光通信网络手册：光纤传输与高速通信的未来

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"《光学通信网络手册》是一本详尽且最新的技术指南，专注于集成的、尖端的光学网络。本书由国际知名专家撰写，深入介绍了光学网络领域，从基本概念到研究级材料，涵盖了所有关键方面，如协议、资源管理、WDM网络中的路由和波长分配、连接管理、生存性、使能技术以及未来趋势。这本书是通信专业人士解决光学网络当前和未来技术挑战的一站式参考资料，结构清晰，便于快速查找，并包含了该领域的领军人物的洞察力。" 光学通信网络是互联网革命的重要组成部分，随着高速传输介质和高速硬件的发展，我们正快速迈向一个单一通信网络支持所有通信活动的时代，这个网络将以光纤作为传输介质，使用光交换/路由器作为节点。《光学通信网络手册》是理解这一转变的关键资源。书中首先对光学通信网络领域进行了深入的介绍，引导读者理解基础理论。接着，作者们探讨了各种核心技术，包括： 1. 协议：在光学网络中，协议是确保不同设备之间有效通信的关键。这些协议可能涉及数据封装、错误检测和纠正、同步以及网络层次间的交互。 2. 资源管理：高效地分配和管理光学网络中的带宽、波长等资源，对于满足用户对高速服务的需求至关重要。 3. 路由和波长分配：WDM（波分复用）网络中的路由和波长分配策略允许多个数据流在同一光纤上同时传输，极大地提高了网络容量。 4. 连接管理：建立、维护和拆除网络连接，确保数据的可靠传输。 5. 生存性：讨论了网络如何应对故障，如通过冗余路径和保护恢复机制来确保服务连续性。 6. 使能技术：包括光电子集成电路、光纤制造技术、光放大器、光开关等，这些都是构建先进光学网络的基础。 7. 未来趋势：展望了光学通信网络的未来发展，如全光网络、软件定义网络（SDN）和网络功能虚拟化（NFV）等新兴技术。这本书不仅对工程师和研究人员有极大的价值，也为教育工作者和学生提供了宝贵的教材。通过深入浅出的解释和丰富的实例，读者可以系统地学习并掌握光学通信网络的核心概念和技术。《光学通信网络手册》作为该领域的权威参考，有助于推动通信行业的进步和发展。

Chapter one: Overview of optical communication networks 3

ﬁber’s potential bandwidth is nearly three orders of magnitude higher than

electronic data rates of a few tens of gigabits per second (Gbps), we need to

tap into this huge optic-electronic bandwidth mismatch. Because the maxi-

mum rate at which an end user — which can be a workstation or a gateway

that interfaces with lower-speed sub-networks — can access the network is

limited by electronic speed, concurrency among multiple user transmissions

should be introduced to exploit the ﬁber’s huge bandwidth.

WDM is a favorite multiplexing technology in optical communication

networks because it supports a cost-effective method to provide concur-

rency among multiple transmissions in the wavelength domain. Several

communication channels, each carried by a different wavelength, are mul-

tiplexed into a single ﬁber strand at one end and demultiplexed at the

other end, thereby enabling multiple simultaneous transmissions. Each

communication channel (wavelength) can operate at any electronic pro-

cessing speed (e.g., OC-192 or OC-768).* For example, a ﬁber strand that

supports 160 communication channels (i.e., 160 wavelengths, each operat-

ing at 40 Gbps) would yield an aggregate capacity of 6.4 Tbps.

Today’s telecom network can be considered to consist of three sub-net-

works: access (spanning about 1 to 10 km), metropolitan (covering about 10

to 100 km), and long haul (extending to 100s or 1000s of km) (see Figure

1.2); and ﬁber is being extensively deployed in all three sub-networks. Typ-

ically, the network topology for access can be a star, a bus, or a ring; for

metro a ring; and for long haul a mesh. Each of these sub-networks has a

different set of functions to perform; hence, each has a different set of chal-

lenges, technological requirements, and research problems. For example, for

the long-haul network, carriers are more concerned with capacity, protection,

Figure 1.1

Past and projected future growth of data and voice trafﬁc.

* OC-n stands for an “optical channel” with data rate of n x 51.84 Mbps approximately.

Relative Load

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

Data

Voice

1333_FrameBook.book Page 3 Tuesday, February 25, 2003 11:33 AM

4 The handbook of optical communication networks

and restoration, while for the metro or access network, carriers are more

concerned with service provisioning/monitoring, ﬂexibility, etc.

The focus of this chapter is to present technological advances, promising

architectures, and exciting research issues in designing and operating

next-generation optical WDM networks that are scalable and ﬂexible. The

next section provides a brief discussion on the important building blocks of

optical WDM networks. This is followed by an overview of access, metro-

politan, and long-haul networks separately. Special attention has been paid

to the long-haul network because there is a tremendous need to develop

new intelligent algorithms and approaches to efﬁciently design and operate

these wide-area-optical-mesh networks built on new emerging technologies.

We present several research topics including routing and wavelength assign-

ment (RWA), fault management, multicasting, trafﬁc grooming, optical

packet switching, and various connection-management problems.

1.2 Enabling WDM technologies

An important factor to consider in the design of a WDM network is the

number of wavelengths to use. The maximum number of wavelengths is

limited by optical device technology and is affected primarily by the total

available bandwidth or spectral range of the components (including the

ﬁber) and the spacing between channels. Conventional ﬁbers have a low

attenuation region between 1335 and 1625 nm with a “water-peak window”

at 1385 nm. New “all-wave” ﬁbers do not have this water peak and hence

can use a larger spectrum (see Figure 1.3). Channel spacing itself is affected

by several factors such as the channel bit rates, optical power budget, non-

linearities in the ﬁber, and the resolution of transmitters and receivers. In

dense

wavelength-division multiplexing (DWDM), a large number of wave-

lengths (>160) is packed densely into the ﬁber with small channel spacing.

