9.SWITCH

BASIC OF SWITCH

1.Switch is an intelligent device.

2.Switches and Bridges are similar devices used on different mediums.

3.Switch are used on twisted pair and fibre medium whereas bridges are used on thick wire and thin  wire medium.

4.switches and bridges are interchangable terms.

5.switch is layer 2 device.

6.switch takes forwarding decision on the basis of MAC table.

7.MAC table is layer 2 table and hence switch is layer 2 device.

SWITCH OPERATION-

                 SWITCH OPERATION

1. Whenever a switch receives a frame on port ,it will read source MAC address and make an entry of this MAC address in its own MAC table against the port number on which it was received.
2. After reading source MAC address, switch will read destination MAC address and refer MAC table to take forwarding decisions.
3. If destination MAC address is listed in MAC table,switch will forward the frame to the appropriate port only and not to all ports.unlike a hub which will forward the frame to all ports.
4. If destination MAC address is listed in MAC table,switch will create multiple copies of frame and forward it to all ports.
5. If switch receives a broadcast frame,switch will create multiple copies of broadcast frame and   forward it to all ports.
6. Switch does not create a broadcast but it will forward a broadcast receive on a port.
7. If source MAC address and destination MAC address are on two different ports,switch will create a logical bridge between the source port and destination port and forward the frame to destination port only.
8. If source MAC address and destination MAC address are on the same port,switch will       discard/drop/block the frame.
9. Switch allows simultaneous communication bandwidth multiple communicating pairs connected on    different ports.

MAC TABLE/CAM TABLE(Content Addressable Memory)-

1. MAC Table is a layer of 2 table.
2. MAC Table can be populated dynamically via self learning or statically by an Admin.
3. To keep MAC Table concise and precise, MAC entries have to be monitored and state entries have to be deleted.
4. Any entries not referred or used for specific period of time is known as state entry.
5. SWITCH will remove state entries from MAC Table.
6. State entry could be 30 minutes or based on manufacturer.
7. Removal of state entries is essential to keep MAC Table concise and precise.
8. Every port of switch has it's own dedicated bandwidth.
9. SWITCH is dedicated bandwidth device.
10. Every port of switch is member of a separate collision domain.
11. SWITCH is a multiple collision domain device.
12. Every port of switch is member of the same broadcast domain.
13. SWITCH is a single broadcast domain device.
14. SWITCH will perform layer 2 as well as layer 1 functions which is taking forwarding decision on the basis of layer 2 address as well as boosting the signal when transmitting out of port.

8.HUBS/REPEATERS

HUBS/REPEATERS

1. HUB is dump device.

2. HUB and REPEATERS are similar device used on different medium.

3. HUBS are used on twisted pair and fiber medium whereas REPEATERS are used on thick wire      and    thin wire medium.

4. HUBS and REPEATERS are interchangable terms.

5. Whenever hubs receives  a signal on port,it will boost the signal and send it out of all other port.

6. HUBS only facilitates communication,they do not participate in communication.

7. HUBS will not only boost the signal but also restore the signal level.

8. Communication is never destined to the hub, It is destined for another node connected through the       hub.

9. After boosting the signal,it is sent out of all ports,except the port on which it was originally                 received.

10. Every port of a hub, shares the same bandwidth.hub is a shared bandwidth device.

11. Every port of hub is a member of the same collision domain.

12. Hub is a single collision domain device.

13. Every port of hub is a member of the same broadcast domain.

14. hub is a single broadcast domain device.

HUBS/REPEATERS

ADVANTAGES-

1. Increased coverage area.

2. Increase in number of computers that can be connected.

DISADVANTAGES-

1. With increase in number of computers,the probability of computer acquiring medium has reduced.

2. With increase in number of computers,the probability of collision has increased.

*Hub is layer 1 device.Any thing that is physical in nature and used between two communicating pairs are known as layer 1 component.

e.g.wires,cables,connectors,pins,voltages boosting and repeating devices 

    are known as layer 1 device.

7.COMMUNICATION TYPES IN NETWORKING

7.COMMUNICATION TYPES IN NETWORKING

      

The network communication types in IPV4 there are 3 types but there is no BROADCAST in IPV6.

1.UNICAST

2.MULTICAST

3.BROADCAST

1.UNICAST

Defination: When communication is sent for  a single device is called as UNICAST communication.

Ethernet is multiaccess medium,when one device send data with only one destination address then packet will go to all device but is ment for only one device is called as UNICAST.

Unicast is a type of communication where data is sent from one computer to another computer.

UNICAST COMMUNICATION

Example:

1) Browsing a website. (Webserver is the sender and your computer is the receiver.)

2) Downloading a file from a FTP Server. (FTP Server is the sender and your computer is the receiver.)

2.MULTICAST

Defination: When packet is sent for group of device then communication is called as MULTICAST communication.

MULTICAST COMMUNICATION

Example:

when multiple clients require same data at the same instance (for example, online TV) we can use multicast instead of unicast.

3.BROADCAST

Defination: When packet is sent for all device in the network is called as BROADCAST communication.

BROADCAST COMMUNICATION

Switches by design will forward the broadcast traffic and Routers by design will drop the broadcast traffic. In other words, Routers will not allow a broadcast from one LAN to cross the Router and reach another Network Segment. The primary function of a Router is to divide a big Broadcast domain to Multiple smaller Broadcast domain.

Example: ARP Request message, DHCP DISCOVER Message

6.Carrier Sense Multiple Access

CSMA/CD (Carrier Sense Multiple Access/Collision Detect):

            

CSMA/CD (Carrier Sense Multiple Access/Collision Detect)

                      

                                  

1.If computer A wants to communicate over the multi-access medium then, it will sence the carrier/medium i.e cable.

