Power-efficient Electronic Burst Switching for Large File

Transactions

Ilijc Albanese

, Sudhakar Ganti

and Thomas E. Darcie

Department of Electrical and Computer Engineering, University of Victoria, Victoria, BC, Canada

Department of Computer Science, University of Victoria, Victoria, BC, Canada

Keywords: IP Networks, Burst Switching, High Speed DWDM Optical Transmission, Optical Network, Overlay

Network, Low Power Networking, Electronic Buffering, Router Power Consumption.

Abstract: Much of the growth in bandwidth demand and power consumption in today’s Internet is driven by the

transport of large media files. This work presents a power-efficient overlay network specifically designed

using electronic burst switching for these large files. The two approaches are presented in which electronic

bursts or media frames (MF) containing >1Mb are routed in a manner similar to UDP or concatenated into

periodic semi-transparent chains and routed using a two-way reservation protocol. Utilization, blocking,

delay and buffer size are compared to UDP/IP by means of simulation. Both approaches dramatically reduce

header-related power consumption. Concatenation also reduces significantly the amount of buffer space

required. A representative router design is evaluated showing a potential energy saving of roughly 80%

relative to standard IP routers.

1 INTRODUCTION

Despite ongoing improvements in bandwidth

capacity and power efficiency, power consumption

in router networks continues to be a concern.

Estimates suggest that Internet-based

communication technologies consume between 2-

3% of power generated globally and that this

number is increasing at a rate of 16-20% per year

(Fettweis and Zimmermann, 2008). As a result,

extensive effort is ongoing to develop new

techniques for minimizing power consumption in

future Internet technologies.

Of particular interest is power consumed in

electronic routers. Numerous studies have shown

that a significant portion of power consumed can be

attributed to header processing on each packet. With

the increasing popularity of bandwidth intensive

applications such as streaming video and the sharing

of large files, studies support the general observation

that file sizes are growing rapidly. Given the large

number of IP packets required for these transactions,

header related power consumption is a key

contributor to the rapid growth of power

consumption in routers. Energy efficiency improves

if larger packets are used for large file transfers. In

response, the maximum IP packet size was extended

from 1500 bytes (B) using Jumbo and Super Jumbo

frames pushing packet sizes to 64KB. However,

these specifications are not in widespread use due to

problems related to backwards compatibility

(psc.edu, 2012) and network latency arising from

integration of very large packets with smaller

packets within the same links. Integration of large

(up to 19.5KB) and standard packets within the same

network was considered (Divakaran and Altman,

2009) showing that the use of larger packets may

reduce power consumption and computational load

required from the network hardware. However,

coexistence of large and small packets in the same

links results in unfairness and higher drop rates for

both types of packets, leading to inefficient

bandwidth and computing power utilization.

This raises the question as to the potential value

of using a separate overlay network for the traffic

associated with large file transfers. While clearly the

introduction of a new overlay network would have

to be predicated on compelling value, it would be

unwise to suggest that, given power consumption

and scaling considerations of IP, a next generation

non-IP switching/routing approach cannot exist.

What might be the form of this new overlay

network? On one extreme, numerous optical

Albanese I., Ganti S. and E. Darcie T..

Power-efﬁcient Electronic Burst Switching for Large File Transactions.

DOI: 10.5220/0004357400430052

In Proceedings of the 2nd International Conference on Smart Grids and Green IT Systems (SMARTGREENS-2013), pages 43-52

ISBN: 978-989-8565-55-6

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

networking approaches offer up to an entire

wavelength for some time, through which GigaByte

(GB) files can be delivered. Optical burst (OBS)

(Jue and Vokkrane, 2005) or flow switching (OFS)

(Chan, 2010), or user-controlled end-to-end

lightpaths (e.g. CAnet4, MONET, CORONET and

GRIPhoN (Mahimkar et al., 2011)) have been

explored fully. For example, an OBS approach

(Yong et al., 2010) uses concatenated data bursts

where the data units are organized as non-contiguous

and non-periodic series of concatenated timeslots

(bursts), which are then handled as a whole in an all-

optical network infrastructure. These optical

approaches are not embraced by industry, in part

because the power efficiency of optical switching is

questionable (Tucker et al., 2009), (Tucker, 2006)

and optical buffers, widely used in most OBS

proposals, have not yet offered a commercially

viable alternative to electronic buffers. Also, while

capable of supporting large bandwidth, targeted

implementations are in the interconnection of

specialized nodes rather than broadly distributed

Internet users.

