2. Passive
Op9cal
Network
• Only
passive
components
between
source
and
des9na9on:
– SpliFers,
Combiners,
Fiber,
Splices…
• Main
standards:
IEEE
EPON
and
ITU-‐T
GPON
• Ethernet
PON
largely
used
standard
• Topology
Architectures:
– Tree,
Ring,
Bus
…
– Tree
is
the
most
used
• OLT,
ONUs,
ODN
• P2MP
in
Downstream,
MP2P
in
Upstream
Network
Infrastructures:
PON:
The
MAC
protocols
2
3. The
MAC
Layer
• Sublayer
of
the
2nd
layer
in
ISO/OSI,
the
Data
Link
layer.
• Medium
Access
Control
• Control
Channel
Access
• Interface
between
Logical
Link
Control
sublayer
and
Physical
Layer
• 4
Major
Problems:
– The
Mul9ple
Access
– The
Bandwidth
Alloca9on
– The
Transmission
Scheduling
– The
QoS
support
• Applica9on
Layer
7
• Presenta9on
Layer
6
• Session
Layer
5
• Transport
Layer
4
• Network
Layer
3
• Data
Link
Layer
2
• Physical
Layer
1
Network
Infrastructures:
PON:
The
MAC
protocols
3
4. Conflict
in
The
Channel
• Mul9point-‐to-‐Point
architecture
in
upstream
direc9on
• 2
main
possible
approaches
to
solve
the
problem:
– Time
Division
Mul9ple
Access
(TDMA)
• Each
ONUs
receives
different
9me
slots
– Wavelength
Division
Mul9ple
Access
(WDMA)
• For
each
ONUs
there’s
a
different
wavelength
Network
Infrastructures:
PON:
The
MAC
protocols
4
5. TDMA
vs
WDMA
• Both
used
to
share
the
upstream
channel
while
avoiding
collision
• WDMA:
– Each
ONU
has
a
precise
wavelength
– Separate
Transceiver
for
each
ONU
(or
Tunable
one)
– High
Cost
• TDMA:
– Common
wavelength
– Same
Type
of
Transceiver
– Easy
to
design,
operate,
manufacture,
maintain.
– Low
Cost
Network
Infrastructures:
PON:
The
MAC
protocols
5
6. Time
Division
Mul9ple
Access
• Fixed
or
Variable
size
Time
Window
• ONU
buffers
frames
un9l
they
are
transmiFed
in
the
assigned
Time
Window.
• Dynamic
Alloca9on
of
Variable
Time
Slots
for
each
ONU,
based
on
their
bandwidth
demand
• Done
through
a
Polling
Mechanism
• Mul9-‐Point
Control
Protocol
(MPCP)
– New
func9on
of
the
MAC
control
sublayer
– Support
dynamic
capacity
alloca9on
and
arbitrates
transmission
of
mul9ple
ONUs
Network
Infrastructures:
PON:
The
MAC
protocols
6
7. The
Mul9-‐Point
Control
Protocol
• Fixed
Slot
Alloca9on
(FSA)
or
Dynamic
Bandwidth
Alloca9on
(DBA),
but
best
perform
on
DBA
• Works
in
2
modali9es:
– Autodiscovery
Mode:
REGISTER,
REGISTER_REQ,
REGISTER_ACK
– Normal
Mode:
REPORT,
GATE
Network
Infrastructures:
PON:
The
MAC
protocols
7
8. Efficient
Polling
Mechanism
(1/2)
• Polling
protocols
based
on
MPCP
opera9ng
in
normal
mode.
a) Poll-‐and-‐stop
• Bandwidth
Waster
b) Interleaved
polling
• More
efficient
c) Interleaved
polling
with
stop
• Waits
for
all
Tx,
before
star9ng
new
polling
cycle
Network
Infrastructures:
PON:
The
MAC
protocols
8
9. Efficient
Polling
Mechanism
(2/2)
• Maximum
Bandwidth
Limit
– OLT
should
limit
maximum
transmission
window
for
each
ONU,
according
to
• Service
License
Agreements
(SLAs)
• Network
Conges9on
Status
• Transmission
Scheduling
– Avoid
data
collision
– OLT
knows
round-‐trip-‐9me
to
every
ONU
• Transmission
Start
Time,
Window
Size
for
next
ONU
– Examples:
• Round
Robin
(RR):
based
on
ONU’s
index
in
polling
table
• Dynamic
Approach:
Longest
Queue
First
(LQF),
Earliest
Packet
First
(EPF)
Network
Infrastructures:
PON:
The
MAC
protocols
9
10. IPAC
vs
BGP
• Interleaved
Polling
Adap9ve
Cycle
Time
– Variable
size
9me
windows,
based
on
#
of
frames
buffered
in
the
respec9ve
ONUs
– No
synchroniza9on
is
needed
among
ONUs
– Polling
message
interleaved
with
frame
transmission
• Less
Overhead,
More
Efficiency
• Bandwidth
Guarantee
Polling
MAC
protocol
– ONUs
differen9ated
in
2
groups:
• Bandwidth
Guaranteed
(BG):
More
priority
• No-‐Bandwidth
Guaranteed
(NBG):
Less
priority
– Total
Upstream
Bandwidth
divided
in
equivalent
Bandwidth
Uni9s
(BU)
– OLT
assign
dynamically
BU
to
ONUs
based
on
their
SLAs
Network
Infrastructures:
PON:
The
MAC
protocols
10
11. Quality
of
Service
• Telecommunica9on
industry
a
lot
interested
in
suppor9ng
QoS,
(SLAs
=
Money)
• Different
Priori9es
for
different
data
flows
– Network
Neutrality
???
• MAC
level:
Priority
Queuing
in
the
ONUs
• Data
is
inserted
in
the
right
queue
based
on
the
Type
of
Service
(ToS)
• ONUs
should
perform
Traffic
Policy
to
avoid
resource
starva9on
in
low-‐priority
packets
Network
Infrastructures:
PON:
The
MAC
protocols
11
12. The
U-‐City
WSN
with
PON
• Ubiquitous
City:
everything
virtually
linked
to
Informa9on
Systems
• WSN
divided
in
clusters:
cluster
head
+
sensor
nodes
• Each
cluster
head
(ONU)
connected
by
a
PON
to
the
Personal
Area
Network
Coordinator
(OLT)
• Sync-‐LS:
9me
frame
divided
in
2
parts:
– Forward
Time:
OLT
sends
beacon
and
forward
data
toward
sensor
nodes.
– Reverse
Time:
Request
message
to
the
OLT
to
grant
Time
Slot
• Sensor
nodes
generate
Emergency
and
Non-‐Emergency
traffic
• Sensor
nodes
send
data
to
their
ONU,
which
has
2
queue:
– Priority
queue
– Best-‐effort
queue
• ONU
allowed
to
transmit
first
from
priority
queue,
then
the
remaining
9me
slots
are
used
for
best-‐effort
queue
Network
Infrastructures:
PON:
The
MAC
protocols
12
13. Conclusion
• MAC
protocols
in
PON,
essen9al
role
for:
– efficient
data
transmission
– collision
avoidance
• TDMA
and
WDMA,
polling
mechanism
and
MPCP
• Examples
of
advanced
protocols
such
as
IPACT,
BGP,
and
Sync-‐LS
• The
importance
of
QoS
in
the
design
of
the
protocols
• Transmission
scheduling
and
Bandwidth
alloca9on
Network
Infrastructures:
PON:
The
MAC
protocols
13
