EVOLUTION OF ACCESS NETWORK part 2

3.0 The Broadband Access Network

A major driver for change has been the widespread adoption of PCs in the home and business. This, in itself, would have been sufficient to cause major changes in how we make use of our networks but the symbiotic relationship with the growth of the internet has completely changed the way many of us communicate and do business. The other main driver for change has been the widespread adoption of mobile phones – in some advanced and developed countries; there are now more mobile phones than there are fixed phone lines. Broadcast networks (TV and radio) are also changing [2], [15]. They have moved from a passive medium to an interactive medium which allows viewers to select “pay-per-view” programmes, choose from a set of camera angles, call up data about a program or send e-mails. One of the major lessons which comes out is that we are looking at much richer, more diverse, easy to use set of services than would have been thought possible even just a few years ago. These services place increasing demands on the technology which provides our networks. What the user wants is a network that is versatile, reliable and cheap. What the service or network provider wants is the ability to react quickly and economically to user needs – whatever they may be. [11], [13], [15].

Compare to others, optical access offers the promise greatly access network bandwidth by up to several gigabit per second (Gbps) – which opens up availability new architectural possibilities.

4.0 Passive Optical Network (PON)

The next generation access network is evolving into a multi-service environment. This process involves several steps and will bring many access technologies into play. For example, in attempt to see this access network ‘bottle neck’ and satisfy bandwidth hungry customer, ADSL technology was introduced. The advantage of the ADSL is no changes are required to the infrastructure except for the need to install new equipment / modem at either end. When VDSL was developed it was hoped to be the next generation to supply customers with more bandwidth to make video and other high bandwidth services feasible. However the destination limitation could not share ADSL advantages of minimal changes to the infrastructure of access network. [16], [17], [18].

PON is an advanced alternative to VDSL which is consists of a ‘tree and branch’ fiber optic network originating from the local exchange to the customer premises with only contains passive components, such as passive optical splitter or couplers. A basic average bit rates in PONs are 20Mbps per customer. But in many research it is burst to higher bandwidths. And upgrading the design is only by changing the equipment at the exchange and customer ends without changing the optical fiber loop. As PONs are an attractive possibility for the future access network, it represents the most ideal of all broadband access architectures namely Fiber-to-the-Home (FTTH). With combination by FTTH and Ethernet technology (EPON) results the best approach which make costs falls and demand for bandwidth increases. EPON can have links of up to 50 km and have been shown in trials, to be capable of working at 10 Giga bps. [19], [20], [21].

4.2 Intelligent Access Nodes

In this optical WDM network, both optical and electronic intelligent network functionality reside in the access nodes which interconnect data flows between the feeder and distribution networks. The role of the feeder access node is to route full optical wavelength channels and individual IP data packets inside wavelength channels toward their destinations. Two key features for access node design are the electronic IP router and the optical wavelength router / transponder inside the node. A third important feature is the ability to direct optical signals to one of the two routers or to completely bypass the routers for transparent optical connections between users. [25], [30]

6.0 Conclusion

Today there are numbers of access network services offered by many telecom companies which is related to broadband connection. A lot of benefit could be gained with proper broadband access network especially in generating a new business types and e-society.

Types of services that could be realized are like:

• Tourism – information base and access to it containing events, conferences, etc.
• Hospital or health care – solutions for telemedicine interactive care, medical administration and tele-learning in health care.
• Schools and education – infostructure to facilitate continuing education through distance and e-learning.
• Cultural heritage – access to archives, libraries and museums.
• Labor market – helping unemployed and job seekers as well as employers by creating and managing databases of job opportunities.
• E-government functions – could provide person to person services without traveling. [34]

The future of video, voice and data communications networking is clearly to converge [35]. Hence carriers are looking to a simple, lower costs and bandwidth sufficient systems. Then these services will not end at this point, but will further increase with potentially improved or new features. Those who have to deal with access network connection will live in interesting times, because there are more convergence of previously desperate services than ever seen before. Strategy has to be right for those who is the service provider, so that they will have the ability to deliver services that will keep customer happy.

EVOLUTION OF ACCESS NETWORK part 1

1.0 Introduction

The ultimate goal of any networking system is to deliver successfully of data including video and voice to the end user in order to enable activities which improve the quality of life through media, videoconferencing, medical imaging, distance learning, virtual reality applications and future multimedia applications. The current trends for user’s requirements for future services can be expected to be more entertaining, visually attractive, life-like services, more mobility, more security, and to be more peer to peer – and group interaction [1, 2]. Even today, when broadband can be served to anywhere with affordable cost, stream-type and transaction-type communication like video interactive, video distribution and networked games become popular to communicate via internet [2], [3]. For example, in some advanced countries even broadcast networks (TV and radio) are also changing. They have moved from a passive medium to an interactive medium which allows viewers to select “pay-per-view” programmes, choose from a set of camera angles, call up data about a program or send e-mails [2].These scenarios happened because of the IP-based communication and internet access experience a continuing rapid growth in business and residential environment - increase of internet broadband services demands among users. Services such as video-conferencing, storage-area networking, Internet audio and telecommuting are likely to replace standard voice and 56kbps data as the dominant profit centers in the next few years [4], [5].

The migration towards IP oriented networks seem to be slow because of copper cable based in the legacy telecom carrier’s networks. As far as the regional telecom carriers provide the internet service through the legacy telephone networks, internet needs among residential users will be saturated in a few years. It is due to expensive access charge, bandwidth bottleneck of the access line and annoying congestion to establish a connection to ISPs (internet service provider) [5]. Prior to 1994, traffic sent over internet was largely text based information with file transfer and email being among the most popular service.

