Module 3

Question 1

Why should you study Protocols & Models (Module 3)?

Answer 1

Devices interoperate by following protocols; models (OSI/TCP/IP) show where rules live and how data flows end to end.

Question 2

What are the three elements present in any communication?

Answer 2

Message source (sender), message destination (receiver), and channel (the medium/path).

Question 3

Define a protocol in networking.

Answer 3

An agreed set of rules/format/timing that devices use to exchange messages over a medium.

Question 4

List five common requirements network protocols define.

Answer 4

Encoding, formatting/encapsulation, size (MTU), timing (flow/timeout/access), delivery options.

Question 5

What is encoding vs decoding?

Answer 5

Encoding converts information into signals/bits for transmission; decoding reverses it at the receiver.

Question 6

What is message encapsulation?

Answer 6

Placing data inside protocol headers/trailers (e.g., HTTP→TCP→IP→Ethernet) so each layer can process it.

Question 7

Why limit message size?

Answer 7

Receivers process smaller units; networks have MTUs; fragmentation adds overhead and loss impact.

Question 8

Name the three timing concepts in communications.

Answer 8

Flow control, response timeout, and access method (who talks when).

Question 9

Give examples of delivery options.

Answer 9

Unicast (1→1), multicast (1→many subscribers), broadcast (1→all in a broadcast domain).

Question 10

What do protocols implement on devices (SW/HW)?

Answer 10

Specific functions and formats for addressing, reliability, flow control, error detection, routing, and app interfaces.

Question 11

In a web fetch, map four key protocols in order.

Answer 11

HTTP (app) → TCP (reliability) → IP (routing) → Ethernet/WLAN (local delivery).

Question 12

What function does TCP provide in that stack?

Answer 12

Reliable, ordered delivery with sequencing, acknowledgments, and flow control (windowing).

Question 13

What function does IP provide?

Answer 13

Logical addressing and routing across networks; routers forward based on destination IP.

Question 14

What does Ethernet/WLAN provide?

Answer 14

Data link framing and local (hop-by-hop) delivery between NICs over the physical medium.

Question 15

What is a protocol suite?

Answer 15

A group of interrelated protocols designed to work together (e.g., TCP/IP).

Question 16

Why visualize suites as a stack?

Answer 16

Each higher layer depends on services of lower layers; separates content from delivery mechanics.

Question 17

Name two historical suites largely replaced by TCP/IP.

Answer 17

AppleTalk and Novell IPX/SPX (supplanted by TCP/IP).

Question 18

List TCP/IP layers top to bottom.

Answer 18

Application, Transport, Internet, Network Access.

Question 19

Give two examples of Application-layer protocols.

Answer 19

HTTP/HTTPS, DNS (also DHCPv4/v6, SMTP/IMAP/POP3, FTP/SFTP/TFTP, REST).

Question 20

What are the two Transport protocols and their styles?

Answer 20

TCP (connection-oriented, reliable) and UDP (connectionless, best-effort).

Question 21

Name three Internet-layer protocols.

Answer 21

IPv4/IPv6, ICMPv4/ICMPv6, NAT (plus routing protocols like OSPF/EIGRP/BGP).

Question 22

Give two Network Access layer items.

Answer 22

Ethernet/WLAN (data link) and ARP (address resolution).

Question 23

What makes TCP/IP “open” and “standards-based”?

Answer 23

Defined in IETF RFCs, publicly available; multi-vendor interoperability.

Question 24

List the seven OSI layers top to bottom.

Answer 24

Application, Presentation, Session, Transport, Network, Data Link, Physical.

Question 25

Map OSI to TCP/IP (high level).

Answer 25

OSI 5–7 ≈ TCP/IP Application; OSI 4 ↔ Transport; OSI 3 ↔ Internet; OSI 1–2 ↔ Network Access.

Question 26

One benefit of using layered models.

Answer 26

Modularity—changes in one layer don’t break others; clear interfaces; common language.

Question 27

Who steers internet standards and RFCs?

