Section 2: Understanding the Host-to-Host Communications Model

Question 1

Describe

Benefits to a Standards-Based, Layered Network Model

Answer 1

• Reduced complexity by breaking network comms into smaller, simpler parts
• Standardizing network components allow diff vendors to provide solutions for separate layers
• Facilitating modular engineering, allowing diff types of network hardware and software to comm w one another
• Ensuring interoperable tech and preventing changes in one layer from affecting other layers
• Accelerating evolution, providing for effective updates and improvements to individual components without affecting other components or having to rewrite the entire protocol
• Simplifying teaching and learning

Question 2

Define

ISO

Answer 2

International Standards Organization

• Independent, nongovernmental organization; world’s largest developer of voluntary international standards
• Created OSI model

Question 3

List

The 7 Layers of the OSI Reference Model

Question 4

Define/ Illustrate/ Interpret

OSI Reference Model​

Answer 4

Open Systems Interconnection Reference Model

• Created by the International Standards Organization (ISO) in 1970’s
• ISO’s goal to standardize data networking protocols to allow global comm’n among all computers and not depend on proprietary networking models
• Provides extensive list of functions and services that can occur at ea layer; also describes interaction of ea layer with layers directly above and below.
• OSI model facilitates understanding of how info travels throughout network.
• Also use OSI model for data network design, operation specifications, and troubleshooting.

Question 5

List

The 7 Layers of the OSI Ref. Model

Answer 5

7. Application Layer
8. Presentation Layer
9. Session Layer
10. Transport Layer
11. Network Layer
12. Data Link Layer
13. Physical Layer

(Please Do Not Throw Sausage Pizzas Away) (1-7)

Question 6

Define

Physical Layer

Answer 6

Defines electrical, mechanical, procedural, & functional specifications needed for activating & maintaining the physical link between end devices.

E.g. connectors, pins, use of pins, electrical currents, encoding, light modulation, etc

Question 7

Define

Data Link Layer

Answer 7

Defines how data is formatted for transmission & how access to physical media is controlled.

Includes error detection & correction to ensure reliable delivery of data.

• Like TCP/IP data link layer, this layer defines protocols for delivering data over a particular single type of physical network (e.g. the Ethernet data link protocols)
• A switch is an example of a layer 2 device.

Question 8

Define

Network Layer

Answer 8

Provides connectivity & path selection between 2 host systems that may be located on geographically separated networks.

• Defines logical addressing, routing (forwarding), & routing protocols used to learn routes, which manages connectivity of global users.
• Routers and IP addresses are Layer 3 objects

Question 9

Define

Transport Layer

Answer 9

Focuses on data delivery between 2 endpoint hosts (e.g. error recovery)

Breaks down large files into smaller segments that are less likely to experience transmission problems

TCP & UDP protocols operate at this layer

• TCP used when data loss during file transfer is not tolerated
• UDP used when data loss during file transfer is tolerated.

Question 10

Define

Session Layer

Answer 10

Establishes, manages, & terminates sessions between 2 communicating hosts

Synchronizing dialog between the presentation layers of the 2 hosts & manages their data exchange.

Provides methods to group multiple bidirecional messages into a workflow for easier management & easier backout of work that happened if entire workflow fails.

E.g. Web servers w many users have many diff comm’n processes open at given time; as result it’s important to keep track of which user communicates on which part- this is done using port numbers.

Question 11

Presentation Layer

Answer 11

Ensures information sent at app layer is readable by app layer of another system

It translates among multiple data formats using a common format

Negotiates data formats (ASCII, image types (JPEG))

• When PC program communicating with another computer, each computer might be using different encoding scheme

Question 12

Define

Application Layer

Answer 12

Provides an interface from application to network by supplying a protocol with actions meaningful to application

E.g. ‘get web page object’

Layer does not provide services to any other OSI layer like other layers, only provides to apps outside OSI model

Establishes availability of intended communication partners

Synchronizes & establishes agreement on procedures for error recovery & control of data integrity

e.g. SMTP & FTP

Question 13

Define

TCP/ IP

Answer 13

Transmission Control Protocol/ Internet Protocol

defines how devices should be connected over Internet & how data should be transmitted between those devices

• provides a common reference for maintaining consistency within all types of network protocols and services.

Not intended to be an implementation specification or to provide sufficient detail to precisely define services of the network architecture.

The primary purpose of this reference model is to help you understand the functions and processes that are involved in data communication.

actually two protocols, but used together so often many people think of them as a single protocol

common in the industry to shorten this term to “IP stack

Question 14

List

The 4 Layers of the TCP/IP Protocol Stack

Answer 14

4. Application Layer
5. Transport Layer
6. Internet (Network) Layer
7. Link (Network Access) Layer

Question 15

Illustration of

OSI Model and TCP/IP Suite

Answer 15

Question 16

Define

Link Layer

TCP/IP Stack

Answer 16

• Layer #1
• Equivalent of both physical and data link layers of OSI model.
• Aka the network access layer
• Involves components such as cables, connectors, and network cards like OSI Layer 1.
• Like Layer 2 of OSI model, link layer of TCP/IP model concerned with hardware addresses.

Question 17

Internet Layer

TCP/IP Stack

Answer 17

• Layer # 2
• Aligns & is equivalent of OSI’s layer # 3 (Network)
  ​

• routes data from source to destination by defining packet and addressing scheme, moving data between link and transport layers, routing packets of data to remote hosts, & performing fragmentation & reassembly of data packets.
• This is layer where IP operates.

Question 18

Transport Layer

TCP/IP Stack

Answer 18

• Layer #3
• This layer is core of TCP/IP architecture.
• Layer where TCP and UDP operate.
• Provides communication services directly to application processes that are running on network hosts.

Question 19

Application Layer

TCP/IP Stack

Answer 19

• Layer #4
• Layers 5, 6, and 7 of the OSI model (Session, Presentation, Application)
• provides applications for file transfer, network troubleshooting, and Internet activities.
• also supports network APIs, which allow programs that have been created for a particular operating system to access the network.

Question 20

Illustrate Concept of

P2P Communication

Answer 20

• ​In network comm’s, each source layer must be able to comm w/ its destination layer
• Layers comm w ea other by means of Protocol Data Units
• Ea protocol layer has its own PDU term

Question 21

Name

Frames

The PDU term for the —- layer

Answer 21

Link Layer

Question 22

Name

Packets

The PDU term for the —- layer

Answer 22

Internet Layer

Question 23

Name

Segments

The PDU term for the —- layer

Answer 23

Transport Layer

Question 24

Name

Data

The PDU term for the —- layer

Answer 24

Application Layer

Question 25

Illustrate Concept of…

Packet Analyzer

Answer 25

a program for analyzing packets used for network troubleshooting, analysis, software and communications, & protocol development