outline layered network modeljjue/optical/l9.pdf• an optical burst contains multiple ip packets...
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1
Optical Burst Switching
Outline
• Introduction to Optical Transport Paradigms
• Optical Burst Switching– Architecture– Burst Assembly– Routing– Signaling– Channel Scheduling– Contention Resolution
• Prioritized Burst Segmentation and Composite Burst Assembly for QoS
• Absolute QoS Differentiation
• TCP over OBS with Burst Retransmission
Optical layer
IP Router
Optical Switch
WDM
Layered Network Model
IP layer
Wavelengths (channels)
(Electronic)
Applications Demands
Voice Over IP
Streaming Video
Grid Computing
Storage Area Networks
Multimedia
Data
Applications Service Requirement
Optical Transport Paradigm
High Bandwidth
Dynamic Provisioning
Service Differentiation
Optical Circuit Switching
Optical Packet Switching
Optical Burst Switching
Optical Circuit Switching
• For each request, set-up a circuit• Static allocation of bandwidth for the entire duration
of the connection
• Pros: – Suitable for smooth traffic (Voice)
• Cons: – Long circuit set-up latency– Inefficient for bursty traffic (Data)
Optical Circuit Switching (cont.)
• Circuit switched networks optimized for Voice
• Data: Accounts of 90% of traffic by 2005
• Data tends to be bursty• Static bandwidth allocation is not efficient
Optical Circuit Switching
2
Optical Packet Switching
• A photonic packet contains a header and the payload
• Packet header is processed all-optically at each node and switched to the next hop
• Pros:– Statistical multiplexing of data– Suitable for bursty traffic
• Cons: – Very fast switching speeds (nanoseconds)
Optical Burst Switching
• An optical burst contains multiple IP packets
• Out-of-band control header transmitted ahead of data burst transfer
• Electronic control plane and optical data plane
• Pros:– Practical alternative to optical packet switching– Statistical multiplexing of data– Suitable for bursty traffic
Motivation for OBS
HighLowMediumLowHighOptical Burst
Switching
HighHighFastLowHighOptical Packet
Switching
LowLowSlowHighLowOptical Circuit
Switching
TrafficAdaptively
Proc. / Sync. Overhead
Switching Speed Req.
SetupLatency
Bandwidth Utilization
Optical Switching Paradigm
OBS combines the best of the two while avoiding their shortcomings
Outline
• Introduction to Optical Transport Paradigms
• Optical Burst Switching– Architecture– Burst Assembly– Routing– Signaling– Channel Scheduling– Contention Resolution
OBS Network Architecture
• Core– Signaling– Scheduling– Contention Resolution
• Edge– Burst Assembly– Routing
Burst Header
Offset Time
Core Node
Edge Node
WDM Link
IngressNode
EgressNode
Input Traffic
Output Traffic
IP
OBS Node Architecture
Switch
2
1 1
2
O/E/O2 2
1 1Control Packets
Data Bursts
Offset Time
ControlWavelengths
DataWavelengths
Scheduler
Control Packet Processing
[U-Buffalo]
3
• Core– Signaling– Scheduling– Contention Resolution
• Edge– Burst Assembly– Routing
Core Node
Edge Node
WDM Link
IngressNode
EgressNode
Input Traffic
Output Traffic
Optical Burst-Switched Network Burst Assembly
• Aggregate multiple (IP) packets going to the same destination into a single burst
• Assembly Mechanisms: Timer-based and Threshold-based
• Timer-based assembly:
– For each fixed timer interval, all the packets in the queue are framed into a single burst
• Threshold-based assembly:
– After a fixed length threshold is reached, all the packets in the queue are framed into a single burst.
Burst Assembly (cont.)
