Internet Protocol - Novell NETWARE 6-DOCUMENTATION Manual

Internet Protocol

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NetWare TCP/IP Administration Guide
responding to the transfer request, known as the server side, generally uses a
well-known TCP port. The client side is typically the active side and initiates
the connection to the passive server side.
Like the UDP datagrams, TCP segments are encapsulated in an IP datagram.
TCP buffers the stream by waiting for enough data to fill a large datagram
before sending the datagram. The stream is unstructured, which means that
before transmission of data, both the sending and receiving applications must
agree on the meaning of the contents of the stream. The TCP protocol uses
full-duplex transmission. Full duplex means that two data streams can flow in
opposite directions simultaneously. Thus, the receiving application can send
data or control information back to the sending application while the sending
application continues to send data.
The TCP protocol gives each segment a sequence number. At the receiving
end of the connection, TCP checks successive sequence numbers to ensure
that all the segments are received and processed in the order of the sequence
numbers. The receiving end sends an acknowledgment to the sender for the
segments received. TCP enables the sender to have several outstanding
segments before the receiver must return an acknowledgment. If the sending
node does not receive an acknowledgment for a segment within a certain time,
it retransmits that segment. This scheme, called positive acknowledgment with
retransmission, ensures that the stream delivery is reliable.
In the TCP/IP protocol suite, all packets are delivered by the IP datagram
delivery service. Packet delivery is not guaranteed by this service. A packet
can be misdirected, duplicated, or lost on the way to its destination. The
service is connectionless because all packets are transmitted independently of
any other packets. This is in contrast to a telephone network, for instance,
where a connection is established and maintained.
To keep track of the delivery status, TCP/IP applications using the IP
datagram delivery service expect to receive replies from the destination node.
IP defines the form that packets must take and the ways that packets are
handled when they are transmitted or received. The form the packet takes is
called an IP datagram. It is the basic unit of information that is passed across
a TCP/IP network. The IP datagram consists of a header and a data section.
The header section contains the sender's (source) IP address and the receiver's
(destination) IP address and other information.
general form of an IP datagram.
Figure 4 on page 19 shows the