RTGWG Working Group Shankar Raman
Internet-Draft Balaji Venkat Venkataswami
Intended Status: Experimental RFC Gaurav Raina
Expires: November 5, 2013 IIT Madras
May 4, 2013
Building power shortest inter-Area TE LSPs using pre-computed paths
draft-mjsraman-rtgwg-intra-as-psp-te-leak-03
Abstract
In this paper, we propose a framework to reduce the aggregate power
consumption of an Autonomous System (AS) using a collaborative
approach between areas within an AS. We identify the low-power paths
within non-backbone areas and then use Traffic Engineering (TE)
techniques to route the packets along the stitched paths from non-
backbone areas / backbone area to other non-backbone areas. Such low-
power paths can be identified by using the power-to-available-
bandwidth (PWR) ratio as an additional constraint in the Constrained
Shortest Path First (CSPF) algorithm. For routing the data traffic
through these low-power paths, the Inter-Area Traffic Engineered
Label Switched Path (TE-LSP) that spans multiple areas can be used.
Extensions to the Interior Gateway Protocols like OSPF and IS-IS that
support TE extensions can be used to disseminate information about
low-power paths in the respective areas (backbone or non-backbone)
that minimize the PWR ratio metric on the links within the areas and
between the areas thereby creating a collaborative approach to reduce
the power consumption.
The feasibility of our approaches is illustrated by applying our
algorithm to an AS with a backbone area and several non-backbone
areas. The techniques proposed in this paper for the Inter-Area power
reduced paths require a few modifications to the existing features of
the IGPs supporting TE extensions. The proposed techniques can be
extended to other levels of Internet hierarchy, such as Inter-AS
paths, through suitable modifications as in [11].
When link state routing protocols like OSPF or ISIS are used to
discover TE topology, there is the limitation that traffic engineered
paths can be set up only when the head and tail end of the label
switched path are in the same area. There are solutions to overcome
this limitation either using offline Path Computation Engine (PCE)
that attach to multiple areas and know the topology of all areas.
This document proposes an alternative approach that does not require
any centralized PCE and uses selective leaking of low-power TE path
information from one area into other areas.
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Low-power routers and switches . . . . . . . . . . . . . . . 4
1.2 Power reduction using routing and traffic engineering . . . 4
2. Methodology of the proposal . . . . . . . . . . . . . . . . . 6
2.1 ABR Operation . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1 Methodology . . . . . . . . . . . . . . . . . . . . . . 7
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2.1.2 ERRATA . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.3 Power Bias . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.4 Advertising Available POWER . . . . . . . . . . . . . . 12
2.1.5 ECMP links . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.6 Dampening the side effects of constant change . . . . . 12
2.1.7 Calculating power shortest paths in an Area . . . . . . 12
2.1.8 Power profiles of Routers and Switches . . . . . . . . . 13
2.1.8.1 Concave and Convex power curves . . . . . . . . . . 15
2.1.8.2 Need to advertise both available power and
consumed power . . . . . . . . . . . . . . . . . . . 17
2.1.9 Power to Available Bandwidth ratio in a TLV . . . . . . 17
2.2 TE Path Head-end Operation . . . . . . . . . . . . . . . . . 20
2.2 Suppression of Frequent updates owing to fluctuation in
power and bandwidth . . . . . . . . . . . . . . . . . . . . 22
2.3 Advantages . . . . . . . . . . . . . . . . . . . . . . . . . 23
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 24
4 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 24
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.1 Normative References . . . . . . . . . . . . . . . . . . . 24
5.2 Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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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 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].
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
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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
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 by using a
centralized PCE (Path Computation Element) as in a hierarchical PCE
approach. Here for each area a PCE is assigned and each such PCE
calculates the path from a head-end router to a tail-end router, both
falling within the same area. When TE paths have to be stitched
across several areas then the hierarchical PCE which may be one level
up from the respective area PCEs is contacted for such a stitching.
