Performance Evaluation of IPv4/IPv6 Networks for Ubiquitous Home-Care Service

Cheng-Chan Hung and Shiow-Yuan Huang

1.Introduction

As a consequence of development in science and technology, the medical sensing technology is evolving from the previous electronic care (e-care) and mobile health(m-health) to ubiquitous care (U-care).What is meant by ubiquity? It means that it covers mobility of sensor networks, security, standards, integration (health system,service model), CAD (computer-assisted decision), and U-home-care (U-healthcare at home).Ubiquitous computing[1], also called pervasive computing, describes environments where a user is surrounded by numerous special-purpose applications running on networked information appliances.It is characterized by physically embedded sensor systems, a ubiquitous network, and application-specific devices.

Recently, there has been an increase in research focused on the production of commercial U-care systems based on the Bluetooth (IEEE 802.15.1), Zigbee (IEEE 802.15.4),wireless fidelity (Wi-Fi), 3G or 3.5G (high speed downlink packet access, HSDPA) generation universal mobile telecommunications system (3G[2]or 3.5G[3]UMTS), and WiMax[4],[5]networking technologies.However, all of these wireless technologies are connected to the Internet via a mobile sensor gateway that connects the wireless network to the backbone network by establishing an IPv6 tunnel and translating IPv4 to IPv6.General gateways, such as the ADSL (asymmetric digital subscriber line) modem, cable modem, and FTTH (fiber to the home) or FTTB (fiber to the building) by VDSL (very high data rate digital subscriber line), connect LANs (local area network) to ISPs(Internet service provider), serving as transmission media gateways associated with different transmission media.The introduction of high-speed data rates, wide bandwidth, and digital and encrypted communication technologies enable the delivery of audio, video, and medical data everywhere.All of above improve on some of the limitations existing m-health technologies[6]and provide a better platform for U-care services.

Most current home networks are asymmetrical networks[7]where the uplink bandwidth is smaller than the downlink bandwidth.This asymmetry is because more data is downloaded than uploaded in general Internet use.This,however, may cause some problems for telemedicine data transmission because sensing data must be uploaded.Furthermore, the common Internet protocol of networks is IPv4 (Internet Protocol version 4).IPv6 (Internet Protocol version 6) is the next generation Internet protocol and has many new features, such as large address space, Internet operations support, an extension of the encrypted authentication mechanism, enhanced addressing capabilities, an automatic addressing mechanism,simplification of the header format, etc.Therefore, using IPv6 is an asset for U-care networks, and the requirements of U-care networks are listed in Table 1.But, recently, in the mostly performance evaluation of telemedicine[8], IPv4 networks are usually used.

In our research, we analyze the performance of IPv6 and IPv4, which transmit UDP (user datagram protocol)and TCP (transmission control protocol) packets in U-home-care systems.The TCP is a connection-oriented protocol in which the TCP packets are transmitted before it establishes a connection.It is a reliable delivery mechanism for data transmission.On the other hand, UDP is a connection-less protocol and is unreliable, but it has the advantage of high transmission efficiency.Thus, UDP is often used to transmit real-time voice and video data on networks, but it needs to meet a higher QoS (quality of service) requirement for telemedicine data transmission.For these reasons, we decide to evaluate the network protocols that are most suitable for U-home-care in the future.

This paper is organized as follows: Section 2 focuses on the U-healthcare requirements of the project and the description of the QoS requirements in U-healthcare networks.Section 3 describes the scenarios of U-home-care in two types of networks.Section 4 illustrates the measurement models that we use to test the application platforms of the U-home-care environment.Section 5 focuses on the performance requirements of medical video data, voice data, and data used in U-home-care.Section 6 concludes with a summary and areas for future research.

2.U-Healthcare Requirements

Along with social and economic developments, medical advances have enabled people to increase their life expectancy with the consequent gradual aging of the population.The problem of an aging population needs urgent attention in the 21st century.

The increasing demands of healthcare for the elderly are the most pressing current need and will continue to grow in the future.Therefore, as we consider the increasing demands for healthcare for the elderly that may include mobile care (m-care), it is necessary to establish a new type of healthcare system that uses the network technology to provide U-care services.When a person urgently needs healthcare, the U-healthcare system can issue an immediate warning through the network so to enable healthcare workers to locate the person quickly and efficiently and provide the necessary emergency treatment.

