Network / System Informations: July 2011

Friday, 1 July 2011

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Point-to-point Communication

The first computer communication systems had each communication channel, e.g. a leased circuit, connecting exactly two computers. This is known as point-to-point communication and has three useful properties.

Each connection is independent of the others and can use appropriate hardware.
The two end points have exclusive access and can decide how to send data across the connection.
Since only two computers have access to the channel, it is easy to enforce security and privacy.

However, point-to-point communications also have disadvantages. The main disadvantage is the proliferation of connections, as illustrated in Figure 1.

Figure 1: Point-to-point connections

In (a), two computers require one connection, while in (b), three computers require three connections. In (c), four computers requires six connections. The number of connections for N computers is proportional to the square of N, namely N(N-1)/2.
In practice, the cost is high because many connections follow the same physical path. Figure 2 illustrates the situation with five computers located in two locations.

Figure 2: Different locations

There are six connections between the two locations, more than the total number of computers being connected. Another computer added to location 1 increases the number of connections between the two locations to nine.
Apart from the fact that point-to-point communication does not scale, as the physical distance between computers increases, the cost of installing the point-to-point connections becomes prohibitively expensive.

LAN Topologies

In the late 1960s and the early 1970s researchers developed a form of computer communication known as Local Area Networks (LANs). These are different from long-distance communications because they rely on sharing the network. Each LAN consists of a single shared medium, usually a cable, to which many computers are attached. The computers co-ordinate and take turns using the medium to send packets.
Unfortunately, this mechanism does not scale. Co-ordination requires communication, and the time to communicate depends on distance - large geographic separation between computers introduces longer delays. Therefore, shared networks with long delays are inefficient. In addition, providing high bandwidth communication channels over long distances is very expensive.
There are a number of different LAN technologies. Each technology is classified into a category according to its topology, or general shape. The first of these is a star topology, as illustrated in Figure 3.

Figure 3: Star topology

The hub accepts data from a sender and delivers it to the receiver. In practice, a star network seldom has a symmetric shape; the hub often resides in a separate location from the computers attached to it.
A network using a ring topology arranges the computers in a circle - the first computer is cabled to the second. Another cable connects the second computer to the third, and so on, until a cable connects the final computer back to the first. This is illustrated in Figure 4.

Figure 4: Ring topology

Once again, the ring, like the star topology, refers to logical connections, not physical orientation.
A network that uses a bus topology consists of a number of computers all connected to a single, long cable. Any computer attached to the bus can send a signal down the cable, and all computers receive the signal. This is illustrated in Figure 5.

Figure 5: Bus topology

The computers attached to a bus network must co-ordinate to ensure that only one computer sends a signal at any time. In addition, the ends of a bus network must be terminated to prevent electrical signals from reflecting back along the bus.

Ethernet

Ethernet is a widely used technology employing a bus topology. The original standard was published by Digital Equipment Corporation, Intel Corporation, and Xerox Corporation in 1982. IEEE currently controls Ethernet standards, e.g. IEEE 802.3 was published in 1985.
In its original form, an Ethernet LAN consists of a single coaxial cable called the ether, but often referred to as a segment. A segment is limited to 500 m in length, with a minimum separation of 3 m between each pair of connections. It operates at 10 Mbps; a later version, Fast Ethernet, operates at 100 Mbps; the latest version, Gigabit Ethernet, operates at 1,000 Mbps or 1 Gbps.

Manchester Encoding

The standard specifies that Ethernet frames are transmitted using Manchester Encoding, which uses the fact that hardware can detect a change in voltage more easily than a fixed value, e.g. RS-232. Technically, the hardware is edge triggered, with the changes known as rising or falling edges. The sender transmits a falling edge to encode a 0 and a rising edge to encode a 1, as illustrated in Figure 6.

