Ethernet

´  The physical layer of the network focuses on hardware elements, such as cables, repeaters, and network interface cards.

´   By far the most common protocol used at the physical layer is Ethernet.

´   For example, an Ethernet network (such as 10BaseT or 100BaseTX) specifies the type of cables that can be used, the optimal topology (star vs. bus, etc.), the maximum length of cables, etc.

´  The data link layer of the network addresses the way that data packets are sent from one node to another.

´   Ethernet uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection). This is a system where each computer listens to the cable before sending anything through the network.

´   If the network is clear, the computer will transmit. If some other node is already transmitting on the cable, the computer will wait and try again when the line is clear. Sometimes, two computers attempt to transmit at the same instant.

´   When this happens a collision occurs. Each computer then backs off and waits a random amount of time before attempting to re-transmit.

´  With this access method, it is normal to have collisions. However, the delay caused by collisions and re transmitting is very small and does not normally effect the speed of transmission on the network.

´  The original Ethernet standard was developed in 1983 and had a maximum speed of 10 Mbps (phenomenal at the time) over coaxial cable.

´   The Ethernet protocol allows for bus, star, or tree topologies, depending on the type of cables used and other factors.

´  This heavy coaxial cabling was expensive to purchase, install, and maintain, and very difficult to retrofit into existing facilities.

´  The current standards are now built around the use of twisted pair wire. Common twisted pair standards are 10BaseT, 100BaseT, and 1000BaseT.

´   The number (10, 100, 1000) and for the speed of transmission (10/100/1000 megabits per second); the "Base" stands for "base-band" meaning it has full control of the wire on a single frequency; and the "T" stands for "twisted pair" cable. Fiber cable can also be used at this level in 10BaseFL.

Fast Ethernet

´  The Fast Ethernet protocol supports transmission up to 100 Mbps. Fast Ethernet requires the use of different, more expensive network concentrators/hubs and network interface cards. In addition, category 5 twisted pair or fiber optic cable is necessary. Fast Ethernet standards include:

´  100BaseT - 100 Mbps over 2-pair category 5 or better UTP cable.

´  100BaseFX - 100 Mbps over fiber cable.

´  100BaseSX -100 Mbps over multimode fiber cable.

´  100BaseBX - 100 Mbps over single mode fiber cable.

Gigabit Ethernet

´  1000BaseT - 1000 Mbps over 2-pair category 5 or better UTP cable.

´  1000BaseTX - 1000 Mbps over 2-pair category 6 or better UTP cable.

´  1000BaseFX - 1000 Mbps over fiber cable.

´  1000BaseSX -1000 Mbps over multi mode fiber cable.

´  1000BaseBX - 1000 Mbps over single mode fiber cable.

for further info please watch the video 

what is the Difference between Switch and Router

What is a router

´  Router is a layer 3 device which works on network layer of OSI model which connects two different networks and it identifies network devices based on their IP addresses.

´  The Routers are the devices used for connecting local network to the other local network/s.

´  They are generally located at the gateway where two or more than two networks connect.

What is a switch

´  Switch is a layer 2 device which works on data link layer of OSI model, it communicates by using frames and it identifies network devices on the bases of MAC addresses or physical addresses.

Router:

1. Mode of transmission:

´                              It Transmits data in the form of packets.

      2. Address:

             It makes use of IP address for the purpose of data transmission.

      3.Layer of OSI Model:

            It makes use of layer 3 of OSI model.

4.Ports

          Routers contain 2 Ports by default like fast Ethernet Ports. However, we can add serial ports explicitly.

      5.Table:

      It makes use of the Routing Table for routes to get to the destination IP.

What is a Protocol

´  What is a Protocol?

´  A protocol is a set of rules that governs the communications between computers on a network.

´  In order for two computers to talk to each other, they must be speaking the same language.

´   Many different types of network protocols and standards are required to ensure that your computer (no matter which operating system, network card, or application you are using) can communicate with another computer located on the next desk or half-way around the world.

´  The OSI (Open Systems Interconnection) Reference Model defines seven layers of networking protocols.

