146 terms

"OSI Model Layers"

OSI Layers in correct number order OSI Layers Functions Devices associated with 3 OSI Layers Encapsulation names to 3 OSI Layers Headers of 3 OSI Layers
Physical Layer
Data-Link Layer
Network Layer
Transport Services
Numbers 1-4
Upper Layers
Numbers 5-7
Physical Layer Function
Provides access to the cables and wireless devices.
Data-Link Layer Function
Provides physical hardware addressing. Frames the packet to ensure data is error-free.
Provides packets with logical IP addressing. Locates the destination IP network
Transport Layer Function
Segments the data. Provides reliable TCP and unreliable UDP connections
Session Layer Function
Starts and ends each session. Provides session isolation
Presentation Layer Function
Formats information into something the Application can use such as JPEG, HTML, or MP3
Application Layer Function
Interfaces with the Application
Device used for Physical Layer
Device used for Network Layer
Device used for Data-Link Layer
Encapsulated name for Transport
Encapsulated name for Network
Encapsulated name for Data-Link
Header for Transport
Source and Destination Ports
Header for Network
Source and Destination IPs
Header for Data-Link
Source and Destination MAC Addresses
Adjacent-layer interaction
The general topic of how on one computer, two adjacent layers in a networking architectural model work together, with the lower layer providing services to the higher layer
On a computer that receives data over a network, the process in which the device interprets the lower-layer headers and, when finished with each header, removes the header, revealing the next-higher-layer PDU.
the process of putting headers ( and sometimes trailers) around some data
A term referring to a data link header and trailer, plus the data encapsulated between the header and trailer.
networking model
A generic term referring to any set of protocols and standards collected into a comprehensive grouping that, when followed by the devices in a network, allows all the devices to communicate. Examples include TCP/IP and OSI
A logical grouping of bytes that includes the network layer header and encapsulated data, but specifically does not include any headers and trailers below the network layer.
Protocol data unit (PDU)
A generic term referring to the header defined by some layer of a networking model, and the data encapsulated by the header (and possibly trailer) of that layer, but specifically not including any lower-layer headers and trailers
Same-layer interaction
The communication between two networking devices for the purposes of the functions defined at a particular layer of a networking model, with that communication happening by using a header defined by that layer of the model. The two devices set values in the header, send the header and encapsulated data, with the receiving device(s) interpreting the header to decide what action to take.
In TCP, a term used to describe a TCP header and its encapsulated data (also called an L4PDU). Also in TCP, the process of accepting a large chunk of data from the application layer and breaking it into smaller pieces that fit into TCP segments. In Ethernet, a segment is either a single Ethernet cable or a single collision domain (no matter how many cables are used).
Enterprise network
a network created by one corporation or enterprise, for the purpose of allowing its employees to communicate
a set of logical rules that devices must follow to communicate
networking devices that connect the parts of the TCP/IP network together for the purpose of routing (forwarding) IP packets to the correct destination
IP host
any device, regardless of size or power, that has an IP address and connects to any TCP/IP network
IP routing or Routing
the process of forwarding the IP packet
refers to the physical connections, or links, between 2 devices and the protocols used to control those links
Ethernet network
implements link-layer protocols
Ethernet frame
A term referring to an Ethernet data link header and trailer, plus the data encapsulated between the header and trailer
Which networking model is used today?
TCP/IP (updated)
Before networking protocols existed, IBM published what?
its System Network Architecture (SNA) networking model in 1974
In the late 1970s, who took on the task of creating an open, vender-neutral networking model?
International Organization for Standardization (ISO)
Which of the following protocols are examples of TCP/IP transport layer protocols? Choose 2 answers
a. Ethernet
d. UDP
f. TCP
Which of the following protocols are examples of TCP/IP data link layer protocols?
a. Ethernet
c. IP
d. UDP
f. TCP
g. PPP
Ethernet and PPP
The process of HTTP asking TCP to send some data and making sure that it is received correctly is an example of what?
Adjacent-layer interaction
The process of TCP on one computer marking a TCP segment 1, and the receiving computer then acknowledging the receipt of TCP segment 1 is an example of what?
Same-layer interaction
The process of a web server adding a TCP header to the contents of a web page, followed by adding an IP header and then adding a data link header and trailer is an example of what?
Data encapsulation
Which of the following terms is used specifically to identify the entity created when encapsulating data link layer headers and trailers?
Which OSI layer defines the functions of logical network-wide addressing and routing?
Layer 3
Which OSI layer defines the standards for cabling and connectors?
Layer 1
Which of the following terms are not valid terms for the names of the seven OSI layers? choose 2 answers
a. Application
b. Data link
c. Transmission
d. Presentation
e. Internet
f. session
Transmission and Internet
What was the outcome of the ISO's work in the 1970s?
