Communication Principles Notes

Communication Protocols

  • Communication occurs in various forms and environments in daily life.
  • Expectations vary depending on the communication method (e.g., internet chat vs. job interview).
  • Each situation has expected behaviors and styles.
  • Before communicating, rules or agreements are established:
    • What method of communication should be used?
    • What language should be used?
    • Is confirmation of message receipt needed?

Why Protocols Matter

  • Computers use protocols to communicate, similar to humans.
  • Protocols are essential for correct communication across networks.
  • Local networks require all hosts to use a common protocol to communicate.
  • Networking protocols define aspects of network communication.

Protocol Characteristics

  • Message format: A specific structure is used for a sent message, depending on the message type and channel.
  • Message size: Rules govern the size of pieces communicated across the network. Long messages are broken into smaller pieces for reliable delivery.
  • Timing: Affects the speed of bit transmission and the timing of data sending and the total data sent in a transmission.
  • Encoding: Messages are converted into bits by the sending host, encoded into patterns (sounds, light waves, or electrical impulses), and decoded by the destination host.
  • Encapsulation: Each message includes a header with addressing information (source and destination) to ensure delivery to the correct application on the destination host.
  • Message pattern: Some messages require acknowledgment before the next message is sent (request/response). Other messages may be streamed without confirmation.

Communication Standards

  • Internet standards manage changes and reliably deliver services (e.g., email).
  • A standard is a set of rules for how something must be done.
  • Networking and internet standards ensure uniform implementation of rules or protocols.
  • Different devices use standards to send information over the internet.

Network Standards Organizations

  • Internet standards are developed through discussion, problem-solving, and testing.
  • Various organizations develop, publish, and maintain these standards.
  • The development and approval process of a proposed standard are recorded in a numbered RFC (Request for Comments) document.
  • The IETF (Internet Engineering Task Force) publishes and manages RFCs for internet standards.

Network Communication Models

The TCP/IP Model

  • Layered models visualize how protocols work together for network communications.
  • Layered models depict protocol operations within each layer and interactions between layers.
  • Benefits of layered models:
    • Assists protocol design by defining information and interfaces for each layer.
    • Fosters competition by enabling products from different vendors to work together.
    • Enables technology changes at one layer without affecting others.
    • Provides a common language for describing networking functions.
  • The first layered model was created in the early 1970s and was referred to as the internet model.
  • It defines four categories of functions for successful communication.

TCP/IP Model Layers and Descriptions

  • Application: Represents data to the user, including encoding and dialog control.
  • Transport: Supports communication between devices across diverse networks.
  • Internet: Determines the best path through the network.
  • Network Access: Controls the hardware devices and media that make up the network.
  • The TCP/IP model is a protocol model because it describes the functions at each layer of protocols within the TCP/IP suite.

The OSI Reference Model

  • Two basic types of models exist for network communication functions:

    • Protocol model: Closely matches a particular protocol suite (e.g., TCP/IP model).
    • Reference model: Describes functions to be completed at each layer but doesn't specify how (e.g., OSI model).

  • The OSI (Open Systems Interconnection) project created the most widely known internetwork reference model.

  • It is used for data network design, operation specifications, and troubleshooting.

  • This model refers to the OSI model.

OSI Model Layers and Descriptions

  • 7 - Application: Protocols for process-to-process communications.
  • 6 - Presentation: Provides a typical representation of data transferred between application layer services.
  • 5 - Session: Services to organize dialogue and manage data exchange.
  • 4 - Transport: Services to segment, transfer, and reassemble data for communications between end devices.
  • 3 - Network: Services to exchange individual data over the network between identified end devices.
  • 2 - Data Link: Protocols describe methods for exchanging data frames between devices over shared media.
  • 1 - Physical: Protocols describe the mechanical, electrical, functional, and procedural means to activate, maintain, and de-activate physical connections for bit transmission.