Table 1 shows the requirements of a U-healthcare network and the solutions IPv6 provides.

Table 1: Requirements of U-care and characteristics in IPv4/v6 networks

2.1 Transmission Parameters and Category of Networks in U-Healthcare Networks

The U-home-care service has three parts: physiology data (vital signals), voice, and video streams[9].In this paper,we discuss the buffer size needed to support medical services to assure that no packets are dropped during transmission.A buffer size of 12 packets for audio service,four packets for medical data, and 25 packets for video service are required.But in the case of [9], an IPv4 medical service network was used.Therefore, in this paper, we will evaluate the requirements for medical data, voice, and video streams, and measure the value of delay, jitter, and packet loss, and try to find the differences between U-healthcare networks using IPv6 and IPv4.

Most current networks in Taiwan access the Internet via ADSL (79.2%)[7], Fiber (8.8%), and Cable Modem (7.2%)networks are also used[7].The characteristics of ADSL networks are that the uplink and downlink bandwidths are asymmetrical, and the uplink bandwidth is relatively small.However, most U-healthcare data are uplink and transmitted from a client to a back-end server.Therefore, to structure a U-healthcare environment for the future, we must consider the issue of ADSL in IPv4 and IPv6 U-healthcare networks.

2.2 Data Rate and QoS Requirements of U-Healthcare

Most healthcare applications can be divided into three kinds: 1) medical data transmission, mainly ECG(electrocardiogram), EEG (electroencephalography), and blood pressure, etc.; 2) audio from a stethoscope or VoIP communication applications; and 3) motion video and endoscopic video transmission.Each has different data rate transmission requirements and QoS (quality of service)requirements.

Problems with network QoS can be recognized by the packet loss, jitter, and delay.These can be further divided into two categories: their affect on medical multimedia and medical data.Regarding medical multimedia, the human ear cannot detect delay below 150 ms of end-to-end delay,so voice jitter or delay cannot be more than 150 ms for the digital audio stethoscope.We refer to [10], where the acceptable delay was about 400 ms.But [11]mentioned that a reasonable delay goal was 250 ms, and for private networks it was 200 ms.For this reason, we chose a delay goal for our network of less than 250 ms as a standard requirement.

Medical data also can be divided into two types:real-time and non-real-time.The real-time data is used for monitoring daily life of patients with chronic conditions and providing emergency notification when the system relays abnormal physiological data.Non-real-time medical data is mainly used for the data transmission of routine information, such as demographic data, laboratory and clinical data, medical history, electromyograms, magnetic resonance images, and digital radiography.Medical multimedia streams are often used in medical diagnosis (e.g.colonoscopy) so that biomedical data must be transmitted along with telemedicine streams.Therefore, we focus on the QoS requirements for our network for telemedicine streams and provide a variety of requirements for QoS in the healthcare appliances referenced in Section 5.We refer to the parameters of the data rates used in our system and in[3]and consolidate them in Table 2.

2.3 Advantage of QoS in IPv6 Networks

In a U-healthcare environment, different data traffics with different classes of QoS requirements have to be transmitted simultaneously.The header in an IPv6 packet is different from that in an IPv4 packet.The IPv6 header has two fields, namely the traffic class and flow label.The priority level of the traffic class is divided into two main categories, congestion-controlled and the non-congestioncontrolled.Congestion control and non-congestion-control priorities are divided into eight grades.Therefore, in an IPv6 network, the information can be divided into two types for QoS; one packet is emergency information and the other is sensor measurement information[12].This designation will protect the transmission of emergency information packets during IPv6 network congestion.This is an additional advantage of IPv6 over IPv4.

3.U-Home-Care Scenarios

The advent of a large number of wireless networking technologies allows a mobile host to be equipped with multiple wireless interfaces (e.g.Bluetooth, Wi-Fi, and 3.5G, etc.), each providing access to different wireless networks.Because of the emergence of these wirelessnetworking technologies, it is possible to develop a ubiquitous healthcare system using a suitable network platform.Furthermore, the number of 3G mobile users is over 55.8% of all mobile users in Taiwan[13].Therefore, to test our U-home-care system, we chose the three currently pervasive wireless networking technologies in Taiwan,namely Bluetooth, Wi-Fi, and 3.5G (HSDPA).

