Ubuntu 13.04 mouse click dosen't work

If your mouse left click suddenly stop working try following commands,

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$ sudo modprobe -r psmouse
$ sudo modprobe psmouse

TCP/IP model

The types of services performed and protocols used at each layer within the TCP/IP model are described in more detail in the following table.

 

Layer	Description	Protocols
Application	Defines TCP/IP application protocols and how host programs interface with transport layer services to use the network.	HTTP, Telnet, FTP, TFTP, SNMP, DNS, SMTP, X Windows, other application protocols
Transport	Provides communication session management between host computers. Defines the level of service and status of the connection used when transporting data.	TCP, UDP, RTP
Internet	Packages data into IP datagrams, which contain source and destination address information that is used to forward the datagrams between hosts and across networks. Performs routing of IP datagrams.	IP, ICMP, ARP, RARP
Network interface	Specifies details of how data is physically sent through the network, including how bits are electrically signaled by hardware devices that interface directly with a network medium, such as coaxial cable, optical fiber, or twisted-pair copper wire.	Ethernet, Token Ring, FDDI, X.25, Frame Relay, RS-232, v.35

OSI 7 Layers Reference Model

These 7 layers further divide the tasks of moving the data across the network into subtask and hence complete one communication cycle between two computers or two network devices. Each layer is assigned a task and the task is completed independently. The OSI layers have the clear and independent characteristics and tasks.

The 7 layers of the OSI models can be divided into upper and lower layers. I have defined the characteristics, tasks and features of each layer separately.

Layer 7: Application Layer

The application layer defines the interfaces for communication and data transfer. This layer also provides and support services such as job transfer, handles network access, e-mail, supports user applications and error recovery.

Protocols: FTP, DNS, SNMP (simple network management protocol), SMTP (simple message transfer protocol), FINGER (which gives user profile information), TELNET (terminal access protocol), TFTP (trivial ftp), BOOTP and SMB protocol are operated on the application layer.

Network Devices: Gateway network device is operated on the application layer.

Layer 6:Presentation Layer

The presentation layer presents the data into a uniform format and masks the difference of data format between two dissimilar systems. It also translates the data from application to the network format. Presentation layer is also responsible for the protocol conversion, encryption, decryption and data compression. Presentation layer is a best layer for cryptography.

Network Devices: Gateway Redirector is operates on the presentation layer.

Layer 5: Session Layer

Session layer establish and manages the session between the two users at different ends in a network. Session layer also manages who can transfer the data in a certain amount of time and for how long. The examples of session layers and the interactive logins and file transfer sessions. Session layer reconnect the session if it disconnects. It also reports and logs and upper layer errors.

Protocols: The protocols that work on the session layer are NetBIOS, Mail Slots, Names Pipes, RPC

Network Devices: Gateway

Layer 4: Transport Layer

Transport layer manages end to end message delivery in a network and also provides the error checking and hence guarantees that no duplication or errors are occurring in the data transfers across the network. Transport layer also provides the acknowledgement of the successful data transmission and retransmits the data if no error free data was transferred.

It also provides and error handling and connectionless oriented data deliver in the network.

Protocols: These protocols work on the transport layer TCP, SPX, NETBIOS, ATP and NWLINK.

Network Devices: The Brouter, Gateway and Cable tester work on the transport layer.

Layer 3: Network Layer

The network layer determines that how data transmits between the network devices. It also translates the logical address into the physical address e.g computer name into MAC address. It is also responsible for defining the route, managing the network problems and addressing. Router works on the network layer and if a sending device does not break the data into the similar packets as the receiving device then network layer split the data into the smaller units and at the receiving end the network layer reassemble the data.

Network layer routes the packets according to the unique network addresses. Router works as the post office and network layer stamps the letters (data) for the specific destinations.

Protocols: These protocols work on the network layer IP, ICMP, ARP, RIP, OSI, IPX and OSPF.

Network Devices: Network devices including Router, Brouter, Frame Relay device and ATM switch devices work on the network layer.