The Open Systems Interconnection (OSI) networking model
Who made the second attempt at creating an open, vender-neutral, public networking model?
U.S. DoD and some volunteers
What does the TCP/IP model use to define a protocol?
It uses documents called Requests for comments (RFC)
How many models does TCP/IP have?
List the layers from bottom to top from the Original TCP/IP model.
Link, Internet, Transport, Application
List the layers from bottom to top from the updated TCP/IP model.
Physical, Data Link, Network, Transport, Application
The original TCP/IP model is listed in what RFC? and What does it do?
1122, which breaks TCP/IP into 4 layers
In the original TCP/IP model, what do the top 2 layers focus more on?
applications that need to send and receive data
In the original TCP/IP model, what does the bottom layer focus on?
how to transmit bits over each individual link
In the original TCP/IP model, what does the Internet layer focus on?
delivering data over the entire path from the originial sending computer to the final destination computer
The link layer has also been refered to as _______ and __________ layer.
network access and network interface
List 3 example protocols for the Application layer
List 2 example protocols for the Transport layer
TCP, and UDP
List an example protocol for the Internet layer
List 3 example protocols for the Link layer
Ethernet, Point-to-point Protocol (PPP), T1
The application layer protocols provide what?
services to the application software running on a computer. The application layer does not define the application itself, but it defines services that applications need.
What does the application protocol HTTP example for the application layer say about what the Application layer provides?
It defines how web browsers can pull the contents of a web page from a a web server. In short, the application layer provides an interface between software running on a computer and the network itself.
To make the request for a web page and return the contents of the web page, the applications use what protocol?
the Hypertext Transfer Protocol (HTTP)
Who created the first web browser and web server in the early 1990s?
Tim Berners-Lee
The full version of most web addresses-- also called ___________(__)-- begins with the letters "___," which means that ____ is used to transfer the web pages.
Uniform Resource Locators (URL)
Transport layer protocols provide what?
services to the application layer protocols that reside one layer higher in the TCP/IP model
What is an example of the services provided by the transport layer?
a service provided by the Transmission Control Protocol (TCP): Error recovery
True or False: Each layer provides a service to the layer above it
TCP/IP needs a mechanism to guarantee delivery of data across a network. To recover from errors, TCP uses what?
the concept of acknowledgments
What can be found in the TCP header and why is it important?
A sequence number (SEQ) and it is important because it allows the detection of a missed message. if 3 messages are sent and message 2 did not go through then it can be detected because the messages that got through go 1,3
A TCP message can also be called what?
a segment
The network layer only has one major protocol: the internet protocol (IP). IP provides several features, but what are two of the most important?
addressing and routing
IP defines two things, what are they?
-each host computer should have a different IP address
-the process of routing so that devices called routers can work like the post office, forwarding packets of data so that they are delivered to the correct destinations
What does the network layer define?
the details of how a network infrastructure should be created so that the network can deliver data to all computers in the network
What are the 2 versions of IP and which one does the world still mostly use?
IPv4 and IPv5
IPv4 is still mostly used around the world
IP defines addresses for several important reasons. List 2 of them.
Each divice that uses TCP/IP--each TCP/IP host-- needs a unique address so that it can be identified in the network. IP also defines how to group addresses together, just like zip codes.
Each IP address has ___ numbers, separated by periods. This style of number is called a __________.
dotted-decimal notation (DDN)
What do routers do?
The receive IP packets on various physical interfaces, make decisions based on the IP address included with the packet, and then physically forward the packet out some other network interface.
The term ________ refers to any device, regardless of size or power, that has an IP address and connects to any TCP/IP network.
IP host
What is IP routing?
when one router looks at the destination address, compares that address to its known IP routes, and chooses to forward the packet to the next router or final destination
The TCP/IP model's original link layer defines what?
the protocols and hardware required to deliver data across some physical network
What does the term link refer to?
the physical connections, or links, between two devices and the protocols used to control those links
What are th four steps that happen when Larry uses the Ethernet to forward an IP packet to Router R1?
○ Step 1: Larry encapsulates the IP packet between an Ethernet header and Ethernet trailer, creating an Ethernet frame.
○ Step 2: Larry physically transmits the bits of this Ethernet frame, using electricity flowing over the Ethernet cabling.
○ Step 3: Router R1 physically receives the electrical signal over a cable, and re-creates the same bits by interpreting the meaning of the electrical signals.
○ Step 4: Router R1 de-encapsulates the IP packet from the Ethernet frame by removing and discarding the Ethernet header and trailer.
The original link layer can be broken into what two major categories?
Functions related directly to the physical transmission of data and those only indirectly related to the physical transmission of data.
Are encapsulation and deencapsulation directly or indirectly related to the physical transmission of data?