First, in our U-home-care scenarios, the front-sensor uses the personal area network (PAN) of the Bluetooth device to obtain the healthcare data (e.g.biomedical data,voice, and video stream).Then, the healthcare data are moved through an intermediate network gateway device(e.g.Notebook, PDA, or mobile phone with Wi-Fi and 3.5G) to transfer information to the Internet.

In the current design, the mobile U-homecare device will choose a suitable gateway (Wi-Fi or 3.5G) in accordance with the available network.The choice will be handled by the USIM (universal subscriber identity module)card, which gives a high priority to Wi-Fi or 3.5G depending on which one has a stronger signal.When the transmission network is selected, the healthcare data will be transferred to the back-end system and recorded for use by various healthcare applications.

3.1 Proposed U-Home-Care Scenario

To create a ubiquitous healthcare environment, the system must consider the attributes of the different environments.To do this, we will divide the front-sensors into two types: (1) the indoor area of care center or home,(2) outdoors in an emergency condition.

We assume that patients with chronic conditions are normally at a care center or at home.In normal circumstances, the biomedical data is captured by a Bluetooth-enabled device and transmitted via Wi-Fi to the healthcare center.Monitoring items include routine biomedical data such as ECG, EEG, blood pressure, and blood glucose.Long-term monitoring and recording is helpful for tracking and treating patients with chronic conditions.

Regarding an outdoor emergency notification and rescue, when patients are outdoors and an emergency arises,the U-home-system will use the same Bluetooth sensors to capture their biomedical data.However, the gateway service is replaced by a 3.5G mobile phone that can provide real-time communication to a first-aid unit via a 3.5G base station.If the first-aid unit cannot reach the individual quickly, hospital experts can provide the necessary first-aid guidance through an informant, and via connection with the informant, and they can diagnose the vital signals.All mentioned above are important factors need to increase the success rate of rescue operations.The foregoing scenarios of the U-home-care are shown in Fig.1.

The transmission system at the frontend of the entire system is constructed with a wireless overlay network(WON) as shown in Fig.1.All of the U-home-care networks are connected through the Internet to the relevant care service center, which provides electronic health records (EHRs), U-healthcare web monitoring services, and a hospital backend, regardless of whether information comes from an indoor Wi-Fi system or an outdoor 3.5G system.

3.2 Layered Architecture of U-Home-Care System

The U-home-care network gateway is over IP networks so we must take into account the transmission performance issues of IPv4 and IPv6 networks.The transmission layers of the system are in the following: (1) delivery starts with Bluetooth sensors that capture healthcare data (e.g.biomedical data, voice, and video), (2) healthcare data are transmitted via TCP or UDP transmission protocols, (3)IPv6/IPv4 network protocols are used, (4) the base station(Wi-Fi or 3.5G) is used, (5) it is via physical media (802.11,HSDPA, Ethernet, Fiber), and (6) it is transmitted to the back-end server’s receiving program.

According to the foregoing description, we have drawn the U-home-care system as a layered architecture, as shown in Fig.2.

4.Measurement Model

4.1 Measurement of the Network Platform

From Fig.1, we constructed the U-home-care network on four different networks: 3.5G HSDPA, ADSL, optical fiber, and Ethernet (802.3ab).Table 3 shows the difference in bandwidth for the ISPs (Internet services providers) of the four network standards.

4.2 Measurement Model

To understand the transmission performance under various parameters of IPv4/v6, we designed a measurement model as shown in Fig.3 for the U-home-care network transmission of biomedical data (TCP), voice, and video(UDP) streams, respectively.We adjusted the four kinds of transmission parameters, the buffer size, packet size, UDP data rate, and TCP data rate in order to measure packet loss,delay, and jitter, and to identify the parameters that provide both performance and QoS in the U-home-care service.

Fig.2.Layered architecture of U-home-care system.

Table 3: Bandwidth of network services in measurement platform of U-home-care

Fig.3.Measurement model.