Layer 2:Data Link Layer

Defines procedures for operating the communication links

Frames packets

Detects and corrects packets transmit errors

Protocols: Logical Link Control

• error correction and flow control

• manages link control and defines SAPs

802.1 OSI Model

802.2 Logical Link Control

Media Access Control

• communicates with the adapter card

• controls the type of media being used:

802.3 CSMA/CD (Ethernet)

802.4 Token Bus (ARCnet)

802.5 Token Ring

802.12 Demand Priority

Network Devices: Bridge

Switch

ISDN Router

Intelligent Hub

NIC

Advanced Cable Tester

Layer 1: Physical Layer

Physical layer defines and cables, network cards and physical aspects. It defines raw bit stream on the physical media. It also provides the interface between network and network communication devices. It is also responsible for how many volts for 0 and how many for 1. Physical layer also checks the number of bits transmitted per second and two ways or one way transmission. Physical layer also dealing with the optical, mechanical and electrical features.

Protocols: Protocols that work on the physical layer are ISDN, IEEE 802 and IEEE 802.2

Network Devices: Hubs, Repeaters, Oscilloscope and Amplifier works on the network devices.

Layer 1+2 protocols

• Ethernet
• GFP ITU-T G.7041 Generic Framing Procedure
• OTN ITU-T G.709 Optical Transport Network also called Optical Channel Wrapper or Digital Wrapper Technology

Layer 2 protocols (Data Link Layer)

• ARCnetre Attached Resource Computer NETwork
• ARP Address Resolution Protocol
• RARP Reverse Address Resolution Protocol
• CDP Cisco Discovery Protocol
• DCAP Data Link Switching Client Access Protocol
• Dynamic Trunking Protocol
• Econetr
• FDDI Fiber Distributed Data Interface
• Frame Relay
• ITU-T G.hn Data Link Layer
• HDLC High-Level Data Link Control
• IEEE 802.11 WiFi
• IEEE 802.16 WiMAX
• LocalTalk
• L2F Layer 2 Forwarding Protocol
• L2TP Layer 2 Tunneling Protocol
• LAPD Link Access Procedures on the D channel
• LLDP Link Layer Discovery Protocol
• LLDP-MED Link Layer Discovery Protocol - Media Endpoint Discovery
• PPP Point-to-Point Protocol
• PPTP Point-to-Point Tunneling Protocol
• Q.710 Simplified Message Transfer Part
• NDP Neighbor Discovery Protocol
• RPR IEEE 802.17 Resilient Packet Ring
• SLIP Serial Line Internet Protocol (obsolete)
• StarLANr
• STP Spanning Tree Protocol
• Token ring is not a protocol but is a topology
• VTP VLAN Trunking Protocol

Layer 2+3 protocols

• ATM Asynchronous Transfer Mode
• Frame relay, a simplified version of X.25 welcome
• MPLS Multi-protocol label switching
• X.25

Layer 1+2+3 protocols

• MTP Message Transfer Part
• NSP Network Service Part

Layer 3 protocols (Network Layer)

• CLNP Connectionless Networking Protocol
• EGP Exterior Gateway Protocol
• EIGRP Enhanced Interior Gateway Routing Protocol
• ICMP Internet Control Message Protocol
• IGMP Internet Group Management Protocol
• IGRP Interior Gateway Routing Protocol
• IPv4 Internet Protocol version 4
• IPv6 Internet Protocol version 6
• IPSec Internet Protocol Security
• IPX Internetwork Packet Exchange
• SCCP Signalling Connection Control Part
• AppleTalk DDP

Layer 3 protocols (Network Layer management)

• IS-IS Intermediate System-to-Intermediate System
• OSPF Open Shortest Path First
• BGP Border Gateway Protocol
• RIP Routing Information Protocol
• ICMP Router Discovery Protocol: Implementation of RFC 1256
• Gateway Discovery Protocol (GDP) is a Cisco protocol similar to IRDP

