CCNA Cisco Certified Network Associate Study Guide - FTP Server

FIGURE 1.13 Data encapsulation
Data Encapsulation 31
is sequenced so the data stream can be put back together on the receiving side
exactly as transmitted.
TCP header
IP header
LLC header
MAC header
Upper layer data
Upper layer data
Data
Data
Data
0101110101001000010
FCS
FCS
Application
Presentation
Session
Transport
Network
Data Link
Physical
Segment
Each segment is then handed to the Network layer for network addressing
and routing through an internetwork. Logical addressing, for example, IP, is
used to get each segment to the correct network. The Network-layer protocol
adds a control header to the segment handed down from the Transport
layer, and it is now called a packet or datagram. Remember that the Transport
and Network layers work together to rebuild a data stream on a receiving
host. However, they have no responsibility for placing their PDUs on a
local network segment, which is the only way to get the information to a
router or host.
The Data Link layer is responsible for taking packets from the Network
layer and placing them on the network medium (cable or wireless). The Data
Link layer encapsulates each packet in a frame, and the frame’s header carries
the hardware address of the source and destination hosts. If the device is
on a remote network, then the frame is sent to a router to be routed through
an internetwork. Once it gets to the destination network, a new frame is used
to get the packet to the destination host.
To put this frame on the network, it must first be put into a digital signal.
Since a frame is really a logical group of 1s and 0s, the Physical layer is
responsible for encapsulating these digits into a digital signal, which is read
PDU
Packet
Frame
Bits