In this measurement scenario, as shown in Fig.4, point A is an immobile U-home-care back-end system to which all of the healthcare data will be transmitted.Point B is a mobile node with Wi-Fi and 3.5G.The purpose is to measure the performance of our U-home-care system and improve the quality of services offered by dimensioning the buffer size, packet size, UDP data rates, and TCP data rates.Several tests were conducted using the system over IPv4/v6 3.5G UMTS and ADSL in urban areas (Taichung).However, after the 3.5G test we found that 3.5G signals are only prevalent in the city area.In our test area (Taichung),3.5G does not have a widespread penetration.For this reason, in subsequent tests, we used only the ADSL network to do the measurements because ADSL has a bandwidth similar to 3.5G.

The measurement scenario we designed is shown in Fig.4.First, we tested the biomedical data transmission without UDP streams and transmitted simultaneously 256 Kbps video streams and 64 Kbps voice streams.We obtained the jitter and packet loss measurements of the ADSL network,which were caused by the UDP streams.

Second, to measure the influence of UDP in biomedical data (TCP) transmission, we selected four types of vital physiological data, digital sphygmomanometer, digital thermometer, respiration, and heart rate, which were sorted and shown in Table 2.These represent the medical data that are most commonly used in indoor monitoring.It is totally about 16 Kbps.In addition, we also select non-real time appliances (bandwidth limits with 64 Kbps/120 Kbps) to facilitate understanding the influence of biomedical data(TCP) transmission.The measurement results are described in Section 5.2.

Fig.4 shows the network layout.We take measurements for QoS at point A, and we measure traffic flow at point B.

5.Measurement Results

To impartially measure the impartial values on Internet,we chose four different test times (off-peak, peak, off-peak,and peak) in a day and take the average test values to record.The actual values of measured environment results are shown in Table 4.

In Taiwan, the 3.5G bandwidth is shared, which is allocated according to the number of users.As a result, the actual bandwidth is not fixed and the network delay is unstable.For this reason, in the following measurement, we used the ADSL network platform that is in common use by the population and care centers.

Fig.4.Measurement scenario of IPv6/IPv4 U-home-care test system.

Table 4: Actual bandwidth & delay in our U-home-care networks

Prior to this evaluation, we measured the traffic using samples of medical streams (voice and video) in the U-home-care environment.We compared this with a telemedicine system developed by [14]that uses MPEG-2 for its video CODEC (coder-decoder) standard.The CODEC standard of our U-home-care system is more efficient.At present, many HD (high definition) video,telecommunication, and telemedicine devices are using the H.264 CODEC video standard.It has a higher compression ratio and a higher quality CODEC than the MPEG-2 CODEC; it is recommended by ITU-T as a video standard.Therefore, we used H.264 in our U-home-care system as the video CODEC standard.In addition, we used G.711,also known as pulse code modulation (PCM).It is a commonly used waveform CODEC with a sampling rate of 8 k samples per second, resulting in a 64 Kbps bit rate.This standard is required by many technologies (e.g.H.320 and H.323 specifications).The medical stream traffic of CODEC is shown in Table 5.

5.1 UDP Jitter Results

First, at point B, we injected a fixed bit rate of UDP streams at 320 Kbps (VoIP at 64 Kbps and video at 256 Kbps).Next, we changed the buffer size in a geometric progression from 1 Kb to 8192 Kb in order to measure the influence of these changes.From the measured results in Fig.5, there is no obvious variation in jitter for the different buffer sizes; the measured values are within the error range of ±1 ms, and the packet loss rate is 0%.However, we can clearly see that the jitter is less at about 4 ms in IPv4 versus IPv6, because the IPv6 network needs tunneling technology to be compatible in IPv4 network.

To test the limitations of ADSL transmission by UDP streams, we simultaneously transmitted two streams at 256 Kbps from point B.The results are shown in Fig.6.(The buffer size is same as in the previous test.) The results show that by increasing the buffer size it can reduce the jitter from 50 ms to 40 ms, but it cannot reduce the packet loss rate (average packet loss rate was 56.14%).Furthermore, we find the effect of buffer size using IPv4 is smaller than that using IPv6.When the buffer size is set to1024 Kb, the jitter in IPv4 can only be reduced about 5 ms.Using IPv6, the jitter can be reduced about 10 ms.As a result, we see that when the buffer size is greater than, or equals to 1024 Kb, it can improve the jitter caused by network bandwidth constraints in the IPv6 network; and if the buffer size is higher than 1 Mb, the jitter will not affect performance.

