Title: Next Generation EPON-based Access Network Architecture
1Next Generation EPON-based Access Network
Architecture
2Access Network
Link between the customer premises and the first
point of connection to the network
infrastructurea point of presence (PoP) or
central office (CO).
3Ethernet in the Last Mile
4Access Bandwidth
5Optical Access
6What 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.
7Basic Architecture of PON
8EPON Downstream
9EPON Upstream
10EPON Configuration
11EPON 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)
12Multiple Access Schemes
13Statistical 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
bandwidth-allocation scheme. - MPCP supports mechanism that can facilitate
various implementation of bandwidth allocation
algorithms.
14Timing 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-T1T5-T3
- RTT T5-T4
- T3-T2 T4-T1
15Multipoint 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
ONUs 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.
16Statistical 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.
17Interleaved polling scheme
18Advantages 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 ONUs 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.
19Ethernet TCP/IP Frame
100Base CU Burst 31 1518Byte Frames per Burst
20DBA 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
21Class-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 per-connection (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).
22Overview of IEEE 802.1D Support for Classes of
Service
- 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 CEOs 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.
23Dynamic Bandwidth Allocation
24Timeslot 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 gt the timeslot will
be transmitted with an unused remainder at the
end.
25Why timeslot adjustment wont work
- Why timeslot adjustment wont work
- Linear increase in offered load requires
exponential increase in timeslot size. - Increased timeslot size will increase timeslot
period gt 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.
26Drawbacks of OLT based DBA
- OLT-ONU is 20km and a control messages (REQUEST
and GRANT) consumes significant portion of the
valuable upstream bandwidth. - ONUs 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.
27Proposed New PON Architecture (In-band Signaling)
ONU
Redirected 1310nm signal
OLT
1550nm
1310nm
ONU
Splitter/ Combiner
- Control Plane
- 1310nm channel
- Data Plane
- Upstream 1310nm channel
- Downstream 1550nm channel
ONU
ONU
28Algorithm (DBA)
Control
Data
Time
Individual ONU update messages
Individual ONU data messages
a) First Phase
a) First Phase
Combining of ONU update messages
Combining of ONU data messages
b) Second Phase
b) Second Phase
Combined ONU update messages
Combined ONU data messages
Combined ONU data messages
Combined ONU update messages
c) Third Phase
c) Third Phase
29Distributed DBA for EPON In-band Control Plane
- Using (Splitter/Combiner) we reflect 1310nm
upstream bound signal. - We use REQUEST Control frames to update all ONUs
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.
30Distributed 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.
31Proposed New PON Architecture (Out-of-band
Signaling)
ONU
Splitter/ Combiner
OLT
ONU
1550nm
1310nm
- Control Plane
- Fixed Wireless LAN
- Data Plane
- Ethernet Passive Optical Network
ONU
ONU
32Distributed DBA for EPON Out-of-band Control
Plane
Control Plane
i
Control
Data
Data Plane
i1
- 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.
33Thesis 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.
34Testbed SETUP
Wireless Access Card
SM Fiber (500 m)
GigE Card
Workstation1 (ONU)
3X3 Splitter/ Combiner
Workstation2 (ONU)
Isolator
SM Fiber (500 m)
SM Fiber (500 m)
SM Fiber (20 Km)
GigE Card
Server (OLT)
Workstation 3 (ONU)