 Internet Society (ISOC) - Responsible for promoting the open development and evolution of

internet use throughout the world.

 Internet Architecture Board (IAB) - Responsible for the overall management and development
of internet standards.
 Internet Engineering Task Force (IETF)- Develops, updates, and maintains internet and TCP/IP
technologies. This includes the process and documents for developing new protocols and
updating existing protocols, which are known as Request for Comments (RFC) documents.
 Internet Research Task Force (IRTF)- Focused on long-term research related to internet and
TCP/IP protocols such as Anti-Spam Research Group (ASRG), Crypto Forum Research Group
(CFRG), and Peer-to-Peer Research Group (P2PRG).
 Internet Corporation for Assigned Names and Numbers (ICANN)- Based in the United States,
ICANN coordinates IP address allocation, the management of domain names, and assignment of
other information used in TCP/IP protocols.
 Internet Assigned Numbers Authority (IANA)- Responsible for overseeing and managing IP
address allocation, domain name management, and protocol identifiers for ICANN.

Institute of Electrical and Electronics Engineers(IEEE, pronounced “I-triple-E”) -

Organization of electrical engineering and electronics dedicated to advancing technological
innovation and creating standards in a wide area of industries including power and energy,
healthcare, telecommunications, and networking. Important IEEE networking standards include
802.3 Ethernet and 802.11 WLAN standard.

 Electronic Industries Alliance (EIA) - Organization is best known for its

standards relating to electrical wiring, connectors, and the 19-inch racks used to
mount networking equipment.
 Telecommunications Industry Association (TIA) - Organization responsible
for developing communication standards in a variety of areas including radio
equipment, cellular towers, Voice over IP (VoIP) devices, satellite
communications, and more.
 International Telecommunications Union-Telecommunication
Standardization Sector (ITU-T) - One of the largest and oldest communication
standards organizations. The ITU-T defines standards for video compression,
Internet Protocol Television (IPTV), and broadband communications, such as a
digital subscriber line (DSL).

Secure Shell (SSH)

 Definition: An in-band method for securely accessing a device's CLI remotely over a network.
 Requirements:
o Active networking services on the device.
o An active interface with a configured IP address.
 Comparison: Unlike a console connection, SSH requires network connectivity.
 Cisco Support: Most Cisco IOS versions include both an SSH server and an SSH client for
establishing secure sessions.

Telnet
 Definition: An insecure, in-band method for remotely accessing a device's CLI over a network.
 Security Concern:
o No encryption – all authentication, passwords, and commands are sent in plaintext.
o Vulnerable to attacks (e.g., packet sniffing).
  Best Practice: Use SSH instead of Telnet for security.
 Cisco Support: Cisco IOS includes both a Telnet server and a Telnet client, but its use is
discouraged in real-world networks.

Physical Network Connection Overview

 Types of Connections:

o Wired: Uses cables.

o Wireless: Uses radio waves.

 Network Interface Cards (NICs):

o Ethernet NICs: For wired connections.
o WLAN NICs: For wireless connections.

 OSI Physical Layer Functions:

o Transfers data link layer frames across network media.
o Encodes and transmits bits as signals.
o Receives encoded bits on end devices or intermediary devices.

Physical Layer Characteristics

The physical layer consists of electronic circuitry, media, and connectors designed by
engineers. It includes three functional areas:
1. Physical Components – Hardware like cables, connectors, and network interfaces.
2. Encoding – Converts data into a format for transmission.
3. Signaling – Defines how bits are represented on the medium.

Key Performance Metrics:

 Bandwidth – Maximum data capacity of a medium(the amount of data that can flow from one
place to another in a given amount of time.)
 Throughput – Actual data transfer rate (the transfer of bits across the media over a given period
of time; usually lower than bandwidth).
 Latency – Time taken for data to travel between two points.
 Goodput – Usable data transfer rate after removing overhead.

Bit Representation by Media:

 Copper Cable – Electrical pulses.
 Fiber-Optic Cable – Light pulses.
 Wireless – Microwave transmissions

Network Media Types

Copper Cabling
 Advantages: Inexpensive, easy to install, low electrical resistance.
 Limitations: Distance restrictions, signal interference from EMI and crosstalk.
 Types of Copper Cabling:
o UTP (Unshielded Twisted Pair):
  Outer jacket for protection.
 Twisted pairs minimize interference.
 Color-coded insulation for identification.
o STP (Shielded Twisted Pair):
 Each pair is foil-wrapped, with an additional metallic shield.
o Coaxial Cable (Coax):
 Two conductors sharing the same axis.
 Used for antennas and cable internet connections.

