ECE 544 Protocol Design Project 2016 Michael Sherman Murtadha Aldeer Leonard T. Park

Network Architecture & Topology Assumptions Service Objective: k-out-of-n “packet datagram” multicast Application Requests Destinations Requests delivery to best K Assumptions Unreliable network with packet loss prob. per link of p Each end node is attached to only one router All links have same characteristics (i.e. hop cost 1 and same MTU 1500 bytes) Small maximum number of nodes (i.e. 50) Routers and links do not fail

Protocol Concept Distance Vector Routing & Multicast Gain from Multiple Shortest Paths Services: reliable delivery, routing auto discovery, K/N multicast, minimum delay Summary of protocol design: - packet structure: source + three destinations addresses - control plane for protocol: distance vector packets - data plane for forwarding: forwarding based on unicast addressing - key algorithms for mcast: Bellman-Ford

Syntax – Packet Formats Control Packets Hello ACK Triggered updates SrcDest.Seq.Payload (pairs of destination & cost) Depends on the no. of hosts: If > MTU, create new PKT SrcDest.Seq.Payload (very small) SrcDest.Seq.Payload (few pairs “dist. & cost”) Need reasonable time out > largest RTT in the network

Syntax – Packet Formats Data Packets SrcDest. 1Dest. 2Dest. 3Seq.Payload

ARQ scheme Stop and WaitGo Back N Selective Repeat EfficiencyEN*E Buffer1+1N+1N+N Retransmission (one PKT is lost) 1N1 Sequence number1+1N+1N+N BWLowHigh (because retransmission involves N PKT) Moderate CPU (processing)LowModerate (NO searching in the sender & NO sorting in the receiver) High (searching in the sender & sorting in the receiver) ImplementationSimpleModerateComplex

Semantics Explanation of each field PacketFieldExplanation Control (unicast) Hello Src.Source address ACK Triggered update Dest.Destination address Seq.Sequence number PayloadHello, Updates or ACK Data (multicast) Src. Source address Dest.1Destination address, 1 Dest.2 Destination address, 2 Dest.3 Destination address, 3 Seq. Sequence number Payload Data 1 Byte Depends in life time, RTT Residual from MTU

Routing Algorithm If timer fired: Send list destinations and costs to neighbors Reset Timer Update received Add cost to sender of update to all costs in update If new destination Or If lower cost route Or if equal cost route on new interface Then: Add to table If Table updated Send triggered Update DestinationCostNext Hop List Dest 14R1 Dest 23R1 R2 Dest 36R3 Basic Distance Vector Algorithm + Equal Cost Paths

Build Forwarding Table from Nexthops Unicast and Multicast share same procedure 1. Find Interface Matching the most addresses from the packet 2. If all, send. Otherwise, Make copy of packet. 1. Remove destinations not matching list from original 2. Remove destinations matching interface list from copy 3. Repeat above steps recursively for each packet. Data Plane Forwarding NexthopInterfaceDestination List R1I1Dest1, Dest2 R2I2Dest2 R3I3Dest3 SrcDest. 3Seq.Payload SrcDest. 1Dest. 2Seq.Payload SrcDest. 1Dest. 2Dest. 3Seq.Payload Original Step2.1 Step2.2

Example Networks: Network 1 D1, D2, D3 D2 D3 D1 D2 D1 D3 Worst case ForwardingRouting Outer Paths are one hop shorter than inner + split Efficiency is 10 links used, vs 8 with MST Each Destination has unique shortest path single entry in routing table.

Example Networks: Network 2 D1, D2, D3 find all shortest paths & choose the one that shares the most destination D1 D2, D3 D2 D3 ForwardingRouting Multiple Shortest path takes same route as MST Preferred interface picks shared path to D1 Two equal cost shortest paths to D1, both pushed to forwarding table.

Key protocol design features (recap) Distance Vector Multiple shortest path No added state in network for more senders Only sender needs to know K Non of the router knows K Performance Multiple shortest path has optimal delay Overhead penalty compared to Minimum Spanning Tree (MST) is at most 3x, due to N=3 Best case is equal to MST In example networks, difference is smaller, 10 vs 8 links used in EX1, and equal performance in EX2 Implementation complexity Algorithm is simple extension to Bellman ford Routing updates only require checking for new shortest or equal cost Routing Table will contain one row per destination, containing list of nexthops Forwarding Table will contain one row per interface Summary