Data Network Fundamentals

Data Network Fundamentals

• Data communication refers to the transfer of information from one point to another.
• Data is represented by a sequence of zeros and ones, handled by computers.
• Communications systems can handle analog or digital data.
• Modern instrumentation is primarily concerned with digital data transfer.

OSI Model

• The OSI model provides a framework for defining specific protocols.
• The model consists of seven layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical.
• Each layer has a specific function:
  • Application Layer: receives information directly from users and displays incoming data.
  • Presentation Layer: represents data independently of the application layer.
  • Session Layer: sets up, coordinates, and terminates connections between applications.
  • Transport Layer: responsible for data transfer between end systems and hosts, using TCP/IP.
  • Network Layer: responsible for packet forwarding, including routing through different routers.
  • Data Link Layer: provides node-to-node data transfer, with two sublayers: MAC and LLC.
  • Physical Layer: represents the electrical and physical representation of the system.

Protocols and Standards

• Protocols are structures used within a communications system to facilitate communication between devices.
• Standards are necessary for developing integrated instrumentation and control systems.
• The OSI model provides a framework for defining specific protocols.
• Examples of physical standards include RS-232, RS-422, RS-423, and RS-485.

Modern Instrumentation and Control Systems

• Data is acquired by measuring instruments and transmitted to a controller, typically a computer.
• The controller transmits data or control signals to control devices, which act upon a given process.
• The main purpose of an instrumentation and control system is to provide control, monitoring, and alarm functions.
• Modern systems use integrated systems such as DCS, PLCs, and smart instruments.

Networking

• There are three broad classes of networks: LANs, MANs, and WANs.
• Network topologies include Star, Ring, and Bus.
• Circuit switching and packet switching are two types of network switching methods.
• Packet switching is cheaper and more efficient, but may have slower transmission rates.

Circuit and Packet Switching

• Circuit switching establishes a direct connection between two ends for the duration of the message exchange.
• Packet switching breaks the message into packets, each carrying the destination address, and transmits them independently.

Network Topologies

• Star topology: a central node or hub connects to outlying nodes on separate communication links.
• Ring or loop topology: nodes are connected in a loop, with data flowing in one direction.
• Bus topology: nodes are connected to a common communication path, with data transmitted in one direction.

Transmission Techniques

• Baseband transmission uses time division multiplexing (TDM) to allow one device to transmit at a time.
• Broadband transmission uses frequency division multiplexing (FDM) to allow multiple devices to communicate simultaneously.

IEEE Standards

• IEEE 802.2 defines services for the LLC sublayer.
• IEEE 802.3 defines the CSMA/CD protocol used by Ethernet.
• IEEE 802.4 defines the token passing bus access method.
• IEEE 802.5 defines the token ring access method.

Ethernet

• Ethernet was developed by Xerox in the 1970s and standardized by Xerox, Digital Equipment, and Intel in 1978.
• It uses the CSMA/CD protocol and is a popular LAN technology.### IEEE LAN Standards
• IEEE 802 is a series of standards administered by the IEEE 802 LAN Standards Technologies Committee.
• The standard has several sections, each with its own co-coordinating committee.
• Some standards have been superseded by ISO standards.

Ethernet

• Uses CSMA/CD as a medium access control method.
• Standard (or thick) Ethernet (10Base5) uses 10 Mbps baseband operation on coaxial cable with a maximum segment length of 500 m.
• Thin Ethernet (10Base2) uses 10 Mbps baseband operation on coaxial cable with a maximum segment length of 185 m.
• 10BaseT uses unshielded twisted pair cables and operates at 10 Mbps.
• 100BaseT is similar to 10BaseT but operates at 100 Mbps.
• 1000BaseT (gigabit Ethernet) is similar to Fast Ethernet, but operates at 1000 Mbps.
• 1BaseT is similar to 10BaseT but limited to a 1 Mbps data rate.

Ethernet Topology

• Standard and thin Ethernet use a bus topology.
• 10BaseT (Ethernet) uses a star configuration.

Fast Ethernet

• Operates at 100 Mbps on different forms of physical media.
• Retains the existing Ethernet MAC layer.
• IEEE 802.3u standard defines:
  • 100BaseTX, which uses two pairs of category 5 UTP or STP.
  • 100BaseFX, which uses two pairs of multimode (or single node) fiber.
  • 100BaseT4, which uses four pairs of category 3, 4 or 5 UTP.

