...\@title^0.1

The VINT project is a joint effort by people from UC Berkeley, USC/ISI, LBL, and Xerox PARC. The project is supported by the Defense Advanced Research Projects Agency (DARPA) at LBL under DARPA grant DABT63-96-C-0105, at USC/ISI under DARPA grant ABT63-96-C-0054, at Xerox PARC under DARPA grant DABT63-96-C-0105. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the DARPA.

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... topology,^1.1

with apologies to Rodgers and Hammerstein

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... TclObject^3.1

In the latest release of ns and nsTcl, this object has been renamed to SplitObjefct, which more accurately reflects its nature of existence. However, for the moment, we will continue to use the term TclObject to refer to these objects and this class.

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...^3.2

As an example, the classes Simulator, Node, Link, or rtObject, are classes that are not derived from the class TclObject. Objects in these classes are not, therefore, TclObjects. However, a Simulator, Node, Link, or route Object is also instantiated using the new procedure in ns.

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... ASRMAgent^3.3

Note that this constructor is embellished to illustrate the features of the variable binding mechanism.

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... cases^3.4

The few places where this might not work are when certain variables might have to be defined or undefined, or otherwise the script contains code other than procedure and variable definitions and executes actions directly that might not be reversible.

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... array^5.1

, an instance variable of a class that is also an array variable

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... delay^6.1

The current version also includes an object to examine the network layer ``ttl'' field and discard packets if the field reaches zero.

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... exists^7.1

For instance, if the sum of the service rates needed is greater than the output link capacity.

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... packets^11.1

This is perhaps unrealistically simple. An ICMP ECHO REQUEST agent would likely wish to process ECHO REPLY messages.

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... OTcl^13.1

It is not intended to be updated after configuration time. Doing so should be possible, but is currently untested.

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...packet.h) ^13.2

Note: PT_NTYPE should remain the last element of this enumeration.

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... produced.^13.3

In some processer architectures, including the Sparc and HP-PA, double-word access must be performed on a double-word boundary (i.e. addresses ending in 0 mod 8). Attempting to perform unaligned accesses result in an abnormal program termination.

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... node^17.1

Refer to Chapter  for details on hierarchical routing and internals of HierNode.

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... routing^17.2

In order to do away with all these different variations of the definition of a node, we are planning to revise the node architecture that would allow a more flexible and modularised construction of a node without the necessity of having to define and be limited to certain Class definitions only.

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... Iridium^18.1

Aside from the link bandwidths (Iridium is a narrowband system only), these parameters are very close to what a broadband version of the Iridium system might look like.

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... Teledesic^18.2

These Teledesic constellation parameters are subject to change; thanks to Marie-Jose Montpetit of Teledesic for providing tentative parameters as of January 1999. The link bandwidths are not necessarily accurate.

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... north.^18.3

Traditionally, the ``right ascension'' of the ascending node is specified for satellite orbits- the right ascension corresponds to the celestial longitude. In our case, we do not care about the orientation in a celestial coordinate system, so we specify the earth-centric longitude instead.

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... stacks.^18.4

In the author's opinion, all network stacks in ns  should eventually have a LinkHead object at the front- the class SatLinkHead would then disappear.

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... model^19.1

Based on the code contributed to ns from the CMU Monarch project.

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... model^19.2

Contributed to ns from the CMU Monarch project.

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... model^19.3

Implemented in ns by Wei Ye at USC/ISI

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... 6.^27.1

In ns v1, each packet included a class field, which was used by CBQ to classify packets. It then found additional use to differentiate between ``flows'' at one trace point. In ns v2, the flow ID field is available for this purpose, but any additional information (which was commonly overloaded into the class field in ns v1) should be placed in its own separate field, possibly in some other header

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... number.^27.2

In ns v1, all packets contained a sequence number, whereas in ns v2 only those Agents interested in providing sequencing will generate sequence numbers. Thus, this field may not be useful in ns v2 for packets generated by agents that have not filled in a sequence number. It is used here to remain backward compatible with ns v1.

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... protocols^31.1

The consideration is that static and session routing strategies/protocols are implemented as agents derived from the Agent/rtProto, similar to how the different dynamic routing protocols are implemented; hence the blurred distinctions.

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... chosen^31.2

This really is undesirable, and may be fixed at some point. The fix will probably be to favor the agents in class preference order. A user level simulation relying on this behavior, or getting into this situation in specific topologies is not recommended.

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... configured^31.3

Link costs can also be used to favour or disregard specific links in order to achieve particular topology configurations.

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... data^38.1

Note that the trace data can also be used to gather certain kinds of trace data. We will illustrate this later.

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...Agent/SRM::recv-data^38.2

Technically, []recv_data invokes the instance procedure recv data sender msgid, that then invokes []recv-data. The indirection allows individual simulation scripts to override the []recv as needed.

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... agent^38.3

Note that this implementation of session message handling is subtly different from that used in wb or described in [11]. In principle, an agent disseminates a list of the data it has actually received. Our implementation, on the other hand, only disseminates a count of the last message sequence number per source that the agent knows that that the source has sent. This is a constraint when studying aspects of loss recovery during partition and healing. It is reasonable to expect that the maintainer of this code will fix this problem during one of his numerous intervals of copious spare time.

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... SimpleTcp.^42.1

A SimpleTcp agent is used solely for web caching simulations. It is actually an UDP agent. It has neither error recovery nor flow/congestion control. It doesn't do packet segmentation. Assuming a loss-free network and in-order packet delivery, SimpleTcp agent simplifies the trace files and hence aids the debugging of application protocols, which, in our case, is the web cache consistency protocol.

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... requests:^42.2

Some PagePool, e.g., PagePool/Math, has only one page and therefore it always returns the same page. Some other PagePool, e.g. PagePool/Trace, has multiple pages and needs a random variable to pick out a random page.

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