Summary & Conclusions

During the course o f the study, a number o f factors have come to our attention as being of major significance. We are acutely aware that we do not have access to proper costing data for the various network possibilities and we are thus left "backing hunches". These are highlighted below :-

1. There appears to be a growing opinion (consensus?) that FTTH will not cost-in in the immediate future and that a broad-band service for the private customer must be launched via FTTC and/or the Fibre/Coax-Hybrid (FCH) approach.

2. There is a rapidly growing interest in Video on Demand (VoD) which in turn concentrates attention on the growing emergence o f a digital data rate in the region o f 2Mbit/s as a potential point o f convergence since it appears to be common to

- compressed video storage for electronic file servers for VoD - ADSL for VoD

- the range of Compact Disc products (CD, CD-ROM, CD-I and CD-V as well as Photo-CD)

3. Taken together, these call into question the ambitious proposals that appeared common with programmes such as EC-RACE for 155Mbit/s provision to the home (CCITT recommendation 1.413).

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Taken together, these do not immediately appear to strengthen the case for the use of WDM!

5. In terms o f transmission to and from the local loop area, if the economics favour the use o f bi-directional operation on a single fibre, then simple WDM seems likely to be strongly advantageous as a way of minimising Near End Cross Talk problems by using different wavelengths for up and down stream signals.

6. The next obvious potential use for WDM is in service differentiation. For example, one might envisage feeding a PON for 64 homes with (order) 70 Mbit/s VoD channels on one wavelength and using 2 other wavelengths for up and down stream TPON telephony. We suggest the advantages of this approach would be>

- ease o f service fusion at the PON entry (using a W MUX) - ease of service separation at the Curb or Customer Terminal - ease o f billing and service management

7. WDM technology also seems ideally placed for service upgrading in that a new service can be overlaid on an existing network with additional receivers only being added to those customers choosing to take it. Existing customers installations remain unchanged.

8. Note in o f the cases 6 & 7 one is balancing the cost o f additional optoelectronics against the cost o f higher data rate TDM transmit and receiver electronics/optoelectronics and software/management complexity. We are not able to assess that trade-off.

9. WDM technology could also be used to address different geographic communities over a single PON. For example, we envisage that one (group of) wavelength(s) might be used to service businesses and another for private users, separated by W MUX at a suitable downstream distance. In practice however we suspect that it will be preferred to provide separate feeder fibres.

145 10. WDM technology could be used to upgrade an installed PON set up for the delivery

of "broadcast TV" services by splitting the final service area into a series of sub- areas, each served via a different wavelength carrier. In this way the balance of capacity could be shifted to provide a number o f carriers exceeding the number of customers so that switched star operation becomes possible.

11. Looking fijrther into the future, we have noted that among the key telecommunications technologies, it is fibre that today has by far the greatest unexploited capability, (e.g., the EDFA window is circa 5000GHz wide yet we use at most a few GHz of spectrum). Since there is no expectation o f a 1000-fold increase in traffic, this raises the philosophical question o f whether there are other ways of exploiting this space.

12. The components to access this empty communications space are rapidly becoming available in the form o f tuneable DFB type lasers, tuneable filters etc. An opportunity that exists.

13. We offer our own “vision” o f the Sparsely-Filled DWDM National Network as one possibility that inexorably leads to a number o f new issues :-

- completely new ways o f multiplexing data into and out of the network - substantially different control characteristics

- different transmission characteristics (greater transparency, lower delay etc.)

- new ways of trading-oflf between transmission and switching.

14. We do not suggest that SF-DWDM is the only such possibility or that it is likely to become commercially attractive in the very short term. We simply offer it as an illustration o f the radically different alternative routes for future development that are now opening up.

5.8 Bibliography

Proceedings The X International Symposium on Subscriber Loops & Services, issls 93, “Communications at a Crossroads”, September 27 - October 1, 1993, Vancouver, British Columbia, Canada

Prycker M. de. Asynchronous Transfer Mode: solution for broadband ISDN, Ellis Horwood, 1991.

Kashima N., Optical Transmission for the Subscriber Loop, Artech House, 1993.

Optical Switching in Networks Collaboration, “Notes from meeting at Heathrow Excelsior”, Wednesday 18* May 1994

John E. Midwinter & Staff, “Potential for Wavelength Division Multiplexing in Local Broadband networks”, 1994

5.9 References

[1] Ishikawa H., “Evolving from Narrowband”, IEEE Communications Magazine, pp. 32-36, 1992

[2] Morillo A., Valtuena R., “A Techno-Economical Evaluation of Alternative Evolution Strategies of the Future Optical Access Network.”, Networks ‘92 “Network Planning for an Open Era”, pp. 19-24, 1992.

[3] Tumolillo A., “What do telcos know about the subscriber loop?”. Telephony, pp. 26-28, 1992.

[4] Morgen D. H , “Fiber-to-the-curb power: Real-world constraints and solutions ”. Telephony, pp. 20-24, 1991.

[5] Lin Y.-K. M., Spears D. R , Yin M., “Fiber-Based Local Access Network Architectures ”, IEEE Communications Magazine, pp. 64-73, 1989.

[6] Bohn P. P., Kania M. J., Nemchik J. M., Purkey R. C , “Fiber in the loop ”, AT&T Technical Journal, pp. 31-43, 1992.

[7] Henry P. S., “High-Capacity lightwave Local Area Networks.’, IEEE Communications Magazine, pp. 20-26, 1989.

[8] Elrefaie A. F , “Multiwavelength Survivable Ring Network Architectures”, ICC’93.

[9] Midwinter J. E., “Sparsely-Filled Densely-Wavelength-Division-Multiplexed networks.”, Photonics in Switching, Technical Digest Conference Edition, pp. 210- 213, March 15-17, 1993

[10] Sabry M., Midwinter J. E , “A Modular and Scalable Transparent optical Network” , ECOC’93 Conference Proceedings, Vol. 3, Post deadline papers, Th. P. 12.12, pp. 97-100, September 12-16, 1993.

[11] Fortenberry R. M , Cai Y , Tucker R , “Optically transparent node for multiple-bit- rate photonic-switched local area network” , OFC/IOOC’93 Technical Digest, Paper TuE4, pp. 21- 22, Feb. 1993

[12] Stem J. R , Ballance J. W , Faulkner D. W , Homung S., Payne D. B , Oakley K., “Passive Optical Local Networks for Telephony Applications and Beyond ”, Electron. Lett., Vol. 23, No. 24, pp. 1255-1257, 1987.

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[13] McMahon D. H., “Doing Wavelength-Divlsion Multiplexing with Today’s Technology.”, IEEE Lts., pp. 40-50, 1992.

[14] Wagher S. S., Kobrinski H , “WDM Applications in Broadband Telecommunication Networks.”, IEEE Communications Magazine, pp. 22-30,

Chapter Six