Figure 6: Manchester encoding

The voltage change that encodes a bit occurs exactly half-way through the time slot. Exactly half-way through the first time slot, the voltage becomes positive (+0.85 v) to encode a 1. Similarly, exactly half-way through the second time slot, the voltage becomes negative (-0.85 v) to encode a 0. If two contiguous bits have the same value, an additional change in voltage occurs at the edge of the time slot.
Manchester Encoding uses a preamble to allow for synchronisation. The preamble consists of 64 alternating 1s and 0s sent before the frame. These produce a square wave with transitions exactly in the middle of each slot. Receiving hardware uses the preamble to synchronise with the time slots. The last two bits of the preamble are both 1s to signal the end of the preamble.

Sharing Ethernet

Ethernet requires multiple computers to share access to the ether. A sender transmits a signal, which propagates towards both ends of the cable. This is illustrated in Figure 7.

Figure 7: Ethernet sharing

The sending computer has exclusive use of the cable during the transmission of the frame. Multiple frames cannot be sent at the same time, all other computers must wait.

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

All computers attached to the Ethernet use CSMA/CD to co-ordinate their activities. A computer wishing to transmit checks for electrical activity on the cable, informally called a carrier. If there is no carrier, the computer can transmit. If a carrier is present, the computer waits for the sender to finish before proceeding.
However, it is possible for two or more computers to detect the lack of carrier and start transmission simultaneously. The signals travel at approximately 70% of the speed of light and interfere with one another. This interference is called a collision. A sending computer monitors the signal on the cable and if it differs from the signal it is sending, then a collision has occurred and the computer stops transmitting.
Following a collision, a computer waits for the cable to become idle before retransmitting. However, if the computers start transmitting as soon as the cable becomes free, another collision will occur. Ethernet requires each computer to delay after a collision. The standard specifies a maximum delay, d, and requires each computer to choose a random delay less than d. In this case, the computer choosing the shortest delay will transmit first.
If subsequent collisions still occur, the computers double the maximum delay (2d, 4d, ...) until the range is large enough for one computer to choose a short delay and transmit without a collision. This technique is called binary exponential backoff.

Wireless LANs

Instead of transmitting signals across a cable, wireless LANs use antennas to broadcast RF signals through the air. All the computers using a wireless LAN share the same radio frequency, so they must take turns to transmit. Wireless LAN transmitters use low power, so the signal only propagates a short distance. In addition, metallic obstructions can block the signal.
This lack of full communication means that wireless LANs cannot use the CSMA/CD mechanism used by Ethernet. Consider the situation illustrated in Figure 8.

Figure 8: Wireless topology

Given a maximum tranmission distance d, computer 2 will receive all transmissions, but computers 1 and 3 will not receive transmissions from each other. Wireless LANs use Carrier Sense Multiple Access/Collision Advoidance (CSMA/CA) to share the air waves. Suppose that computer 1 wants to send a frame to computer 2. It first sends a short Request To Send (RTS) control message. Computer 2 receives the RTS and responds with a short Clear To Send (CTS) control message. Now computer 1 can transmit its frame.
In Figure 8, computer 3 will not receive the RTS from computer 1, but it will receive the CTS from computer 2 - so it knows that it must wait. In the event of computers 1 and 3 both sending a control message to computer 2 at the same time, they apply random backoff before resending. Since control messages are much shorter than data frames, the probability of a second collision is much lower than with conventional Ethernet.

IBM Token Ring

Most LANs that employ ring technology use an access mechanism known as token passing. A token ring operates as a single, shared medium. When a computer wants to send data, it must wait until it obtains the token, when it is in control of the ring as illustrated in Figure 9.

Figure 9: Token ring network

All stations except the sender forward bits around the ring. The sender compares the data being received with the data being sent to ensure that no transmission errors have occurred. The receiver makes a copy of the message as it passes the bits round the ring.
Co-ordination is achieved by using a special message called a token. A computer wanting to transmit must wait for the token to arrive. It removes the token from the ring and uses the ring to transmit data. After sending one frame it retransmits the token; this token passing guarantees that stations wanting to transmit will take turns. Ensuring there is one, and only one, token on the ring is handled by the ring hardware.

