Network devices

Let’s take a look at the network devices commonly found in today’s LANs..HubsA hub serves as a central point to which all of the hosts in a network connect to. A Hub is an OSI Layer 1 device and has no concept of Ethernet frames or addressing. It simply receives a signal from one port and sends it out to all other ports. Here is an example 4-port Ethernet hub (source: Wikipedia):Today, hubs are considered obsolete and switches are commonly used instead.SwitchesLike hubs, a switch is used Read more […]

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Unicast, multicast, and broadcast addresses

There are three types of Ethernet addresses:1. unicast addressesUnicast addresses represent a single LAN interface. A unicast frame will be sent to a specific device, not to a group of devices on the LAN:The unicast address will have the value of the MAC address of the destination device.2. multicast addressesMulticast addresses represent a group of devices in a LAN. A frame sent to a multicast address will be forwarded to a group of devices on the LAN: Multicast frames have a value of 1 in Read more […]

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MAC & IP addresses

MAC addressA Media Access Control (MAC) address is a 48-bit (6 bytes) address that is used for communication between two hosts in an Ethernet environment. It is a hardware address, which means that it is stored in the firmware of the network card.Every network card manufacturer gets a universally unique 3-byte code called the Organizationally Unique Identifier (OUI). Manufacturers agree to give all NICs a MAC address that begins with the assigned OUI. The manufacturer then assigns a unique value Read more […]

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Ethernet frame

We have already learned that encapsulated data defined by the Network Access layer is called an Ethernet frame. An Ethernet frame starts with a header, which contains the source and destination MAC addresses, among other data. The middle part of the frame is the actual data. The frame ends with a field called Frame Check Sequence (FCS).The Ethernet frame structure is defined in the IEEE 802.3 standard. Here is a graphical representation of an Ethernet frame and a description of each field in the Read more […]

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Ethernet explained

Ethernet is the most used networking technology for LANs today. It defines wiring and signaling for the Physical layer of the OSI model. For the Data Link layer, it defines frame formats and protocols.Ethernet is described as IEEE 802.3 standard. It uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method and supports speeds up to 100 Gbps. It can use coaxial, twisted pair and fiber optic cables. Ethernet uses frames to with source and destination MAC addresses to deliver Read more […]

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Cisco three-layer hierarchical model

Because networks can be extremely complicated, with multiple protocols and diverse technologies, Cisco has developed a layered hierarchical model for designing a reliable network infrastructure. This three-layer model helps you design, implement, and maintain a scalable, reliable, and cost-effective network. Each of layers has its own features and functionality, which reduces network complexity.Here is an example of the Cisco hierarchical model:Here is a description of each layer:Access – controls Read more […]

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IEEE Ethernet standards

Ethernet is defined in a number of IEEE 802.3 standards. These standards define the physical and data-link layer specifications for Ethernet. The most important 802.3 standards are:10Base-T (IEEE 802.3) – 10 Mbps with category 3 unshielded twisted pair (UTP) wiring, up to 100 meters long.100Base-TX (IEEE 802.3u) – known as Fast Ethernet, uses category 5, 5E, or 6 UTP wiring, up to 100 meters long.100Base-FX (IEEE 802.3u) – a version of Fast Ethernet that uses multi-mode optical fiber. Up to Read more […]

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Encapsulation

The term encapsulation is used to describe a process of adding headers and trailers around some data. This process can be explained with the four-layer TCP/IP model, with each step describing the role of the layer.  For example, here is what happens when you send an email using your favourite email program (such as Outlook or Thunderbird):the email is sent from the Application layer to the Transport layer.the Transport layer encapsulates the data and adds its own header with its own information, Read more […]

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Wide area network

The term wide area network is used to describe a network that spans multiple geographic locations. Consider an example. A company has two offices, one in London and one in Berlin. Both offices have a LAN. If the company connects these two LANs together using WAN technology, a WAN is created.The key difference between LANs and WANs is that the company usually doesn’t own WAN infrastructure. A company usually leases WAN services from a service provider. A WAN spanning multiple cities could look Read more […]

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Half duplex and full duplex

In telecommunication, a duplex communication system is a point-to-point system of two devices that can communicate with each other in both direction. These two types of duplex communication systems exist in Ethernet environments:half-duplex – a port can send data only when it is not receiving data. In other words, it cannot send and receive data at the same time. Network hubs run in half-duplex mode in order to prevent collisions. Since hubs are rare in modern LANs, the half-duplex system is not Read more […]

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Network router explained

A router is a network device that routes packets from one network to another. It is usually connected to two or more different networks. When a packet comes to a router port, the router reads the address information in the packet to determine out which port the packet will be sent. For example, a router provides you with the internet access by connecting your LAN with the Internet.NOTE A router is most commonly an OSI Layer 3 device, since its forwarding decision is based on the information of the Read more […]

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Network switch explained

Just like hubs and bridges, a switch is used to connect multiple hosts together, but it has many advantages over them. Switch is an OSI Layer 2 device, which means that it can inspect received traffic and make forwarding decisions. Each port on a switch is a separate collision domain and can run in a full duplex mode (photo credit: Wikipedia).A switch manages the flow of data across a network by inspecting the incoming frame’s destination MAC address and forwarding the frame only to the host for Read more […]

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Local area network (LAN)

The term local area network (LAN) is commonly used to describe a network of devices in a limited area (a house, office, building…). This type of network is usually capable of achieving high data transfer rate (up to 10 Gbps!) at low cost. Examples of this type of network are a small office network inside a single building or your home network.A typical SOHO (small office/home office) LAN consist of PCs, printers, switches, routers, and cabling that connects all these devices together. The following Read more […]

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Network bridge explained

A network bridge is a device that divides a network into segments. Each segment represent a separate collision domain, so the number of collisions on the network is reduced. Also, because each collision domain has its own separate bandwidth, a bridge also improves the overall network performance.NOTE Unlike hubs, bridges allow multiple devices to send at the same time. This is why there are considered to be predecessors of network switches. A bridge works at the Data link layer (Layer 2) of Read more […]

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OSI & TCP/IP models

OSI modelOSI (Open Systems Interconnection) model was created by the International Organization for Standardization (ISO), an international standard-setting body. It was designed to be a reference model for describing the functions of a communication system. The OSI model provides a framework for creating and implementing networking standards and devices and describes how network applications on different computers can communicate through the network media.The OSI model has seven layers, with each Read more […]

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Network hubs explained

A hub serves as a central point to which all of the hosts in a network connect to. It is an OSI Layer 1 device and has no concept of Ethernet frames or addressing – it simply receives the signal from one port and sends it out to all other ports. Here is an example 4-port Ethernet hub (image source: Wikipedia):As mentioned above, hubs have no way of distinguishing out which port a signal should be sent to; instead, an electrical signal is sent out each port. All nodes on the network will receive Read more […]

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What is a network?

A computer network can be described as a system of interconnected devices that can communicate using some common standards (called protocols). These devices communicate to exchange resources (e.g. files and printers) and services.Here is an example network consisting of two computers connected together:In the example above, the two computers are directly connected using a cable. This small network can be used to exchange data between just these two computers.What if we want to expand our network? Read more […]

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