18-08-2012, 03:05 PM
MPLS Technology on IP Backbone Network
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INTRODUCTION
MPLS stands for Multiprotocol Label Switching, is a technology
proposed by Internet engineering Task Force (IETF) it was
designed to facilitate several problems areas in the internet
including routing performance and is increasingly being adopted
by service providers in their core networks. MPLS solutions are
to be used with Layer2 and Layer 3 Protocols. A label is a short
fixed length identifier that is used to forward the packets. With
MPLS, labels are attached to the packets at the ingress point to
an MPLS network. Within the network the labels are used to
route the packets without regard to the original packets header
information, These labels can be stacked as a LIFO labels
enabling MPLS to be combined for transport and distribution.
MPLS header is 32 bits long [5]. The label field gives
information needed to forward the packet and is the basis upon
which MPLS switching operations occur. The COS bits affect
the scheduling and or discard algorithms applied to the packet as
it is transmitted through the network. These bits are not
modified by the embedded implementation of MPLS. The Stack
bit is set to 1 for the last entry in the label stack and 0 for all
other label stack entries. The TTL field is decremented by 1
each time the packet passes through a router. The packet is
discarded when the TTL reaches zero.
MPLS ARCHITECTURE
Multiprotocol Label Switching (MPLS) is a tunneling
technology used in many service provider networks [3]. The
most popular MPLS-enabled application in use today is the
MPLS virtual private network. MPLS VPNs were developed to
operate over MPLS networks, but they can also run over native
IP networks. This offers providers flexibility in network
deployment choices, improved routing system scalability and
greater reach to customers. The key element is the ability to
encapsulate MPLS packets in IP tunnels. In an MPLS network,
each LSP is created over the best path selected by the IGP,
towards the destination network. An IGP (OSPF or IS-IS) is
used to propagate routing information to all routers in an MPLS
domain to determine the best path to specific destination
networks. Each hop within the network core forwards packet
based on the label, not IP information, until the final label
switch is reached where the label is discarded and normal IP
forwarding resumes.
MPLS OPEARTION
In general, MPLS has two planes [6]:-
a) Control Plane: - The Control Plane is responsible for the
routing information exchange and label distribution between
adjacent devices. It uses standard routing protocols such OSPF
routing, IS-IS and BGP to exchange information with other
routers to build and IP forwarding table or label forwarding
information base. It also needs label distribution protocols such
as LDP.
b) Data Plane: - The Data Plane is responsible for forwarding
packets according to the destination IP address or label using LFIB
managed by the control plane. The Data plane is a simple
label based forwarding engine i.e independent of the type of
routing protocol or label distribution protocol running on the
control plane.
Benefits of the MPLS VPN
a) Scalability: A well executed MPLS based VPN deployment
is capable of supporting tens of thousands of VPNs over the
same network. MPLS based VPNs scale well because they do
not require the full mesh, end to end site peering across the
network.
b) Traffic Engineering: By deploying traffic engineering in the
core, services provider network engineers can implement
policies to help ensure the optimal traffic distribution and
improve the over all network utilization. MPLS enables traffic
engineering by allowing traffic to be directed through a specific
path based on least cost routing, link utilization, latency, jitter
and other factors.
CONCLUSION AND FUTURE WORK
The rapidly increasing volume of Internet traffic has forced ISPs
to find the ways to increase the capacity of their networks.
Those ISPs that have kept pace with time by transitioning to
new backbone technologies have been successful in increasing
their market share. So, for this MPLS is an emerging technology
and by no means a perfect solution to current IP network
problems. It provides much better Traffic Engineering capability
than the other networks. MPLS operates in coordination with IP
Routing and its main objective is to provide the speed of
switching to Layer 3. Introduction of labels provides an effective
alternative and evades the need of large routing table lookups
and results in fast routing. However, the telling factor of MPLS
is its ability to manage and classify the traffic in order to provide
better utilization of resources. Hence, this technology is used to
effectively resolve integration and traffic engineering issues in
carrier networks. MPLS VPN provides benefits that service
providers need urgently in their networks, such as scalability,
manageability and reliability. But Security is the major issue in
this Technology.