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 …
OSI model OSI (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 …
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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 …
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 …
The term encapsulation is used to describe a process of adding headers and trailers around some data. For example, here is what happens when you send an email using your favourite email program (like Outlook or Thunderbird): the email is sent from the Application layer to the Transport layer. the Transport layer encapsulates the data and adds …
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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. …
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 …
MAC address A 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 …
There are three types of Ethernet addresses: unicast 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. multicast addresses – represent a group of devices in a LAN. A frame sent to a multicast address will be forwarded to a …
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Network devices Hubs A 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 …
Difference between a full duplex and half duplex. 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 …
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full-duplex – all nodes can send and receive on their port at the same time. There are no collisions in full-duplex mode, but the host NIC and the switch port must support the full-duplex mode. Full-duplex Ethernet uses two pairs of wires at the same time instead of a single wire pair like half-duplex. full-duplex Capable of transmitting and receiving over the same channel simultaneously. In pure digital networks, …
Half-duplex data transmission means that data can be transmitted in both directions on a signal carrier, but not at the same time. For example, on a local area network using a technology that has half-duplex transmission, one workstation can send data on the line and then immediately receive data on the line from the same …
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, …
There are three cable types commonly used for Ethernet cabling: coaxial, twisted pair, and fiber-optic cabling. In today’s LANs, the twisted pair cabling is the most popular type of cabling, but the fiber-optic cabling usage is increasing, especially in high-performance networks. Coaxial cabling is generally used for cable Internet access. Let’s explain all three cable …
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Ethernet cables can come in two forms when it comes to wiring: Straight-through cable This cable type has identical wiring on both ends (pin 1 on one end of the cable is connected to pin 1 at the other end of the cable, pin 2 is connected to pin 2 etc.): This type of cable …
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The IP addresses are divided into three different types, based on their operational characteristics: 1. unicast IP addresses – an address of a single interface. The IP addresses of this type are used for one-to-one communication. Unicast IP addresses are used to direct packets to a specific host. Here is an example: In the picture above …
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TCP/IP defines five classes of IP addresses: class A, B, C, D, and E. Each class has a range of valid IP addresses. The value of the first octet determines the class. IP addresses from the first three classes (A, B and C) can be used for host addresses. The other two classes are used …
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Subnetting is the practice of dividing a network into two or more smaller networks. It increases routing efficiency, enhances the security of the network and reduces the size of the broadcast domain. Consider the following example: In the picture above we have one huge network: 10.0.0.0/24. All hosts on the network are in the same subnet, which …
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Subnet mask An IP address is divided into two parts: network and host parts. For example, an IP class A address consists of 8 bits identifying the network and 24 bits identifying the host. This is because the default subnet mask for a class A IP address is 8 bits long. (or, written in dotted …