—Each mobile network architecture able to meet the traffic requirements of future 5G services com... more —Each mobile network architecture able to meet the traffic requirements of future 5G services comes with its own set of benefits vs. requirements for the radio and the transport segments. This paper focuses on the energy performance of four mobile network architectures, each one with different splitting options for the baseband processing functions. The radio segment under exam is based on a new radio access technology referred to as 5G-NX, while the transport segment is based on wavelength division multiplexing (WDM). The energy consumption of each mobile network architecture is weighted against (i) the benefits for the radio segment as a function of the level of centralization of the baseband processing resources and (ii) the required transport capacity and consequently the power consumption levels needed to accommodate the backhaul, midhaul, and/or fronthaul traffic generated at each base station. Our results show that a fully centralized radio access network (C-RAN) with centralization of all the baseband functions is not a practical approach for 5G mobile networks, while a partially centralized C-RAN architecture in which the physical layer baseband processing is performed at the base station site represents a promising solution.
Mobile networks are the largest contributor
to the carbon footprint of the telecom sector and
the... more Mobile networks are the largest contributor to the carbon footprint of the telecom sector and their contribution is expected to rapidly increase in the future due to the foreseen traffic growth. Therefore, there is an increasing urgency in the definition of green mobile network deployment strategies. This paper proposes a four-step design and power assessment methodology for mobile networks, taking into consideration both radio and transport segments. A number of mobile network deployment architectures for urban residential areas based on different radio (i.e., macro base station, distributed indoor radio, femto cell) and transport (i.e., microwave, copper, optical fiber) technologies are proposed and evaluated to identify the most energy efficient solution. The results show that with low traffic the conventional macro base station deployment with microwave based backhaul is the best option. However, with higher traf- fic values heterogeneous networks with macro base stations and indoor small cells are more energy effi- cient. The best small cell solution highly depends on the transport network architecture. In particular, our results show that a femto cell based deployment with optical fiber backhaul is the most energy efficient, even if a distributed indoor radio architecture (DRA) deployment with fiber fronthaul is also a competitive approach.
Abstract—Hybrid optical switching (HOS) is a switching paradigm that aims to combine optical circ... more Abstract—Hybrid optical switching (HOS) is a switching paradigm that aims to combine optical circuit switching (OCS), optical burst switching (OBS) and optical packet switching (OPS) on the same network. In this paper we present a control plane for HOS networks. The control plane employs GMPLS for configuring the virtual topology, and a HOS control layer for performing the resource reservation and data scheduling. Furthermore, two node architectures are introduced to be managed by the proposed control plane, namely all- ...
2014 16th International Conference on Transparent Optical Networks (ICTON), 2014
ABSTRACT Datacentres are experiencing a tremendous increase in the amount of network traffic due ... more ABSTRACT Datacentres are experiencing a tremendous increase in the amount of network traffic due to cloud services and many other emerging applications. It is expected that the required bandwidth for an exascale supercomputer node will grow 20 times every 4 years (i.e., 20Pb/s in 2016 and 400Pb/s in 2020) [1]. However, the total power consumption that can be afforded by one datacentre is only allowed to increase at a much lower rate (i.e., 2 times every 4 years, 10MW in 2016 and 20MW in 2020) due to thermal dissipation constraints [1]. The consumers of energy in datacentres are IT equipment (e.g. servers, network equipment, etc.) and other supporting facilities (e.g. lighting, cooling, etc.). In order to identify how efficiently a datacentre uses its power, a measure called power usage effectiveness (PUE) is defined as the ratio of the total facility power to the IT equipment power. Many efforts have been put on reducing PUE. For instance, a smart selection of datacentre location could greatly reduce the energy required for cooling and significantly improve PUE. It was very recently reported that Facebook carefully chose the location and launched Arctic datacentre (consisting of three 28,000 square-meter buildings) in Sweden [2]. By utilizing icy conditions in the Arctic Circle, their datacentre can reach a PUE around 1.07 [2]. Such a low level of PUE implies that in modern datacentres major focus on energy savings should be moved to IT equipment. Currently, network equipment in a datacentre may take up to approximately 20% of the total energy consumed by IT equipment and this value is expected to grow in the future [3]. Thus, in order to sustainably handle ever-increasing traffic demand it becomes of extreme importance to address the energy consumption issue in datacentre networks (DCNs), which provide interconnections among different servers within a datacentre as well as interfaces to the Internet. Typically, DCNs include several tiers, namely edge, aggregation and core.- In order to reduce energy consumption and increase bandwidth, the majority of the research efforts so far have been focusing on optical interconnects (e.g., reviewed in [1]) for core/aggregation tiers (i.e., switching among different racks). It should be noted that the power consumed by the switches at the edge tier (i.e., at the top of the rack ToR), which interconnect the servers located in the same rack, is dominant (up to 90% of the total power consumed by all types of switches in DCNs [4]) because of a huge number of ToR switches. Therefore, improving energy-efficiency at the level of ToR should be considered in the first place in order to decrease the overall DCN power consumption. Optical interconnects can be used to increase the energy efficiency at the ToR. On the other hand, to design proper optical interconnects at ToR it is of high importance to understand the characteristic of the traffic generated by the servers and its specific requirements. A number of key points (such as traffic locality, multicast capability, variable flow capacity, burstiness, etc.) that are summarized from the literature [5-7] should be taken into account. However, there have been very few studies on this problem. Therefore, we would like to discuss and compare several possibilities based on optical solutions, which can offer dynamic and flexible optical connections for datacentre traffic within the rack.
