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.