08-10-2012, 11:42 AM
Unified MPLS for Multiple Applications –Transport Profile
Unified MPLS for Multiple.pdf (Size: 239.96 KB / Downloads: 48)
Abstract
This paper outlines important packet and
transport network convergence opportunities
& challenges, and illustrates how Multiprotocol
Label Switching (MPLS) has been
extended to address them. The industry has
faced and has been facing many questions
about what the correct way to ensure a successful
network convergence is, especially
considering the operational and sometimes
organizational changes needed to realize
the full cost-saving potential of a de-layered
packet & transport network. This paper
highlights how past and currently proposed
extensions transform the time-tested MPLS
protocol suite into something very suitable
for next generation transport networks &
services.
INTRODUCTION
Communication networks have evolved and converged significantly over the past century, however, within large networks,
many overlayed or parallel ‘silo’s of service or application specific connectivity solutions have been built, and in many
cases have dedicated support organizations and systems. Further network convergence - and removal of such silos - is
driven by both business and technology factors to reduce operational costs whilst delivering new services and thereby
generate higher revenue and profits.
One inherent challenge in network convergence is that while an operator invests in new infrastructure and offers new services,
they must also sustain the existing legacy services & related infrastructure. In this period of transition, the revenue
from legacy services is typically in a mature to declining stage, while underlying infrastructure becomes outdated, and
often expensive to upgrade. For the transition phase, a more common, future-proof & adaptable infrastructure is needed
to scalably deliver current generation services and also deliver newer generation services over the future time. This
flexible generation of infrastructure delivers higher return on investments. Examples of equipment exhibiting this characteristic
can be found in multiple generations of transport equipment – from ADM through MSPP to POTP (Packet Optical
Transport Platform) and also strongly in the network Edge, where an extremely high degree of network convergence support
is now available in today’s ultra-flexible Multi-Service Edge Routers.
MPLS Extensions Driven by Transport Requirements
The principal extensions driven by Transport networks requirements are focused on data plane OAM and management.
Although legacy MPLS has an existing suite of OAM tools (such as BFD for LSPs & LSP Ping and LSP traceroute), the
toolset was originally architected for IP network optimization and consequently cannot achieve the precision desired
for transport applications. The toolset was focused on the most common deployment scenarios, being: the LDP control
plane, penultimate hop popping in the data plane, LSP merging and equal cost multi-path, all of which primarily address
MPLS scalability, but at the expense of measurability.
The extensions provided by the MPLS-TP project are aimed primarily at addressing the operational, administrative, and
management needs of transport operators. As these needs are grounded in operational experience, it turns out that they
also apply to other uses of MPLS, as they become more pervasive. These new or extended features include:
• Continuity Check and Connectivity Verification
• Alarm Management (AIS, RDI, Client Fail Indication)
• Diagnostics (Route Tracing, Loopback, Path Locking)
• Performance Monitoring (Packet Loss, Delay Measurement & Throughput Estimation)
• Fast protection switching
The transport profile of MPLS (MPLS-TP) focuses on a subset of legacy MPLS behaviors to which enhanced OAM can
be applied. In particular the focus is on “connection oriented” behavior and the ability for MPLS to be operational without
a distributed control plane. This has always been possible but with functional gaps. What has been added is the ability
to delegate control functions such as resilience, monitoring and management to the data plane, and the OAM suite has
been enhanced in order to permit this. The fundamental fault management tools, LSP Ping and BFD are carried forward
but with enhancements and additional protocols to support protection switching, alarm management and administrative
functions.
MPLS Profiles
MPLS, like many standard protocol suites, has many options. The historical method for addressing this is to define a
profile and its applicability. That is, one defines a specific combination of options from the full suite. The combination is
chosen to work well together, and to address a specific need. Such a specific combination (with or without the applicability,
depending upon the specific case) is what is classically called a protocol profile.
The MPLS-TP project as defined by ITU & IETF does not provide such a profile. Rather it provides a set of extensions to
MPLS that can be used to address specific needs. Given those new features, and many existing capabilities of MPLS,
the obvious question is ”what interoperable set of capabilities will meet the transport operational needs.” i.e., what profile
will address the problem. This gets slightly complicated, as not all operators have the same view on how they want to
run their networks.
First, any such profile would have to contain the basics of label switching, and support for label stacks. In addition, any
transport profile would have to include the basic OA&M mechanism. While one could imagine implementations with
fewer features, a profile that allows for flexible use, effective network operations, and device interoperability needs to
include all of those components. All devices which are able to be the starting point for an LSP must support the use of
backup LSPs with diverse paths, with the usage triggered by OA&M events from the data plane, without network management
or control plane signaling.
Network Convergence with MPLS
MPLS is the one technology currently available that allows true multi service architecture to be built on a single converged
network infrastructure. With the advent of MPLS Traffic Engineering (TE) and Pseudowire technology, the MPLS and
PWE3 protocol suite has been used to support TDM, ATM, Frame Relay, IP and Ethernet transport services on a single
converged network. The traffic engineering and resiliency properties of MPLS support the stringent latency and jitter requirements
needed for many TDM services and ATM services. These services are critical to applications such as 2G and
3G Mobile Backhaul as well as legacy enterprise interconnect services.
The same base technologies allow the Ethernet and IP services to be provided over the same network infrastructure.
This allows applications such as 3G and 4G mobile backhaul, IPTV, Broadband Access and many others to be provided
with the SLAs required by these applications and yet making the most efficient use of the network resources.
Because profiles of MPLS are built on this strong base, they inherit the properties, and allow these same services to be
provided over a more streamlined and cost reduced network infrastructure. The infrastructure can be tailored not only
in function but also in terms of cost to the area of the network architecture where it resides, while keeping a consistent
technology base and therefore consistent behavior, management and operations. For example, using MPLS toward the
access of the network would have required using a full featured MPLS Label Switched Router that typically included
hardware-based IP forwarding. This is the same router functionally that would be used in the core of the network, but
only scaled down in terms of capacity which doesn’t lead to significant cost reduction.