Hybrid architectures have been studied in which

both electronic and optical switching are combined

(Aleksic et al., 2011) to simultaneously handle

packets, bursts and TDM circuits. A large reduction

in the power consumption is achieved by selecting

adaptively which part of the node to activate based

on a per-flow evaluation of the data to be routed

while the other blocks are put in sleep or low-power

mode. While potentially powerful, this approach

requires the complex integration of disparate

switching and control elements, some of which (like

OBS and optical delay lines) have not proven

compelling individually.

A more incremental overlay network approach is

electronic burst switching (EBS) (Peng et al., 2010).

Following the OBS model, bursts are assembled at

edge burst switches and switched electronically at

core switches. It was concluded that using large

bursts (> 1 Mb) may lead to reduction in header-

related power consumption in core switches, but the

power consumed by burst assembly negates much of

the advantage gained in core switching.

In this paper we continue along the path of EBS.

Users share the bandwidth of an overlay network,

which we presume to be statically provisioned, using

electronic switches or routers specifically designed

to handle large file transactions. Unlike (Peng et al.,

2010), we eliminate burst assembly at edge switches

and consider direct end-to-end delivery of large

“media” frames (MF) (roughly 1-10Mb) to users

through an overlay to next-generation optical access

networks. Free from the constraints of coexisting

with highly granular and dynamic IP traffic, this

EBS overlay network can be designed specifically

for the efficient delivery of the large data

transactions that did not exist when the Internet was

conceived. Compared to traditional IP routers,

switch reconfiguration can be far less dynamic since

only very large packets are supported. Unlike

proposed optical alternatives, this can be

accomplished using available electronic buffers in a

form that is entirely compatible with today’s highly

efficient cross-point switch arrays.

Our objective is to enable a significant reduction

in power consumption of network hardware while

optimizing the use of resources. We first explore

routing MFs using a standard UDP protocol (MF-

UDP). UDP is selected for this study, rather than

TCP, as this avoids numerous complexities that add

little insight to a comparison with conventional IP

and, as discussed later, gives the best case scenario

for IP. Based on simple hardware considerations,

network performance simulations and comparison

with traditional UDP, we arrive at the anticipated

conclusion that router power consumption is reduced

dramatically, but performance is otherwise

unaffected and larger buffers are needed.

We then consider using concatenations of MFs

into periodic semi-transparent chains (MFCs) and

the scheduled transmission of these MFCs using a

two-way reservation mechanism. While such a

scheduling mechanism would be inappropriate for

traditional IP traffic, the large size of each MFC

(e.g. 1 GB) makes scheduling both manageable and

worthwhile. Also, the structure of an MFC makes it

easy to condense information on its configuration

with minimal control plane information, minimizing

the amount of information to be processed at each

node to schedule the chain and reducing the

probability of control plane collisions. Simulation

results show increased utilization efficiency and

decreasing buffer requirements in comparison to

MF-UDP as well as standard UDP. An MFC router

is designed based on a commercially available cross-

point switch array and power consumption is

estimated to be roughly 20% of that of a standard IP

router.

The paper is organized as follows: Section 2

provides an overview of the reference network

architecture in the context of transactions of large

files. Section 3 compares, using OMNeT++

simulation, traditional UDP to MF-UDP in

supporting representative large transactions. In

Section 4, chains of media frames (MFCs) are

introduced, along with exemplary admission control

SMARTGREENS2013-2ndInternationalConferenceonSmartGridsandGreenITSystems

and scheduling algorithms, and compared to UDP

and MF-UDP. Router implementation is discussed in

Section 5, where implications on power

consumption are considered and a representative

MFC router is evaluated.