Fibre Distributed Data Interconnect (FDDI) Topology

A major disadvantage of token ring networks is that the failure of a single computer or connection will disable the complete network. FDDI transmits data at 100 Mbps, uses optical fibres to interconnect computers, and uses redundancy to overcome failures. This is illustrated in Figure 10.

Figure 10: FDDI network

In (a), the outer ring is used to transfer data. In (b), a station has failed and the adjacent stations detect the disconnection and reconfigure to use the reverse path to form a closed ring. This process of reconfiguring is called self-healing and FDDI is known as a self-healing network.

Internetworking Technology

Internetworking Basics

An internetwork is a collection of individual networks, connected by intermediate networking devices, that functions as a single large network. Internetworking refers to the industry, products, and procedures that meet the challenge of creating and administering internetworks.
The following articles provide information about internetworking basics:

LAN Technologies

A LAN is a high-speed data network that covers a relatively small geographic area. It typically connects workstations, personal computers, printers, servers, and other devices. LANs offer computer users many advantages, including shared access to devices and applications, file exchange between connected users, and communication between users via electronic mail and other applications.
The following articles provide information different LAN technologies:

WAN Technologies

A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.
The following articles provide information about the various protocols and technologies used in WAN environments:

Internet Protocols

The Internet protocols are the world's most popular open-system (nonproprietary) protocol suite because they can be used to communicate across any set of interconnected networks and are equally well suited for LAN and WAN communications. The Internet protocols consist of a suite of communication protocols, of which the two best known are the Transmission Control Protocol (TCP) and the Internet Protocol (IP). The Internet protocol suite not only includes lower-layer protocols (such as TCP and IP), but it also specifies common applications such as electronic mail, terminal emulation, and file transfer. This article provides a broad introduction to specifications that comprise the Internet protocols. Discussions include IP addressing and key upper-layer protocols used in the Internet. Specific routing protocols are addressed individually later in this document.
The following articles provide information about different IOS IP technologies:

Bridging and Switching

Bridges and switches are data communication devices that operate principally at Layer 2 of the OSI reference model. As such, they are widely referred to as data link layer devices. Several kinds of bridging have proven important as internetworking devices. Transparent bridging is found primarily in Ethernet environments, while source-route bridging occurs primarily in Token Ring environments. Translational bridging provides translation between the formats and transit principles of different media types (usually Ethernet and Token Ring). Finally, source-route transparent bridging combines the algorithms of transparent bridging and source-route bridging to enable communication in mixed Ethernet/Token Ring environments. Today, switching technology has emerged as the evolutionary heir to bridging-based internetworking solutions. Switching implementations now dominate applications in which bridging technologies were implemented in prior network designs. Superior throughput performance, higher port density, lower per-port cost, and greater flexibility have contributed to the emergence of switches as replacement technology for bridges and as complements to routing technology.
The following articles provide information about the technologies employed in devices loosely referred to as bridges and switches:

Routing

Routing is the act of moving information across an internetwork from a source to a destination. Along the way, at least one intermediate node typically is encountered. Routing is often contrasted with bridging, which might seem to accomplish precisely the same thing to the casual observer. The primary difference between the two is that bridging occurs at Layer 2 (the link layer) of the OSI reference model, whereas routing occurs at Layer 3 (the network layer). This distinction provides routing and bridging with different information to use in the process of moving information from source to destination, so the two functions accomplish their tasks in different ways.
The following articles provide information different routing technologies:

Network Management

Network management means different things to different people. In some cases, it involves a solitary network consultant monitoring network activity with an outdated protocol analyzer. In other cases, network management involves a distributed database, auto polling of network devices, and high-end workstations generating real-time graphical views of network topology changes and traffic. In general, network management is a service that employs a variety of tools, applications, and devices to assist human network managers in monitoring and maintaining networks.
The following articles provide information different network management technologies:

