towards a convergent digital home network infrastructure

S. Nowak et al.: Towards a Convergent Digital Home Network Infrastructure 1695

Contributed Paper Manuscript received 10/13/11 Current version published 12/27/11 Electronic version published 12/27/11. 0098 3063/11/$20.00 © 2011 IEEE

Towards a Convergent Digital Home Network Infrastructure

Stefan Nowak, Member, IEEE, Falk-Moritz Schaefer, Member, IEEE, Marcin Brzozowski, Rolf Kraemer, Member, IEEE, and Ruediger Kays, Member, IEEE

Abstract —Many communication standards are available to

set up consumer home networks. An intelligent combination of wired and wireless communication technologies allows exploiting many technology specific advantages while compensating disadvantages. Such a convergent digital home network infrastructure increases robustness, coverage range and availability of applications and services. In this paper, we discuss the general concept of such home networks. We present the Inter-MAC convergence sublayer as a very first approach to this concept. With the help of a typical scenario we demonstrate its feasibility. The recently initiated standardization activity IEEE P1905.1 is introduced. A global standard for convergent digital home networks can be the basis for a user-friendly network of consumer electronic devices in the home.

Index Terms — Convergent Digital Home Network, IEEE P1905.1, Inter-MAC, Hybrid Home Network.

I. INTRODUCTION

Recently, the IEEE working group P1905.1 has been established and started developing a global standard for Convergent Digital Home Networks (CDHNs) [1]. The main concept of CDHNs is to exploit the heterogeneity of communication technologies available in today’s home environments to improve the overall connectivity and Quality of Experience (QoE). This is achieved by integrating wired and wireless communication technologies into one convergent home network infrastructure.

Although several communication standards are available to set up consumer home networks, there will not be a single transmission technology which is able to efficiently support

Part of the research leading to these results has received funding from the

European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement n° 213311 also referred to as OMEGA.

Stefan Nowak and Falk-Moritz Schaefer are with the Communication Technology Institute, Department of Electrical Engineering and Information Technology, TU Dortmund University, Dortmund, Germany (e-mail: [email protected]; [email protected]).

Marcin Brzozowski is with the Wireless Communication Systems Department of the Institute for High Performance Microelectronics (IHP), Frankfurt(Oder), Germany (e-mail: [email protected]).

Rolf Kraemer is head of the Wireless Communication Systems Department of the Institute for High Performance Microelectronics (IHP), Frankfurt(Oder), Germany (e-mail: [email protected]).

Ruediger Kays is head of the Communication Technology Institute, Department of Electrical Engineering and Information Technology, TU Dortmund University, Dortmund, Germany (e-mail: [email protected]).

all applications and services in home networks. Many of these applications and services put diverse requirements on the underlying network or even depend upon a dedicated technology. Anyway, the desired flexibility can be achieved by integrating existing and emerging digital transmission technologies into a single convergent home network. An intelligent combination of wired and wireless technologies seems to be a promising solution in terms of robustness, availability and coverage range. Due to this flexibility new applications and services become possible. Hence, a generally accepted CDHN standard can have a significant impact on many consumer electronic (CE) devices.

Thanks to the increasing capacity of broadband access networks (e.g. fiber-to-the-home, very high speed digital subscriber line or cable internet), already today network operators are able to provide their customers with a rich variety of services, e.g. IPTV or media on demand. As the capacity of access networks increases, the home network more and more turns into a bottleneck for such high data rate services. However, the digital content has to be distributed somehow to be made available everywhere in the home. At the same time, the number and heterogeneity of CE devices, e.g. TV sets, set-top boxes, tablet PCs etc., is constantly increasing. Above that, smart home appliances are currently entering the home network market. For all this, a reliable and robust communication infrastructure in the home is required. This infrastructure needs to be retrofittable, in the best case without new wires. Furthermore, it has to be easy to install, easy to maintain as well as easy to use.

