Performance and Traffic Management of Internet Protocols over ATM

Performance and Traffic Management of Internet Protocols over ATM Raj Jain The Ohio State University Columbus, OH 43210 [email protected] http://www.cis.ohio-state.edu/~jain Raj Jain

The Ohio State University

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Dime Sale

One Megabit memory, One Megabyte disk, One Mbps link, One MIP processor, 10 cents each..... Raj Jain


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Overview q q q q q

Why worry about traffic management? ATM Traffic Management TCP/IP over ATM How to improve TCP/IP over ATM? Our Contributions to ATM Research

Raj Jain


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Trends q

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Communication is more critical than computing.Greeting cards contain more computing power than all computers before 1950. Last 10 years: Personal computing Next 10 years: Collaborative computing Past: Corporate networks (Intranets) Future: Intercorporate networks (Extranets) Internet: 0.3 M hosts in Jan 91 to 9.5 M by Jan 96 ⇒ More than 5 billion (world population) in 2003 URL is more important than a company's phone number

Raj Jain


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Future Year 1980

In 1990, the memory will be so cheap that you will not have to worry about paging, swapping, virtual memory, memory hierarchy, and.... Raj Jain


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Why Worry About Congestion? Q: Congestion problem be solved when?: q Memory becomes cheap (infinite memory)? q Links become cheap (very high speed links)? 19.2 kb/s q Processors become cheap? A: None of the above. SS SS SS

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File transfer time = 5 mins

No buffer

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Old age

1 Mb/s


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SS

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Time = 7 hours Raj Jain

Congestion (Cont) A A BB

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CC SS All links 1 Gb/s

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Congestion is a dynamic problem. Static solutions are not sufficient Traffic management is required even during underload Traffic management is important for continuous media Raj Jain


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ATM Traffic If you throw it away, you won’t miss much.

It . is flat. No variability Just schedule it right.

ATM

It varies a lot.

Big pipe! Don’t worry about shortage. Raj Jain


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Traffic Management on the Info Superhighway 1 CAC

2 Shaping

3 UPC

Scheduling 4 5 Selective

7 Traffic Monitoring and feedback

6 Frame Discard Raj Jain


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Traffic Mgmt Functions q q q q q q q

Connection Admission Control (CAC): Can quality of service be supported? Traffic Shaping: Limit burst length. Space-out cells. Usage Parameter Control (UPC): Monitor and control traffic at the network entrance. Network Resource Management: Scheduling, Queueing, resource reservation Priority Control: Cell Loss Priority (CLP) Selective Cell Discarding: Frame Discard Feedback Controls: Network tells the source to increase or decrease its load. Raj Jain


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Classes of Service

Guaranteed

Standby

Joy Riders The Ohio State University

Confirmed 11

Raj Jain

Classes of Service q

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ABR (Available bit rate): Source follows network feedback. Max throughput with minimum loss. UBR (Unspecified bit rate): User sends whenever it wants. No feedback. No guarantee. Cells may be dropped during congestion. CBR (Constant bit rate): User declares required rate. Throughput, delay and delay variation guaranteed. VBR (Variable bit rate): Declare avg and max rate. m rt-VBR (Real-time): Conferencing. Max delay guaranteed. m nrt-VBR (non-real time): Stored video.

Raj Jain


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Explicit Rate Scheme Destination Destination

Source Source

Change rate to 12.3 Mbps q

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Invented DECbit scheme in 1986: Bit ⇒ Go up/Down m Used now in Frame Relay (FECN) m Used in ATM (EFCI) In July 1994, we proposed Explicit Rate Approach. Current standard. Feedback via “Resource Management” (RM Cells) Raj Jain


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Bit-based vs Explicit Rate

Go Go left left

Go Go 30 30 km km East East 35 35 km km South South Raj Jain


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ERICA Switch Algorithm q

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Each manufacturer has its own explicit rate switch algorithm Explicit Rate Indication for Congestion Avoidance (ERICA) is the most thoroughly analyzed algorithm Shown to be efficient, fair, fast transient response, able to handle bursty TCP traffic ERICA+ allows low delay even at 100% utilization and provides stability in the presence of high frequency VBR background traffic Being implemented by several vendors. Software implementation feasible. Raj Jain


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Internet Protocols over ATM q

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ATM Forum has designed ABR service for data UBR service provides no feedback or guarantees Internet Engineering Task Force (IETF) prefers UBR for TCP

Raj Jain


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ABR or UBR?

