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Application
MPLS powers access networks
MPLS-equipped SDH and SONET switches will make access networks
more efficient by helping them connect directly to the core network bypassing
edge routers, says Abhinav Singh
 Telcos are
looking for ways to lower acquisition costs and improve the efficiency of their
access networks. Many carriers already have MPLS (Multi Protocol Label Switching)
capabilities in their core network, i.e., in the backbone. With MPLS at the
core, carriers now want to extend the benefits of MPLS to their access networks.
Dr Kumar N Sivarajan, chief technology officer, Tejas Networks says, “Since
many carriers have deployed or have plans to deploy MPLS in the backbone to
offer data services, they want to extend the same to their access networks to
increase efficiency and lower TCO.” MPLS is efficient at packetising and
can carry virtually any kind of data traffic. Kumar adds, “We are going
to see SDH and SONET switches with MPLS capabilities directly talking to the
core network.”
MPLS at the access level
Traditional SDH and SONET switches lack MPLS capabilities. Additional investments
in edge routers have to be made to convert data packets into MPLS so that they
can talk to the MPLS in the core network. As data services mushroom, today’s
practice of mapping data traffic onto TDM (Time Division Multiplexing) circuits
becomes impractical. To improve the efficiency of their access networks, carriers
plan to take advantage of statistical multiplexing. The current generation of
SONET/SDH transport and switching equipment lacks packet awareness to perform
the functions required and the current mode of operation works out to be expensive
for providers because of the growth in data traffic.
The large volumes of data traffic in a traditional SONET/SDH access network
consume a large number of TDM circuits, leading to the premature deployment
of additional transport gear despite the fact that the lines are lightly utilised.
Traditional SONET/SDH equipment takes traffic coming from customer premises
equipment and maps that traffic onto TDM circuits. Adding to the high cost of
this architecture is the inefficient use of interfaces on edge data equipment
such as IP routers and ATM switches (these sit on the edge and act as a bridge
between the core and access networks). This equipment connects to the SONET/SDH
gear via discrete or channelised interfaces to extract data traffic and deliver
the required service. As TDM circuits are under-utilised, edge-router and switch
ports are also under-utilised and an excess number of ports is required.
The upshot is stranded bandwidth. Carriers are turning to
MPLS for a solution to this problem. Says Kumar, “Building access networks
with SONET/SDH with in-built MPLS encapsulation capabilities allows the use
of TDM channels for voice and leased line applications while providing the efficiencies
of a packet-switched network for high-volume data traffic.”
MPLS scores over ATM and Ethernet
When compared to ATM cell switching technology, MPLS stands out. Although the
properties of ATM cell switching ensure that it is well-suited to deliver high-quality
voice along with data over low-speed circuits, it lacks efficiency and performance
of data traffic, especially IP, and does not map very efficiently onto ATM cells.
Ethernet on the other hand has the capacity and efficiency to packetise the
access network, and in some cases, carriers are starting to deploy it for this
purpose. However, Ethernet is limited in its ability to carry different types
of traffic. It can handle IP but lacks the ability to transport legacy ATM and
FR (Frame Relay) traffic. Furthermore, Ethernet still lacks the operational,
administrative and maintenance capabilities that carriers require in their access
networks.
Deployments poised to surge
The time is ripe for a new architecture that adds packet intelligence to the
access network and permits carriers to get the most from the bandwidth that
is already deployed. MPLS is flexible enough to serve in this role on the network’s
edge. A new generation of SONET/SDH equipment is emerging that adds packet awareness
and performs statistical multiplexing in the access network via MPLS in conjunction
with other link layer technologies. This new architecture paves the way for
greater efficiency and convergence in the access network and allows carriers
to greatly reduce their costs. Equipment vendors are already in the trial stage,
demonstrating this technology to carriers. Early adopters of this technology
are expected to start deployments in 2005.
abhinav@expresscomputeronline.com
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