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Reducing Power Consumption using BGP
draft-mjsraman-rtgwg-inter-as-psp-02

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Shankar Raman , Balaji Venkat Venkataswami , Gaurav Raina
Last updated 2012-05-02
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draft-mjsraman-rtgwg-inter-as-psp-02
RTGWG Working Group                                        Shankar Raman
Internet-Draft                                Balaji Venkat Venkataswami
Intended Status: Experimental RFC                           Gaurav Raina
Expires: November 3, 2012                                   I.I.T Madras
                                                             May 2, 2012

                 Reducing Power Consumption using BGP 
                  draft-mjsraman-rtgwg-inter-as-psp-02

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 Traffic Engineering (TE) techniques 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
   constraint in the Constrained Shortest Path First (CSPF) algorithm.
   For re-routing the data traffic through these low-power paths, the
   Inter-AS Traffic Engineered Label Switched Path (TE-LSP) that spans
   multiple AS can be used. 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. Since calculating the low-power paths can be
   computationally intensive, a graph-labeling heuristic is also
   proposed. This heuristic reduces the computational complexity but may
   provide a sub-optimal low-power path. 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.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

 

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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 . . . . . . . . . . .  6
       2.1.1 Constructing network topology using BGP strands  . . . .  6
       2.1.2 PWR ratio calculation  . . . . . . . . . . . . . . . . .  7
         2.1.2.1 Earlier method of computing numerator of PWR
                 ratio. . . . . . . . . . . . . . . . . . . . . . . .  9
       2.1.3 Explicit routing using TE-LSPs . . . . . . . . . . . . . 10
     2.2 LOW-POWER PATHS  . . . . . . . . . . . . . . . . . . . . . . 11
         2.2.0.1 Algorithm 1 ASBR low-power path algorithm  . . . . . 12
         2.2.0.2 Algorithm 2 PCE low-power path algorithm . . . . . . 12
       2.2.1 Illustration . . . . . . . . . . . . . . . . . . . . . . 12
       2.2.3 Equivalence class with total ordering  . . . . . . . . . 13
         2.2.3.1 Algorithm 3 PCE low-power path algorithm with 
 

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                 graph labeling . . . . . . . . . . . . . . . . . . . 14
     2.3 Implementation notes and Discussion  . . . . . . . . . . . . 15
     2.4 Conclusion and Future Work . . . . . . . . . . . . . . . . . 17
     2.5 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
   3  Security Considerations . . . . . . . . . . . . . . . . . . . . 21
   4  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 21
   5  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     5.1  Normative References  . . . . . . . . . . . . . . . . . . . 21
     5.2  Informative References  . . . . . . . . . . . . . . . . . . 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22

 

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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 Multi-Protocol Label Switching (MPLS) technology. MPLS label
   switched paths that traverse multiple AS carry traffic from a head-
   end to a tail-end. The AS use the Border Gateway Protocol (BGP) for
   exchanging routing and topology 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. The CSPF algorithm is run on this AS
   level topology with the consumed-power-to-available-bandwidth (PWR)
   ratio as a constraint, to determine the low-power path from the head-
   end to the tail-end. The PWR ratio can be exchanged among the
   collaborating AS using BGP. Explicit routing can be achieved between
   the head-end and the tail-end through the low-power paths connecting
   the AS using the Inter-AS Traffic Engineered Label Switched Path (TE-
   LSP) that span multiple AS.

   Calculation of such low-power paths can be computationally intensive
   and hence certain heuristics may be needed to reduce the computation
   time. A graph-labeling heuristic is proposed to reduce the
   computation time, which may lead to sub-optimal low-power paths. We
   illustrate our approaches by applying it to a subset of the Internet
   topology. The rest of the paper is organized as follows: In Section
   II, we discuss in detail the pre-requisites for the algorithm.
   Section III introduces the proposed technique which uses the CSPF
   algorithm to calculate the low-power paths. We also show that by
   using a graph-labeling technique, we can reduce the computational
   complexity of the low-power path algorithm, but may obtain a sub-
   optimal low-power path. In Section IV, we discuss the implementation
   issues. We present our conclusion and future work in Section V.