Answer 27

ISOC/IAB oversee; IETF develops/maintains TCP/IP; IRTF handles long-term research.

Question 28

Who coordinates domains IPs, and ports?

Answer 28

ICANN (policy) and IANA (assignments of IP blocks, DNS roots, TCP/UDP port numbers).

Question 29

Name two electronic/communications standards bodies.

Answer 29

IEEE (802.3 Ethernet, 802.11 WLAN) and TIA/EIA; also ITU-T for telecom/broadband/video.

Question 30

Define segmentation and its two benefits.

Answer 30

Splitting data into smaller pieces; enables multiplexing (many flows share links) and efficient retransmission of only lost parts.

Question 31

What is sequencing and who handles it?

Answer 31

Numbering segments so the receiver reorders data; provided by TCP.

Question 32

Name the PDU at each layer (TCP/IP terms).

Answer 32

Application: Data; Transport: Segment (TCP)/Datagram (UDP); Internet: Packet; Data Link: Frame; Physical: Bits.

Question 33

Describe encapsulation order for a web page sent.

Answer 33

App data + HTTP → TCP segment → IP packet → Ethernet/WLAN frame → bits on the wire.

Question 34

Describe de-encapsulation at the receiver.

Answer 34

Bits → Frame (L2) → Packet (IP) → Segment (TCP) → Data (HTTP) → App.

Question 35

Differentiate L3 vs L2 addresses purpose.

Answer 35

L3 IP: end-to-end delivery across networks; L2 MAC: hop-to-hop delivery between NICs on the same link.

Question 36

Do IP source/destination addresses change hop by hop?

Answer 36

No—IP src/dst remain end-to-end; routers rewrite only L2 headers per hop.

Question 37

Do MAC addresses change hop by hop?

Answer 37

Yes—each hop uses the sender NIC’s MAC as source and next hop’s MAC as destination.

Question 38

Same LAN communication: which MAC is the L2 destination?

Answer 38

The target host’s MAC (direct delivery within the broadcast domain).

Question 39

Different LANs: which MAC is the first-hop L2 destination?

Answer 39

The default gateway’s MAC (router interface on the local network).

Question 40

Why must hosts have a default gateway configured?

Answer 40

So packets to remote networks can be sent to a router for forwarding.

Question 41

What is multicast used for?

Answer 41

Efficient one-to-many delivery to subscribed receivers (e.g., streaming, routing updates) without broadcasting to all.

Question 42

Give one example each: broadcast and unicast on Ethernet.

Answer 42

Broadcast: ARP Request, DHCP Discover; Unicast: SSH to a switch SVI.

Question 43

Which protocol resolves IPv4 L3→L2 on Ethernet?

Answer 43

ARP maps IP addresses to MAC addresses within a LAN.

Question 44

What does ICMP provide?

Answer 44

Messaging for errors and diagnostics (e.g., ping/echo, time exceeded).

Question 45

Name two application setup protocols used before HTTP.

Answer 45

DNS (name resolution) and DHCP (address assignment) or SLAAC/DHCPv6 in IPv6.

Question 46

Why do open standards matter for home gear?

Answer 46

Interoperability—different vendors’ devices (e.g., router + client) work using common protocols like 802.11, IPv4/6, DHCP.

Question 47

Access method example on Wi-Fi and why it exists.

Answer 47

CSMA/CA—stations check channel and back off to reduce collisions on shared wireless media.

Question 48

What is NAT’s high-level purpose?

Answer 48

Translate private/internal addresses to public addresses for internet access; conserves IPv4 and adds a basic boundary.

Question 49

What happens if a frame exceeds MTU on a link?

Answer 49

It must be fragmented (if allowed) or dropped; fragmentation adds overhead and can reduce performance.

Question 50

Summarize the end-to-end flow for a web request.

Answer 50

Client encodes/encapsulates HTTP→TCP→IP→L2; hops rewrite L2 only; server de-encapsulates up the stack; responses follow the reverse path.