Transcript 14-Specific_system_PON

Specific Systems:
Passive Optical Networks
(PONs)
#14
Victor S. Frost
Dan F. Servey Distinguished Professor
Electrical Engineering and Computer Science
University of Kansas
2335 Irving Hill Dr.
Lawrence, Kansas 66045
Phone: (785) 864-4833 FAX:(785) 864-7789
e-mail: [email protected]
http://www.ittc.ku.edu/
All material copyright 2006
Victor S. Frost, All Rights Reserved
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Outline
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What is a PON?
Types of PON
PON Architecture
EPON
– How EPON works
– EPON Protocol
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What is a PON
• A passive optical network is a point-to-multi-point
architecture for delivering last-mile connectivity without
any active components in the distribution network.
• A Passive Optical Network consists of
– an optical line terminator (OLT) located at the Central Office
(CO)
– set of associated optical network units-ONUs, (or optical
network terminals-ONTs) located at the customer’s premise.
– optical distribution network (ODN) comprised of fibers and
passive splitters or couplers for connectivity
• Information Flows
– Downstream Point to multipoint (P2MP)
– Upstream  Shared
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FTTx
• Fiber To The x
(FTTx)
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– x = H = Home
– x = C = Curb or x =
N = Neighborhood
– x = P = Premises
– x = B = Business or
x = O = Office
*From: Gerd Keiser, “ FTTX, Concepts and Applications,” Wiley, 2006
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PON Topologies
From: Glen Kramer and Gerry Pesavento, “Ethernet Passive Optical Network
(EPON): Building a Next-Generation Optical Access Network”,
IEEE Communications Magazine, February 2002
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PON
Advantages/Disadvantages
• Advantages
– Increase bandwidth to Gb/s or higher in the future using
multiple wavelengths
– Increase reach between CO and customer
– Reduce fiber cost, one fiber to OTL to optical splitter
– Support downstream broadcast
• Analog video
• Digital Video
• Video over IP
– Reduce cost via use of passive
• Disadvantages
– Cost
– Need to deploy new infrastructure
 replace copper with fiber
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Types of PONs
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A/BPON – ATM Based PONs/Broadband based PONs
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Based on ATM technology
Two downstream wavelengths (1550nm and 1490nm) and one upstream wavelength (1490nm).
The 1550nm channel will be used for an RF or IP video overlay.
ITU standard G.983
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Shares up to 2.5Gbps shared bandwidth among 32 users;
Uses same wavelength plan of BPON.
ITU standard G.984
Main attribute supports multiple protocols
GPON – Gigabit PONs
ATM,
Ethernet
TDM
EPON – Ethernet Based PONs
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All data encapsulated in Ethernet frames (note customer premises equipment dominated by
Ethernet interfaces)
Two downstream wavelengths (1550nm) and one upstream wavelength (1310nm).
Shares 1.25Gbps in shared bandwidth
GigaEthernet PON (GePON) increases shared bandwidth to 2.5Gbps.
IEEE 802.3ah
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VLAN (IEEE 802.1Q)
Prioritization (IEEE 802.1p)
GPON and EPON are currently the major alternative technologies
 focus here is on EPONs
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Types of PONs
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EPON Downstream flows
Note ONU can be associated
with multiple users
Passive Splitter
Number of users typically limited to 64  splitting loss
Modified from: Glen Kramer and Gerry Pesavento, “Ethernet Passive Optical Network
(EPON): Building a Next-GenerationOptical Access Network”,
IEEE Communications Magazine, February 2002
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EPON Upstream flows
ONU/OLT distances vary
- Need power control
- Guard times to overcome sync errors
•All ONUs are in time sync
•Time slots can carry multiple Ethernet Frames
•Permission to send in a time slot done by the OLT using a
Multipoint control protocol (MPCP)
Modified from: Glen Kramer and Gerry Pesavento, “Ethernet Passive Optical
Network(EPON): Building a Next-GenerationOptical Access Network”,
IEEE Communications Magazine, February 2002
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MAC Protocols
• Initialization-auto-discovery mode
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Ranging
MAC address
Synchronization
Assign Logical Link identifier (LLID)
• EPON is treated as a collection of logical
point-to-point links by higher layers
Reserved
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From Glen Kramer,
“Ethernet Passive
Optical Networks,”
McGraw-Hill, 2005
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MPCP-Normal Mode
• OLT sends a GATE message to give ONU
access to transmit
• ONU sends a REPORT message to tell the
OLT its state, e.g., buffer contents
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*From: Jun Zheng and Hussein T. Mouftah, “Media Access Control for
Ethernet Passive Optical Networks: An Overview,”
IEEE Communications Magazine, February 2005
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MPCP-Normal Mode
From: Michael P. McGarry, Martin Maier, and Martin Reisslein Ethernet PONs:
A Survey of Dynamic Bandwidth Allocation (DBA) Algorithms
IEEE Communications Magazine, Vol. 42, No. 8, pages S8-S15, August 2004
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MPCP-Normal Mode
• Uses a polling like mechanism, i.e., cycle based
• Higher layer at OLT instructs the transmission of
a GATE message to ONUi, containing
– Time stamp
– Granted start time
– Granted transmission window
• ONUi receives GATE message
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Synchronizes clock (avoids collisions in the down stream)
Transmits at the start time
Continues to transmit up to the granted window
Transmission opportunity may send multiple Ethernet
frames (variable length)
– REPORT message included in the transmission window
– No fragmentation is allowed
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MPCP-Normal Mode
• REPORT message
– Time stamp
– Bandwidth demands of the ONU