UTP Cabling
 Structure: Four pairs of color-coded twisted copper wires in a plastic sheath.
 Interference Prevention:
o Cancellation – Twisting cancels out noise.
o Varying Twist Rates – Different twists per pair reduce crosstalk.
 Standards:
o Defined by TIA/EIA and IEEE.
 Common Types:
o Ethernet Straight-through – Connects different device types.
o Ethernet Crossover – Connects similar devices.
o Rollover (Cisco Proprietary) – Connects a workstation to a router console port.

Fiber-Optic Cabling
 Advantages:
o Higher bandwidth and longer distances than copper.
o Less signal attenuation.
o Immune to EMI and RFI.
 Structure:
o Made of thin, pure glass strands.
o Encodes data as light impulses.
 Uses:
o Enterprise networks, FTTH, long-haul, and submarine cable networks.
 Connectors:
o ST, SC, LC, Duplex LC.
 Patch Cords:
o SC-SC, LC-LC, ST-LC, SC-ST (multimode or single-mode).

Wireless Media
 Uses electromagnetic signals (radio/microwave frequencies).
 primary way users connect to home and enterprise networks
 Limitations:
o Coverage area – Signal range is limited.
o Interference – Affected by obstacles and electronic devices.
o Security risks – More vulnerable to unauthorized access.
o Shared medium issues – Multiple users impact performance.

 cellular and satellite out of scope(nằm ngoài phạm vi) for this module
 Types of Wireless Media:
 o Specifications
 Data to radio signal encoding
 Frequency and power of transmission
 Signal reception and decoding requirements
 Antenna design and construction
 Wireless Standards:
o Wi-Fi (IEEE 802.11) – Wireless LAN.
o Bluetooth (IEEE 802.15) – Short-range personal connections.
o WiMAX (IEEE 802.16) – Wireless broadband access.
o Zigbee (IEEE 802.15.4) – Low-power IoT applications.
 WLAN Components:
o Wireless Access Point (AP) – Connects wireless users to the network.
o Wireless NIC Adapters – Enable wireless communication on devices.

Wireless LAN
 Required Devices:

o Access Point (AP): Connects wireless devices to a wired network.

o Wireless NIC: Enables wireless communication for devices.

 WLAN Standards: Ensure compatibility and interoperability between devices.

 Benefits:
o Reduces wiring costs.
o Enhances device mobility.

 Security Considerations: Implement strict security policies to prevent unauthorized

access.

Wireless Standards
Wi-Fi (IEEE 802.11)
 Used in WLANs (Wi-Fi).
 Uses CSMA/CA to avoid collisions.
 Certified by the Wi-Fi Alliance.

Bluetooth (IEEE 802.15)

 WPAN standard for short-range communication.
 Uses device pairing.
 Range: 1–100 meters.

WiMAX (IEEE 802.16)

  Wireless broadband standard.
 Uses point-to-multipoint topology.

Zigbee (IEEE 802.15.4)

 Low-power, short-range communication.

 Used in IoT, industrial automation (e.g., smart lighting, medical devices).

The Data Link Layer

Functions of the Data Link Layer (Layer 2):
 Provides Media Access: Enables upper layers to access the network media without
concern for its type.

 Encapsulation: Receives data from Layer 3 (IPv4/IPv6) and encapsulates it into frames.
 Media Control: Manages how data is placed on and received from the physical media.
 Frame Exchange: Ensures the exchange of frames between network endpoints.
 Data Forwarding: Directs received encapsulated data to the appropriate upper-layer
protocol.
 Error Detection: Identifies and discards corrupt frames to maintain data integrity.

Definition of a Node: A node is any device that can receive, create, store, or forward data in a
network. Nodes can be categorized into:

 End devices: Laptops, mobile phones, and other user devices.

 Intermediary devices: Ethernet switches, routers, and other network infrastructure
components.

Role of the Data Link Layer: The data link layer (Layer 2) plays a critical role in network
communication by:

 Providing a connection between upper-layer protocols and the physical media.

 Encapsulating Layer 3 packets (e.g., IPv4 or IPv6) into Layer 2 frames.
 Managing data placement and reception over the network media.
 Ensuring successful transmission by adding addressing information (e.g., MAC
addresses).
 Detecting and rejecting corrupted frames to ensure data integrity.

Importance of the Data Link Layer: Without the data link layer:

 Network layer protocols such as IP would need to support all types of media directly.
 Any new network technology or medium would require modifications to IP, making it
less adaptable.

Encapsulation Process:
  The data link layer adds Ethernet destination and source NIC (Network Interface Card)
information to Layer 3 packets.
 It then converts this data into a format compatible with the physical layer (Layer 1) for
transmission over the network.

