Energy Consumption In Access Networks

OFC/NFOEC 2008 a1561_1.pdf OThT6.pdf

Energy Consumption in Access Networks Jayant Baliga+, Robert Ayre, Wayne V. Sorin, Kerry Hinton, Rodney S. Tucker ARC Special Research Centre for Ultra-Broadband Information Networks, +National ICT Australia University of Melbourne, Vic 3010, Australia [email protected]

Abstract: We present a comparison of energy consumption of access networks. We consider passive optical networks, fiber to the node, point-to-point optical systems and WiMAX. Optical access technologies provide the most energy-efficient solutions. © 2008 Optical Society of America OCIS codes: (060.4250) Networks, (060.2330) Fiber optics communications

1. Introduction Energy consumption is becoming a key environmental, social and political issue [1]. In previous papers [2, 3], we estimated that the Internet currently consumes around 1% of total electricity consumption in broadband enabled countries. As Internet access speeds increase the power consumption of the equipment used to access the Internet will also increase. In [3] we showed that currently and in the medium term future the majority of this power is consumed in the access network. In this paper we analyse and compare the energy consumption of optical and wireless access networks. We present a network-based model of the power consumption using example data from major equipment vendors. We consider fiber to the home using passive optical networks (PONs) [4], fiber to the node (FTTN) combined with very high speed digital subscriber line (VDSL) [4], point-to-point (PtP) optical systems [4] and worldwide interoperability for microwave access (WiMAX) [5]. The relative energy consumption for each technology is determined as a function of the average access rate to each user. We show that at access speeds from 1 Mb/s to 1 Gb/s optical access networks are more energy efficient than WiMAX. 2. Modelling the Network The basic IP network, as used by Internet Service Providers (ISPs), can be logically split into three main layers - the access network, the metropolitan and edge networks and the core network. The access network connects each home to one of the edge nodes. In this section we outline some options for a high-speed access network and estimate their power consumption using published specifications of representative commercial equipment. This allows us to compare the energy consumed by the different access options. We acknowledge that the particular equipment we have selected may not be the best in its class, but our data are representative of the few items of equipment for which manufacturers openly publish power consumption data. Our analysis does not include power consumed by home networking equipment. The power consumption per user Puser of all four access technologies can be expressed as: Puser =

2PTU 2PRN + + PCPE , A ≤ AMAX M TU M RN

(1)

where PCPE, PRN and PTU are the powers consumed by the customer premises equipment (i.e. the modem), the remote node and the terminal unit at the central office, respectively. MRN and MTU are the number of users or subscribers that share a remote node and the number of users that share a terminal unit, respectively. The parameter A is the average access rate in Mb/s and AMAX the maximum access rate achievable by the access technology. The first and second terms on the right hand side of (1) include a factor of two to account for additional overheads such as external power supplies and cooling requirements [6]. Table 1 lists example values of the parameters for each access technology. In the following we explain the details of the parameters for each access technology. 2.1 Passive Optical Network (PON) A fiber to the premises installation most commonly takes the form of a shared PON, in which an access concentrator or Optical Line Terminal (OLT) is located at the central office, and serves a cluster of access modems or Optical Network Units (ONUs) located at each of the customers' premises [4]. The capacity per customer in PON networks is determined by backhaul capacity, ONU average access rates, and the number of ONUs that share a connection to an OLT. We consider a GE-PON access network, providing a symmetric 1 Gb/s connection from each ONU to the OLT, which is shared among many users. The particular equipment used in our model is the Wave7 ONT-E1000i ONU and NEC CM7700S OLT. This OLT is capable of controlling up to 8 GE-PON systems (256 users) and has a

978-1-55752-855-1/08/$25.00 ©2008 IEEE

Authorized licensed use limited to: Univ of Texas at Dallas. Downloaded on October 10, 2008 at 16:25 from IEEE Xplore. Restrictions apply.