OSI Model and TCP/IP Model Comparison

  • The TCP/IP model visualizes interactions of protocols within the TCP/IP suite.
  • It describes networking functions specific to TCP/IP protocols.
  • Protocols in the TCP/IP suite are described in terms of the OSI reference model.
  • Functions at the internet layer in TCP/IP are in the network layer of the OSI model.
  • Transport layer functionality is the same in both models.
  • OSI Layer 3 (network) maps to the TCP/IP internet layer, handling routing and addressing.
  • OSI Layer 4 (transport) maps to the TCP/IP transport layer, handling reliable data delivery.
  • The TCP/IP application layer includes protocols for end-user applications.
  • OSI model Layers 5, 6, and 7 are used as references by application developers.
  • The OSI model separates the data link layer from the physical layer

Data Encapsulation

  • Encapsulation is the process where protocols add their information to the data.
  • At each stage of the process, a PDU (Protocol Data Unit) has a different name to reflect its new functions.
  • PDUs passing down the stack:
    • Data (Data Stream)
    • Segment
    • Packet
    • Frame
    • Bits (Bit Stream)
  • Encapsulation is a top-down process where each layer adds its header and passes it down.

De-encapsulation

  • Data is de-encapsulated as it moves up the stack.
  • Each layer strips off its header and passes the data up to the next layer.
  • Process:
    • Received as Bits (Bit Stream)
    • Frame
    • Packet
    • Segment
    • Data (Data Stream)

Data Access

  • Both the data link and network layers use addressing to deliver data from source to destination.
  • Network layer addresses are responsible for delivering the IP packet from the original source to the final destination.
  • Data link layer addresses are responsible for delivering the data link frame from one NIC to another on the same network.

Layer 3 Logical Addresses

  • The IP packet contains two IP addresses:
    • Source IP address: The IP address of the sending device (original source).
    • Destination IP address: The IP address of the receiving device (final destination).
  • An IP address contains two parts:
    • Network portion (IPv4) or Prefix (IPv6): The left-most part, indicating the network group.
    • Host portion (IPv4) or Interface ID (IPv6): The remaining part, identifying a specific device.

Devices on the Same Network

  • Devices on the same network share the network portion of the address.

Role of Data Link Layer Addresses

  • When devices are on the same Ethernet network, the data link frame uses the MAC address of the destination NIC.
  • MAC addresses are physically embedded into the Ethernet NIC and are local addressing.
    • The Source MAC address is that of the originator on the link.
    • The Destination MAC address is always on the same link as the source.

Devices on a Remote Network

  • When the source and destination have a different network portion, they are on different networks.

  • When the final destination is remote, Layer 3 provides Layer 2 with the local default gateway IP address (router address).

  • The default gateway (DGW) is the router interface IP address that is part of the LAN and serves as the "door" to other locations.

  • All devices on the LAN must know this address.

  • Once Layer 2 on PC1 forwards to the default gateway (Router), the router then can start the routing process of getting the information to actual destination.

  • The MAC addressing for the first segment is :

    • Source – AA-AA-AA-AA-AA-AA (PC1) Sends the frame.
    • Destination – 11-11-11-11-11-11 (R1- Default Gateway MAC) Receives the frame.

Data Link Addresses

  • Data link addressing is local, so it has a source and destination for each segment.
  • The MAC addressing for the first segment is:
    • Source: (PC1 NIC) sends frame
    • Destination: (First Router- DGW interface) receives frame
  • The MAC addressing for the second hop is:
    • Source: (First Router- exit interface) sends frame
    • Destination: (Second Router) receives frame
  • The MAC addressing for the last segment is:
    • Source: (Second Router- exit interface) sends frame
    • Destination: (Web Server NIC) receives frame
  • The L3 IP addressing does not change from segment to segment like the L2 MAC addressing.
  • The L3 addressing remains the same since it is global and the ultimate destination is still the Web Server.