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

 

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   <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 Constructing network topology using BGP strands

   The Inter-AS topology can be modeled as a directed graph G = (V; E;
   f) where the vertices (V) are mapped to AS and the edges (E) map the
   link that connect the neighboring AS. The direction (f) on the edge,
   represents the data flow from the head-end to the tail-end AS. To
   obtain the Inter-AS topology, the approach proposed in [5] is used.
   In this approach, it is shown that a sub-graph of the Internet
   topology, can be obtained by collecting several prefix updates in
   BGP. This is illustrated in Figure 1 which shows the different graph
   strands of AS that are recorded from the BGP packets. Each vertex in
   this graph is assigned a weight according to the consumed-power-to-
   available-bandwidth (PWR) ratio of the AS, as seen by an Autonomous
   System Border Router (ASBR) that acts as an entry point to the AS.
   Figure 2 shows the strands merged together to form the topology sub-
   graph. In this figure, the weight of the vertices are mapped to the
   ingress edges. A reference AS level topology derived from 100 strands
   of AS-PATH-INFO received by an AS in the Internet is presented in
   Figure 3 in [9].

   0.2       0.05      0.1
   (A) ----> (B) ----> (D)

   0.1       0.03      0.2
   (D) ----> (G) ----> (H)

   0.03      0.5       0.3
   (G) ----> (E) ----> (X)

   0.5       0.5       0.5       0.1
   (C) ----> (B) ----> (H) ----> (X)

   0.05      0.5       0.3
   (B) ----> (E) ----> (X)

   Figure 1: Different strands obtained from BGP updates, where vertices
   A,B,C,D and G represent the head-end AS. D,H and X form the tail-end
   AS. The vertex weights refer to the PWR ratio of the AS, and the
   direction of the link shows the next AS hop.

 

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                    0.5
          (C)  +----------------+
        0.5|  /                 |
           | /                  |
      0.05 V/ 0.1   0.03   0.2  V
   (A)--->(B)--->(D)--->(G)--->(H)
           |             |      |
           |          0.5|      | 0.1
           |             V      V
           +----------->(E)--->(X)
              0.5           0.3

   Figure 2:Combining the strands to get the topology of the Internet.
   The PWR ratio is mapped to the the ingress link of the ASBR and not
   to the AS.

2.1.2 PWR ratio calculation

   In the topology sub-graph, each AS is expected to share its PWR
   ratio. In order to calculate this ratio we need to calculate the
   consumed power in the AS and the maximum bandwidth available with an
   ASBR.

   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
   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
 

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   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.

   The PWR ratio must be computed and disbursed much ahead of time
   before the Inter-AS TE-LSP explicit path or route is computed using
   the CSPF algorithm. The correctness of this ratio is of importance to
   compute the Inter-AS TE-LSP route through the green AS. 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 4: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 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 2 is
   obtained by using such a mapping function on the ingress links.

2.1.2.1 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
 

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   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
   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.

2.1.3 Explicit routing using TE-LSPs

   We assume that the head-end and the tail-end may reside in different
   AS and the path is along multiple intervening AS. The way to generate
   this path is by using Traffic Engineered Label Switched Paths (TE-
   LSPs). TE-LSPs can influence the exact path (at the AS level) that
   the traffic will pass through. This path can then be realized by
   providing these set of low-power consuming AS to a protocol like
   Resource Reservation Protocol (RSVP). RSVP-TE then creates TE-LSPs or
   tunnels, using its label assigning procedure. The routers use these
   low-power paths created by the explicit routing method rather than
   using the conventional shortest path to the destination. By this way,
   we can influence exclusion of a number of high power AS on the way
   from the head-end to the tail-end AS. For example, the dotted line in
   Figure 5 represents the explicit route that is chosen by making use
   of such TE-LSPs from head-end AS A to the tail-end AS X. Note that if
   number of hop was the metric used by CSPF, then the route chosen is
   the path with 3 hops.

 

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                    0.5
          (C)  +----------------+
        0.5|  /                 |
           | /                  |
      0.05 V/ 0.1   0.03   0.2  V
   (A)...>(B)...>(D)...>(G)...>(H)
           |             |      .
           |          0.5|      . 0.1
           |             V      V
           +----------->(E)--->(X)
              0.5           0.3

   Figure 5:Low-power path is represented by the dotted lines. This low-
   power path has a longer number of hops than the conventional shortest
   path.

