In the not too distant future, a
major portion of end-user access points to the telephony, data and
entertainment networks is expected to be based on fiber infrastructure. Even
today, new housing developments in many places around the world are built with
fiber-based connections to the home, and network providers are conducting
field-testing and experiments with fiber access. Eventually, fiber access is
predicted to replace the old copper infrastructure the world over.
In order to provide a worthy alternative to the existing
infrastructures, the new technology should be, among other things,
cost-efficient, broad-banded, and easy to maintain and deploy. Of these
requirements, probably the main and most important feature is that it must
support all existing services as well as offer new required services. These
services include voice, data, and video/television-broadcast traffic.
"Ethernet in the First
Mile" (EFM) is an upcoming standard currently being drafted by
the 802.3ah task force in the IEEE organization. It will define an
access standard based on the Ethernet protocol for several media architectures
and physical link types. The main (and most complex) track in the standard
deals with Ethernet over Passive Optical Network (EPON).
EPON deals with a
symmetric point-to-multi-point connection at very high speeds (Currently 1Gb/s,
in the future 10Gb/s and even more). A unique network management protocol has
been devised – Multi Point Control Protocol (MPCP). Current
numbers refer to the connection of up to 64 end points per PON fiber (a factor
of optical intensity, which is affected by the number of users and the distance
from the central office), but this number may change in the future. The traffic
is multiplexed using time-division-multiple-access (TDMA). EPON offers great
flexibility in dynamic bandwidth allocation, allowing anything from a strict
and even division of the bandwidth among all end-points, to giving all
bandwidth to a single end point (both in the uplink and downlink directions).
Taking advantage of this flexibility requires sophisticated bandwidth
management.
In order to efficiently answer
the requirements for the multi-user and multi-services network, EPON solutions
must support quality of service (QoS) as part of their bandwidth
allocation and scheduling schemes.
Project Goals
In this project we will attempt
to explore some of the aspects of QoS bandwidth allocation in the 802.3ah EPON
architecture. Since this is a novel network model and a very extensive field,
one would only expect to expose but a hint of what is waiting down the road of
QoS in EPON.
Several general traffic types
will be defined, that would represent real traffic in the network, each with
its own QoS requirements (bandwidth, delay, jitter, etc.).
The bandwidth allocation process
can be divided into several sub-processes (that may or may not be orthogonal to
each other):
- Gathering of the input for the decision making process (such as bandwidth requests or the bandwidth definitions for each end unit).
- Dividing the available bandwidth between the end units (determining the quota for each) within a defined time-frame.
- Scheduling the allocated quotas of all end units for the defined time frame.
- Informing the end units when they are allowed to broadcast (parallel to the frequency of the scheduling changes).
For each of these sub-processes
there are many work modes and algorithms that may be thought up and compared.
Since there are so many approaches that can be used, the goal of this project
is not to provide a complete and optimal solution, but rather to present a
preliminary comparison of several algorithms, in order to get a
"feel" of where to go next.
This current project will
concentrate on a narrow section of the network – mainly the bandwidth
allocation in the uplink direction. This refers to information flowing from the
end units - Optical Network Units (ONUs) in our case, to the
central office equipment - the Optical Line Termination (OLT).
Several assumptions regarding the
network will be made, that would allow us to concentrate on the aspects being
tested (such as assuming that the number of end units is in a steady state and
that there are no connections/disconnections of end units).
Advancement Plan:
- Familiarization with: EPON Standard and the MPCP protocol, Ethernet and Gigabit Ethernet protocols, QoS, standard bandwidth allocation schemes.
- Definition of the exact model to be tested in the project.
- Design and analysis of several simple bandwidth allocation schemes for the model.
- Network Simulation - Familiarization with the OPNET simulator and decision whether to base it on existing resources (existing DOCSIS or Ethernet modules) or to construct a tailored solution.
- Test of selected schemes in simulation.
Project Environment
It seems that OPNET will be adequate
as the base for simulation.
No special hardware is needed.
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