2014 16th International Conference on Transparent Optical Networks (ICTON), 2014
ABSTRACT The growing popularity of cloud and multimedia services is increasing the traffic volume... more ABSTRACT The growing popularity of cloud and multimedia services is increasing the traffic volume that each datacenter (DC) needs to handle. As a consequence, the serious bottlenecks in DC networks in terms of both capacity and energy consumption need to be addressed. DC networks typically consist of edge tier, aggregation tier and core tier, which interconnect different servers within a DC as well as provide the interfaces to the Internet. Current large-scale DC network architectures are based on the fat-tree three-tiers topology [1] and on electronic switches, which are not able to scale to meet future traffic requirements in a sustainable manner. Reducing the power required by the inter- and intra-rack communication inside DCs through use of optical technology opens a way to solve this problem. However, the current optical switching technologies are not able to support the dynamic DC traffic, and hence, new optical interconnect architectures are needed. Several optical switching architectures have been recently proposed to replace the aggregation and core tiers of current DC networks with a high-capacity optical switch [1][2]. However, the largest amount of energy in current DC networks is consumed in the edge tier by the electronic top-of-the-rack (ToR) switches. Therefore, the optical switching in the aggregation-core tier doesn't solve the problem. Moreover, the majority of the optical DC network architectures proposed so far can be categorized as optical circuit switching or optical packet switching. Unfortunately, there are certain limitations associated with these optical switching technologies for their application in DC networks. Namely, optical circuit switching architectures are not able handle the bursty and highly variable DC traffic while optical packet switching usually makes use of electronic buffers, which limit scalability and increase energy consumption. To reduce the energy consumption in the edge tier, we propose a novel optical broadcast-and-select - rchitecture at the ToR. In this architecture, each server is equipped with an optical network interface (ONI) and is connected to the other servers in the same rack through a N×2 coupler, where N represents the number of servers in the rack. In addition, in order to provide both fine switching granularity and high scalability, we propose the use of the elastic optical networking paradigm [3]. Consequently, each ONI will be equipped with a bandwidth variable transceiver (BVT), which provides the ability to tune wavelength and change dynamically the number of the occupied spectral slots. In this way, the capacity can be varied from 1 Gb/s to 100 Gb/s and beyond on a per-server level. On the other side, the inter-rack communications are handled by a large singlesided optical core switch. One of the commercially available single-sided switches is fabricated using the beam steering technology [4], where the maximum number of switch ports available so far is 192 and a 500-port matrix is under development. Larger single-sided switches can be realized by combining several stages of smaller switch matrices. The results of a preliminary study show that the proposed architecture is able to significantly reduce the energy consumption with respect to other solutions [1][2].