2.2 LOW-POWER PATHS

   In this section we present the low-power path 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
   Path Computation Elements (PCEs) in their respective AS. The
   algorithms for the ASBRs and PCEs are given as Algorithm 1, 2 and 3.

 

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2.2.0.1 Algorithm 1 ASBR low-power path algorithm

   Require: Weighted Topology Graph T=(AS, E, f)

   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 PARALLEL 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 PARALLEL PROCESS 1
   ,br 12: BEGIN PARALLEL PROCESS 2
   13: while RSVP packets arrive do
   14: Send and Receive TE-LSP reservations in the explicit path;
   15: Update routing table with labels for TE-LSP;
   16: end while
   17: END PARALLEL PROCESS 2
   18: end if
   19: End

2.2.0.2 Algorithm 2 PCE low-power path algorithm
   Require: Weighted Topology Graph T=(AS, E, f)
   Require: Source and Destination for Inter-AS TE LSP with sufficient  
            bandwidth
   1: Begin
   2: if ROUTER == PCE then
   3: Calculate the shortest paths from the head-end to the
   tail-end using CSPF with PWR ratio as the metric;
   4: if no path available then
   5: Signal error;
   6: end if
   7: if path exists then
   8: Send explicit path to head-end to construct path;
   9: end if
   10: Continue passively listening to BGP updates to update
   T=(AS, E, f);
   11: end if
   12: End

2.2.1 Illustration

   We now illustrate the proposed technique with a simple example.
 

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   Consider the AS level topology sub-graph shown in Figure 5
   constructed using the strands shown in Figure 1. The PWR ratio
   calculated at an ASBR which represents the metric for the AS is
   assigned to the ingress link. For example, AS H has two edges coming
   into it: one from B and the other from G. Note that the power metrics
   for the two strands are different as G to H is lower than that of B
   to H. This means that the lower power metric into H is better if the
   path from G to H is chosen rather than the one from B to H. This is
   illustrated in the Figure 5 using dotted lines. To construct a path
   with A as the head-end AS and X as the tail-end AS, from the AS level
   topology we see that the path A, B, H, X and A, B, E, X have the
   shortest number of hops. However by using CSPF with the PWR ratio
   metric as the constraint, we see that the path A, B, D, G, H, X is
   power efficient. The routing choice will however be based on the
   reservation of the bandwidth on this path. Given that available
   bandwidth exists to setup a TE-LSP, the explicit path A, B, D, G, H,
   X is chosen. The Resource Reservation Protocol (RSVP) adheres to its
   usual operation and tries to setup a path. If bandwidth is not
   available in the low-power path thus calculated, then we may fall
   back to other paths like A, B, H, X or A, B, E, X provided there is
   available bandwidth in these paths. The low-power path algorithm
   given as Algorithm 2 is executed by the PCE. Algorithm 1 prepares the
   topology and feeds it as input to the PCE as a weighted topology
   graph. Using the CSPF algorithm to calculate a route from a source to
   destination could be time consuming for a large networks. But the
   topology is dynamically updated and hence the computation of the
   shortest paths can be triggered based on need. We now give a
   heuristic method based on graph-labeling that reduces the computation
   time but could trade-off the optimal low-power path.

2.2.3 Equivalence class with total ordering

   The heuristic is based on avoiding high PWR ratios. The approach
   partitions the weighted links into equivalence classes based on a
   range of PWR values. For each partition a labeling is applied such
   that each link in the partition has the same label. A total ordering
   relationship is then defined on the equivalence class. The heuristic
   then starts including partitions with minimum label value iteratively
   until we get a connected component, which includes the head-end and
   tail-end AS. We apply the CSPF algorithm with the weights as label
   values on this sub-graph to obtain the low-power path. The modified
   algorithm which uses this scheme is given in Algorithm 3. It should
   be noted that this algorithm could provide sub-optimal power paths as
   the intermediate steps carry incomplete Internet topology
   information.

