Ccna Study, Chapter One

Front 1

What is the OSI Application Layer?

Back 1

Layer 7 of the OSI Reference Model that defines the interface between the communications software and any applications that need to communicate outside the computer on which the application resides. For example, a web browser is an application on a computer. The browser needs to get the contents of a web page; OSI Layer 7, which defines the protocols, used on behalf of the application to get the web page.

Hint 1

Telnet, HTTP, FTP, WWW browsers, NFS, SMTP gateways (Eudora, CC:mail), SNMP

Front 2

What is the OSI Presentation Layer?

Back 2

Layer 6, which its main purpose is to define data formats, such as ASCII text, EBCDIC text, binary, BCD, and JPEG. Encryption also is defined by OSI as a presentation layer service. For example, FTP enables you to choose binary or ASCII transfer. If binary is selected, the sender and receiver do not modify the contents of the file. If ASCII is chosen, the send translates the text from the sender's character set to a standard ASCII and send the data. The receiver translates back from the standard ASCII to the character set used on the receiving computer.

Hint 2

JPEG, ASCII, EBCDIC, TIFF, GIF, PICT, encryption, MPEG, MIDI

Front 3

What is the OSI Sesssion Layer?

Back 3

The session layer, layer 5, defines how to start, control, and end conversations (called 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. For example, an automated teller machine transaction in which you withdraw cash from your checking account should not debit your account and then fail before handing you the cash, recording the transaction even though you did not receive money. The session layer creates ways to imply which flows are part of the same session and which flows must complete before any are considered complete.

Hint 3

RPC, SQL, NFS, NetBIOS names, AppleTalk ASP, DECnet SCP

Front 4

What is the OSI Transport Layer?

Back 4

Layer 4, which contains protocols that provide a large number of services. Although Layers 5 through 7 focus on issues related to the application, Layer 4 focuses on issues related to data delivery to the other computer—for instance, error recovery, segmentation of large application data blocks into smaller ones for transmission, and reassembly of those blocks of data on the receiving computer.

Hint 4

TCP, UDP, SPX

Front 5

What is the OSI Network Layer?

Back 5

Layer 3, which defines end-to-end delivery of packets. To accomplish this, the network layer defines logical addressing so that any endpoint can be identified. It also defines how routing works and how routes are learned so that the packets can be delivered. The network layer of OSI defines most of the details that a Cisco router considers when routing. For example, IP running in a Cisco router is responsible for examining the destination IP address of a packet, comparing that address to the IP routing table, fragmenting the packet if the outgoing interface requires smaller packets, and queuing the packet to be sent out to the interface.

Hint 5

IP, IPX, AppleTalk DDP

Front 6

What is the OSI Data-Link Layer?

Back 6

The data link layer (Layer 2) specifications deliver data across one particular link or medium. These protocols are necessarily concerned with the type of media in question; for example, 802.3 and 802.2 define Ethernet for the IEEE, which are referenced by OSI as valid data link layer (Layer 2) protocols. Other protocols, such as High—Level Data Link Control (HDLC) for a point-to-point WAN link, deal with the different details of a WAN link.

Hint 6

IEEE 802.3/802.2, HDLC, Frame RElay, PPP, FDDI, ATM, IEEE 802.5/802.2

Front 7

What is the OSI Physical Layer?

Back 7

Layer 1 contains specifications, which are also typically standards from other organizations that are referred to by OSI, that deal with the physical characteristics of the transmission medium. Connectors, pins, use of pins, electrical currents, encoding, and light modulation are all part of different physical layer specifications. Multiple specifications sometimes are used to complete all details of the physical layer. For example, RJ-45 defines the shape of the connector and the number of wires or pins in the cable. Ethernet and 802.3 define the use of wires or pins 1, 2, 3, and 6. So, to use a Category 5 cable with an RJ-45 connector for an Ethernet connection, Ethernet and RJ-45 physical layer specifications are used.

Hint 7

EIA/TIA-232, V.35, EIA/TIA-449, RJ-45, Ethernet, 802.3, 802.5, B8ZS

Front 8

What are the Four Layers of the TCP/IP Networking Model?

Back 8

Application, Transport, Internetwork, Network Interface

Front 9

What are the benefits of layered protocol specifications.

Back 9

-Easier to learn -Easier to develop (reduced complexity allows easier program changes and faster product evolution). -Multivendor interoperability (creating products to meet the same networking standards means that computers and networking gear from multiple vendors can work in the same network. -Modular engineering (One vendor can write software that implements higher layers--for examples, a web browser--and another can write software that implements the lower layers--for example, Microsoft's built0in TCP/IP software in its operating systems.