Network Interface Card (NIC); Switching Techniques; Multiplexing

Network Interface Card (NIC)

What is a NIC?

A Network Interface Card (NIC) is the circuit board used to connect computers to the network.

• In most cases, this is an Ethernet card plugged into a computer's motherboard.
• Also called: Network Adapter, Network Card, LAN Card.

Functions of NIC

1. Converts data from computer format to network signal format (and vice versa)

Controls data flow between computer and network 3. Contains MAC address burned into ROM 4. Provides physical connection (RJ-45 port, SFP slot, Wi-Fi antenna)

Types of NIC

Switching Techniques

What is Switching?

Switching is the process of forwarding data from source to destination through intermediate devices in a network.

Types of Switching

7.1 Circuit Switching

A dedicated physical path is established between sender and receiver before data transmission.

A ----dedicated path established---- B
       (path held until call ends)

Process:

1. Call Setup — establish dedicated circuit
2. Data Transfer — data flows through fixed circuit
3. Circuit Teardown — release the circuit

Characteristics:

7.2 Packet Switching

Data is divided into packets; each packet travels independently through the network.

Data --> [Packet 1] --> [Packet 2] --> [Packet 3]
Each packet can take different routes and arrives at destination
Packets reassembled at destination

Sub-types:

Characteristics:

7.3 Message Switching (Store-and-Forward)

Entire message is stored at each intermediate node, then forwarded.

A --> Node 1 (stores message) --> Node 2 (stores message) --> B

• Old method; not used much today
• Example: Email systems (historically)

Circuit Switching vs Packet Switching Comparison

Multiplexing

What is Multiplexing?

Multiplexing is the technique of combining multiple signals (from multiple sources) into one signal for transmission over a shared medium.

Source 1 ─┐
Source 2 ─┤──> MULTIPLEXER ──>[single channel]──> DEMULTIPLEXER ──> Source 1
Source 3 ─┤                                                     ──> Source 2
Source 4 ─┘                                                     ──> Source 3
                                                                 ──> Source 4

Types of Multiplexing

8.1 FDM — Frequency Division Multiplexing

• Different signals assigned different frequency bands on the same medium.
• Signals transmitted simultaneously in their respective frequency bands.
• Used for: AM/FM radio, cable TV, telephone.

Frequency band:  [Signal 1 | Signal 2 | Signal 3 | Signal 4]
                  100-110Hz  110-120Hz  120-130Hz  130-140Hz

8.2 TDM — Time Division Multiplexing

• Each signal gets a time slot in a repeating cycle.
• Signals take turns using the full bandwidth.

Time:   |Slot1|Slot2|Slot3|Slot4|Slot1|Slot2|...
Signal: | S1  | S2  | S3  | S4  | S1  | S2  |...

Types of TDM:

• Synchronous TDM — fixed time slots (even if no data to send, slot is wasted)
• Asynchronous TDM (Statistical TDM) — slots allocated only when data is available (efficient)

8.3 WDM — Wavelength Division Multiplexing

• Used in fiber optic networks.
• Different signals carried on different wavelengths of light.
• DWDM (Dense WDM) — many closely spaced wavelengths; very high capacity.

8.4 CDM — Code Division Multiplexing (CDMA)

• Each signal uses a unique code to spread over the entire frequency band.
• All signals transmitted simultaneously on the same frequency.
• Used in 3G mobile networks, GPS.