ABSTRACT The expected growth of traffic demand may lead to a dramatic increase in the network ene... more ABSTRACT The expected growth of traffic demand may lead to a dramatic increase in the network energy consumption, which needs to be handled in order to guarantee scalability and sustainability of the infrastructure. There are many efforts to improve energy efficiency in communication networks, ranging from the component technology to the architectural and service-level approaches. Because data centers and content delivery networks are responsible for the majority of the energy consumption in the information and communication technology sector, in this paper we address network energy efficiency at the architectural and service levels and propose a unified network architecture that provides both intra-data-center and inter-data-center connectivity together with interconnection toward legacy IP networks. The architecture is well suited for the carrier cloud model, where both data-center and telecom infrastructure are owned and operated by the same entity. It is based on the hybrid optical switching (HOS) concept for achieving high network performance and energy efficiency. Therefore, we refer to it as an integrated HOS network. The main advantage of the integration of core and intra-data-center networks comes from the possibility to avoid the energy-inefficient electronic interfaces between data centers and telecom networks. Our results have verified that the integrated HOS network introduces a higher number of benefits in terms of energy efficiency and network delays compared to the conventional nonintegrated solution. At the service level, recent studies demonstrated that the use of distributed video cache servers can be beneficial in reducing energy consumption of intra-data-center and core networks. However, these studies only take into consideration conventional network solutions based on IP electronic switching, which are characterized by relatively high energy consumption. When a more energy-efficient switching technology, such as HOS, is employed, the advantage of using distributed video cache servers becomes less obvious. In this paper we evaluate the impact of video servers employed at the edge nodes of the integrated HOS network to understand whether edge caching could have any benefit for carrier cloud operators utilizing a HOS network architecture. We have demonstrated that if the distributed video cache servers are not properly dimensioned they may have a negative impact on the benefit obtained by the integrated HOS network.
Abstract In this paper we analyze three possible optical network architectures for the next gen-e... more Abstract In this paper we analyze three possible optical network architectures for the next gen-eration Internet core. Firstly, we consider an implementation of a current core network based on the IP/MPLS control plane and electronic switches. Then, we refer to two possible implementations of a Hybrid Optical Switching (HOS) network, namely all-optical hybrid HOS and optical/electronic hybrid HOS. HOS is a new switching paradigm that combines circuits, bursts and packets on the same network, and has the potential to reduce energy ...
Providing wireless broadband access to rural and remote areas is becoming a big challenge for wir... more Providing wireless broadband access to rural and remote areas is becoming a big challenge for wireless operators, mostly because of the need for a cost-effective and low energy consuming mobile backhaul. However, to the best of our knowledge, energy consumption of different options for backhauling of future rural wireless broadband networks has not been studied yet. Therefore, in this paper we assess the energy consumption of future rural wireless broadband network deployments and backhaul technologies. In the wireless segment, two deployment strategies are considered, one with macro base station only, and one with small base stations. In the backhaul segment, two wireless, i.e., microwave and satellite, and one optical fiber based (i.e., long reach passive optical networks) solutions are considered. These options are compared in terms of their ability to satisfy coverage, capacity and QoS requirements of a number of rural users in the time span that goes from 2010 until 2021. From the presented results it is possible to conclude that wireless backhaul solutions can significantly increase the energy consumption of the access network. In contrast, the long reach PON based backhaul has much higher energy efficiency and in the long term might be a better choice for wireless operators
ABSTRACT To address the urgent need for high-capacity, scalable and energy-efficient data center ... more ABSTRACT To address the urgent need for high-capacity, scalable and energy-efficient data center solutions, we propose a novel data center network architecture realized by combining broadcast-and-select approach with elastic channel spacing technology. We demonstrate that the proposed architecture is able to scale efficiently with the number of servers and offers lower energy consumption at a competitive cost compared to the existing solutions.
—Each mobile network architecture able to meet the traffic requirements of future 5G services com... more —Each mobile network architecture able to meet the traffic requirements of future 5G services comes with its own set of benefits vs. requirements for the radio and the transport segments. This paper focuses on the energy performance of four mobile network architectures, each one with different splitting options for the baseband processing functions. The radio segment under exam is based on a new radio access technology referred to as 5G-NX, while the transport segment is based on wavelength division multiplexing (WDM). The energy consumption of each mobile network architecture is weighted against (i) the benefits for the radio segment as a function of the level of centralization of the baseband processing resources and (ii) the required transport capacity and consequently the power consumption levels needed to accommodate the backhaul, midhaul, and/or fronthaul traffic generated at each base station. Our results show that a fully centralized radio access network (C-RAN) with centralization of all the baseband functions is not a practical approach for 5G mobile networks, while a partially centralized C-RAN architecture in which the physical layer baseband processing is performed at the base station site represents a promising solution.
