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Packet Striping Hari Adiseshu@Washington University 1
Packet Striping Hari Adiseshu@Washington University 2
Reliable and Scalable Packet Striping Hari Adiseshu Guru Parulkar - - PowerPoint PPT Presentation
Reliable and Scalable Packet Striping Hari Adiseshu Guru Parulkar - - PowerPoint PPT Presentation
Reliable and Scalable Packet Striping Hari Adiseshu Guru Parulkar George Varghese Washington University in St. Louis 1 Hari Adiseshu@Washington University Packet Striping Introduction u Packet Striping * using multiple links as a single
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Packet Striping Hari Adiseshu@Washington University 3
Current Striping Techniques
u Usually at the physical level (Inverse
Multiplexing)
u Physical level striping has drawbacks u Wanted: packet striping at a logical level u Multilink PPP provides framing, not load
sharing
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Packet Striping Hari Adiseshu@Washington University 4
Packet Striping Reference Model
Channel Resequencing Algorithm Channel Striping Algorithm
Sender Receiver Desirable properties: Desirable properties: Desirable properties: Load Sharing Load Sharing Load Sharing FIFO delivery FIFO delivery FIFO delivery Assume: All Channels are FIFO Assume: All Channels are FIFO Assume: All Channels are FIFO
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Packet Striping Hari Adiseshu@Washington University 5
Overview of Talk
u How to achieve load sharing u How to achieve FIFO delivery u How to recover from packet loss u Experimental results
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Packet Striping Hari Adiseshu@Washington University 6
Contributions
u Provide a transformation of a class of fair
queuing algorithms into striping algorithms providing load sharing
u Provide a specific instance of such a fair
queuing algorithm
u Show how to achieve Quasi-FIFO delivery
at the receiver
u Show how to recover from packet loss
through periodic marker packets
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Packet Striping Hari Adiseshu@Washington University 7
RR Striping Algorithm 100 1 100 2 100 3 100 4 100 1 100 2 100 4 100 3 Equal Sized Packets
Round Robin Striping
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Packet Striping Hari Adiseshu@Washington University 8
RR Striping Algorithm 200 1 100 2 200 3 100 4 200 1 100 2 100 4 200 3 No Load Sharing with unequal sized packets
Round Robin Striping
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Packet Striping Hari Adiseshu@Washington University 9
Causal Fair Queuing Algorithm
Use function f(s) to select queue Transmit packet p at head of queue Update state using function g(s, p) f(s)
Load Sharing Algorithm
f(s)
CFQ and Load Sharing
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Packet Striping Hari Adiseshu@Washington University 10
Load Sharing
u CFQ algorithms - FQ algorithm in which
queue to be served depends only on packets sent so far
u CFQ algorithms can be modeled as repeated
applications of two functions
u Theorem: Causal FQ algorithms can be
transformed into load sharing algorithms with the same fairness properties
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Packet Striping Hari Adiseshu@Washington University 11
Surplus Round Robin (SRR)
u Example of a CFQ algorithm u Each input queue associated with a
Quantum and a Deficit Counter (DC)
u Queues served in round robin order u At each visit to a queue, DC is incremented
by Quantum
u Each queue served as long as DC is
positive
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Packet Striping Hari Adiseshu@Washington University 12
SRR CFQ Algorithm
400 7 250 1 300 2 400 5 200 6 300 3 Output Channel 400 5 200 6 300 2
DC1 = -50 DC2 = -100 DC1 = 500 DC2 = 500
Round 1 400 7 300 3 150 4
DC1 = 0 DC2 = 0 DC1 = 450 DC2 = 400
Round 2 Queue 1 Queue 2
DC1 = 0 DC2 = 0
Initialization
Quantum = 500
SRR Causal Fair Queuing
250 1 150 4
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Packet Striping Hari Adiseshu@Washington University 13
SRR Transform Algorithm
400 7 250 1 300 2 200 3 400 4 300 5 Input Queue 400 7 300 5 150 6
DC1 = 0 DC2 = 0 DC1 = 450 DC2 = 400
Round 2 Output Channel 1 Output Channel 2
DC1 = 0 DC2 = 0
Initialization
Quantum = 500
SRR Transform for Load Sharing
200 3 400 4 300 2
DC1 = -50 DC2 = -100 DC1 = 500 DC2 = -500
Round 1 250 1 150 6
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Packet Striping Hari Adiseshu@Washington University 14
SRR Results
u SRR transform provides load sharing if the
Quantum associated with each channel is proportion to its capacity, and is greater than the maximum packet size
