidth exhausted increases. This power curve beyond a point is
intolerable with respect to power guzzling.
^
|
P | .
o | .
w | .
e | .
r | .
| .
c | .
o | .
n | .
s | .
u.| .
------------------------------------>
| Available Bandwidth exhausted
The third profile that we will consider is a linear curve. In other
words just a straight line. Here delta-C/delta-B is a constant.
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^
|
P | .
o | .
w | .
e | .
r | .
| .
c | .
o | .
n | .
s | .
u.| .
------------------------------------>
| Available Bandwidth exhausted
2.4.2.1 Concave and Convex power curves
Given that there are 3 kinds of major profiles in the router power
consumption, what line would we like to pick. This is an important
point when choosing the metric to pick the low power paths.
(a) If the confrontation is between 2 first profile routers the lower
of the 2 would be considered as shown below. The lower curve offers
better power savings for each GB of bandwidth transported.
^
|
P | .
o | .
w | . .
e | . .
r | . .
| . .
c | . .
o | . .
n | . .
s | . .
u.| .
------------------------------------>
| Available Bandwidth exhausted
(b) If the confrontation is between 2 second profile routers the
upper curve offers more power savings per GB of bandwidth.
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^
|
P | . .
o | . .
w | . .
e | . .
r | . .
| . .
c | . .
o | . .
n | . .
s | .
u.| .
------------------------------------>
| Available Bandwidth exhausted
(c) When the confrontation is between a first profile curve and a
second profile curve, it would be optimal to pick (as shown below)
the lower of the curves because it gives us lesser power consumed for
every GB of traffic routed / switched. Here the exponential curve is
the one that offers lesser amount of power consumed per GB of traffic
is chosen. But when it gets to a point that the two curves intersect
it would be more optimal to pick the tapering curve. Thus at the
meeting point of the 2 curves the exponential curve becomes more
costly and the tapering one gives us more GB for the power buck. Thus
this switchover from one curve to the other (in other words from the
exponential curve to the tapering one) does the trick in terms of
finding an optimal solution.
^ .
| .
P | . .
o | (*)
w | . .
e | . .
r | . .
| . .
c | . .
o | . .
n | . .
s | . .
u.| ..
------------------------------------>
| Available Bandwidth exhausted
(*) Metric switchover point from Consumed Power to Available Power.
2.4.2.3 Need to advertise both available power and consumed power
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Thus the above sections have shown that both the available power and
the consumed power MUST be advertised so that case (c) can be
deciphered and the switchover of the curves be done and the
appropriate router be chosen for the rest of the bandwidth to be
switched over to.
Thus there will exist Consumed-Power to Available Bandwidth ratio and
the Available Power to Available Bandwidth ratio. Both the ratios are
computed and the lower value chosen. The Available Power can be
judged from the calibration process such as the one carried out by
independent test organizations as in [12]. An example of their
calibration is referred to in [12].
2.4.3 Conclusion and Future Work
In this paper, we proposed a scheme for reducing the power
consumption of the Internet using collaborative effort between AS.
The BGP best path algorithm is run with suitable modifications in
step (4) as described by using the PWR ratio as a parameter. The PWR
ratio is advertised through the ingress links of the ASBRs associated
with AS using BGP updates. The Modified BGP Best Path Selection
Algorithm finds out the low-power consuming AS that can route data
packets for a set of prefixes. This entails adopting routes by
choosing entry points to an AS that give energy saving paths. Our
work complements the current schemes for reducing power consumption
within a router such as switching off or bringing to power-idle-state
certain select components within the forwarding and lookup
mechanisms.
Normally the ASes have SLA agreements between each other to carry X
amount of traffic from say a provider A. If the AS representing the
ISP then advertises fake figures to carry more traffic than is
mandated by the SLA agreement with other providers, then it is to
that ISPs detriment since by advertising a better PWR ratio it
invites more traffic through it thus getting paid less and carrying
more traffic. This is not in the best interest of the ISP. This is so
because in the final analysis the Power Shortest Path computed would
include it regardless of the amount of traffic to be carried thus
causing it to invite more traffic through it than it has accepted,
even much more than its capacity. Hence it would be advisable for
that ISP to advertise proper PWR ratios and NOT on the lower side of
the spectrum. If it advertises HIGHER PWR ratios it would not be
chosen, and hence that could be a policy measure NOT to accept any
traffic at all since its capacity may be filled up with existing
traffic. So advertising on the LOWER side would lead to lesser amount
of benefit with respect to dollar per bit transported, and on the
HIGHER side would be to exclude it from carrying any traffic that
wanted to use the Power Shortest Path.
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We also propose that there be a governing body in the IETF or outside
it or sponsored by the IETF to verify the power ratios advertised are
indeed valid or approximately closer to the actual consumption. A
link up for each ISP with a power application level gateway to ensure
proper ratios are advertised could be mandated amongst at least the
co-operating ISPs (ASes).
