MAC Sublayer (Fast Ethernet)

 When Ethernet speed increased from 10 Mbps to 100 Mbps (Fast Ethernet), they
didn’t change the MAC sublayer.
(This part controls how devices access the network.)
 But one change was made:
They stopped using bus topology (one shared cable) and only kept star topology (all
devices connect to a central device).

⭐ Two types of star setups:

1. Half-Duplex:
o Devices are connected using a hub (basic central device).
o Only one device can send at a time.
o Uses CSMA/CD to avoid collisions.
2. Full-Duplex:
o Devices connect to a switch with memory buffers.
o Both sides can send and receive at the same time.
o No need for CSMA/CD because there's no collision.
o But CSMA/CD is still included for backward compatibility with older Ethernet.

🔄 Autonegotiation

This is a smart feature in Fast Ethernet.

It allows two connected devices (like a computer and a hub/switch) to agree on automatically:

 The speed (10 Mbps or 100 Mbps)

 The mode (half-duplex or full-duplex)

📌 Why is autonegotiation useful?

 Helps different types of devices work together.

 Allows devices with multiple speeds/modes to adjust automatically.
 Helps a computer know what a hub/switch can do.

⚙️Implementation (How it is physically set up)

Fast Ethernet can be built in two main ways, depending on the type of cable:
1. Two-Wire Systems

 Use 2 pairs of wires.

 Cables used:
o 100Base-TX → Shielded Twisted Pair (STP)
o 100Base-FX → Fiber Optic Cable

2. Four-Wire System

 Uses 4 pairs of wires

 Cable used:
o 100Base-T4 → Unshielded Twisted Pair (UTP)

🧾 Simple Summary Table:

Implementation Cable Type Wires Used Name

100Base-TX STP (shielded) 2 pairs Fast Ethernet
100Base-FX Fiber optic 2 fibers Fast Ethernet
100Base-T4 UTP (unshielded) 4 pairs Fast Ethernet

Let me know if you'd like a simple diagram or visual to go along with this!

4o

A local area network (LAN) is a small network that connects computers within a short area—
like inside a building or a school campus.

At first, LANs were used only inside an organization to share files, printers, and other resources.
But nowadays, most LANs are also connected to bigger networks like the Internet or a Wide
Area Network (WAN).

Over time, many technologies were used to build LANs—like Ethernet, Token Ring, Token
Bus, FDDI, and ATM LAN.

But among all these, Ethernet became the most popular and widely used LAN technology
because it's simple, fast, and low-cost.

FDDI (Fiber Distributed Data Interface)

 FDDI is a type of high-speed network technology used in LANs.

 It was mostly used in the 1980s and 1990s for big companies and campuses.
 FDDI uses fiber optic cables, which are faster and can cover long distances (up to 200
km).
  It provides speeds of up to 100 Mbps, which was very fast at that time.

How FDDI works:

 It uses a dual-ring system (two loops of cables), so if one ring fails, the other keeps the
network running. This makes it very reliable

IEEE Standards Frame Format Addressing Ethernet Evolution Standard Ethernet Fast Ethernet Gigabit
Ethernet Ten-Gigabit Ethernet in easy wording explain

ChatGPT said:

Sure! Here's a simple explanation of the IEEE Standards, Frame Format, Addressing, and the evolution
of Ethernet (Standard, Fast, Gigabit, Ten-Gigabit Ethernet):

1. IEEE Standards (for Ethernet)

 IEEE (Institute of Electrical and Electronics Engineers) sets the rules for how networks should
work.
 For Ethernet, the standard is called IEEE 802.3.
 This standard defines how data is sent over cables and how devices communicate on a network.

2. Frame Format (Ethernet Frame)

 Data is sent in small chunks called frames.

 An Ethernet frame has parts like:
o Preamble: Tells the receiver that data is coming.
o Destination Address: The address of the device that will receive the data.
o Source Address: The address of the sender.
o Data: The actual message or file being sent.
o CRC (error checking): Helps check if the data was received correctly.