u K rounds after initialization, the difference
between data actually sent over a channel i and the amount that actually should have been sent is bounded by Quantumi
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Packet Striping Hari Adiseshu@Washington University 15
Contributions
u Provide a transformation of a class of fair
queuing algorithms into striping algorithms providing load sharing
u Provide a specific instance of such a fair
queuing algorithm
u Show how to achieve Quasi-FIFO delivery
at the receiver
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Packet Striping Hari Adiseshu@Washington University 16
FIFO delivery
u Guaranteed FIFO - add sequence number to
packets
* not always possible, e.g.. ATM cells, transparent Ethernet striping
u Quasi-FIFO - FIFO in the absence of
packet loss
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Packet Striping Hari Adiseshu@Washington University 17
100 3 100 2 100 4 100 1 Time Axis Physical Reception 100 3 100 2 100 4 100 1 Time Axis Logical Reception
Logical Reception
u Receiver
Buffering
u Receiver
simulation
- f the
sending algorithm
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Packet Striping Hari Adiseshu@Washington University 18
SRR CFQ Algorithm SRR Transform Algorithm
Quasi-FIFO reception using SRR
Sender Sender Receiver Receiver
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Packet Striping Hari Adiseshu@Washington University 19
Quasi-FIFO result
u The combination of a transformed version
- f a CFQ algorithm at the sender, and the
CFQ algorithm at the receiver provides Quasi-FIFO delivery
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Packet Striping Hari Adiseshu@Washington University 20
SRR Transform Algorithm
Sender
100 6 100 4 100 2 100 5 100 3 100 1 100 3 100 1 100 2 100 4 100 5 100 6
Input Queue Input Queue Channel 1 Channel 1 Channel 2 Channel 2
Effect of Packet Loss
SRR CFQ Algorithm
100 3 100 1 100 2 100 4 100 5 100 6
Output Queue Output Queue Receiver
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Packet Striping Hari Adiseshu@Washington University 21
Effect of Packet Loss
SRR Transform Algorithm
Sender
100 12 100 10 100 8 100 11 100 9 100 7 100 9 100 7 100 8 100 10 100 11 100 12
Input Queue Input Queue Channel 1 Channel 1 Channel 2 Channel 2
Effect of Packet Loss
SRR CFQ Algorithm
100 11 100 9 100 8 100 10
Output Queue Output Queue
Packet 7 is lost Packet 7 is lost Buffered Buffered Buffered
Receiver
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Packet Striping Hari Adiseshu@Washington University 22
Recovery from Packet Loss
u Synchronization depends on shared state between sender
and receiver
u On packet loss, the shared state is lost u Solution: propagate state periodically from the sender to
the receiver
u For the specific case of SRR algorithm, state consists of
Round Number, and Deficit Counter values for each link
u Periodically propagate these values to the receiver using
marker packets
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Packet Striping Hari Adiseshu@Washington University 23
Sync Recovery
SRR Transform Algorithm
Sender
100 18 100 16 100 14 100 17 100 15 100 13 100 15 100 13 100 14 100 16 100 17 100 18
Input Queue Input Queue Channel 1 Channel 1 Channel 2 Channel 2
SRR CFQ Algorithm
100 15 100 13 100 14 100 16 100 17 100 18
Output Queue Output Queue
G=7M
Marker causes receiver to skip channel Marker causes receiver to skip channel
100 12 100 12
Buffered Buffered Buffered
Receiver
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Packet Striping Hari Adiseshu@Washington University 24
IP IP IP IP Convergence Convergence Layer Layer Data Link Data Link Interface Interface strIPe strIPe IP IP Convergence Convergence Layer Layer Data Link Data Link Interface Interface
strIPe layer
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Packet Striping Hari Adiseshu@Washington University 25
Ethernet Ethernet ATM ATM
Experimental Setup
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Packet Striping Hari Adiseshu@Washington University 26
NetBSD Implementation
2 4 6 8 10 12 14 16 18 20 10 20 30
ATM Channel Capacity (Mbps) Application Level Throughput (Mbps)
Sum of Ethernet and ATM Throughputs SRR, logical reception SRR, no logical reception GRR, logical reception GRR, no logical reception RR, logical reception RR, no logical reception Contributions
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Packet Striping Hari Adiseshu@Washington University 27
Experimental Results
u Throughput with SRR matched aggregate
throughput
u Throughput more with resequencing u Throughput of SRR greater than other
variants
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Packet Striping Hari Adiseshu@Washington University 28