Business Data Communication and Networking

The Internet of Things (IoT) is a network of physical objects (things) such as sensors, appliances, vehicles and machines embedded with software and connectivity, which collect and exchange data over the Internet without direct human interaction. Examples are smart homes, wearable devices and smart agriculture.

HTTP (HyperText Transfer Protocol) is the application layer protocol of the World Wide Web. It defines how a web client (browser) requests web pages and resources from a web server and how the server responds. It is stateless and uses TCP port 80 (HTTPS uses port 443).

• It allows many signals to share a single communication link, so the bandwidth/channel capacity is used efficiently.
• It reduces the cost of cabling and equipment, since fewer physical links are needed.

Asynchronous transmission is a data transmission method in which data is sent one character (byte) at a time, with each character framed by a start bit and one or more stop bits. There is no common clock between sender and receiver, and gaps of arbitrary length can be present between characters. Keyboard-to-computer communication is an example.

An IP address is used to uniquely identify a host/device on a network and to locate it (host and network identification), so that data packets can be addressed and routed from the source to the destination across networks.

A network interface card (NIC) is needed to connect a computer or device to a network. It gives the device a unique MAC address, converts data between the computer's format and the network signals (wired or wireless), and controls access to the transmission medium for sending and receiving data.

A virtual LAN (VLAN) is a logical grouping of devices on one or more physical LANs, configured on switches, so that they behave as if they are on the same separate LAN regardless of their physical location. Each VLAN is a separate broadcast domain; communication between VLANs requires a router (or layer 3 switch). It improves security, performance and management.

• It provides secure, encrypted access to a private network (for example, a company network) for remote users over the public Internet.
• It connects branch offices at different locations securely and cheaply, without leased lines. It also hides the user's IP address and protects privacy on public networks.

• Dial-up
• DSL / ADSL
• Fibre to the home (FTTH)
• Cable modem, wireless (Wi-Fi, WiMAX), mobile data (3G/4G/5G), satellite and leased line are also used (any three are enough).

Network management is the process of administering, monitoring, configuring, securing and maintaining a computer network so that it works efficiently and reliably. It covers fault, configuration, accounting, performance and security management (FCAPS), and is often done with protocols and tools such as SNMP.

The main components of a network are:

• Nodes/hosts (end devices): computers, servers, printers, phones, which send and receive data.
• Transmission media: wired (twisted pair, coaxial, fibre optic) or wireless (radio, microwave, satellite) paths that carry the signals.
• Network interface card (NIC): connects a device to the network and provides its MAC address.
• Connecting/networking devices: hub, switch (connects devices in a LAN), router (connects different networks and routes packets), bridge, gateway, modem and access point.
• Protocols: rules for communication, such as TCP/IP, HTTP, FTP.
• Network software and operating system: software which manages resources, security and services.

Cloud computing provides computing resources over the Internet on demand, and its three service models are:

• Infrastructure as a Service (IaaS): The provider supplies virtualised hardware: servers, storage, networking. The user manages the operating system, middleware and applications. Examples: Amazon EC2, Microsoft Azure VMs, Google Compute Engine.
• Platform as a Service (PaaS): The provider supplies a platform (OS, runtime, database, development tools) for developers to build, test and deploy applications without managing the infrastructure. Examples: Google App Engine, Heroku, Azure App Service.
• Software as a Service (SaaS): Complete applications are delivered over the Internet through a browser on a subscription basis, with everything managed by the provider. Examples: Gmail, Google Docs, Microsoft 365, Salesforce.

Twisted pair cable: It consists of pairs of insulated copper wires twisted around each other, which reduces electromagnetic interference and crosstalk. It is of two types: unshielded (UTP, with categories like Cat5e and Cat6) and shielded (STP, with a metal shield). It is cheap, light, easy to install and used in LANs (RJ-45 connectors) and telephone lines, with a limit of 100 m per segment and speeds up to Gbps.

Coaxial cable: It has a central copper conductor surrounded by an insulating layer, a metallic braided shield and an outer plastic jacket. The shield gives better protection from noise and allows higher bandwidth and longer distance than twisted pair. It is more expensive and less flexible. It is used in cable television, broadband cable Internet and older Ethernet (10Base2, 10Base5), with BNC or F-type connectors.

