TCP/IP Tutorial and Technical Overview - IBM Redbooks

If the client workstation initiating the registry
receives no defense packets, it is assumed that
its name has been successfully registered.
p-node name registration This method occurs much in the same manner
as b-node registration. However, instead of
broadcasting the name registration packet on
UDP port 137, the client workstation unicasts the
packet directly to a NetBIOS Name Server
(NBNS). If the requested name has already
been registered with the NBNS, a negative reply
is returned to the client. Otherwise, a positive
reply indicates the acceptance of the name
registration.
One other service offered by the Name Service is the name query. Much like
DNS, this allows clients to query NetBIOS for the IP address of another computer
in the network. To use this service, a client workstation builds a name query
request, which is sent on UDP port 137. Again, there are two methods for this.
The b-node method broadcasts the packet and waits for a response from the
workstation that owns the name. In the p-node method, the workstation sends
the request directly to a NBNS server.
Session Service
RFC 1001 indicates that NetBIOS should provide reliable sessions. It also
indicates that message exchanges should be fully-duplexed and sequenced.
Therefore, the Session Service offered by NetBIOS mimics the TCP architecture
(see 4.3, “Transmission Control Protocol (TCP)” on page 149). The Session
Service uses TCP port 139 to achieve this and includes the following network
primitives, all of which can be compared to socket API calls (see 11.2.1, “The
socket API” on page 410):
call Creates a NetBIOS session. This is similar to the connect()
socket API call.
listen Awaits a call command from another host. This is similar to the
listen() socket API call.
send Sends a message over a NetBIOS session. This is similar to the
sendmsg() socket API call.
receive Receives a message over a NetBIOS session. This is similar to
the recvmsg() socket API call.
hang up Terminates a session. This is similar to the close() socket API
call.
Chapter 14. File-related protocols 549