1.1 Explain concepts related to the Open Systems Interconnection (OSI) reference model. Flashcards
What is Transport Control Protocol (TCP)?
A connection-oriented protocol good for File Transfer, Email, Web Page request. Uses a three-way handshake each time (SYN, SYN ACK, & ACK)
What is User Datagram Protocol (UDP)
A connection-less protocol with no guarantee of delivery; has speed advantage; good for audio/video streamming.
What is a Maximum Transmission Unit (MTU)?
This protocol determines the largest frame a particular technology can handle.
What is an MTU mismatch?
When packets are too large for a particular technology like Ethernet, which uses 1500-byte frames, they are fragmented.
What is a Path MTU Discovery (PMTU)?
A setting that sets a “Do NOT fragment (DF) flag” to the IP packet; it determines the best MTU setting automatically.
What is an MTU Black Hole?
Since PMTU runs under ICMP, if ICMP is being blocked, PMTU will not work. This can be remedied by turning off IMP blocking in the firewall.
What is OSI Layer 1?
- Physical Layer (PDNTSPA)
- Signaling, cabling, connectors
- Transmits logical bits (1s and 0s)
- Devices include NICs, repeaters, concentrators.
What is OSI Layer 2?
- Data Link Layer (PDNTSPA)
- This is the MAC layer where physical addressing on a device, error detection, and reliable data transfer
- Devices include ATM, switches, and bridges; protocols include PPP and ARP.
What is Link-Layer Control (LLC)?
Happens at Layer 2, governs sequence number and acknowledgements.
What is Media Access Control (MAC)?
Happens at Layer 2, governs data transfer and collision handling.
What is OSI Layer 3?
- Network Layer (PDNTSPA)
- This is where the logical addressing, route selection, Fragmentation and re-assembly happens (frames), packets.
- Devices include bridges and routers; protocols used include IP, ICMP, IPSec.
What is OSI Layer 4?
- Transport Layer (PDNTSPA)
- End-to-end connections, flow control and reliability happen at this layer.
- Protocols include TCP and/or UDP.
What is OSI Layer 5?
- Session Layer (PDNTSPA)
- This is where inter-host or inter-application communication happens.
- Control Protocols (Start & end), Tunneling protocols
- Protocols include RTCP, PPTP, and RPC.
What is OSI Layer 6?
- Presentation Layer (PDNTSPA).
- This is where compatible syntax, data formats, and application encryption happens at.
- Character encoding happens here with ASCII, UNICODE, or EBCDIC.
- Protocols commonly used here are SSL/TLS
Wha tis OSI Layer 7?
- Application Layer (PDNTSPA)
- This is where network processes and data is passing to the finished product.
- Protocols include HTTP, FTP, DNS, POP3
What layer does the signaling, cabling or connector issues arise from?
Layer 1
What layer would you be utilizing the following troubleshooting issues from: cabling, punch-downs, running loopback tests, test/replace cables, swap adapter cards?
Layer 1
This layer is also referred to as the “routing” layer.
Layer 3 - Network Layer
This layer can also be referred to as the “post office” layer
Layer 4 - Transport Layer
What layer deals with starting, stopping and restarting; deals with control protocols and tunneling protocols?
Layer 5 - Session Layer
What layer deals with SSL/TLS and application encryption; what happens just before the user sees it?
Layer 6 - Presentation Layer
OSI In-Action Example for going to G-mail.
- Physical: Electrical Signals
- Data Link: Ethernet
- Network: IP encapsulation
- Transport: TCP encapsulation
- Session: Link the presentation to the transport
- Presentation: SSL encryption
- Application: https://mail.google.com