3. Addressing

 Every device in a network has a unique MAC address (Media Access Control).
 It’s a 48-bit number, usually written like this: 00:1A:2B:3C:4D:5E.
 Ethernet uses MAC addresses to know where to send data.
4. Evolution of Ethernet (Speed & Use)

Type Speed Cables Used Use

Standard
10 Mbps Coaxial or Twisted Pair Older networks, slow speed
Ethernet

Common in offices and homes

Fast Ethernet 100 Mbps Twisted Pair (Cat5)
(older)

1000 Mbps (1 Very common in modern

Gigabit Ethernet Twisted Pair (Cat5e/Cat6)
Gbps) networks

10-Gigabit 10,000 Mbps (10 Fiber optic or high-quality Used in data centers and large
Ethernet Gbps) Cat6a/Cat7 networks

In Summary (Simple Words):

 IEEE 802.3: The rulebook for Ethernet.

 Frame: Like a digital envelope that carries data.
 MAC Address: The name tag of each device.
 Ethernet Evolution:
o Started slow (10 Mbps),
o Then became faster (10
?0 Mbps),
o
ow it’s super fast (1 Gbps, 10 Gbps+).

Why is SFD important?

 Without the SFD, the receiver wouldn’t know where the data begins.
 It helps computers read and understand the frame properly.

What does it do?

 The SFD tells the receiving computer:

👉 "Hey! The actual data is starting now."
 It marks the start of the real Ethernet frame.

1. Unicast Addressing – One to One

 Unicast means sending data from one device to one specific device.
 It's like sending a private message to one friend.
💻 ➡️
(Sender → One Receiver)

Example:

 Your computer sends a file to one specific printer.

 Your phone connects to one specific website server.

✅ Used in normal communication between devices.

2. Multicast Addressing – One to Many (Selected Group)

 Multicast means sending data from one device to a group of devices, but not everyone
on the network.
 It's like sending a message to a WhatsApp group—only group members get it.

💻 ➡️💻💻
(Sender → A group of Receivers)

Example:

 A video conference system sends a live stream to several users in a meeting.

The broadcast destination address is a special case of the multicast address

in which all bits are 1s.

The least significant bit of the first byte defines the type of address.
If the bit is 0, the address is unicast; otherwise, it is multicast.

Standard Ethernet (Old Version - 10 Mbps)

 The first version of Ethernet worked at 10 megabits per second (Mbps).

 It’s mostly outdated now, but it's important to learn it to understand newer types like Fast
Ethernet, Gigabit Ethernet, and 10-Gigabit Ethernet.

🧠 Access Method: CSMA/CD (Carrier Sense Multiple Access with

Collision Detection)

🧭 What is it?

 It’s a smart way for computers to take turns using the same network cable.
  Before sending data, each computer "listens" to check if the cable is free.

🚦 How It Works (Step-by-Step):

1. Carrier Sense:
👉 The computer checks if anyone else is already using the cable.
2. Multiple Access:
👉 Many computers share the same cable.
3. Collision Detection (CD):
👉 If two computers send data at the same time by mistake, they detect the collision, stop, and
try again later.

🔄 Example of a Collision (Simple View):

 Computer A starts sending data.

 Computer B doesn't hear A's signal yet (due to a delay), so it also sends data.
 Their signals crash into each other (this is a collision).
 Both A and B stop sending and try again after waiting a random time.

🕓 Why Collisions Happen?

 Because of signal travel time (called propagation delay).

 Even though a computer checks the cable before sending, the signal from another computer
might still be traveling, so it doesn't know the cable is actually busy.

📊 Key Diagram (Figure 3.7):

 Shows how A and B's signals collide in the middle of the cable.
 Also shows how C tries to send but is affected by the collision too.

💡 Main Point:

 CSMA/CD helps reduce collisions, but it can’t stop them completely.

 When a collision is detected, computers stop sending and try again later.
 This method was used in Standard Ethernet (10 Mbps).

Implementations of wires ?

🧑‍💻 1. Standard Ethernet (10 Mbps)

  Speed: 10 Megabits per second (Mbps)
 Cabling: Coaxial cable (old) or twisted pair (like phone wire)
 Uses: Early local area networks (LANs)
 Access Method: CSMA/CD (listens before sending to avoid collisions)
 Frame Size: Minimum 64 bytes

🟢 Slowest among the three, but it was enough for basic file sharing and internet back then.

⚡ 2. Fast Ethernet (100 Mbps)

 Speed: 100 Mbps (10x faster than Standard Ethernet)

 Cabling: Twisted pair (Cat 5) or fiber optic
 Popular Type: 100BASE-TX (uses two wire pairs)
 Still uses CSMA/CD if running in half-duplex mode

🟡 Much faster, better for offices needing more speed for file transfers, printing, or streaming.

