NFD’s Content Store

The Contest Store (CS) is implemented as a set of CS entries), ordered by the full data name including the implicit digest. To manage entries, CS adopts a cache policy interface (nfd::cs::Policy), invoked any time a CS entry is added, removed, updated, or used.

By default, ndnSIM uses NFD’s Content Store with an option to use an old-style ndnSIM-specific content store implementations (see Old Content Store Implementations). The supported cache replacement policies are the following:

NFD’s Content Store Policies
nfd::cs::lru	Last Recently Used (LRU)
nfd::cs::priority_fifo	Priority-Based First-In-First-Out (FIFO)

For more detailed specification refer to the NFD Developer’s Guide, section 3.3.

To control the maximum size and the policy of NFD’s Content Store use StackHelper::setCsSize() and StackHelper::setPolicy() methods:

ndnHelper.setCsSize(<max-size-in-packets>);
ndnHelper.setPolicy(<replacement-policy>);
...
ndnHelper.Install(nodes);

Examples:

• To set CS size 100 on node1, size 1000 on node2, and size 2000 on all other nodes. LRU replacement policy for node 1, priority FIFO for the rest:

  ndnHelper.setCsSize(100);
  ndnHelper.setPolicy("nfd::cs::lru");
  ndnHelper.Install(node1);
  
  ndnHelper.setCsSize(1000);
  ndnHelper.setPolicy("nfd::cs::priority_fifo");
  ndnHelper.Install(node2);
  
  NodeContainer allOtherNodes;
  for (NodeList::Iterator i = NodeList::Begin(); i != NodeList::End(); ++i) {
    if (*i != node1 && *i != node2) {
      allOtherNodes.Add(*i);
    }
  }
  ndnHelper.Install(allOtherNodes);
  

• To effectively disable NFD content store an all nodes

  Minimum allowed value for NFD content store maximum size is 1. If 0 is specified, it will be assumed that the old content store implementation should be used.

  ndnHelper.setCsSize(1);
  ...
  ndnHelper.Install(nodes);
  

CS entry

The Data packet, along with other necessary fields, are stored in a CS entry. Each entry contains:

• the Data packet
• flag indicating whether the Data packet is unsolicited
• the timestamp at which the cached Data becomes stale

Old Content Store Implementations

We have also ported the old ndnSIM 1.0 content store implementations to the new code base. These implementations feature different cache replacement policies, but have very limited support for Interest selectors. If your scenario relies on proper selector processing, do not use these implementations as the simulation results most likely be incorrect.

To select old content store implementations, use StackHelper::SetOldContentStore():

ndnHelper.SetOldContentStore("<content store implementation>",
                            ["<optional parameter>", "<optional parameter's value>" [, ...]]);
...
ndnHelper.Install (nodes);

Available old content store implementations are listed in the following table:

Simple content stores
ns3::ndn::cs::Lru	Least recently used (LRU) (default)
ns3::ndn::cs::Fifo	First-in-first-Out (FIFO)
ns3::ndn::cs::Lfu	Least frequently used (LFU)
ns3::ndn::cs::Random	Random
ns3::ndn::cs::Nocache	Policy that completely disables caching
Content stores with entry lifetime tracking These policies allow evaluation of CS enties lifetime (i.e., how long entries stay in CS)
ns3::ndn::cs::Stats::Lru	Least recently used (LRU)
ns3::ndn::cs::Stats::Fifo	Least frequently used (LFU)
ns3::ndn::cs::Stats::Lfu	Random
ns3::ndn::cs::Stats::Random	Policy that completely disables caching
Content stores respecting freshness field of Data packets These policies cache Data packets only for the time indicated by FreshnessPeriod.
ns3::ndn::cs::Freshness::Lru	Least recently used (LRU)
ns3::ndn::cs::Freshness::Fifo	Least frequently used (LFU)
ns3::ndn::cs::Freshness::Lfu	Random
ns3::ndn::cs::Freshness::Random	Policy that completely disables caching
Content store realization that probabilistically accepts data packet into CS (placement policy)
ns3::ndn::cs::Probability::Lru	Least recently used (LRU)
ns3::ndn::cs::Probability::Fifo	Least frequently used (LFU)
ns3::ndn::cs::Probability::Lfu	Random
ns3::ndn::cs::Probability::Random	Policy that completely disables caching

Examples:

• Select simple LRU policy on node1, simple FIFO policy on node2, and simple random policy on other nodes with maximum CS sizes of 10000 packets:

  ndnHelper.SetOldContentStore("ns3::ndn::cs::Lru", "MaxSize", "10000");
  ndnHelper.Install(node1);
  
  ndnHelper.SetOldContentStore("ns3::ndn::cs::Fifo", "MaxSize", "10000");
  ndnHelper.Install(node2);
  
  ndnHelper.SetOldContentStore("ns3::ndn::cs::Random", "MaxSize", "10000");
  ...
  ndnHelper.Install(otherNodes);
  

Note

If MaxSize parameter is omitted, then will be used a default value (100).

Note

If MaxSize is set to 0, then no limit on ContentStore will be enforced

• Disable CS on node2

  ndnHelper.SetOldContentStore("ns3::ndn::cs::Nocache");
  ndnHelper.Install(node3);
  

• Track lifetime of CS entries (must use ns3::ndn::cs::*::LifetimeStats policy):

  void
  CacheEntryRemoved(std::string context, Ptr<const ndn::cs::Entry> entry, Time lifetime)
  {
      std::cout << entry->GetName() << " " << lifetime.ToDouble(Time::S) << "s" << std::endl;
  }
  
  ...
  
  ndnHelper.SetOldContentStore("ns3::ndn::cs::Stats::Lru", "MaxSize", "10000");
  ...
  ndnHelper.Install(nodes);
  
  // connect to lifetime trace
  Config::Connect("/NodeList/*/$ns3::ndn::cs::Stats::Lru/WillRemoveEntry", MakeCallback(CacheEntryRemoved));
  

• Get aggregate statistics of CS hit/miss ratio (works with any policy)

  The simplest way tro track CS hit/miss statistics is to use CsTracer, in more details described in Metrics Section.

  CsTracer::InstallAll("cs-trace.txt", Seconds(1));