The concept of CDHNs directly tackles these issues by implementing a convergence mechanism below the Internet Protocol (IP), i.e. the network layer. As IP is agnostic about the underlying transmission technologies and therefore cannot incorporate technology specific features, the heterogeneous network infrastructure needs to be combined on a lower layer. Only that way homogeneous access to the network can be guaranteed for high data rate services and applications including seamless link switching and detailed Quality of Service (QoS) management. Although convergence of technologies does usually not happen in the CE industry, this does not hold for communication technologies used by CE devices. This is due to the mere fact that wired and wireless technologies coexist in typical home networks. Especially, wireless technologies are needed to allow for portable applications. Smart home appliances will certainly rely on a different type of technology as multimedia streaming does.

1696 IEEE Transactions on Consumer Electronics, Vol. 57, No. 4, November 2011

Therefore, the IEEE P1905.1 working group defines abstraction layers which are located on top of different technology-dependent medium access control (MAC) layers. Thereby, a single interface for all technologies can be provided to upper layers, e.g. IP or middleware layers. The abstraction layer shall support dynamic interface selection for the transmission of packets arriving from any interface. The standard is supposed to specify procedures, protocols and guidelines to provide a simplified user experience with respect to network management and network extension. Furthermore, neighbor and topology discovery as well as path selection and QoS negotiation, network control and management are considered. Currently, four communication technologies are addressed, i.e. IEEE 802.3, IEEE 802.11, MoCA 1.1 (Media over Cable) and IEEE P1901. The standard is supposed to be extensible to include future home networking technologies, too. The first products with a single chip solution, which are compliant to the IEEE P1905.1 standard, are expected to be released in the near future.

In this paper, the general concept of CDHNs is introduced. Emphasis is put on its significance for consumer home networks and CE devices. An important step towards a CDHN infrastructure is achieved by the Inter-MAC concept [2], which is also addressed within this paper. A very first implementation and a proof-of-concept demonstration of a CDHN are presented in this paper. The remainder is organized as follows. In Section II, the general concept of CDHNs is introduced. Section III summarizes relevant work on convergence mechanisms. The Inter-MAC sublayer is described in detail in Section IV. Furthermore, the first prototypic implementation of the Inter-MAC sublayer is reviewed. Based on this implementation, an exemplary home network scenario is sketched and evaluated in Section V. Finally, in Section VI we draw a conclusion and point out future needs for research.

II. CONVERGENT DIGITAL HOME NETWORKS

A. Technologies for CDHNs

In Fig. 1, an exemplary home network setup is shown. There are several typical CE devices scattered across the home. Each device may be associated with one or more applications and is equipped with one or more communication interfaces. A broadband access network provides the consumer with very high data rates in both directions, i.e. uplink and downlink. Based on power line communication (PLC), a stable and robust backbone network can be set up, which is capable of delivering high data rates with good robustness and coverage range. For example, the two competing standards IEEE 1901 [3] and ITU G.hn [4] will offer data rates of up to approximately 1 Gb/s. In this way, existing cabling can easily be reused. In contrast to this, Ethernet [5] is a widespread solution for robust backbone networks; however, cabling might have to be retrofitted. In addition, a radio media network based on the widely deployed family of wireless local area network (WLAN) standards based on IEEE 802.11 [6][7] connects end devices without need for new wires.

Fig. 1. Example home network setup showing different devices, applications and transmission media.

Intelligent home appliances can be integrated by a low-rate, but very reliable wireless control/sensor network. IEEE 802.15.4 [8], Z-Wave or Bluetooth low energy technologies [9] can be used for this purpose. The control network may also be used for the overall management of the network including signaling tasks, since it is highly scalable and offers a large coverage range as well as high robustness. For instance in [10], IEEE 802.15.4 has been combined with a WLAN based on IEEE 802.11 to reliably deliver high rate media content with high QoS requirements.

The “last meter” between a set-top box and a media rendering device can either be established by a very high rate wireline connection, e.g. an HDMI cable, or by an ultra-high rate wireless communication link. Especially for portable devices the latter represents a comfortable and convenient solution. Such a wireless connectivity can be based on the upcoming IEEE 802.11ad standard [11] operating in the 60 GHz ISM band. Additionally, there are emerging technologies which become available for consumers soon, e.g. visible light communication [12] or infrared light-communication.