Data Channel
Control Channel
IP Packet
Time or length threshold is reached
A header is generated and sent out
Burst Assembly
Node
IP Packet Queues
DST
0
1
N
A unique packet queue for every destination egress node
Burst transmitted after offset time
Burst Aggregation Delay in ms
[U-Buffalo]
Assembly Framework• Parameters
– Burst Length: Minimum – Maximum– Threshold: fixed-sized burst in the network– Timer: constant burst arrivals into the network– Burst Priority: mapping IP classes to burst priorities
Pros/Cons• Burst Length
– Long Bursts – High aggregation delay; low control overhead– Short Bursts – Low aggregation delay; high control overhead
Guidelines• Select assembly mechanism based on higher-layer application
requirement• Select burst length based on optical-layer requirements
• Core– Signaling– Scheduling– Contention Resolution
• Edge– Burst Assembly– Routing
Core Node
Edge Node
WDM Link
IngressNode
EgressNode
Input Traffic
Output Traffic
Optical Burst-Switched Network Routing
• Source Routing: – All the edge nodes know the complete topology of the network– Source chooses the fixed shortest path to destination
• Fixed Shortest Path Routing– Minimum number of hops (lower loss)– Minimum total physical distance (lower delay)
• Extensions/Research Issues:– Fixed alternate path routing– Dynamic source routing (load balancing)– Intra- domain and Inter-domain routing
4
• Core– Signaling– Scheduling– Contention Resolution
• Edge– Burst Assembly– Routing
Core Node
Edge Node
WDM Link
IngressNode
EgressNode
Input Traffic
Output Traffic
Optical Burst-Switched Network Classification of Signaling Techniques
• Direction– One-way (unacknowledged)– Two-way (acknowledged)
• Initiation– Source– Destination– Intermediate
• Resource– Persistent– Non-persistent
• Reservation – Immediate– Delayed
• Release– Explicit– Implicit
• Computation– Centralized– Distributed
Signaling Technique
• Distributed and Non-Persistent techniques
• Reservation Mechanism: Based on the start of the reservation– Immediate Reservation: Immediately after the control heater – Delayed Reservation: At the start of the burst
• Release Mechanism: Based on the release of the reservation– Implicit Release: based on burst length information – Explicit Release: explicit release control packet used
HeaderBurst
Offset
Immediate Reservation
DelayedReservation
ImplicitRelease
Explicit Release
REL
Tell-and-wait (TAW) Signaling
Direction: Two-way Initiation: Source (SIR) / Destination (DIR) Reservation: ImmediateRelease: Explicit
• Header contains source, destination
• Pros:
– Lower loss: burst sent only after bandwidth reservation in the core
• Cons:
– High path setup latency
REL
REL
REL
REL
Just-In-Time (JIT) Signaling
Direction: One-way Initiation: SourceReservation: ImmediateRelease: Explicit
• Header contains Src and Dst• Header sent out while the burst is
being assembled• Burst sent after assembly (ensure
that min offset has reached)• Explicit release message send after
data burst transmission or an In-Band-Terminator (IBT) sent with the data burst
Src DstHeader
δ
δ
δBurst
Time
ST
REL
REL
REL
Just-Enough-Time (JET) Signaling
Direction: One-way Initiation: SourceReservation: Delayed Release: Implicit
• Header contains burst length, offset time, source, destination
• Pros:– Low path setup delay– High bandwidth utilization
• Cons:– Higher data loss due to contention
for resources in the core
Src DstHeader
δ
δ
δBurst
Offset
Time
ST
Offset time = δ * (No. of Hops) + ST
Note: Burst Aggregation Delay in ms; Offset time in order of μs
5
Summary: Signaling Techniques
ExplicitImmediateSourceOne-wayJust-In-Time (JIT)
ImplicitDelayedSourceOne-wayJust-Enough-Time (JET)
ExplicitImmediateSrc (SIR)/ Dst (DIR)
Two-wayTell-And-Wait (TAW)
ReleaseReservationInitiationDirectionSignaling Techniques
Tradeoff: Efficiency vs. Simplicity
Just-In-Time (JIT)
0
0Header
1
1
Control Channel
Data Channel
2
2
0REL HeaderHeader
0
0Header
1
1
2
2
OT0
OT1OT1
Control Channel
Data Channel
Just-Enough-Time (JET)
• Core– Signaling– Scheduling– Contention Resolution
• Edge– Burst Assembly– Routing
Core Node
Edge Node
WDM Link
IngressNode
EgressNode
Input Traffic
Output Traffic
Optical Burst-Switched Network
Channel Scheduling
• Which output channel to use?– If none is available, use contention resolution
• Two categories of scheduling algorithms– Without void filling
• Maintain the latest available time on every channel– Latest Available Unscheduled Channel (LAUC)– First Fit (FF)
– With void filling• Maintain the starting and ending time for every scheduled burst
on every channel– Latest Available Unscheduled Channel with Void Filling (LAUC-VF)– First Fit with Void Filling (FF-VF)
Channel Scheduling (cont.)