2 NETWORK TOPOLOGY

AND LARGE FILE FLOWS

Our discussion is framed by the reference network

architectures shown in Figures 1 and 2. Fig. 1 shows

a hierarchical network representative of the current

state-of-the-art comprising various sizes of routers

(access, edge, and core) connected to a transport

network through various sizes of add-drop

multiplexers.

Figure 1: Reference Architecture.

Primary examples of large-file transactions can be

super- imposed onto this reference architecture.

These examples include: 1) Regionally-cached

download: In this case large media files are

downloaded from regional cached distribution

servers at the end points of Content Delivery

Networks (CDN), through Metro and access to end-

users. Driven by rapid proliferation of video-related

download applications, these downloads represent a

significant fraction of traffic growth, and therefore

are the focus of this study. Other important

transactions include: 2) Source-to-cache distribution:

To deliver and update content to CDN servers, large

files must be distributed from sources, typically

across a core network, to the regional cache; 3) End-

to-end file transfers: For peer-to-peer applications,

or for files for which widespread distribution is not

anticipated, the regional cache is bypassed and files

are transacted through Metro and access, possibly

across the core network, directly to an end-user.

An overlay network designed specifically for

large file transactions might look like Fig. 2. Each of

the “media” boxes parallels a present-day IP

counterpart and supports the origination or

termination (media client interface (MCI)), access

bypass (media access bypass (MAB)), admission

(media access router (MAR)), and efficient end-to-

end routing (media backbone router (MBR)), in

accordance with the principles described below for

MFs. In addition, it is convenient to consider

regional storage of MFs in a media frame cache

(MCa).

Figure 2: Media Frame Overlay Architecture.

Our intention is not to restrict application to

specialized nodes (e.g., campuses), but rather to

reach broadly distributed consumers, methods must

be established to transport MFs through access.

Two possible solutions are represented in Fig. 2.

A conservative approach involves an application

operable between the MCI and the MAR such that

using traditional broadband access alone, MFs and

MFCs are assembled or disassembled at the MAR.

This functionally is parallel to the burst assembly

routers proposed for use in OBS and EBS. A

preferred approach involves engaging the evolution

of optical access standards, where standards for 10

Gb/s PON have emerged recently, to enable higher

dedicated bandwidths perhaps through wavelength

overlays. MFs and MFCs would then be assembled

at the user end point or client directly.

3 MEDIA FRAMES VERSUS

CONVENTIONAL IP

We first explore the issues associated with migrating

very large file transfers to a separate overlay

network in which the standard unit of bandwidth is a

media frame (MF) containing roughly 1-10 Mb of

data plus overhead. In (Peng et al., 2010) it was

concluded that although using large packets would

Power-efficientElectronicBurstSwitchingforLargeFileTransactions

lead to considerable power savings, increasing the

frame size beyond 1Mb would only marginally

increase the energy efficiency of an EBS node.

However, using larger frames also reduces the

required reconfiguration speed of the switch fabric,

minimizing requirements on switching speed and

inefficiency introduced during transitions.

Overhead may include address, priority,

concatenation details (specifying MFCs, as

discussed later), coding, guard time and

management information. Given the very large

capacity within each MF, considerable header

information (e.g. 10 KB) can be included with

minimal impact on throughput. Structure may be

defined to facilitate error correction, segmentation,

security, file compression, and easy assembly from a

large numbers of smaller IP packets.

An obvious method for networking with MFs is

to adopt the same concepts as used with TCP/UDP,

allowing each MF to be routed in accordance with

predefined routing tables through a connectionless

queuing network. While the dynamics are

considerably different than with < 1500 B UDP

packets, the underlying issues are the same.