Table 5: Medical stream traffic of CODEC in the evaluation test

To understand the effect of packet size, we changed the packet size in the setup; the parameters of packet size were increased from 64 bits to 4096 bits, by geometric progression.We discovered that the relative effects of jitter and packet loss were dependent on the packet size in IPv4/v6, which are obvious as shown in Fig.7 and Fig.8,respectively.We also find that the best packet size is 1024 bits, because a higher packet size results in a substantial increase in jitter.When the packet size is less than 1024 bits,it increases the packet loss rate.

Finally, we also attempted to transmit two 256 Kbps streams by changing the packet size at point B and obtaining the packet loss rate at point A.The results were a packet loss rate of over than 50%.We do not provide the results.

Fig.5.UDP transmission jitter with different buffer sizes in IPv4/v6 (ADSL).

Fig.6.Two parallel streams transmission jitter with different buffer sizes in IPv4/v6 (ADSL).

Fig.7.UDP packet size affects jitter in IPv4/v6 (ADSL).

Fig.8.UDP packet size affects packet loss rate in IPv4/v6(ADSL).

5.2 Effects of the Interaction of UDP Streams and TCP Biomedical Data

The measurements of section 5.1 are all of UDP stream transmission tests.However, in the U-home-care service, it is necessary to regularly transmit the biomedical data of patients with chronic conditions to the back-end server.The purpose of this section is to understand the effects of UDP streams for biomedical data transmission.As listed in Table 2, U-home-care applications require a delay of less than 250 ms.Therefore, we chose 250 ms as the limit of delay.Jitter is technically the measurement of the variability over time of the latency across a network.It should be less than 100 ms.If the value of jitter is smaller than 100 ms, it can be corrected.However, to maintain a jitter of less than 100 ms, medical data stream transmission must be reduced in this network.

A.Effects of Jitter

We tested three speeds of TCP data rates: 120 Kbps,64 Kbps, and 16 Kbps in an IPv4/v6 network.In total, there are six test samples.The buffer size is set at 1024 KB as the test standard (refer to Section 5.1).We changed the UDP data rate and observed the effect on UDP stream biomedical data transmission.We observed, as shown in Fig.9, that the TCP 16 Kbps transmission in IPv4/v6 has low jitter and the difference in jitter is small in both.This is consistent with the expected results.

In addition, the results for jitter at TCP 64 Kbps and TCP 120 Kbps transmission in IPv4/v6 show that jitter in IPv6 are lower than that in IPv4.For this reason, we find that high TCP data rate transmission has advantages in IPv6 over IPv4.Furthermore, when the UDP data rate is over 256 Kbps, the jitter will be somewhat lower than at the other, smaller UDP data rate.We will discuss the reason for this result in Section C.B.Effects of Delay

Fig.9.Effect of jitter in both UDP streams and TCP medical data transmits (ADSL).

Next, we measured the effects of TCP delay in biomedical data transmission caused by UDP streams.From Fig.10, we can see that the maximum value for the stable transmission at TCP 16 Kbps (i.e., TCP delay<250 ms) is around the UDP stream of 192 Kbps; however, the maximum value of the stable transmission at TCP 64 Kbps is around the UDP stream of 128 Kbps; and in TCP 120 Kbps, it is around the UDP stream of 64 Kbps.In this case, the TCP delay, measured by UDP streams at a higher data rate (over 192 Kbps), will significantly increase the rate of delay.In summary, the delay in IPv6 is less than that in IPv4.Furthermore, it is more apparent in the TCP data rates, especially at 120 Kbps.