WiMAX (Worldwide Interoperability for Microwave Access, IEEE 802.16) is a wireless broadband technology for metropolitan areas, covering distances of tens of kilometres.

Working:

• A WiMAX base station (tower) is connected to the Internet backbone through a high-speed wired link (fibre or leased line).
• The base station transmits signals by microwave radio to subscriber stations (a WiMAX receiver/modem at homes or offices, or mobile devices) within its coverage area, up to about 50 km, in line-of-sight and non-line-of-sight modes.
• Point-to-multipoint links serve many users from one tower, while point-to-point microwave links connect base stations to each other (backhaul).
• Data is transmitted using OFDM with speed up to about 70 Mbps, with QoS and encryption for security.

It is used to provide broadband access in rural or remote areas where laying cable is difficult.

The transport layer provides end-to-end communication between processes on different hosts. Its main functions are:

• Process-to-process delivery: uses port numbers to deliver data to the correct application.
• Segmentation and reassembly: splits messages into segments and reassembles them using sequence numbers.
• Connection control: connection-oriented (TCP) or connectionless (UDP) service.
• Flow control: prevents a fast sender from overwhelming a slow receiver.
• Error control and reliability: detects lost, corrupted or duplicate segments and retransmits them (acknowledgements in TCP).
• Congestion control and multiplexing: shares the network among many applications.

A Virtual LAN (VLAN) divides one physical switch network into several logical broadcast domains, independent of physical location.

• Each switch port is assigned to a VLAN (port-based VLAN), or membership is decided by MAC address or protocol.
• Frames are tagged with a VLAN ID using IEEE 802.1Q when they travel over trunk links between switches.
• A switch forwards frames only to ports in the same VLAN, so broadcast traffic stays inside the VLAN.
• Communication between different VLANs needs a router (or Layer-3 switch), known as inter-VLAN routing.

This improves security, reduces broadcast traffic and makes management flexible.

A Local Area Network (LAN) connects computers within a small area such as a building or campus. Its main components are:

• Computers/workstations and servers: end devices that use and provide resources and services.
• Network Interface Card (NIC): hardware that connects a device to the network and provides its MAC address.
• Transmission media: twisted-pair, coaxial or fibre-optic cable, or wireless (Wi-Fi).
• Hub/Switch: central connecting device. A hub repeats signals to all ports; a switch forwards frames only to the intended port using MAC addresses.
• Router: connects the LAN to other networks such as the Internet.
• Access point: connects wireless devices to the wired LAN.
• Connectors and network operating system/protocols: RJ-45 connectors, and software such as TCP/IP that manages communication and sharing of resources (printers, files).

VPN (Virtual Private Network) is a technology that creates a secure, encrypted private connection over a public network such as the Internet, so remote users or sites can communicate as if they were on a private network.

How it works:

1. The user starts a VPN client and authenticates with the VPN server (username/password, certificate).
2. A secure tunnel is established between the client and the VPN server using protocols such as IPsec, SSL/TLS, L2TP or PPTP.
3. Each data packet is encapsulated in a new packet and encrypted, so intermediate routers cannot read it.
4. The VPN server decapsulates and decrypts the packet and forwards it to the destination on the private network (or Internet). Replies return through the same tunnel.
5. The user's traffic appears to come from the VPN server's IP address, hiding the real address.

Uses: secure remote access to office networks, connecting branch offices cheaply (instead of leased lines), and protecting privacy on public Wi-Fi.

The network design process is built on the following blocks:

1. Requirements analysis: identify business goals, users, applications, traffic volume, performance, security and budget needs.
2. Technology and topology selection: choose the topology (star, tree, etc.), media (copper, fibre, wireless), devices (switches, routers) and protocols.
3. Logical design: IP addressing plan, subnetting, VLANs, routing, naming and security policy.
4. Physical design: cable layout, device placement, rack and power plan, and selection of vendors and equipment.
5. Implementation: installing, configuring and testing equipment.
6. Testing and documentation: verifying performance against requirements and recording the design.
7. Monitoring and maintenance: network management, upgrades, troubleshooting and capacity planning.

CRC is an error-detection method in which the sender appends a check value (remainder) computed by binary division with a generator polynomial; the receiver repeats the division to detect errors.