Voice/Data Integration Technologies

Voice/data integration is important to network designers of both service providers and enterprise. Service providers are attracted by the lower-cost model-the cost of packet voice is currently estimated to be only 20 to 50 percent of the cost of a traditional circuit-based voice network. Likewise, enterprise network designers are interested in direct cost savings associated with toll-bypass and tandem switching. Both are also interested in so-called "soft savings" associated with reduced maintenance costs and more efficient network control and management. Finally, packet-based voice systems offer access to newly enhanced services such as Unified Messaging and application control. These, in turn, promise to increase the productivity of users and differentiate services.
Integration of voice and data technologies has accelerated rapidly in recent years because of both supply- and demand-side interactions. On the demand side, customers are leveraging investment in network infrastructure to take advantage of integrated applications such as voice applications. On the supply side, vendors have been able to take advantage of breakthroughs in many areas, including standards, technology, and network performance.
The following article provides information about Voice/Data Integration Technologies:

Voice/Data Integration Technologies

Wireless Technologies

Wireless communication is the transfer of information over a distance without the use of electrical conductors or "wires".[1] The distances involved may be short (a few meters as in television remote control) or long (thousands or millions of kilometers for radio communications). When the context is clear, the term is often shortened to "wireless". Wireless communication is generally considered to be a branch of telecommunications.
It encompasses various types of fixed, mobile, and portable two way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, garage door openers and or garage doors, wireless computer mice, keyboards and headsets, satellite television and cordless telephones.
The following article provides information about Wireless Technologies:

Wireless Technologies

Cable Access Technologies

Historically, CATV has been a unidirectional medium designed to carry broadcast analog video channels to the maximum number of customers at the lowest possible cost. Since the introduction of CATV more than 50 years ago, little has changed beyond increasing the number of channels supported. The technology to provide high-margin, two-way services remained elusive to the operator.
Cable television (CATV) is a unidirectional medium carrying broadcast analog video channels to the most customers possible at the lowest possible cost to the CATV service provider. Since the introduction of CATV more than 50 years ago, little has changed beyond increasing the number of channels supported.
The following article provides information about Cable Access Technologies:

Cable Access Technologies

Dial-up Technology

Dialup is simply the application of the Public Switched Telephone Network (PSTN) to carry data on behalf of the end user. It involves customer premises equipment (CPE) device sending the telephone switch a phone number to direct a connection to. The AS3600, AS5200, AS5300, and AS5800 are all examples of routers that have the capability to run a PRI along with banks of digital modems. The AS2511, on the other hand, is an example of a router that communicates with external modems.
Since the time of Internetworking Technologies Handbook, 2nd edition, the carrier market has continued to grow, and there have been demands for higher modem densities. The answer to this need was a higher degree of interoperation with the telco equipment and the refinement of the digital modem: a modem capable of direct digital access to the PSTN. This has allowed the development of faster CPE modems that take advantage of the clarity of signal that the digital modems enjoy. The fact that the digital modems connecting into the PSTN through a PRI or a BRI can transmit data at more than 53 K using the V.90 communication standard attests to the success of the idea.
The following article provides information about Dial-up Technology:

Dial-up Technology

Security Technologies

With the rapid growth of interest in the Internet, network security has become a major concern to companies throughout the world. The fact that the information and tools needed to penetrate the security of corporate networks are widely available has increased that concern.
Because of this increased focus on network security, network administrators often spend more effort protecting their networks than on actual network setup and administration. Tools that probe for system vulnerabilities, such as the Security Administrator Tool for Analyzing Networks (SATAN), and some of the newly available scanning and intrusion detection packages and appliances, assist in these efforts, but these tools only point out areas of weakness and may not provide a means to protect networks from all possible attacks. Thus, as a network administrator, you must constantly try to keep abreast of the large number of security issues confronting you in today's world. This article describes many of the security issues that arise when connecting a private network to the Internet.
The following article provides information about Security Technologies:

Security Technologies

Quality of Service Networking

Quality of Service (QoS) refers to the capability of a network to provide better service to selected network traffic over various technologies, including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and 802.1 networks, SONET, and IP-routed networks that may use any or all of these underlying technologies. The primary goal of QoS is to provide priority including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics. Also important is making sure that providing priority for one or more flows does not make other flows fail. QoS technologies provide the elemental building blocks that will be used for future business applications in campus, WAN, and service provider networks. This article outlines the features and benefits of the QoS provided by the Cisco IOS QoS.
The following articles provide information about Quality of Service:

Network Caching Technologies

Although the volume of Web traffic on the Internet is staggering, a large percentage of that traffic is redundant-multiple users at any given site request much of the same content. This means that a significant percentage of the WAN infrastructure carries the identical content (and identical requests for it) day after day. Eliminating a significant amount of recurring telecommunications charges offers an enormous savings opportunity for enterprise and service provider customers.
Web caching performs the local storage of Web content to serve these redundant user requests more quickly, without sending the requests and the resulting content over the WAN.
The following article provides information about Network Caching Technologies:

Network Caching Technologies

IBM Network Management

IBM network management refers to any architecture used to manage IBM Systems Network Architecture (SNA) networks or Advanced Peer-to-Peer Networking (APPN) networks. IBM network management is part of the IBM Open-Network Architecture (ONA) and is performed centrally by using management platforms such as NetView and others. It is divided into five functions that are similar to the network management functions specified under the Open System Interconnection (OSI) model. This article summarizes the IBM network management functional areas, ONA network management architecture, and management platforms.
The following article provides information about IBM Network Management:

IBM Network Management

Multiservice Access Technologies

Multiservice networking is emerging as a strategically important issue for enterprise and public service provider infrastructures alike. The proposition of multiservice networking is the combination of all types of communications, all types of data, voice, and video over a single packet-cell-based infrastructure. The benefits of multiservice networking are reduced operational costs, higher performance, greater flexibility, integration and control, and faster new application and service deployment.
The following article provides information about Multiservice Access Technologies:

Multiservice Access Technologies

Internetworking Basics

LAN Technologies

WAN Technologies

Internet Protocols

Bridging and Switching

Routing

Network Management

Voice/Data Integration Technologies

Voice/Data Integration Technologies

Wireless Technologies

Wireless Technologies

Cable Access Technologies

Cable Access Technologies

Dial-up Technology

Dial-up Technology

Security Technologies

Security Technologies

Quality of Service Networking

Network Caching Technologies

Network Caching Technologies

IBM Network Management

IBM Network Management

Multiservice Access Technologies

Multiservice Access Technologies

OSI Layer Model

Layer 1 - Physical

Physical layer defines the cable or physical medium itself, e.g., thinnet, thicknet, unshielded twisted pairs (UTP). All media are functionally equivalent. The main difference is in convenience and cost of installation and maintenance. Converters from one media to another operate at this level.

Layer 2 - Data Link

Data Link layer defines the format of data on the network. A network data frame, aka packet, includes checksum, source and destination address, and data. The largest packet that can be sent through a data link layer defines the Maximum Transmission Unit (MTU). The data link layer handles the physical and logical connections to the packet's destination, using a network interface. A host connected to an Ethernet would have an Ethernet interface to handle connections to the outside world, and a loopback interface to send packets to itself.
Ethernet addresses a host using a unique, 48-bit address called its Ethernet address or Media Access Control (MAC) address. MAC addresses are usually represented as six colon-separated pairs of hex digits, e.g., 8:0:20:11:ac:85. This number is unique and is associated with a particular Ethernet device. Hosts with multiple network interfaces should use the same MAC address on each. The data link layer's protocol-specific header specifies the MAC address of the packet's source and destination. When a packet is sent to all hosts (broadcast), a special MAC address (ff:ff:ff:ff:ff:ff) is used.

