Transcript Next Generation EPON-based Access Network Architecture

Next Generation EPONbased Access Network
Architecture
Access Network
Customer
Premise
Access Link
Merto PoP / CO
Link between the customer premises and the first point of
connection to the network infrastructure—a point of presence
(PoP) or central office (CO).
Ethernet in the Last Mile
Access Bandwidth
Optical Access
What is Passive Optical Network
►
Passive Optical Networks (PON) are point-to-multipoint
optical networks with no active elements in the signals’
path from source to destination.
►
Advantages of PON
 PON allows longer distances between CO and customer: 20 km for
PON vs. 5.5 km for DSL
 PON provides higher bandwidth.
 Allows downstream continuous broadcasting (video).
 Eliminates electronic devices in the middle of the network.
 Allows easy upgrades to higher bit rates or additional wavelengths.
Basic Architecture of PON
EPON Downstream
EPON Upstream
EPON Configuration
EPON Performance
► EPON
Media Access Control (MAC) uses
Ethernet framing and line coding.
► Downstream channel uses true broadcast.
► Packets extracted by the MAC addresses.
► Not different from any shared-medium
Ethernet LAN.
► Upstream transmission uses multiple access.
► Which multiple access scheme? (Problem)
Multiple Access Schemes
Statistical TDMA
► Time
synchronization among ONUs cannot be
easily achieved:
 Who drives the clock?
 How do we achieve synchronization?
► Ethernet
in the first mile task force (IEEE 802.3ah)
recommends Multipoint Control Protocol (MPCP).
 Work is still in progress.
 MPCP is not concerned with a particular bandwidthallocation scheme.
 MPCP supports mechanism that can facilitate various
implementation of bandwidth allocation algorithms.
Timing Issues
Ranging - RTT
Measurement
1. OLT sends GATE at absolute
T1
2. ONU receives GATE at T2,
and resets local counter to show
T1
3. ONU sends REPORT at time
T3, showing timestamp T4
4. OLT receives REPORT at
absoluteT5
►
RTT = T2-T1+T5-T3
RTT= T5-T4
T3-T2 = T4-T1
Multipoint Control Protocol (MPCP)
Operation
►
This protocol relies on two Ethernet messages: GATE and
REPORT.
 (Additionally MPCP defines REGISTER REQUEST, REGISTER, and
REGISTER ACK messages used for an ONU’s registration.)
►
A GATE message is sent from the OLT to an ONU.
 It is used to assign a transmission timeslot.
►
►
A REPORT message is used by an ONU to convey its local
conditions (such as buffer occupancy, and the like) to the
OLT to help the OLT make intelligent allocation decisions.
Both GATE and REPORT messages are MAC (media access
control) control frames (type 88-08) and are processed by
the MAC control sublayer.
Statistical multiplexing
► Burst
time and size are hard to predict.
► Must use schemes with feedback (like polling).
► Hub polling would work, but walk times are very
large.
► Roll-call polling also works, but it requires ONUs to
listen to each other.
 PON should be deployed as a broadcasting star or
passive ring (too restrictive).
► Proposed
IEEE EFM standard solution: Interleave
polling routines in time.
Interleaved polling scheme
Advantages of Interleaved Polling
Scheme
►
Bandwidth utilization.
 If only one ONU is active, it can use up to 600 Mbps (with 5 μs
guard band).
►
Lower delay.
 Delay is bounded by RTT, not frame time. Under maximum load
behaves like TDMA system.
►
No ONU’s synchronization necessary.
 ONU sends data immediately on receiving (processing) the control
message (Grant). No centralized framing necessary.
►
All “smarts” are in OLT.
 OLT may use various scheduling algorithms based on SLA, type of
traffic, etc.
►
Fast detection of disconnected ONU.
 Disconnected ONU “consumes” only ~0.0005% of PON bandwidth.
Ethernet TCP/IP Frame
100Base CU Burst: 31 1518Byte Frames per Burst
DBA Scheme

This algorithm is cycle-based, where a cycle is defined as the
time that elapses between two executions of the scheduling
algorithm.

The ONU will be granted the requested number of bytes, but
no more than a given predetermined maximum WMAX
(maximum transmission window). If Reqi is the requested
bandwidth of ONUi and Granti is the granted bandwidth,
Granti is then equal to
Grant i  
TMAX
Reqi
WMAX
if Reqi  WMAX
if Reqi  WMAX

