Ethernet hub

An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer (layer 1) of the OSI model. Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision. In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC or Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments.

Hubs are now largely obsolete, having been replaced by network switches except in very old installations or specialized applications.

Technical information

Physical layer function

A network hub is an unsophisticated device in comparison with a switch. As a multiport repeater it works by repeating bits (symbols) received from one of its ports to all other ports. It is aware of physical layer packets, that is it can detect their start (preamble), an idle line (interpacket gap) and sense a collision which it also propagates by sending a jam signal. A hub cannot further examine or manage any of the traffic that comes through it: any packet entering any port is rebroadcast on all other ports. A hub/repeater has no memory to store any data in – a packet must be transmitted while it is received or is lost when a collision occurs (the sender should detect this and retry the transmission). Due to this, hubs can only run in half duplex mode. Consequently, due to a larger collision domain, packet collisions are more frequent in networks connected using hubs than in networks connected using more sophisticated devices.

USB 3.0

USB 3.0 (renamed to USB 3.1 Gen 1 in 2015) is the third major version of the Universal Serial Bus (USB) standard for interfacing computers and electronic devices. Among other improvements, USB 3.0 adds the new transfer mode SuperSpeed (SS) that can transfer data at up to 5 Gbit/s (625 MB/s), which is about ten times faster than the USB 2.0 standard. USB 3.0 connectors are usually distinguished from their USB 2.0 counterparts by blue color-coding of the receptacles and plugs, and the initials SS.

A successor standard, USB 3.1 (renamed to USB 3.1 Gen 2 in 2015), was released in July 2013 with the new transfer mode SuperSpeed+ that can transfer data at up to 10 Gbit/s (1.25 GB/s, twice the rate of USB 3.0), bringing its theoretical maximum speed on par with the first version of the Thunderbolt interface.

Overview

The USB 3.0 specification is similar to USB 2.0 but with many improvements and an alternative implementation. Earlier USB concepts like endpoints and four transfer types (bulk, control, isochronous and interrupt) are preserved but the protocol and electrical interface are different. The specification defines a physically separate channel to carry USB 3.0 traffic. The changes in this specification make improvements in the following areas:

Packet Tracer

Packet Tracer is a cross-platform visual simulation program designed by Cisco Systems that allows users to create network topologies and imitate modern computer networks. The software allows users to simulate the configuration of Cisco routers and switches using a simulated command line interface. Packet Tracer makes use of a drag and drop user interface, allowing users to add and remove simulated network devices as they see fit. The software is mainly focused towards Certified Cisco Network Associate Academy students as an educational tool for helping them learn fundamental CCNA concepts. Students enrolled in a CCNA Academy program can freely download and use the tool free of charge for educational use.

In addition to simulating certain aspects of computer networks, Packet Tracer can also be used for collaboration. As of Packet Tracer 5.0, Packet Tracer supports a multi-user system that enables multiple users to connect multiple topologies together over a computer network. Packet Tracer also allows instructors to create activities that students have to complete. Packet Tracer is often used in educational settings as a learning aid. Cisco Systems claims that Packet Tracer is useful for network experimentation.

USB

USB, short for Universal Serial Bus, is an industry standard developed in the mid-1990s that defines the cables, connectors and communications protocols used in a bus for connection, communication, and power supply between computers and electronic devices. It is currently developed by the USB Implementers Forum.

USB was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as smartphones, PDAs and video game consoles. USB has effectively replaced a variety of earlier interfaces, such as serial and parallel ports, as well as separate power chargers for portable devices.

Overview

In general, there are three basic kinds or sizes related to the USB connectors and types of established connection: the older "standard" size, in its USB 1.1, 2.0, and 3.0 variants (for example, on USB flash drives), the "mini" size (primarily for the B connector end, such as on many cameras), and the "micro" size, in its USB 1.1, 2.0, and 3.0 variants (for example, on most modern mobile phones).

Network interface controller

A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter or physical network interface, and by similar terms) is a computer hardware component that connects a computer to a computer network.

Early network interface controllers were commonly implemented on expansion cards that plugged into a computer bus. The low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard.

Modern network interface controllers offer advanced features such as interrupt and DMA interfaces to the host processors, support for multiple receive and transmit queues, partitioning into multiple logical interfaces, and on-controller network traffic processing such as the TCP offload engine.

Purpose

The network controller implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as Ethernet, Fibre Channel, Wi-Fi or Token Ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same local area network (LAN) and large-scale network communications through routable protocols, such as Internet Protocol (IP).