the addition of NetBIOS "Node Status" query, dynamic registration and conflict marking packets. They are encapsulated in UDP. Later implementation includes an optional Scope part of the name, making NetBIOS name hierarchical like DNS, but this is seldom used. In addition, to start a session or to send a datagram to a particular host rather than to broadcast the datagram, NBT will have to determine the IP address of the host with a given NetBIOS name; this is done by broadcasting a "Name Query" packet, and/or sending it to the NetBIOS name server. The response will have the IP address of the host with that name. NBNS is one of the first proper dynamic peer-to-peer distributed name registration services. The NBNS protocol was brought into disrepute by Microsoft: it earned a bad name for being 'chatty', swamping networks with dynamic registration traffic on multiple protocols (IPX/SPX, NBF and TCP/IP) as people badly misconfigured their machines and their networks. The principles implemented in NBNS have been reimplemented many times, including in such systems as zeroconf and MobileIP. Datagram distribution service Datagram mode is "connectionless"; NetBIOS datagrams are sent over UDP. A datagram is sent with a "Direct Unique" or "Direct Group" packet if it's being sent to a particular NetBIOS name, or a "Broadcast" packet if it's being sent to all NetBIOS names on the network. Session service Session mode lets two computers establish a connection for a "conversation", allows larger messages to be handled, and provides error detection and recovery. Sessions are established by exchanging packets. The computer establishing the session attempts to make a TCP connection to port 139 on the computer with which the session is to be established. If the connection is made, the computer establishing the session then sends over the connection a "Session Request" packet with the NetBIOS names of the application establishing the session and the NetBIOS name to which the session is to be established. The computer with which the session is to be established will respond with a "Positive Session Response" indicating that a session can be established or a "Negative Session Response" indicating that no session can be established (either because that computer isn't listening for sessions being established to that name or because no resources are available to establish a session to that name). Data is transmitted during an established session by Session Message packets. TCP handles flow control and