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Intelligent transport or not? Raj Jain


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Observations About ABR q

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ABR performance depends upon the switch algorithm. Assuming ERICA. (Ref: http://www.cis.ohio-state.edu/~jain/) No cell loss for TCP if switch has Buffers ≈ 4 × RTT. No loss for any number of TCP sources w 4 × RTT buffers. No loss even with VBR background. W/o VBR, 3×RTT buffers will do. Under many circumstances, 1× RTT buffers may do. Required buffers depend upon RTT, feedback delay, switch parameters, and characteristics of VBR. Raj Jain


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Observations about UBR No loss for TCP if Buffers = Σ TCP receiver window q Required buffering depends upon number of sources. q Receiver window > RTT for full throughput q Unfairness in many cases. q Fairness can be improved by proper buffer allocation, selective drop policies, and scheduling. q No starvation ⇒ Lower throughput shows up as increased file transfer times = Lower capacity Conclusion: UBR may be OK for: LAN, w/o VBR, Small number of sources, AND cheap implementation The Ohio State University Raj Jain q

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ABR vs UBR Source Source

ATM

Router Router Dest. Dest.

Source Source Router Router ABR Queue in the source Pushes congestion to edges Good if end-to-end ATM Fair Good for the provider

Dest. Dest.

UBR Queue in the network No backpressure Same end-to-end or backbone Generally unfair Simple for user Raj Jain


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TCP: Observations q

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With enough buffers in the network, TCP can automatically fill any capacity. TCP performs best when there is NO packet loss. Even a single packet loss can reduce throughput considerably. Slow start limits the packet loss but loses considerable time. Bursty losses cause more throughput degradation than isolated losses. For each packet loss, much time is lost due to timer granularity. Raj Jain


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Source Based Mechanisms q q q q q q q

Slow start Fast Retransmit and Recovery (FRR): Degrades perf. Modified FRR (New Reno) Selective Acknowledgement CLP Probe: Send packets with CLP=1 Cell Pacing: Evenly space out cells Smaller Segments

Raj Jain


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Switch Based Mechanisms q

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Partial Packet Discard (PPD): Discard when the buffers become full. Early Packet Discard (EPD): After a threshold, discard full packets. Selective Drop: After threshold, drop only overloading circuits Guaranteed Rate: Reserve bandwidth for UBR Per-class scheduling, No new signaling. Guaranteed Frame Rate Raj Jain


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ATM Research at OSU q

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Traffic Management: m ERICA+ Switch Algorithm m Internet Protocols over ATM m Multi-class Scheduling Voice/Video over ATM Performance Testing ATM Test bed: OCARnet

Raj Jain


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Multi-class Scheduling CBR rt-VBR nrt-VBR ABR

UBR

Ensures no-starvation for all classes even under overload. q Each class has an allocation = Guaranteed under overload q Some classes need minimum delay ⇒ have priority. q Some classes are greedy. Left-over capacity is fairly allocated. The Ohio State University Raj Jain q

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Voice/Video over ATM q

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Speech suppression ⇒ Unused bandwidth can be used by data Cannot be used by voice. Hierarchical compression of Video Different users can see different bandwidth video Multipoint ABR Real-time ABR

Raj Jain


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Real-Time ABR q

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Compressed video is VBR. VBR is subject to connection denial. Compression parameters can be adjusted dynamically In situations, where reduced service is preferable over connection denial, such as in tactical environments, Video over ABR is preferable over no Video. ABR divides the available bandwidth fairly among contending connections By proper control, ABR can be designed to reduce delay ⇒ Real-time ABR Raj Jain


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OSU National ATM Benchmarking Lab q

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Started a new effort at ATM Forum in October 1995 Defining a new standard for frame based performance metrics and measurement methodologies We have a measurement lab with the latest ATM testing equipment. Funded by NSF and State of Ohio. The benchmark scripts can be run by any manufacturer/user in our lab or theirs. Modeled after Harvard benchmarking lab for routers Raj Jain


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OCARnet q q

Ohio Computing and Communications ATM Research Network Nine-Institution consortium lead by OSU m Ohio State University m Ohio Super Computer Center m OARnet KSU KSU CSU CSU UT UT m Cleveland State University vBNS m Kent State University WSU WSU Cleveland m University of Dayton 155 M OAR OAR UD m University of Cincinnati UD OSC m Wright State University OSC 622 M OSU UC OSU UC m University of Toledo Raj Jain


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Summary

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Traffic management is the key for quality of service ATM has sophisticated traffic management ABR pushes congestion to edges. UBR performance can be improved. OSU is leading ATM Traffic and performance management research. Raj Jain


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References q

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All our ATM Forum contributions and papers are available on-line at http://www.cis.ohio-state.edu/~jain/ Specially see “Recent Hot Papers” and “References on Recent Advances in Networking” ATM Forum, http://www.atmforum.com

Raj Jain


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Thank You!

Raj Jain


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