B. Convergence Mechanism and Topology Considerations

Each networking technology is associated with a specific or limited range of applications. The devices use separated and dedicated network interfaces. The goal of CDHNs is to overcome the separate treatment of technology domains. All available technologies are integrated into a single, logically homogeneous network. As a result, each device accesses the home network by exactly a single network layer interface. Applications and services become decoupled from a specific networking technology and “see” the home network simply in its entirety. To achieve this convergence, multiple data link layers have to be integrated below IP within the communication protocol stack.

In general, a CDHN is characterized by a mesh topology, which provides path redundancy (over different technology-dependent links) and an increased coverage range. The heterogeneity within the network is hidden from the network layer and from the consumer, i.e. from services and applications.


Fig. 2. Convergent Digital Home Network, technology-dependent and technology-independent views.

Fig. 2 shows a CDHN topology comprising three technology domains. There are devices which only support one technology, whereas others support two or even all three technologies available in this example. Those devices may work as bridges between two technologies. Looking down from a network layer perspective, the network looks homogeneous. The network layer is provided with exactly one interface for all available technologies. Legacy devices, which do not support CDHN functionality, are outside the network, but can stay connected through an edge device supporting CDHN functionality. In case a device offers interfaces to more than just one transmission technology, the most appropriate technology for the requested communication has to be selected. By multi-hop communication there can be several paths in the network to connect two devices.

These paths again can consist of several links using different technologies. Hence, it is necessary to select the most appropriate path within the network. Such paths can differ with respect to their support of different QoS criteria. Whereas one path may introduce only very small latency, another one might be much more reliable in terms of packet errors. Devices supporting more than just one technology have to switch between different technologies when serving as interim hop.

C. CDHN Device Architecture

Based on these considerations, we propose a generic CDHN device architecture as depicted in Fig. 3. It is introduced in the communication protocol stack as a convergence sublayer below IP as shown in Fig. 4. The main tasks of the convergence sublayer are network monitoring and link

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Fig. 3. Generic CDHN device architecture.

Fig. 4. Convergence sublayer between layer 2 and layer 3 in the ISO OSI protocol stack; different home networking technologies are integrated by means of retrofittable adapters.

monitoring as well as neighborhood discovery. Additionally, path selection and technology selection have to be performed while accounting for QoS.

The architecture can roughly be divided into entities intended for decision making and decision enforcement. In the upper part, decisions are taken based on the knowledge obtained from network monitoring and path selection algorithms. Once a decision has been made, the lower part of the architecture has to enforce this decision. For example, packets arriving from a neighbored device need to be switched to a specific technology interface.

For this, the lower part of the architecture can be thought of as a multi-technology switch which in general needs to be very fast. This switch holds a forwarding table that is maintained by the control and management entities. Switching between technologies needs to be done in a standardized way. For example, the switching part has to support a unique frame format. The control and management entities, i.e. the “intelligent” part of the architecture, are open for innovative ideas as well as efficient algorithms and strategies. Chipset manufacturers may implement the control and management


“intelligence” differently while using standardized switching formats and interfaces. The communication between both architectural parts is based on events and triggers which are exchanged between individual entities. Several services are provided to upper layers, e.g. the support of middleware.

III. RELATED WORK

A. Convergence below the Network Layer

The idea of establishing convergence in heterogeneous networks has already been reported in the literature in various contexts [13]-[19]. A widespread protocol for managing heterogeneous network topologies is the Link Layer Topology Discovery (LLTD) by Microsoft [20]. It supports wired networks based on Ethernet or PLC as well as wireless networks based on IEEE 802.11. It is a proprietary framework supporting applications or higher layer protocols in discovery of link layer topologies and QoS related measurements within a network. It does not integrate path selection or technology selection mechanisms. Furthermore, it focuses on IEEE 802.x technologies. Similar vendor specific solutions exist, however, there is also a vendor-neutral standard maintained by the IEEE, i.e. the Link Layer Discovery Protocol (LLDP) [21].

Moreover, the IEEE standard 802.21 [22][23] for Media Independent Handover (MIH) has been released in 2008. It defines entities, commands, events and services to facilitate horizontal as well as vertical handovers. The former are handovers within a single mobile access technology, whereas the latter refer to handovers between different mobile access technologies. Handover decision making and information exchange are not specified, but left for higher layers.