WMAX
 N  Guardtotal 
Transmissi on_Speed




Class-of-Service Considerations
►
Performance in EPON can be characterized by several
parameters:
 bandwidth
 packet delay (latency), delay variation, jitter
 packet-loss ratio
►
►
►
►
Quality of service (QoS) refers a networks’ to ability to
provide bounds on some or all these parameters on a perconnection (flow, session) basis.
Not all networks, however, can maintain per-connection
state or even identify connections.
To support diverse application requirements, networks
separate all the traffic into a limited number of classes and
provide differentiated service for each class.
Such networks are said to maintain classes of service
(CoS).
Overview of IEEE 802.1D Support for
Classes of Service
1.
2.
3.
4.
5.
6.
7.
Network control. Characterized by a “must get there” requirement to
maintain and support the network infrastructure.
Voice. Characterized by less than 10-ms delay, and hence maximum
jitter [oneway transmission through the local-area-network (LAN)
infrastructure of a single campus].
Video. Characterized by less than 100-ms delay.
Controlled load. Important business applications subject to some form
of “admission control,” be that preplanning of the network requirement
at one extreme to bandwidth reservation per flow at the time the flow
is started at the other.
Excellent effort. Or “CEO’s best effort,” the best-effort-type services
that an information services organization would deliver to its most
important customers.
Best effort. LAN traffic as we know it today.
Background. Bulk transfers and other activities that are permitted on
the network but that should not affect the use of the network by other
users and applications.
Dynamic Bandwidth Allocation
Timeslot utilization is less than 100%
►
►
Packets cannot be fragmented.
If the next packet to be transmitted is larger than the
remainder of timeslot, the packet will wait for the next
timeslot => the timeslot will be transmitted with an
unused remainder at the end.
Why timeslot adjustment won’t work
► Why
timeslot adjustment won’t work
► Linear increase in offered load requires
exponential increase in timeslot size.
► Increased timeslot size will increase timeslot
period => will increase packet delay.
► Timeslot adjustment should be based on traffic
load.
► However, due to burstiness of traffic at every
timescale, no load prediction is possible based on
previous load.
Drawbacks of OLT based DBA
► OLT-ONU
is 20km and a control messages
(REQUEST and GRANT) consumes significant
portion of the valuable upstream bandwidth.
► ONU’s traffic changes dynamically and very bursty
in nature thus most recent buffer status is not at
hand when OLT makes DBA allocation.
► CoS cannot be truly support by centralized DBA
decision as OLT relies on inter-ONU scheduling for
optimal solution and hence fails to take into
account critical QoS parameters while arbitrating
between ONUs.
Proposed New PON Architecture
(In-band Signaling)
ONU
Redirected
1310nm signal
1550nm
OLT
1310nm
ONU
Splitter/
Combiner
Control Plane:
 1310nm channel
Data Plane:
 Upstream: 1310nm channel
 Downstream: 1550nm channel
ONU
ONU
Algorithm (DBA)
Control
Data
[Time]
Individual ONU update messages
ONU
OLT
ONU
ONU
a) First Phase
ONU
OLT
ONU
ONU
ONU
ONU
ONU
b) Second Phase
Combined ONU
data messages
3xN S/C
ONU
ONU
ONU
OLT
Combined ONU data messages
3xN S/C
Combined ONU
update messages
c) Third Phase
ONU
Combining of ONU data messages
b) Second Phase
OLT
ONU
3xN S/C
3xN S/C
OLT
ONU
a) First Phase
Combining of ONU update messages
Combined ONU
update messages
3xN S/C
3xN S/C
OLT
Individual ONU data messages
c) Third Phase
ONU
ONU
ONU
Distributed DBA for EPON:
In-band Control Plane
► Using
(Splitter/Combiner) we reflect 1310nm
upstream bound signal.
► We use REQUEST Control frames to update all
ONU’s of the current ONUs’ buffer info.
► After receiving all updates from all ONUs (max.
64), each ONU independently run DBA and arrive
at one unique timeslot allocation per ONU.
► A copy of the REQUEST also propagates to OLT
and it also can run the same DBA to know which
ONU is transmitting when.
► CoS could be easily factored into the DBA decision.
Distributed DBA for EPON:
In-band Control Plane (Cont.)
►A
portion of the upstream bandwidth is consumed
to establish the control plane, however it is very
small (less than 5%).
► Time synchronization among ONUs is an issue:
 Fixed downstream frame sizes could be used to derive
time synchronization.
 The average radius from the Splitter/Coupler to ONUs is
less than 1km and we propose to have a fixed distance
of 1 km to avoid time delay issues.
► The
proposed cycle time (window size) is 2ms
 Optimized cycle time would be investigated under
various traffic load and QoS requirements.
Proposed New PON Architecture
(Out-of-band Signaling)
1550nm
ONU
Splitter/
Combiner
ONU
OLT
1310nm
Control Plane:
 Fixed Wireless LAN
Data Plane:
 Ethernet Passive Optical Network
ONU
ONU
Distributed DBA for EPON:
Out-of-band Control Plane
i
i+1
►
►
►
Control Plane
Control
Data
Data Plane
Since ONUs are with in less than 2km diameter, we can use
fixed wireless to establish the control plane.
Control information from the ith window is used to run DBA
for timeslot allocation per ONU.
Out-of-band signaling relieves the upstream channel to be
fully utilized for data traffic only.
Thesis Proposal
► To
develop and implement a fully distributed
EPON-based dynamic bandwidth allocation
algorithm.
► The work will be carried out in two stages:
 Simulation studies using OPNET and other tools.
 Physical implementation of DBA in the lab test bed.
 Simulation data will be compared to the empirical data
obtained from the lab experiments.
► The
proposed Next Generation EPON-based
Architecture will unleash the Access bandwidth
bottleneck and support total packed-based QoS
guaranteed new applications.
Testbed SETUP
Wireless Access Card
GigE Card
SM Fiber (500 m)
Workstation1 (ONU)
Isolator
3X3
Splitter/
Combiner
Workstation2 (ONU)
SM Fiber (500 m)
SM Fiber (500 m)
SM Fiber (20 Km)
GigE Card
Server (OLT)
Workstation 3 (ONU)