The communication sequence example starts with Host 1 sending data and then reverses when Host 2 has data to send. This pattern is typical of two-way communications. This phantom byte can be confusing when you have just learned that the sequence number field increments only when data is sent. This capability is called a window. The amount of TCP buffer space the receiver has advertised The window will always be the lower of these two values.
Available bandwidth is based on data transferred without error.
If a packet is lost in transit, the sender assumes the network is congested. The window continues to slide to the right as acknowledgments are received. When buffer space becomes available again, the receiver sends another packet with the new window size defined. When you examine TCP-based communications using a protocol analyzer, interpreting the sequence number and the acknowledgment number information can be confusing. Figure 4 illustrates the EtherPeek summary window and provides some pointers on how to interpret the sequence numbers shown.