Development of IP Network System forElectric Power Using Cable Modems
by Osamu Usami *, Kouichi Kamimura *, Katsuji Ito *2, Tetsuya Kugizaki *2,
Hiroyasu Hayakawa *2, Nobuya Shinoda *3, Masashi Tabara *3,
Kazutaka Shimoosako *2, Tomohiro Arasawa *2,
Takeshi Kawaguchi *2 and Motoharu Tanaka *2

We developed an IP network system for power line customers to operate in theyear 2000. The main objects of developing this IP system are an amazing systemprice reduction compared to the growingly popular 1:1 transmission system, and also a variety of
applications for individual customers with customer security assurance.
The main scheme of this optical system adopts branches of the 8x4 passive double star opticalsystem. To develop speed and cost efficiency, we selected a mass produced cable modem,
which accepts IP and ATM controlling protocols that can be used for PDS optical networks.
Another important aim is to assure a channel capacity with high Quality of Service (QoS) totransport customer data with sufficient reliability.
Since this system started operation customer numbers have gradually increased, and the system has demonstrated its design efficiency and cost performance. The skeleton and the structureof the system and the equipment are described below.

ABSTRACT1.

INTRODUCTION

The current power line information transmission method
for meter-reading is 1:1 information transmission, and the
upstream gathering scheme uses a hierarchical structureof equipment based on HDLC tansmission in which information is restructured to each frame length at each node.
This conventional system confronts the difficulties ofextending newly added bits in frames, which meant flexible insertion of new customer information was impossible.
IP network systems are flexible and generally used incommunication network systems, among which the cable
modem-equipped LAN system is well-known and is easily
expandable to cover a large area. This system has a flat
structure compared to the current hierarchy step-up structure, so a network arrangement can be adopted for any
area and time, and a variety of QoS is applicable to customers for newly developed services or Internet services.
We carefully examined the problems of current power network communication and developed a practical optical IP
network system for power line information. An outline isgiven below.

*

Tokyo Electric Power Company
Transport Products Dept., Network Div.
*3 WT Team, FITEL-Network Lab.
*2

2.

OUTLINE OF THE SYSTEM

2.1 Structure of System
1) Outline of the system is shown in Figure 1.
2) Equipment and connecting scale numbers (Table 1)
are shown below.
• IP managing equipment• Headend (HE) modem equipment• Headend (HE) controlling equipment• Optical branching couplers• Power line customer terminal (Terminal II)
2.2 Structure of Network(1) Upper network
Current system hosts are accommodated in the current
packet network. Among them is the electric power meterreading host. Our newly developed IP network systemruns in an Ethernet system. So, connecting each network
requires protocol conversion. Also developed is IP managing equipment (IP Manager), which converts upper network protocols into IP network protocols and vice versa.
(2) IP network developed
The newly developed IP network includes HE equipment
which runs the current ATM system, and has Terminal
Equipment including a cable modem board corresponding
with HE. The Ethernet packet is modulated into cells andis transported between HE and Terminals, so the numberof cells is controlled under the design speed for theassured transportation bit rate under ATM. Use of cells is

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IP network

Upper network

PDS network

Optical branchPower line
information hostTerminal II

IP manager
Packetnetwork

Power
meter

HE centerequipment

Power line equipment
status information

Meter-reading host
HE controlling equipment

Figure 1

Table 1No
1

2
3

System diagram.

Capacity of the system.

Equipment

Maximum connecting numbers of equipment

IP manager

4 channels x 600

Power meter(2400)
HE center equipment

6 channels x 32

Terminal II(192)
Terminal II

2Power meterclassified into fixed bit rate use (CBR: Constant Bit Rate)and cooperative bit rate use (VBR: Variable Bit Rate). The
downstream transmission is modulated in 64 Quadrature
Amplitude Modulation (QAM) and has 1 channel with amaximum speed of 30.34 Mbps. The upstream transmission is modulated in Quadrature Phase Shift Keying(QPSK) and has free use of six channels, each with amaximum speed of 2.56 Mbps. We selected the CBR
method because it provides the most reliable transmissionof information for electric power equipment, even in a
crowded state.
(3) PDS network
The transmission medium is optical fiber, which is connected to a Passive Double Star (PDS) network. The final
stage of the optical network has optical branching couplers of 1x8 and 1x4, and a maximum branching of 32
customers in one optical network block, and has a standard length of ca 20 km.

