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