In our approach, we propose a collaborative approach by the
respective areas in calculating low-power paths that result in power
reduction within an AS. This document proposes an alternative
approach that does not require any centralized PCE and uses selective
leaking of low-power TE path information from one area into other
areas. The core of most ISP ASes use the Multi-Protocol Label
Switching (MPLS) technology. MPLS label switched paths that traverse
multiple areas carry traffic from a head-end to a tail-end that can
be situated in different areas within the AS. The AS uses the
Interior Gateway Protocol (IGP) for exchanging routing related
information. The topology of one area is not revealed to the other in
OSPF-TE and IS-IS-TE.
The CSPF algorithm as proposed here is run on a specific area with
the available power-to-bandwidth (PWR) ratio as a constraint, to
determine "k" (where k is a suitable number) low-power-paths from the
head-end to the tail-end within the same area. The low-cost power
paths that minimize the PWR ratio can be exchanged among the
collaborating areas using IGP-TE TLVs that we propose in this
document. Explicit routing using RSVP-TE (for signalling) then can be
achieved between the head-end and the tail-end routers traversing
multiple areas through these low-power paths connecting the head-end
and tail-end using the Inter-Area Traffic Engineered Label Switched
Path (TE-LSP) that span multiple areas.
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2. Methodology of the proposal
There are three known solutions to inter-area TE
(a) hop expansion at area boundaries where the head end can only
choose the path to area boundary rather than right to tail end,
(b) centralized PCE is attached to all areas and is aware of entire
topology, and
(c) path stitching by designating ABRs acting as BGP route
reflectors.
It is of course possible to build out low-power paths through the
above techniques but they suffer limitations such as not knowing for
certain whether the path exists a-priori. This document proposes a
technique where a-priori low-power paths are pre-computed in the
various areas and are leaked into other areas so that provisioning
these paths is done much more quicker than is otherwise possible.
Assume {N} as the set of nodes in a network running link state
routing protocol and {N' } be the set of nodes that are known to be
the endpoints of the traffic engineered paths. The topology {N, E}
has been divided into hierarchical areas with backbone area as the
second level that connects first level of all non-backbone areas. We
assume the network runs either OSPF-TE or ISIS-TE for establishing TE
paths. The set of nodes {N'} can be situated in any non-backbone area
or the backbone area. Nodes in {N'} may become aware of being
potential endpoints through offline configuration.
Once the nodes in {N'} become aware of being TE endpoints, they
advertise themselves in a special TLV in TE link state information.
We would term this "TE Endpoint TLV". In OSPF, they would advertise a
newly defined TLV in TE LSA and in ISIS, they would advertise a newly
defined TLV in TE LSP. Apart from nodes in {N'} the area border
routers or ABRs advertise another newly defined TLV that we would
term as "Area Border TLV".
2.1 ABR Operation
Apart from standard OSPF/ISIS ABR functions, each ABR should discover
the TE endpoints in every area attached to it. Assume for an ABR, let
the set discovered be {Ai, Nj}. The ABR should compute k-power-
shortest-paths to every element in {Ai, Nj} based on the constraints
applicable to the network. The constraint applied here is the
minimization of the PWR ratio which is defined as follows.
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For a given router that is an ABR for an area (straddling the
backbone and non-backbone), a set of k-shortest paths that can be
potentially be used as a link towards a TE endpoint are identified.
2.1.1 Methodology
For each router / switch there exist linecards and each linecard has
a set of ports or sometimes just one port of high capacity. This
usually applies on routers and switches that are either single
chassis or multi-chassis in their characterisation. By single chassis
we mean that there exists a single chassis and slots for the Route
Processor Card (one or more of these) typically upto to two of them,
and one or more slots for linecards each having their respective
characteristics such as number of ports (port density), type of such
ports (SONET, ethernet, ATM etc..) usually depending on the link
layer technology they support. Links are connections between ports on
these linecards to other ports on linecards of other single chassis
or multi-chassis system. A multi-chassis system is one that has
multiple such chassis interconnceted amongst each other to form a
single logical view of the system. Both single and multi-chassis have
linecards and respective ports on these linecards. Multi-chassis
typically have a switch fabric chassis which connects each of these
chassis to each other or to chassis of other multi-chassis or single
chassis systems.