2.It will check wheather,there is any communication on same medium is going on i.e sensing carrier.

3.If there any communication is going on then computer A will wait else if it is found medium as free then it will start to send data on medium and communication will continue.

4.If at a same time computer A and computer D sensed carrier and found that medium is free then both are send their data at a same time at that time collision between both data will occur.

5.So because of collision packet or data gets corrupted and sent to all computers then they will detect collision.

  

How collision is detected:

Because of every frame cyclic redundancy check bit is added.

If collision occurs then FCS,CRC and DATA gets separated then computer will detect that collision has occurred.  

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance):

1.When collision gets detected and  all device gets corrupt data then all devices will goes in Integral Wait State.

2.Which device is near the collision that device is first goes in Integral Wait State.

3.In Integral Wait State that device can not transmit any data.

4.which device first went in Integral Wait State that device will first came out from the Integral Wait State.

5.then by the preference all device will get a chance to send the data,this technique is known as collision avoidance.

5.1 Serial Technology

2.Serial Technology

Serial Technology means Low Bandwidth | high cost | High coverage -> Preferred for WAN

High Coverage:

Amplitude of signal in serial technology is +12V or -12V.

It gives high coverage i.e. signal lost for long distance.

Low Bandwidth:

When amplitude of signal is more, coverage increase but frequency decreases, so eventually bandwidth decreases.

Point to Point:

It's Point to Point network.

Point to Point 

No MAc address required:

As it is point to point network it does not require physical/MAc address because destination is unique.

If 1--> +12 V
If 0--> -12 V

ISDN --> 64kbps--> 2 Mbps
T1--> 1.544 Mbps (US,JAPAN,CANADA)
E1--> 2.048 Mbps (Rest of world)

5.Networking Technology

Networking Technology

Technology:- This is a platform on the basis of which products are manufactured.

EX:-Technology-->LCD and Product-->TV,Mobile etc. 

There are two types of networking technology,

1.Ethernet Technology

2.Serial Technology

1.Ethernet Technology

Ethernet technology means High Bandwidth | Low cost | Low coverage -> Preferred for LAN

          The term Ethernet refers to the family of local-area network (LAN) products covered by the IEEE 802.3 standard that defines what is commonly known as the CSMA/CD protocol. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD ) protocol. Three data rates are currently defined for operation over optical fiber and twisted-pair cables:

• 10 Mbps—10Base-T Ethernet

• 100 Mbps—Fast Ethernet

• 1000 Mbps—Gigabit Ethernet

Ethernet technology standards:

* wired 802.3 (IEEE)

* wirless 802.11 (IEEE)

Protocol: ARPA (Host Name Server Protocol)

2.Serial Technology

Serial Technology means Low Bandwidth | high cost | High coverage -> Preferred for WAN

  

4.6 Wireless LANs

4.6 Wireless LANs

        More and more networks are operating without cables, in the wireless mode. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations, servers, or hubs. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. 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 (free to download), 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.

A NOTE ON ENCRYPTION: As of this writing 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 discussed previously 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 - How many times have you hears "Wait a minute, I just lost my connection?" Because of the interference caused by electrical devices and/or items blocking the path of transmission, 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.

4.5 Installing Cable - Some Guidelines

4.5 Installing Cable - Some Guidelines

1. When running cable, it is best to follow a few simple rules:
2. Always use more cable than you need. Leave plenty of slack.
3. Test every part of a network as you install it. Even if it is brand new, it may have problems that will be difficult to isolate later.
4. Stay at least 3 feet away from fluorescent light boxes and other sources of electrical interference.
5. If it is necessary to run cable across the floor, cover the cable with cable protectors.
6. Label both ends of each cable.
7. Use cable ties (not tape) to keep cables in the same location together.

4.4 Fiber Optic Cable

4.4 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.

Fiber optic cable

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

Specification	Cable Type
10BaseT	Unshielded Twisted Pair
10Base2	Thin Coaxial
10Base5	Thick Coaxial
100BaseT	Unshielded Twisted Pair
100BaseFX	Fiber Optic
100BaseBX	Single mode Fiber
100BaseSX	Multimode Fiber
1000BaseT	Unshielded Twisted Pair
1000BaseFX	Fiber Optic
1000BaseBX	Single mode Fiber
1000BaseSX	Multimode Fiber

4.3 Coaxial Cable

4.3 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.

Coaxial cable

      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.

Coaxial Cable Connectors

          The most common type of connector used with coaxial cables is the Bayone-Neill-Concelman (BNC) connector. Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather screw, onto the cable.

                                                     
                                                                     

BNC Connector

4.2 Shielded Twisted Pair (STP) Cable

4.2 Shielded Twisted Pair (STP) Cable

            Although UTP cable is the least expensive cable, it may be susceptible to radio and electrical frequency interference (it should not be too close to electric motors, fluorescent lights, etc.). 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

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).

4.1 Unshielded Twisted Pair (UTP) Cable

4.1 Unshielded Twisted Pair (UTP) Cable

           Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks.

Unshielded twisted pair

           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).

Categories of Unshielded Twisted Pair

Category	Speed	Use
1	1 Mbps	Voice Only (Telephone Wire)
2	4 Mbps	LocalTalk & Telephone (Rarely used)
3	16 Mbps	10BaseT Ethernet
4	20 Mbps	Token Ring (Rarely used)
5	100 Mbps (2 pair)	100BaseT Ethernet
	1000 Mbps (4 pair)	Gigabit Ethernet
5e	1,000 Mbps	Gigabit Ethernet
6	10,000 Mbps	Gigabit Ethernet

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.

RJ-45 connector