Give 2 examples of steps from the data link layer
Encapsulation and addressing
What is an example of a step from the physical layer?
bit transmission
The term segment refers to what layer?
Transport layer
The term packet refers to what layer?
Network layer
The term Frame refers to what layer?
Link layer
Define the OSI Application layer
This layer provides an interface between the communications software and any applications that need to communicate outside the computer on which the application resides. It also defines processes for user authentication.
Define the OSI Presentation Layer
This layer's main purpose is to define and negotiate data formats, such as ASCII text, EBCDIC text, binary, BCD, and jpeg. Encryption is also defined by OSI as a presentation layer service.
Define the OSI Session Layer
This layer defines how to start, control, and end conversations (Called sessions). This includes the control and management of multiple bidirectional messages so that th application can be notified if only some of the series of messages are completed. This allows the presentation layer to have a seamless view of an incoming stream of data.
Define the OSI Transport Layer
This layer's protocols provide a large number of services. Although OSI layers 5 through 7 focus on issues related to the application, layer 4 focuses on issues related to data delivery to another computer (for example, error recovery and flow control).
Define the OSI Network Layer
This layer defines three main features: logical addressing, routing (forwarding), and path determination. Routing defines how devices (typically routers) forward packets to their final desitination. Logical addressing defines how each device cah have an address that can be used by the routing process. Path determination refers to the work done by routing protocols to learn all possible routes and choose the best route.
Define the OSI Data Link Layer
This layer defines the rules that determine when a device can send data over a particular medium. Data link protocols also define the format of a header and trailer that allows devices attached to the medium to successfully send and receive data.
Define the OSI Physical Layer
This layer typically refers to standards from other organizations. These standards deal with the physical characteristics of the transmission medium, including connectors, pins, use of pins, electrical currents, encoding, light modulation, and the rules for how to activate and deactivae the use of the physical medium
List protocols and specifications, and devices for the Application, presentation and session layers
Protocols and specifications- HTTP, Telnet, FTP, SMTP, POP3, VOIP,SNMP
Devices- Hosts and firewalls
List protocols and specifications and devices for the Transport layer
Protocols and specifications- TCP and UDP
Devices- Hosts and firewalls
List protocols and specifications and devices for the Network layer
Protocols and specifications- IP
Devices- Router
Do routers support more than one layer and if so which layers does it support
Yes and Layers 1,2, and 3
List protocols and specifications and devices for the Data Link Layer
Protocols and specifications- Ethernet (IEEE 802.3), HDLC
Devices- LAN switch, wireless access point, cable modem, DSL Modem
List protocols and specifications and devices for the Physical layer
Protocols and specifiecations- RJ-45, Ethernet (IEEE 802.3)
Devices- LAN hub, LAN repeater, cables
Summarize the benefits of layered protocol specifications
Less complex, Standard interfaces, Easier to learn, easier to develop, multivendor interperability, and modular engineering
Instead of using terms like segment, packet and frame to refer to various layers and their respective encapsulated data, OSI uses what more generic term?
Protocol data unit (PDU)
What does PDU represent?
the bits that include the headers and trailers for that layer, as well as the encapsulated data.
Orginal (OLD) TCP/IP Model TOP --> BOTTOM
Application,Transport,Network,Data Link,Physical
The protocols HTTP,POP3, and SMTP operate at the _____ layer?
The protocols UDP and TCP work at the _____ layer?
Internet (Network)
The protocol IP works at what layer?
Ethernet, point-to-point(PPP), and T1 work at what layer?
Sequence Number (SEQ)
Each TCP header shows a _____ ______ with each message.
The process of forwarding packets is called ____.
Application,Presentation,Session,Transport,Network,Data Link,Physical
What is the OSI model? TOP --> BOTTOM
Data Link
Ethernet (IEEE 802.3),HDLC, work at the ___ ___ layer.
Protocol Data Unit
PDU stands for ___ __ ___.
open systems interconnection (OSI)
Application layer function examples
File, print, message, database, application services
Provides UI
Presentation layer functions
Data encryption, compression, and translation services
Session layer functions
Dialog control (keeps different applications' data separate)
Transport layer functions
End to end connection
Network functions
Data link functions
Physical layer functions
Transport layer data unit
Breaking data into smaller chunks for transfer
Transmission Control Protocol
User Datagram Protocol
T/F - Segments provide a "read receipt"
Segments not acknowledge (are/are not) retransmitted
Layer 3 data transfer unit
Layer 2 data transfer unit
MAC address is __ bits, _ bytes, and shown as __ hex digits
48, 6, 12
The last 6 hex digits of a MAC address are
unique to a device
The first 6 hex digits of a MAC address are
used to identify the manufacturer
Layer 1 data transfer unit