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Understanding End-to-End Packet Delay in Network Subnets

This document explores end-to-end packet delay calculations in a store-and-forward network from Router 1 to Router 6. It considers various scenarios, including queue delays at intermediate routers and calculates delays under different configurations (link lengths, bandwidths, propagation speeds, and packet sizes). Key results highlight the impact of queuing delays, with examples derived from real traffic conditions, providing essential insights for network performance optimization.

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Understanding End-to-End Packet Delay in Network Subnets

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  1. Sample Network PerformanceProblems Networks: Sample Performance Problems

  2. W1 T X Z W2 W Y Host L W3 Host M AP Host A W4 2 3 4 1 5 Host B 16 nodes 14 11 Host J 17 12 Host C 15 6 13 10 7 Host H 9 8 Host D Host G Host E Host F Networks: Sample Performance Problems

  3. Host A 1 14 15 17 6 Host H 1. What is the end-to-end packet latency in this store-and-forward subnet from router 1 to router 6 ? Assume: All links: 2.5 km; C = 100Mbps; propagation speed = 200m/microsec. queuing delay = processing delay =0; packet size = 1000 bytes Solution: end-to-end packet delay = 4 (equal hops) x link delay link delay = PROC +QD + TRANS + PROP = 0 + 0 + transmission time + propagation delay 1000 bytes 8 x 103 bits transmission time = ------------- = ----------------- = 8 x 10-5 = 80 microseconds. 100 Mbps 108 bps 2500 m prop delay = ---------------------- = 12.5 microseconds 200 m/ microsec link delay = 92.5 microseconds end-to-end subnet delay = 4 x 92.5 = 370 microseconds Networks: Sample Performance Problems

  4. Host A 1 14 15 17 6 Host H 2. What is the end-to-end packet delay in this store-and-forward subnet from router 1 to router 6 under the scenario that when a packet from router 1 arrives at router 15 there are three packets enqueued for the link to router 17? Assume: All links: 2.5 km; C = 100Mbps; propagation speed = 200m/microsec. processing delay =0; all packet sizes = 1000 bytes Implied Assumption: queues at 1, 14, and 17 are empty when the packet arrives at node 15. Required Insight: there will be no queuing delay at 17 even if all three queued packets are going to 6. Solution: end-to-end packet delay = 4 (equal hops) x link delay + queuing delay at node 15. link delay = PROC +QD + TRANS + PROP = 0 + 0 + transmission time + propagation delay 1000 bytes 8 x 103 bits transmission time = ------------- = ----------------- = 8 x 10-5 = 80 microseconds. 100 Mbps 108 bps 2500 m prop delay = ---------------------- = 12.5 microseconds 200 m/ microsec link delay = 92.5 microseconds queueing delay at node 15 = 3 packets * transmission time = 3* 80 microseconds = 240 microseconds end-to-end subnet delay = 4 x 92.5 + 240 = 610 microseconds Networks: Sample Performance Problems

  5. Host A 1 14 15 17 6 Host H What is the end-to-end packet delay in this store-and-forward subnet from router 1 to router 6 under the scenario that when a packet from router 1 arrives at router 15 there are three packets enqueued for the link to router 17? 3.a AssumeNow All links: 2.5 km; C = 10Mbps; propagation speed 200m/microsec. processing delay = 0; all packet sizes = 1000 bytes 3.b AssumeNow All links: 25 km; C = 100 Mbps; propagation speed 200m/microsec. processing delay = 0; all packet sizes = 1000 bytes 4.a AssumeNow All links: 2.5 km; C = 100Mbps; propagation speed 200m/microsec. processing delay = 10 microsecs; all packet sizes = 1000 bytes 4.B AssumeNow All links: 2.5 km; C = 100Mbps; propagation speed 200m/microsec. processing delay = 10 microsecs; all packet sizes = 3000 bytes Networks: Sample Performance Problems

  6. Food for Thought Host E 9 13 15 17 4 AP W1 5. How does the end-to-end packet delay determination change when we send a packet from Host E to wireless Host W1? 8 13 15 17 16 3 Host F Host L Z 6. How does the end-to-end packet delay determination change when we send a packet from Host F to Host Z that is on the Ethernet LAN? Networks: Sample Performance Problems

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