SaLbEa
SaLbEa
LAUC
LAUC-VF
D0
D1
D2
D3
Wavelengths
D0
D1
D2
D3
First Fit
FF-VF
LAUC
LAUC
Channel Scheduling Techniques
LAUTi , GAPiO(W)LAUC
S(i,j), E(i,j)O(W log(n))FF-VF
S(i,j), E(i,j) , GAPiO(W log(n))LAUC-VF
LAUTiO(W)FF
State Information
TimeComplexity
SchedulingTechniques
W: # of data channels; n: # of burst currently scheduled
LAUTi : Latest available unscheduled time on channel i
S(i,j) : Starting time of burst j on channel i ; E(i,j) : Ending time of burst j on channel i
GAPi : time difference between the starting time of the arriving burst and LAUTi (or the ending time of the previous burst)
6
Optical Burst-Switched Network
• Core– Signaling– Scheduling– Contention Resolution
• Edge– Burst Assembly– Routing
Core Node
Edge Node
WDM Link
IngressNode
EgressNode
Input Traffic
Output Traffic
Data Burst Contentions
• Contention occurs when more than one burst attempts to go out of same output wavelength at the same time
• Unique to all-optical networks– Traditional networks employ electronic buffering to resolve contentions– Lack of optical buffers (cannot store light)
Core Switch
Drop Entire Burst
• Drop Policy– One of the bursts will be dropped in its entirety– Even though overlap between the bursts may be minimal
Optical Buffering
• Achieved through Fiber Delay Lines (FDLs)
• Several different FDL architectures proposed– Feed-Forward (above) / Feed-Backward (loop)– Input-Buffer / Output-Buffer– Share-per-Port / Share-per-Node
• Issues– Limited buffer capacity (200 km = 1 ms)– Additional hardware cost– Affect signal quality
Burst in
FDLs
Delayed Burst out
Input-Buffer Architecture
Bursts are buffered before actually scheduling them onto a specific wavelength on the intended output fiber
Output-Buffer Architecture
Bursts are buffered after scheduling them onto a specific wavelength on the intended output fiber
Wavelength Conversion
• Converting the wavelength of an incoming channel to another wavelength at the outgoing channel
• All-optical wavelength converters
• Techniques– Four Wave Mixing– Cross Gain Modulation– Cross Phase Modulation
• Issues:– Additional hardware cost
7
Deflection Routing
• Deflect contending bursts to alternate port
• Pros– Save bandwidth: A
dropped burst wastes the bandwidth on the partially established path
– Save time: The delay becomes very large when retransmitting a blocked burst in long-distance links
– No additional hardware cost• Cons
– Out-of-sequence delivery– Potential looping
• Loopless Deflection Routing
F G H I J
A B C D E
Without Deflection
With Deflection
A DB C E A DB C I J E
Tot
al T
rans
. Tim
e
Tot
al T
rans
. T
ime
Deflection Nodes
Tim
eSa
ved
Without Deflection With DeflectionA DB C EA DB C E A DB C I J E
Tot
al T
rans
. Tim
e
Tot
al T
rans
. T
ime
Deflection Nodes
Tim
eSa
ved
Without Deflection With Deflection
[U-Tokyo]
Core Switch
Burst Segmentation
Original burst
Contending burst
Tail Dropping
Head Dropping
Dropped Segments
• When contention occurs, only overlapping segments are dropped
• Two Approaches: Head Dropping and Tail Dropping
V.M. Vokkarane and J. P. Jue, “Burst Segmentation: An Approach for Reducing Packet Loss in Optical Burst Switched Networks,” SPIE/Kluwer Optical Networks Magazine, vol. 4, no. 6, pp. 81-89, Nov.-Dec. 2003.