C.Effects of Packet Loss Rate

Finally, we discuss packet loss rates.From Fig.11, we observe the following: (1) in both IPv4 and IPv6 at TCP 16 Kbps, when the UDP stream of data rate is 256 Kbps, the packet loss is 0%; (2) in IPv4 at TCP 64 Kbps and at UDP 192 Kbps, there is a 1% to 3% packet loss, but in IPv6, a 41% packet loss is introduced at UDP 320 Kbps; and (3) in IPv4 at TCP 120 Kbps and UDP 64 Kbps, a packet loss rate of 2.5% or 64% is produced, but in IPv6, a UDP data rate higher than 256 Kbps results in a packet loss of 17% or 65%.From these tests, we find that, under the same conditions, the packet loss rate in IPv6 is lower than that in IPv4.

Regarding the discussions in Section A, we find that with a UDP data rate of over 256 Kbps, the jitter is lower than that at other relatively smaller UDP data rates.By comparison with Fig.9 to Fig.11, we find that when the UDP data rate is at 256 Kbps, because of the limitations of ADSL uplink bandwidth, there is transmission congestion at point B which produces a packet loss.Because the UDP packet is dropped by the network (i.e., packet loss), the TCP delay is significantly increased.By contrast, the jitter in UDP packets is reduced at point A.However, it may be possible to use packet loss as a compromise to attain a lower jitter in the less sensitive multi-media transmission.For use in medical data transmission, however, it is inappropriate.

Fig.10.Effect of delay in both UDP streams and TCP medical data transmission (ADSL).

Fig.11.Packet loss rate in both UDP streams and TCP medical data transmission (ADSL).

In summary, from the previous tests, we see that in IPv6 networks, the jitter, delay, and packet loss rates are a little better than those in IPv4 networks.Our tests also illustrate that there is no difference in IPv4/v6 network performance when the transmission of UDP data rates is less than 64 Kbps.At present, our U-home-care applications use a TCP data rate at about 16 Kbps for real-time transmission,and the UDP data rate for telemedicine is about 256 Kbps.In the future, with a wider application of U-healthcare,there will be a need for higher transmission rates for data and a higher mobility.Based on the needs of our system,and the results of our tests, IPv6 networks will be a better choice for U-healthcare in the future.

6.Conclusions

Most home networks in Taiwan have an uplink bandwidth of 242 Kbps of ADSL or 232 Kbps of 3.5G,separately.Due to the U-healthcare requirements given in Section 2, and the measurement results of Section 5, we see the effects of different data rates for TCP and UDP data transmission in U-homecare networks.If the buffer size is set to 1024 Kb, and the packet size is set to 1024 bits, then the transmission of medical data at 256 Kbps UDP stream and 16 Kbps TCP is possible.This rate is sufficient to provide for critical medical data transmission in the U-home-care network.However, transmission of data rate at 272 Kbps over the ADSL uplink with a limit of 256 Kbps will cause the network to become congested and packet loss will occur.We must assume the use of different networks(IPv4/v6) for U-healthcare services.Doing so will not only enhance the efficacy of telemedicine but also allow for the Internet-based service of U-healthcare to reach most families with an inexpensive, widespread, and pervasive broadband network (ADSL).Unfortunately, when it is necessary to send high-definition, real-time medical streams (above 1544 bps uplink bandwidth), it cannot be done using 3.5G or ADSL networks.There is an option of using fiber, but using fiber has high monthly fees and it cannot be installed everywhere due to capacity issues.

In addition, from the results in Section 5, we find that the values of IPv4/v6 which deal with the large traffic of medical data transmission are nearly in between.However,the performance of IPv6 is still relatively good.Although the majority of the current IPv6 is via IPv4 networks, and establishing a tunnel, dual stack routers or a translator leads to increased overhead for the network, it does improve the advantages of IPv6 that cannot be fully utilized (e.g.simplifying header and route optimization).With the increasing usage in the All-IP age in the future, the U-home-care service built on the IPv6 network will have advantages and will be established as an effective system for a better class of U-home-care services.

When mature 3.75G high-speed uplink packet access(HSUPA), 4G (LTE or WiMax) networks, and the base stations all become widely available, they will provide greater flexibility in QoS for U-home-care data with the further ability to handle a large number of medical streams.At that point, individuals will be able to perform an in-depth diagnosis in their home environments to have access to clinical nursing staff and hospital doctors via telemedicine systems.Our long-term goal is to see simultaneous transmission of real-time medical information,the transmission of high-resolution and high-bandwidth images, and other medical data without any cross interference.

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