To explore this in detail, both UDP and MF-UDP

network simulators were built using OMNeT++

(OMNeT++, 2012) and the performances compared

in terms of link utilization, buffer space occupied

and delay per GB of data transferred. UDP was

simulated using 1500B packets and MF-UDP using

1Mb packets. Droptail queues were used for both

1Mb and 1500B UDP packets. For standard UDP

packets the maximum buffer size was set to 1000

packets, corresponding to roughly 1.5MB. Buffers of

the same size were used for MF-UDP.

A dumbbell topology was considered for the

simulations (Figure 3). While more complex

topologies could be simulated, this represents the

case of our reference network (Figure 2) with a

congested link between multiple source servers and

end users.

The capacity of each link is set to 10Gib/s (i.e.

10*2^30 Gb/s according to IEC standard) and each

source is offering the network an average load of

roughly 1.33 Gb/s. Various load conditions were

tested by activating more source-destination pairs

and the offered load was made to vary from 25% to

150% of the bottleneck link capacity (corresponding

to from 2 to 12 source-destination pairs). Each

source transmits data to one destination only and all

sources compete for the same bottleneck link.

Compared to UDP, the router switch fabric

becomes far less dynamic. Reconfiguration occurs

far less frequently (by 3 orders of magnitude).

Figure 3: Topology Used for Simulations.

It remains to be seen if an MF-router can be

designed to exploit this less dynamic reconfiguration

and negligible header processing with a sufficiently

large net increase in power efficiency to justify a

separate overlay network. This is addressed further

in Section 5.

4 CONCATENATED MEDIA

FRAMES

While UDP-like MF routing dramatically eases

processing (header and switch reconfiguration) over

traditional IP, performance is otherwise essentially

the same. We now consider the potential impact of

concatenation of MFs into larger structured chains

(MFCs). Concatenation creates single entities that

would contain an entire large transaction, for

example a multi-GB movie download. Discussion

centers on two key considerations: scheduling and

transparency. Scheduling and admission control

become worthwhile for such large transactions and

these can be used to increase resource utilization and

minimize buffer size. However, serving such large

transactions continuously in time introduces

significant latency for waiting transactions and is

incompatible with the lower end-user client and

access network throughputs. Making each MFC

partially transparent overcomes both problems. We

limit our discussion here to a simple functional

description of a representative methodology,

including MFC structure, transparency, signaling

and scheduling algorithm, then compare

performance to conventional UDP and the MF-UDP

described in Section 3.

4.1 Media Chain Transparency

A MFC with transparency degree 3 (defined as the

number of interstices between two consecutive MFs

in a chain plus 1) is illustrated in Figure 4.

Using periodic semi-transparent chained data

structures provides five primary functions. First,

given the large size of each MF, concatenations of

multiple MFs without transparency would introduce

substantial latency by occupying network resources

SMARTGREENS2013-2ndInternationalConferenceonSmartGridsandGreenITSystems

Figure 4: An Example of How Two MFCs, MF-UDP

Frames and Voids Fit in a Channel.

for substantial durations. The use of transparency

allows servicing multiple MFCs without introducing

long delays, albeit at a slower data rate. Secondly, a

fixed transparency simplifies scheduling of large

amount of data with minimal computational load.

Third, the semi-transparent structure of each MFC

allows the use of buffering as a means to affect the

relative timing of an MFC with respect another in

order to interleave MFCs competing for the same

link, but without buffering entire chains. Our hope is

that this use of the buffer will enable significant

savings in buffer space occupied relative to the UDP

and MF-UDP of Section 3. Fourth, we anticipate bit

rates of 10Gb/s in access networks at a time when

bandwidths in core networks will be 100Gb/s.

Transmission from access must then be up-shifted in

rate, resulting in, for this case, 10% time occupancy.

This would be accommodated naturally by a core

transparency degree 10 times higher than that used

in the access. Finally, for file transfer applications

one desires to send as much information as fast as

possible. For this transparency is a disadvantage.

However, streaming applications have evolved to

deliver segments of large files spread out over long

time periods. A large transparency degree can be

used to emulate streaming delivery while retaining

the other worthwhile attributes described above.

