1.1 OSI Model

Flashcards reviewing the OSI Model and Networking Concepts

OSI Model

Conceptual overview of data movement; helps troubleshoot network issues by starting from the physical layer and moving upwards.

Layer 1: Physical Layer

Deals with the physical aspects of networking, including cable types, connectors, pinout formats, signal voltage/frequency, speed, bandwidth, maximum distance, and topology.

Physical Layer Components

Type of cable, Type of connector, Pinout format for cables, Voltage and frequency of signal, affecting: Speed, Bandwidth, Maximum distance for use & Topology

Protocols/Technologies at the Physical Layer

USB, Ethernet, Bluetooth, DSL, ISDN, and T-carrier links (T1 and T3).

Topology

The physical arrangement of hardware components in a network (e.g., mesh, star/hub, spine and leaf, point to point, hybrid).

Layer 2: Data Link Layer

Deals with fundamental communication between devices, MAC addresses, and error detection/correction. Uses MAC addresses for device identification.

MAC address

Hardware address of a device’s network adapter card.

Switch

Extended unique identifier switch

Data Link Layer Troubleshooting

Loop back tests, Test/replace cables, Swapping adaptor cards

Frame

The logical grouping of data at the data link layer.

Protocols at the Data Link Layer

HDLC, L2TP, PPP, STP, VLANs

Layer 3: Network Layer

Responsible for routing data packets, using IP addresses to determine the best path for data to take through the network.

Routing Layer

Decides how to forward traffic & Uses IP address

Packet

The logical grouping of data at the network layer.

Static Routes

Routes manually added to routing table.

Dynamic Routes

Protocols like Routing Information Protocol (RIP) and Open Shortest Path First (OSPF). They communicate routing information between networked devices.

Layer 4: Transport Layer

Transport information from one device to another, similar to a post office; uses protocols like TCP and UDP.

Layer 4: Function

Can fragment frames through the network router packet

Layer 5: Session Layer

Breaks up data into pieces (TCP segments or UDP datagrams) and reassembles it upon arrival. Provides error checking, service addressing, and segmentation.

Error checking

Check data is sent and received correctly.

Service addressing

Ensure data is passed to the right service at upper OSI model layers

Segmentation

Break down data into packets of manageable sizes for lower layers to handle

Buffering

data is temporarily stored and waits for device to become available. Can cause problem is sending device transmits data faster than reciving device can manage

Windowing

Data is sent in groups of segments that only require one acknowledgment. The size of the window is established when the session between 2 devices is established.

Layer 5: Session Layer Responsibilities

Sets up connections between devices, manages communication (start, stop, restart), and synchronizes data between applications. Protocols include NetBIOS, NFS, SMB.

Communication Management

Manages sybchornisation of data between applications on two devices & Sets up connection between two applications

Layer 6: Presentation Layer

Negotiates data format, character encoding, and encryption. Translates data for the application layer. Commonly combined with the application layer. (SSL/TLS)

Data Conversion

Converts data from or to application layer for other layers

Data Formats

JPEG, TIFF, GIF - ASCII, EBCDIC - MPEG, MP3, MIDI

Layer 7: Application Layer

Provides network services to applications, such as HTTP, FTP, DNS, POP3, SSH, BGP, DHCP, NTP, RTP, SIP, SMTP, SMB, FTP, HTTP, HTTPS, IMAP, POP3. Interacts directly with the user.

Function

Takes requests and data from users and passes it down the layers

Wireshark

Shows the top-to-bottom sections corresponding to layers 1-7 of the OSI model, including electrical signals, IP encapsulation, TCP encapsulation, and SSL encryption.

Encapsulation

Adding protocol information (header and trailer) to data as it passes through layers

Decapsulation

Removing protocol information from data as it passes through layers

PDU (Protocol Data Unit)

The unit of data worked with at each layer (e.g., packet or frame).