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