This layer ensures seamless communication between devices by standardizing data transmission
across various media types.

IEEE 802 LAN/MAN Data Link Sublayers

 IEEE 802 LAN/MAN Standards: Covers Ethernet LANs, WLANs, WPANs, and
metropolitan area networks.
 Two Sublayers:

 Logical Link Control (LLC) (IEEE 802.2):

o Connects networking software (upper layers) with device hardware (lower layers).
o Identifies the network layer protocol (IPv4, IPv6) used in the frame.
 Media Access Control (MAC) (IEEE 802.3, 802.11, 802.15):
o Responsible for data encapsulation (frame delimiting, addressing, error
detection).
o Manages media access control, enabling communication over shared or
dedicated media.

 Encapsulation & Control:

 Frame delimiting ensures synchronization.

 Addressing provides source and destination info.
 Error detection identifies transmission errors.
 Media access control regulates data transmission, mainly in half-duplex mode.

Network Packet Transmission Across Different Media

 Varied Network Environments:

 Ethernet LANs have multiple hosts contending for network access, managed by the
MAC sublayer.
 Serial links connect only two devices (e.g., routers), eliminating the need for MAC
techniques.

 Router Interface Functions:

 Encapsulates packets into appropriate frames for each link.

 Uses suitable media access control for different transmission methods.
 Transitions across multiple data link layers as packets move between networks.

 Layer 2 Functions at Each Hop:

 1. Receives a frame from a medium.
2. De-encapsulates the frame to extract the Layer 3 PDU (packet).
3. Re-encapsulates the packet into a new frame for the next link.
4. Forwards the frame to the next network segment.

Data Link Layer Standards

 Definition: Unlike upper-layer TCP/IP protocols, data link layer protocols are not defined by
RFCs.
 IETF Role: Manages TCP/IP upper-layer protocols but not network access layer functions.
 Standardization Organizations:
o IEEE – Defines Ethernet, Wi-Fi, and other network standards.
o ITU – Regulates global telecommunication standards.
o ISO – Establishes international networking standards.
o ANSI – Develops U.S. national standards for networking.

Physical and Logical Topologies

1. Definition of Topology:
o Network topology refers to the arrangement and relationships of network devices and
their interconnections.

2. Two Main Types of Topology:

o Physical Topology:
 Identifies the physical connections between end devices (e.g., computers,
servers) and intermediary devices (e.g., routers, switches, access points).
 May include specific device locations, such as room numbers and rack positions.
 Common types: Point-to-Point and Star.
o Logical Topology:
 Defines how data is transmitted between devices.
 Represents virtual connections using device interfaces and Layer 3 IP addressing
schemes.
 Influences the type of network framing and media access control (MAC) used.

3. Relation to the Data Link Layer:

o The data link layer works with the logical topology to control data access in the
network.
o The logical topology determines the framing method and media access control
techniques used for communication.

Point-to-Point WAN Topology

 Direct connection between two nodes without sharing media.

 Uses serial communication protocols like PPP for simple data transfer.
 No need for MAC addressing since frames only travel between two nodes.
 Ethernet point-to-point requires checking the destination of incoming frames.
 Indirect connections via intermediary devices do not change the logical topology.
LAN Topologies

1. Modern LAN Topologies:

o Star topology: End devices connect to a central Ethernet switch.
o Extended star: Multiple Ethernet switches interconnect to expand the network.
o Advantages: Easy installation, scalability, and troubleshooting.

2. Point-to-Point Ethernet:
o Used when only two devices are connected, such as two routers.

3. Legacy LAN Topologies:

o Bus topology: Devices are chained together and terminated at both ends, often using
coax cables.
o Ring topology: Devices connect in a closed loop without termination. Used in Token
Ring and FDDI networks.

Half and Full Duplex Communication

1. Half-Duplex:
o Devices can transmit or receive, but not simultaneously.
o Used in WLANs, legacy bus topologies, and Ethernet hubs.
o Only one device can send data at a time.

2. Full-Duplex:
o Devices can transmit and receive at the same time.
o Ethernet switches operate in full-duplex mode by default.
o More efficient than half-duplex.

3. Duplex Mismatch:
o Occurs when two connected devices use different duplex settings.
o Causes inefficiency and latency in data transmission.

Access Control Methods

1. Multiaccess Networks:
o Allow multiple devices to access the network simultaneously.
o Ethernet LANs and WLANs are examples.

2. Contention-Based Access (Half-Duplex, Competing for Media)

o CSMA/CD: Used in legacy Ethernet bus networks (detects collisions).
o CSMA/CA: Used in WLANs (avoids collisions).

