Back to Basics — Networking — the better understanding with basics
What is a Network?
Network is connecting more than two computers by a cable or by a wireless radio connection so that they can exchange information.
How do we connect to a network?
We can create a simple computer network by using a device called a switch to connect all the computers in your network to each other. We connect with network cable that is plugged to the computer using a jack in your computer which is connected to the network interface which is the electronic circuit.
How about Wireless Network?
In wireless network, the computers use wireless network adapters that communicate via radio signals. If our computer does not support, we can get an external wireless network adapter an plug into USB port. We need a device called wireless access point (WAP) to enable the computers to properly connect. In home networks, WAP is bundles with a device called route, which lets you connect to the internet and so it is called wireless router.
All wireless routers has built in firewalls. the firewalls helps protect the computers on the network from the imminent dangers of the internet.
What is a Client and Server?
The network computer that contains the hard drives, printers and other resources that are shared with other network computers is a server. Any computer that is not a server is called client.
In most networks, a server computer is dedicated to do sole task of providing shared resources, such as hard drives and printers, to be accessed by the network client computers. This type of servers is a dedicated server because it can perform no other task than network services.
Alternatively, some computers in a networks can act as both client and server which does sharing of resources as well as do the processing tasks. these computers are called peer-to-peer network.
What is LAN?
Local Area Network — In this type of network, computers are relatively close together such as within the same office or building.
A LAN can contain a hundreds or even thousands of computers. All the connected computers are connected together within close proximity.
What is WAN?
These networks spacn a large geographic territory such as entire city or a region or even a country. EAN are typically used to connect two or more LANs that are relatively far apart. The geographic distance not the number of computers involved makes a network WAN. The WAN will have a grand sum of two computers but will span more than 3000 miles
What is MAN?
This kind of network is smaller than a typical WAN but larger than LAN. Typically MAN connects two or more LANs within the same city that are far enough apart that the networks cannot be connected via a simple cable or wireless connection
What is the Network Infrastructure?
Consider the network infrastructure of a LAN where it is connections in a small proximity. They consists of many physical elements —
Cables — These run though walls and ceiling spaces to reach the destination
Patch Panels — these allow cables to be organized at a central location
Network Switches — A switch is an intermediate device that sits between the networked devices that allows those devices to communicate with each other.
Wireless Access Points — WAP lets devices connect wirelessly to the network. Depending on the size of your network and the physical space your users occupy, you may need more than one WAP. Each WAP needs to be connected to the LAN via a cabled switch connection.
At least one router — A router enables the network to the outside world. The most common use of a router is to connect the LAN to the internet. However, routers can also be used to connect one LAN to another.
What is Network Protocols?
A protocol provides a precise sequence of steps that each element of a network must follow to enable communications. They also define the precise format of all data that is exchanged in a network.
A standard is a detailed definitions of a protocol that has been established by a standards organization and that vendors follow when they create the products.
Network standards are organized into a framework called the Open Systems Interconnection (OSI) Reference model. It establishes a hierarchy for protocols so that each protocol can deal with just one part of the overall task of data communications.
OSI model has 7 distinct layers —
- Physical Layer — Describes the mechanical and electrical details of network components such as cables, connectors and network interfaces.
- Data Link Layer — Describes the basic techniques that networks use to uniquely identify devices on the network and the means for one device to send information over the physical layer to another device, in form of data packets. Switches operate at the data link layer which means they manage the efficient transmission of data packets from one device to another.
- Network Layer — Handles the routing of data across networks. Routers operate at the network layer.
- Transport Layer — Provides for reliable delivery of packets
- Session Layer — Establishes sessions between network applications.
- Presentation Layer — converts data so that systems that use different data formats can exchange information.
- Application Layer — Allows application to request network services.
What is Network Topology
Network Topology refers to the shape of how the computers and other network components are connected to each other.
Nodes — A node is a device that is connected to the network. Network topology deals with how the nodes of a network are connected to each other.
Packet — A packet is a message that is sent over the network from one node to another node. The packet includes the address of the node that sent the packet, the address of the node the packet is being sent to and the data.
Bus Topology
In this topology the nodes are strung together in a line. The key to understanding how a bus topology works is to think of the entire network as a single cable with each node tapping into the cable so it can listen in on the packets being sent over that cable.
In this topology every node on the network can see every packet that is sent on the cable. Each node looks at each packet to determine whether the packet is intended for it. If so, the node claims the packet. If not, ignore the packet.
If the cable in network breaks, the entire network is efficiently disabled.
Star Topology
In a star topology, each network node is connected to a central device called a hub or a switch. Star topologies are commonly used with LANs. If a cable in a star network breaks only the node connected to that cable is isolated from the network.