Layer 3 - Network

NFS uses Internetwork Protocol (IP) as its network layer interface. IP is responsible for routing, directing datagrams from one network to another. The network layer may have to break large datagrams, larger than MTU, into smaller packets and host receiving the packet will have to reassemble the fragmented datagram. The Internetwork Protocol identifies each host with a 32-bit IP address. IP addresses are written as four dot-separated decimal numbers between 0 and 255, e.g., 129.79.16.40. The leading 1-3 bytes of the IP identify the network and the remaining bytes identifies the host on that network. The network portion of the IP is assigned by InterNIC Registration Services, under the contract to the National Science Foundation, and the host portion of the IP is assigned by the local network administrators. For large sites, the first two bytes represents the network portion of the IP, and the third and fourth bytes identify the subnet and host respectively.
Even though IP packets are addressed using IP addresses, hardware addresses must be used to actually transport data from one host to another. The Address Resolution Protocol (ARP) is used to map the IP address to it hardware address.

Layer 4 - Transport

Transport layer subdivides user-buffer into network-buffer sized datagrams and enforces desired transmission control. Two transport protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), sits at the transport layer. Reliability and speed are the primary difference between these two protocols. TCP establishes connections between two hosts on the network through 'sockets' which are determined by the IP address and port number. TCP keeps track of the packet delivery order and the packets that must be resent. Maintaining this information for each connection makes TCP a stateful protocol. UDP on the other hand provides a low overhead transmission service, but with less error checking. NFS is built on top of UDP because of its speed and statelessness. Statelessness simplifies the crash recovery.

Layer 5 - Session

The session protocol defines the format of the data sent over the connections. The NFS uses the Remote Procedure Call (RPC) for its session protocol. RPC may be built on either TCP or UDP. Login sessions uses TCP whereas NFS and broadcast use UDP.

Layer 6 - Presentation

External Data Representation (XDR) sits at the presentation level. It converts local representation of data to its canonical form and vice versa. The canonical uses a standard byte ordering and structure packing convention, independent of the host.

Layer 7 - Application

Provides network services to the end-users. Mail, ftp, telnet, DNS, NIS, NFS are examples of network applications.

