The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...
The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ... The ns Manual (formerly ns Notes and Documentation)1 - NM Lab at ...
mrtObject class There is one mrtObject (aka Arbiter) object per multicast capable node. This object supports the abilityfor a node to run multiple multicast routing protocols by maintaining an array of multicast protocols indexed by the incominginterface. Thus, if there are several multicast protocols at a node, each interface is owned by just one protocol. Therefore,this object supports the ability for a node to run multiple multicast routing protocols. The node uses the arbiter to performprotocol actions, either to a specific protocol instance active at that node, or to all protocol instances at that node.addproto{instance, [iiflist]}getType{protocol}all-mprotos{op, args}start{}stop{}notify{dummy}dump-mroutes{file-handle, [grp], [src]}join-group{G, S}leave-group{G, S}upcall{code, s, g, iif}drop{rep, s, g, iif}adds the handle for a protocol instance to its array of protocols. The secondoptional argument is the incoming interface list controlled by the protocol.If this argument is an empty list or not specified, the protocol is assumed torun on all interfaces (just one protocol).returns the handle to the protocol instance active at that node that matchesthe specified type (first and only argument). This function is often used tolocate a protocol’s peer at another node. An empty string is returned if theprotocol of the given type could not be found.internal routine to execute “op” with “args” on all protocol instances activeat that node.start/stop execution of all protocols.is called when a topology change occurs. The dummy argument is currentlynot used.dump multicast routes to specified file-handle.signals all protocol instances to join 〈S, G〉.signals all protocol instances to leave 〈S, G〉.signalled by node on forwarding errors in classifier; this routine in turnsignals the protocol instance that owns the incoming interface (iif) byinvoking the appropriate handle function for that particular code.Called on packet drop, possibly to prune an interface.In addition, the mrtObject class supports the concept of well known groups, i.e., those groups that do not require explicitprotocol support. Two well known groups, ALL_ROUTERS and ALL_PIM_ROUTERS are predefined in ns.The class mrtObject defines two class procedures to set and get information about these well known groups.registerWellKnownGroups{name}getWellKnownGroup{name}assigns name a well known group address.returns the address allocated to well known group, name. If name is not registeredas a well known group, then it returns the address for ALL_ROUTERS.McastProtocol classfunctions:start{}, stop{}getStatus{}getType{}upcall{code args}This is the base class for the implementation of all the multicast protocols. It contains basic multicastSet the status_ of execution of this protocol instance.return the status of execution of this protocol instance.return the type of protocol executed by this instance.invoked when the node classifier signals an error, either due to a cache-miss or a wrong-iif forincoming packet. This routine invokes the protocol specific handle, handle-〈code〉{} withspecified args to handle the signal.A few words about interfaces. Multicast implementation in ns assumes duplex links i.e. if there is a simplex link from node 1to node 2, there must be a reverse simplex link from node 2 to node 1. To be able to tell from which link a packet was received,multicast simulator configures links with an interface labeller at the end of each link, which labels packets with a particular265
and unique label (id). Thus, “incoming interface” is referred to this label and is a number greater or equal to zero. Incominginterface value can be negative (-1) for a special case when the packet was sent by a local to the given node agent.In contrast, an “outgoing interface” refers to an object handler, usually a head of a link which can be installed at a replicator.This destinction is important: incoming interface is a numeric label to a packet, while outgoing interface is a handler to anobject that is able to receive packets, e.g. head of a link.30.2.2 Extensions to other classes in nsIn the earlier chapter describing nodes in ns (Chapter 5), we described the internal structure of the node in ns. To briefly recapthat description, the node entry for a multicast node is the switch_. It looks at the highest bit to decide if the destination isa multicast or unicast packet. Multicast packets are forwarded to a multicast classifier which maintains a list of replicators;there is one replicator per 〈source, group〉 tuple. Replicators copy the incoming packet and forward to all outgoing interfaces.Class Node Node support for multicast is realized in two primary ways: it serves as a focal point for access to the multicastprotocols, in the areas of address allocation, control and management, and group membership dynamics; and secondly, itprovides primitives to access and control interfaces on links incident on that node.266
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<strong>and</strong> unique label (id). Thus, “incoming interface” is referred to this label <strong>and</strong> is a number gre<strong>at</strong>er or equal to zero. Incominginterface value can be neg<strong>at</strong>ive (-1) for a special case when the packet was sent by a local to the given node agent.In contrast, an “outgoing interface” refers to an object h<strong>and</strong>ler, usually a head of a link which can be i<strong>ns</strong>talled <strong>at</strong> a replic<strong>at</strong>or.This destinction is important: incoming interface is a numeric label to a packet, while outgoing interface is a h<strong>and</strong>ler to anobject th<strong>at</strong> is able to receive packets, e.g. head of a link.30.2.2 Exte<strong>ns</strong>io<strong>ns</strong> to other classes in <strong>ns</strong>In the earlier chapter describing nodes in <strong>ns</strong> (Chapter 5), we described the internal structure of the node in <strong>ns</strong>. To briefly recapth<strong>at</strong> description, the node entry for a multicast node is the switch_. It looks <strong>at</strong> the highest bit to decide if the destin<strong>at</strong>ion isa multicast or unicast packet. Multicast packets are forwarded to a multicast classifier which maintai<strong>ns</strong> a list of replic<strong>at</strong>ors;there is one replic<strong>at</strong>or per 〈source, group〉 tuple. Replic<strong>at</strong>ors copy the incoming packet <strong>and</strong> forward to all outgoing interfaces.Class Node Node support for multicast is realized in two primary ways: it serves as a focal point for access to the multicastprotocols, in the areas of address alloc<strong>at</strong>ion, control <strong>and</strong> management, <strong>and</strong> group membership dynamics; <strong>and</strong> secondly, itprovides primitives to access <strong>and</strong> control interfaces on links incident on th<strong>at</strong> node.266
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