There is a technical distinction between a hub ad the switch. Hub does not know anything about the computers that are connected to each of its ports. So, when computer receives a packet, it send the copy of the packet to all the other nodes to receive it. With switch, it knows who requested the packet and sends the received packet to the exact node.
A way to expand the star topology with the growing need is to use a technique called daisy-chaining. when you use it, a switch is connected to another switch as if it were one of the nodes on the star. then this second switch serves as the center of a second star.
Ring Topology
Here the packets are sent around the circle from computer to computer. Each computer looks at each packet to decide whether the packet was intended for it. If not, the packet is passed on to the next computer n the ring.
Mesh Topology
Mesh has a multiple connections between each of the nodes on the network. One advantage is that if one cable breaks, the network can use an alternative route to deliver its packets.
Mesh Networks are often used to link switches in a LAN. If any one of them breaks, it can still send data with other switches. this is common in MAN and WAN. These networks use routers to route packets from network to network for reliability and performance reasons, routers are usually arranged in a way that provides multiple paths between any two nodes on the network in a mesh like arrangement.
More about Cables
Twisted-pair Cable
This is called twisted pair cable because inside the outer sheath of the cable are four pairs of small insulated wire. the wires are 24 gauge, which means they are about half a millimeter in diameter. These pairs are color coded: blue, green, orange and brown. The two wires that makes up the pair are twisted together in a way that prevents the electrical signals within each pair from interfering with each other pairs. To accomplish this, each pair is twisted at a different rate. the max length of the single run of cat-5e able is 100 meters.
This cable is able to carry network data at speeds of up to 1 gigabit per second(Gbps) the newer and expensive Cat-6 cable carry data at up to 10 Gbps but can sustain that speed for only 55 meters
RJ45 Connectors
Twisted pair cable is attached to network devices using a special type of connector called RJ45, which is small block of plastic with eight metal contacts. RJ45 connectors resemble a telephone connector but are larger.
RJ45 connectors comes in both male(plug) and female(receptacle) varieties. typically, the male connector is installed on the cables and the female connectors are installed in equipment. Thus, to connect a cable to a computer, you plug the male RJ45 plug on the cable into the female RJ45 receptacle on the computer.
Patch panels and Patch cables
A patch panel is a group of RJ45 receptables on a single metal plate, usually attached to a 19 inch equipment rack. Patch panels are used to bring cables run from individual computer locations to a single location where they can then be patched to other equipment using patch cables.
It is simply a short length of twisted pair cable with an RJ45 plug on both ends. Patch cables are usually 3 to 10 feet in length but longer lengths are occasionally used.
Patch panels typically have either 24 or 48 ports. Depending on the size of your network, you may have more than one patch panel at a single location. For example, large network may have four 48 port patch panels to support a total of 192 computers.
It’s job is to simply to provide central collecting point for all your network cables so that you can easily use patch cables to connect the cables to other devices such as switches or servers.
Repeaters and Hubs
A repeater is a layer-1 device that is designed to circumvent the maximum length limitation of twisted pair network cables. A repeater contains two RJ45 ports which are connected internally by an amplifier. Electrical signals received on either of the two ports are boosted by the amplifier and sent through the other port. This, the cables on both ends of the repeater can be up to 100 meters. the repeater efficiently doubles the reach of the cable.
A hub is the repeater with more than two ports. these ports can each connect to another device on the network such that as a client computer a server or printer. A port on a hub can also connect to another hub so that an eight port hub can connect to seven computers and other eight port hub which can connect to seven more computers.
the electrical signal received on any of the hub’s ports is amplified and repeated on all the other ports in the hub. So all devices connected to either of the ports sees the messages.
They are almost never used anymore. That is because simply repeating all incoming signals on all ports is an incredibly bad idea. They are replaced with switches.
Switches
A switch is a layer-2 device that is similar to a hub in that it allows you to connect more than one device, and the packets reeived on one port are relayed on other port. The difference is that switch is able to examine the actual contents of the data that it receives. A switch looks at the destination address and repeats the incoming packet only on the port that can deliver the packet to the intended destination.
Network Interface
It is the electronic circuitry that allows a device to connect to a network. Each network interface provides a port, which is the plug-in point for the interface.
A network interface might be a separate add-on card for a computer, in which case the interface is called a network interface card(NIC). On some devices, such as printers, separate network interface cards are still common. Port, interface, adapter are all used interchangeably.
MAC Addresses
Each network interface must have a unique identifier called a MAC address (Media Access Control). It is unique through out the world.
MAC addresses are important because they provide the means for a network to keep track of the devices that make up the network. The physical address is sometimes used as synonym for MAC addresses. They are part of layer 2. This layer is responsible for exchange of basic information on the network. The ability to identify every device on a network is the key component of enabling that to happen.