´  DNS - Domain Name System - translates network address (such as IP addresses) into terms understood by humans (such as Domain Names) and vice-versa

´  DHCP - Dynamic Host Configuration Protocol - can automatically assign Internet addresses to computers and users

´  FTP - File Transfer Protocol - a protocol that is used to transfer and manipulate files on the Internet

´  HTTP – Hyper Text Transfer Protocol - An Internet-based protocol for sending and receiving webpages

´  IMAP - Internet Message Access Protocol - A protocol for e-mail messages on the Internet

´  IRC - Internet Relay Chat - a protocol used for Internet chat and other communications

´  POP3 - Post Office protocol Version 3 - a protocol used by e-mail clients to retrieve messages from remote servers

´  SMTP - Simple Mail Transfer Protocol - A protocol for e-mail messages on the Internet

for more detail please watch the video:

Wireless networks

q  More and more networks are operating without cables, in the wireless mode.

q  Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations, servers, or hubs.

q  Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data.

q  Information is relayed between transceivers as if they were physically connected.

q  For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission, or by satellite.

´  Wireless networks are great for allowing laptop computers, portable devices, or remote computers to connect to the LAN.

´  Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables.

´  The two most common types of infrared communications used in schools are line-of-sight and scattered broadcast.

 Line-of-sight communication means that there must be an unblocked direct line between the workstation and the transceiver

´  If a person walks within the line-of-sight while there is a transmission, the information would need to be sent again.

´  This kind of obstruction can slow down the wireless network.

´   Scattered infrared communication is a broadcast of infrared transmissions sent out in multiple directions that bounces off walls and ceilings until it eventually hits the receiver.

´  Networking communications with laser are virtually the same as line-of-sight infrared networks.

Wireless standards and speeds

´  The Wi-Fi Alliance is a global, non-profit organization that helps to ensure standards and interoperability for wireless networks, and wireless networks are often referred to as WiFi (Wireless Fidelity). The original Wi-Fi standard (IEEE 802.11) was adopted in 1997.

´   Since then many variations have emerged (and will continue to emerge). Wi-Fi networks use the Ethernet protocol.

Standard	Max Speed	Typical Range
802.11a	54 Mbps	150 feet
802.11b	11 Mbps	300 feet
802.11g	54 Mbps	300 feet
802.11n	100 Mbps	300+ feet

Wireless Security

´  Wireless networks are much more susceptible to unauthorized use than cabled networks.

´  Wireless network devices use radio waves to communicate with each other.

´  The greatest vulnerability to the network is that rogue machines can "eves-drop" on the radio wave communications.

´   Unencrypted information transmitted can be monitored by a third-party, which, with the right tools , could quickly gain access to your entire network, steal valuable passwords to local servers and online services, alter or destroy data, and/or access personal and confidential information stored in your network servers.

´   To minimize the possibility of this, all modern access points and devices have configuration options to encrypt transmissions.

´  These encryption methodologies are still evolving, as are the tools used by malicious hackers, so always use the strongest encryption available in your access point and connecting devices.

´  ENCRYPTION:

´  WEP (Wired Equivalent Privacy) encryption can be easily hacked with readily-available free tools which circulate the internet.

´   WPA and WPA2 (WiFi Protected Access versions 1 and 2) are much better at protecting information, but using weak passwords or passphrases when enabling these encryptions may allow them to be easily hacked.

´  If your network is running WEP, you must be very careful about your use of sensitive passwords or other data.

´  Three basic techniques are used to protect networks from unauthorized wireless use.

´   Use any and all of these techniques when setting up your wireless access points:

´  Encryption.

´  Enable the strongest encryption supported by the devices you will be connecting to the network. Use strong passwords (strong passwords are generally defined as passwords containing symbols, numbers, and mixed case letters, at least 14 characters long).

´  Isolation.

´  Use a wireless router that places all wireless connections on a subnet independent of the primary private network.

´  This protects your private network data from pass-through internet traffic.

´  Hidden SSID.

´  Every access point has a Service Set IDentifier (SSID) that by default is broadcast to client devices so that the access point can be found.

´   By disabling this feature, standard client connection software won't be able to "see" the access point.

´  However, the eves-dropping programs  can easily find these access points, so this alone does little more than keep the access point name out of sight for casual wireless users.

Advantages of wireless networks:

´  Mobility - With a laptop computer or mobile device, access can be available throughout a school, at the mall, on an airplane, etc.

´   More and more businesses are also offering free WiFi access ("Hot spots").

´  Fast setup - If your computer has a wireless adapter, locating a wireless network can be as simple as clicking "Connect to a Network" -- in some cases, you will connect automatically to networks within range.

