GMPLS: Interoperability Plus

In today’s market conditions, survival of a telecom service provider
depends on efficient utilization of all the resources viz. network, manpower,
frequency spectrum, and IT infrastructure. However, maximum RoI can be derived
from the efficient use of the most precious resource of all–the network.

Most of the service providers have networks consisting of multi-domain,
multi-technology and multi-vendor equipment. One big issue is of
interoperability between these equipment and their integration into a single
operating support system (OSS)/business support system (BSS). It is almost
impossible for different proprietary implementations to interoperate unless the
vendors jointly develop these implementations. Therefore, a common industry
standard is important, and fortunately, various segments of the industry are
working towards it. Generalized Multi-Protocol Label Switching (GMPLS) is the
solution that can help service providers reduce operational expenditure as well
as increase the services they offer to their

customers.

Evolution
of GMPLS

Today’s transport network infrastructure provides excellent performance
and reliability for voice traffic, the bulk of traffic prior to 1995. Since
1995, however, there has been a dramatic increase in data traffic primarily
driven by Internet’s explosive growth. The service providers need solution
that enables them to carry a large volume of voice and data traffic, and
management of network devices in a most cost-efficient manner. This urge of
service providers is the main driving factor in the evolution and enhancement of
the MPLS suite of protocol, resulting in emergence of GMPLS.

GMPLS has evolved from MPLS–the original Internet Engineering Task Force (IETF)
standard intended to enhance the forwarding performance and traffic engineering
intelligence of packet-based (ATM, IP) networks. With support from the IETF and
the Optical Internetworking Forum (OIF), it is fast becoming an industry
standard. GMPLS extends these switch capabilities so that it is not only
packet-switch capable (PSC), but also time division multiplexing capable (TDMC),
fiber switch capable (FSC), and lambda switch capable (LSC). Therefore unlike
MPLS, which is supported mainly by routers and data switches, GMPLS can be
supported by a variety of optical platforms including SONET ADMs, Optical
Cross-connects (OXCs) and DWDM systems. This will allow an entire
infrastructure, extending from the access network to the core network to utilize
a common control plane.

Objectives of GMPLS

Development of GMPLS began with the promise that it is possible to implement
full integration of provisioning for all traffic types. GMPLS was thus developed
with the goal of creating a single suite of protocols that would be applicable
to all service and transport traffic. The main objectives for defining the GMPLS
standards are:

n Interoperability between
equipment from multiple vendors

n Automated network resource
management

n Traffic engineering

n Rapid end-to-end service
deployment and provisioning

n Automated network protection and
restoration

n Service level agreement

n Optical virtual private networks
(O-VPN)

GMPLS brings the intelligence and dynamic circuit (or path) provisioning of
packet services to TDM and wavelength services. Its extensions offer a common
mechanism for data forwarding, signaling, and routing on transport networks.
GMPLS, thereby extends the MPLS label and label switched path (LSP) mechanisms
to create generalized labels and generalized LSPs. These extensions affect
routing and signaling protocols for activities, such as label distribution,
traffic engineering, and protection and restoration.

GMPLS emphasizes on the control plane that performs connection management for
the data plane for both packet switched capable (PSC) interfaces and non-packet
switched interfaces. The non-packet switched interface includes TDM Capable, LSC,
and FSC. The MPLS requires the LSP be set up between routers at both ends, while
GMPLS extends the concept of LSP setup beyond routers. The LSP in GMPLS can be
set up between any similar types of label switching devices at both ends. For
example, the LSP can be set up between SDH add/drop multiplexers (ADM) to form a
TDM LSP; the LSP can also be set up between two wavelength switching capable
systems to form a LSC LSP; or the LSP can be set up between fiber
switching-capable photonic cross-connect systems to form an FSC LSP. In GMPLS,
different types of interfaces work together by nesting one LSP inside another.
This functionality allows the system to scale better by forming a forward
hierarchy.

The Building Blocks

The GMPLS control plane is made of several building blocks and these
building blocks are based on well-known signaling and routing protocols that
have been extended and/or modified to support GMPLS. Only one new specialized
protocol is required to support the operations of GMPLS, a signaling protocol
for link management.

GMPLS is indeed based on the traffic engineering (TE) extensions to MPLS,
known as MPLS-TE. GMPLS extends the two signaling protocols defined for MPLS-TE
signaling, i.e. RSVP-TE and CR-LDP. Following are the major enhancements to
these signaling protocols in order to meet the GMPLS requirements of traffic
engineering:

n Supports the set-up of bi-directional LSPs for network protection

n Signaling for the establishment of
a back-up path (protection information)

n Expediting label assignment via
suggested label

n Waveband switching support–set
of contiguous wavelengths switched together

GMPLS also extends two traditional intra-domain link-state routing protocols
already extended for TE purposes, i.e. OSPF-TE and IS-IS-TE. Following are the
major enhancements to these routing protocols in order to meet the GMPLS
requirements of traffic engineering:

n Advertising of link-protection
type (1+1, 1:1, unprotected, extra traffic)

n Forwarding adjacency LSP for
improved scalability

n Accepting and advertising links
with no IP address–link ID

n Incoming and outgoing interface ID

n Shared risk link group (SRLG)–diversity
routing of paths for protection and restoration that is different from the
primary path

