Technology Interoperation in ATM Management
by Stelios Sartzetakis
Providing cost-effective network survivability and availability;
fast-responding, reliable fault detection and self-healing mechanisms,
distributed dynamic routing functions with inherent load balancing
capabilities, efficient VP layer design and dynamic network reconfiguration
functions in an ATM network is a complicated task. Emerging technologies
and standards are needed for the operation and management of ATM
networks. The ACTS REFORM project used a number of these including:
ATMF UNI and PNNI, OMG CORBA and Component Model and TINA NRA
thus demonstrating the applicability, coexistence and interoperation
of some of these technologies.
Having the network provider’s viewpoint in mind, who is offering
QoS-based, switched, on-demand connectivity services, the REFORM
project designed, implemented and tested a prototype system which
provides the necessary means and functions for ensuring network
resilience (availability & survivability) within acceptable levels,
and in a cost effective manner. The REFORM system covers the configuration,
performance and fault management functional areas. REFORM’s control
plane system (embedded in the network elements) hosts the required
connection-oriented network layer functionality in addition to
the REFORM-specific fast-responding fault detection, self-healing
and QoS-based dynamic routing functions. The management plane
system is concerned with the initial configuration and on-going
dynamic management of the ATM VP layer. Specifically it hosts
dynamic VPC bandwidth management, VP layer design and dynamic
reconfiguration, fault management (filtering and correlation)
functions as well as generic configuration and network resource
monitoring functions.
The entire REFORM system operates through a hierarchical model
at different levels of time-scale and abstraction. The REFORM
management system integrates the tasks of network planning and
dimensioning with dynamic configuration, fault and performance
management. The network planning and dimension functions lie at
the heart of the REFORM system facilitating cost-effective network
operation and enabling the implementation of the operator’s business
policy regarding service provisioning for the range of services
being offered. Dynamic configuration, fault, and performance management
are required for continuously optimising the performance of the
network according to actual usage levels. Traditionally, these
areas have been handled by disjoint systems for network planning,
configuration management, performance management and fault management.
In our view, network management is much more than a data collection
exercise for supporting configuration, fault and performance reports
to be subsequently fed to network operators to determine the next
course of action. REFORM considers network management functions
as built-in, automated and intelligent facilities, which respond
to changes in network conditions as and even before they happen.
A human-orientated model of decision making may no longer be always
viable for ensuring the cost-effective management of complex,
multi-service networks. Network management functions need to actively
interact with the network, exploiting and complementing the capabilities
of the Network Elements (NEs), and therefore should be seen as
an extension of embedded NE functionality.
REFORM used networks built from multi-vendor NEs in its trials.
As of today, implementations of the same signalling protocol by
different vendors rarely fully inter-work and co-operate. Furthermore,
the other REFORM control plane components were required to co-operate
with the signalling components for collecting statistics and providing
routing information. This level of interaction with embedded capabilities
is not feasible with today?s commercially available NEs, as access
to the internal functionality of the network equipment is very
limited. To overcome these problems, the notion of the REFORM
Node was introduced. The REFORM Node incorporates the control
plane functions of the REFORM system, allowing vendor-independent
interaction with the NEs and uniform signalling and routing functions
throughout the network. This is achieved by isolating vendor-specific
technology from the system components through an intermediate
adaptation layer to the specific NE. An existing ATM Forum UNI
3.0 signalling stack implementation was modified in order to offer
uniform signalling capabilities at both UNI and NNI reference
points of the REFORM Node. However it should be noted that any
NNI protocol eg B-ISUP, PNNI could have been used. Appropriate
modifications according to the REFORM model for QoS provisioning
had to be made.
The PNNI specification can be seen as containing two parts: the
routing protocol and the signalling protocol. The PNNI routing
protocol was used as the basis for dynamic routing in REFORM.
The REFORM QoS-based routing algorithm runs over the PNNI topology
information distribution mechanisms. The PNNI routing protocol
specifications constitute a rich platform for building intelligent
routing schemes. PNNI routing protocols may co-exist with other
signalling systems, which support source node or hop-by-hop routing.
However, some routing schemes, such as the one adopted by REFORM,
may be of a hybrid nature combining the merits of centralised
and distributed routing. The PNNI specifications should not be
seen as dictating the particular routing scheme to be applied,
but rather as a framework enabling distributed exchange of topology
information.
In the REFORM system, a hybrid routing scheme is adopted shown
in the figure. The centralised part (residing in the management
plane) defines the admissible routes per source-destination and
CoS (distinct Class of Service) so that the QoS requirements of
the CoSs and certain network-wide cost-effective criteria are
met. The distributed part is responsible for influencing the routing
decisions (from the many possible pre-defined admissible routes),
according to actual traffic conditions, with the purpose to drive
the network towards a load-balanced state. This hybrid routing
scheme maintains the merits of dynamic routing and at the same
time harnesses routing dynamicity to operate within the overall
network operational policies with respect to QoS provisioning.
Experimen-tation has shown that the distributed PNNI routing protocols
can interoperate with overlying network management systems for
QoS-based routing.
CORBA was used as the ultimate integration means that allows transparent
communication not only between distributed objects, but also between
objects located in the same machine; eg between two components
in the same network node. In the same way that CORBA insulates
distributed applications from network details it also abstracts
implementations from operating system peculiarities. We are in
no doubt that future management frameworks will be based on distributed
object technologies, with CORBA being a prime candidate. It is
also likely that CORBA can be used in the control plane to support
open, object-oriented network layer functionality, though this
requires lightweight operations and mappings of its protocols
over specific network technologies such as ATM AAL5. The use of
the OMG Component Model in the REFORM control plane was a step
in this direction.
The REFORM system is one of the first attempts to validate the
TINA NRA (Telecommunications Information Networking Architecture
Network Resource Architecture) in a practical network management
application encompassing configuration, performance and fault
management aspects. REFORM field trials were conducted on several
testbeds: the ACTS EXPERT testbed in Basel, Switzerland, and on
ATM networks in Norway, Greece and Japan.
The REFORM system realisation showed that the evolution towards
flexible telecommunications systems built from off-the-shelf intelligent
software and hardware components is feasible in the near future.
The project REFORM was part of the ACTS programme. The other partners
were NTT, Telenor, OTE, Alcatel, UCL, NTUA, Skelton, IONA, with
Algosystems as the co-ordinator. Further information can be found
at: http://olympus.algo.com.gr/acts/reform/public.htm
Please contact:
Stelios Sartzetakis - ICS-FORTH
Tel: +30 81 39 1727
E-mail: stelios@ics.forth.gr