´  Cost - Setting up a wireless network can be much more cost effective than buying and installing cables.

´  Expandability - Adding new computers to a wireless network is as easy as turning the computer on (as long as you do not exceed the maximum number of devices).

Disadvantages of wireless networks:

´  Security - Be careful. Be vigilant. Protect your sensitive data with backups, isolated private networks, strong encryption and passwords, and monitor network access traffic to and from your wireless network.

´  Interference - Because wireless networks use radio signals and similar techniques for transmission, they are susceptible to interference from lights and electronic devices.

´  Inconsistent connections –

´  wireless connections are not nearly as stable as those through a dedicated cable.

´  Speed - The transmission speed of wireless networks is improving; however, faster options (such as gigabit Ethernet) are available via cables.

´  If you are only using wireless for internet access, the actual internet connection for your home or school is generally slower than the wireless network devices, so that connection is the bottleneck.

´  If you are also moving large amounts of data around a private network, a cabled connection will enable that work to proceed much faster.

Types of cables:

´  Un-shielded Twisted Pair (UTP) Cable

´  Shielded Twisted Pair (STP) Cable

´  Coaxial Cable

´  Fiber Optic Cable

Twisted pair:

two varieties:

´   shielded and unshielded.

´  The quality of UTP may vary from telephone-grade wire to extremely high-speed cable.

´  The cable has four pairs of wires inside the jacket.

´  Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices.

´   The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot.

´  The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated six categories of wire (additional categories are emerging).

´  Unshielded Twisted Pair Connector

´  The standard connector for unshielded twisted pair cabling is an RJ-45 connector.

´   This is a plastic connector that looks like a large telephone-style connector.

´  A slot allows the RJ-45 to be inserted only one way.

´   RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry.

´  This standard designates which wire goes with each pin inside the connector.

Shielded Twisted Pair (STP) Cable:

´  Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference .

´  If you must place cable in environments with lots of potential interference, or if you must place cable in extremely sensitive environments that may be susceptible to the electrical current in the UTP, shielded twisted pair may be the solution.

´   Shielded cables can also help to extend the maximum distance of the cables.

´  Shielded twisted pair cable is available in three different configurations:

1. Each pair of wires is individually shielded with foil.
2. There is a foil or braid shield inside the jacket covering all wires (as a group).
3. There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).

Coaxial Cable:

´  Coaxial cabling has a single copper conductor at its center.

´   A plastic layer provides insulation between the center conductor and a braided metal shield .

´  The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

´  Although coaxial cabling is difficult to install, it is highly resistant to signal interference.

´  In addition, it can support greater cable lengths between network devices than twisted pair cable.

´   The two types of coaxial cabling are thick coaxial and thin coaxial.

´  Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals.

´   The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable has been popular in school networks, especially linear bus networks.

´  Thick coaxial cable is also referred to as thicknet.

´   10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals.

´  The 5 refers to the maximum segment length being 500 meters.

´   Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor.

´  This makes thick coaxial a great choice when running longer lengths in a linear bus network.

´  One disadvantage of thick coaxial is that it does not bend easily and is difficult to install.

Fiber Optic Cable:

´  Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials.

´  It transmits light rather than electronic signals eliminating the problem of electrical interference.

´  This makes it ideal for certain environments that contain a large amount of electrical interference.

´   It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting.

´  Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair.

´  It also has the capability to carry information at vastly greater speeds.

´  This capacity broadens communication possibilities to include services such as video conferencing and interactive services.

´  The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify.

´  10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals.

´  The center core of fiber cables is made from glass or plastic fibers .

´   A plastic coating then cushions the fiber center, and kevlar fibers help to strengthen the cables and prevent breakage.

´   The outer insulating jacket made of teflon or PVC

´  There are two common types of fiber cables -- single mode and multimode.

´  Multi-mode cable has a larger diameter; however, both cables provide high bandwidth at high speeds.

´  Single mode can provide more distance, but it is more expensive.

Networking Devices

Equipment can be divided into two types :

■ End user devices—Include computers, printers, scanners, and other devices that provide services directly to the user.

■ Network devices—Include all devices that connect the end-user devices to allow them to communicate.

Repeaters

´  Repeaters are networking devices that exist at Layer 1,  (physical layer), of the OSI reference model.