Therefore, the standard offers rather a generic infrastructure for the implementation of handovers. It strongly relies on the cooperation of further standardization bodies (3GPP/ 3GPP2, IEEE 802.16, IEEE 802.11) which need to define technology specific MIH service access points. Furthermore, higher layers need to be integrated with MIH functionality (e.g. MobileIP). Although there are some testbed implementations, the deployment and realization of practical handover scenarios strongly rely on the adoption by operators of mobile access networks.

B. Convergence above the Network Layer

A lot of research and development work is dedicated to middleware layers for local networks [24] and access networks [13]. Middleware layers try to introduce convergence on top of the protocol stack. Usually, they provide a unified representation of available services within the network to a wide range of applications. In contrast to convergence mechanisms on lower layers, a middleware only has limited influence on the underlying communication technology. Often a reliable network infrastructure is simply taken for granted.

C. Interim Conclusion

For a user friendly dynamic home network, service representation can be implemented by a middleware layer, whereas the underlying infrastructure can be provided by an

intelligent and dynamic technology combination on lower layers. In this way, convergence mechanisms below and above IP can complement each other.

Different methods for managing heterogeneous networks exist; however, a more comprehensive approach is required. For this topology discovery, a convergence mechanism for communication technologies and path selection for a heterogeneous meshed home network accounting for QoS need to be combined. Such an approach is represented by the Inter-MAC concept, which has been first introduced in [2]. It includes a meshed network architecture, network wide management of QoS, routing of flows within the home network as well as elaborated security concepts below the network layer. Being deeply integrated within the protocol stack, it allows significantly improving the consumer’s QoE. Furthermore, it is designed to integrate any home networking technology, both commercially available and emerging ones. Additionally, the Inter-MAC concept is designed to support legacy devices, i.e. devices within the home network without dedicated Inter-MAC functionality.

IV. INTER-MAC

A. Inter-MAC Reference Architecture

A reference architecture implementing the Inter-MAC concept has been introduced in [25]. It comprises a control plane, a data plane and a management plane. The “intelligence” of a network node is located in the control plane where information about the network state is gathered and all decisions are taken. The main components of the control plane are the path selection engine, the QoS engine, the monitoring engine and the Inter-MAC adapters. The data plane is a multi-technology switch forwarding packets based on the information maintained in a switching table. The management plane enables a network wide management, e.g. by aggregating information from all network nodes and providing an user interface. The main functional entities of the Inter-MAC sublayer are shortly outlined in the following subsections.

B. Inter-MAC Functional Entities

1) Path Selection There may be redundant paths in a CDHN, which differ in

terms of number of hops, latency, maximum throughput, reliability and robustness. Each path may consist of links using different transmission technologies. To find an end-to-end path through the CDHN across multiple hops, a path selection procedure is performed. Similarly to the Dynamic Source Routing Protocol (DSRP) [26], several signaling messages are defined. In the beginning of the path selection procedure, a path request message (PREQ) is pushed to each interface. Intermediate nodes receiving a PREQ re-broadcast the PREQ to their remaining adjacent nodes and a link metric within the PREQ is updated. A sequence number prevents from loops caused by the flooding procedure. Any feasible metric or combination of metrics can be used. It has to reflect


the QoS parameters of interest for the respective flow. The reference implementation described below uses the available link capacity across a path. Additionally, probe frames are used for link discovery and link diagnosis. After the destination node receives a PREQ, it responds with a path reply message (PREP). The source node collects all incoming PREPs and selects the most suitable path. This path is activated by sending a path confirmation message (PCNF) along the selected path. All forwarding tables of the affected nodes are updated accordingly.

2) Monitoring The path selection procedure strongly relies on the

knowledge of an individual node about the current network state. This information is collected and maintained by the monitoring engine. It receives raw information on the interface status. Based on this information, it calculates more sophisticated link statistics. In case of certain events, event subscribers, i.e. involved engines, are provided with a corresponding trigger. For example, the monitoring engine triggers the path selection engine with events such as LinkUp or LinkDown detection.