Layer 3.5 protocols

• HIP Host Identity Protocol

Layer 3+4 protocol suites

• AppleTalk
• DECnet
• IPX/SPX
• Internet Protocol Suite
• Xerox Network Systems

Layer 4 protocols (Transport Layer)

• AH Authentication Header over IP or IPSec
• ESP Encapsulating Security Payload over IP or IPSec
• GRE Generic Routing Encapsulation for tunneling
• IL Originally developed as transport layer for 9P
• SCTP Stream Control Transmission Protocol
• Sinec H1 for telecontrol
• SPX Sequenced Packet Exchange
• TCP Transmission Control Protocol
• UDP User Datagram Protocol

Layer 5 protocols (Session Layer)

• 9P Distributed file system protocol developed originally as part of Plan 9
• NCP NetWare Core Protocol
• NFS Network File System
• SMB Server Message Block
• SOCKS "SOCKetS"

Other protocols

• Controller Area Network (CAN)

Layer 7 protocols (Application Layer)

• ADC, A peer-to-peer file sharing protocol
• AFP, Apple Filing Protocol
• BACnet, Building Automation and Control Network protocol
• BitTorrent, A peer-to-peer file sharing protocol
• BOOTP, Bootstrap Protocol
• CAMEL, an SS7 protocol tool for the home operator
• Diameter, an authentication, authorization and accounting protocol
• DICOM includes a network protocol definition
• DICT, Dictionary protocol
• DNS, Domain Name System
• DHCP, Dynamic Host Configuration Protocol
• ED2K, A peer-to-peer file sharing protocol
• FTP, File Transfer Protocol
• Finger, which gives user profile information
• Gnutella, a peer-to-peer file-swapping protocol
• Gopher, a hierarchical hyperlinkable protocol
• HTTP, Hypertext Transfer Protocol
• IMAP, Internet Message Access Protocol
• Internet Relay Chat (IRC)
• ISUP, ISDN User Part
• XMPP, an instant-messaging protocol
• LDAP Lightweight Directory Access Protocol
• MIME, Multipurpose Internet Mail Extensions
• MSNP, Microsoft Notification Protocol (used by Windows Live Messenger)
• MAP, Mobile Application Part
• NetBIOS, File Sharing and Name Resolution protocol - the basis of file sharing with Windows.
• NNTP, News Network Transfer Protocol
• NTP, Network Time Protocol
• NTCIP, National Transportation Communications for Intelligent Transportation System Protocol
• POP3 Post Office Protocol Version 3
• RADIUS, an authentication, authorization and accounting protocol
• Rlogin, a UNIX remote login protocol
• rsync, a file transfer protocol for backups, copying and mirroring
• RTP, Real-time Transport Protocol
• RTSP, Real-time Transport Streaming Protocol
• SSH, Secure Shell
• SISNAPI, Siebel Internet Session Network API
• SIP, Session Initiation Protocol, a signaling protocol
• SMTP, Simple Mail Transfer Protocol
• SNMP, Simple Network Management Protocol
• SOAP, Simple Object Access Protocol
• STUN, Session Traversal Utilities for NAT
• TUP, Telephone User Part
• Telnet, a remote terminal access protocol
• TCAP, Transaction Capabilities Application Part
• TFTP, Trivial File Transfer Protocol, a simple file transfer protocol
• WebDAV, Web Distributed Authoring and Versioning
• DSM-CC Digital Storage Media Command and Control

Switching Techniques

Circuit Switching

This method involves the physical interconnection of two devices. A good example of circuit switching involves the Public phone network. A data example would be the classic A/B switch!

Packet Switching

Packet Switching techniques switch packets of data between destinations. Traditionally, this applied to X.25 techniques, but this also applies to TCP/IP and IPX/SPX routers also. Proprietary Frame Relay switches can switch voice signals.

Message Switching

Message Switching techniques were originally used in data communications. An example would be early "store and forward" paper tape relay systems. E-Mail delivery is another example of message switching. In voice systems, you can find Voice Mail delivery systems on the Internet. The classic "forward voice mail" capability in some voice mail systems is another example.