4.2 Signalling and Control

Signaling is needed to establish and update the

network state, schedule MFC transmission,

acknowledge receipt, and many other functions.

Information about an entire MFC, including length,

scheduling information, priority, etc. can be easily

contained within each MFC, MF in an MFC, or a

small separate control packet. Signaling could be

‘in-band’ using periodic time slots within the MF

transport structure, or ‘out-of-band’. Our preference

is to exploit the ubiquitous availability of traditional

IP networks for out-of-band signaling. In what

follows, we assume that each of our media access

and backbone routers (MAR, MBR in Fig. 2) are

able to signal through a suitable IP network.

Global Control: Since each signaling event

corresponds to of order 1 GB of data, the number of

signaling events is small. It is then reasonable to use

a centralized ‘state server’ to provide each router

with global path, timing, and occupancy

information. Each router updates status to the state

server regularly, and the state server is able to

calculate paths and approve initiation of a request

for MFC scheduling, as discussed below. The state

server must know the topology and is then able to

make globally informed decisions to queries from

routers. It is also useful to know the propagation

time between nodes for efficient scheduling.

Numerous methods can be implemented, like the

ranging protocol used in PON, to estimate these

times and report them to the scheduling server.

Distributed Control: Each router communicates

directly with its neighbors and the state server. Each

router continually updates the state server of status

and load, and MARs request path and approval for

MFCs from the state server. Approval does not

guarantee success, but suggests high probability.

Communication between routers along the path

determines ultimate success, as described below.

This minimizes latency in each MFC request-grant

negotiation.

4.3 Scheduling

The objectives of scheduling are to organize

transmission of concatenated chains in such a way as

to minimize hardware complexity and power

consumption, to maximize link utilization and to

minimize buffer requirements. All of these

objectives can be addressed through the use of an

Expected Arrival Time (EAT

) of the MFC to the

next node in its path. This is computed based on the

physical distance between the nodes, which is

assumed to be known by each scheduling node, and

included in a control packet CP (< 1 Kb). The CP is

used to reserve resources for its associated MFC

along its path. Many variations of the scheduling

algorithm can be considered. For purposes of

simulation, we defined an example that comprises

the following basic steps:

- MFCs assembled at end user machine.

- A request packet containing at least the length of

MFC, transparency degree, source and destination

address is sent to media access router (MAR).

- MAR queries state server for path, propagation

time associated with each hop in path.

- MAR estimates a Time-to-Transmit (TT)

parameter. All routers along path use TT to search

Power-efficientElectronicBurstSwitchingforLargeFileTransactions

for available time slots. TT is determined based on

transmission and propagation delay from user to

the MAR, hop distances along path and processing

time for control packets at each node.

- MAR generates control packet (CP) and sends it to

next node along path. CP contains

sender/destination address, length of MFC,

transparency degree, expected arrival time

(EAT[Ni]), and ID that associates each CP to an

MFC. EAT[Ni] indicates to the node receiving the

CP the amount of time, after the reception of the

control packet, before the arrival of first bit of the

MFC .

- EAT field in CP is updated before forwarding CP

to next hop node, in order to account for the

additional transmission, buffering and processing

delays at each node. This continues until

destination (egress MAR) is reached or until the

reservation process fails.

- If reservation succeeds, confirmation packet is sent

over IP network directly to source node which

starts transmission of MFC. If reservation fails, a

“NACK” packet is sent over reverse path to free

resources and source will retry after random back-

off time.

Since the estimated EAT for the MFC is

computed using the physical hop delay (known

globally) and the expected arrival time is carried in

the CP, there is no need for network-wide

synchronization. A local timer at each node keeps

track of the time differences between the reception

of the CP and the expected arrival time of its relative

MFC. The guard time in each MF compensates for

the time uncertainties in this estimation process.

