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Multimedia applications
and
Optical networks
Sitaram Asur, Sitha Bhagvat,
Mohammad Kamrul Islam ,Rajkiran Panuganti
Overview
 Optical Networks - Advantages & Overheads
 Requirements of Multimedia Applications
 Issues
 Protocol –level
 Network –level
 Scheduling & QoS
 Circuit switching
 OBS
 OLS
Optical Networks
Can provide very high bandwidth ( > 20TB/s per
fiber)
 Traditional optical networks are circuit switched



Transition to packet switched
Wavelength Div Multiplexing (WDM) or TDM

Multiparty communication possible – required in
multimedia appl.

Not easy to integrate with current Internet
•

No efficient O/E or E/O conversion is present.
No Optical RAM  no buffering
l-Mux
Fibers
Out
Optical
Space Switch
l160
...
Add ports
...
...
...
...
Optical
Space Switch
l2
...
Fibers
In
Optical
Space Switch
l1
...
WDM (Wavelength Div Multiplexing)
Drop ports
The challenge of multimedia
 Support for continuous media
 Quality of service management
 Packet Delay – delay sensitive
 Jitter
 Bandwidth
 Packet-loss ratio guarantee
 But, loss tolerant
 Multiparty communication
 Requires ’multicast’ support
 Different requirement of QoS
Protocols
 Traditional Protocols like TCP cannot utilize all the
available Bandwidth
 New Protocols - Fast, Fair, Friendly
 High utilization of the abundant bandwidth
 Intra-protocol fairness
 TCP friendly
 Common Issues solved by New Protocols
 Acknowledgement
 Congestion control
 Bandwidth Estimation – necessary to utilize it efficiently
UDT (UDP-based Data Transport)
 Acknowledgement

UDT uses timer-based selective acknowledgement
 Congestion control


AIMD - Does not meet efficiency objective
UDT uses modified AIMD algorithm to use 90% of the available
Bandwidth
 Bandwidth Estimation – necessary to utilize it efficiently


Link capacity estimation and available BW estimation
UDT uses packet-pair method for bandwidth estimation
 Avoiding Congestion collapse

Cause :- from increasing control traffic - costs both substantial
BW and CPU time
• Occurs if processing time is large

UDT increases expiration time to avoid congestion collapse
Scheduling in Circuit Switching
 Scheduling necessary for high bandwidth utilization in
Lambdas
 Circuit switched networks – fixed bandwidth allocation
 Fixed bandwidth allocation  low bandwidth utilization
 Solution – Use knowledge of data sizes to ‘schedule’ calls
 What rate should network assign for a particular transfer?
Varying-Bandwidth List Scheduling (VBLS)
 Input
 Known data size
 Maximum bandwidth limit
 Desired start time
 The scheduler returns a time-range
capacity allocation vector assigning
varying bandwidth levels in different
time ranges for the transfer
VBLS
:Available time ranges
S1
TRC1
S2
2
( F 2  2, Treq2  1, Rmax
 2)
TRC2
3
( F 3  5, Treq3  3, Rmax
 3)
S3
Shared single link
1
1
( F 1  2, Treq
 1, Rmax
 2)
TRC3
Circuit
Switch
Ch. 1
Ch. 2
D
Ch. 3
Ch. 4
 (t )
t=1
t=2 t=3 t=4 t=5
4
3
2
1
time
Advantages of VBLS
 Time-Range-Capacity vector allocation for vectors
 Allows Scheduler to backfill holes
 VBLS allows users to take advantage of subsequent
availability of network
 VBLS better than Packet Switching in ease of
implementation, management of pricing mechanisms for
resource allocation
 Disadvantage – need to reprogram the circuit switch multiple
times
Evolution of Optical Networking
Network Efficiency
Optical Provisioning, Reconfiguration, and Switching
Strategies
True Convergence of
IP and Optical Layer
Static
Highly Dynamic
Optical Label/Burst
Switching
Dynamic
Reconfigurable
Optical Networks
Addresses carrier needs*:
Reconfigurable
• Bandwidth utilization
Optical Networks
• Provisioning time
Point-to-Point
Optical Transport
Past
• Scalability
Inflexible reconfigurability
High Management Complexity
Present
Future
*RHK Carrier Survey
Next Generation Optical Network
 IP over all-optical Wavelength Division Multiplexing (WDM)
layer
Optical Burst Switching (OBS)
 Combines the best of packet and circuit switching
and avoid their shortcomings.
 First a control packet is sent using a separate
(control) channel (wavelength).
 Configure the intermediate node and reserves BW.
 Without waiting for the reservation ACK, data
“burst” follows the control packet but using
different channel.
How OBS works
 At ingress Edge router E/O conversion occurs.
 At Edge router, IP packets are assembled into a data burst.
 From Edge router, Control packet sent to Core router to
setup a path
 Data burst sent in the same path using different wavelength.
3 Switch
Configuration
4 Burst
forwarding
Core (TX)
Edge
Router
(NY)
1 Burst
assembly
Legacy
Interface
(IP)
Edge
Router
(CA)
2 Control packet
Core (OH)
5 Burst
disassembly
Legacy
Interface (IP)
Scheduling at OBS Core
 Two basic scheduling algorithms:
 LUAC ( Latest available unscheduled channel)
Fiber Delay Lines
(FDLs)
Illustration of LAUC algorithm, (a) channel 2 is selected, (b) channel 3 is chosen.
Scheduling at OBS Core
LUAC is simple but inefficient channel usage due to gaps/voids.
 LUAC –VF (LUAC with void Filling)

