Upload
alayna-mabbitt
View
226
Download
7
Tags:
Embed Size (px)
Citation preview
1
School of Computing Science
Simon Fraser University
CMPT 771/471: Internet Architecture & CMPT 771/471: Internet Architecture & Protocols Protocols
TCP-Friendly Transport ProtocolsTCP-Friendly Transport Protocols
2
Motivations
Congestion Control Prevents congestive network collapse
Improve Quality of Service (QoS) for UDP Control transmission rate
Fair bandwidth utilization Prevents starvation of TCP traffic ~95% of Internet traffic are TCP
In short, a TCP-Friendly protocol based on UDP
3
Approaches
Resources Reservation Impossible to know exact bandwidth May leads to over-allocate
Priority Mechanisms Require supports by path routers
Adaptive Sending Rate Easy to implement, application level Can adapt to changes in bandwidth availability Improve QoS through loss reduction
4
Adaptive Sending Rate
Congestion Control Achieved by varying sending rate
12+ algorithms for calculating transmission rate
Main idea is to use TCP throughput model All claims to be the most effective
Loss-Delay Based Adjustment Algorithm (LDA) TCP like approach Increase sending rate during network under-load Uses feedback to accurately measure RTT Intended for video and audio streaming Network and Operating System Support for Digital Audio
and Video (NOSSDAV ‘98)
5
Loss-Delay Based Adjustment Algorithm
Loss-Delay Based Adjustment Algorithm (LDA)
Start with a small value, 10 kb/s Additive increase rate (AIR) If packet drop, back off to initial value (10 kb/s) Increase until similar rate as TCP
Relies on feedback Uses Real Time Protocol (RTP) on top of UDP Feedback contains losses and round-trip time (RTT)
How much to increase? Bf = bandwidth factor AIR = initial value (10 kb/s)
BfAIRAIRi *
6
Loss-Delay Based Adjustment Algorithm
How do we calculate ?
r = current transmission rate b = bottleneck bandwidth
Calculating bottleneck bandwidth b = probe packet size / gap between 2 probe
packets
Two sequential packets with small gap means less delay
b
rBf 1
Bf
Understanding TCP
Detecting Congestion Recall TCP average throughput Fairness mean we must not exceed
Recall TCP average throughput simplistic model
TCP throughput is inversely proportional to RTT and square root of packet loss probability p
pRTTpX
2
31)(
7
8
Loss-Delay Based Adjustment Algorithm
Calculating RTT No ACK in UDP Use feedback report
Where t= arrival time, = time elapsed since last report, and = last received sender report
LSRDLSR ttt
DLSRtLSRt
9
Performance of LDA
LDA and TCP
10
Performance of LDA
LDA scalability
11
In Theory, It Works
Not In Practice Additional network overhead (RTP) Additional application level complexity Rogue UDP process could starve TCP-Friendly
protocols
Performance Driven UDP is intended to be light weight and fast TCP-Friendly protocols would have to yield to UDP Developers are lazy, they want the fastest
connection with minimal amount of work
12
Summary
TCP-Friendly Protocols UDP based protocols with congestion control Able to sense the network and adjust send rate
accordingly Promote fair bandwidth sharing
Prevents Network Collapse Work together with TCP to balance bandwidth
Fill The Gap TCP-Friendly protocols can fill the gap between TCP
and UDP
13
References
TCP-Friendly, Advanced Networking: Pittsburgh Supercomputing Center, http://www.psc.edu/networking/projects/tcpfriendly/
D. Sisalem, H. Schulzrinne, “The Loss-Delay Adjustment Algorithm: A TCP-friendly Adaptation Scheme”, Network and Operating System Support for Digital Audio and Video (NOSSDAV ‘98), Cambridge, UK, July 8-10, 1998.
J. Mahdavi, S. Floyd, TCP-Friendly Unicast Rate-Based Flow Control http://www.psc.edu/networking/papers/tcp_friendly.html
Lorenzo Vicisano, Luigi Rizzo (Pisa) and Jon Crowcroft, TCP-like Congestion Control for Layered Multicast Data Transfer (INFOCOM ‘98).