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Consider the following topology as one that falls within an area...
Router A Router B Router C
+---+---+ +---+---+ +-------+
| | | | | | | | |
|LC1|LC2| |LC1|LC2| |LC1|LC2|
| | | | | | L11 | | |
| P1| P1| | P1| P1|-------------- P1| P1|---+
| P2| P2|--+ | P2| P2| L12 | P2| P2| |
| P3| P3| | L4 | P3| P3|-------------- P3| P3| |
| P4| P4|--+----------- P4| P4| +---- P4| P4| |
| P5| P5| | +----P5| P5--+ L5 | | P5| P5| |
| | | | | | | | | | | | | | | | |
+-|-+-|-+ |L3 | +---+---+ | | +---+-|-+ | L13
| | | +------------+-------+ | |
| |L2 | L5 | | |
| +----+------------+ | | |
| | | | | |
|L1 | | |L6 | |
| | Router D | | Router E L12| | Router F
| | +---+---+ | | +---+---+ | |+-------+
| | | | | |L2 | | | | | || | |L
| | |LC1|LC2| | | |LC1|LC2| | ||LC1|LC2|1
| | | | | | | | | | | || | |4..
| +-| P1| P1---+ | | P1| P1|------+ || P1| P1|->
| | P2| P2| L7 +--- P2| P2| +--P2| P2|->
| | P3| P3|-------------- P3| P3| L10 | P3| P3|->
+----------| P4| P4| +---- P4| P4|-------------- P4| P4|
| P5| P5| | +-- P5| P5| +----- P5| P5|
| | | | | | | | | | | | |
+-|-+---+ L8 | | +---+---+ L9 | +---+---+
+---------------+ +------------------+
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The table of links between the various routers (which are assumed to
be single chassis systems) is as follows...
+--------+----------+-----------+-----------+-----------+----------+
| Links | Routers | LC <> LC | Port Conn.| Capacity |Available |
| | | | | |Bandwidth |
+--------+----------+-----------+-----------+-----------+----------+
| L1 | A <> D | LC1<>LC1 | P5<>P4 | 10G | 7.5 |
| L2 | A <> D | LC2<>LC2 | P5<>P1 | 10G | 6.0 |
| L3 | A <> D | LC2<>LC1 | P2<>P1 | 10G | 4.0 |
| L4 | A <> B | LC2<>LC1 | P4<>P4 | 10G | 3.0 |
| L5 | B <> C | LC1<>LC1 | P5<>P4 | 10G | 3.5 |
| L6 | B <> E | LC1<>LC1 | P6<>P2 | 10G | 1.0 |
| L7 | D <> E | LC2<>LC1 | P3<>P3 | 10G | 6.0 |
| L8 | D <> E | LC1<>LC1 | P5<>P4 | 10G | 1.5 |
| L9 | E <> F | LC1<>LC2 | P5<>P5 | 100G | 20.0 |
| L10 | E <> F | LC2<>LC1 | P4<>P4 | 10G | 2.5 |
| L11 | B <> C | LC2<>LC1 | P1<>P1 | 10G | 3.0 |
| L12 | E <> C | LC2<>LC2 | P1<>P5 | 10G | 2.0 |
| L13 | C <> F | LC2<>LC1 | P1<>P2 | 10G | 1.0 |
| L14 | F <> OA | LC2<> | P1<> | | |
| | | | | | |
+--------+----------+-----------+-----------+------------+---------+
In the above topology assume all point-to-point links between the
routers. For now we will deal with P2P links alone and not venture
into Broadcast Multi-access links or Non-Broadcast Multi-access links
etc.. It is suffice to show how the scheme works for P2P links and
then move more specifically to other types of networks to demonstrate
this method of calculating the power topology of the network in the
figure.