Sender:

1. Choose a generator $G$ of $r+1$ bits.
2. Append $r$ zeros to the data.
3. Divide (modulo-2, using XOR) the padded data by $G$.
4. Replace the appended zeros by the $r$-bit remainder to form the codeword.

Receiver: divides the received codeword by the same $G$. If the remainder is zero, the data is accepted; otherwise an error is detected and the frame is discarded or retransmitted.

Example: data $1101011$, $G = 1011$ ($r=3$). Padded data: $1101011000$. Modulo-2 division by $1011$:

• $1101 \oplus 1011 = 0110$, bring down digits and continue, giving remainder $001$.

Transmitted codeword: $1101011001$. Dividing it by $1011$ at the receiver gives remainder $000$, so no error is detected.

CRC detects all single-bit errors, all burst errors shorter than $r+1$ bits, and most longer bursts.

Types of networks

By geographical coverage:

• PAN (Personal Area Network): a few metres, e.g. Bluetooth between phone and headset.
• LAN (Local Area Network): a building or campus, high speed, privately owned (Ethernet, Wi-Fi).
• MAN (Metropolitan Area Network): a city, e.g. cable TV network or a city-wide ISP network.
• WAN (Wide Area Network): countries or continents, e.g. the Internet, using leased lines or satellites.

By other criteria: peer-to-peer vs client-server (by roles), and wired vs wireless (by medium).

OSI reference model

The Open Systems Interconnection model, defined by ISO, divides network communication into seven layers. Each layer serves the layer above and uses the services of the layer below.

1. Physical layer: transmits raw bits over the medium; defines voltage, cables, connectors, data rate, topology and transmission mode. Devices: hub, repeater.
2. Data link layer: node-to-node delivery of frames; framing, physical (MAC) addressing, error detection (CRC), flow control and media access control. Devices: switch, bridge.
3. Network layer: source-to-destination delivery of packets; logical (IP) addressing, routing and congestion control. Device: router.
4. Transport layer: end-to-end, process-to-process delivery; port addressing, segmentation, flow and error control, reliability (TCP, UDP).
5. Session layer: establishes, manages and terminates sessions; dialog control and synchronization (checkpoints).
6. Presentation layer: translation, encryption/decryption and compression so that data is in a form the application understands (e.g. ASCII, JPEG).
7. Application layer: provides network services to users, e.g. HTTP, FTP, SMTP, DNS.

Data flow: the sender's data passes down from layer 7 to 1, each layer adding its header (encapsulation); the receiver passes it up, stripping headers (decapsulation).

Advantages: standardizes interoperability between vendors, simplifies design and troubleshooting by modularity, and lets each layer change independently.

Need for routing

A network consists of many interconnected networks, and a packet may have to pass through several intermediate devices to reach its destination. Routing is the process of selecting the best path for packets from source to destination. It is needed to:

• forward packets between different networks (inter-networking),
• find the best (shortest, cheapest or fastest) path,
• avoid failed links and congestion by using alternative paths,
• make the Internet scalable by organising networks hierarchically.

Types of routing

1. Static routing

• Routes are entered manually by the administrator.
• Simple, low overhead and secure, but does not adapt to failures; suited to small networks.

2. Dynamic routing

• Routers learn and update routes automatically by exchanging information using routing protocols.
• Adapts to topology changes; suited to large networks, but uses more CPU, bandwidth and is more complex.
• Types of algorithms:
  • Distance vector (e.g. RIP): each router shares its routing table with neighbours; uses Bellman-Ford and hop count.
  • Link state (e.g. OSPF): each router floods link information, builds a full network map and runs Dijkstra's shortest-path algorithm.
  • Hybrid (e.g. EIGRP, BGP for path vector between autonomous systems).

3. Default routing: a special route used when no specific route matches, typically towards the ISP.

Routing can also be classified as interior (within an autonomous system, e.g. RIP, OSPF) and exterior (between autonomous systems, e.g. BGP).

Router

A router is a Layer-3 network device that connects two or more networks and forwards packets between them based on IP addresses and its routing table. It selects the best path, separates broadcast domains, and often provides NAT, firewall and DHCP services, for example connecting a home LAN to the Internet.