A Management System for PLC Networks Using SNMP ... - IEEE Xplore

A Management System for PLC Networks Using SNMP Protocol Diogo Nunes de Oliveira∗ , Thiago Lara Vasques∗ , Fl´avio Henrique Teles Vieira∗ , Get´ulio Antero de Deus J´unior∗ , Marcelo Stehling de Castro∗ , S´ergio Granato de Ara´ujo∗ , Elton Mendes de Souza† , Jos´e Gonc¸alves Vieira† , Ov´ıdio Craveiro de Oliveira J´unior† , Aderbal Borges‡ and Roberto Ibrahim Brihi Badur§ ∗ School

of Electrical and Computer Engineering Federal University of Goi´as Goiˆania, Goi´as 74.605-010 Emails: [email protected], thiago [email protected], [email protected], [email protected], [email protected], [email protected] † Energy Company of Goi´as Superintendent of New Business Goiˆania, Goi´as 74.805-180 Email: [email protected], [email protected],[email protected] ‡ Innovation Consulting Goiˆania, Goi´as 74.000-000 Email: [email protected] § BLM Invac¸o ˜ es Tecnol´ogicas Goiˆania, Goi´as 74.000-000 Email: [email protected]

of networks. The PLC technology also brings different equipments to the Internet world. All the technologies intended to provide Internet such as the PLC, must ensure the availability and correct operation of network devices. In this regard, reactive control techniques can be applied to maintain the correct and optimized operation of the network when technical problem happen. In order to reduce the need for intervention by the network administrator involving traffic and device monitoring, Network Management Systems (NMSs) have been designed and applied. An NMS is a software or a set of softwares used to monitor network devices. The NMS is responsible for verifying device information and when necessary, to notify the network administrator about the obtained results. Most of management solutions do not allow automated data modifications of network devices. Besides, free NMS solutions do not cover all management areas [10] In this paper, we present a management solution based on an open source software named Nagios, which allows the modification of values of network devices, covering all management areas [7]. The proposed management system is designed to manage Power Line Communications (PLC) networks [5] and replace proprietary management solutions which are currently used. The use of open source software brings greater control capability over the PLC network once it provides better knowledge of communication system and the possibility of adding control improvements [3].

Abstract—Access technologies for data transmission, such as xDSL, Wi-Fi and cable modem are widely used once they support high data transmission rates at low cost. Among these technologies, Power Line Communications (PLC) is an alternative promising solution. In order to get control over a telecommunication network operation, including PLC, it is necessary to use management techniques. Besides network control, these management techniques are intended to provide maximum knowledge of the system behavior and of involved devices. In this paper, we present a management solution model applied to PLC networks. In order to develop the proposed management system for PLC networks, we made use of a free software called Nagios. Practical evaluation tests showed that the proposed management model is scalable, reliable and can provide effective control of PLC networks in order to guarantee the required services to the users1 .

I. I NTRODUCTION PLC technology transmits data over power network, which presents high capilarity, due to the fact that it is present in most residences. Since most of its structure already exists, power supply concessionaries started investing in PLC technology to stop being only a power supply concessionary and to also become a telecommunication company. In the 90s, the use of computer networks with Internet access considerably expanded. The growth of Internet also increased the amount different equipments and the complexity 1 This work have been sponsored by CELG-D (Energy Company of Goi´ as Distribution) through financial support via R&D Projects regulated by ANEEL (National Agency of Electrical Energy).

978-1-4244-5010-7/10/$26.00 ©2010 IEEE

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The remainder of the paper is organized as follows. In Section II, we present an overview of the PLC network technology. Network management, Simple Network Management Protocol (SNMP), PLC networks management and NAGIOS software are discussed in Section III. In Section IV, we describe the PLC network architecture and the proposed PLC network management system. In Section V, we present some test results for the PLC management system applied to the considered network architecture. We conclude in Section VI.