4.4 Simulation

The scheduling algorithm was implemented (details

to be published) using OMNeT++ and the same

topology used in Section 3. Each MF is assumed to

contain 1Mb of data and each MFC is defined as the

concatenation of 8000MF (i.e. 1GB of data). A fixed

transparency degree of 8 was chosen for all MFC

simulations. The performances of the MFC-based

transport are then compared to those of UDP sources

using MF (1Mb) and standard UDP packets

(1500B).

Given the functioning of the algorithm presented

in Section 4.3, the payload bits arrive at the node

only if the reservation process was successful. In

order to compare this to a connectionless protocol as

in Section 3 (UDP) it was assumed that each source-

destination pair would attempt to transmit on

average the same amount of data. Hence for the

UDP cases (both standard and MF-UDP) the

“offered load” is the load physically reaching the

bottleneck node. For the MFC case, the offered load

is computed based on the number of reservation

attempts per second. The maximum buffer size

allowed for the bottleneck router (router 1 of Figure

3) was set to be 1.5MB for all cases.

4.5 Simulation Results

Link Utilization: As can be seen in Figure 5 the

link utilization is very close for all 3 approaches

tested for load conditions up to ~74%. Beyond this

point the higher cost of dropping larger frames

comes into play and the bandwidth efficiency of

MF-UDP is reduced. For load greater than ~90%

load packet dropping also affects standard UDP and

its utilization drops below that of MFC. MFC

utilization is ~9% higher for higher loads.

Figure 5: Link Utilization Vs Offered Load.

The highly structured MFC and the scheduling

algorithm allow interleaving large amounts of data

with link utilization similar to that of time division

multiplexed systems and performance consistently

better than both other cases under high load

conditions.

Packet Dropping and Blocking: Packet

dropping (two UDP cases) and blocking (MFC) are

presented Figure 6. The random nature of the arrival

for UDP packets allows for the possibility of filling

the queue at the bottleneck node even if maximum

load has not yet been reached. In the reservation-

oriented MFC system call blocking only occur after

the maximum bottleneck link capacity has been

effectively reached.

It is important to note that when a packet is

dropped, payload bits are discarded and these may

have already used resources along their path (buffer

space, switching power, bandwidth, etc.). When an

MFC request is blocked, we are simply rejecting an

attempt to transfer the data and not the data itself.

SMARTGREENS2013-2ndInternationalConferenceonSmartGridsandGreenITSystems

Figure 6: Packet Dropping and Call Blocking Vs Offered

Load.

This advantage of reservation-based mechanisms in

terms of efficiency of resource usage is well known.

Delay: To compare the delay performance a

1GB transaction was taken as a reference quantity.

For MFCs, upon failing a resource reservation

attempt, the source simply backs off for a random

amount of time before re-attempting the reservation

procedure. The back-off time is exponentially

distributed with an average equal to the duration of

an entire chain. Re-transmission attempts were also

taken into account in the delay performance

measurement, as shown in Figure 7. Up until 75%

load, the delay experienced by the MFC system is

virtually identical to that of both UDP cases. Beyond

this point using MFCs reduces delay. Besides

offering equal delay performances to UDP for the

majority of the range of operation of the network,

MFC also provides reliable data transfer, which

cannot be achieved by UDP due to the statistical

nature of arriving packets.

Figure 7: Delay (per GB of data transferred) Vs Offered

Load.

Buffer Size: As shown in Figure 8, the buffer size

required at low load for MFC and MF-UDP is higher

than that occupied by standard UDP (with MF-UDP

occupying the largest buffer space). As the load

increases (>88%) MFC requires considerably less

buffer space than both MF-UDP and standard UDP,

which beyond a certain load quickly start to fill

buffers up to the maximum capacity.

Figure 8: Buffer Occupancy Vs Offered Load.

The periodic data structure of the MFC and the

scheduling algorithm bound the required buffer

space to about 2-5 times less than that of both UDP

approaches.

Figure 9: Buffer Occupancy Vs Offered Load for Various

Frame Sizes for MFC.

For both UDP and MF-UDP the buffers are required

to avoid dropped packets, while for MFC the buffers

are used to align MFCs in time with scheduled slots.