Each linecard consumes a certain amount of power and it is vendor
dependent as to how the power consumed relates to the Available
Bandwidth on any of the links to which the linecard connects to. It
is possible that the said topology of routers come from one vendor or
from multiple vendors. It is assumed that the algorithm proposed will
have the power consumed by a linecard available as a readable value
in terms of W or kW or whichever measurable metric that is provided
by the vendor.
It is possible that some of the Linecards are more capable than the
others. Consider that Router A is a more capable router with more
powerful linecards with higher port density. This is not shown in the
figure, but assume so. LC1, LC2 on Router A could be consuming more
power than the other Linecards on other routers. The main reason
could be that LC1 and LC2 may have higher port density or higher
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speed ports than the other routers. In order to calculate the power
consumed on a link by a linecard it is important that we normalize
the power as power consumed per port. Here the ports are normalized
to lowest common denominator. If all links in the topology have 10G
port capacity then the power calculated should be in terms power
consumed per 10G port.
Assuming we have done this normalization we go on to calculate the
POWER metric for each of the ports involved in a link which is
derived as follows...
POWER metric = Power consumed per XG (normalized bandwidth) port
for a given -------------------------------------------------
Port on a LC Available Bandwidth on that port
Assume link L1. The ports concerned are both 10G and the ports are P5
on Router A and P4 on Router D. For calculating the POWER metric for
a link which we will call PWRLINK we calculate the POWER metric for
each side of the link and average the two to get PWRLINK.
So PWRLINK for L1 = POWER for P5 on LC1 + Power for P4 on LC1
on Router A on Router D
============================================
2
The above can also be weighted if there is a multi-capacity port on
one side of the link and not on the other. A multi-capacity link is
one which provides multiple bandwidth capabilities such (1G/10G/100G)
for example but auto-negotiates with other end to provide a lesser
than highest capacity service.
The PWRLINK metrices once calculated are flooded in already defined
OSPF-TE-LSA as an adapted TE-metric and is typically flooded as a
link characteristic.
It is important to note that the denominator for POWER metric is
Available Bandwidth instead of Available Bandwidth on that port. The
Available Bandwidth is measured in terms of intervals and not as
discrete quantities. This is in order not to flood PWRLINK metrics
into the OSPF area in LSAs very frequently as Bandwidth may
constantly change. The same applies to POWER metric as well.
Once the LSAs have been flooded the Routers run CSPF on the graph of
the topology with PWRLINKs assigned to the links and calculate the
PWRLINK based paths which consume the least power. The shortest power
paths based on this topology can be used for forwarding high
bandwidth streams and to optimally use power within the area.
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The Available Bandwidth column shows the Available bandwidth of the
link corresponding to the row and column intersection. This figure is
used as the numerator in the POWER metric computation for that port.
2.1.2 ERRATA
ERRATA : Previously the experiments were carried out with Available
Utilization since only 10G and 100G ports were considered. This
baselines the metric to 10G ports and proportionality thereof. But in
reality the actual Available Bandwidth needs to be considered for
real world experiments. Hence this draft has been changed to reflect
the Available Bandwidth to be taken as the denominator of the formula
thereof.
In our previous experiments the 100G link if it showed a utilization
of 0.2 would end up as a high POWER metric and hence would be totally
avoided. In reality this link may have been a more power optimal link
given that if it had a first power profile (Please refer section on
Power Profiles). Dividing the Power consumed or Available Power by
the Available Bandwidth gives a better picture of how much power cost
per Gb is consumed and normalizes the metric amongst links of varying
bandwidth.
An earlier version of this document rev-00 contained a different
algorithm to compute the k-shortest-power-paths. From the
experimental results gathered it was seen that the said algorithm was
prone to errors with respect to direction of traffic and
unnecessarily complex for the solution. Hence it has been set aside
for a more simple yet better one mentioned in this revision.