Cell Switching

Cell Switching is similar to packet switching, except that the switching does not necessarily occur on packet boundaries. This is ideal for an integrated environment and is found within Cell-based networks, such as ATM. Cell-switching can handle both digital voice and data signals.

The Difference Between Hubs, Switches and Routers

Hub

A common connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

Switch

In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.

Router

A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP.s network. Routers are located at gateways, the places where two or more networks connect. Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP (Internet Control Message Protocol) to communicate with each other and configure the best route between any two hosts.

The Differences Between Hubs, Switches, and Routers on the Network

The functions of a router, hub and a switch are all quite different from one another, even if at times they are all integrated into a single device. Let's start with the hub and the switch since these two devices have similar roles on the network. Each serves as a central connection for all of your network equipment and handles a data type known as frames. Frames carry your data. When a frame is received, it is amplified and then transmitted on to the port of the destination PC. The big difference between these two devices is in the method in which frames are being delivered.

In a hub, a frame is passed along or "broadcast" to every one of its ports. It doesn't matter that the frame is only destined for one port. The hub has no way of distinguishing which port a frame should be sent to. Passing it along to every port ensures that it will reach its intended destination. This places a lot of traffic on the network and can lead to poor network response times.

A switch, however, keeps a record of the MAC addresses of all the devices connected to it. With this information, a switch can identify which system is sitting on which port. So when a frame is received, it knows exactly which port to send it to, without significantly increasing network response times. And, unlike a hub, a 10/100Mbps switch will allocate a full 10/100Mbps to each of its ports. So regardless of the number of PCs transmitting, users will always have access to the maximum amount of bandwidth. It's for these reasons why a switch is considered to be a much better choice then a hub.

Routers are completely different devices. Where a hub or switch is concerned with transmitting frames, a router's job, as its name implies, is to route packets to other networks until that packet ultimately reaches its destination.

A router is typically connected to at least two networks, commonly two Local Area Networks (LANs) or Wide Area Networks (WAN) or a LAN and its ISP's network . for example, your PC or workgroup and EarthLink. Routers are located at gateways, the places where two or more networks connect. Using headers and forwarding tables, routers determine the best path for forwarding the packets. Router use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

All routers have a WAN Port that connects to a DSL or cable modem for broadband Internet service and the integrated switch allows users to easily create a LAN. This allows all the PCs on the LAN to have access to the Internet and Windows file and printer sharing services.

Some of the more high-end or business class routers will also incorporate a serial port that can be connected to an external dial-up modem, which is useful as a backup in the event that the primary broadband connection goes down, as well as a built in LAN printer server and printer port.

So, in short, a hub glues together an Ethernet network segment, a switch can connect multiple Ethernet segments more efficiently and a router can do those functions plus route TCP/IP packets between multiple LANs and/or WANs; and much more of course.

SUBNET

    A subnet allows the flow of network traffic between hosts to be segregated based on a network configuration. By organizing hosts into logical groups, subnetting can improve network security and performance.

Subnet Mask

Perhaps the most recognizable aspect of subnetting is the subnet mask. Like IP addresses, a subnet mask contains four bytes (32 bits) and is often written using the same "dotted-decimal" notation. For example, a very common subnet mask in its binary representation

11111111 11111111 11111111 00000000

is typically shown in the equivalent, more readable form

255.255.255.0

Applying a Subnet Mask

A subnet mask neither works like an IP address, nor does it exist independently from them. Instead, subnet masks accompany an IP address and the two values work together. Applying the subnet mask to an IP address splits the address into two parts, an "extended network address" and a host address.

For a subnet mask to be valid, its leftmost bits must be set to '1'. For example,

00000000 00000000 00000000 00000000

is an invalid subnet mask because the leftmost bit is set to '0'.

Conversely, the rightmost bits in a valid subnet mask must be set to '0', not '1'. Therefore,

11111111 11111111 11111111 11111111

is invalid.