OFC/NFOEC 2008 a1561_1.pdf OThT6.pdf

4 Gb/s uplink to the network edge. Each ONU consumes approximately 5 W. The remote node does not consume any power as the access network is designed to be passive between the ONU and the OLT. The NEC CM7700S OLT consumes 100 W. 2.2 Fiber to the Node (FTTN) A hybrid FTTN network can be used when customers are already served by good-quality copper pairs [4]. Optical fiber is used to connect the central office to a remote street cabinet close to a cluster of customers, and the existing copper pair wires are used for the final feed to the customer premises. We are principally interested in the power consumption of high speed architectures. Therefore, we only examine the option of VDSL2 for an FTTN network, which provides an access rate of 100 Mb/s. We do not consider the currently available alternative, ADSL2+ since it is limited to just 24 Mb/s. Each remote node houses a VDSL access multiplexer (DSLAM) which communicates with several homes through the existing copper wires and connects back to the network edge through two GE-PON ONUs. The equipment used in our model is the Zyxel VES-1616F-34 DSLAM at the remote node and an NEC VF200F6 VDSL modem at each home. The VDSL2 DSLAM can connect to 16 users and consumes approximately 85W, which includes 10 W for the two upstream ONUs. The VDSL2 modem consumes 10W. 2.3 Point-to-Point Optical Access Network (PtP) As demand for services and the resulting traffic per user grows, PON and FTTN architectures can be enhanced through increases in data rates or the use of additional wavelength channels (WDM) [4]. However, the highest access speeds are currently only achievable though a dedicated PtP optical fiber link between the customer premises and the network access node. This network is also future proof, providing scope for future expansion. In modelling a PtP network, we consider a Cisco 4503 Ethernet Switch, housed in the central office or network edge node. The switch has 72 Gb/s of capacity and its ports can be configured for either upstream or downstream traffic depending on the desired average data rate A. The customer premise equipment (CPE) at each home is a TC Communications TC3300 optical media converter to convert the electrical signal used in the home network to an optical signal for transmission over fiber. A Cisco 4503 Switch consumes 466 W while each TC Communications TC3300 home unit consumes 4 W. There is no remote node. 2.4 WiMAX The most flexible architecture to deploy is one which uses a fixed point wireless access network. Currently, the most promising high speed wireless access technology is WiMAX [5]. WiMAX allows for access rates of up to 70 Mb/s and has a reach of over 48 km. However, typically interference in urban areas limits access speeds to about 22 Mb/s and distances of less than 7 km, with degraded speeds at higher distances [8]. The base station at the remote node uses a GE-PON ONU to communicate to an upstream OLT. In our model we use the Axxcelera ExcelMax Base Station, which supports up to six broadcast sectors each operating at 22 Mb/s. Each home has an Axxcelera ExcelMax FD-FDD CPE. The Axxcelera ExcelMax Base Station consumes about 803 W, which includes 600 W for the Base Station chassis, 6x33 W for the six antennae and 5 W for the upstream ONU. The fixed point outdoor customer premises unit consumes 20W. Table 1 Example values for the variables in Equation 1. PTU

MTU 72 Gb/s 1Gb/s + A

PRN

MRN

PCPE

AMAX

0

N/A

4W

1 Gb/s

PtP

466 W

PON

100 W

4Gb/s A

0

N/A

5W

1 Gb/s

FTTN

100 W

4Gb/s A

85 W

16

10 W

100 Mb/s

WiMAX

100 W

4Gb/s A

803 W

150 Mb/s A

20 W

22 Mb/s

3. Power and Energy Consumption Fig. 1 shows the power consumption per user for PON, FTTN, PtP and WiMAX access networks versus average access rate. The relationship between average access rate and number of users is given in Table 1. The most powerefficient access network, for access rates below 300 Mb/s, is the PON architecture. WiMAX has high power consumption at access rates above 1 Mb/s because very few users are able to share the relatively low bandwidth base stations. A network using FTTN and VDSL consumes 2 to 3 times the power of a PON. This is mainly due to the extra power required by the VDSL switching equipment at the remote node. At data rates above 300 Mb/s the point-

Authorized licensed use limited to: Univ of Texas at Dallas. Downloaded on October 10, 2008 at 16:25 from IEEE Xplore. Restrictions apply.