2.1.3 Power Bias
Assume in the figure that there exist Routers A and D and that there
is a bias on the link L1 in such a way that Router D computes a POWER
metric of 10 and the Router D computes a POWER metric of 2 on the
ports P5 and P4 respectively. Now the PWRLINK would be 6 for that
link L1. Thus even if one side is excessively power guzzling then the
PWRLINK moves up and thus is less preferred in the CSPF algorithm and
path computation based on the Power topology.
If there is no bias and both the sides of the link are optimal in
their power usage then the metric stays low even if more streams are
sent on it. This is the main objective that is set out for router and
switch manufacturers in the single chassis and multi-chassis world,
in that they are incentivised to manufacture linecards that are not
power hungry even if the number of packets flowing through them is
high and thus the Bandwidth Available is also reasonably on the
higher side compared to other routers.
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For those manufacturers who set a high power value for even minimal
traffic, the vendors that dont would win out in the end.
2.1.4 Advertising Available POWER
Please see section 2.1.8 for more information on why Available POWER
plays a crucial role in determining the choice of routers based on
the Power metric.
2.1.5 ECMP links
It is possible that multiple links would have the same PWRLINK metric
after a computation cycle. In such a case load-balancing techniques
can be used to keep the ECMP links in a steady state with respect to
each other. Depending on the Available Bandwidth thereafter it is
possible that the ECMP links may no longer be Equal cost but UCMP or
Unequal Cost Paths.
2.1.6 Dampening the side effects of constant change
It is recommended in this draft that the implementation of the
proposal be adaptive, infrequent in computation to the extent
possible without sacrificing adapting to the dynamism and also reduce
any frequent oscillations. The actual methods to adopt for this
computation are outside the scope of this document.
2.1.7 Calculating power shortest paths in an Area
Assume the following topology where A,B,C etc.. are routers and
corresponding labelled edges with weights are the links. These
weights are the current values of the PWRLINK attribute that has been
flooded in the LSAs through the Area concerned. Assume B is the ABR
for Area 1 and the routers A and C are the Area 0 core routers. The
rest of the routers are assumed to be in Area 1. Once the power
topology of the Area 1 has been calculated as shown below with the
PWRLINK attributes being assigned to the links, Constrained shortest
path can be run from the ABR to any of the other routers say H, E , X
etc.. The CSPF algorithm takes the constraint in terms of the PWRLINK
attributes along with other attributes to construct a power shortest
path from say router B to other routers in Area 1.
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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
Once the path has been computed it is possible to use RSVP-TE to
construct the power shortest path with the TE-LSP being instantiated
with the labels appropriately placed in the routers on the power
shortest path. In this topology, assume one would want to construct a
path from B to X then the dotted path shows the path constructed and
to be used by a set of flows or streams of packets belonging to
multiple flows as seen fit by the router B. If the PWRLINK metrics
change after due course of time then another power shortest path that
possibly traverses the same path (if the SUM of PWRLINKs doesnt
exceed any other path's metrics' SUM) or some other path would be
constructed. Specifically this method makes use of traffic-
engineering signalling protocols as the method to place the streams
from point X to point Y (where X and Y are routers).
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
2.1.8 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
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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.
^
|
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
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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.
^
|
P | .
o | .
w | .
e | .
r | .
| .
c | .
o | .
n | .
s | .
u.| .
------------------------------------>
| Available Bandwidth exhausted
2.1.8.1 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
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(b) If the confrontation is between 2 second profile routers the
upper curve offers more power savings per GB of bandwidth.
^
|
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.
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^ .
| .
P | . .
o | (*)
w | . .
e | . .
r | . .
| . .
c | . .
o | . .
n | . .
s | . .
u.| ..
------------------------------------>
| Available Bandwidth exhausted
(*) Metric switchover point from Consumed Power to Available
Power.