Monitoring is performed almost independently of the underlying transmission technologies. If Inter-MAC adapters are provided for a specific technology, a conversion mechanism within the adapters assists the monitoring engine in interpreting the offered information. Existing elements of PHY and MAC management information bases can be reused [27]. In contrast to this, if no detailed information is provided by the technology itself, the link capacity can be preconfigured or derived from an interface stress test. The data plane monitors the current link occupation by counting length and number of frames which have been sent and received. Furthermore, packet loss rate and delay as well as jitter can be measured.

3) Inter-MAC Adapters and Common Semantic Language To benefit from the Inter-MAC concept in the best way,

each technology should be equipped with a specific Inter-MAC adapter. It provides more precise measurements and estimations than obtainable by the technology-independent probe frame mechanism. For wireless technologies, such as IEEE 802.11n, an improved estimate can be calculated by means of an Inter-MAC adapter as described below.

To mediate between different communication technologies, a common semantic language has been developed [27]. The machine-readable language based on XML can be understood by each Inter-MAC entity. It allows for describing various service classes and application classes and provides means to describe link metrics of underlying MAC protocols. Based on these descriptions, technology-dependent conversion formulae can be derived, which enable the calculation of metrics on a technology-independent level. Example conversion formulae for wireless LAN based on IEEE 802.11 are presented in [27].

4) QoS Engine and Middleware Adapters Middleware adapters have been defined which allow for the

integration of different applications and middleware layers, such as UPnP, UPnP QoS [28] or SIP [29]. The QoS engine

HopLimit4 SequenceNumber20 QoSClass8

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Fig. 5. Inter-MAC header as proposed in [30].

communicates QoS requirements delivered by application layers or middleware layers to the Inter-MAC and performs admission control. For any QoS request, the QoS engine generates a network wide unique flow identifier and triggers the path selection engine to establish a new end-to-end path which meets the corresponding QoS requirements.

A flow can only be admitted in case there is a path that meets the associated QoS requirements or there is a flow with a lower priority that can be dropped instead. In case of heavy network congestion or link failures, flows are dropped starting with the lowest priority. 5) Packet Encapsulation and Security

An Inter-MAC header [30] is added to each packet running through the Inter-MAC sublayer. Its format is shown in Fig. 5.

A detailed security concept on the data link layer is included. Similar to IPSec, the payload is encrypted by the Inter-MAC source node and can only be decrypted by the destination node. An encryption mechanism based on CCMP [6] as well as a key management protocol with a security controller was proposed to ensure the existence of secure keys per communication pairs within the network. Furthermore, new security mechanisms, e.g. used by IPv6, can be integrated within the security concept of the Inter-MAC. On the basis of authentication mechanisms different depth of trust within the Inter-MAC network can be generated.

C. Inter-MAC Reference Implementation

The feasibility of the Inter-MAC concept is demonstrated by a reference implementation based on off-the-shelf PCs running a Linux OS. A schematic diagram of the implementation is shown in Fig. 6. Further details and a performance evaluation are described in [31]. Only a short overview of the most important aspects is given here.

As the data plane comprises time-critical functionality such as high-speed packet forwarding, it is implemented in Linux kernel space. In contrast to this, the control plane implements the network management functionality and runs in Linux user space allowing for more flexibility. The data plane adapter and the control plane interface implement the communication between user space and kernel space. The control plane maintains and modifies the forwarding table within the data plane. The data plane communicates various link events triggered by probe frames. As the data plane generates probe frames in the technology-independent code, LinkDown events


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Fig. 6. Schematic diagram of the Inter-MAC reference implementation based on a Linux OS [31]

can be detected for any technology connected to the Inter-MAC. Moreover, the data plane monitors data rates on a per stream basis and periodically reports the current statistics to the monitoring engine. The data plane core receives packets from different transmission technologies and the local interface to the network layer offered to the system. Incoming packets are forwarded according to the entries in the forwarding table.

