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ECE 544 Protocol Design Project 2016. Minitha Jawahar Ramyaa Parthasarathy Sanjeevi Thirumurugesan. Network Service and Architecture. Implementation of k-out-of-n “packet datagram” multicast. Service Objective: SOS packets generation for emergency situations. Topology Assumptions.
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ECE 544 Protocol Design Project 2016 Minitha Jawahar Ramyaa Parthasarathy Sanjeevi Thirumurugesan
Network Service and Architecture • Implementation of k-out-of-n “packet datagram” multicast. • Service Objective: SOS packets generation for emergency situations.
Topology 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) • Maximum destinations possible are 3 • Packet doesn’t get corrupted while transmission • Routers do not face heavy traffic, due to the nature of application • Network address is statically assigned • The routers are sparsely connected.
Protocol Concept • The packet header contains three destination addresses • Aims at sending packets to k out of n destinations through the shortest possible path, checking for common routers. • Control plane runs a simple recursive algorithm (DFS) to find all the paths from the sender to the destinations. • Path Vector Routing Protocol is used to update the routing table of all possible paths. • Reliability is provided by individual ACKs and timeout retransmissions. • Stop and wait ensures easy and reliable delivery.
Syntax – Packet Formats • The inter-network addressing is done by a 2 byte addressing scheme. • Host addresses can be differentiated from router addresses • Control plane messages include Link State Messages, DFS update and ACK Packet Header:
Semantics • The K-field is interpreted as the number of destinations out of 3 that is selected by the user. • The source and destination addresses are 2 bytes long • The K-field is 1 byte long.
Routing Algorithm • Link state advertisements are used by routers to construct a graphical view of the network • DFS update messages are then exchanged between routers, as they learn about all the possible ways to reach other destinations • The routing table for each router comprises of all the possible paths computed using path vector routing and DFS( Depth First Search ) • Path vector routing - finds the path to a destination and sends it back to the router. • DFS - calculates all such paths.
Data Plane Forwarding If K=3, The three paths with combined effective least number of hops is selected as the optimum path for the three destinations If K=2, Out of the three paths, the two shortest ones are selected. The third address field is nulled If K=1, The shortest path is selected with the other two being nulled Whenever a split occurs, the appropriate destination address field(s) is nulled
Example Networks: Network 1 C B K=2 A D E F G At Router A At Router B
Forwarding Table After finding the optimum paths, the forwarding table is built. For example, at router C, when k=3
Example Networks: Network 2
Summary • The design uses a combination of DFS and path vector to update the routing table with all possible paths to the destinations from that router. • It decides on the path to each destination based on combined least hop count • Each router has as many columns as the total number of routers with multiple path choices in their routing table. And also has a forwarding table built with destination and next hop info. • The algorithm is simple, but the Update messages could be bandwidth intensive as it advertises the whole path. But the algorithm has guaranteed minimum hop traversal. .
