Networking Basics: Message Encoding and Delivery

Message Encoding

• Messages are converted into bits by the sending host.
• Each bit is encoded into patterns of sounds, light waves, or electrical impulses depending on the network media.
• Destination host receives and decodes the signals to interpret the message.

Message Formatting and Encapsulation

• Messages are formatted for letters and addressing letters, which is required for proper delivery.
• Encapsulation is putting the letter into the addressed envelope.
• Each computer message is encapsulated in a specific format, called a frame, before being sent over the network.
• A frame acts as an envelope, and includes a destination address and source address.

Message Size

• Humans break long messages into smaller parts or sentences.
• Long messages are broken into smaller pieces in order to travel across a network.
• Each piece is sent in a separate frame with its own addressing information.
• A receiving host will reconstruct multiple frames into the original message.

Message Timing

• Hosts on a network need to know when to begin sending messages and how to respond when collisions occur, this is called access method.
• Flow control is used by source and destination hosts to negotiate correct timing, to avoid overwhelming the destination and to ensure information is received.
• Hosts on the network have rules that specify how long to wait for responses and what action to take if a response timeout occurs.

Message Delivery Options

• Unicast Message: One-to-one delivery
• Multicast Message: One-to-many delivery
• Broadcast Message: One-to-all delivery

Protocols

• Protocol suites are implemented by hosts and networking devices in software, hardware or both.
• Protocols are viewed in terms of layers, with each higher level service depending on the functionality defined by the protocols in the lower levels.

Network Protocols

• Networking protocols define a common format and set of rules for exchanging messages between devices
• Common networking protocols include Hypertext Transfer Protocol (HTTP), Transmission Control Protocol (TCP), and Internet Protocol (IP).

Protocol Interaction

• Communication between a web server and web client is an example of an interaction between several protocols:
  • HTTP - an application protocol governing the way a web server and a web client interact.
  • TCP - transport protocol that manages the individual conversations.
  • IP – encapsulates the TCP segments into packets, assigns addresses, and delivers to the destination host.
  • Ethernet - allows communication over a data link and the physical transmission of data on the network media.

TCP/IP Protocol Suite

• TCP/IP communication process:
  • The webserver prepares the Hypertext Markup Language (HTML) page.
  • The HTTP application layer protocol sends the data to the transport layer.
  • The transport layer breaks the data into segments and identifies each.
  • Next the IP source and destination addresses are added, creating an IP Packet.
  • The Ethernet information is then added creating the Ethernet Frame, or data link frame.
  • This frame is delivered to the nearest router along the path towards the web client.
  • Each router adds new data link information before forwarding the packet.

TCP/IP Communication Process (Cont.)

• Receiving data link frames from the web server:
  • The client processes and removes each protocol header in the opposite order it was added.
  • The Ethernet header is removed first.
  • The IP header is removed next.
  • The Transport layer header is removed next.
  • Finally the HTTP information is processed and sent to the client's web browser.

Open Standards

• Open standards encourage interoperability, competition, and innovation.
• Standards organizations are usually vendor-neutral, non-profit organizations established to develop and promote the concept of open standards.

Internet Standards

• Internet Society (ISOC) - promotes open development and evolution of Internet use globally.
• Internet Corporation for Assigned Names and Numbers (ICANN) - coordinates IP address allocation and management of domain names.
• Internet Architecture Board (IAB) - management and development of Internet standards.
• Internet Assigned Numbers Authority (IANA) - manages IP address allocation, domain name management, and protocol identifiers for ICANN.
• Internet Engineering Task Force (IETF) - develops, updates, and maintains Internet and TCP/IP technologies.
• Internet Research Task Force (IRTF) - focused on long-term research related to Internet and TCP/IP protocols.

Electronics and Communications Standard Organizations

• Institute of Electrical and Electronics Engineers (IEEE) - dedicated to advancing technological innovation and creating standards in a wide area of industries including networking.
• Electronic Industries Alliance (EIA) - standards related to electrical wiring, connectors, and network racks.
• Telecommunications Industry Association (TIA) standards for radio equipment, cellular towers, Voice over IP (VoIP) devices, and satellite communications.
• International Telecommunications Union- Telecommunication Standardization Sector (ITU-T) standards for video compression, Internet Protocol Television (IPTV), and broadband communications.

The Benefits of Using a Layered Model

• Assisting in protocol design, since protocols at each layer have defined functions.
• Fostering competition because products from different vendors can work together.
• Preventing technology changes in one layer from affecting other layers.
• Providing a common language to describe networking functions and capabilities.

The OSI Reference Model

• Application: contains protocols used for process-to-process communications.
• Presentation: provides for common representation of the data.
• Session: provides services to the presentation layer to organize its dialogue and to manage data exchange.
• Transport: defines services to segment, transfer, and reassemble the data.
• Network: provides services to exchange the individual pieces of data over the network between identified end devices.
• Data Link: provides methods for exchanging data frames between devices over a common media.
• Physical: describes the mechanical, electrical, functional, and procedural means to transmit bits across physical connections.

The TCP/IP Protocol Model

• Created in the early 1970s for internetwork communications
• Open standard.
• Also called The TCP/IP Model or the Internet Model.

OSI Model and TCP/IP Model Comparison

• In the OSI model, the network access layer and the application layer of the TCP/IP model are further divided to describe discrete functions that must occur at these layers.

Data Access

• Devices on the Same Network:
  • The network layer addresses, or IP addresses, indicate the original source and final destination.
  • The left-most part of the address indicates which network the IP address is a member of, this is known as the network portion.
  • The remaining part of the address identifies a specific device on the network, this is known as the host portion.
  • The data link frame which uses MAC addressing, is directly sent to the receiving device.
  • The source MAC address is the address of the sending device.
  • The destination MAC address is the address of the receiving device.

Data Access

• Devices on a Remote Network:
  • Sending to a remote network - the source and destination IP addresses represent hosts on different networks.
  • The data link frame cannot be sent directly to the remote destination host.
  • This frame is sent to the default gateway (nearest router interface) and the router removes the received Layer 2 information and adds new data link information before forwarding out the exit interface.

Conclusion

• Explains how rules facilitate communication.
• Explains the role of protocols and standards organizations in facilitating interoperability in network communications.
• Explains how devices on a LAN access resources in a small to medium sized business network.