The Internet Encyclopedia (Volume 3)

P1: JDV

DeNoia WL040/Bidgolio-Vol I WL040-Sample.cls June 20, 2003 17:57 Char Count= 0

780 WIDEAREA ANDMETROPOLITANAREANETWORKS

subscribers in a neighborhood typically share data net-

working capacity on the aggregate cable that carries traffic

back to the provider’s central service location. This is dif-

ferent from a leased-line approach, where access capacity

is dedicated from each subscriber location all the way to

the provider’s POP. In the United States, cable providers

are regulated differently from other public telecommu-

nications providers, and may not suffer the same conse-

quences for unavailable service.

Management

Management for MANs and WANs typically began with

proprietary systems sold to service providers by each man-

ufacturer of telecommunications switching equipment.

Networks composed of equipment from multiple vendors

thus contained multiple management systems. Equip-

ment management and service management functions

are often tied together by anOperations Support System

(OSS) in order to automate operations (e.g., performance

monitoring), administration (e.g., ordering and billing),

maintenance (e.g., diagnostics, fault detection and iso-

lation), and provisioning (OAM&P) functions. Many ser-

vice providers tailored what they could acquire as a basic

OSS in order to accommodate their own specific sets of

equipment and services, making it difficult to share infor-

mation, provide consistent management data in a mul-

tiprovider environment, and keep up to date with new

functional requirements. This often leaves customers who

need services from multiple providers without a single,

coherent view of their enterprise WAN resources.

Beginning in 1988, the Telecommunication Standard-

ization sector of the International Telecommunication

Union (ITU-T, formerly the Consultative Committee on In-

ternational Telephony and Telegraphy, CCITT) set about

establishing the precepts for a standardTelecommunica-

tions Management Network(TMN). While the concept of

a TMN encompasses the entire set of OAM&P applica-

tions in the network, what they do, and how they com-

municate, ITU-T standards focus on the information re-

quired and how it should be communicated rather than

how it is processed (M.3000 recommendation series). Two

types of telecommunications resources are encompassed:

managed systems (such as a switch), which are called

network elements (NE), and management systems, usu-

ally implemented as operations systems (OS). TMN stan-

dards are organized into interface specifications that de-

fine the interconnection relationships possible between

resources. Figure 4 shows the relationship between the

TMN and the telecommunication network for which it is

responsible.

TMN is based on the Open Systems Interconnec-

tion (OSI) management framework, using object-oriented

principles and standard interfaces to define communica-

tion for purposes of managing the network. The primary

interface specification, Q3, allows direct communication

with an OS. Any network component that does not im-

plement Q3 may not access an OS directly, but must go

through a mediation device (MD) instead. Legacy equip-

ment and systems that rely on proprietary ASCII messages

for communication are accommodated by means of a

Q-adapter (QA) that can translate between messages

NE

NE

NE

OS

Data

network

OS

OS

Telecommunication

network

Q3 TMN

Figure 4: TMN and the network it manages.

representing the legacy information model and the

object-oriented representation expected in today’s TMN.

TMN defines a layered architecture (ITU-T standard

M.3010) as a logical model for the functions involved

in managing a telecommunication network effectively

(Table 3). The object is to create a framework for inter-

operability across heterogeneous operation systems and

telecommunication networks that is flexible, scalable, re-

liable, easy to enhance, and ultimately, inexpensive to op-

erate. Standard management services have been defined

for alarm surveillance (Q.821), performance management

(Q.822), traffic management (Q.823), ISDN service profile

management (Q.824), call detail recording (Q.825), and

routing management (Q.826).

Differences around the World

Creating and operating WANs or MANs in different coun-

tries may present challenges well beyond identifying a ser-

vice provider and getting connections established. A par-

ticular type of service may not be available in the desired

location, or a single provider may not offer services in ev-

ery location, or the capacity required may not be available.

Such differences may be due to telecommunication infras-

tructure of varying ages and technologies, or to different

regulations on service offerings in various countries. For

example, T1 service is readily available in most U.S. cities.

Mexico, however, employs the European standard hier-

archy. Thus E1 service would need to be ordered (if it is

available) to connect a business location in Mexico to one

in the United States, and the differences in capacity and

framing would have to be handled appropriately by the

network equipment at each end of the link.

In some countries, telecommunication is a regulated

industry subject to many government-imposed rules, and