🚀 3. Gigabit Ethernet (1000 Mbps or 1 Gbps)

 Speed: 1 Gigabit per second (1000 Mbps)

 Cabling: Twisted pair (Cat 5e, Cat 6) or fiber optic
 Popular Type: 1000BASE-T (works over standard Ethernet cables)
 Usually runs in full-duplex (no CSMA/CD needed)

🔵 Very fast, great for modern networks with heavy data use like video calls, gaming, cloud
access.

Wireless communication is growing very fast. More and more people want to connect their
devices without using wires or cables.

You can now find wireless networks (Wi-Fi) in many places like:

 Colleges
 Offices
 Public areas like cafes and airports.

In this section, we will talk about two types of wireless technologies used in local area networks
(LANs):

1. Wi-Fi (IEEE 802.11) – also called wireless Ethernet. It's used for larger areas like
homes, schools, and businesses.
 2. Bluetooth – used for short distances, like connecting your phone to wireless headphones
or speakers.

IEEE 802.11 MAC Sublayer Addressing Mechanism (Wi-Fi)

 IEEE 802.11 is the technical name for Wi-Fi.

 The MAC sublayer (Media Access Control) is a part of the network that helps devices
send and receive data.
 Each Wi-Fi device has a unique address called a MAC address.
 A MAC address is a 12-digit (or 48-bit) unique number that identifies a device on the
network (like your phone or laptop).

🧠 Example: A MAC address looks like this: 3A:F4:12:9C:55:AB

📬 Just like your home has a unique address, each device has a MAC address so the network
knows where to send the data.

Wire less addressing

🔗 Bluetooth Addressing

 Bluetooth also uses its own version of a MAC address.

 It's called a BD_ADDR (Bluetooth Device Address).
 It is also a 48-bit unique number that helps Bluetooth devices recognize and connect to
each other.

🧠 Example: Just like Wi-Fi, each Bluetooth device (like your earbuds or smartwatch) has its own
unique address.

🧾 Easy Summary:

Feature Wi-Fi (IEEE 802.11) Bluetooth

Address name MAC address BD_ADDR
Address size 48 bits (12-digit hex number) 48 bits
Purpose Identify devices on a Wi-Fi network Identify Bluetooth devices
Example use Laptop connecting to router Phone connecting to earbuds

Bluetooth Network Types

1. Piconet (Small Network)

  A piconet is a small Bluetooth network.
 It has up to 8 devices:
o 1 primary device (the “boss”)
o 7 secondary devices (the “workers”)

 Secondary devices (like wireless headphones or keyboards) follow the timing and signals of
the main (primary) device (like your phone or laptop).

 The primary device controls when and how the secondaries talk or send data.

 You can also have up to 8 extra devices in a “parked” mode:

 These parked devices are connected and synced but are not actively sending or
receiving data.
 To activate a parked device, one active device must be parked first — because only 8
devices can be active at a time.

2. Scatternet (Network of Piconets)

 A scatternet is formed when multiple piconets connect together.

 A device can be a secondary in one piconet and primary in another.
 This device acts as a bridge, passing messages between the two piconets.
 This way, devices can belong to more than one piconet, enabling larger Bluetooth
networks.

Point-to-Point WANs (Wide Area Networks)

 What is it?
A point-to-point WAN connects two distant devices using a direct line, often provided by
telephone companies.

56K Modems

 These are traditional devices that let you connect to the Internet over regular phone lines.
 Uploading data (sending data from you to the Internet): limited to about 33.6 kbps
because the signal needs to be converted (sampled) to digital.
 Downloading data (receiving data from the Internet): can be up to 56 kbps because no
sampling is needed.
 The 56 kbps speed comes from how phone lines handle voice signals (8,000 samples/sec
× 7 bits per sample = 56,000 bps).
DSL Technology (Digital Subscriber Line)

 DSL uses regular telephone lines but is much faster than modems.
 xDSL stands for a group of DSL types like ADSL, SDSL, HDSL, and VDSL.

ADSL (Asymmetric DSL)

 Designed mainly for home users.