Mobile networks are the largest contributor
to the carbon footprint of the telecom sector and
the... more Mobile networks are the largest contributor to the carbon footprint of the telecom sector and their contribution is expected to rapidly increase in the future due to the foreseen traffic growth. Therefore, there is an increasing urgency in the definition of green mobile network deployment strategies. This paper proposes a four-step design and power assessment methodology for mobile networks, taking into consideration both radio and transport segments. A number of mobile network deployment architectures for urban residential areas based on different radio (i.e., macro base station, distributed indoor radio, femto cell) and transport (i.e., microwave, copper, optical fiber) technologies are proposed and evaluated to identify the most energy efficient solution. The results show that with low traffic the conventional macro base station deployment with microwave based backhaul is the best option. However, with higher traf- fic values heterogeneous networks with macro base stations and indoor small cells are more energy effi- cient. The best small cell solution highly depends on the transport network architecture. In particular, our results show that a femto cell based deployment with optical fiber backhaul is the most energy efficient, even if a distributed indoor radio architecture (DRA) deployment with fiber fronthaul is also a competitive approach.
Abstract—Hybrid optical switching (HOS) is a switching paradigm that aims to combine optical circ... more Abstract—Hybrid optical switching (HOS) is a switching paradigm that aims to combine optical circuit switching (OCS), optical burst switching (OBS) and optical packet switching (OPS) on the same network. In this paper we present a control plane for HOS networks. The control plane employs GMPLS for configuring the virtual topology, and a HOS control layer for performing the resource reservation and data scheduling. Furthermore, two node architectures are introduced to be managed by the proposed control plane, namely all- ...
2014 16th International Conference on Transparent Optical Networks (ICTON), 2014
ABSTRACT Datacentres are experiencing a tremendous increase in the amount of network traffic due ... more ABSTRACT Datacentres are experiencing a tremendous increase in the amount of network traffic due to cloud services and many other emerging applications. It is expected that the required bandwidth for an exascale supercomputer node will grow 20 times every 4 years (i.e., 20Pb/s in 2016 and 400Pb/s in 2020) [1]. However, the total power consumption that can be afforded by one datacentre is only allowed to increase at a much lower rate (i.e., 2 times every 4 years, 10MW in 2016 and 20MW in 2020) due to thermal dissipation constraints [1]. The consumers of energy in datacentres are IT equipment (e.g. servers, network equipment, etc.) and other supporting facilities (e.g. lighting, cooling, etc.). In order to identify how efficiently a datacentre uses its power, a measure called power usage effectiveness (PUE) is defined as the ratio of the total facility power to the IT equipment power. Many efforts have been put on reducing PUE. For instance, a smart selection of datacentre location could greatly reduce the energy required for cooling and significantly improve PUE. It was very recently reported that Facebook carefully chose the location and launched Arctic datacentre (consisting of three 28,000 square-meter buildings) in Sweden [2]. By utilizing icy conditions in the Arctic Circle, their datacentre can reach a PUE around 1.07 [2]. Such a low level of PUE implies that in modern datacentres major focus on energy savings should be moved to IT equipment. Currently, network equipment in a datacentre may take up to approximately 20% of the total energy consumed by IT equipment and this value is expected to grow in the future [3]. Thus, in order to sustainably handle ever-increasing traffic demand it becomes of extreme importance to address the energy consumption issue in datacentre networks (DCNs), which provide interconnections among different servers within a datacentre as well as interfaces to the Internet. Typically, DCNs include several tiers, namely edge, aggregation and core.- In order to reduce energy consumption and increase bandwidth, the majority of the research efforts so far have been focusing on optical interconnects (e.g., reviewed in [1]) for core/aggregation tiers (i.e., switching among different racks). It should be noted that the power consumed by the switches at the edge tier (i.e., at the top of the rack ToR), which interconnect the servers located in the same rack, is dominant (up to 90% of the total power consumed by all types of switches in DCNs [4]) because of a huge number of ToR switches. Therefore, improving energy-efficiency at the level of ToR should be considered in the first place in order to decrease the overall DCN power consumption. Optical interconnects can be used to increase the energy efficiency at the ToR. On the other hand, to design proper optical interconnects at ToR it is of high importance to understand the characteristic of the traffic generated by the servers and its specific requirements. A number of key points (such as traffic locality, multicast capability, variable flow capacity, burstiness, etc.) that are summarized from the literature [5-7] should be taken into account. However, there have been very few studies on this problem. Therefore, we would like to discuss and compare several possibilities based on optical solutions, which can offer dynamic and flexible optical connections for datacentre traffic within the rack.