Then the growth of the World Wide Web (WWW) require bigger bandwidth and higher speed as it consists of files with large number of bits, and became the base for animated graphics, audio and low-rate video. Each of these capabilities then has been pushing the need for increasingly higher-speed access [5], [6].

This paper will focus on 2 main purposes:

a) To give an overview on access network technology - the implementation and the idea how these existing technological evolution likely to able to serve the requirement.

b) To describe the basic of broadband access and why optical access is a favorite among others.

2.0 Access Network

Access network is the connection from local exchange to the customer premises. It forms the first part of a link to the national telecommunications infrastructure as each local exchange is linked to a trunk exchange and acts as an interface between the customer and the core network [7], [8]. It collects small data flows from end-users in the distribution network area, which are binded to larger flows in the feeder network area. The larger flows are then easier to transport at high speed in the backbone network. It will covers relatively small areas, up to 50 or 100 kilometers across. Link lengths may be short enough that no amplifiers and signal regenerators are needed. [4], [6]

Twisted-pair telephone line is the access medium used by the majority of individual residential subscribers today. Over the time, a number of technologies have been introduced to provide faster data speeds over this medium [7], [8]. Coax / optical fiber systems were originally introduced for video-broadcast applications. Because of these systems are inherently broadband, techniques have been developed to use this advantage to provide high-speed data transmission, principally for residential Internet access.

2.1 Types of Access Network

Listed below are types of access network technology which are commonly in used today. Most of it is dominated by copper wire and considered as the legacy telecom carrier networks. [9], [10]

• POTS – the Plain Old Telephony Service. Originally designed for voice, it is now carries voice, fax and internet traffic.
• ISDN – the Integrated Service Digital Network. This was the first attempt to optimize the telecommunications networks for services other than voice and is widespread around Europe and Asia.
• Leased lines – which provide a fixed point-to-point connection to users. They come with many forms and bandwidths.
• Wireless local loop – which replace part of the copper network with fixed wireless links. This has advantages in some situations but is not yet universally applicable.
• GSM – Global System for Mobile communications. This is rapidly expending digital mobile phone network Europe and Asia. It is good for voice and provides limited data (including internet) capabilities.
• IP – the Internet Protocol. This was intended for internet communication but is finding wider application. In its present standard form it has limitations which make it difficult to use for some services, notably voice.
• ATM – Asynchronous Transfer Mode. This was the first serious contender for providing broadband multi-service networks is currently able to handle voice and video better than unenhanced IP can.

Number of subscriber worldwide increase drastically when the Internet boom starts in 1995. To support this situation, many telecommunication companies are looking for new alternatives to improve their services. These technologies used the existing networks infrastructure but capable of supporting high speed communications.

• Passive Optical Network – Provide fiber communications without expensive electronics. They are well suited to enhancing existing networks by replacing the copper between the Local Exchange and a flexibility point. A similar approach can be used with CATV networks, for instance in a Hybrid Fiber Coax system.

• ADSL – Asymmetric Digital Subscriber Line. Enables a broadband always-on connection to be provided over a copper pair (typically of 2 Mbps downstream and 512kbps upstream).
• Cable modems – provide a shared broadband interactive link over cable TV networks. This would typically allow a user to have 2Mbps link.
• GPRS – are enhancement to GSM to provide a mobile service more suited to data.
• Power line – Some operators have provided services using the electricity distribution network for communications. This has greatly potential but there are a number of problems to overcome.
• Fixed wireless access – systems which use radio links to provide connections to customers in fixed locations. It is suitable for broadcast as well as broadband telecommunications.

IP based communication and internet access is the dominant factor that contributes to the requirement for wider bandwidth and real-time broadband services. To support these types of applications, what had been described above seems to be not enough. Researcher from Telecommunication Companies or other organizations keep developing new ways and method to meet this requirement. Listed below are some of the considered future technology which is on the horizon.

• VDSL – provides very high speed symmetric communication over short copper pairs (or coax cable TV) for the last few hundred meters to the user and is used in conjunction with fiber
• EPON (FttH) – Ethernet PON, the combination of two technologies would provide an almost unlimited bandwidth to individual users, but the economics are still not clear.
• IPv6 – is an improved form of the Internet Protocol which offer much better addressing and can provide the Quality of Service control needed for service such as voice.
• UMTS – is the 3^rd generation of mobile systems and allow data communications at about 2Mbps.
• Low Earth Orbit satellites and High Altitude Platform Stations – considerably reduce the problems caused by the transmission time to and from geostationary satellites but not yet been proven commercially viable. [2], [11]

As mentioned previously, the copper access network has become a legacy as the basic copper lines have barely changed since the days of Alexander Graham Bell, in comparison with exchange and home equipment. Equipment in the local exchange has advanced considerably since days of the human operator with the introduction of computerized switching and routing allowing faster, more reliable connections [4]. Exchange advancements have been matched in customer premises equipment such as PCs, which have increased dramatically in operating speed with 2 GHz machine speeds being commonplace compared with 100MHz few years ago. Also people are now used to 10Mbps or 100Mbps internet access in the office, with 1GHz Ethernet cards now commercially available. Converged networks of integrating telephony, data and cable TV with a single method of broadband access capabilities open up the market for the transmission and exchange for delivery of multimedia, entertainment and information to the home [12], [13],[14]. There are many competing visions of what future architecture telecommunications will take. It is however, very clear that future networks will be ‘broadband’ in their access capabilities.

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