This results in a buffer size that depends much more

on the size of the MF within the MFC than on the

offered load. This dependency is shown in Figure 9

where various media frame sizes were tested for

MFC. Varying frame size results in virtually

identical performances in terms of blocking

probability and utilization but a significant increase

of the required buffer space. Similarly, reducing the

MF size for each MFC can reduce the buffer space.

Increasing the frame size for the MF-UDP case

would result in buffer sizes that would simply

become impractical. In the MFC case using frames

larger than 1Mb may enable a relaxation of the

reconfiguration speed for the switch fabric as well as

a reduction of the CPU utilization (see section 5.1)

while keeping the buffer size limited.

Power-efficientElectronicBurstSwitchingforLargeFileTransactions

5 DISCUSSION

AND ANTICIPATED BENEFITS

Results for MFC indicate a considerable advantage

in terms of buffer size as well as a large reduction in

processing power with respect to UDP. A

comparison with TCP would have been useful in

that, unlike UDP and more like MFC, TCP can

guarantee the correct delivery of the file transferred.

TCP acknowledgements and retransmissions would

have made the delay per GB much higher and

bandwidth utilization much lower than that achieved

with UDP. In other words, for our simulation study

UDP is the best-case scenario for IP networking.

5.1 Impact on Router Power

Consumption

In (Aleksic, 2009) the issue of power consumption

in large scale networks is addressed concluding that

power consumption of header related functions is far

larger than that consumed by the switching fabric.

Apparently, most power is consumed in data

processing functions (i.e. header parsing, address

lookup, etc.), which must be carried out for each

packet traversing a router.

MF-UDP and MFC offer significant reductions

in the number of packets to be processed. Consider a

state-of-the-art router working at 1 Tb/s. Depending

on the manufacturer such a router can consume

about 4 KW (CRS-3, 2012), (T1600, 2012), or an

overall energy per bit of roughly 4 nJ/b.

Estimates of the power consumption of the

various functional blocks of a similar IP router can

be found in (Tucker et al. 2009). From this study it is

clear that, other than power supply and cooling

blocks, which are largely dependent on the energy

needed by the other blocks, the forwarding engine

consumes the most power, using about 32% of the

energy supplied to the router.

Assuming an average packet size of 10 Kb

(caida.org, 2012) means that a 1 Tb/s router will

have to perform header related operations

approximately 10^8 times per second (CRS-3,

2012). Organizing data in MFCs carrying roughly 1

GB of payload can reduce this by many orders of

magnitude.

In addition, the required processing speed is

reduced so that a much slower processing unit can

handle the same data throughput. From the study

presented in (Wang et al.,2006) it is also reasonable

to say that the use of large frames, together with

organizing the data within the sources in large

blocks (i.e. MFs) will allow a significant reduction

in CPU utilization in terms of number of memory

accesses and IRQs that the CPU has to handle. This

may lead to additional power savings in data storage

servers.

Given the large size of the MFs, requirements on

the reconfiguration speed are significantly relaxed,

as well as the amount of control information needed

to drive the switch fabric, with further impact on the

power consumption. Further reduction in the amount

of control information is achieved when using

MFCs, as a result of the predictability of the periodic

payload.

5.2 Power Consumption of Example

MFC Router

A schematic of an MFC-based router based on a

commercially available cross-point switch array is

shown in Figure 10.

Figure 10: Concatenated Media Frame Router.

Input data is converted into the electrical domain

and data streams from each channel are de-

multiplexed into their constituent MFCs. Each MFC

is then delayed by the amount indicated in its

associated CP. The number of buffer queues needed

depends on the number of chains the device is able

to handle and is given by # of dedicated buffer

queues = # of input channels * # of MFCs per

channel. The total buffer size also depends on the

number of simultaneous flows the device must

handle and the transparency degrees of the chains.

At the output of the buffer stage, chains

competing for the same output channels are

synchronized in order to allow interleaving. MFCs

are then passed to the switch fabric, which simply

routes each MFC to the appropriate output with no

further buffering or processing.