In the current version of the Inter-MAC implementation, an adapter for IEEE 802.11n off-the-shelf network interface cards has been included. The driver has been modified to periodically report the wireless channel busy fraction [32]. The developed Inter-MAC adapter also offers a service to the control plane to inquire an estimate for the possible throughput to a specific station. Additionally, the received signal strength indicator (RSSI) for signals originating from nearby access points within the network is reported to support intra-technology handovers. Further details on the practical implementation are reported in [31].

V. EXAMPLE SCENARIO AND BENCHMARKS

The Inter-MAC reference implementation has been successfully deployed in a home network demonstration environment. Detailed benchmarks and details about the test environment are given in [31]. The IEEE 802.11n network

Fig. 7. Exemplary home network scenario.

interface cards use the 2.4 GHz ISM band with 40 MHz bandwidth and are equipped with two antennas. All results were obtained in a real network setup with commercially available products. For sake of simplicity, we describe a simple, but representative use case. To demonstrate self-configuration and self-healing capabilities enabled by the Inter-MAC, a dynamic home network scenario as depicted in Fig. 7 is considered.

In the given scenario Gigabit Ethernet is deployed as a reliable backbone for the home network. It consists of five network devices with Inter-MAC functionality, each located in a separate room. A home media server delivers two HDTV streams at approximately 20 Mb/s to legacy media clients, i.e. an hard disk recorder and an HDTV flat panel. These are connected to a network extender (N3) implementing the Inter-MAC and offering three different interfaces, i.e. PLC, WLAN and Ethernet. This is a typical situation when users watch a video while recording another one on a hard disk recorder.

As indicated in Fig. 10, the home gateway, which simultaneously serves as media server (N1), provides two Ethernet interfaces (ETH1, ETH2). So does the desktop PC in the home office (N2). A laptop located in the kitchen (N5) is equipped with a WLAN interface (WLAN) and two Ethernet interfaces. An inter-technology bridge in the hall (N4) is used to extend the coverage range of the home network by bridging Ethernet and PLC.

In Fig. 8, the traffic measured at N3 is shown depending on the respective interface and time. Fig. 9 depicts the aggregated data rate versus time which is delivered to the media devices (HDTV flat panel and hard-disk recorder) connected to N3.

The individual steps of the scenario as shown in Fig. 10 are described in the following and the individual changes of the network state are tracked:

(a) In the initial state of the setup, all devices are powered up and all associated interfaces are available. When a stream setup is requested at N1, the Inter-MAC automatically searches for the best suited path within the network. This procedure is repeated periodically. In this particular case, the path N1N2N3 has been found for both streams since only


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reliable Gigabit Ethernet connections are used (cf. Fig. 8, 0-20s). The remaining interfaces at the devices N3, N4 and N5 are exchanging probe frames as there is currently no ongoing user data traffic. In this way, the connectivity in the meshed network as well as the corresponding link capabilities can be monitored proactively.

(b) The desktop PC (N2) is turned off. N1 recognizes both interrupted Ethernet links N1N2 and N2N3. The path selection at N1 is triggered (cf. Fig. 8: 21s).

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(c) After the path selection procedure is completed, new paths have been found and the streams are assigned. Both streams are now using the path via Ethernet and PLC, i.e. N1N5N4N3. Although already transmitting one stream, the PLC link still provides a higher link capacity than the wireless link. If N5 was located closer to N3, a wireless link with better quality could have potentially been established. In this case, the second stream may have been routed via WLAN instead (N1N5N3).

Fig. 10. Subsequent steps of the presented home network scenario.


(d) The PLC link N4N3 malfunctions. The path selection at N1 is triggered once again. In this case, the path selection at N1 routes all traffic across the WLAN connection N5N3. In Fig. 8 (50-80s), it can be seen that the throughput of the wireless link jitters much more than that of the Ethernet or PLC link due to frame losses and the aggregation scheme used in IEEE 802.11n.

(e) After some time, the PLC link is detected as working again. This fact is recognized by the path selection mechanism at N1 and all user data is transmitted across the PLC link, N1N5N4N3 (cf. Fig. 8: 80-100s).

(f) The desktop PC is powered up again and the original Gigabit Ethernet links become available again. As probe frames are exchanged, the path selection engine detects the all-Ethernet path to N3. The user data is again routed via N1N2N3 (cf. Fig. 8: 100-170s).