Illustration of LAUC-VF algorithm.
Buffer allocation at Edge Router
 Buffering is required when creating a data burst by
assembling the IP packets of same class.
 How long assembling continues: till maximum threshold burst
size or timeout.
 If finds available wavelength, send it.
 If not, the scheduler keeps the buffer till it gets an
available channel or maximum buffering time .

High priority packets have longer buffering time and hence
experience less dropping.
Bandwidth Allocation at Core Switch
 Bandwidth allocation of class N at time t Bn(t)& Bandwidth
allocation ratio Rn
 Higher priority packets has larger value of Fn and hence
lower Rn.
 When a data burst of class X found no free channel at the
output port:



Scheduler looks a channel with higher Rn value.
It preempts that channel and schedule the burst of class X
If no such channel is found, it drops the burst.
 Observations: Multimedia applications with larger Fn have
smaller dropping probability.
Optical Label Switching (OLS)
 OLS enables packet switching and multiplexing in the optical domain
 Packet forwarding is based on an optical header
 Header is sub-carrier multiplexed with the optical data
 The “label” field in the optical header determines packet forwarding
 Data is delayed while the header is examined
 Routers erase and re-insert the label in the optical header

Enable optical time slot switching and multiplexing in subwavelength
domain independent of packet protocols

No need for end-to-end network synchronization
High Bit Rate
Optical Packet
Low Bit Rate
Subcarrier Label
Label and Packet
Forwarded
Fiber
Optical Header
Extraction Unit
Label Extracted
for Processing
Only low cost
electronics
required to
process the label
in parallel
Advantages of OLS
 Only the optical label needs to be converted.
 Payload stays optical, which provides transparency to packet bit-
rate and data format
 Enables dynamic optical switching and routing from the optical
circuit to the packet level of granularity

Convergence of both types to a single platform
 Routers can be shrunk to chip-sized elements that consume two
to three orders of magnitude less power than their electrical
counterparts
 Facilitates support for quality of service (QOS), class of service
(COS) and traffic engineering.
Applications






Next Generation Internet;
Data exchange communications;
Virtual Private Networking (VPN);
Analog/digital communications;
Voice over Internet Protocol (VoIP); and
Broadcasting and video conferencing.
Modern Features of OLS Routers
 Multicast contention resolution
 To support multicast of multimedia applications
 Optical Time to Live
 Weighted TTL - OSNR
 Label generation and packet classification
 based on QoS/CoS requirements
Multicast Contention Resolution in OLS
 Multimedia conferencing and streaming are growing fast
 Multicast in router saves network resources
 Absence of optical logical circuits and buffers to generate copies
 Solution : Extra ports on OLS core routers to handle multicast

Port contains Multi-Wavelength Converter
 Contention resolution and arbitration a challenge
 Solution: Multicast Contention Resolution Algorithm
Multicast Contention Resolution
Sad
Label generation and packet Classification
 OLS edge routers implement packet aggregation and label
processing
 Edge routers provide different QoS/CoS policies to client
applications.
 Label includes the packet length, CoS, source address,
destination address etc.
 Edge routers at the end points de-aggregates the packets,
classifies and maps the packets to different QoS policies.
References
 Phuritatkul, J., Ji, Y., “Buffer and Bandwidth Allocation
Algorithms for Quality of Service Provisioning in WDM
Optical Burst Switching Networks”, Lecture Notes in
Computer Science, Vol.3079, pp.912-920, 2004
 Qiao, C., Yoo, M., Dixit, S., “OBS for Service Differentiation
in the Next-Gen Optical Network”, IEEE Commu. Magazine,
Feb. (2001) 98-104
 Zhong Pan, Haijun Yang et al, “Advanced Optical-Label
Routing System Supporting Multicast, Optical TTL, and
Multimedia Applications”, IEEE Journal of Lightwave
Technology, Vol 23, No 10, October 2005
 R. Ramaswami and K. Sivarajan, Optical Networks: A Practical
Perspective, Morgan Kaufmann Publishers, 1998
 B. Mukherjee, Optical Communication Networks, McGraw Hill,
1997
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