The use of technologies like dense wave division multiplexing (DWDM) implies
that we can now have a very large number of parallel links between two directly
adjacent nodes (hundreds of wavelengths, or even thousands of wavelengths if
multiple fibers are used). Such a large number of links was not originally
considered for an IP or MPLS control plane, although it could be done. Some
adaptations of that control plane are thus required in the GMPLS context. The
link management protocol (LMP) was specified for this purpose. The main
functions of LMP are as follows:

n IP control channel maintenance:
Mechanism to maintain control channel connectivity

n Link verification: Verify the
physical connectivity of the data bearing link between the neighboring nodes

n Link-property correlation:
Identification of the link properties of the adjacent nodes

n Managing link failures: Fault
localization and fault notification

Benefits
of GMPLS

A GMPLS network offers improved network efficiency and flexibility. GMPLS
allows each network layer to be managed according to its unique attributes. It
enables utilization of the inherent differences of the network layers to ensure
optimal use of network resources. New service offerings enabled by GMPLS mean
new revenue opportunities for service providers.

Network provisioning: GMPLS enables faster and more accurate provisioning. In
a GMPLS network, edge devices can become peers of GMPLS core devices, for
dynamic end-to-end provisioning. If the edge devices are not GMPLS-aware, GMPLS
can still be used to ease the provisioning burden in the core network in the
same style as switched PVCs in ATM.

Traffic engineering: Effective traffic engineering is one of the keys for
maximizing return on investment while improving service offerings.
Implementation of GMPLS Traffic Engineering (TE) and optical extensions for
routing and signaling protocols provide enhanced network information,
intelligent path computation and common signaling to packet, TDM, and wavelength
services.

Bandwidth on demand: Services with quality of service (QoS) constraints and
the large bandwidth increments they need are extremely difficult to provision in
real-time on a layered network. GMPLS-enabled architecture allows any
combination of fine grain packet LSPs to coarse grain STM-64 (OC-192) LSPs.
Thus, service providers deploying GMPLS networks in a consolidated network will
be able to offer a customer, for example, an STM-4 (OC-12) from Mumbai to
Singapore in the morning and an STM-64 (OC-192) from Mumbai to New Delhi the
same afternoon, while making optimal use of all network resources.

Differentiated services: A GMPLS network enables service providers to manage
traffic across all layers. They can view all the network layers and efficiently
allocate resources to the most appropriate layer, thereby tailoring
differentiated services to their customers’ varied and changing needs, while
reducing costs through optimal resource usage.

Service level agreements: GMPLS enables service providers to reap greater
benefits through more comprehensive and flexible service level agreement (SLA)
offerings to customers. With resource allocation not longer restricted to a
specific network layer, service providers have greater flexibility in designing
and enforcing SLAs, which can be used to generate new revenues.

Cost effective services: GMPLS offers service providers a vehicle to help
them migrate their networks from the current complex and costly architectures to
simpler, more efficient models. Service providers who deploy GMPLS will not only
see significant savings through improved network efficiencies, but will be able
to offer advanced, revenue-rich services to existing and new customers.

GMPLS Issues

There are some issues with GMPLS that deserve attention. These issues are
briefly discussed below:

Network management systems: The most important parameter in managing a
traditional IP network e.g., the Internet, is address reachability. GMPLS
network-management system needs to keep track of thousands of LSPs for their
operational status, routing paths, and traffic engineering. This makes the GMPLS
network management system more complex as compared to the traditional ones.

Interworking: Interworking in the control plane is very complicated as
different suites of protocols are used in separate networks such as routing,
private network-to-network interface in ATM versus OSPF—TE in GMPLS networks.
GMPLS switching can be packet-based, TDM-based, wavelength-based,
waveband-based, or fiber-based. Several industry forums are currently addressing
the specifics of interworking between these networks. Some of the prominent
forums are MPLS Forum, the ATM Forum, and the Frame Relay Forum.

Security: Traditional IP routing reads the contents of the header of a
received packet to determine the next hop for it. Though time-consuming, this
step helps in establishment of firewalls, as the source and destination
information is available in the packet headers that are globally unique. In
contrast, in GMPLS/MPLS, labels are used which are understood and used
internally only by the GMPLS device itself. As such, these labels cannot be used
for network-security purposes. One way to establish security in a GMPLS network
is to enforce access security during the connection set-up time, like other
connection-oriented networks like X.25 or ATM.

Network stability: When a new resource is deleted or added in a GMPLS
network, the set of control information that is exchanged is larger than that of
a traditional IP network. While not tested, theoretically, an MPLS/GMPLS network
would take a relatively longer time to achieve a stable state than would a
traditional IP network when the network is disrupted.

Lalit Bansal and Mehul Sanghavi consultants, Infosys Technologies