3.

OPTICAL NETWORK

3.1 Outline of Optical Network
The information summarizing stage of the optical network
has IP-M equipment distributed in main branch offices
connected to the current packet network, and each IP-M
has several HE systems.
1) Each HE system has dual ports for upper informationtransmission routes.
2) Each HE system has a single port for a lower information transmission route, due to recycling of information contents, required information time, summingof information bits at every cycle, and current information accuracy.

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3.2 Design Conditions of Optical Network
In accordance with practical grouping numbers, the system design conditions are selected as follows:
1) Maximum optical path dynamic range: ca 20 dB-37
dB.
2) Maximum optical path length: up to ca 50 km.
3) Maximum optical branching number: 32.
A 32 branch means 8x4, double stage branches of 8branch and 4-branch in accordance with time and district
for customer's needs.
Selection of a practical optical dynamic range considers
real optical cable loss and joints, and optical branch losses. Standard length is selected to cover maximum numbers under the location distribution condition of local centers and customers. Optical attenuator or detour center isadopted.
3.3

Calculating Dynamic Loss of Optical Path
LengthA calculating model pattern is introduced in the optical
dynamic loss calculation between HE and terminals. The
model is divided into two sections:1) Optical equipment and connecting devices with typical loss sections
e.g., optical equipment installed in buildings, repeating
stations, and terminal stations
2) Optical transmission media of a long span with typicalloss sections
e.g., cable sections, branching cable sections including
junction boxes
Modeling a typical structure element into equivalent loss
figures, and its corresponding section by the calculating
series method, the system dynamic loss is summarized as
total loss amount, and these figures are identified as typical standard values. If figures are out of range, remodelingis done by calculating the standard range with thearrangement of attenuators. A flow-chart of convenient
calculations is supplied, and a personal computing program is developed. A typical design model is shown in
Figure 2.

Furukawa Review, No. 21

2002Station A

Station B

HE

Attenuator

1x8 Opticalbranch coupler

Customer

1x4 Opticalbranch coupler

Terminal II

Optical connector joint
Optical fiber fused joint
Optical fiber

Figure2Power meter

Optical path design.

Power line

Terminal II

IP manager

Gathering

Polling

Power equipment information

PacketingFormat arrangement(Standard condition)

Gathering

Power equipment information(Changed condition)

PacketingFormat arrangement

GatheringFormat arrangement

Gathering

Protocol conversion

Packeting

Protocol conversion

Meter-reading

Power

host

equipment hostPolling

Meter-reading information

4.

Figure 3

Information flow diagram.

OUTLINE OF SYSTEM PROCEDURE

IP-Manager
System 1

4.1 Basic Operation
The system operation is classified into three types. The
flow of data is shown in Figure 3.
1) Normal data gathered of customer's electric powerusage2) Changing status of the customer's electric power
apparatus
3) Reading electric power meter
4.2 Communication between IP-M and Terminal II
IP-M is a repeating center with protocol conversion originating from the current upper network host. Terminal II isa newly developed multi-function terminal with meterreading and Ethernet transmission.
(1) Communication protocol
Communication between IP-M and Terminal II is User
Datagram Protocol/Internet Protocol (UDP/IP) method.
The UDP method requires no retry call, so to ensure security an upper level application protocol operates.
(2) Polling sequence
IP-M communication requires duplex transmission, and it
has a single downstream transmission medium, so a
duplicate polling method is adopted. Its polling sequence
is discussed below. Figure 4 is the communication diagram.
IP-M gives successive duplicate polling frames startingfrom system 1 and system 2 to the specified Terminal II.
Terminal II receives duplicate polling information and