• Basic idea: to provide packet-level loss granularity in OBS• Burst is divided into segments• Each segment consist of single or multiple IP packets/ATM cells
Burst Segmentation
Signaling Issues
2
1
ba aST
Does tail-dropping have signaling overhead at downstream nodes?
a
OBS CORE
Node 1
Node N
ac
c
b2
1
2
1
2
1
ST
ST
NO
Segmentation in Void Filling
Non-Preemptive [No Signaling Overhead]
Preemptive [QoS Reasons; Additional Signaling Overhead]
Simulation Network
14-node NSFNET
Assumptions
NOWavelength ConversionNOOptical Buffering10 μsSwitching Time1500 bytesPacket Length10 Gb/sLink Transmission Rate 100 μs (exponentially distributed)Average Burst LengthPoissonBurst Arrivals
8
Packet Loss Performance
Segmentation
Drop
Log Scale
Presentation Outline
• Introduction to Optical Transport Paradigms
• Optical Burst Switching
• Prioritized Burst Segmentation Framework– Burst Segmentation – Prioritized Scheduling – Composite Burst Assembly
Differentiated Services
• Problem: To differentiate bursts based on application specific requirements in an all-optical core network
• Standard IP-based techniques are not applicable– IP differentiation primarily based on electronic buffering
• Design criteria – Provide 100% class isolation– Scalable: support multiple priorities in the network
Additional Offset-based QoS
• Concept: Earlier the control packet reaches the node, higher the probability of a successful reservation for the data burst
• Higher priority bursts : Longer offset time
0
0Header
Burst
OT0
1
1
OT1
Control Channel
Data Channel
• Issue:
– Not scalable: since the offset increases with number of priorities
Prioritized Burst Segmentation Framework
• Efficient utilization of network resources
• Support for different classes of traffic
Composite Burst Assembly PrioritizedScheduling
BurstSegmentation
IEEE JSAC 2003, SPIE/Kluwer Optical Networks 2003, IEEE [ICC, OFC, GLOBECOM] 2002
Prioritized Burst Segmentation Framework
• Burst-level differentiation– Burst priorities– Differentiated scheduling and contention resolution
• Original burst – burst that is scheduled earlier• Contending burst – burst that arrives later
• Packet-level differentiation– Packet classes– Composite burst assembly – differentiated location of
packets within a burst
9
Core Switch
Burst Segmentation
Original burst
Contending burst
Tail Dropping
Head Dropping
Dropped Segments
• When contention occurs, only overlapping segments are dropped
• Two Approaches: Head Dropping and Tail Dropping
Contention Resolution Policies
• Drop Policy: – Drop the entire contending burst
• Deflect Policy: – Deflect the contending burst to the alternate port– If the alternate port is busy, drop the burst
• Segment Policy: – Segment the original burst– Drop the tail segments – Transmit the contending burst
Core Switch
Segmentation with Deflection
a ab
a`
a`
b
• Segment-First Policy:– Segment the original burst
– Deflect/Drop the tail segments
– Transmit the contending burst
Core Switch
Segmentation with Deflection (cont.)
a a
bb
• Deflect-First Policy:– If alternate port available
• Deflect the contending burst– If alternate port busy
• Segment original burst • Drop the tail segments• Transmit the contending burst
– 100% class isolation– Scalable to support multiple priorities in the network
Core Switch
Core Switch
Low Priority
High Priority
High Priority
Low Priority
Prioritized Scheduling
Case 1
Case 2
Contention Resolution Schemes
• DP: Drop Policy– Drop entire contending burst
• SDP: Segment-Drop Policy– Segment original burst and drop segments
• DDP: Deflect-Drop Policy– Attempt to deflect contending burst, otherwise drop it
• SFDP: Segment-First and Deflect Policy– Segment original burst– Attempt to deflect segments, otherwise drop
• DFSDP: Deflect-First, Segment, and Drop Policy– Attempt to deflect contending burst, otherwise– Segment original burst and drop segments
10
Loss Probability Delay Composite Burst Assembly
Core Switch
High Priority
High Priority
Case 1
A A A A A
B B A A A
B B A A A
High Priority
High PriorityCore Switch
Case 2 Composite Class Bursts
Single Class Bursts
Prob. Loss
A A A A A
Composite Burst Assembly (cont.)
