D.W. Faulkner

Optical networks for local loop applications

Some of the options for optical technology within the local loop environment are examined. In particular, passive shared access networks have been considered in some detail. These networks show great promise for delivering existing telephone services to small to medium business customers (4-30 lines) economically by the early 1990s. Extending fiber to the home will also be possible by virtue of a similar passive network infrastructure for customers requiring new broadband services beyond the single telephone line. For one-line plain old telephone service (POTS) customers, an intermediate approach of terminating the fiber network at the final network distribution point, with copper retained for the final leg, may be used prior to the provision of broadband services. A key feature of the passive optical network architecture is the use of wavelength-division multiplexing (WDM) as an upgrade strategy, allowing graceful upgrading from telephone services to multichannel high-definition television (HDTV) on gigabit/second bearers and full two-way switched broadband services employing wavelength routing across the network. >

Low-cost digital passive optical networks

Techniques for reducing the cost of providing digital telephony and broadband services to the home over passive optical networks are proposed. These include the use of optical transceivers in an optical TDMA (time-division multiple access) telephony system and using low-cost consumer technology in providing a digital CATV (cable television) service using TDM (time division multiplexing).<<ETX>>

An experimental broadband and telephony passive optical network

An experimental passive optical network that demonstrates the integrated delivery of telephony and broadband services to a variety of business and residential customers over a typical local loop is described. Telephony is provided over a 112-way split at 1300 nm, and broadband services (asynchronous transfer mode and single-channel video at 155 Mb/s, and 2.2 Gb/s 32-channel video) are provided over a 28-way split. Two approaches to the addition of broadband services are used: coarse-grained WDM (wavelength-division multiplexing) with 20-nm channel spacing in the 1300-nm window, and high-density WDM with 1-nm spacing in the 1500-nm window. Optical technology solutions are described for providing different levels of service to various customer types, including a single-mode wavelength multiplexer with 1-nm channel spacing, a hybrid integrated demultiplexer/receiver with 20-nm channel spacing, and a tunable optical filter with 0.6-nm FWHM (full-width at half-maximum) bandwidth.<<ETX>>

Passive optical telephony networks and broadband evolution

A passive optical local access network for telephony applications is proposed which can evolve a future broadband ISDN (integrated services digital network). A laboratory demonstrator has been constructed which can deliver a 144-kb/s ISDN channel, or the equivalent to 128 customers from a single fiber exchange. Options for evolution to broadband ISDN are discussed with emphasis on choice of multiplexing technique. A novel TDM (time-division multiplexing) sampling technique for demultiplexing and selecting digital video channels at the customer end is described. A 323-channel capability has been demonstrated at 2.2 Gb/s over an experimental optical network.<<ETX>>

Evolution scenarios for optical telecommunication networks using multiwavelength transmission

The authors discuss how the transition in telecommunication networks taking place with increasing use of fiber in all segments of the networks, together with the increasing demand for broadband services, will lead to new network architectures. The customer access portion of these networks may have a large geographical range and high functionality, and may encompass switching functions. The increased use of optical routing based on wavelength multiplexing is likely to be employed in both the core and access portions of the new architectures. Among others, these developments will mean that fewer conventional crosspoint switches are required to support future broadband networks. >

Recent developments in PON systems standards in ITU-T

Recommendations for Broadband Passive Optical Networks (B-PON) and Gigabit Capable Passive Optical Networks (G-PON) are now reaching maturity in ITU-T. Many vendors are offering conformance with the B-PON series of standards and products with G-PON conformance are emerging. These systems typically operate over a maximum 20 km, 32-way split optical distribution network. The capacity of B-PON ranges from 155/155 Mbit/s symmetrical to 1240/620 Mbit/s asymmetrical transmission. G-PON extends this capacity to 2.4/2.4 Gbit/s and allows more efficient transmission of Ethernet. This paper presents an update on the status of standards on passive optical networks systems with emphasis on recent developments in Q.2/15 of ITU-T.

Broadband digital transmission over passive optical networks

The authors propose a low-cost digital technique for broadband transport which is capable of transparently carrying distribution quality video, data, and digital audio services economically over a passive optical network. Two possible upgrade routes from unidirectional to bidirectional services are discussed, one using optical technology, the other using electrical techniques. The use of digital transmission, with its inherent scrambling abilities, enables access to switched services to be controlled and generates an architecture suitable for a bidirectional service with no switching necessary at the head end. By locating shared transcoders at the head end, low-cost, high-bit-rate transmission can be used in the access network where the onus is on cheap terminal equipment, and an economic gateway to low-bit-rate transmission in the core network can be provided. The authors also discuss a video coding technique implemented in field programmable gate array technologies that encodes PAL at around 57 Mb/s, should be capable of encoding NTSC at around 45 Mb/s, and delivers video at a weighted SNR (signal-to-noise ratio) of 52 dB.<<ETX>>

Comparative performance of intensity modulation schemes for HDTV transmission on single-mode fibre

This paper builds upon earlier work concerned with high definition television (HDTV) transmission for application in the future optical fibre local telephone network. The HDTV signal is introduced by reference to the NHK system originating in Japan and the HD-MAC system supported in Europe. Both digital and analogue intensity modulation schemes for HDTV transmission on single mode fibre are then assessed in relation to transmission bandwidth, receiver signal to noise ratio, multiplexing capabilities, terminal complexity and cost. The practical implementation of a high speed pulse code modulated (P04) HDTV single mode fibre transmission system is then discussed. Details of the implementation of a sub-carrier frequency modulation (SCFM) system are then followed by a description of the practical realisation of a novel wideband pulse frequency modulation (PFM) system again for HDTV transmission on single mode fibre. Modification of this latter system for square wave frequency modulation (SWFM) is then discussed. Finally performance data on the aforementioned systems are presented and compared in order to determine specific trade-offs associated with these modulation techniques for optical fibre HDTV transmission.

Passive optical network performance with time division multiplexing (TDM) and ATM

This paper reports on the investigation of the traffic throughput performance of passive optical networks using both time division multiplexing (TDM) and asynchronous transfer mode (ATM) transmission techniques. In particular discrete event computer simulation techniques are utilized to study the performance of these networks under asymmetric traffic loading conditions. The performance characteristics obtained demonstrate the degradation of the network traffic throughput using TDM, whereas ATM transmission proves resilient to even high levels of asymmetric traffic loading on the passive optical network.

Full service access networks: experimental realization and performance

This paper describes how an experimental full services access network has been constructed at BT Labs and presents views on how its performance could be improved to meet the reliability and traffic loading requirements expected in real applications such as fiber to the business and fiber to the cabinet. The experimental network included: asynchronous transfer mode (ATM) switch, an ATM passive optical network (PON), very high speed digital subscriber loop (VDSL) customer drop and ATM forum 25 Mbit/s customer network. The design and realization of the VDSL customer drop, the signaling system and the interfaces between the system elements formed a major part of the design and construction work at BT Labs. The ability to cope with varying service demand and achieving the necessary quality of service are important requirements for roll-out systems. This paper describes how these requirements could be met in the design of future proprietary equipment.