OSI Layer

OSI Model Reference Table

Layer	Function	Protocols	Network Components
Application User Interface	Used for applications specifically written to run over the network Allows access to network services that support applications; Directly represents the services that directly support user applications Handles network access, flow control and error recovery Example apps are file transfer,e-mail, NetBIOS-based applications	DNS; FTP; TFTP; BOOTP; SNMP;RLOGIN; SMTP; MIME; NFS; FINGER; TELNET; NCP; APPC; AFP; SMB	Gateway
Presentation Translation	Translates from application to network format and vice-versa All different formats from all sources are made into a common uniform format that the rest of the OSI model can understand Responsible for protocol conversion, character conversion,data encryption / decryption, expanding graphics commands, data compression Sets standards for different systems to provide seamless communication from multiple protocol stacks Not always implemented in a network protocol		Gateway Redirector
Session Syncs and Sessions	Establishes, maintains and ends sessions across the network Responsible for name recognition (identification) so only the designated parties can participate in the session Provides synchronization services by planning check points in the data stream => if session fails, only data after the most recent checkpoint need be transmitted Manages who can transmit data at a certain time and for how long Examples are interactive login and file transfer connections, the session would connect and re-connect if there was an interruption; recognize names in sessions and register names in history	NetBIOS Names Pipes Mail Slots RPC	Gateway
Transport Packets; Flow control & Error-handling	Additional connection below the session layer Manages the flow control of data between parties across the network Divides streams of data into chunks or packets; the transport layer of the receiving computer reassembles the message from packets A train is a good analogy => the data is divided into identical units Provides error-checking to guarantee error-free data delivery, with on losses or duplications Provides acknowledgment of successful transmissions; requests retransmission if some packets don’t arrive error-free Provides flow control and error-handling	TCP, ARP, RARP; SPX NWLink NetBIOS / NetBEUI ATP	Gateway Advanced Cable Tester Brouter
Network Addressing; Routing	Translates logical network address and names to their physical address (e.g. computername ==> MAC address) Responsible for addressing determining routes for sending managing network problems such as packet switching, data congestion and routing If router can’t send data frame as large as the source computer sends, the network layer compensates by breaking the data into smaller units. At the receiving end, the network layer reassembles the data Think of this layer stamping the addresses on each train car	IP; ARP; RARP, ICMP; RIP; OSFP; IGMP; IPX NWLink NetBEUI OSI DDP DECnet	Brouter Router Frame Relay Device ATM Switch Advanced Cable Tester
Data Link Data frames to bits	Turns packets into raw bits 100101 and at the receiving end turns bits into packets. Handles data frames between the Network and Physical layers The receiving end packages raw data from the Physical layer into data frames for delivery to the Network layer Responsible for error-free transfer of frames to other computer via the Physical Layer This layer defines the methods used to transmit and receive data on the network. It consists of the wiring, the devices use to connect the NIC to the wiring, the signaling involved to transmit / receive data and the ability to detect signaling errors on the network media	Logical Link Control error correction and flow control manages link control and defines SAPs 802.1 OSI Model 802.2 Logical Link Control	Bridge Switch ISDN Router Intelligent Hub NIC Advanced Cable Tester
Data Link Data frames to bits		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
Physical Hardware; Raw bit stream	Transmits raw bit stream over physical cable Defines cables, cards, and physical aspects Defines NIC attachments to hardware, how cable is attached to NIC Defines techniques to transfer bit stream to cable	IEEE 802 IEEE 802.2 ISO 2110 ISDN	Repeater Multiplexer Hubs Passive Active TDR Oscilloscope Amplifier

VPN technologies

Site-to-Site VPNs

Site-to-site VPNs provide an Internet-based WAN infrastructure to extend network resources to branch offices, home offices, and business partner sites. All traffic between sites is encrypted using IPsec protocol and integrates network features such as routing, quality of service, and multicast support. Cisco VPNs also offer:

Reliable and high-quality transport of complex, mission-critical traffic, such as voice and client server applications
Simplified provisioning and reduced operational tasks for network designs
Integrated advanced network intelligence and routing for a wide range of network designs

Remote Access VPNs

Remote access VPNs extend almost any data, voice, or video application to the remote desktop, emulating the main office desktop. With this VPN, you can provide highly secure, customizable remote access to anyone, anytime, anywhere, with almost any device. Cisco remote access VPNs:

Create a remote user experience that emulates working on the main office desktop
Deliver VPN access safely and easily to a wide range of users and devices
Support a wide range of connectivity options, endpoints, and platforms to meet your dynamic remote access needs

The TCP/IP model

TCP/IP is based on a four-layer reference model. All protocols that belong to the TCP/IP protocol suite are located in the top three layers of this 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

For resolving LAN issues

Company Name: Data Solutions

Address:

Data Solutions,
Madathil Buildings,
Pakkil P.O.,
Nattakom,
Kottayam-686012

Phone: 0481 2361305

www.datasolutions-india.com

support@datasolutions-india.com

Nature of Work: Network Implementations and Support

About the Company

Data Solutions is a leading provider of network infrastructure (LAN and WAN) and structured cabling all over India. We provide infrastructure design and installation for voice, data, video and wireless networks. Our solutions include state of the art network infrastructure from simple analogue telephone systems to advanced high speed copper and Fiber Optics data networks.

