42.8.3 Optical amplifiers

Erbium doped fibre amplifier technology has made great strides in the last three years. By using such amplifiers at both ends of an optical link, it is possible to greatly increase the maximum distance between transmitter and receiver, with distances up to 300km being predicted for links that employ low loss optical fibre cables, (c.f. present day optical inks at 565Mbit/s which can typically span 40-70km). This great increase in span capability holds out the prospect of interconnecting the majority of large centres of popula­tion in Europe by unrepeatered line systems i.e. the line systems consist of two LTEs plus cable, without any intervening simple repeaters. (Drop and insert repeaters are a different case, as they are deployed to drop and insert traffic, rather than solely to boost the amplitude of the optical signals). The resulting extinction of con­ventional line system repeaters means that the SDH RSOH in the STMs will eventually become redundant for terrestrial systems.

In addition to this, there is also the future proofing that results from replacing a conventional, electronically regenerating repeater, with a repeater that merely amplifies the transiting optical signals. Optical amplifiers are largely hit rate independent, hence it should he possible to upgrade the capacity of a line system by merely changing the LTEs, and not the repeaters. This idea is particularly exciting for undersea line systems where a major part of the total system cost lies in the repeaters. Up till now, these have always been constrained to operate at a fixed bit rate.

42.8.4 Optical switching

The use of optical switching, together with various forms of Wave­length Division Multiplexing (WDM), will lead to a requirement for yet another layer in the SDH hierarchy beyond the STM section layer. Real high speed optical switching, together with wavelength conversion is still some way in the future, hence there is no pressure to extend SDH at present.

42.8.5 Memory and processing power

As soon as it becomes economically feasible, more memory and processing power will be installed in individual SDH network elements. The use of this capability to support ever larger blocks of software will results in the average software download action trans­ferring ever more bytes, thus putting a strain on the Embedded Communication Channels (ECCs) that are built into the STM SOHs. There is also the chance that larger quantities of more sophisticated element control software will result in more management traffic between network elements and between elements and their control­lers, further increasing the load on the existing ECCs. Thus, at some point in the future is very likely that the SDH standards will have to be altered to expand the capacity of the ECCs beyond their current rates of 192 and 576kbit/s.

42.9 Conclusion

SDH is here to stay as the dominant public network transmission standard of this decade. However, the effects of the full range of SDH standards will probably be felt over a much wider area of telecommunications, because of their general applicability. For example the mere existence of the SDH optical interface specifica­tions will probably lead to their use in a variety of non-SDH applications, simply because there is a dearth of competing stand­ards. Another example is that of the SDH network recommendations, G.SNA1/2, which, with relatively little modification, are applicable to a wide variety of non-SDH networks, in particular, plesiochronous networks.

1. Learn the following technical words and word-combinations:

47.2

1.	transfer mode	режим передачи (переноса)
2.	traffic load	информационная нагрузка (трафик)

42.7.1

3.

o supercharge

перегружать

42.7.2

4.

inconsistency

противоречивость, несогласованность

42ю7ю3

5.	LAN-local area network	локальная вычислительная сеть
6.	circumference	окружность, длина окружности
7.	MAN – metropolitan area network)	(обще-) городская сеть
8.	WAN – wide-area network	глобальная (вычислительная) сеть

42.8.1

9.

heat dissipation

теплоотдача

42.8.2

10.	cabling	накладка кабеля; система кабелей
11.	calling volume	интенсивность потока вызовов

42.8.3

12.

LTE – line termination equipment

оконечная аппаратура линии

42.8.4

13.

WDM – wavelength division multiplexing

спектральное разделение; спектральное уплотнение

42.8.5

14.	EEC –1. error correcting code; 2. embedded communication channels	1.код с исправлением ошибок 2.встроенные каналы вязи
15.	processing power	вычислительная мощность

Exercise 2 Read the text 42.7- 42.9

Exercise 3 Find the Russian equivalents for the following English technical word-combinations:

1.	packet transfer techniques
2.	constant traffic load
3.	the switching machines
4.	the current front runner
5.	the network access nodes
6.	Switched Multimegabit Data Service (SMDS)
7.	Fiber Distributed Data Interface (FDDI)
8.	rack space
9.	an optical interconnect cable
10.	Erbium doped fiber amplifier technology
11.	unrepeatered line systems
12.	transiting optical signals
13.	high speed optical switching
14.	the average software download action
15.	more sophisticated element control software
16.	wavelength conversion

Exercise 4

Find the English equivalents for the following Russian technical word-combinations:

1.	коммерческое использование ATM коммутаторов
2.	инновационные идеи
3.	излишний, чрезмерный, ненужный
4.	аварийное состояние
5.	коммутируемые услуги многомегабитовых данных
6.	распределяемые данные
7.	неуменьшающийся, неослабеваемый
8.	перекрестные искажения
9.	нехватка, недостаток
10.	реле цикла

Exercise 5

Answer the following questions:

1.Does SDH currently have any real competitors?

2.What is ATM standard aimed at?

3.What are several other Fast Packet techniques aimed at?

4.What is the best way to view Frame Relay?

5.Why can a Frame Relay network deliver much higher throughputs than an X.25 network?

6.What is Switched Multimegabit Data Service aimed at?

7.What are some problems, relating to the maximum delay that an FDDI ring can withstand?

8.What will equipments implementing the SDH standards be strongly influenced by?

9.What does faster, smaller and cheaper traffic handling lead to?

10.What are the advantages to optical interconnection?

11.What devices are used to increase the maximum distance between transmitter and receiver?

12.Does the extinction of line system repeaters mean that the SDH RSOH in the STMs will eventually become redundant for terrestrial systems?

13.Is there any pressure to extend SDH at present?

Exercise 6

Make a short report on perspectives of memory and processing power (part 42.8.5)

Exercise 6

a) Translate into Russian in writing part 42.8.1,42.8.2 and 42.8.4.

b) Translate into Russian in writing part 42.8.3.