III. SNMP P ROTOCOL , NAGIOS AND PLC N ETWORK M ANAGEMENT A. SNMP According to [6], network management includes provision, integration and coordination of hardware elements and software as well as testing, checking, configuration, analysis, evaluation and controlling of network resources in order to attain desired performance and quality of service requirements. Therefore, the purpose of network management is to provide information and verification tools that allow the reduction of time of equipment unavailability or communication networks services as well as to guarantee quality of service. A network management system is composed of network manager, network agents and network management protocol. The network manager is a network device that includes software that is able to collect or receive information from the managed device. The network agent is a software installed on a network device which must be managed and the network management protocol is the protocol used to exchange management information between manager and agent [9]. The Management System, which is implemented in the equipment manager, has a database of information. The database stores the information of the managed objects of the agents. The agents also have the database management, which store the values of their own managed objects. A management task can occur through a request made by the manager to the agent. The agent sends the manager a response to the consult undertaken by the manager or the manager, or the agent may notify the manager about values that the agent encountered itself without any request performed by the manager. The notification occurs when unexpected values of objects are found. According to [10], SNMP is a protocol used to manage IP network devices and uses a management database, namely MIB (Management Information Base). The management tasks are performed through nine SNMP operations. The main SNMP operations are: • Get: the operation in which the manager queries the agent for specific information, for example, how long ago did the the last boot happen or how many packets were received with error by some data communication interface; • Set: it is performed when the SNMP manager wants to modify some specific information in the MIB of the SNMP agent. Not all MIB informations can be changed by the operation set; • Response: the package that contains the SNMP response to the the query performed after the reception of an operation get.

II. PLC N ETWORK T ECHNOLOGY OVERVIEW The PLC physical environment is very hostile for data transmission, because it was not designed for this purpose. Therefore, there is a series of power line properties that adversely affect communications such as cable attenuation, multiple-path propagation and noise [5]. The PLC uses the frequency band allocated to broadcasting (shortwave communications) and part of the VHF radio frequency range used by public services (police, firefighters, civil defense). The typical range of frequencies used by the PLC network is between 1.7 MHz and 30 MHz [5]. Generally, a PLC network is made up of a concentrator device (Head End), repeaters and Customer Termination Units (Customer Premise Equipment - CPE) [3]. A. Types of Access in PLC Network Technologies According to [1], PLC networks can be of two types: indoor power line communication and outdoor power line communication. Indoor power line communication is a PLC network existing indoors, such as in homes and in commercial buildings. In these environments, interference sources are caused mostly by lighting equipment, small engines and other small electric equipment. Outdoor power line communication is a PLC network existing in open environment, where the PLC signal travels over the transmission and distribution electricity system. In this case, the performance is more affected by lightning, switching, the influence of capacitor banks, transformers and electrical engines. B. Chipsets Chipset is the equipment processor that allows high rates of data transmission, relocation of frequency range and all management features provided by specific protocols such as the Simple Network Management Protocol (SNMP) [10]. There are several chipset manufacturers that are at the forefront of research aimed at developing PLC technology, specifically in research areas of lower susceptibility to noise and high rates of data transmission. In the early days of the BPL technology, the first generation of PLC devices were able to provide a transmission rate up to 14 Mbps. In the second and current generation, the developed chipsets raised this rate up to 200 Mbps. The third generation promises rates between 400 Mbps and 1Gbps [3].