2.1.8.2 Need to advertise both available power and consumed power
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].
Here given below is the formula for calculating the Available Power
to Available Bandwidth ratio also called the Available POWER metric.
Available
POWER metric = Available Power consumed per XG
(normalized bandwidth) port
for a given ----------------------------------
Port on a LC Available Bandwidth on that port
2.1.9 Power to Available Bandwidth ratio in a TLV
As per [RFC3630] the Link TLV can be used to carry this power to
available Bandwidth ratio with an additional sub-TLV of the link TLV.
The sub-type number 11 is recommended to be defined for this purpose.
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[RFC 3630] states in section 2.2.1 and we QUOTE ...
2.1.10 Link TLV
The Link TLV describes a single link. It is constructed of a set of
sub-TLVs. There are no ordering requirements for the sub-TLVs.
Only one Link TLV shall be carried in each LSA, allowing for fine
granularity changes in topology.
The Link TLV is type 2, and the length is variable.
The following sub-TLVs of the Link TLV are defined:
1 - Link type (1 octet)
2 - Link ID (4 octets)
3 - Local interface IP address (4 octets)
4 - Remote interface IP address (4 octets)
5 - Traffic engineering metric (4 octets)
6 - Maximum bandwidth (4 octets)
7 - Maximum reservable bandwidth (4 octets)
8 - Unreserved bandwidth (32 octets)
9 - Administrative group (4 octets)
10 - Power-to-Multicast-replication-capacity (4 octets)
11 - Consumed-Power-to-Available-Bandwidth (4 octets)
12 - Available-Power-to-Available-Bandwidth (4 octets)
This memo defines sub-Types 1 through 9. See the IANA Considerations
in [RFC3630] section for allocation of new sub-Types.
The Link Type and Link ID sub-TLVs are mandatory, i.e., must appear
exactly once. All other sub-TLVs defined here may occur at most
once. These restrictions need not apply to future sub-TLVs.
Unrecognized sub-TLVs are ignored.
Various values below use the (32 bit) IEEE Floating Point format. For
quick reference, this format is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Exponent | Fraction |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
S is the sign, Exponent is the exponent base 2 in "excess 127"
notation, and Fraction is the mantissa - 1, with an implied binary
point in front of it. Thus, the above represents the value:
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(-1)**(S) * 2**(Exponent-127) * (1 + Fraction)
It is proposed that we use the Power-to-Available-Bandwidth ratio as
a 32 bit IEEE floating Point format field for the purpose of this
document.
Assume the following topology in a non-backbone area after
calculating the PWR ratio in a given stage of the algorithm.
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
Here (B) is a Area Border Router and has to ingress links into it
from (C) and (A) which are in the backbone area. Connectivity within
the backbone area are not shown here. Assume (C) and (A) are
connected in some way with other routers in the backbone area.
Routers (D), (G), (E), (H), (X) are routers in the non-backbone area.
Routers (H), (E) and (X) are potential TE endpoints. The PWR metrics
shown here on the edges within the area represent metrics for a
specific TE endpoint. The metrics on edges (C)->(B) and (A)->(B) are
for any traffic ingressing through (B) into the non-backbone area
heading towards any TE endpoint (H), (E) or (X).
The number of constraints is likely to be few and the most widely
used constraints are TE metric, link groups and bandwidth. But no
restriction is assumed on use of other constraints. Thus here we add
the PWR metric of a link as an additional constraint. Once the ABR
computes k-power-shortest-paths to every {Ai, Nj} it has topology
information about, it advertises the k-power-shortest-paths as a
reachability vector in a newly defined "TE Reachability Vector TLV".
Consider an example network show below. TEh is head-end and TEt is
tail-end of a TE path, ABR1 and ABR2 are area border routers.
