NS-3 is not an extension of ns-2. It is a new simulator, written from scratch.
The project will continue to maintain ns-2 while NS-3 is being built, and will study transition and integration mechanisms
NS2 Simulator [ Ns2 vs NS3]
NS2 use OTcl
NS2 is depends upon the NS-1 and REAL simulators
NS2 is USC ISI & Sourceforge, volunteers.
For visualization ns2 is use NAM only.
Scalability feature s2 scalability feature
The ns2 uses the ping, vat, telnet, FTP, multicast FTP, HTTP, probabilistic and trace driven traffic generators, webcache
Ns2 uses Queueing: Diffserv, DropTail, RED, RIO, WFQ SRR, Semantic Packet Queue, REM, Priority, VQ ping, vat, telnet, FTP, multicast FTP, HTTP, probabilistic and trace driven traffic generators, webcache.
NS2 uses Unicast: IP, Mobile IP, generic dist. vector and link state, IPinIP, source routing, Nixvector ,Multicast: SRM, generic centralized, MANET: AODV, DSR, DSDV, TORA, IMEP.
Ns2 has TCP (many variants), UDP, SCTP, XCP, TFRC, RAP, RTP Multicast: PGM, SRM, RLM, PLM in transport layer.
NS3 Simulator [NS2 vs NS3]
Ns3 use python as scripting language.
Ns3 based on ns-2, GTNets.
Current support of ns3 is that NSF, INRIA, GT, WashU & volunteers .
For visualization ns3 use NS-3-viz, pyviz, nam, iNSpect .
Scalability feature of ns3 is distributed simulation.
In application layer ns3 uses the sockets-like API and peer-to-peer protocols are used. .
In link layer the new 802.11 model, 802.11 variants (mesh, QoS), 802.16 (WiMax), TDMA, CDMA, GPRS are presented in ns3.
The full IPv4 support, full IPv6 support, NAT XORP/Click Routing support: BGP, OSPF, RIP, IS-IS, PIM-SM, IGMP/MLD are involved in ns3 network layer.
TCP stack emulation (Linux, BSD), DCCP, additional high speed TCP variants are handled in ns3 transport layer.