B. Nagios Nagios is a free software program under the GPL (General Public License) license version 2 and it was designed for Linux operating systems Unix [7]. It is is a network and system monitoring application that verifies equipments and services,

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and generates alarms when required. Some Nagios key features are: • Network information monitoring; • Network equipment monitoring; • Easy creation of plugins, which allow the administrator to develop their own findings; • Possibility of creating hierarchy of devices, allowing detection and distinction between equipment that are ’dead’ and equipment that are out of reach; • Ability to define event handlers, which enables a proactive management. There are several free tools with open source code, which fit or not in GPL, and have one or even various features simular to Nagios. Besides the fact that Nagios has all those features described, it can be used for most of the functional areas of network management applied to networks PLC/BPL. Nagios uses the client/server model, but it differs from other NMS implementations based on the same model. All management is done by Nagios using plugins. The plugins are external programs developed in any compiled or interpreted language that follows the Posix pattern (development pattern used for Linux/Unix). Plugins must be developed as a program that can be executed by the running operating system (Linux or Unix), or should work as a command that can be run manually from a shell. Then, Nagios must be configured to run the plugin and wait for a returned value, which represents the state of the service or device that is being monitored. Each value has a particular meaning to Nagios. The possible values are 0, which means an OK status; 1, which means that device or service deserves atention; 2, which means the resource is in critical state or; 3, unknown/undefined.

information that are specific to DS2 MIB are: device internal temperature (plSysTemp.0), signal-to-noise ratio (plPhyByMACRXSNR), number of equipments connected to the master PLC (plMACNumConnectedNodes), type (plSysNodeType) and method of operation of the equipment (plSysNodeMode), IP addressing (plSysStaticIPAddress), working frequency (plBasicCentralFrequency) and bandwidth (plBasicBandwidth). The main advantage of our management system is its automated proactive capability. Unfortunately, this type of proactive capability (automatic) can only be provided to DS2 chipset based PLC devices. That is, the management of other chipsets is not automatic, i.e., the device responses must be made by a human being. Such function can be provided by any other common management system. IV. D ESIGN OF PLC N ETWORK M ANAGEMENT S YSTEM U SING SNMP A. Architecture of the PLC/DS2 Network Nagios is a management system able to perform accounting, performance and failure management, but it is not able to cover two functional areas of management: security and configuration. These two functional areas are as important as the other three. Therefore, to replace the proprietary management systems, which are able to cover all functional areas of management, it was necessary to integrate solutions to Nagios server which could fullfill the NMS, covering all functional areas of management [3]. Through the use of network sniffing tools debugging IMS (Ilevo NMS), it was possible to find out in detail how to run the configuration and security steps. A PLC device based on DS2 chipset gets its configuration through remote boot. When it is connected to the network, it searches for a Dynamic Host Control Protocol (DHCP) server. When this server is found, the network settings, such as IP address, are obtained from it. Among the all information retrieved, the device also retrieves the IP number of the Trivial File Transfer Protocol (TFTP) server and the name of the configuration file to be used by this equipment. Thus, the device retrieves the file configuration from that TFTP server. This file indicates how the PLC equipment will work. In DS2 chipsets, the Headend (HD) is responsible for performing access control of the PLC modems (CPEs). It might allow access to all PLC modems, perform control access based on MAC address list or implement authentication through the Remote Authentication Dial In User Service (RADIUS). Table I compares the proposed NMS and other proprietary known PLC NMS. The use of free softwares as base of this PLC NMS turns it into a very flexible, scalable and pro-active PLC NMS. In [11], a PLC NMS is presented that was designed to manage a PLC Network Trial implemented in Korea. As the Korea PLC NMS, our proposal (CELG/UFG NMS) was developed based on concepts such as the use of free software and the capability to manage PLC devices from different manufacturers. However, the main advantage of our proposal is that the amount of available information is greater, since our PLC NMS does not use proxy SNMP agent based on