An alternative WDM technology with a smaller number of wavelengths (<

Figure 1.2

Telecom network overview.

Long Haul

- 100s–1000s km

- Mesh

Metro (Interoffice)

- 10s of km

- Rings

Access

- A Few km

- Hubbed Rings, PONs

Users

1333_FrameBook.book Page 4 Tuesday, February 25, 2003 11:33 AM

6 The handbook of optical communication networks

The EDFAs with gain spectrum of 30 to 40 nm each (typically in the 1530

to 1560 nm range; see Figure 1.4) can be interconnected to broaden their gain

bandwidth. This “ampliﬁer circuit” is referred to as an ultrawide-band

EDFA, which can fully exploit the expanded low-attenuation region of the

new “all-wave ﬁber” (see Figure 1.4).

OADMs — also referred to as wavelength add-drop multiplexers

(WADMs) — are employed to take in (add) and take out (drop) individual

wavelengths from an optical ﬁber completely in the optical domain (i.e.,

without any conversion of the optical signal into electronic domain).

OADMs, which can add and drop a speciﬁc predeﬁned channel (or a group

of channels), are said to be ﬁxed-tuned (or static) and the technology for

manufacturing them is mature. Reconﬁgurable OADMs (ROADMs), with

add-drop wavelengths that can be controlled by an external stimulus (e.g.,

by software) are said to be tunable (or dynamic). ROADMs are more pow-

erful because they can adapt to the ﬂuctuating trafﬁc demand but the tech-

nology for building ROADMs is still in nascent stage.

When the network topology is a mesh, where nodes are interconnected

by ﬁbers to form an arbitrary graph, an additional ﬁber interconnection

device is needed to route the signals from an input port to the desired output

port. These devices are called optical crossconnects (OXCs). They can either

transparent

(to bit rates and signal formats) in which signals are switched

all-optically

or be

opaque

in which incoming signals are converted from

optical to electronic domain and switched electronically. A possible architec-

ture for a transparent OXC is presented in Figure 1.5, where all signals on

a particular wavelength (e.g.,

) arriving on M input ﬁbers are switched

separately by a wavelength-speciﬁc MxM switch. As more and more wave-

lengths are packed into a ﬁber, the size of the OXCs is expected to increase.

Among several technologies (e.g., bubble, liquid crystal, thermo-optic, holo-

graphic, electro-optic, LiNbO

, etc.) used for building all-optical OXCs,

MEMS (micro-electro-mechanical-systems) based OXCs are becoming pop-

ular because of their compact design, low power consumption, and promise

Figure 1.5

An optical crossconnect (OXC) of size NM x NM (N is the number of

wavelengths; M is the number of incoming/outgoing ﬁbers).

1333_FrameBook.book Page 6 Tuesday, February 25, 2003 11:33 AM

Chapter one: Overview of optical communication networks 7

for high port count.

For details on emerging MEMS-based OXC architec-

tures, please refer to Reference 5.

1.3 Access networks

The access network connects the subscribers (home or business) to the service

providers; in other words, it serves as the “last mile” (as well as the “ﬁrst

mile”) of the information ﬂow. To meet the growing trafﬁc demand, service

providers expend most of their effort on increasing the bandwidth on their

backbone network. But little has changed in the access network. It is now

the general opinion that the last mile has become a bottleneck in today’s

network infrastructure.

Optical technology is a promising candidate for

solving the bandwidth problem in access networks because it can provide

at least 10 to 100 times more bandwidth over a larger coverage area. The

next wave in access network deployment will bring the ﬁber to the building

(FTTB) or to the home (FTTH), enabling Gbps speeds at costs comparable

to other technologies such as digital subscriber line (DSL) and hybrid ﬁber

coax (HFC).

Three optical technologies are promising candidates for the next-gener-

ation access networks: point-to-point topologies, passive optical networks,

and free-space optics.

1.3.1 Point-to-point topologies

Point-to-point dedicated ﬁber links can connect each subscriber to the tele-

com central ofﬁce (CO), as illustrated in Figure 1.6a. This architecture is

simple but expensive due to the extensive ﬁber deployment. An alternative

approach is to use an active star topology, where a curb switch is placed

close to the subscribers to multiplex/de-multiplex signals between the sub-

scribers and the CO. This alternative in Figure 1.6b is more cost effective in

terms of deployed ﬁber. A disadvantage of this approach is that the curb

switch is an active component that requires electrical power as well as

backup power at the curb-unit location.

1.3.2 Passive optical networks

Passive optical networks (PONs) replace the curb switch with a passive

optical component such as an optical splitter (Figure 1.6c). This is one of the

several possible topologies suitable for PONs including tree-and-branch,

ring, and bus. PON minimizes the amount of ﬁber deployed, total number

of optical transceivers in the system, and electrical power consumption.

Currently, two PON technologies are being investigated: ATM PONs

(APON) and Ethernet PONs (EPON). APON uses ATM as its layer-2 proto-

col; thus, it can provide quality-of-service features. EPON carries all data

encapsulated in Ethernet frames, and can provide a relatively inexpensive

solution compared to APON. EPON is gaining popularity and is being

1333_FrameBook.book Page 7 Tuesday, February 25, 2003 11:33 AM

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光通信网络手册：光纤传输与高速通信的未来

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