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TEh2---R2 R4-----TEt2
\ /
\ /
TEh1---R1----ABR1-----Rb1-----Rb2-----ABR2----R3----TEt1
Area 1 Backbone Area2
In this example, ABR1's TE Reachability vector TLV for area 1 and
area 0 are given below.
{ ABR1, [<TEh1, <Path info 1>>, <TEh2, <Path info 2>>]}
{ ABR1, ABR2, [<TEt1, <Path info 3>>, <TEt2, <Path info 4>>]}
Here the vector TLVs are arranged as per increasing PWR metric
associated with each path. That is the summation of all PWR metrics
of the links in the path is done and the vector TLVs are ordered in
increasing order of PWR metric sums. So the lowest-cost-power path is
listed first and so on. If the least cost power path is to be chosen
then the path in the first TLV is chosen.
Similarly ABR2's TE Reachability vector TLV for area 2 and area 0 are
given below.
{ ABR2, [<TEt1, <Path info 3>>, <TEt2, <Path info 4>>]}
{ ABR2, ABR1, [<TEh1, <Path info 1>>, <TEh2, <Path info 2>>]}
The first thing to be noted is that head-ends are also considered as
TE-endpoints. Essentially this means any head-end or tail-end of a
inter-area TE-LSP can be considered as tail-end or head-end
respectively.
Note that the reachability vector advertised by ABR1 also contains
the reachability vector of ABR2. For example, if ABR2 is brought up
first, then it is likely that ABR1 would only have the following as
TE Reachability vector TLV for area 0 before ABR2 computes path to
the TE endpoints in area 2. { ABR1, ABR2 }
Note that <Path info> TLV would only contain the aggregate of link
attributes namely cost, bandwidth etc and most importantly the PWR
metric as well but not the complete path of intermediate nodes. For
example, <Path info 1> may be a set of <2, admin-group-1|admin-group-
2, 1Gbps> (where the 1Gbps could be the minimum bw available along
the path). The above example topology has only one path from ABRs to
TE endpoints. The number of path info "k" may have a default value or
can be configured by the operator on all nodes.
2.2 TE Path Head-end Operation
When any TE application requests TE path to be setup to an endpoint
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that is not present in the same area, the head-end scans the TE
Reachability vector TLVs advertised by ABRs and selects the path
using the <Path info> contained in the vector TLVs.
Here is an example with multiple paths in area 1, backbone and area 2
called Figure 2.0
TEh3----R5---ABR3----Rb3-----Rb4------ABR4----R6--TEt4
\ / ___/ \ ___/
\ / / \/
TEh2---R2---ABR5------Rb5--------ABR6---R4-----TEt2
/ \ \____ /\___
/ \ \ / \
TEh1---R1----ABR1-----Rb1-----Rb2-----ABR2----R3----TEt1
Area 1 Backbone Area2
In this topology in figure 2.0 taking the tail-ends represented in
the diagram, it is noted that TEt4 is reachable via ABR4, ABR6 and
ABR2 as well. The TE reachability TLVs advertised by ABR6 for area 2
would be multiple to each tail-end since there exist multiple paths
to reach at least most of them in area 2 once a packet reaches any of
the ABRs in area 2.
Here again the least cost power shortest path is listed first and so
on.
{ ABR6, [<TEt4, <Path info 1>>, <TEt4, <Path info 2>>, <TEt2, <Path
Info 3>>, etc.. }
For area 0 the TE reachability TLV would be
{ ABR6, ABR1, [<TEh1, <Path info 4>>, <TEh1, <Path info 5>>...]}
{ ABR6, ABR5, [<TEh1, <Path info 6>>, <TEh1, <Path info 7>>...]}
{ ABR6, ABR3, [<TEh1, <Path info 8>>, <TEh1, <Path info 9>>...]}
For the sake of brevity we do not enumerate all path information
possible as it would be quite extensive.