All valid subnet masks contain two parts: the left side with all mask bits set to '1' (the extended network portion) and the right side with all bits set to '0' (the host portion), such as the first example above.

Classes of IP Addresses, IP Broadcast and IP Multicast

IPv4 Address Classes

The IPv4 address space can be subdivided into 5 classes - Class A, B, C, D and E. Each class consists of a contiguous subset of the overall IPv4 address range. With a few special exceptions explained further below, the values of the leftmost four bits of an IPv4 address determine its class as follows:

Class	Leftmost bits	Start address	Finish address
A	0xxx	0.0.0.0	127.255.255.255
B	10xx	128.0.0.0	191.255.255.255
C	110x	192.0.0.0	223.255.255.255
D	1110	224.0.0.0	239.255.255.255
E	1111	240.0.0.0	255.255.255.255

All Class C addresses, for example, have the leftmost three bits set to '110', but each of the remaining 29 bits may be set to either '0' or '1' independently (as represented by an x in these bit positions):

110xxxxx xxxxxxxx xxxxxxxx xxxxxxxx

Converting the above to dotted decimal notation, it follows that all Class C addresses fall in the range from 192.0.0.0 through 223.255.255.255.

IP Address Class E and Limited Broadcast

The IPv4 networking standard defines Class E addresses as reserved, meaning that they should not be used on IP networks. Some research organizations use Class E addresses for experimental purposes. However, nodes that try to use these addresses on the Internet will be unable to communicate properly.

A special type of IP address is the limited broadcast address 255.255.255.255. A broadcast involves delivering a message from one sender to many recipients. Senders direct an IP broadcast to 255.255.255.255 to indicate all other nodes on the local network (LAN) should pick up that message. This broadcast is 'limited' in that it does not reach every node on the Internet, only nodes on the LAN.

Technically, IP reserves the entire range of addresses from 255.0.0.0 through 255.255.255.255 for broadcast, and this range should not be considered part of the normal Class E range.

IP Address Class D and Multicast

The IPv4 networking standard defines Class D addresses as reserved for multicast. Multicast is a mechanism for defining groups of nodes and sending IP messages to that group rather than to every node on the LAN (broadcast) or just one other node (unicast).

Multicast is mainly used on research networks. As with Class E, Class D addresses should not be used by ordinary nodes on the Internet.

IP Loopback, IP Private Addresses, and IPv6 Address Types

IP Loopback Address

127.0.0.1 is the loopback address in IP. Loopback is a test mechanism of network adapters. Messages sent to 127.0.0.1 do not get delivered to the network. Instead, the adapter intercepts all loopback messages and returns them to the sending application. IP applications often use this feature to test the behavior of their network interface.

As with broadcast, IP officially reserves the entire range from 127.0.0.0 through 127.255.255.255 for loopback purposes. Nodes should not use this range on the Internet, and it should not be considered part of the normal Class A range.

Zero Addresses

As with the loopback range, the address range from 0.0.0.0 through 0.255.255.255 should not be considered part of the normal Class A range. 0.x.x.x addresses serve no particular function in IP, but nodes attempting to use them will be unable to communicate properly on the Internet.

Private Addresses

The IP standard defines specific address ranges within Class A, Class B, and Class C reserved for use by private networks (intranets). The table below lists these reserved ranges of the IP address space.

Definition: Intranet is the generic term for a collection of private computer networks within an organization. An intranet uses network technologies as a tool to facilitate.

Why use Python language for application development ratherthan other programming languages?

Python is just the language for you.

• Python is simple to use, but it is a real programming language, offering much more structure and support for large programs than shell scripts or batch files can offer.
• Python also offers much more error checking than C, and, being a very-high-level language, it has high-level data types built in, such as flexible arrays and dictionaries.
• Python allows you to split your program into modules that can be reused in other Python programs.
•  Python is an interpreted language, which can save you considerable time during program development because no compilation and linking is necessary.