Cycle 1

System 2

Terminal II

Power meter
Cycle 2

Figure 4

Polling flow diagram.

allows first access and rejects second access to prevent
transmission channel congestion. The answer from
Terminal II is returned to IP-M in duplicate frames, each
into system 1 and system 2. With the response, IP-M
judges that its polling request was received by Terminal II.
With no response by time-out from Terminal II, IP-M
makes retry polling access to Terminal II.
(3) Meter-reading access
When Terminal II decodes meter-reading information
repeated through IP-M from the meter-reading host, theterminal accesses the electric power meter requested forthe consumed electric power digits. The terminal receives99

IP packet 1

Meter-reading
information hostIP packet 2
ATM cellIP-manager

Controlling
ATM cellFigure shows that IP packet 2 has higher priority, ensuring a higher
level of transmission speed by utilizing ATM cells. Controlling ATM cellis used for communication between HE and terminal II.

Terminal II

Figure 7

Collision controlling packet assembly.

Power meter

Figure 5

Meter-reading flow diagram.

HE Equipment

Cable modem
Power onSelf-check test

1

Standard polling cycle
IP-manager
System 1
System 2

4

ACK
Response
5

Terminal II

Connection request

Send connection ACK

2

Search of controlling cell

3

Increase of out-put power
until HE connection request
is accepted

6

Send ACK

Changed status
information

Send end of gain control
7

8

Send ACKPower equipment

9

Changed status

Figure 8
Figure 6

the requested consumed power information data from thepower meter and sends it to the host through IP-M. Figure
5 shows the meter-reading diagram.
(4) Changed status gathering
Normal communication between IP-M and Terminal II has
the starting information at IP-M, but this section ofchanged status gathering has the starting point at
Terminal II. To have a short response in the emergent
change of electric power status, the terminal starts to takepollings to IP-M, and IP-M returns the responding acks to
the terminal. Terminal II acknowledges the admittance of
IP-M with respect to the changed electric statuses. In theactual response task, faster information out of either system 1 or system 2 is sufficient, and a duplicate systemruns in an apparently normal status. Figure 6 shows flow
diagrams of changed status gathering for the electric
power apparatus.
The important point is that this system has the assurance of QoS from CBR transmission and collisions ofsimultaneous change statuses of terminals are clearly
avoided to inform IP-M without any delay time.
4.3 Outline of Equipment Operation
4.3.1 Operation of IP-M
IP-M is located in the interface of the upper current packeting network and the lower IP network. Then the IP-M
controls the polling system to Terminal IIs, and it converts
upper host request protocols to lower IP requests withdata assembling and vice versa. Another task of IP-M is

100

Optical power level controlling sequence flow.

Status information flow diagram.

as a DHCP (Dynamic Host Configuration Protocol) server
for automatic address delivering to Terminal IIs.
4.3.2 Operation of HE Modem System(1) HE communication method
The HE of LAN center has an optical tree topological connection to Terminal IIs. Every HE and Terminal II has thesame type of modem, and all Terminal IIs within a block
have the same transmission media and physically cooperative use. The IP network has a transmission variable
packet of 64 bytes to 1518 bytes, so direct transmission of
the packet from one terminal stops communication to others. We selected practical ATM modems of high-speed
networking devices to solve this congestion problem. The
fact is that a real IP packet is split into 53 byte ATM headed cells and its cell transmission equally uses every terminal coming into equal terminal communication.
(2) Collision restriction
A Passive Double Star (PDS) network inevitably involves
the possibility of transmission collision. So, to prevent collisions, a control center is introduced to distribute controlling ATM cells for transmissions of each terminal and its
QoS control. Figure 7 shows the packet and cell arrangement of collision control.
(3) Automatic optical power level control
This cable modem system has an Automatic Gain Control(AGC) function for equalizing imbalances at local distances, so a certain constant power input can be attained,
notwithstanding the area distances of Terminal IIs. So thisFurukawa Review, No. 21