 

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2.2.3.1 Algorithm 3 PCE low-power path algorithm with graph labeling
   Require: Weighted Topology Graph T=(AS, E, f)
   Require: Source and Destination for Inter-AS TE LSP with             
            sufficient bandwidth
   1: Begin
   2: if ROUTER == PCE then
   3: Group the links into N partitions with a label for                
      each partition depending on the PWR ratio
   4: Sort the labels in ascending order.
   5: repeat
   6: Include the links that have the least label value;
   7: Remove the partition with this label;
   8: until there is a path from the head-end to tail-end AS
   9: Calculate the low-power path using labels from the                
      head-end to the tail-end using CSPF ;
   10: if no path available then
   11: Signal error;
   12: end if
   13: if path exists then
   14: Send explicit path to head-end to construct path;
   15: end if
   16: Continue passively listening to BGP updates to                   
       update T=(AS, E);
   17: end if
   18: End

 

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                 +------(1245)-----+
                / G    /            \G
               /      / Y            \
              V      /           Y    \
           (1339)   +   (6785)<------(1377)----+
             |      |     |           /        |
             | G    |   G |          + G       V R
             |      |     V          V      (2485)
             V      |   (1006)    (3426)--+    |
           (34234)  |   Y |      G  |     |    | R
             |      |     V         V     |    V
             | G    |   (11229)   (4563)  | (5677)
             V      |   Y |         |     V     | R
           (23411)  |     V     Y   +-->(7786)<-+
             |      +-->(1485)<--------/  |
             |          Y |               | R
             |            V               V
             |          (15467)        (8298)
             | G        G |               | R
             |            |               |
             |            V               V
             +--------->(16578)<-------(9732)

   Figure 6:Application of the graph-labeling heuristic. We consider 3
   labels "G" < "Y" < "R". Using algorithm 3 the "G" path from the head-
   end AS 1245 to the tail-end AS 16578 is chosen in the first
   iteration.

   2.2.4 Illustration of graph labeling

   We briefly illustrate the graph-labeling algorithm using Figure 6. In
   this diagram we have categorized the links into three partitions
   based on the PWR ratio. PWR ratio less than 0:1 are labeled as G,
   between 0:1 to 0:3 are labeled as Y and the rest as R. The total
   ordering is defined as G < Y < R, where the G links have low PWR
   ratios than the Y links. The path could be established through the AS
   that have G as the ingress link; the path being 1245, 1339, 34234,
   23411 and 16578.

2.3 Implementation notes and Discussion

   In this section we present some notes on feasibility of
   implementation of our scheme in a live network. First, the requested
   bandwidth should be available on the low-power path, but the CSPF
   algorithm is run with multiple constraints, one of which is the
   bandwidth requirement for the flows to be transported through the TE-
   LSP. The PWR ratio can then be applied to the available paths thus
   computing the low-power paths. Second, as we are using traffic
 

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   engineering with link state routing protocols, there is a reliable
   flooding process that are triggered when updates about the change in
   characteristic arise. We propose addition of some 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
     +-------------------------------------------------------------+
     |          32 bit Autonomous System Number                    |
     +-------------------------------------------------------------+
     |            PWR Ratio for the AS                             |
     +-------------------------------------------------------------+
     |          Advertising ASBR's IP router ID                    |
     +-------------------------------------------------------------+
     |          64 bit sequence number for restarts, aging         |
     |             and comparison of current PWR Ratio.            |
     +-------------------------------------------------------------+

   Figure 7: Proposed PDU format with an added attribute for AS-PATH-
   POWER-METRIC

   In MPLS-TE 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 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 7. The frequency of
   the updates for this attribute should be fixed to avoid network
   flooding.

   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
 

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   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 8: 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 9: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
   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 8 which shows a set of strands that derive a topology
   as in Figure 9. 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 Conclusion and Future Work

 

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   In this paper, we proposed a scheme for reducing the power
   consumption of the Internet using collaborative effort between AS.
   The topology of the Internet is represented using a graph model and
   derived using the strands obtained from the AS-PATH attribute of the
   BGP updates. CSPF algorithm is run on this topology by using the PWR
   ratio as a constraint. The PWR ratio is advertised through the
   ingress links of the ASBRs associated with AS using BGP updates. The
   CSPF algorithm finds out the low-power consuming AS that can route
   data packets from a head-end to a tail-end. Explicit routing is
   handled through the use of TE-LSPs. This entails adopting routes by
   choosing entry points to an AS that give energy saving paths. Since
   using CSPF can be time consuming a heuristic algorithm to derive the
   low-power paths using graph-labeling was proposed. 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.

