ch03 IP Addressing.pdf - The Cisco Learning Network

4 Chapter 3: IP Addressing
TABLE 3-2 TCP Segment Components
TCP Field Name
Length
(in bits) Definition
Source Port 16 Identifies which application is sending information
Destination Port 16 Identifies which application is to receive the information
Sequence Number 32 Maintains reliability and sequencing
Acknowledgement Number 32 Used to acknowledge received information
Header Length 4 Number of 32-bit words that comprise the header
Reserved Field 6 Currently not used (set to all zeroes)
Code Bits 6 Defines control functions, like synchronization
Window Size 16 Indicates the number of segments allowed to be sent before
waiting for an acknowledgment from the destination
Checksum 16 CRC of the header and encapsulated application data
Urgent Field 16 Points to the any urgent data in the segment
Options 0-32
Data Application data (not part of the TCP header)
The segment is composed of a header, followed by the application data. Without any
options, the TCP header is 20-bytes in length.
TCP’s Multiplexing Function TCP, and UDP, provide a multiplexing function
for a device: This allows multiple applications to simultaneously send and receive data.
With these protocols, port numbers are used to differentiate the connections. Port
numbers are broken into two basic categories:
well-known port numbers (sometimes called
Be familiar with the
TCP field names, especially the fact that
a TCP segment contains a sequence and
acknowledgment number as well as a
window size.
reserved port numbers) and source connection
port numbers. Each application is assigned a
well-known port number that is typically
between 1 and 1,023. Any time you want to
make a connection to a remote application, your
application program will use the appropriate
well-known port number.
As you saw in Table 3-2, however, there happens to be two port numbers in
the segment: source and destination. When you initiate a connection to a remote