C. PLC Network Management In this paper, we present a PLC management solution. This network management system was designed to be used by Energy Company of Goi´as (CELG), which has partnered with Federal University of Goi´as (UFG) to carry out a research and development project involving the management of PLC networks [8]. This work also presents the results obtained in managing a network using this PLC NMS. The proposed PLC NMS was developed using Nagios as the central software. To perform the PLC network management, the SNMP protocol should be used. Notice that one of our objectives is to propose a management system that is able to monitor devices from different PLC manufacturers. Different manufacturers often develop specific MIBs. However, the major PLC manufacturers use DS2 chipset [3]. Once the information management is defined in the chipset, all equipments with the same chipset gather the same MIB. Therefore, it was possible to develop a management system capable of managing PLC networks that consist of different devices from different manufacturers. Since the PLC devices share the same objects in their MIB, it was necessary to conduct a verification of the objects in DS2 Chipset MIB and then develop the corresponding plugins in Nagios capable of managing PLC network [3]. Some important

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TABLE I C OMPARISON B ETWEEN M OST OF P ROPRIETARY PLC NMS S AND THE P ROPOSED PLC NMS. Technology Control Automated Fault Management Manage Heterogeneous Devices Management Scalability Software Documentation

Most Proprietary Average No No/Low No/Low Manufacturer

AES cryptographic standard in conjunction to SNMP protocol. This initial test can be seen the first step to the implementation of the proposed PCL NMS [2]. In order to create a PLC/DS2 Management system that could completely replace proprietary solutions, all functional areas of management should be covered. That is, all existing features and functions presented by these proprietary solutions must be implemented. Thus, it was necessary to implement the same services related to configuration and security management. Due to this need, we integrated the Nagios to the following softwares: DHCP-Server, TFTP-server and FreeRadius. All of these softwares are free, following our proposal to develop a PLC NMS based on free softwares [3].

Proposed High Yes Yes High Community

a generic MIB as the Korea PLC NMS does. The proposed management system can retrieve information that is specific to DS2 PLC chipsets, such as concentrators’ temperature, transfer and reception rates between a node and its concentrator, bits per carrier, signal-noise ratio and VoIP statistics. In our PLC network testing scenario, different types of equipments were used. Table II presents the considered device manufacturers and models.

C. Management Plugins Nagios management architecture, which is based on plugins, makes this NMS a very scalable one. It is possible to develop a plugin to search for a vast quantity of information. It is also possible to create and automated pro-active NMS. It is only necessary to analyze how to gather the required information, and then develop the plugin to do such work. The proposed NMS focus on PLC management, but due to Nagios scalability, the NMS may also be used to manage other kinds of TCP/IP networks. For instance, in a network interconnected through optical fiber, it is possible to manage routers or switches used in the backbone, which makes it possible to retrieve the concentrator’s ports status. If any segment of the fiber has been broken, Nagios can detect that faulty, since it may retrieve the concentrator’s port status as down. By evaluating the MIB objects, we could develop plugins to be used by Nagios [7]. One of the designed plugins verifies any object value and compares it to the values configured as limits. If the value received is lower than the first limitting value, that service or device is assumed to be in normal condition. If the value is among the first and second value, this object is considered to be in state of alert. If the value obtained is greater than the second limiting valued, then the object is in a critical condition [3]. In order to automate the task of managing the PLC network, this developed plugin has also been implemented with the ability to take decisions and improve the performance of PLC devices. PLC devices with DS2 chipsets have an object defined in its DS2 MIB named plSysConfDownloadConf, which can be used to force the PLC device to retrieve a configuration file from the TFTP server, even if that equipment has already defined its settings during startup. Through a SNMP Set operation, the plugin can change this object value, setting it to the TFTP server IP address and the name of a file containing the configuration to be implemented to this PLC device. This will cause the equipment to search for the file on the TFTP server and implement the settings configured in the specified file. Therefore, due to the existence of the plSysConfDownloadConf object, the plugin could be developed to change the behavior of the PLC device and improve its performance [3].

TABLE II PLC D EVICES . Type Master FD FD CPE TD CPE CPE CPE

Manufacturer Ilevo Ilevo Ilevo Ilevo Ilevo Ilevo Ilevo Defidev

Model ILV2010 ILV2020 ILV2020 ILV201 ILV2010 ILV211 ILV211 AV200

Operation Headend Repeater Headend CPE Repeater CPE CPE CPE

Mode LV MV MV LV LV LV LV LV

Quantity 2 3 3 3 2 2 4 1

Figure 1 illustrates a CGI Status Map for the PLC network deployed in our research project which is composed of the components given in Table II.