• Probability of loss of a packet in a burst increases from head to tail of the burst
• System Parameters– Number of input packet classes (edge)– Number of burst priorities (core)
• Illustration: – Number of input packet classes = 4– Number of burst priorities = 2
Packet Class: A B C D
Burst Priority: 0 1(Highest)
AAAAAAAA
DDDDDDDD
Assembled Burst Contents
BBBBBBBB
CCCCCCCC
Burst Priority
0
0
1
1
4 Packet Class 2 Burst Priorities
AAAABBBB
Assembled Burst Contents
CCCCDDDD
Burst Priority
0
1
Composite Class Burst
Single Class Burst
AAAAAAAA
DDDDDDDD
Assembled Burst Contents
Timer & Threshold
BBBBBBBB
CCCCCCCC
Burst Priority
0
1
2
3
Threshold
Threshold
Threshold
Aggregation
AAAAABBB
DDDDDDDD
Assembled Burst
Timer & Threshold
BBBBBCCC
CCCCCDDD
Burst Priority
0
1
2
3
Threshold
Threshold
Threshold
Aggregation
Single Class Burst
Composite Class Burst
4 Packet Class 4 Burst Priorities
11
Generalized Burst Assembly Framework
• Parameters– Burst Destination– Burst Priority– Burst Length: Minimum/Maximum total number of packets in a
burst of a given priority– Packet Class Threshold: Minimum/Maximum number of packets of
a given class in a burst of given priority– Packet Class Location: Location of various packet classes within a
burst– Assembly trigger:
• Timer-based• Threshold based
– Total number of packets reaches threshold– Number of packets of given class(es) reach threshold
• Traffic grooming: packet destination may not necessarily correspond to burst destination
Prioritized Burst Segmentation Summary
• Objective: Minimize packet loss and provide application specific services in an OBS network– Burst Segmentation:
• reduced packet loss due to contentions– Prioritized Scheduling:
• differentiates services (100% class isolation)• Scalable solution to multiple priorities
– Composite Burst Assembly: • Further enhance differentiation between traffic
4:2 Mapping under Single Burst Assembly
One output port of an ingress node
Output link
4:2 Mapping under Composite Burst Assembly
Output link
One output port of an ingress node
Burst Priority
Packet Class
NOWavelength ConversionNOOptical Buffering10 μsSwitching Time1250 bytesPacket Length10 Gb/sLink Transmission Rate 100 packetsFixed Burst LengthPoissonBurst Arrivals
Simulation Assumptions
• 14-node NSFNET
• Input traffic ratios for packet classes:
A - 10%, B - 20%, C - 30%, and D - 40% (A: Highest)
• Class A Timeout - 50 ms
Prioritized Scheduling:Packet Loss Performance
• Contention resolution Scheme 3– Segmentation without deflection
High Priority
Low Priority
Traffic: 20% High – 80% Low
12
Composite Burst AssemblyPacket Loss Performance
4 Packet Classes: 2 Burst Priorities
Absolute QoS in OBS Networks
QoS Models
• Relative QoS Model– Provides relative service differentiation– High-priority class has better performance than low-priority
class
• Absolute QoS Model– Provides worst-case service guarantee– Necessary to support QoS sensitive applications
Absolute QoS Model in OBS
Input Traffic
Core Node
Edge Node DWDM Link
Ingress Node Egress Node
Input Traffic
Output Traffic
AdmissionControl
Absolute QoSDifferentiation atEach Core Node
• Core– Channel Scheduling: Guarantee Maximum Per-node Loss
• Edge– Admission Control– Resource Provisioning
Channel Scheduling Mechanisms
• Early drop – Intentionally drops the bursts of lower-priority class
• Wavelength grouping – Schedules the bursts on the provisioned wavelengths
Guarantee End-to-End Loss Requirement
• : MAX end-to-end loss probability of Class i• : MAX per-node loss probability of Class i • : Network diameter• To compute based on
13
Early Drop Mechanism
Standard Drop Mechanism Early Drop Mechanism
• Two Early Drop schemes to decide– Early Drop by Threshold: drops lower-priority bursts when loss of
higher-priority bursts exceeds the Max. loss threshold– Early Drop by Span: drops lower-priority bursts in order to guarantee loss
of higher-priority bursts in a certain range
High priorityLow priority
Early Drop Mechanism (cont.)
