WDM Multicasting via Optical Burst / Label Switching By Krishna Kishore Konakanchi Fall /23/01

Overview Introduction Protocols requiring global knowledge of WDM layer topology only Algorithms to construct a M-cast Forest given global knowledge of both WDM layer topology and multicast capability of the switches Re-routing protocol without global topology as well as multicast capability info Future work

Introduction Supporting IP Multicasting over WDM networks has many advantages including data rate and coding transparency for multicast Main issue - multicast in WDM without changing the semantics of IP All switches in WDM network are not MC i.e some are MI MC switch - can switch one incoming path onto many downstream MI switch - Incoming signal can be passed through to only one downstream

Layers 0-3 Characteristics (IP,ATM,SONET,WDM) Network Factors IPATMSONETWDM Data Protocol Unit(PDU) Varied –packet size 53 byte cellSTS-1(45 Mbps) Format Independent  Channel BWVaried(logic) Fixed (Physical) Fixed (Physical) Protocol LayerNetwork (layer 3) Link (layer 2) Physical (layer 1) Optical (layer 0) Connection Type Connection less Connection Oriented QOSPossibleYesNOPossible Traditional Role RoutingSwitchingCross Connects Cross Connects * Technology Strength Simple,easy - scale,robust Multi service Integration High speed Transport High – speed Transport * WDM Emerging Technology

Protocols with global WDM topology Knowledge Given a shortest path m-cast tree constructed by MOSPF these protocols form a m-cast forest avoiding branching at a MI nodes if present Protocol 1 –Re-route to source : MI switch having more than 1 downstream sends request towards source to find alternate path. MC switch along the path acknowledges by establishing new LSP –no new modification to the SPT –no hiding of routes from IP layer –WDM need not know detail functionality of IP layer

Protocols with global WDM topology Knowledge (cont.) Protocol 2 –Re-route to Any : determines paths to nodes on the tree other than any of its children whose costs are less than that of the path to source. Worst case is path to source –Results in BW savings without substantial increase in cost Consider following scenario where –Source node : 1 –MI Node : 2 –Destinations : 3, 4 & 5

Shortest Path by MOSPF

Protocols 1 & 2 - Scenarios Protocol 1 Protocol 2 Req. & Ack Req. & Ack

Implementation & Results Protocols 1 & 2 were implemented in C & OPNET Additional cost of forest constructed by 2nd re- routing protocol when compared with original cost of tree is around 5% in a network with switches, 50% of which are MI and 50% belong to a session 2nd protocol can cut down cost by half when compared to the 1st protocol.

Protocols with global WDM topology Knowledge and MC Info Approach 1 –Construct forest based on any multicast tree –At each branching MI switch, remove all downstream links except one, thus breaking the tree into base sub-tree and several superNodes –Reconnect the base sub-tree with the closest possible super node without using any removed link

Protocols with global WDM topology Knowledge and MC Info (cont.) When its not possible to combine the base sub-tree with any supernode, removed links are used to form new LSP’s Resulting forest will consist of multiple source routed trees. This is very similar to Re-route to Source.

KMB Tree heuristic to construct Mcast Tree Given a graph “G” (modeling a network) and set of multicast destination say “Z” The algorithm to construct the m-cast tree as follows : –Construct a complete directed distance graph G 1 = (V 1,E 1,c 1 ) –Find the minimum spanning tree T 1 of G 1 –Construct a sub-graph G s of G by replacing each edge in T 1 by its corresponding shortest path in G

KMB Tree heuristic to construct Mcast Tree (cont.) –Find the minimum spanning tree T s of G s –construct a Steiner Tree T H from T S by deleting edges in T S if necessary, so that all the leaves in T H are Steiner points. Worst Case Time complexity O(|S||V| 2 )

Approach 1 - Example A B C D E F GH

Approach 1 (cont.) From previous fig., the cost of the M-cast forest can be given as 2(AB + BC + CD) + DE + EG + EH + DF This approach is very relevant in cases where the higher layer is oblivious to the MI-nature of some of the nodes. E.g IP over WDM

Protocols with global WDM topology Knowledge and MC Info (cont.) Approach 2 –Every member switch including the source acts as a super node –repeatedly combine the super-nodes into one until only one super node containing all members are left –when finding shortest path bet. 2 super nodes, only paths without MI nodes are considered –the downstream of a branching MI node may forward multicast data to other down-streams thought an OB/LSP

Approach 2 - Example A B C D F GH E E F

Approach 2 (cont.) The cost with this approach is given by AB + BC + CD + 2(DE) + EG +EH+DF Gives the near optimal solution to the problem of multicasting in a network where some/many nodes do not have the It has been found that cost of forest using alg. 2 is much lower than the 1st

Distributed Re-routing protocol with neither Global Topology Nor MC Info Basic idea - local multicast forwarding cache A branching MI switch sends a “purge” message to all but one downstream switch Each purged switch then floods a “grow” request to its neighbors –direct grow : only neighbors already on the forest can reply to the request –indirect grow : if a neighbor is not on the forest then it can still relay the request

Advantages of this Protocol Uses only local information of WDM layer Does not require any change to the IP multicasting protocol Uses DVMRP as the IP multicast protocol, which is most widely used in the internet Even if a MI switch is purged out, it can very easily grow back into the forest with the grow schemes

Distributed Protocol - Repair Message MC Repair MI Repair Purge MC = Multicast-capable switch MI = Multicast-incapable switch Repair Messages

Distributed Protocol - Purge Message Purge MC X Repair Y Z MI X Y Z Purge Repair Purge MC = Multicast-capable switch MI = Multicast-incapable switch Purge Messages Gro w

Repair & Purge MI can use randomly some heuristics to select down stream switch to send repair messages Purged switch without any attached member need not have to grow back to reduce signaling. Grow Scheme Direct Grow Scheme Indirect Grow Scheme Neighbor not on multicast tree may replay grow request

Work to be done… The results obtained from the different methods discussed are not comparable due to mismatch of parameters used. They need to be generalized and have to be run with same parameters to compare the cost arrived at. The distributed protocol developed needs to be implemented and its performance evaluated in terms of BW and latency reduction.

Work to be done…(cont.) These results must be compared with the results obtained from the other approaches New heuristics for supporting MOSPF, protocols for PIM-SM and mechanisms to provide QoS in multicasting can also be given an insight.