   This Power shortest Path calculation can be taken care of a Path
   Computation Element (PCE) unit that could be either be a process
   running on a linecard on a ASBR, or even a core router or an offline
   engine that is passively listening to the BGP updates within the AS
   without spitting out any routes of its own. The PCE architecture has
   already been proposed in the ietf and even has a separate working
   group for itself. These offline or linecard engines are currently
   being sold in the market by the networking majors and other companies
   that develop hardware and software for the PCE. All the PCE needs to
   do is to accept configuration and passively listen to BGP updates
   from various peers or even be a client for a route reflector, thus 

   a) Accepting these BGP updates 

   b) Extracting the AS PATH information from these updates

   c) Then constructing the inter-AS topology 

   d) Apply the PWR metric that comes along in these BGP updates to the
   edges of the graph

   e) Then compute the power shortest path as required by the
   configuration.

   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
 

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   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.

   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 points on which this proposal by us innovates is as follows.

   a) There has been no effort prior to this to build an inter-AS
   topology with a weighted graph based on a PWR ratio. On this point it
   breaks a new path that would lead to inter-AS co-operation that
   contributes to power reduction overall in the internet. The paper
   suggested for OSPF by [10] deals with intra-Autonomous-system
   scenario rather than an inter-AS one. It is also to be noted that the
   IGP such as OSPF / IS-IS or any other link-state protocol for that
   matter is expected to capture the energy consumption of each router
   within the Autonomous system as in paper [10] to help get a hold on
   the overall average within the AS, or even sum up the total of all
   the power consumption within the AS with such intra-AS IGP LSA. This
   contributes to the PWR ratio proposed in our idea. Thus the intra-AS
   metric contributes to the PWR ratio. [10] proposal deals with
   primarily paths setup within an AS and not inter-AS paths. Thus the
   fundamental problem it solves is different while the problem we solve
   relates to the inter-AS paths which run across ASes from a head-end
   AS to a tail-end one.

   b) The other aspect of innovation is to use BGP as the piggyback
   protocol upon which this scheme stands. There has been no effort
   earlier to approach the internet power reduction problem with BGP as
   the mode of transport of the energy ratios and coupling it with the
   inter-AS topology built with AS-PATH-INFO information.
 

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   The above 2 are key aspects of innovation.

   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 PSP
   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 and the LSAs 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. Further it can be noted that the proposed
   algorithms might lead to increased latency as the number of hops
   increase, which could be critical for time sensitive applications.
   Since the PWR ratio could vary dynamically with traffic, the impact
   of traffic on the algorithm would also be of interest.

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. We would like
   to acknowledge that a version of this paper has been accepted in
   IARIA conference ENERGY 2012.

 

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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

   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC1776]  Crocker, S., "The Address is the Message", RFC 1776, April
              1 1995.

   [TRUTHS]   Callon, R., "The Twelve Networking Truths", RFC 1925,
              April 1 1996.

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.
 

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              [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.

              [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

   [EVILBIT]  Bellovin, S., "The Security Flag in the IPv4 Header",
              RFC 3514, April 1 2003.

   [RFC5513]  Farrel, A., "IANA Considerations for Three Letter
              Acronyms", RFC 5513, April 1 2009.

   [RFC5514]  Vyncke, E., "IPv6 over Social Networks", RFC 5514, April 1
              2009.

Authors' Addresses

   Shankar Raman
   Department of Computer Science and Engineering
   I.I.T Madras,
   Chennai - 600036
   TamilNadu,
   India.

   EMail: mjsraman@cse.iitm.ac.in

 

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   Balaji Venkat Venkataswami
   Department of Electrical Engineering,
   I.I.T Madras,
   Chennai - 600036,
   TamilNadu,
   India.

   EMail: balajivenkat299@gmail.com

   Prof.Gaurav Raina
   Department of Electrical Engineering,
   I.I.T Madras,
   Chennai - 600036,
   TamilNadu,
   India.

   EMail: gaurav@ee.iitm.ac.in

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