1. ECE 544 Protocol Design Project 2016
Minitha Jawahar
Ramyaa Parthasarathy
Sanjeevi Thirumurugesan

2. Network Service and Architecture
Implementation of k-out-of-n “packet datagram” multicast.
Service Objective: SOS packets generation for emergency situations.

3. 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.

4. 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. 4

5. 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: 5

6. 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.

7. 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.

8. 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

9. Example Networks: Network 1 C B K=2 A D E F G At Router A A B C D E F
ADECB
AFGECB
ABC
ADEC
AFGEC
ABCED AD
AFGED
ABCE
ADE
AFGE
ABCEGF
ADEGF AF
ABCEG
ADEG
AFG
At Router B B BA
BCEDA
BCEGFA
BADEC
BAFGEC BC
BAD
BAFGED
BCED
BCEGFAD
BADE
BAFGE
BCE
BADEGF
BAF
BCEDAF
BCEGF
BADEG
BAFG
BCEDAFG
BCEG

10. Forwarding Table
After finding the optimum paths, the forwarding table is built.
For example, at router C, when k=3
Router C
Next Hop D1 - D2 E D3
Router E
Next Hop D1 - D2 D3 G

11. Example Networks:
Network 2 11

12. 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. . 12