The Conundrum
Riverstone believes in the old adage: if
it ain't broke, don't fix it. Carriers have
a large investment in ATM and Frame Relay
networks that they have depreciated over
time and that still have useful life left.
More importantly, these networks support
the carriers existing revenue generating
customers.
However, the advent of
Ethernet services is inexorable. The customer
need for higher bandwidth and reduced communications
costs can be met only with an Ethernet infrastructure.
What is a carrier to do? If they make a
sweeping change to their network to deploy
Ethernet, they will have to spend an enormous
amount of capital expenditure. In addition,
it forces them to operate parallel infrastructures
during the time they migrate their customers
from one to the other. Also, imagine the
chaos that could result if the move does
not go smoothly especially with a large
corporation that has a multitude of sites
like a financial institution or a diverse
manufacturing company.
That is why Riverstone
advocates an evolutionary approach to Ethernet
services and VPLS. Customers who currently
use circuit-based VPNs such as Frame Relay
and ATM should not have to change every
connection in every site in order to implement
a new IP or Ethernet VPN for their corporate
links. Customers who wish to use high-speed
Ethernet services within a single metro
area should still be able to connect and
communicate with smaller sites that are
happy with the lower bandwidth service they
currently use.
VPN Continuity
We call this VPN Continuity and the key
to providing it is VPLS. The Martini drafts
specify how L2 traffic can be transported
over an MPLS-enabled IP backbone. They include
details for mapping Ethernet VLANs, Frame
Relay DLCIs, and ATM Virtual Circuits to
MPLS Label Switched Paths (LSPs) or tunnels.
This provides the connectivity needed to
provide existing VPNs over an MPLS core
network. However, this isn't enough. Customers
want to mix and match different access methods
but still have connectivity between, say,
Ethernet sites and ATM sites. The extra
mile that Riverstone goes is to provide
this mapping between different access networks.
The common denominator and the key to achieving
this is the Ethernet VLAN. Since 95% of
all customer traffic starts and ends on
an Ethernet LAN, the Ethernet packet is
the ideal common format that can be used
to map between the various link layer standards
so that the customer can receive and transmit
the data in the format most convenient to
them. Customer traffic is uniquely identified
into VLANs and the VLAN id is mapped into
a corresponding MPLS label. And by using
standard internetworking RFCs for translating
Ethernet frames to Frame Relay packets and
ATM cells, there is no need to change any
equipment at the customer premise unless
they wish to upgrade to a higher speed service.
As an example, consider
a large bank. It uses Frame Relay to connect
its branches and higher speed ATM connections
for its headquarters and data centers. For
security and disaster recovery reasons,
it wishes to outsource and replicate its
data centers in secure facilities but needs
a high-speed LAN link between the data centers
and HQ. Also, some of the larger banks wish
to offer new online, Web-based services
to its customers, which places more bandwidth
requirements on the network at unpredictable
times. Additionally, the bank wishes to
build an extranet with partners, such as
building societies and insurance companies
and stockbrokers.
Figure
1: Connecting Regional Branches, Headquarters
and the Data Center with ATM and Frame Relay
The existing bank network
is provided by a national carrier based
on Frame Relay and ATM services as shown
in Figure 1 above.
The bank's main carrier
installs a high-speed metro MPLS network
based on Gigabit Ethernet to connect the
headquarters and the dual data centers.
Connections can be made at 100 to 1,000
Mbps across this metro network. At the edge
of the metro network, the ATM and Frame
Relay access networks continue to connect
into the main metro. Also, the carrier provides
IP VPN connections through its L3 MPLS core
to connect to partners and to the international
branches. The "superbranches"
requiring more flexible bandwidth can be
added when required. The complete transformation
is shown in Figure 2 below.
Fig 2: Evolving Toward the MAN - Frame
Relay used in conjunction with Metro Ethernet
Benefits of Evolution
With an evolutionary approach, carriers
can continue to reap the returns from their
investments in ATM and Frame Relay. They
can start building out VPLS based Ethernet
networks in an orderly fashion that assures
service and business continuity for all
their customers. As shown in the example,
at locations where service requirements
have increased, Ethernet maybe used to satisfy
the customer. The remaining locations of
a customer's VPN may continue to remain
on the existing networks. Solutions like
evolutionary VPLS and VPN Continuity provide
the perfect vehicle for carriers who wish
to increase customer loyalty by meeting
their needs while simultaneously supporting
internal goals of revenue growth and cost
reduction for increased profitability.