It is possible that there may be already setup LSPs which are being
used for transit traffic on the backbone or in other non-backbone
areas. It is also feasible to advertize already set up LSPs in the
path info; no additional TLV is required for that purpose. The case
where this may be useful would be if such transport LSPs exist in the
backbone area and there is a willingness to provide higher preference
to these LSPs to carry transit LSPs over backbone.
There can be selective suppression of advertisements to other areas
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(backbone or non-backbone) of LSPs if these are existing LSPs setup
along a path which are utilized to a greater degree. If underutilized
with respect to the PWR metric a more favourable metric could be
advertized to other areas.
For example, backbone area transport LSPs will be advertized as
transit LSPs which would provide connectivity to LSP sections lying
in non-backbone areas and would be updated more frequently since they
facilitate inter-Area TE.
Once a path in the TLV has been used for reserving bandwidth for
traffic over that path, then it is withdrawn from the advertisements
so that it becomes unusable. Another path may be computed over the
same path but with possibly a different PWR metric sum since it is
possible that the traffic over that path could have changed the PWR
metrices in the edges along that path.
2.2 Suppression of Frequent updates owing to fluctuation in power and
bandwidth
Using the power consumed and the bandwidth available as discrete
quantities will result in frequent oscillations. Such a step would
result will result in frequent re-computations of the shortest power
paths. For the sake of suppression of such frequent updates, it is
possible to handle the PWR metric as falling within reasonable
intervals of thresholds. If the interval in which PWR metric lies is
moved out of and another interval is reached then the update is sent
out in the IGP-TE mechanism. Otherwise if the interval in which the
PWR metric lies is not moved out of then the updates are not sent.
Suitable thresholds can be arrived at after suitable calibration
through tests.
Routers may have step levels in which they increase power consumption
when they additively are loaded with more large bandwidth consuming
multicast or unicast streams. Calibrating these levels may be useful
for implementing this scheme. It is possible that such calibrated
thresholds can be used for advertising the PWRLINK ratios in the OSPF
LSA advertisements. This would be useful for bringing down the
frequency of updates or advertisements from a line-card about its
PWRLINK ratio. When power consumption meanders within a certain given
interval these ratios need not be re-advertised even if further
unicast and/or multicast streams are added to it. The incentive is to
recognize a linecard that does not drastically change power
consumption even if large bandwidth streams are added onto it for
forwarding and thus give it credit for its power optimal functioning.
If a router tends to consume the highest level of power even when
carrying low amounts of unicast and multicast streams on its line
card, it would automatically have a poor ratio when compared to a
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router that efficiently uses power when considering the Available
Bandwidth being observed. The best case would be a low power
consuming line-card or a router filled with such line cards that does
not leave its power interval no matter how much ever capacity is
sought to be used on it. But that would be an ideal condition but it
is definitely an idealistic scenario towards which the router
manufacturers should look at.
2.3 Advantages
1) The TE Reachability vector TLV contains the aggregate of all link
attributes along with TE constraints and so the head-end of the TE
path can explicitly select the ABR that connects the destination area
even though it does not know the complete topology of the backbone
area.
2) As the TE reachability vector contains only the aggregate
attributes of k-power-shortest-paths, the flooding overhead to
support the mechanism is limited.
3) Centralized path computation element is not required for
supporting inter-area power-shortest-path TE. The additional overhead
of computing k-power-shortest-paths on ABR can be solved by
offloading the computation overhead to additional processor in multi-
core platforms.
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3 Security Considerations
None.
4 IANA Considerations
New TLV types for OSPF and IS-IS for the new TLVs that have been
introduced need to be assigned.
5 References
5.1 Normative References
5.2 Informative 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.
[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.
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[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] Shankar Raman et al., draft-mjsraman-rtgwg-inter-as-psp-01.txt,
Work in Progress, February 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
EMail: balajivenkat299@gmail.com
Prof.Gaurav Raina
Department of Electrical Engineering
IIT Madras
Chennai - 600036
TamilNadu
India
EMail: gaurav@ee.iitm.ac.in
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