Fig. 1.

CGI Status Map.

B. Implementation of the PLC Network Management System Some tests were carried out to verify how intensively the network and network manager performance can be injured by the use of cryptography algorithms. In these tests, we used the

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V. C APABILITIES AND P ERFORMANCE OF THE PLC M ANAGEMENT S YSTEM

As an example, it is possible to use this first designed plugin to analyze the signal-to-noise ratio (plPhyByMACRXSNR object). If the value obtained is out of the range of a acceptable value, the plugin sends a Set message to the device, forcing it to search for a new configuration file. This configuration file must contain the policy GENERAL SIGNAL MODE with a value different from the current one, which is set up at the device. It means that if the device is configured to work at window 13 (set of frequencies used in OFDM of PLC), it will be reconfigured to work in window 6. This modification will affect the signal-to-noise ratio [3]. Regarding network traffic control, we developed some solutions also based on inserting plugins to Nagios. We developed a plugin to choose a frequency window that provides the highest transmission and receiving rate for the PLC devices. This plugin changes the frequency window directly by a set SNMP operation. That is, it does not need to inform the TFTP server and file to be transferred to the PLC device. This plugin also sets all PLC devices to the same window and measure the average transfer and receiving rate of all PLC devices. This procedure is done for each window. The window that presents the best transfer and receiving averaged rate is chosen as the best one, and the network is configured to work in that window. We also developed another plugin concerned to managing the PLC network flows [3]. The network traffic generated by a certain device is calculated, and if that flow is detected to be above a certain value, then a Set command is sent to the PLC concentrator, forcing it to get another configuration file. The configuration file in turn must contain the policies to control traffic. For instance, if the desired traffic shaping is 128 kbps for upstream and 512 kbps for downstream, then the file must contain the lines PROFILE MAX TXPUT TX.2 = 128 and PROFILE MAX TXPUT RX.2 = 512. This action is intended to avoid network congestion [3]. Figure 2 shows a fluxogram representing the proactive behavior of the proposed PLC NMS. The same server runs the following programs: Nagios, DHCP-Server, TFTPd and NetSNMP. If Nagios detects some network or device problem or mismatch, an SNMP Set message is sent to the associated device, changing its plSysConfDownloadConf object value. The equipment in turn, retrieves the new configuration file, which must have been previously stored on the TFTP server.

Fig. 2.

Nagios monitors the equipments presented in Table II. Through the management of equipments some problems can be detected. Several features of the PLC devices are monitored by the proposed PLC NMS. Some of these features are traffic generated by the CPEs, the amount of erroneous SNMP packets that have been transmitted, latency, reception and transmission rate. Figure 3 presents the status of several statistics of one CPE. Notice that all status are represented as normal, since, acording to the warning and critical values that have been configured, Nagios could determinate the retrieved values are as expected.

Fig. 3.

CPE’s Management.

The same features are monitored on repeaters and Headends, while adding the management information of temperature. Repeaters and headends provide the current temperature in its MIB, since it is a very important information. The interruption of one of these devices due to high temperature can damage part or even the entire operation of the PLC network. Figure 4 presents the temperature history of the HeadEnd device. This screen allows the administrator to see all temperature states reached by the HeadEnd in a given time period. In Figure 4, it can be observed a Headend in critical status, which means that this equipment reached temperatures above normal. The monitoring results is represented by the colors: green, yellow and red. The green color shows that the equipment was at the correct temperature at that time. However, in some moments that equipment temperature reached alarming (yellow) and critical (red) status, demonstrating instability in the operation of equipment. The detection of the problem by Nagios enabled CELG technical staff to solve the heating problem. Notice that the flexibility of the proposed PLC NMS allows the administrator to classify the state of a monitored object as normal, warning or critical. Besides the capability of equipment monitoring, the proposed NMS is capable of improving network performance through traffic flow control. This job is done through the developed plugins described in the earlier section. The proposed traffic control plugins choose the best frequency window in terms of transmission and reception rates of each PLC device. Table III shows the results of transmission (TX) and reception (RX) rates for each PLC device (CPE) at different frequency windows. All tests were sequentially carried out on the same day. That is, the tests were performed in the same environment,

