Simulation:

• NS.
  This is the simulator that I use, so this is the only simulator that I know about directly.
• PDNS (Parallel/Distributed NS).
  "The PADS research group at Georgia Tech has developed extensions and enhancements to the ns simulator to allow a network simulation to be run in a parallel and distributed fashion, on a network of workstations." Last supported for ns-2.27 (Januayr 2004).
• Georgia Tech's Dynamic Network Emulation Backplane Project.
  "The backplane enables the user/modeler to bring multiple network simulators together and harness their models in a single experiment... The backplane also supports incorporation of actual network applications into the execution, to execute over the emulated network."
• GloMoSim/Parsec.
  "In GloMoSim we are building a scalable simulation environment for wireless and wired network systems. It is being designed using the parallel discrete-event simulation capability provided by Parsec."
  • QualNet: QualNet is a commercial simulator that grew out of GloMoSim.
• SSF (Scalable Simulation Framework).
  This includes SSF Network Models (SSFNet), with "open-source Java models of protocols (IP, TCP, UDP, BGP4, OSPF, and others), network elements (hosts, routers, links, LANs), and assorted support classes for realistic multi-protocol, multi-domain Internet modeling and simulation", and a gallery of baseline networks with models of large, realistic BGP topologies, heavily congested networks, and validation models, together with model descriptions and associated publications.
• Dartmouth SSF (DaSSF).
  "Dartmouth SSF (DaSSF) is a process-oriented, conservatively synchronized parallel simulator, which is designed for but not exclusively for simulating very large scale multi-protocol communication networks. DaSSF is a C++ implementation of Scalable Simulation Framework (SSF)."
• GTnetS
  "The Georgia Tech Network Simulator (GTNetS) is a full-featured network simulation environment that allows researchers in computer networks to study the behavior of moderate to large scale networks."
• JavaSim, now renamed to J-Sim.
• OMNET++.
  OMNET++ is free for academic and non-profit use, and contains IP, IPv6, MPLS, mobility, and ad-hoc simulations.
• The M5 Simulator.
  M5 simulates TCP/IP performance with full-system support with detailed I/O models and three CPU models.
• HEGONS.
  "HEGONS is a HEterogeneous Grooming Optical Network Simulator that supports mixed routing and wavelength assignment algorithms and optional wavelength conversions capability on each node. The goal of Hegons is the evaluation of different dynamic routing and wavelength assignment (RWA) algorithms in WDM optical networks."

Peer-to-peer simulators:

• The State of Peer-to-Peer Simulators and Simulations,
  S. Naicken B. Livingston A. Basu S. Rodhetbhai I. Wakeman D. Chalmers CCR, April 2007.
• Tools for Peer-to-Peer Network Simulation,
  internet-draft draft-irtf-p2prg-core-simulators, work in progress.

Commercial simulators:

• OpNet.
  OpNet is a leading commercial network simulator, including a "library of detailed protocol and application models including Multi-Tier Applications, Voice, HTTP, TCP, IP, OSPF, BGP, EIGRP, RIP, RSVP, Frame Relay, FDDI, Ethernet, ATM, 802.11 Wireless LANs, MPLS, PNNI, DOCSIS, UMTS, IP Multicast, Circuit Switch and many more... The Standard Model Library includes hundreds of vendor specific and generic device models including routers, switches, workstations, and packet generators". (From the OpNet Modeler Brochure.)
• Other commercial simulators:
  Netwiser (including a network simulator);
  Shunra (for performance testing for applications).
  NetScale, a scalable network simulation tool based on patented mathematical developments, from a start-up company stemming from INRIA.
  NetSim is a commercial network simulator for use at the undergraduate level, mostly at use in India.

Emulation, and simulation/emulation/experiment transitions:

• Utah's Netbed is based on Emulab.
  "Netbed strives to preserve the control and ease of use of simulation, without sacrificing the realism of emulation and live network experimentation."
• The Wisconsin Advanced Internet Laboratory (WAIL) "offers Emulab/Netbed capability ... plus the ability to incorporate topologies of a large number of Cisco routers into Emulab experiments".
• Colorado's nsclick simulation environment.
  "nsclick is the Click Modular Router embedded inside of the ns-2 network simulator. With minor modifications, a Click routing graph may run both on an actual system as well as under ns-2."
• Network Emulation with the NS Simulator
  "Special objects within the simulator are capable of introducing live traffic into the simulator and injecting traffic from the simulator into the live network."
• The Network Simulation Cradle for ns-2, from the WAND Network Research Group.
  "The Network Simulation Cradle (NSC) is a framework which allows real world TCP/IP network stacks to be used inside a network simulator."
• Dummynet can be used to introduce queue and bandwidth limitations, delays, packet losses, and multipath effects.
• Modelnet from Duke is an emulation environment for evaluating distributed services such as caching, network content distribution, and peer-to-peer systems.
• IMUNES is a network emulation framework based on FreeBSD.
• Washington University's Open Network Lab is a system with high performance routers that allows users to run experiments remotely.
• Commercial network emulation products include PacketStorm and NetDisturb.