As can be inferred from Fig. 9, almost seamless switching between different technologies is enabled by the Inter-MAC. In this example paths consist of several hops, resulting in small degradations in the QoE. However, all streams are maintained and the network reconfigured itself autonomously. By intelligent buffer concepts and efficient chipset implementations of the multi-technology switch within each device, these QoE degradations can be significantly reduced or even eliminated.

VI. CONCLUSION

In this paper, we have given an overview of the general CDHN concept and introduced a generic CDHN device architecture. The feasibility of the CDHN concept has been demonstrated by implementing the Inter-MAC sublayer. By its self-configuration and self-healing capabilities a dynamic heterogeneous and meshed home network can be set up.

Among other work, the Inter-MAC concept initiated the standardization in IEEE P1905.1. A sustainable success of the standard and further developments will strongly depend on the fact, to which extent the specification can be adapted to many different types of homes and network configurations. Furthermore, to integrate intelligent home appliances and to enable machine-to-machine communication in the home, a control network, e.g. IEEE 802.15.4 or Z-Wave, needs to be added to the set of supported communication technologies. Thereby, the overall integration of home networks into the smart grid is enabled.

All in all, there is a great need for future research work, as there are many open questions in the emerging field of convergent home networks. Efficient device and network architectures have to be identified. Furthermore, efficient algorithms for all tasks performed by CDHN devices need to be found including energy efficiency considerations, e.g. intelligent power management of devices and network interfaces. An efficient interaction of high-rate CDHN technologies with a low-rate control and sensor network still needs to be established.

ACKNOWLEDGMENT

All developments regarding the Inter-MAC, i.e. concept, architecture, algorithms and demonstrator have been initiated and developed during the FP7 ICT project OMEGA funded by the European Commission under grant agreement n° 213311. The authors would like to acknowledge all contributions of their colleagues leading to the success of the project.

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[20] MS-LLTD, “Link Layer Topology Discovery (LLTD) Protocol Specification,” Microsoft Corporation, August 30, 2010.

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BIOGRAPHIES Stefan Nowak (M’09) received his diploma degree in electrical engineering from TU Dortmund University, Germany, in 2007. Currently, he is a PhD candidate at the Communication Technology Institute of the same university. His research interests cover various aspects of digital communication systems, home networking and technology convergence in home networks.

Falk-Moritz Schaefer (M’10) received his diploma degree in Communication Engineering from TU Dortmund University, Dortmund, Germany, in 2010. In 2008 he studied at Hong Kong University of Science and Technology. Currently, he is a PhD candidate at the Communication Technology Institute, TU Dortmund University. His research interests include methods for the

management of local wireless networks. Marcin Brzozowski received his diploma degree in computer science from BTU Cottbus, Germany, in 2006. Currently he is working with embedded systems and sensor networks in IHP Germany. His research interests include computer networks and operating systems.

Rolf Kraemer (M’79) received his diploma and Ph.D. degrees in electrical engineering and computer science from the Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen, Germany, in 1979 and 1985, respectively. He worked for 15 years in R&D of communication and multimedia systems at Philips Research Laboratories in Hamburg and Aachen. Since

1998, he has been a professor of systems at the Brandenburg University of Technology, Cottbus, Germany. He also leads the Wireless Communication Systems Department of the Institute for High Performance Microelectronics (IHP), where his research focus is on wireless Internet systems, spanning from application to system-on-chip. He is cofounder and serves as technical advisor of the startup company Lesswire AG. He has published more than 150 conference and journal papers and holds 16 international patents. He is a member of the IEEE Computer Society, the VDE-ITG, and the German Informatics Society.

Ruediger Kays (M’03) received his diploma and Dr.-Ing. degrees in electrical engineering from TU Dortmund University, Germany in 1981 and 1986, respectively. He was then with Grundig AG, Germany, where he was responsible for the research and advanced development department. Since 1999, he is a professor for communications technology at TU Dortmund University. His research interests include radio technologies for local

networks, car-to-car communication and video signal processing for electronic media.

towards a convergent digital home network infrastructure

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