Part 1 — Difference between TCP and UDP

Parameter	TCP	UDP
Nature	Connection-oriented (3-way handshake)	Connectionless
Reliability	Reliable — ACK, retransmission, sequencing	Unreliable best-effort
Ordering	Yes, via sequence numbers	No
Flow control	Sliding window (rwnd)	None
Congestion control	Slow start, congestion avoidance, fast recovery	None
Header	20–60 bytes	Fixed 8 bytes
Data unit	Byte-stream segment (no message boundaries)	Datagram (preserves message boundaries)
Multiplexing	Port numbers	Port numbers
Overhead / speed	Higher overhead, slower	Lightweight, faster
Use cases	HTTP, FTP, e-mail, file transfer	DNS, DHCP, VoIP, streaming, gaming

Part 2 — Socket addresses for the given communication

Given:

• Client IP $= 122.45.12.7$, ephemeral port $= 51000$
• Server IP $= 200.112.45.90$, well-known port $= 161$

Concept: a socket address = (IP address, port number) pair. The port selects the process on a host, while the IP selects the host itself. A TCP/UDP connection (or datagram exchange) is identified by the pair of socket addresses — source and destination.

Step 1 — Server (destination) socket:

$$\text{Server socket} = (200.112.45.90,\ 161)$$

Step 2 — Client (source) socket: the client uses its own IP with an ephemeral (temporarily assigned) port chosen above 49151.

$$\text{Client socket} = (122.45.12.7,\ 51000)$$

Step 3 — The pair of socket addresses:

$$\boxed{(\text{Client: } 122.45.12.7:51000) \quad \longleftrightarrow \quad (\text{Server: } 200.112.45.90:161)}$$

• Destination socket = (200.112.45.90, 161) — the well-known port 161 (SNMP's standard port) identifies the server process.
• Source socket = (122.45.12.7, 51000) — the ephemeral port 51000 identifies the client process and lets the server's reply be demultiplexed back to it.
• Traffic from client to server is addressed to 200.112.45.90:161 with source 122.45.12.7:51000; the response simply reverses these two addresses.

Final answer: socket addresses = (122.45.12.7, 51000) and (200.112.45.90, 161), i.e. 122.45.12.7:51000 ↔ 200.112.45.90:161.