These are 48 bits in length, which means that more than 280 trillion devices can be assigned unique MAC addresses before they run out. When we write we write six octets separated by hyphens. An octet is a group of eight binary bits, written as a two-digit number in hexadecimal notation which uses A through F in addition to digits 0 through 9 to represent the value of each octet. A typical MAC addresses looks like 48–2C-6A-1E-59–3D
If we want to see MAC addresses of your computer open Command Prompt and type ipconfig/all This address is shown as Physical address.
The MAC address is technically associated with a network interface not with the device that uses that interface.
In order for any device to connect to the internet, it should contain the network interface. This is unique MAC address which is primary way to distinguish one device from another.
Pondering Packets
The devices in the network exchange the information with one another. This is accomplished using the packets. A network packet always originates at a single network interface called the sender and it is usually sent to a single network interface called the destination
A packet is similar to an envelope that you would send through standard mail delivery. It includes the MAC address of both the sender and the destination, as well as some other interesting header information, along with a payload that contains the actual data being sent by the packet.
The payload of an Ethernet packet may be a packet created by some higher-level protocol such as IP.
The term frame is often used instead of packet, but technically they are not quite same. Every packet begins with a preamble, which consists of 56 bits of alternating zeros and ones. this preamble is used by the electronic circuitry of the interfaces to get their clocks synchronized properly so they accurately read the rest of the packet. It is the rest of the packet technically called frame.
Ethernet has standard packet format that all packets sent on an ethernet network must follow.
- Preamble — It consists of 56 bits of alternating ones and zeros and is used to synchronize the precise timing required to reach packet data.
- Start — of — frame marker — Single byte that indicates that the frame is about to begin.
- Destination MAC address(6 bytes)
- Sender MAC address(6 bytes)
- Tag — used to support Virtual LAN and is optional. VLAN divides two or more distinct LANs on a shared physical infrastructure
- Ethertype(2 bytes) — This field indicates the specific protocol that is contained in the payload
- Payload — contains the actual data from 46 bytes to 1500 bytes. If more, then it is broke into multiple packets and sent separately which is reassembled at the destination.
- Frame Check Sequence ( 4 bytes) — Ensure that the frame data was sent correctly. The interface that sends the packet uses an algorithm to calculate a 4 byte number based on the content of the frame and saves this number in FCS field. When packet is received, the receiving interface repeats the calculation and then makes sure that the number recorded in the FCS portion of the packet matches the number it calculated. If the numbers disagree, the packet is garbled in transmission and is discarded.
Contemplating Collisions
One of the basic principles of Ethernet is that multiple devices can be connected to media and that all devices connected to this media can and should examine every packet that is sent on the media.
Every packet contains MAC addressed of the intended recipient. So when an interface detects and incoming packet, it inspects the recipient MAC address and compares it with its own MAC address. If the addresses match, the interface passes the packet up to the next higher protocol typically IP protocol. Otherwise, it ignores the packet.
The use of hubs on the Ethernet propagates the shared cable through the network. That is because a hub simply amplifies any packet that arrives on any port and then forwards to all other ports in hub. So if more than one computer tries to transmit the packet at the same time, the packets will collide.
When two or more interfaces shared on a single cable, there is always the possibility that two or more interfaces will try to send information at the same time. this is called collision. The result of a collision between 2 packets is that both packets will be destroyed in the process and will need to resent again.
Switches solve this problem and eliminates the problem of collisions by forwarding the packets only to cable segments that the destination devices are connected to rather than forwarding them throughout the entire network.
Dealing with Broadcast Packets
Not all the packets on an Ethernet network are intended for a single destination. Some are meant to broadcast and should be received by every device on the network. To send a broadcast packet. the sending interface sets the destination to FF-FF-FF-FF-FF-FF.
One of the most common users of broadcast packets is Dynamic Host Configuration Protocol (DHCP) which allows computers to join a network to be assigned an IP address. When a network interface ins first connected to a network, it sends out a broadcast message requesting the address of the network’s DHCP server. Every device on the network share sees this picket. But only the DHCP service will respond.
Wireless Networks
- Just like a wired network, a device connecting to a wireless network does so via a network interface.
- A wireless adapter includes a radio transmitter and receiver rather than a physical cable connection.
- Every wireless network adapter has a MAC address
- Rather than a switch or a hub, wireless devices connect to a wireless Access point(WAP)
- Collisions are possible on a WAP, just as there are on a hub.
- there is no equivalent wireless witch that reduces collision problem. WAPs are hubs in that every device that connects to the access point is competing for the same bandwidth.
- Whenever the WAP sends a packet, all devices connected to the access point must inspect the packet to determine the MAC address destination. And if two devices try to send packets at the same time, a collision will occur. This is one of the inherent reasons that wireless networking is slower than wired networking.
Happy Learning!!