2002merit is used in the optical design of transmission equipment in an optical PDS network. Figure 8 shows the AGC
sequence in an optical network. The live cable modem of
the Terminal II starts to give a connect request in the minimum status level, and boosts up the power level until theHE response returns. Then we get a constant HE input
signal level.
4.3.3 HE Controlling Equipment
Using special HE controlling software, we set communication parameters, maintenance of Terminal IIs for registering and deleting, communication status observing, recording status, and user status.
4.3.4 Operation of Terminal II
Terminal II operates to let an electric consumer accessthe value of consumed power under a host request, andalso counts pulses of power consumed. When the consumer has the electricity statuses of power equipment,
Terminal II also accumulates on-off signal bits for theirstatuses. Terminal II also gets access every four minutes
from the host, and gathers consumed power values andpower apparatus statuses at every corresponding time.
When electric power apparatus experiences a change ofstatus, the terminal II starts to operate to give informationon the changed status spontaneously to IP-M, even without access from IP-M. Table 2 shows the specification of acable modem. Table 3 shows the specification of optical
PDS network transmission equipment.
Table 2

HE center equipment.

Photo 2

Terminal equipment.

Photo 3HE control equipment.

Outline of cable modem specification.

Term

Downstream

Upstream

30.336 Mbps

2.56 Mbps

Modulation type

64-QAM

QPSK

Frequency band

300-MHz Band

30-MHz Band

6 MHz

1.8 MHz

Transmission speed

Bandwidth

Viterbi / Reed-Solomon

Reed-Solomon

Encryption

DES, 40-bit key

DES, 40-bit key

RF level

45 - 75 dB µV

78 - 118 dB µV

23 dB (10-9 BER)

16 dB (10-9 BER)

Error correction Integrated

Required CN

Table 3

Photo 1

Outline of optical transmission equipment.
Downstream

Upstream

Center frequency

Term

300 MHz

30 MHzModulation type

64-QAM

QPSK

Transmission medium

Single mode optical fiber of 1.3 µm
zero-dispersion shift

Optical channel

1.31-µm band
Modulated optical amplitude(rms) less than 21 µW,

Optical output level+8 dBm (max)Optical input level- 8.2~ - 30.1 dBm-

45~75 dB µV

78~118 dB µV

greater than 1.38 mW

RF level
Optical connector

SC-PC

101

5.

CONSTRUCTION AND SETTINGS OFTERMINAL II

Construction and settings of Terminal II has the following
two design merits.
(1) Compact size
Smaller size with upgraded functions are achieved withthe same size of current box. We use a new function communication board and currently use existing connecting
terminals installed outside.
(2) Simplified terminal communication settings
We simplified address setting and parameter setting forcounting electricity consumption from the power meter,
which is normally done with a personal computer carriedin the field. We simplified field settings, so setting time is
reduced to a few hours instead of several days. The main
checking work is done by IP-M and HE controller locatedat the center.

6.

SUMMARY

Having developed an IP network system for the first timein Japan for electric power communication using a cable
modem, we reduced total system cost and improved customer IP information system security and QoS withouttransmission collision problems. We have also achieved
the expected system functions and actual effects.

7.

FURTHER STUDY

A power line customer IP information system requires avariety of flexible network responses for constantly varying
customer information requests. Transmission speed
improvements and network flexible access applications
are coming on line.

REFERENCES
1) T. Katou: Technical Papers of Cable LAN System: Special
Meeting of Cable LAN VII, 1998. (in Japanese)
2) N. Maruyama: Technique of Communication Protocol, Ohm 1997.
(in Japanese)

Manuscript received on January 11, 2002.

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2002