-Section 3: OSI Model Flashcards
OSI
Open Systems Interconnection (7 Layers)
What are the OSI Model/Stack seven layers
- Physical (Please)
- Data Link (Do)
- Network (Not)
- Transport (Throw)
- Session (Sausage)
- Presentation (Pizza)
- Application (Away)
OSI Model Layer 1
Physical
OSI Model Layer 2
Data Link
OSI Model Layer 3
Network
OSI Model Layer 4
Transport
OSI Model Layer 5
Session
OSI Model Layer 6
Presentation
OSI Model Layer 7
Application
MAC Address
Media Access Control Address - 48-bit Hexadecimal address assigned to NIC. First 24 bits represent vendor code, second 24 bits are a unique value.
Layer 1 (Physical) Examples
Cables (Ethernet, Fiber); RF (WiFi, Bluetooth); Infrastructure (Hub, WAP, Media Converter)
Layer 2 (Data Link) Examples
NIC; Bridges; Switches
LLC
Logical Link Control - sublayer of Data Link (Layer 2) that controls synchronization, multiplexing, flow control and error-checking.
Layer 3 (Network)
▪ Forwards Traffic with Logical Address (IP)
▪ Logical addressing
▪ Switching (Not Switches. Switches are Layer 2).
▪ Route Discovery and Selection
▪ Connection Services (Augments Layer 2 for improved reliability) - a.) Flow Control; b.) Packet reordering - supports sending packets over multiple links and routes.
Layer 3 (Network) Examples
▪ Routers
▪ Multilayer switches (Functions as Switch and Router)
▪ IPv4 protocol
▪ IPv6 protocol
▪ Internet Control Message Protocol (ICMP)
Layer 4 (Transport)
▪ Dividing line between upper and lower layers
▪ Data is sent as segments
▪ TCP/UDP
▪ Windowing
▪ Buffering
TCP (Layer 4 Transport)
Transmission Control Protocol
▪ Connection-oriented protocol
▪ Reliable transport of segments- If segment dropped,
detects and resends
▪ Acknowledgements received for successful communications.
UDP (Layer 4 Transport)
▪ Connectionless protocol
▪ Unreliable transport of segments
▪ No retransmission
▪ Good for audio/video streaming
▪ Lower overhead for increased performance
Layer 4 (Transport) Examples
▪ TCP
▪ UDP
▪ WAN Accelerators
▪ Load Balancers
▪ Firewalls
TCP Windowing
Adjusts to send more/less data per segment based on retransmissions.
Layer 5 (Session)
▪ Setting up sessions
▪ Maintaining sessions
▪ Tearing down sessions
Layer 5 (Session) Setting Up a Session
▪ Check user credentials
▪ Assign numbers to session to identify them
▪ Negotiate services needed for session
▪ Negotiate who begins sending data
Layer 5 (Session) Maintaining a Session
▪ Transfer the data
▪ Reestablish a disconnected session
▪ Acknowledging receipt of data
Layer 5 (Session) Tearing Down a Session
▪ Mutual - After the transfer is done
▪ Other party disconnecting
Layer 5 (Session) Examples
▪ H.323 - Setup, maintain, and tear down a voice/video
▪ NetBIOS - Share files over a network
Layer 6 (Presentation)
▪ Functions (App Services, Service Advertisement)
▪ Data formatting
▪ Encryption
Layer 6 (Presentation) Examples
▪ HTML, XML, PHP, JavaScript, …
▪ ASCII, EBCDIC, UNICODE, …
▪ GIF, JPG, TIF, SVG, PNG, …
▪ MPG, MOV, …
▪ TLS, SSL, …
Layer 7 (Application)
▪ Provides application-level services (Low level apps like File Transfer, Network Transfer,… Not Word, NotePad,…)
▪ Layer where users communicate with the computer
▪ Application Services and Services Advertisement
Packet Switching - Layer 3 (Network)
AKA Routing - Data is divided into packets and forwarded
Circuit Switching - Layer 3 (Network)
Dedicated comm. link path
Message Switching - Layer 3 (Network)
Similar to Packet Switching except packets can be stored before forwarded.
Layer 3 (Network) Route Discovery and Selection
Router Protocols - RIP; OSPF; EIGRP
ICMP (Layer 3 - Network)
Internet Control Message Protocol (ICMP)
▪ Used to send error messages and operational information about an IP destination
▪ Not regularly used by end-user applications
▪ Used in troubleshooting (ping and traceroute)
Layer 7 (Application) - Application Services
Application services unite communication components from more than one network application.
(E.g., File transfers and File Sharing, e-Mail, Remote Access, Network Management, Client/Server processes.)
Layer 7 (Application) - Service Advertisement
Some applications send announcements about services they offer, some register with AD instead. (e.g. printer, file server).
Layer 7 (Application) -
▪ E-mail (POP3, IMAP, SMTP)
▪ Web Browsing (HTTP, HTTPS)
▪ Domain Name Service (DNS)
▪ File Transfer Protocol (FTP, FTPS)
▪ Remote Access (TELNET, SSH)
▪ Simple Network Management Protocol (SNMP)
TCP/IP Model
AKA TCP/IP Stack or DoD Model. Alternative to OSI Model that offers network designers a more relevant model since it is based on TCP/IP and only has 4 layers.
TCP/IP Model Layer 1 (Network Interface)
Incorporates features of OSI Layers 1 (Physical) and 2 (Data Link)
Physical and Electrical Characteristics; How to transmit bits; How the interface uses the medium.
TCP/IP Model Layer 2 (Internet)
Similar to OSI Layer 3 (Network)
▪ Packages data into IP datagrams
- Contains source and destination IPs
- Forwards datagrams between hosts across the networks
▪ Routes IP datagrams across networks
▪ Connectivity occurs externally
TCP/IP Model Layer 2 (Internet) - Examples
▪ IP - Internet Protocol
▪ ICMP - Internet Control Message Protocol (network devices use to communicate problems with data transmission - Number 1 use is reporting errors.)
▪ ARP - Address Resolution Protocol (IP address to MAC address)
▪ RARP - Reverse Address Resolution Protocol (MAC Address to IP address)
ICMP
Internet Control Message Protocol - Network devices use to communicate problems with data transmission - Number one use is reporting errors.
ARP
Address Resolution Protocol - IP address to MAC address. (Layer 2 - Data Link to Layer 3 - Network Layer)
RARP
Reverse Address Resolution Protocol - MAC Address to IP address. (Layer 3 - Network to Layer 2 - Data Link)
TCP/IP Model Layer 3 (Transport)
Similar to OSI Layer 4 (Transport)
▪ Provides communication session management between hosts
▪ Defines level of service and status of connection used for transport
TCP/IP Model Layer 3 (Transport) - Examples
▪ TCP
▪ UDP
▪ RTP
TCP/IP Model Layer 4 (Application)
Combined features of OSI Layers 5 (Session), 6 (Presentation), and 7 (Application)
▪ Defines TCP/IP application protocols
▪ Defines how programs interface with the transport layer service
▪ Layer with which the user interacts
TCP/IP Model Layer 4 (Application) - Examples
▪ HTTP, TELNET, FTP, SNMP, DNS, SMTP, SSL, TLS, …