Data Solutions started operating in 2004 with 10 members include both engineers and field support team now 25 members our strength. Completing many projects includes Banking, Hostels, Apartments, Gov. Sector and private companies etc

We take up both LAN and WAN projects also done Security Systems and Voice projects

Our main services include the following

WAN Technologies
Leased line
ISDN
MPLS
Broadband
VPN related installation

LAN Technologies
Cat5 & Cat6 Structured cabling
Optical Fiber

Wireless Technologies
Wireless networking using LinkSys, Dax etc equipments

Hardware & Software
PC and Laptop related issues OS
Application software and anti virus software

Voice technologies
Cisco IP Phone
Call Center and Office setup using Analog & IP Phones
Call manager & CME based setup

Security Systems(CCTV)
CCTV circuits and Bio metric
Access card

Electrical Works
All type of electrical work

Analog phones and FAX
EPBX
All type of telephone intercom works

www.datasolutions-india.com

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Junior.1994.DVDRip.XviD-RS
Kindergarten.Cop.1990.iNTERNAL.DVDRip.XViD-AVi
Last.Action.Hero.1993.INTERNAL.DVDRIP.XVID-UbM
Predator.SE.1987.PROPER.DVDRip.XviD-MEDiAMANiACS
Pumping.Iron.1977.DVDRip.XviD-FRAGMENT
Raw.Deal.1986.PROPER.DVDRip.DivX-MDX
Red.Heat.1988.DVDRip.XviD.AC3.iNTERNAL-QiM
Red.Sonja.1985.iNTERNAL.DVDRip.XviD-TM
Terminator.1984.INTERNAL.AC3.DVDRiP.DiVX-MDX
Terminator.2.1991.WS.DVDRip.XviD.iNT-EwDp
Terminator.3.Rise.Of.The.Machines.DVDRip.XviD-DiAMOND
Terminator.Salvation.DVDRip.XviD-iMBT
The.6th.Day.2000.SE.iNTERNAL.DVDRiP.XViD-aGGr0
The.Rundown.DVDRip.XviD-iMBT
The.Running.Man.1987.PROPER.DVDRip.XviD-VH-PROD
Total.Recall.1990.iNTERNAL.DVDRip.XviD-iLS
True.Lies.1994.iNTERNAL.DVDRip.XviD-iLS
Twins.1988.DVDRip.Xvid.iNT-420RipZ

BGP States

BGP cycles through five states as it runs:

• Idle— Searching for neighbors

• Connect— TCP three-way handshake complete with neighbor

• Open Sent— BGP Open message has been sent

• Open Confirm— Response received (otherwise go to Active state)

• Established— BGP neighborship is established

BGP States

BGP cycles through five states as it runs:

• Idle— Searching for neighbors

• Connect— TCP three-way handshake complete with neighbor

• Open Sent— BGP Open message has been sent

• Open Confirm— Response received (otherwise go to Active state)

• Established— BGP neighborship is established

OSPF States

The following list describes each possible state of a neighbor relationship:

• Down— This is the first OSPF neighbor state. It means that no information (hellos) has been received from this neighbor.

• Attempt— This state is only valid for manually configured neighbors in an NBMA environment. In Attempt state, the router sends unicast hello packets every poll interval to the neighbor from which hellos have not been received within the dead

interval.

• Init— This state indicates that the router has received a hello packet from its neighbor, but the receiving router's ID was not included in the hello packet.

• 2-Way— This state indicates that bi-directional communication has been established between two routers.

• Exstart— Once the DR and BDR are elected, the actual process of exchanging linkstate information can start between the routers and their DR and BDR.

• Exchange— In the exchange state, OSPF routers exchange database descriptor

(DBD) packets.

• Loading— In this state, the actual exchange of link-state information occurs.

• Full— In this state, routers are fully adjacent with each other. All the router and

network LSAs are exchanged and the router databases are fully synchronized.