2014 16th International Conference on Transparent Optical Networks (ICTON), 2014
ABSTRACT The growing popularity of cloud and multimedia services is increasing the traffic volume... more ABSTRACT The growing popularity of cloud and multimedia services is increasing the traffic volume that each datacenter (DC) needs to handle. As a consequence, the serious bottlenecks in DC networks in terms of both capacity and energy consumption need to be addressed. DC networks typically consist of edge tier, aggregation tier and core tier, which interconnect different servers within a DC as well as provide the interfaces to the Internet. Current large-scale DC network architectures are based on the fat-tree three-tiers topology [1] and on electronic switches, which are not able to scale to meet future traffic requirements in a sustainable manner. Reducing the power required by the inter- and intra-rack communication inside DCs through use of optical technology opens a way to solve this problem. However, the current optical switching technologies are not able to support the dynamic DC traffic, and hence, new optical interconnect architectures are needed. Several optical switching architectures have been recently proposed to replace the aggregation and core tiers of current DC networks with a high-capacity optical switch [1][2]. However, the largest amount of energy in current DC networks is consumed in the edge tier by the electronic top-of-the-rack (ToR) switches. Therefore, the optical switching in the aggregation-core tier doesn't solve the problem. Moreover, the majority of the optical DC network architectures proposed so far can be categorized as optical circuit switching or optical packet switching. Unfortunately, there are certain limitations associated with these optical switching technologies for their application in DC networks. Namely, optical circuit switching architectures are not able handle the bursty and highly variable DC traffic while optical packet switching usually makes use of electronic buffers, which limit scalability and increase energy consumption. To reduce the energy consumption in the edge tier, we propose a novel optical broadcast-and-select - rchitecture at the ToR. In this architecture, each server is equipped with an optical network interface (ONI) and is connected to the other servers in the same rack through a N×2 coupler, where N represents the number of servers in the rack. In addition, in order to provide both fine switching granularity and high scalability, we propose the use of the elastic optical networking paradigm [3]. Consequently, each ONI will be equipped with a bandwidth variable transceiver (BVT), which provides the ability to tune wavelength and change dynamically the number of the occupied spectral slots. In this way, the capacity can be varied from 1 Gb/s to 100 Gb/s and beyond on a per-server level. On the other side, the inter-rack communications are handled by a large singlesided optical core switch. One of the commercially available single-sided switches is fabricated using the beam steering technology [4], where the maximum number of switch ports available so far is 192 and a 500-port matrix is under development. Larger single-sided switches can be realized by combining several stages of smaller switch matrices. The results of a preliminary study show that the proposed architecture is able to significantly reduce the energy consumption with respect to other solutions [1][2].
ABSTRACT The expected growth of traffic demand may lead to a dramatic increase in the network ene... more ABSTRACT The expected growth of traffic demand may lead to a dramatic increase in the network energy consumption, which needs to be handled in order to guarantee scalability and sustainability of the infrastructure. There are many efforts to improve energy efficiency in communication networks, ranging from the component technology to the architectural and service-level approaches. Because data centers and content delivery networks are responsible for the majority of the energy consumption in the information and communication technology sector, in this paper we address network energy efficiency at the architectural and service levels and propose a unified network architecture that provides both intra-data-center and inter-data-center connectivity together with interconnection toward legacy IP networks. The architecture is well suited for the carrier cloud model, where both data-center and telecom infrastructure are owned and operated by the same entity. It is based on the hybrid optical switching (HOS) concept for achieving high network performance and energy efficiency. Therefore, we refer to it as an integrated HOS network. The main advantage of the integration of core and intra-data-center networks comes from the possibility to avoid the energy-inefficient electronic interfaces between data centers and telecom networks. Our results have verified that the integrated HOS network introduces a higher number of benefits in terms of energy efficiency and network delays compared to the conventional nonintegrated solution. At the service level, recent studies demonstrated that the use of distributed video cache servers can be beneficial in reducing energy consumption of intra-data-center and core networks. However, these studies only take into consideration conventional network solutions based on IP electronic switching, which are characterized by relatively high energy consumption. When a more energy-efficient switching technology, such as HOS, is employed, the advantage of using distributed video cache servers becomes less obvious. In this paper we evaluate the impact of video servers employed at the edge nodes of the integrated HOS network to understand whether edge caching could have any benefit for carrier cloud operators utilizing a HOS network architecture. We have demonstrated that if the distributed video cache servers are not properly dimensioned they may have a negative impact on the benefit obtained by the integrated HOS network.