Ethernet Protocol Operation

• All data transfer is in the form of a packet or frame.
• Each packet consists of an envelope containing control information and the actual message data.
• Each node examines the destination address and reads the data if the frame is directed at that node.

Frame Structure

• Preamble: 7 bytes, each with the binary value 10101010.
• Start of frame delimiter: 1 byte, with the binary value 10101011.
• Destination Address: 16 or 48 bits, depending on the system configuration.
• Length Indicator: 2 bytes, specifying the length of the data field.
• Data: 46 to 1500 bytes in length.
• Frame Check Sequence: 32-bit cyclic redundancy check value for error detection.

Network Devices

• Modem: enables a computer to send or receive data over telephone or cable lines.
• Types of Modem:
  • Simplex: transmits data in one direction.
  • Half-duplex: transmits data in both directions, but only one at a time.
  • Full-duplex: transmits data in both directions simultaneously.
• Ethernet Card (NIC): connects computers to Ethernet LAN and communicates with other devices on the LAN.
• Router: transmits data from one LAN to another if both networks support the same set of protocols.
• Switch: connects devices to Ethernet networks through twisted pair cables and uses packet switching technique to receive, store, and forward data packets.

Cabling Basics

• Twisted pair cables: the most economical solution for data transmission, allowing for rates of up to 180 Mbps on communication links of up to 100 meters.
• Types of Twisted Pair Cables:
  • Shielded Twisted Pair (STP)
  • Unshielded Twisted Pair (UTP)
• EIA-568 standard divides UTP cables into five application categories:
  • Category 1: low-speed data and analogue voice
  • Category 2: ISDN data
  • Category 3: high-speed data and LAN (10 Mbps)
  • Category 4: extended distance LAN
  • Category 5: extended frequency LAN (100 Mbps)
• Coaxial cables: used for antennas operating between the HF band of frequencies up to the SHF band around 2 GHz.

Routing Algorithms

• Non-Adaptive Routing Algorithm:
  • Also known as static routing algorithm
  • Routing process is designed in advance and stored in the router after booting
  • Doesn't affect with the change of network topology and traffic
  • Examples:
    • Flooding: every incoming packet is sent to all the outgoing links except the one from it has been reached.
    • Random walks: a packet sent by the node to one of its neighbors randomly.
• Adaptive Routing Algorithm:
  • Also known as dynamic routing algorithm
  • Routing changed based on the network topology and traffic### Fiber-Optic Cables
• Normally used for digital signal transmission
• Capabilities satisfy future data communication requirements
• Transmission rates in Gigabits per second (Gbps), with current systems operating at around 10 Gbps
• Benefits include:
  • Enormous bandwidth
  • Low signal attenuation
  • Inherent signal security
  • Low error rates
  • Noise immunity
  • Logistical considerations (light, small, and safe for hazardous areas)
  • Total galvanic isolation between ends

Routing Algorithm

• Provides the best path from source to destination based on "least-cost path"
• Divided into two categories: adaptive and non-adaptive
• Three types of algorithms:
  • Centralized algorithm: uses global information and computes the least cost path
  • Isolation algorithm: uses local information and decides routing based on neighboring links
  • Distributed algorithm: computes the least cost path based on iterative calculations

IP Addressing

• IP version 4 (IPv4) addresses: 32 bits in length, typically communicated in dotted decimal format
• Broken into four octets (1 octet = 8 bits)
• IP version 6 (IPv6) addresses: 128 bits in length, provides enough globally unique IP addresses
• IP address classes: A, B, C, D (Multicast), and E (Reserved)
• Class A, B, and C addresses defined based on the number of bits in the network portion
• Subnetting: allows creation of multiple logical networks within a single Class A, B, or C network

Subnetting

• Extends the mask using bits from the host ID portion to create a subnetwork ID
• Example: 192.168.5.0/24 with a mask of 255.255.255.0 can be subnetted

Private IP Addressing

• RFC 1918 addresses reserved for internal network infrastructure
• Includes three blocks of IP address space:
  • 10.0.0.0 – 10.255.255.255 (10.0.0.0/8)
  • 172.16.0.0 – 172.31.255.255 (172.16.0.0/12)
  • 192.168.0.0 – 192.168.255.255 (192.168.0.0/16)