Fluxogram of the Management System.

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Fig. 4.

an effective management system can be of great importance in order to prevent the network against noise and failures. Regarding PLC network management, proprietary solutions are commonly used, but this practice is not appropriate once proprietary solutions do not support managing different manufacturers devices and are not able to perform automated proactive management. The proactive management was one of the main focus during the development of the proposed PLC NMS and could be implemented by creating proactive and automated plugins, which are able to dynamically change settings of PLC devices. Briefly speaking, we proposed and implemented a proactive PLC network management system based on free software that can manage different manufacturers devices. And mostly important, we demonstrated that our PLC network management system can provide the correct operation of the PLC network, guaranteeing some required constraints of services to the users such as a minimum transmission rate and optimized frequency window allocation.

Heating Problem in HeadEnd.

just with a few minutes difference from each other. That criteria had to be taken to guarantee that the result would not be influenciated different temperature conditions. By analyzing the results presented in Table III, one can conclude that window 13 provides the best TX/RX values for the equipments in the considered PLC network. The implemented plugins of the NMS do this analysis and control. The plugin verifies all results and decides which frequency window is more adequate. Further, the plugin sends SNMP set operation to the master PLC changing its frequency window to the best one. Once the master PLC has its frequency window changed, all CPEs are adjusted to work at that same frequency spectrum. Notice that without the application of the NMS, we observe a smaller TX/RX rates to the PLC network.

ACKNOWLEDGMENT This work was accomplished with the collaboration of the Laboratory of Simulation (LABSIM), School of Electrical and Computer Engineering, Federal University of Goi´as, En´ ergy Company of Goi´as (CELG), Fotˆonica Tecnologia Optica LTDA, Furukawa Industrial S.A., and funded by CAPES, a Brazilian research support foundation and by ANEEL, through Aneel contract PRGE-675/2007 (02/11/2008).

TABLE III TX/RX R ATES IN W INDOWS 1 TO 16. 1 Device CPE 1 CPE 2 CPE 3 CPE 4 Average

32/36 1/2 56/73 43/69 33/45 6

Device CPE 1 CPE 2 CPE 3 CPE 4 Average

77/5 4/88 151/94 4/4 59/48 12

Device CPE 1 CPE 2 CPE 3 CPE 4 Average

66/88 4/8 64/60 75/10 53/42

Frequency Window 3 4 TX/RX (Mbps) 2/2 2/2 55/7 1/2 2/11 2/2 38/38 59/55 56/63 9/28 42/3 66/8 12/17 26/18 45/20 Frequency Window 7 8 10 TX/RX (Mbps) 1/13 1/6 1/1 1/1 1/1 1/1 35/10 29/28 20/9 1/1 28/25 10/6 8/9 12/9 Frequency Window 13 14 15 TX/RX (Mbps) 66/126 6/13 6/6 93/53 97/7 3/2 95/184 131/136 120/125 68/104 4/112 9/103 80/117 60/67 35/59 2

R EFERENCES 5

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66/6 71/7 80/84 5/4 55/25 11 4/49 4/67 127/134 34/62 16 -

VI. C ONCLUSION In this paper, we presented a management system developed for Power Line Communications network management. One of the main impediments to the advance of PLC technology is the existing power lines that do not follow normative standards, causing noise on data transmission. Thus,

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