CCNA Cisco Certified Network Associate Study Guide - FTP Server

The OSI Reference Model 15
before sending the next segment. When it sends a segment, the transmitting
machine starts a timer and retransmits if it expires before an acknowledgment
is returned from the receiving end.
In Figure 1.7, the sending machine transmits segments 1, 2, and 3. The receiving
node acknowledges it has received them by requesting segment 4. When it
receives the acknowledgment, the sender then transmits segments 4, 5, and 6. If
segment 5 doesn’t make it to the destination, the receiving node acknowledges
that event with a request for the segment to be resent. The sending machine will
then resend the lost segment and wait for an acknowledgment, which it must
receive in order to move on to the transmission of segment 7.
FIGURE 1.7 Transport layer reliable delivery
The Network Layer
Sender Receiver
1 2 3 4 5 6 1 2 3 4 5 6
Send 1
Send 2
Send 3
Send 4
Send 5 Connection lost!
Send 6
Send 5
Ack 4
Ack 5
Ack 7
The Network layer is responsible for routing through an internetwork and
for network addressing. This means that the Network layer is responsible for
transporting traffic between devices that are not locally attached. Routers, or