Overlay Network and Data Transmission Over Wireless

For EE290T

Minghua Chen

EECS@UC, Berkeley

Outline

Overlay network & virtual overlay network Data transmission over wireless

Improving TCP performance over wireless Improving video performance over wireless

Overlay Network

What is overlay network? “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 Send(): reliable_send(), fast_send()…

Why overlay network? Deploy/testing new protocol/service with minimal affecting the

lower IP infrastructure 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 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 congestionnot 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)

Need some point on route to set the ELN bit Link Layer based solution

LL retransmission In WLAN, After LL retransmission, packet loss rate ~ 3%*

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?

Can’t distinguish packet loss with wireless link congestion Has reached the end?

How about ad-hoc

One Point of View

S BS Relay R1

11

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

LL-TCP-AWARED sits here

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)

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

Pkt No.1 2 3 4 5 6 7

Importance index (I_index)

Sending reference value: S(i) = F(I_index(i), D_index(i))F – function

I_index(i) – importance indexD_index(i) – deadline index

*Send out packet in increasing order of S(i)*

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 Reliable data transmission: cake has gone… Real-time data transmission: is there a cake?