3. Controlled Access (Deterministic, Waiting for Turn)

o Each node gets a dedicated time to use the medium.
o Examples: Legacy Token Ring, Legacy ARCNET (inefficient).
4. Modern Ethernet:
o Operates in full-duplex, so access control is not needed.
 DATA LINK RFAME
The Frame

 The data link layer encapsulates IPv4 or IPv6 packets with a header and a trailer to create a
frame for transmission.
 Three basic parts of a frame:
1. Header – Contains control information for processing the frame.
2. Data – The actual payload (encapsulated network layer packet).
3. Trailer – Provides error-checking and other control information.
 Different data link layer protocols have different frame structures, depending on the network
type.
 WLAN frames include additional control information for collision avoidance, making them
larger than Ethernet frames.
 In fragile environments (e.g., wireless networks), more control fields are added to ensure
reliable delivery.

Frame Fields

Purpose of Framing:

 Breaks data into structured groupings that can be recognized, transmitted, and decoded by
network nodes.
 Control information is added in headers and trailers to ensure successful transmission.

Generic Frame Fields:

1. Frame Start and Stop Indicators: Mark the beginning and end of the frame.
2. Addressing: Contains source and destination MAC addresses.
3. Type: Specifies the Layer 3 protocol (e.g., IPv4 or IPv6).
4. Control: Includes flow control mechanisms (e.g., Quality of Service (QoS) for
prioritizing VoIP traffic).
5. Data: Holds the actual payload (packet header, transport header, and data).
6. Error Detection (Trailer): Uses Cyclic Redundancy Check (CRC) in the Frame
Check Sequence (FCS) field to detect errors during transmission.

Error Detection & CRC Process:

 Before transmission, the sender calculates a CRC value (logical summary of frame contents).
 The CRC is placed in the FCS field in the trailer.
 The receiver recalculates the CRC and compares it with the received CRC.
o If they match, the frame is valid.
 o If they don’t match, the frame is corrupt and discarded.

This process ensures data integrity despite potential interference or signal distortion.

Layer 2 Addresses

 Physical (MAC) addresses are used at the Data Link Layer to transport frames within a local
network.
 The frame header contains the destination and source MAC addresses.
 MAC addresses are unique to each device and do not change when moving between networks.
 Unlike Layer 3 (IP) addresses, MAC addresses do not indicate network location.
 When an IP packet travels through multiple networks, each router replaces the Data Link layer
addresses while keeping the IP address unchanged.

Layer 2 vs. Layer 3 Addresses

 Layer 2 (MAC) addresses are only used for local delivery within the same network.
 Layer 3 (IP) addresses remain unchanged and help route data across multiple networks.
 A router is required to move data between networks:
o It receives a frame using the MAC address.
o It removes the frame to check the IP address.
o It determines the best path and creates a new frame to send the packet to the next
network segment.

LAN and WAN Frames

LAN (Local Area Network) vs. WAN (Wide Area Network)

1. Ethernet Protocols for LANs:

o Wired LANs: Use Ethernet protocols.
o Wireless LANs (WLANs): Use IEEE 802.11 protocols designed for multiaccess
networks.
2. WAN Protocols:
o Used for point-to-point, hub-spoke, and full-mesh topologies.
o Common WAN protocols included:
 Point-to-Point Protocol (PPP)
 High-Level Data Link Control (HDLC)
 Frame Relay
 Asynchronous Transfer Mode (ATM)
 X.25
o Transition: These are being replaced by Ethernet in WANs.
3. Layer 2 and Layer 3 Interaction:
o In a TCP/IP network, all OSI Layer 2 protocols work with IP at OSI Layer 3.
o The choice of Layer 2 protocol depends on the logical topology and physical
media.
4. Media Access Control:
 o Each protocol manages media access for specified Layer 2 topologies.
o Network devices at the data link layer include NICs on computers, routers, and
Layer 2 switches.
5. Technology and Network Topology:
o The choice of Layer 2 protocol is determined by the network technology.
o The technology is chosen based on network size, geographic scope, and required
services.

LAN Specifics:

 High Bandwidth: LANs use high bandwidth technologies for supporting large numbers
of hosts.
 Geographic Scope: Suitable for small areas (e.g., single building or campus).
 Cost-Effective: High user density makes high bandwidth technology cost-effective.

WAN Specifics:

 Cost Considerations: High bandwidth is usually not cost-effective for large geographic
areas (e.g., cities).
 Lower Bandwidth Capacity: Due to the cost of long-distance links and signal
transmission technologies.

Data Link Layer Protocols:

 Ethernet
 802.11 Wireless
 Point-to-Point Protocol (PPP)
 High-Level Data Link Control (HDLC)
 Frame Relay