Installation guide

Network Infrastructure for EtherNet/IP™
Understanding the Basics of Network Protocols
2-7
The following descriptions summarize the TCP packet fields.
• Source Port and Destination Port: Identifies the source and destination processes that are
to receive TCP services.
• Sequence Number: Typically specifies the number assigned to the first byte of data in the
current message.
• Acknowledgment Number: Contains the sequence number of the next byte of data the
sender expects to receive.
• Data Offset: Indicates the number of 32-bit words in the TCP header.
• Reserved: Reserved for future use.
• Flags: Carries a variety of control information used for connection establishment, and
termination.
• Window: Specifies the size of the buffer space available for incoming data.
• Checksum: Indicates if a header or data was damaged in transit.
• Urgent Pointer: Points to the first non-urgent data byte in the packet.
• Options: Specifies various TCP options.
• Data: Contains upper-layer information.
Internet Protocol (IP)
Internet Protocol (IP) is the primary Layer 3 protocol in the TCP/IP suite. In addition to
inter-network routing, IP provides error reporting as well as fragmentation and reassembly of
information units called datagrams for transmission over networks with different maximum data
unit sizes. IP represents the foundation of the TCP/IP suite.
Public IP addresses are globally unique, 32-bit numbers assigned by the Network Information Center
(NIC). Globally unique addresses permit IP networks anywhere in the world to communicate with each
other. In control networks, users may assign IP addresses within “private” IP address ranges. Examples of
“private” IP address ranges include 10.x.x.x, 172.16-31.x.x, and 192.168.x.x. The IP addresses in these
“private” control networks must be assigned so that they are also unique on the network. The setting of
identical addresses on the same network will disrupt proper operation.
An IP address is divided into three parts. The first part designates the
network address, the second part
designates the
subnet address, and the third part designates the host address.