OFC/NFOEC 2008 a1561_1.pdf OThT6.pdf

to-point optical access network becomes the most power efficient as the statistical multiplexing gains inherent in a PON no longer apply. A useful measure of the efficiency of a network is the energy consumed per bit of data transferred [3]. Fig. 2 shows the energy consumed per bit by each access network. At low bit rates the energy per bit is dominated by the fixed power consumption of the customer access modem. The energy per bit for fiber-based access networks drops rapidly as the average access rate increases. For access rates in the region of 100 - 1000 Mb/s, the energy per bit is less than 0.1µJ.

Fig. 1. Power consumption per user for typical access networks.

Fig. 2. Energy per bit of typical access networks.

4. Influence of User Population Density In our analysis we have implicitly assumed that there will always be sufficient customers within the reach of both the central office and the remote node to fully utilise the network. To illustrate the influence of user population density on network performance, we have plotted additional symbols on the curves in Fig. 1. The symbols indicate the maximum average access rates that each technology can achieve at user population densities from 0.01 users/km2 to 10 users/km2. Users located more than 7 km (for WiMAX) and 300 m (for FTTN with VDSL2) from the remote node are unable to achieve the highest data rates available with the particular technology [8, 9]. For this reason the maximum average access rate achievable by WiMAX and FTTN degrades as the user population density decreases. The most dramatic effect can seen for the FTTN solution where an access rate of only 25 Mb/s is achievable at a user population density of about 1 user/km2. However, this access rate is still greater than that of WiMAX and uses only one tenth of the power consumption. PON and PtP have reaches in excess of 20 km with no degradation in bit rates at higher distances, and so are able to service very low population densities at their maximum access rate. 5. Conclusions We have presented a power consumption model for future high speed access networks using published specifications of representative commercial equipment. Power and energy consumptions are compared for point-topoint optical links, passive optical networks, fiber to the node and WiMAX. Passive optical networks and point-topoint optical networks are the most energy-efficient access solutions. 6. References [1] M. Gupta and S. Singh, “Greening of the Internet,” ACM SIGCOMM, Karlsruhe, Germany, Aug. 2003. [2] J. Baliga, K. Hinton and R. Tucker, “Energy Consumption of the Internet,” COIN-ACOFT, June, 2007. [3] J. Baliga, R. Ayre, K. Hinton and R. Tucker, “Power Consumption of the Internet,” submitted to IEEE Comms. Mag. [4] P. Chanclou, S. Gosselin, J. Palacios, V. Alvarez, E. Zouganeli, “Overview of Optical Broadband Access Evolution,” IEEE Comm. Mag., p. 29, Aug. 2006. [5] WiMAX Forum. [Online]. Available at: http://www.wimaxforum.org [6] J. Koomey, H. Chong, W. Loh, B. Nordman and M. Blazek, “Network electricity use associated with wireless personal digital assistants,” ASCE J. Infrastructure Systems, vol. 10, pp. 131-137, Sep. 2004. [7] Axxcelera Broadband Wireless. [Online]. Available at: http://www.axxcelera.com [8] Alcatel, “WiMAX, making ubiquitous high-speed data services a reality,” Jun. 2004. [Online]. Available at: http://www.alcatel-lucent.com [9] Ronald Heron, “FTTx Architecture Transition Strategies,” NFOEC, Anahaim, USA, Mar. 2007.

Authorized licensed use limited to: Univ of Texas at Dallas. Downloaded on October 10, 2008 at 16:25 from IEEE Xplore. Restrictions apply.