Transport Layer Protocols - Novell NETWARE 6-DOCUMENTATION Manual

Transport Layer Protocols

3. The IP layer creates a packet with a data portion containing the TCP
segment. The IP layer adds a packet header containing source and
destination IP addresses.
4. The IP layer also determines the physical address of the destination
computer or intermediate computer on the way to the destination host. It
passes the packet and the physical address to the Data-Link layer. A
checksum is computed on the IP header.
5. The Data-Link layer transmits the IP packet in the data portion of a data-
link frame to the destination computer or an intermediate computer. If the
packet is sent to an intermediate computer, steps 4 through 7 are repeated
until the destination computer is reached.
6. At the destination computer, the Data-Link layer discards the data-link
header and passes the IP packet to the IP layer.
7. The IP layer checks the IP packet header. If the checksum contained in the
header does not match the checksum computed by the IP layer, it discards
the packet.
8. If the checksums match, the IP layer passes the TCP segment to the TCP
layer.
9. The TCP layer computes a checksum for the TCP header and data. If the
computed checksum does not match the checksum transmitted in the
header, the TCP layer discards the segment. If the checksum is correct and
the segment is in the correct sequence, the TCP layer sends an
acknowledgment to the source computer and passes the data to the
application.
10. The application on the destination computer receives a stream of bytes,
just as if it were directly connected to the application on the source
computer.
The Transport layer of the TCP/IP protocol suite consists of two protocols,
UDP and TCP. UDP provides an unreliable connectionless delivery service to
send and receive messages. TCP adds reliable byte stream-delivery services
on top of the IP datagram delivery service.
The ports numbered between 1 and 1,023 are well-known port numbers. For
dynamically bound ports, an application requests that UDP assign a port to
15
Understanding