Transcript Overlay Network and Data Transmission over Wireless

Overlay Network and Data
Transmission Over Wireless
For EE290T
Minghua Chen
EECS@UC, Berkeley
Outline
 Overlay network & virtual overlay network
 Data transmission over wireless
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Improving TCP performance over wireless
Improving video performance over wireless
Overlay Network
 What is overlay network?
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“A configuration within which a base network is used to
support some second network, “layered” upon the underlying
infrastructure”
Another layer, logical network
Virtual overlay network – the interface used to provide service
are virtual
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Send(): reliable_send(), fast_send()…
 Why overlay network?
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Deploy/testing new protocol/service with minimal affecting the
lower IP infrastructure
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IPv6 TestBed
Multicast
QoS
Content Addressable Network (CAN, a hash lookup system)
Example – v6 Over v4 Overlay
“Backbone” Network
The Challenges
 Assume underlying infrastructure can
guarantee the bandwidth (even latency)
between overlay nodes
 Still need trust between AS
 Management
 Combine all extended services overlay into
one overlay
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Heterogeneous multimedia distribution overlay
network
Multicast overlay network
ON’s Advantages & Disadvantages
 Advantages
 Can apply RSVP, providing isolation (e.g., flow
isolation
 Flexible security approach (IPSec, PK/SK)
 New service (anycast etc)
 Disadvantages
 Efficiency
 Latency
 How many nodes need to be modified?
 What if one day the underlying network changes to
support all the functionalities?
Improving TCP Performance over
Wireless
 Problem
Packet may get loss on wireless due to channel error or
hand-off
 TCP treat packet loss as hint for congestionnot
necessarily decrease congestion window size  low
bandwidth usage efficiency
 Solution: shield sender from error-based packet loss
 Split connection
 End-to-End with error loss notification (ELN)
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Need some point on route to set the ELN bit
Link Layer based solution
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LL retransmission
 In WLAN, After LL retransmission, packet loss rate ~ 3%*
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LL-SMART-TCP-AWARED (snoop+sack)
 +30% improvement compare to LL retransmission
*:A TRACE-BASED APPROACH FOR MODELING WIRELESS CHANNEL BEHAVIOR -- G. Nguyen et.al
@1996
Architecture
Comparison
What Improves TCP Over Wireless
 Shield sender from the effect of the packet loss due to wireless
channel error loss
 LL retransmission
 TCP-AWARED
 Prepare for hand-off
 Multicast the data on fly to nearby BS when the MS is in
hand-off period
 Do this in LL?
 Drawbacks of LL-SMART-TCP-AWARED
 Need to modify the Link layer
 What if there is another hop between BS and MH?
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Can’t distinguish packet loss with wireless link congestion
 Has reached the end?
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How about ad-hoc
One Point of View
LL-TCP-AWARED sits here
1
BS
S
1
Relay
R
1
Packet No. 1 arrived BS, but loss at Relay point due to congestion
on Relay point
-- When the BS notice there is a packet loss between BS—Relay,
he could not distinguish this loss between congestion-based or
channel-error-based
Improving Multimedia Transmission
Performance over Wireless
 Use FEC
Real-time multimedia may not afford long-time
retransmission
 Modify UDP protocol
 Traditional UDP: small part error in packet  drop the entire
packet – there are still some useful information in the
corrupted packet
 UDP-lite: pass the partly corrupted packet to upper layer
 CUDP: Vertical Packet Coding (VPC, similar to interleaving)
+ improved UDP-lite (use the frame error information to help
decoder to locate the error position (thus can do error
concealment)
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But need to modify the layers to enable information exchange
between the layers
CUDP result
Improving Multimedia Transmission
Performance over Wireless
 Scheduling:
 Instead of sending packets only in deadline order, try to
send them in app-specified order (e.g., importance or
deadline order)
 When need scheduling: in-order delivery could not
guarantee all the packets meet its deadline (e.g., when
bandwidth decrease due to channel error)
 How to scheduling
 Important packet first
 Send lower important packet iff
 Important packets would meet their deadline
 Current lower important packet won’t miss the deadline
Scheduling
Sending reference value: S(i) = F(I_index(i), D_index(i))
F – function
I_index(i) – importance index
D_index(i) – deadline index
*Send out packet in increasing order of S(i)*
Importance index (I_index)
1
2
3
4
5
6
7
Pkt No.
An Example [46]
Transmit this layer 3 packet if and only if all the layer0/1/2
packets in following frames will “successful” transmit over
wireless link; “successful” is in a probabilistic means.
So…
 All these works on multimedia over wireless focus on
 How to combat with channel error
 What should we do when packet loss happens
 But one step back
 @ what rate should we send multimedia data?
 Send @ maximum available rate, how?
 Over wired network: TCP-friendly
 Over wireless network?...
 Could we reduce the number of packet loss in case of
hand-off, temporary out-of-range and channel error?
 LL retransmission – cost: out of order delivery + delay
 How about hand-off?
Summary
 Overlay network shows some good properties.
But not sure about its future, whether it is a
temporary solution or it will be a long-lived
service-providing logic infrastructure
 Data transmission over wireless
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Reliable data transmission: cake has gone…
Real-time data transmission: is there a cake?