Cisco 200-120 Question Answer

200-120 Question 10

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.

Correct Answer: A,C
Explanation/Reference: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 manage ment of multiple bidirectional messages so that the application can be notified if only some of a series of messages are completed. This allows the presentati on 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 inc lude. 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 function s are error recovery and flow control. The transport layer may provide for retransmission, i.e., error recovery, and may use flow control to prevent unnecess ary 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 incomin g 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 inc luded. 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 d efines how routing works and how routes are learned; and how to fragment a packet into smaller packets to accommodate media with smaller maximum transmission un it 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 m ost 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 defi ne 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.