 Asymmetric means download speeds (Internet → you) are faster than upload speeds
(you → Internet).
 The line is divided into different channels:
o Channel 0: For voice calls.
o Channels 1-5: Unused to separate voice and data.
o Channels 6-30: For upstream data (you sending data).
o Channels 31-255: For downstream data (Internet sending data).
 You get faster downloads because most home users download more than they upload.

Other DSL Types

 SDSL (Symmetric DSL): Equal speeds for download and upload, good for businesses.
 HDSL: Used for T-1 line replacement, covers longer distances without extra equipment.
 VDSL: Very fast speeds but only works over short distances, can use fiber or coaxial
cables.

Cable Modems

 Cable companies also offer high-speed Internet by using their TV cable networks.
 Traditional cable TV was one-way (only from the cable company to your home).
 Newer HFC (Hybrid Fiber-Coaxial) networks use fiber optics partway and coaxial
cable for the last part to your home.
 The cable bandwidth is split into:
o Video band: For TV channels.
o Downstream data band: Internet data coming to your home.
o Upstream data band: Data you send back to the Internet.
 Since many users share the cable, they share bandwidth using time-sharing, meaning you
take turns sending or receiving data.

T Lines (T-1 and T-3)

 T lines are high-speed digital telephone lines.

  T-1: Data rate of 1.544 Mbps (like 24 voice channels combined).
 T-3: Much faster at 44.736 Mbps (like 28 T-1 lines combined).
 Fractional T lines let customers share part of a T line instead of using the whole thing.

SONET (Synchronous Optical Network)

 A standard for transmitting high-speed data over fiber-optic cables.

 SONET turns electrical signals into optical signals to send huge amounts of data.
 Data rates start at 51.84 Mbps and go way up, much faster than T-3 lines.

PPP (Point-to-Point Protocol)

 PPP is a protocol to manage data transfer over point-to-point links like phone lines or
cable.
 It only covers the physical and data link layers.
 PPP frames have fields for start/end flags, addresses, control info, data, and error
checking.
 It has two important control protocols:
o LCP (Link Control Protocol): Manages setting up and closing the connection.
o NCP (Network Control Protocol): Manages carrying different network layer
protocols like IP.

PPPoE (PPP over Ethernet)

 Designed for situations where many users share one physical Internet connection over
Ethernet, like DSL or cable.
 PPPoE finds the user's Ethernet address, then starts a PPP session, allowing each user to
connect individually to the Internet.

Here is a simplified explanation of Switched WANs and related technologies in easy wording
for better understanding:

3.4 Switched WANs (Wide Area Networks)

🔹 What is a Switched WAN?

 A switched WAN is a large network that connects many users across big areas (like a
country).
  It uses switches (devices with many input/output ports) to connect users.
 Inside the network, there's a mesh of point-to-point connections between the switches.

🌐 Switched WAN vs. LAN

Feature LAN Switched WAN

Topology Star topology Mesh with switches
Connection Type Connectionless (no setup needed) Connection-oriented (setup needed)
Addressing Uses source and destination Uses connection ID (label)

🔸 X.25

 Introduced in 1970s.
 First popular switched WAN used to connect computers.
 Worked at 3 layers (including network layer), which caused issues with IP packets
(which already work at network layer).
 Example: Like putting a car inside a truck to move it — inefficient.
 Too much error checking because media were unreliable back then → slow speed.

🔸 Frame Relay

 Made to replace X.25.

 Works at physical and data link layers only.

✅ Advantages:

1. High Speed: Supports up to 44.736 Mbps.

2. Bursty Data Support: Allows data to be sent at variable speeds (e.g., 6 Mbps for 2 sec,
then 0 Mbps).
o T-1 line = fixed rate (not suitable for bursty data).
o Frame Relay = Bandwidth on demand.
3. Less Overhead: Because today's media (like fiber optics) are more reliable, error
checking is left to upper layers.

🔸 ATM (Asynchronous Transfer Mode)

 A very high-speed switched WAN technology using cell-based data transfer.

🎯 Design Goals of ATM:

 Work efficiently with optical fiber.

 Support existing networks (like IP).
 Be low-cost and fast.
 Be connection-oriented (reliable).
 Move most tasks to hardware (speed up).

📦 ATM Cells and Multiplexing

 Uses fixed-size cells (53 bytes total → 5 bytes header + 48 bytes data).
 Why fixed-size?
o Helps in fast, predictable routing.
 Uses Asynchronous Time Division Multiplexing (TDM):
o Sends a cell only when available (no fixed timing for each channel).

