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04/11/23 Anue Systems, Inc.
www.anuesystems.com
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v1.0 - 20050426
Document Cover Sheet
Project Number PN-3-3175-RV2
Document Title Network model for G.8261
Source Anue Systems
Contact Name: Chip Webb Complete Address: 9111 Jollyville Rd Austin, TX 78759
Phone: 512-527-0453x102 Fax: Email: [email protected]
Distribution TR-30.3
For Incorporation Into TIA Publication x For Information
Intended Purpose of Document (Select one) Other (describe) -
The document to which this cover statement is attached is submitted to a Formulating Group or sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of which provisions are hereby incorporated by reference.
Abstract
Like TIA-921, ITU-T G.8261 seeks to model delay and loss in packet networks. This document describes a model used for G.8261 and shows comparisons between that model results and actual laboratory measurements.
Telecommunications Industry Association TR-30.3/08-12-016Lake Buena Vista, FL December 8 - 9, 2008
04/11/23 Anue Systems, Inc.
www.anuesystems.com
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Problem statement
G.8261 currently describes a way (in Appendix VI) to test sync Interworking Functions by building a testbed.
But -- it’s not repeatable.
04/11/23 Anue Systems, Inc.
www.anuesystems.com
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Initial results matchInput profile Measured result
04/11/23 Anue Systems, Inc.
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A test bed Measure delay under G.8261 Appendix VI test
conditions…..
04/11/23 Anue Systems, Inc.
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Model-based impairment profiles
Build a bottom-up model of each network element
Construct test scenarios by connecting together various model elements and run a simulation Validate end-to-end results
Still has shortcomings As network changes, model params must also change New technologies may require new model elements Harder to make a general model than to measure one
sample
04/11/23 Anue Systems, Inc.
www.anuesystems.com
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Why create a software model?
Creating a model and validating it against real networks provides valuable insight to guide further work Which device parameters are most
important What metrics work best What’s the best way to test
(interop/conformance) Understand tradeoffs in system deployment
04/11/23 Anue Systems, Inc.
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Discrete event simulation of test bed..
One way to model is to use a discrete event simulator
Develop models for the switches and dummy traffic generators.
Anue is developing one such model for MEF18 testing.
This is just the beginning of modeling Further refinements are possible
04/11/23 Anue Systems, Inc.
www.anuesystems.com
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Switch model Three main blocks in the switch model
Ingress, Queuing, Egress Ingress block:
Each input port has one. Makes forwarding decisions (L2/L3) There’s no contention here. Introduces delay (store/forward or cut-through)
Queuing block: One or more queues per output port. Holds packets till sent
out. Contention can happen here. Queue has limited size (shared) Queue memory allocated in N-byte chunks. May implement congestion avoidance (e.g. WRED) Introduces queuing delay and packet loss.
Egress: Each output port has one. Services queues at the port’s bit
rate. If multiple output queues, contention can also happen here
(e.g. Strict Priority, WRR, WFQ)
04/11/23 Anue Systems, Inc.
www.anuesystems.com
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Model assumptions
Initial focus is queuing delays In the forward direction only
All switches are non-PTP capable (asynch)
No priority or congestion avoidance Wire delay is constant Assume each switch has at least one
flip-flop domain transfer Ignore oscillator noise
04/11/23 Anue Systems, Inc.
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Model parameters
Ten switches (based on G.8261) Dummy load is Traffic Model 2 Queue size is 64k bytes
Allocated and deallocated in 64 byte chunks All links are gigabit Measure delay 1000 times per second
Model outputs Packet delay Packet drop
04/11/23 Anue Systems, Inc.
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But can’t realistically simulate all packets
A 24-hour simulation of a 10 hop network built out of GE switches and operating at 50% load with 1400 byte (avg) packets represents about 40 Billion packets.
That’s half a petabit. If you watched HDTV for two years
straight, without sleeping, it would use about that many bits.
04/11/23 Anue Systems, Inc.
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Example model results (20% load TM2)
Reference (test bed)S/W Model Results
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Simulation Results MEF18, 6.2a
Based on G.8261 Appendix VI Test Case 3
04/11/23 Anue Systems, Inc.
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Simulation Results MEF18, 6.6a
Based on G.8261 Appendix VI Test Case 5 (congest 100s)
