Section 3: Host to Host Communications

What is the TCP/IP Stack?

A protocol stack consisting of multiple protocols including TCP (Transmission Control Protocol) and IP (Internet Protocol); its 7-layered approach divides operations into related groups of actions at each layer.

What is the name of Layer 7 in the OSI Model?

Application

What is the name of Layer 6 in the OSI Model?

Presentation

What is the name of Layer 5 in the OSI Model?

Session

What is the name of Layer 4 in the OSI Model?

Transport

What is the name of Layer 3 in the OSI Model?

Network

What is the name of Layer 2 in the OSI Model?

Data Link

What is the name of Layer 1 in the OSI Model?

Physical

Which TCP/IP layer corresponds to OSI's Application, Presentation, and Session layers?

Application

Which TCP/IP layer corresponds to OSI's Transport layer?

Transport

Which TCP/IP layer corresponds to OSI's Network layer?

Internet

Which TCP/IP layer corresponds to OSI's Data Link and Physical layers?

Link

. What is the key practical difference between the OSI model and the TCP/IP stack in terms of real-world use?

The OSI model is conceptual/reference-only; the TCP/IP stack is the protocol suite actually used to transmit data on real networks

The OSI [...] layer defines how data is formatted for transmission and how access to physical media is controlled.

Data Link

The OSI [...] layer ensures that information sent at the application layer of one system is readable by the application layer of another system.

Presentation

The OSI [...] layer establishes, manages, and terminates sessions between two communicating hosts.

Session

This OSI layer defines services to segment, transfer and reassemble the data for individual communications between end devices.

Transport Layer

This OSI layer provides connectivity and path selection between two host systems that may be located on geographically separated networks.

Network Layer

Which OSI layer defines the specifications needed for activating, maintaining, and deactivating the physical link between end devices?

Physical Layer

Which OSI layer provides network services to the applications of the user?

Application Layer

What is a Local Area Network (LAN)?

A network that connects devices within a single localized area, such as one office or campus.

What is a Wide Area Network (WAN)?

A network connection linking geographically separate sites (e.g., connecting routers at two different offices).

What is the key functional difference between a switch and a router?

A switch connects devices within a single network (LAN); a router connects and forwards traffic between different networks.

List the 6 characteristics used to evaluate a network design.

Topology, speed, cost, security, availability, scalability, reliability

In network design, what does "avoiding a single point of failure" address?

Availability — ensuring no single component failure takes down the network.

What network design characteristic refers to a network's ability to grow without requiring a redesign

Scalability

What is encapsulation in the OSI model?

The process of wrapping data with a header (and sometimes trailer) from each layer as it moves down the stack from sender to receiver, from Layer 7 down to Layer 1.

What is de-encapsulation, and at which end of a transmission does it occur?

The process of stripping off each layer's header as data moves up the stack, from Layer 1 to Layer 7 — occurs at the receiver.

Which OSI layers are referred to as the "upper layers," and who are they primarily relevant to?

Layers 5–7 (Session, Presentation, Application) — primarily relevant to application developers rather than network engineers

What network device operates at each of these OSI layers: Layer 1, Layer 2, Layer 3?

Layer 1 (Physical) — hub; Layer 2 (Data Link) — switch; Layer 3 (Network) — router

At the Data Link layer, what key piece of addressing information is included in the header?

The MAC address (source and destination)

When a switch receives a frame, what does it check in the Layer 2 header to decide whether to process or discard it?

The destination MAC address — if it doesn't match, the device discards the packet.

What term describes a networking problem caused by a physical issue such as an unplugged cable?

A "Layer 1 problem"

What is a PDU (Protocol Data Unit)?

The general term for the entire unit of communication between two hosts, encompassing all layers from Layer 7 down to Layer 1

What is the PDU called at the Application layer?

Data

What is the PDU called at the Transport layer?

Segment

What is the PDU called at the Internet/Network layer?

Packet

What is the PDU called at the Link/Data Link layer?

Frame

Although "packet" is officially the Layer 3 PDU, how is the term commonly (informally) used?

Often used loosely to refer to the entire communication between two hosts, regardless of layer.

Which two protocols make up the core of the TCP/IP suite, and what does each stand for?

TCP (Transmission Control Protocol) and IP (Internet Protocol)

What distinguishes the Application layer from all other OSI layers in terms of service direction?

It does not provide services to any other OSI layer — it's the only layer that doesn't serve a layer above it.

What does "data integrity" mean in the context of the Application layer's error recovery function?

Checking that data has not been altered or corrupted in transit.

What does the Presentation layer do when two communicating systems use different data encoding schemes?

Translates between the different data formats into a common format so both systems can read the data.

How does the Session layer handle a scenario like a web server with many simultaneous users?

It establishes and keeps track of multiple concurrent sessions between the server and each connecting host.

Besides establishing/managing/terminating sessions, what two other functions does the Session layer perform?

Offers efficient data transfer (Class of Service) and exception reporting of upper-layer problems

What addressing format does old legacy Frame Relay use at the Data Link layer (as opposed to Ethernet's MAC address)?

DLCI (Data Link Connection Identifier) numbers

Besides formatting data for transmission and controlling media access, what additional function does the Data Link layer typically provide?

Error detection and correction, to help ensure reliable delivery of data

What kind of information does the Physical layer's specifications typically define? (name at least 3 examples

Voltage levels, physical data rates, maximum transmission distances, and physical connector types.

What does the Physical layer enable at its most basic level?

Transmission of bits (1s and 0s) between end devices.