PPPoE simplifies and enhances the end-user experience by allowing the
dynamic selection of service offerings or retail ISPs in wholesale networks,
much as TV viewers select channels. With PPPoE, access control, billing
and service type can be controlled per-user offering ISPs many new ways
of increasing revenues and offering new services.
When a router receives the frame, it reads the control information provided
by the CPE then it strips the control information from the frame. It
passes the frame up to the next layer, following the instructions that
appeared in the control portion of the frame. Each subsequent layer
will perform this same de-encapsulation process. With PPPoE this needs
to be done with the Ethernet header, the PPPoE header, and then the
PPP header leaving the TCP/IP payload. This operation is then done in
reverse when the frame comes from the provider through the termination
device to the CPE. This CPU intensive and memory intensive process leaves
many trouble areas in Next Generation and Legacy routers, as well as
this function has to be done at wire speed to not impact time sensitive
applications such as VoIP.
Figure 1 — Total PPPoE Frame size
ISSUE CAUSED BY TERMINATING PPPOE ON A ROUTER
Terminating PPPoE is a CPU/memory-intensive process. Terminating PPPoE
on hardware intended for routing and optimized for this service therefore
greatly reduces its routing capability. For example, a router capable
of routing 96,000 sessions generally can terminate only 8000 PPPoE sessions
under real-world conditions. This is only about 8% of the router's originally
estimated capacity. Starting with zero customers, a network built out
to reach capacity in five years without router-terminating PPPoE would
reach capacity in approximately 4.8 months with the added overhead of
PPPoE termination. The cost of buying more routing hardware to regain
the lost capacity can be prohibitive.
Impact on Delivering New Services
As next-generation routers are introduced, new services and features,
such as Voice over IP (VoIP), become easier to deliver — if router
capacity is available to offer them. But a next-generation router operating
at peak usage due to PPPoE termination does not have the resources available
to offer next-generation services. This forces large capital investment
to purchase a second router to regain the network capacity required
for the new services and features.
With the small margins of profit per customer on broadband Internet
connections, using expensive next-generation routers to terminate PPPoE
dramatically increase the time necessary to recover the cost of installing
an average customer. If a router could operate at maximum capacity this
would not be an issue. But with a router handling only 8% of expected
capacity; the cost per subscriber to route and terminate PPPoE can be
as high as $15 per subscriber.
At a profit margin per customer of only $2 per month, achieving profit
after other installation costs (modem, software, and so on) have been
covered would take approximately 7.5 months.
The PPPoE server is a single point of failure in a network. If this
one piece of equipment, which all customers must access to get online,
fails, all customers can no longer access the Internet. This results
in increased call center traffic and higher operating costs per customer.
Multiple PPPoE servers capable of seamless loading balancing are the
answer to this problem — but traditional and next-generation routers
that include PPPoE functionality do not offer native load-balancing
technology. Considering the high cost of next-generation routers, the
unavailability of built-in load balancing limits the network engineer's
options for creating a redundant network capable of 99.999% uptime.
SOLUTION: OFFLOAD PPPOE
As the previous section has shown, terminating PPPoE on existing router
hardware is a costly approach to leveraging the value of PPPoE connectivity.
This PPPoE termination problem can be simply and efficiently addressed
by introducing to the network a unit designed specifically and only
for PPPoE termination. Figure 4 illustrates this solution. The PPPoE
termination unit in this case is the Fine Point Networks ServPoET BMS,
shown connected between a PPPoE aggregation unit and the legacy (or
THE RESULTS AND BENEFITS OF OFFLOADING PPPOE
Offloading PPPoE from either legacy routers or next-generation equipment
affords multiple advantages to a service provider, including increased
network capacity, faster return on investment, and lower per-subscriber
Increased Network capacity
Offloading PPPoE termination from the router increases available network
capacity by a factor of approximately 11. Now the router is no longer
a bottleneck, and network resources are optimized for more efficient
routing, bandwidth usage and value-added service delivery.
The router is freed to route the amount of prospective customers it
was built out to handle, regaining its target threshold capacity. The
full router capacity is now available for the introduction of value-added
and next-generation services.
A Load-Balanced, Redundant Network
The low cost of units designed specifically to terminate PPPoE sessions
makes for a much more cost-effective solution than using routers to
terminate PPPoE. The money saved allows the purchase of multiple PPPoE
termination units, allowing the service provider to build and support
a redundant network for 99.999% uptime.
A unit specifically designed for PPPoE termination can be engineered
to include native clustering technology. One such unit, the Fine Point
Networks ServPoET BMS, can be clustered to enable automatic load balancing
of PPPoE network traffic among clustered units for improved service
levels. The ServPoET SmartCluster™ technology evenly distributes
sessions among cluster members, automatically removing members that
fail or become unreachable. New cluster members can be hot-added to
expand an existing cluster for additional capacity and performance,
allowing administrators to scale their services with unprecedented time
and cost savings.
Return on Investment
With the small margins of profit per customer on Broadband Internet
connections a cost effective solution can dramatically decrease the
time necessary to recover the cost of installing a customer. Per-customer
time to profitability is greatly reduced.
In many cases, the result is an elevenfold increase in the life of
the network before heavy capital must be invested to expand or upgrade
it. The life span of the router is also increased because it is not
continually working at 90 to 100% CPU and memory capacity, increasing
the time before the unit fails and must be taken offline for service.
Lower Per-Subscriber Cost
Using a unit specifically designed for terminating PPPoE can reduce
cost per subscriber to as little as $2. Installing a PPPoE termination
unit is a one-time cost, so the cost to terminate each subscriber decreases
as the unit’s in-service time increases.
Assuming a service provider per-customer profit margin of only $2 per
month, it would take approximately 7.5 months to gain profit per customer
after the cost of other installation aspects (modem, software, and so
on—approximately $15 per subscriber) are covered. With this new
model, profits begin immediately after installation costs have been
covered — typically, beginning with the second month of service.
Figure 6 compares the two PPPoE termination options.
Offloading PPPoE from a legacy or next-generation router to dedicated
PPPoE termination hardware allows a service provider to free valuable
network resources and expand the network without high capital investment.
Especially when load-balancing-capable PPPoE termination hardware is
used, offloading PPPoE can reduce time to profitability per customer
and speed the delivery of value-added and next-generation Internet services.