In order to estimate the power consumed by our

proposed router shown in Figure 10, the VSC3144-

11 has a switching capacity of 1.2 Tb/s with a power

consumption of about 20 W (Vitesse, 2012).

SMARTGREENS2013-2ndInternationalConferenceonSmartGridsandGreenITSystems

Regarding the buffer stage, values for the power

consumption of electronic memories are largely

dependent on implementation and size. If we assume

our MFC router would use a memory with similar

size and structure to that used in (CRS-3, 2012),

using the data on power consumption for a router

from (Tucker et al., 2009) gives roughly 200 W for

the buffer stage power consumption. Similarly we

can estimate the power consumption of O/E/O

blocks (including Tx/Rx equipment) to be about

280W.

The forwarding and routing engine, using about

32% and 11% of the total energy consumed by a

standard IP router, respectively Tucker et al., 2011)

(i.e. a total of ~720W (CRS-3, 2012) ), are grouped

in the “control” block of Figure 10 and, as a result of

the drastic reduction in the number packet processed

will be most likely reduced to negligible levels.

The input de-multiplexing stage, which de-

multiplexes MFCs from each channel, can be

modeled by (Tucker, 2011):

DeMUX



(1)

Where

is the energy per bit for a 1:2 de-

multiplexer and k is the number of output ports.

Assuming 2010 technology,

= 10 pJ (Vitesse,

2012). We can set k = 144 in Equation (1) obtaining

a total energy for the input stage of about 71W or 71

pJ/b.

Aside from power supply and cooling equipment,

the power consumed by the MFR would be roughly

571W. Power supply and cooling would consume

about 33% of the power consumed by the rest of the

device (Peng et al., 2010), leading to total power

consumption for the MFR of roughly 759W. This is

roughly 19% that of a state-of-the-art IP router

working in the same throughput range and load

conditions (CRS-3, 1012). This is dominated by the

power consumed by the buffer stage. Recognizing

that these buffers function more like slowly

reconfigurable delay lines than the buffers used in

typical IP routers, further study may reveal even

more significant reductions in power consumed.

6 CONCLUSIONS

In this paper we study the potential advantages of

using an overlay network in which only large media

frames (MFs) (1-10Mb) or concatenated frames

(MFCs) are used to efficiently transfer large files.

Numerical simulation is used to compare the use of

MFs using a traditional UDP routing protocol (MF-

UDP) to traditional UDP. Little difference is

observed in delay, utilization and throughput, while

the large packets dramatically reduce header-related

processing load.

In an effort to reduce buffer size and improve

resource utilization, a reservation-based networking

approach is developed using MFCs and compared to

MF-UDP and UDP through simulation. A

reservation system is defined for scheduling MFC

transmission, eliminating wasted network resources

since data leaves the source only if service is

guaranteed. Results show that buffer size can be

reduced by at least a factor of 2 under high load

conditions and the scheduling of large transactions

can increase efficiency to close to 100%. Further

advantages of using periodic, semi-transparent

MFCs is the ability to schedule large amount of data

with minimal header processing and to reduce the

reconfiguration speed requirements of the switch

fabric, ultimately reducing power consumption.

A representative MFC router is designed and

power consumption is estimated, under conservative

assumptions, to be roughly 20% that of a traditional

IP router.

Other ongoing studies include methods to allow

coexistence of scheduled MFCs and directly routed

MF-UDP within the same routers and links, and

extension of the simulations to other network

topologies. Our objective is to more definitively

articulate the cost-benefit trade-off, where the cost is

the rather large barrier associated with the creation

of a new overlay network.

In summary, the use of very large packets (MFs)

and concatenations of these (MFCs) offers an

interesting path to more power-efficient networking

for the dominant and rapidly growing portion of

Internet traffic that comprises very large (i.e. 1 GB)

transactions.

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SMARTGREENS2013-2ndInternationalConferenceonSmartGridsandGreenITSystems