´   data  is transformed into either electrical or light pulses that pass along the networking medium. These pulses are called signals.

´  When signals leave a transmitting station, they are clean and easily recognizable.

´  However, the longer the cable length, the weaker and more deteriorated the signals become as they pass along the networking medium.

´  The purpose of a repeater is to regenerate and retime network signals at the bit level(0,1), allowing them to travel a longer distance on the medium.

Hubs

´  The purpose of a hub is to regenerate and retime network signals.

´  The characteristics of a hub are similar to those of a repeater.

´   A hub is a common connection point for devices in a network.

´  Hubs commonly connect segments of a LAN.

´  A hub contains multiple ports. When a packet arrives at one port, it is copied tocthe other ports so that all the LAN’s segments can see all the packets.

      Hub do  broadcast which increase a load on network.

´  Because hubs and repeaters have similar characteristics, a hub is also called a multiport repeater.

´  The difference between a repeater and a hub is the number of cables that connect to the device.

´  Whereas a repeater typically has only two ports, a hub generally has

´  from four to 20 or more ports.

´  Whereas a repeater receives on one port and repeats on the other, a hub receives on one port and transmits on all the other ports

´  The following are the most important properties of hubs:

´   

´  Hubs amplify signals.

´  Hubs propagate signals through the network.

´  Hubs do not require filtering.

´  Hubs do not require path determination or switching.

´  Hubs are used as network-concentration points.

Network Interface Cards

´  Network interface cards (NICs) are considered Layer 2 devices

´   NIC throughout the world carries a unique code, called a Media Access Control (MAC) address.

´  This address controls data communication for the host on the LAN.

´  The NIC controls the access of the host to the medium.

Bridges

´  A bridge is a Layer 2(data link layer) device designed to create two or more LAN segments, each of which is a separate collision domain.

´   In other words, bridges were designed to create more usable bandwidth. The purpose of a bridge is to filter traffic on a LAN to keep local traffic local yet allow connectivity to other parts (segments) of the LAN for traffic that is directed there.

´  Every networking device has a unique MAC address on the NIC.

´  The bridge keeps track of which MAC addresses are on each side of the bridge and makes forwarding decisions based on this MAC address list.

´  Bridges filter network traffic by looking only at the MAC address. Therefore, they can rapidly forward traffic representing any network layer protocol.

´  bridges look only at MAC addresses, they are not concerned with network layer protocols.

´    bridges are concerned only with passing or not passing frames, based on their destination MAC addresses.

´  Bridges are more “intelligent” than hubs. That is, they can analyze incoming frames and forward (or drop) them based on addressing information.

´   Bridges collect and pass packets between two or more LAN segments.

´  Bridges create more collision domains, allowing more than one device to transmit simultaneously without causing a collision.

´  Bridges maintain MAC address tables.

Layer 2 Switches

´  Layer 2 switches, also called LAN switches or workgroup switches, often replace shared hubs and work with existing cable infrastructures to ensure that the switches are installed with minimal disruption of existing networks.

´  Like bridges, switches connect LAN segments, use a table of MAC addresses to determine the segment on which a frame needs to be transmitted, and reduce traffic.

´  Switches operate at much higher speeds than bridges.

´  Switches are data link layer devices that, like bridges, let multiple physical LAN segments be interconnected into single larger networks.

´   Similar to bridges, switches forward and flood traffic based on MAC addresses.

´  Because switching is performed in hardware, it is significantly faster than the switching function performed by a bridge using software.

Routers

´  A router, is a type of internetworking device that passes data packets between networks based on Layer 3(network layer) addresses.

´   A router can make decisions regarding the best path for delivery of data on the network.

´   Layer 3 allows the router to make decisions based on network addresses instead of individual Layer 2 MAC addresses.

´  Routers also can connect different Layer 2 technologies, such as Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI).

´  Routers also commonly connect Asynchronous Transfer Mode (ATM) and serial connections.

´  However, because of their capability to route packets based on Layer 3 information,routers have become the backbone of the Internet and run the IP protocol.

´  The purpose of a router is to examine incoming packets (Layer 3 data), choose the best path for them through the network, and then switch them to the proper outgoing port.

´  Routers are the most important traffic-regulating devices on large networks.

´  Routers let virtually any type of computer communicate with any other computer anywhere in the world.