Networking Basics and OSI Model Quiz

Network Communication Overview

• Network communication involves the movement of information from one software application on a computer to another via a physical medium.
• The OSI model describes how this process unfolds.
• The model is used by major companies to develop detailed specifications for interfaces.
• It is a detailed specification of actual interfaces but the committee determined to establish a common reference model.
• This model helps others use the detailed interfaces that form standards for data packet transmission.

Network Structure

• The network edge consists of hosts (clients and servers) commonly located in data centers.
• Access networks utilize physical media (wired or wireless) for communication links.
• Routers form the core of the network functioning as interconnected networks.

MAC Addresses

• MAC addresses operate at the Data Link layer.
• If a host lacks the MAC address of another host on a local area network, the operating system retrieves it.

IP Addresses

• IP addresses uniquely identify devices on the internet or an intranet.
• An IP address is 32 bits long which is separated by 4 bytes (octets).
• The first part of an IP address marks the network, while the last segment indicates the host.

Classes of IP Addresses

• IP addresses are grouped into classes A, B, and C based on the amount of potential IP addresses.
• Each organization's IP addresses are unique and available for use on the internet.

Private IP Addresses

• Private IP addresses are dedicated by a network administrator for use within private intranets separated from the internet.
• Public IP addresses are used for internet access.

Dynamically Assigned IP Addresses

• Dynamic IP addresses are assigned for a single session, while static addresses stay permanent.
• Internet Service Providers (ISPs) connect individuals and businesses to the internet.

Network Address Translation (NAT)

• NAT addresses the problem of private IP addresses not being permitted on the internet.
• It assigns a single public IP address to all other hosts on the network for internet access.

The Network Core

• The core consists of interconnected routers.
• Packet switching involves breaking application messages into packets for transmission across multiple routers.
• Each packet is transmitted across links at full link capacity.

Loss and Delay

• Packets queue up in router buffers when the packet arrival rate momentarily exceeds the link's throughput.
• Packets that arrive when all buffers are full result in losses.

Circuit Switching

• All resources for a call are dedicated, ensuring no sharing.
• This dedicated nature facilitates guaranteed, circuit-like performance.

Packet Switching versus Circuit Switching

• Packet switching enables more users to utilize the network, whereas circuit switching is limited strictly to a fixed number of users.
• Packet switching works with 35 users at an extremely high probability.
• The possibility of 10 concurrent users is less than 0.0004.

OSI Model (Open System Interconnection)

• OSI stands for Open System Interconnection.
• Information is transferred from one software application to another via a physical medium.
• Companies began in 1983 to create a detailed specification of actual interfaces.
• A common global model was chosen for others to use in creating standards for data packet transmissions.

OSI Model Layers

• The OSI Model comprises seven layers (layers 1-7).
• Each layer has specific functions and protocols.
• The Application, Presentation, and Session layers handle application protocols.
• The Transport layer handles protocols such as TCP and UDP.
• The Network layer provides address resolutions for a host (ARP), including the locating of hosts on a LAN and the discovery of IP addresses.
• The Physical and Data Link layers form the foundational protocol layers.
• The Data Link Layer Layer manages communication channels (wired and wireless) allowing adjacent nodes to connect.

Protocols at Network Layers

• TCP and UDP are utilized to communicate within the network layer or internet layer.
• ARP is responsible for finding a host on the LAN.
• RARP discovers the internet address of a host on a LAN.
• ICMP communicates transmission problems to devices needing this information.

Protocols at Data Link and Physical Layers

• PPP is used over phone lines allowing a computer to connect to a network with a modem. This is the most utilized protocol for handling network transmission.

Link Layer (terminology)

• Nodes represent hosts and routers.
• Links connect adjacent nodes.
• The link layer encapsulates datagrams into frames.

Link Layer (context)

• Datagrams are transferred across different links via various protocols.
• Services offered by link protocols can differ, some can provide reliable data transmission while others may not.
• The analogy to transportation depicts how various layers function in communication.

Link Layer Services

• Framing encapsulates datagrams into frame headers and trailers.
• Link access manages channel access for shared media.
• MAC addresses, which differ from IP addresses, identify sources and destinations within the frame headers.

Link Layer Services (more)

• Flow control regulates data transmission between adjacent nodes.
• Error detection recognizes errors due to signal attenuation or noise, signaling for retransmission or discarding frames.
• Error correction identifies and corrects bit errors without retransmission.

Where is the Link Layer Implemented?

• The link layer operates within every host or adapter (NIC), usually a chip residing in a host or adapter.
• Protocols, such as Ethernet (card, 802.11) and its associated chipsets, embody implementation of link and physical layers.
• They attach to the hosts system buses for functionality.

Data Link Layer Frame Sections

• A data link layer frame encompasses a header that includes the source and destination addresses, as well as control bytes.
• The payload section carries the message being delivered.
• The trailer contains error correction and detection bits (FCS).
• Flags mark the start and end of the frame.

Multiple Access Links, Protocols

• Point-to-point links (like PPP for dial-up) connect between specific nodes.
• Broadcast links (like Ethernet) feature multiple simultaneous transmissions over a shared medium (interference is possible).

