Networking & Cellular
E02 OSI & TCP/IP Model — Study Guide
This guide covers OSI & TCP/IP Model as part of Networking & Cellular. Start with the vocabulary, then try to answer each question before revealing the answer. Connect these facts to a real network or cellular connection and practice the subject in the arcade when you are ready.
Acronyms first
| Term | Meaning |
|---|---|
| PDU | Protocol Data Unit |
Key facts
Stack the OSI layers from Layer 1 (bottom) to Layer 7 (top).
Physical → Data Link → Network → Transport → Session → Presentation → Application
Order the PDUs from Layer 7 down to Layer 1 (encapsulation).
Data → Segment → Packet → Frame → Bit
Order the TCP/IP model layers from top to bottom.
Application → Transport → Internet → Network Access
How many layers does the OSI model have?
7
The OSI mnemonic 'Please Do Not Throw Sausage Pizza Away' runs from…
Layer 1 to Layer 7
The mnemonic 'All People Seem To Need Data Processing' starts at which layer?
Application (Layer 7)
Besides standardization and compatibility, the OSI model is commonly used for…
troubleshooting
In the OSI model discussion, the user is imagined to be at 'layer 8'.
True
Data encapsulation is compared to putting a letter inside…
an envelope (header/trailer)
Encapsulation happens when information travels…
down the stack (7 → 1), adding headers
Decapsulation happens when information travels…
up the stack (1 → 7), removing headers
What is the PDU for Layers 5, 6 and 7?
Data
Which layer is called the 'visual layer' and is closest to the user?
Application (Layer 7)
The Application Layer IS the application itself (e.g., Chrome).
False
HTTP/HTTPS, Telnet/SSH, FTP/TFTP, DHCP/DNS, POP3/IMAP/SMTP, SNMP/LDAP live at which layer?
Application (Layer 7)
Telnet & SSH are Layer 7 protocols used for…
Remote access
FTP & TFTP are used for…
File sharing
SNMP & LDAP are used for…
Host/Network management
POP3, IMAP & SMTP are used for…
Email
DHCP & DNS are categorized as…
Networking support
At which layer does raw user data begin transmission — not yet encoded or encapsulated?
Application (Layer 7)
Which layer reformats data so one system's application layer can read another's (think .jpeg, .docx, .exe)?
Presentation (Layer 6)
Data compression, coding (ASCII, EBCDIC, UTF-8), and encryption/decryption are duties of…
Presentation (Layer 6)
Encryption is PRIMARILY done at which layer?
Layer 6 — Presentation
TLS/SSL security protocols are listed at which OSI layer?
Presentation (Layer 6)
ASCII and JPEG are listed as services of which layer?
Presentation (Layer 6)
'Save as…' is the analogy for data entering which layer?
Presentation (Layer 6)
Which layer controls connections between computers and establishes request/response communication?
Session (Layer 5)
Which is the first layer discussed that uses a client/server concept?
Session (Layer 5)
Check-pointing, suspending, restarting, and terminating sessions is the job of…
Session (Layer 5)
Layer 5 is said to have a 'semi-permanent ____'.
dialogue
Authentication and Authorization are listed as services of which layer?
Session (Layer 5)
What gets tagged to the data at the Session Layer?
A Session ID
Which layer manages reliability and quality of traffic?
Transport (Layer 4)
What is Layer 4's PDU?
Segment
Splitting a too-large Layer 4 segment into pieces, reassembled in order at the destination, is called…
Segmentation
Flow control & congestion avoidance and security functionalities like firewalls are Layer ___ duties.
4 (Transport)
Which hardware is listed at Layer 4?
Firewalls
TCP and UDP are protocols of which layer?
Transport (Layer 4)
Which layer transfers packets from source to destination via one or more networks?
Network (Layer 3)
What is Layer 3's PDU?
Packet
Forwarding/routing packets, IP addressing, and fragmentation are duties of…
Network (Layer 3)
Fragmentation is the Layer 3 version of which Layer 4 process?
Segmentation
Which hardware operates at Layer 3?
Routers
IPv4/IPv6, ICMP, IGMP, IPSec and NAT are protocols at which layer?
Network (Layer 3)
Which layer transfers data between ADJACENT network nodes in a WAN or on the same LAN segment?
Data Link (Layer 2)
What is Layer 2's PDU?
Frame
Detecting (and sometimes correcting) Layer 1 errors is the responsibility of…
Data Link (Layer 2)
Which hardware operates at Layer 2?
NICs and Switches
IEEE 802.3 is…
Ethernet
IEEE 802.11 is…
Wi-Fi
Which group are listed as Layer 2 WAN protocols?
HDLC / Frame Relay / MPLS / PPP
ARP and MAC addresses are listed at which layer?
Data Link (Layer 2)
Which copper cable is 'old, reliable over short distances'?
Coaxial
Which twisted-pair has a shielded jacket for infrastructure use?
STP
100BASE-T and 1000BASE-T both support up to what distance?
100 m
40GBASE-T supports up to…
30 m on STP, full duplex only
Which Ethernet standards are FULL DUPLEX ONLY and STP?
10GBASE-T and 40GBASE-T
PoE provides what over Ethernet?
DC power
Which fiber type has ONE transmission path — expensive, faster, further?
Single-mode
Which fiber type has multiple paths — cheap, slower, shorter?
Multi-mode
Fiber optic cabling (per OSI deck) uses light pulses and ____ communication.
simplex
PSTN is the 'analog' phone system being replaced by…
VoIP
VoIP uses which two protocols?
RTP (delivery) and H.323 (call management)
A Layer 2 header AND trailer are added to a packet to make a…
Frame
Which layer specifies physical and electrical components and moves bits across the network?
Physical (Layer 1)
What is Layer 1's PDU?
Bit
Match: FM radio, walkie-talkie, phone call →
Simplex, Half-duplex, Full-duplex
Amplifiers, repeaters, hubs, wires/antennas are hardware of which layer?
Physical (Layer 1)
DSL is listed as a technology of which layer?
Physical (Layer 1)
Who developed the TCP/IP model?
DARPA and the DoD
The TCP/IP model predates both the global internet and the OSI model.
True
The TCP/IP model is also called…
the DoD Model or 'internet model'
How many layers does the TCP/IP model have?
4
TCP/IP 'Network Access' layer combines which OSI layers?
Physical and Data Link (1–2)
TCP/IP 'Application' layer combines which OSI layers?
Session, Presentation, Application (5–7)
OSI Network Layer 3 becomes which TCP/IP layer?
Internet
Which model is more widely used in academics?
OSI
Which model is the standard for practical use by network engineers today?
TCP/IP
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