The aspect of innovation in this proposal is to use BGP as the
piggyback protocol upon which this scheme stands.
When links and switches are gated or put into low-power state within
an AS, the power-consumption automatically drops at the aggregate
level, as a result of which the PWR ratio would be a lower figure
advertised through BGP and thus this AS would attract more Power
Shortest Path traffic through it. Thus the links within the AS and
the switches within it would function more optimally if it had more
traffic that went along paths that were originally put in low-power
state thus utilizing the paths more effectively, when attracting
traffic.
There exist MIBs today that have object identifier for power consumed
in a router. Maybe all the related components within it may NOT be
listed with regards to power consumed. But the overall power consumed
by the Router / Switch is gettable. Once it is advertised in a opaque
Link-State-Advertisement say in the form of a TLV (Type Length Value)
and the LSAs (Link State Advertisements) are flooded through the
network in an AS, all routers get a uniform picture of which router
consumes what power. This method already exists for Traffic
engineering Database LSAs that are advertised as LSAs for the purpose
of traffic engineering within an AS. We are merely piggybacking on
this capability to calculate the PWR ratio at the ASBR which amongst
others is yet another Router / Switch of the AS.
Our future work includes looking into computing low-power paths
within AS as well.
2.5 Acknowledgements
Shankar Raman would like to acknowledge the support by BT Public
Limited (UK) under the BT IITM PhD Fellowship award. Balaji Venkat
and Gaurav Raina would like to acknowledge the UK EPSRC Digital
Economy Programme and the Government of India Department of Science
and Technology (DST) for funding given to the IU-ATC. Vasan Srini
would like to thank Dr.(Prof).Kamakoti of the Computer Science and
Engineering department for his support.
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3 Security Considerations
No specific security considerations apart from the usual
considerations with respect to authenticating BGP messages / updates
from BGP neighbors is necessary for this scheme.
4 IANA Considerations
A new optional transitive non-discretionary attribute needs to be
provided by IANA for carrying the PWR ratio across the Internet in
the specified format in BGP.
5 References
5.1 Normative References
TBD
5.2 Informative References
REFERENCES
[1] G. Appenzeller, Sizing router buffers, Doctoral
Thesis, Department of Electrical Engineering, Stanford
University, 2005.
[2] A. P. Bianzino, C. Chaudet, D. Rossi and J. L.
Rougier, A survey of green networking research, IEEE
Communications and Surveys Tutorials, preprint.
[3] J. Baliga, K. Hinton and R. S. Tucker, Energy
consumption of the internet, Proc. of joint international
conference on optical internet, June 2007, pp. 1-3.
[4] J. Chabarek, J. Sommers, P. Barford, C. Estan, D.
Tsiang and S. Wright, Power awareness in network design
and routing, Proc. of the IEEE INFOCOM 2008, April 2008,
pp. 457-465.
[5] B. Venkat et.al, Constructing disjoint and partially
disjoint InterAS TE-LSPs, USPTO Patent 7751318, Cisco
Systems, 2010.
[6] M. Xia et. al., Greening the optical backbone network:
A traffic engineering approach, IEEE ICC Proceedings, May
2010, pp. 1-5.
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[7] W. Lu and S. Sahni, Low-power TCAMs for very large
forwarding tables, IEEE/ACM Transactions on Computer
Networks, June 2010, vol. 18, no. 3, pp. 948-959.
[8] B. Zhang, Routing Area Open Meeting, Proceedings of
the IETF 81, Quebec, Canada, July 2011.
[9] M.J.S Raman, V.Balaji Venkat, G.Raina, Reducing Power
consumption using the Border Gateway Protocol, IARIA
conferences ENERGY 2012.
[10] A.Cianfrani et al., An OSPF enhancement for energy
saving in IP Networks, IEEE INFOCOM 2011 Workshop on Green
Communications and Networking
[11] http://www.cisco.com/en/US/tech/tk365/
technologies_tech_note09186a0080094431.shtml, BGP best
path selection algorithm.
[draft-ietf-idr-aigp] P. Mohapatra et.al, The Accumulated
IGP metric attribute for BGP,
https://datatracker.ietf.org/doc/draft-ietf-idr-aigp/,
November 2012.
Authors' Addresses
Shankar Raman
Department of Computer Science and Engineering
IIT Madras
Chennai - 600036
TamilNadu
India.
EMail: mjsraman@cse.iitm.ac.in
Balaji Venkat Venkataswami
Department of Electrical Engineering
IIT Madras
Chennai - 600036
TamilNadu
India.
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EMail: balajivenkat299@gmail.com
Prof.Gaurav Raina
Department of Electrical Engineering
IIT Madras
Chennai - 600036
TamilNadu
India.
EMail: gaurav@ee.iitm.ac.in
Vasan Srini
Department of Computer Science and Engineering
IIT Madras
Chennai - 600036
TamilNadu
India.
Email: vasan.vs@gmail.com
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