Abstract In this paper we analyze three possible optical network architectures for the next gen-e... more Abstract In this paper we analyze three possible optical network architectures for the next gen-eration Internet core. Firstly, we consider an implementation of a current core network based on the IP/MPLS control plane and electronic switches. Then, we refer to two possible implementations of a Hybrid Optical Switching (HOS) network, namely all-optical hybrid HOS and optical/electronic hybrid HOS. HOS is a new switching paradigm that combines circuits, bursts and packets on the same network, and has the potential to reduce energy ...
Providing wireless broadband access to rural and remote areas is becoming a big challenge for wir... more Providing wireless broadband access to rural and remote areas is becoming a big challenge for wireless operators, mostly because of the need for a cost-effective and low energy consuming mobile backhaul. However, to the best of our knowledge, energy consumption of different options for backhauling of future rural wireless broadband networks has not been studied yet. Therefore, in this paper we assess the energy consumption of future rural wireless broadband network deployments and backhaul technologies. In the wireless segment, two deployment strategies are considered, one with macro base station only, and one with small base stations. In the backhaul segment, two wireless, i.e., microwave and satellite, and one optical fiber based (i.e., long reach passive optical networks) solutions are considered. These options are compared in terms of their ability to satisfy coverage, capacity and QoS requirements of a number of rural users in the time span that goes from 2010 until 2021. From the presented results it is possible to conclude that wireless backhaul solutions can significantly increase the energy consumption of the access network. In contrast, the long reach PON based backhaul has much higher energy efficiency and in the long term might be a better choice for wireless operators
ABSTRACT To address the urgent need for high-capacity, scalable and energy-efficient data center ... more ABSTRACT To address the urgent need for high-capacity, scalable and energy-efficient data center solutions, we propose a novel data center network architecture realized by combining broadcast-and-select approach with elastic channel spacing technology. We demonstrate that the proposed architecture is able to scale efficiently with the number of servers and offers lower energy consumption at a competitive cost compared to the existing solutions.
Uploads
to the carbon footprint of the telecom sector and
their contribution is expected to rapidly increase in
the future due to the foreseen traffic growth. Therefore,
there is an increasing urgency in the definition
of green mobile network deployment strategies. This
paper proposes a four-step design and power assessment
methodology for mobile networks, taking into
consideration both radio and transport segments. A
number of mobile network deployment architectures
for urban residential areas based on different radio
(i.e., macro base station, distributed indoor radio,
femto cell) and transport (i.e., microwave, copper,
optical fiber) technologies are proposed and evaluated
to identify the most energy efficient solution. The
results show that with low traffic the conventional
macro base station deployment with microwave based
backhaul is the best option. However, with higher traf-
fic values heterogeneous networks with macro base
stations and indoor small cells are more energy effi-
cient. The best small cell solution highly depends on
the transport network architecture. In particular, our
results show that a femto cell based deployment with
optical fiber backhaul is the most energy efficient,
even if a distributed indoor radio architecture (DRA)
deployment with fiber fronthaul is also a competitive
approach.
to the carbon footprint of the telecom sector and
their contribution is expected to rapidly increase in
the future due to the foreseen traffic growth. Therefore,
there is an increasing urgency in the definition
of green mobile network deployment strategies. This
paper proposes a four-step design and power assessment
methodology for mobile networks, taking into
consideration both radio and transport segments. A
number of mobile network deployment architectures
for urban residential areas based on different radio
(i.e., macro base station, distributed indoor radio,
femto cell) and transport (i.e., microwave, copper,
optical fiber) technologies are proposed and evaluated
to identify the most energy efficient solution. The
results show that with low traffic the conventional
macro base station deployment with microwave based
backhaul is the best option. However, with higher traf-
fic values heterogeneous networks with macro base
stations and indoor small cells are more energy effi-
cient. The best small cell solution highly depends on
the transport network architecture. In particular, our
results show that a femto cell based deployment with
optical fiber backhaul is the most energy efficient,
even if a distributed indoor radio architecture (DRA)
deployment with fiber fronthaul is also a competitive
approach.