Multiple Access Protocols

• Multiple access protocols use distributed algorithms to manage channel sharing on a shared-medium network.

MAC Protocols: Taxonomy

• Channel partitioning divides the channel into smaller segments (time slots, frequency, or code).
• Random access allows collisions and recovery.
• "Taking turns" involves nodes accessing the channel sequentially.

Error Detection

• Error Detection and Correction bits (EDC) provide redundancy for error checking or may incorporate header fields within the data.
• Larger EDC fields enhance detection and correction rates.

Error detection Methods

• Parity checking and two-dimensional bit parity are utilized for single bit detection and correction.
• A checksum detects errors in transmitted packets (used primarily at the Transport Layer).
• CRC (Cyclic Redundancy Check) is a method used to check the message by appending and comparing against computed values to detect errors.

Network Layer

• The network layer encapsulates segments into datagrams at the sending host.
• At the receiving end, the datagrams are delivered to the appropriate segments.
• Network layer protocols are found in every host and router.
• Routers analyze packet header sections within all datagrams. This analysis is critical to determining the appropriate destination path.

The Internet Network Layer

• Routing protocols, such as RIP, OSPF, and BGP, determine the path selection.
• IP (Internet Protocol) is in charge of addressing conventions and handling datagrams.
• ICMP (Internet Control Message Protocol) handles errors and routing communication.
• Forwarding tables are crucial for local routing.

Two Key Network-Layer Services

• Forwarding moves datagrams from a router's input to an appropriate output port.
• Routing defines the route a packet takes. Routing algorithms are responsible for establishing routes.

Interplay Between Routing and Forwarding

• A Routing algorithm establishes end-to-end paths throughout a network.
• A Forwarding table determines local network routing within a current router.

Transport Layer

• A transport layer provides logical communication between application processes running on different hosts.
• The sending side segments messages into packets.
• The receiving side reassembles segments into app messages.
• Several transport protocols, such as TCP and UDP, exist for different application needs.

Transport Layer Services

• Transport protocols contain mechanisms for error control, flow control, and congestion control, to monitor and track the data packets, identify and manage errors and duplications and resend data to fix any missing data.

Transport-Layer Protocols

• TCP provides reliable, in-order delivery with congestion control and flow control mechanisms, and connection setup.
• UDP provides unreliable, unordered delivery.
• TCP/UDP has greater functionality for ensuring delivery compared to the more "bare bones" structure of UDP.

Transport Layer: Multiplexing/Demultiplexing

• Multiplexing at the sender involves handling data from several sockets and adding transport headers.
• Demultiplexing at the receiver involves directing received segments to the appropriate sockets.

How Demultiplexing Works

• The host receives IP datagrams, which contain important header fields like source/destination IP addresses and port numbers.
• Based on these header fields, the host directs the datagram's segments to the appropriate socket.

UDP (User Datagram Protocol)

• UDP is a lightweight, connectionless protocol.
• Its simplicity enables faster implementation.
• No need for connection setup adds speed.
• Suitable for streaming applications, DNS, and SNMP (Simple Network Management Protocol).

UDP Segment Header

• UDP packets consist of source and destination port numbers, length fields, and checksum fields.

TCP (Transmission Control Protocol)

• TCP is a connection-oriented, reliable, ordered protocol for byte streams.
• No message boundaries.
• Pipelined, using segments with congestion and flow control.
• TCP operates using send and receive buffers.

TCP Segment Structure

• TCP segments contain sequence numbers, acknowledgement numbers, receive windows, options (variable length), and application data fields.

TCP Sequence Numbers and Acknowledgements

• Sequence Numbers track bytes transmitted within segments.
• Acknowledgements confirm the receipt of data segments.
• A critical element of TCP is to handle out-of-order segments.

TCP Reliable Data Transfer

• TCP implements mechanisms for reliable data transmission.
• Retransmissions occur for timeouts or duplicate acknowledgments.
• Transmission timers and acknowledgments are important features of TCP's robust data transfer system.

TCP Connection Management

• TCP establishes a three-way handshake for initiating a connection.
• Closing a connection involves a four-way transaction or a handshake procedure (TCP FIN control segment exchange).

Networking Standards Organizations

• ANSI (American National Standards Institute) determines standards for industry fields like chemical engineering.
• EIA (Electronic Industries Alliance) is a trade organization for electronic manufacturing firms.
• TIA (Telecommunications Industry Association) sets standards for info technology, wireless, satellite, fiber optics and telephone equipment.
• ISO (International Organization for Standardization) creates global standards to facilitate information exchange.
• ITU (International Telecommunication Union) manages international communications, such as radio frequencies or telephone specifications.
• ISOC (Internet Society) is a professional organization supporting the creation and maintenance of Internet standards.
• IAB (Internet Architecture Board) provides technical advice and management.
• IETF (Internet Engineering Task Force) develops and sets standards for how systems communicate via the internet. IANA and ICANN manage IP addressing and domain names.