🧩 ATM Architecture

 Users (endpoints) connect to ATM switches.

 Switches connect using high-speed links.
 Connections are virtual (not physical wires from start to end).

🛣️Three Types of Paths:

1. Transmission Path (TP): Physical cable/fiber between switches.

2. Virtual Path (VP): Like a highway between two switches.
3. Virtual Circuit (VC): Like a lane on the highway for one specific connection.

💡 Each connection is identified using:

 VPI (Virtual Path ID) and

 VCI (Virtual Circuit ID)
➡️Together: (VPI, VCI) = unique path for the data.

🧱 ATM Layers

1. Physical Layer:
o Deals with cables, bit signals, encoding.
o Works with T-lines and SONET.
2. ATM Layer:
 Adds 5-byte headers to 48-byte data to make 53-byte cells.
o
Manages routing, switching, multiplexing.
o
3. AAL (ATM Adaptation Layer):
o Used only at endpoints (like routers).
o Converts various data (IP, video, voice) into ATM cells.

🔹 AAL5:

 Used for carrying IP packets.

 Adds an 8-byte trailer + padding.
 Breaks data into 48-byte chunks.

💬 Summary (in Easy Words):

 Switched WANs use switches and connections that must be set up before sending data.
 X.25 was old, slow, and had too much error checking.
 Frame Relay is faster, supports variable speed data, and has less overhead.
 ATM is very fast, uses small fixed cells, and is great for voice, video, and data — all
treated equally.
 ATM uses virtual paths and virtual circuits to manage traffic efficiently

ChatGPT said:

Sure! Here's a simplified and easy-to-understand summary of Switched WANs and the technologies
X.25, Frame Relay, and ATM:

Switched WANs (Wide Area Networks) – Simplified

 Large networks covering cities or countries.

 Users connect at different points.
 Inside, there are switches connected in a web (mesh).
 These switches direct data across the network.

Switched WANs vs LANs (Local Area Networks)

Feature LAN Switched WAN

Topology Star Mesh (multiple paths via switches)

Connection Connectionless (no setup) Connection-oriented (setup first)

 Feature LAN Switched WAN

Identifiers Source/Destination addresses Connection IDs (labels)

X.25 – Old but Reliable (1970s)

 One of the first switched WAN protocols.

 Used to connect computers across distances.
 Slow because of too much error checking.
 Three-layer protocol (not ideal for IP).
 Inefficient for IP—like putting a small car in a big truck.

Frame Relay – Faster Replacement

 Came after X.25.

 Works at physical and data link layers.
 Faster: Up to 44.736 Mbps.
 Good for bursty data—sends more when needed.
 Low overhead: Assumes modern lines are reliable.
 No error checking at lower levels (done higher up).

ATM (Asynchronous Transfer Mode) – For Speed

 Made for very fast networks, like fiber optics.

 Uses small fixed-size cells (53 bytes total):
o 5 bytes = header (routing info)
o 48 bytes = actual data
 Efficient and predictable due to fixed size.
 Connection-oriented (like phone calls).
 Uses hardware (not software) for faster switching.

ATM Structure:

 End devices (e.g., routers) connect to ATM switches.

 Switches connect through high-speed lines.

Types of Paths:

 Transmission Path (TP): Physical cable/fiber

  Virtual Path (VP): Like a highway
 Virtual Circuit (VC): Like a lane on the highway
→ Identified by VPI (Path ID) and VCI (Circuit ID)

ATM Layers (from top to bottom)

1. Application Adaptation Layer (AAL)

o Converts data (IP, voice, video) into cells
o AAL5 used for IP → adds a trailer and splits into 48-byte chunks
2. ATM Layer
o Adds 5-byte header to make a full 53-byte cell
o Routes and switches the cells
3. Physical Layer
o Sends data as bits over fiber/cable
o Works with systems like SONET and T-3

✅ Summary Table

Feature X.25 Frame Relay ATM

Speed Slow Medium–High Very High

Error Checking Heavy (slow) Light Handled by higher layers

Data Unit Packets Frames Fixed-size Cells (53 bytes)

Layers Used 3 layers 2 layers 3 layers

Use Today Mostly obsolete Some legacy use Rare but used in some telco systems