• Traffic statistics for class i traffic– : Burst arrival counter– : Burst drop counter– : Online burst loss probability
Early Drop by Span (EDS)
• : span between MIN and MAX loss threshold
• When each Class 1 (low) burst arrives, – If less than MIN loss threshold, no intentional dropping
– If between MIN and MAX loss threshold, drops Class 1 burst with a probability of
– If greater than MAX loss threshold, drops Class 1 burst
Wavelength Grouping Mechanism
• Two wavelength grouping schemes– Static wavelength grouping (SWG)– Dynamic wavelength group (DWG)
• : MIN # of wavelengths provisioned for Class 0 traffic– Computed by Erlang B Formula based on
• : # of wavelengths provisioned for Class 1 traffic– Obtained by
Static wavelength grouping Dynamic wavelength grouping
Wavelength Wavelength
Integrated EDS and WG
• If burst “should” be dropped according to EDS, it is given Label L1• If burst “should not” be dropped according to EDS, it is given Label L0• Do not drop bursts until WG stage• In WG stage, assign minimum number of wavelengths for bursts with
Label L0, and remaining wavelengths for bursts with Label L1• Allows Class 1 bursts to sometimes use Class 0 wavelengths if they are
not being used
Markov Chain Model
14
EDS/EDT Loss Probability Loss Probability ReferencesArchitecture and Signaling• C. Qiao and M. Yoo, "Choices, Features and Issues in Optical Burst Switching," Optical Networks Magazine, Vol.
1, No. 2, pp. 36-44, 2000.• C. Qiao and M. Yoo, "Optical Burst Switching - A New Paradigm for an Optical Internet," Journal of High Speed
Networks, Vol. 8, No. 1, pp.69-84, 1999 • L. Xu, H.G. Perros, and G. Rouskas, "Techniques for optical packet switching and optical burst switching," IEEE
Communications Magazine, Vol. 39, No. 1 , pp. 136-142, Jan. 2001. • J.Y. Wei, and R.I. McFarland Jr., "Just-in-time signaling for WDM optical burst switching networks," IEEE Journal
of Lightwave Technology, vol. 18, issue 12, pg. 2019-2037, Dec. 2000. Burst Assembly• K. Dolzer and C. Gauger, "On burst assembly in optical burst switching networks - a performance evaluation of Just-
Enough-Time," Proceedings 17th International Teletraffic Congress (ITC 17), Salvador, September 2001. • V.M. Vokkarane, K. Haridoss, and J.P. Jue, "Threshold-Based Burst Assembly Policies for QoS Support in Optical
Burst-Switched Networks," Proceedings, SPIE OptiComm 2002, Boston, MA, vol. 4874, pp. 125-136, July 2002. Channel Scheduling and Contention Resolution• Y. Xiong, M. Vanderhoute, and H.C. Cankaya, "Control architecture in optical burst-switched WDM networks,"
IEEE JSAC, vol. 18, no. 10, pp. 1838-1854, Oct. 2000. • V.M. Vokkarane and J.P. Jue, "Burst Segmentation: an Approach for Reducing Packet Loss in Optical Burst-
Switched Networks," SPIE/Kluwer, Optical Networks Magazine, vol. 4, no. 6, pp. 81-89, Nov./Dec., 2003. • V. M. Vokkarane et al, “Channel Scheduling Algorithms using Burst Segmentation and FDLs for Optical Burst-
Switched Networks,” Proceedings, IEEE ICC 2003, Anchorage, AK, May 2003Quality-of-Service:
• M. Yoo, C. Qiao and S. Dixit, "QoS Performance in IP over WDM Networks," IEEE JSAC, Vol. 18, No. 10, pp. 2062-2071, Oct. 2000.
• V.M. Vokkarane and J.P. Jue, "Prioritized Burst Segmentation and Composite Burst Assembly Techniques for QoS Support in Optical Burst-Switched Networks," IEEE JSAC, vol. 21, no. 7, pp. 1198-1209, Sept. 2003.
• Q. Zhang, V.M. Vokkarane, J.P. Jue, and B. Chen, "Absolute QoS Differentiation in Optical Burst-Switched Networks," UTD Technical Report UTDCS-45-03, Oct. 2003.