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Which of the following correctly describe steps in the OSI data encapsulation process?

Which of the following correctly describe steps in the OSI data encapsulation process?
(Choose two.)

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A.
The transport layer divides a data stream into segments and may add reliability and flow
control information.

B.
The data link layer adds physical source and destination addresses and an FCS to the
segment.

C.
Packets are created when the network layer encapsulates a frame with source and
destination host addresses and protocol-related control information.

D.
Packets are created when the network layer adds Layer 3 addresses and control
information to a segment.

E.
The presentation layer translates bits into voltages for transmission across the physical
link.

Explanation:
The Application Layer (Layer 7) refers to communications services to applications and is the
interface between the network and the application. Examples include. Telnet, HTTP, FTP,
Internet browsers, NFS, SMTP gateways, SNMP, X.400 mail, and FTAM.
The Presentation Layer (Layer 6) defining data formats, such as ASCII text, EBCDIC text,
binary, BCD, and JPEG. Encryption also is defined as a presentation layer service.
Examples include. JPEG, ASCII, EBCDIC, TIFF, GIF, PICT, encryption, MPEG, and MIDI.
The Session Layer (Layer 5) defines how to start, control, and end communication sessions.
This includes the control and management of multiple bidirectional messages so that the
application can be notified if only some of a series of messages are completed. This allows
the presentation layer to have a seamless view of an incoming stream of data. The
presentation layer can be presented with data if all flows occur in some cases. Examples
include. RPC, SQL, NFS, NetBios names, AppleTalk ASP, and DECnet SCP
The Transport Layer (Layer 4) defines several functions, including the choice of protocols.
The most important Layer 4 functions are error recovery and flow control. The transport layer

may provide for retransmission, i.e., error recovery, and may use flow control to prevent
unnecessary congestion by attempting to send data at a rate that the network can
accommodate, or it might not, depending on the choice of protocols. Multiplexing of incoming
data for different flows to applications on the same host is also performed. Reordering of the
incoming data stream when packets arrive out of order is included. Examples include. TCP,
UDP, and SPX.
The Network Layer (Layer 3) defines end-to-end delivery of packets and defines logical
addressing to accomplish this. It also defines how routing works and how routes are learned;
and how to fragment a packet into smaller packets to accommodate media with smaller
maximum transmission unit sizes. Examples include. IP, IPX, AppleTalk DDP, and ICMP.
Both IP and IPX define logical addressing, routing, the learning of routing information, and
end-to-end delivery rules. The IP and IPX protocols most closely match the OSI network
layer (Layer 3) and are called Layer 3 protocols because their functions most closely match
OSI’s Layer 3.
The Data Link Layer (Layer 2) is concerned with getting data across one particular link or
medium. The data link protocols define delivery across an individual link. These protocols
are necessarily concerned with the type of media in use. Examples includE. IEEE
802.3/802.2, HDLC, Frame Relay, PPP, FDDI, ATM, and IEEE 802.5/802.2.

2 Comments on “Which of the following correctly describe steps in the OSI data encapsulation process?”

  2. Henry P says:

    D is actually the correct answer. I have verified with two different sites.

    Explanation

    The transport layer segments data into smaller pieces for transport. Each segment is assigned a sequence number, so that the receiving device can reassemble the data on arrival.

    The transport layer also use flow control to maximize the transfer rate while minimizing the requirements to retransmit. For example, in TCP, basic flow control is implemented by acknowledgment by the receiver of the receipt of data; the sender waits for this acknowledgment before sending the next part.

    -> A is correct.

    The data link layer adds physical source and destination addresses and an Frame Check Sequence (FCS) to the packet (on Layer 3), not segment (on Layer 4) -> B is not correct.

    Packets are created when network layer encapsulates a segment (not frame) with source and destination host addresses and protocol-related control information. Notice that the network layer encapsulates messages received from higher layers by placing them into datagrams (also called packets) with a network layer header -> C is not correct.

    The Network layer (Layer 3) has two key responsibilities. First, this layer controls the logical addressing of devices. Second, the network layer determines the best path to a particular destination network, and routes the data appropriately.

    -> D is correct.

    The Physical layer (not presentation layer) translates bits into voltages for transmission across the physical link -> E is not correct.




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