– OLT receives the report and allocated
bandwidth
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MPCP-Normal Mode
• Each ONU is polled once in a cycle
• Upper limit on the granted
transmission window controls
– Maximum bandwidth allocated to ONU
– Insures all ONUs have an opportunity to
transmit
– There can be different polling policies
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MPCP-Normal Mode
• Poll and stop
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– Like master slave
– Receive REPORT before
generating next GATE
– No ONU sync needed
– Poor throughtput
• Interleaved Polling
– Send GATE before receiving
the REPORT
– OLT does not have upto date
ONU state information
• Interleaved polling with stop
– Use all reports in previous
cycle to determine
allocations in next cycle
*From: Jun Zheng and Hussein T. Mouftah, “Media Access Control for
Ethernet Passive Optical Networks: An Overview,” IEEE Communications
Magazine, February 2005
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Bandwidth allocation in the OLT
• Transmission scheduling
– Round Robin
– Descending order of reported queue
length largest queue first (LQF)
– Dynamic allocation
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Dynamic Bandwidth Allocation
• Interleaved Polling with Adaptive Cycle
Time (IPACT)
– Let n = cycle number
– G(n) = Grant window
– Q(n) ONU buffer size (backlog) that will be
during G(n)
– Q(n) generated at instant ONU generated
REPRT message
– Q(n) is used to calculate the grant window size
in next cycle, G(n+1)
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Dynamic Bandwidth Allocation
• Interleaved Polling with Adaptive
Cycle Time (IPACT)
• If Q(n) = 0 OLT still generates GATE
• Allocation methods
– Fixed service: Always gives Maximum
transmission window (MTW)
– Limited service: Window size is set to
max(MTW, Q(n))
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Dynamic Bandwidth Allocation
• Interleaved Polling with Adaptive Cycle Time
(IPACT)-continued
– Constant Credit service: Window size is set to
Q(n) + credit
• Accounts for packets arriving to the ONU after REPORT
sent
• Credit too big  wasted BW
• Credit too small  increase delay
– Linear credit: similar to constant credit, but the size of
credit is proportional to the requested window
– Elastic Service
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Maximum cycle time is enforced = N*MTW; N= #ONU
No limit on MTW
Accumulated size of last N grants < N*MTW
A backlogged ONU could get a grant of N*MTW
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Dynamic Bandwidth Allocation
• Problem: Traffic arrives at ONU after
REPORT sent but before GATE arrives,
OLT dose not know about this traffic
• Let A(n-1) = traffic arriving between
request for n-1 cycle and the grant for the
nth cycle
• D(n) = G(n) –[Q(n-1) + A(n-1)]
• Grant based on G(n+1) = G(n) – aD(n);
for stability 0<a<2
• Control loop has to be desinged to be
stable and avoid excessive oscillations
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Bandwidth guaranteed polling: (BGP)
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Divided ONUs into two disjoint sets:
bandwidth guaranteed
Non-bandwidth guaranteed (best effort)
Bandwidth guaranteed nodes are characterized by their service level
agreement (SLA) with the network provider
Upstream capacity is divided into “equivalent bandwidth units”, e.g.,
Upstream capacity = 1 Gb/s
N = 64
equivalent bandwidth unit = 10 Mb/s
Then there are 100 equivalent bandwidth units
OLT has two tables
ONUs with guaranteed bandwidth
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# rows = # bandwidth units
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Not fixed
ONUs without guaranteed bandwidth
Rows in guaranteed bandwidth table can be used for best effort ONUs
OLT polls best effort ONUs in order they appear in their table and during
time allocated for empty rows in guaranteed bandwidth table
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Bandwidth guaranteed polling: (BGP)
From: Michael P. McGarry, Martin Maier, and Martin Reisslein Ethernet PONs:
A Survey of Dynamic Bandwidth Allocation (DBA) Algorithms
IEEE Communications Magazine, Vol. 42, No. 8, pages S8-S15, August 2004
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Intra-ONU queueing and scheduling
• Approaches
– OTL can control
• REPORT messages in
status in each queue,
MPCP supports up to 8
queues
• GATE then responds
for a specific queue
– ONU can control
• REPORT message
relfects aggagerate
state of the ONU
• ONU schedules
transmissions
– Strict priority
– Non-strict priority
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References #14
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Assi, C.M., et al., Dynamic bandwidth allocation for quality-of-service over Ethernet
PONs. Selected Areas in Communications, IEEE Journal on, 2003. 21(9): p. 1467-1477.
Hajduczenia, M., EPONs - revolution in access networks.
Haran, O., EPON vs. GPON: a practical comparison. 2005.
Keiser, G., FTTX concepts and applications. Wiley series in telecommunications and
signal processing. 2006, Hoboken, N.J.: John Wiley & Sons : IEEE. xvii, 293 p.
Kramer, G., Ethernet passive optical networks. Communications engineering series.
2005, New York: McGraw-Hill Professional. xvii, 307 p.
Kramer, G. and G. Pesavento, Ethernet passive optical network (EPON): building a nextgeneration optical access network. Communications Magazine, IEEE, 2002. 40(2): p. 6673.
Kunigonis, M., FTTH explained: delivering efficient customer bandwidth and enhanced
services. 2005.
McGarry, M.P., M. Maier, and M. Reisslein, Ethernet PONs: a survey of dynamic
bandwidth allocation (DBA) algorithms. Communications Magazine, IEEE, 2004. 42(8):
p. S8-15.
Pesavento, G., Ethernet passive optical network (EPON) architecture for broadband
access Optical Networks Magazine 2003.
Upadhyay, P., Passive optical networks. 2005.
Zahr, S.A. and M. Gagnaire, An analytical model of the IEEE 802.3ah MAC protocol for
EPON-based access systems. 2006. p. 1-5.
Zheng, J. and H.T. Mouftah, Media access control for Ethernet passive optical
networks: an overview. Communications Magazine, IEEE, 2005. 43(2): p. 145-150.
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References
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