Saturday, January 31, 2009

Understanding Protocol Suites

After knowing the importance of protocol in communication,designers have chosen to divide the communication problem into sub pieces and to design a protocol for each of the sub piece instead of having a single giant protocol that specifies complete details for all possible forms of communications.Doing so makes each protocol easier to design,analyze,implement and test.The main advantage of dividing communication software into multiple protocols increases flexibility because it allows subsets of protocols to be used as added.The division into separate protocols must be chosen carefully to ensure the resulting communication system is efficient and effective.To avoid duplication of effort,each protocol should handle part of the communication problem not handled by other protocols.

To make efficient implementation possible,protocols should be designed so that,they can share data structures and information.Finally,the combination of protocols should handle all possible hardware failures or other exceptional conditions.Now the main question that arises in front of us is that how can one guarantee that protocols will work together.The answer of this question lies in an overall design plan that means instead of developing each protocol in isolation,protocols are designed and developed in complete,cooperative sets called suites or families.Each protocol in a suite solves one part of the communication problem;together they solve the entire communication problem.Furthermore,the entire suite is designed to make interactions among protocol efficient.

Friday, January 30, 2009

Need for Protocols

As all we know that basic communication hardware consists of mechanisms that can transfer bits from one point to another.However,using raw hardware to communicate is analogous to programming by entering 1s and 0s but it is cumbersome and inconvenient.To aid programmers,computers attached to a network use complex software that provides a convenient,high level interface for applications.The software handles most low level communication details and problems automatically,making it possible for applications to communicate easily.Thus,most application programs rely on network software to communicate that means hey do not interact with network hardware directly.All parties involved in a communication must agree on a set of rules to be used when exchanging messages and such type of agreement is known as protocol.This term is also applied to computer communications meaning of which "a set of rules that specify the format of messages and the appropriate action required for each message is known as a network protocol or a computer communication protocol."The software that implement such rules is called as protocol software.

Wednesday, January 28, 2009

Significance of Internetworking and TCP/IP

Internetworking has become one of the most important ideas in modern networking.In fact,Internet Technology has revolutionized computer communication.Most large organizations already use internetworking as the primary computer communication mechanism.Smaller organizations and individuals are beginning to do so well.More important,in addition to private internet,the TCP/IP technology has made possible a global internet that reaches schools,commercial organizations,and government and military sites in all populated countries around the world.The worldwide demand for internetworking products has affected most companies that sell networking technologies.

Competition has increased because new companies have been formed to sell hardware and software need for internetworking.In addition may companies have modified their protocol designs to accommodate internetworking.In particular,most network protocols were originally designed to work with one network technology and one physical network at a time.To provide internetworking capabilities,companies have extended the designs in two ways:the protocols have been adapted to work with many network technologies and new features have been added that allows the protocols to transfer data across internet.

Tuesday, January 27, 2009

Public and Private Networks

When applied to a network,the term public refers to the availability of the service,not to the data transferred.In particular,most public networks provide private communications i.e when a computer sends a message across a public network,only the intended recipient receives the copy.Some public networks permit a group of computers to communicate analogous to a telephone conference hall.However,the public network doesn't use the broadcast technology.That is,the public network doesn't have a broadcast address nor it does forward broadcast packets.

The chief advantage of a private network is that owner has full control over both the technical decisions and policies.In addition to this it also have some disadvantages like a large private network can be expensive to install and maintain.In addition to purchasing the network hardware,a corporation must hire and train a staff to install,manage and operate the network.

On the other hand the chief advantage of a public network are flexibility and the ability to use state of the art networking without maintaining the technical expertise. public network is flexible because an arbitrary subscriber at a arbitrary location can connect to the network at any time.Furthermore,connections between a computer owned by one organization and a computer owned by another can be made broken the same way a public telephone system allows voice connections to be made or broken

Friday, January 23, 2009

Concept of ISDN

Integrated Services Digital Network(ISDN) is launched by telephone companies and used to provide large scale digital services to subscribers.ISDN provides digitized voice and data to subscribers over conventional local wiring.ISDN uses the same type of twisted pair copper wiring as the analog telephone system.If we discuss from the subscribers point of view then ISDN offers three separate digital channels designated B,B and D(usually written 2B+D).The two B channels operates at a speed of 64 Kbps,are intended to carry digitized voice and data or compresses videos, on the other hand the D channel which operates at 16 Kbps,is intended as a control channel.In general,a subscriber uses the D channel to request services which are then supplied over the B channels.The subscriber can also use the D channel to manage a session that is in progress or to terminate a session.Finally,both the B channels can be combined or bonded together to produce a single channel with effective data rate at 128 Kbps.The 2B+D channels are known as ISDN Basic Rate Interface(BRI).Infact,ISDN uses a form of time division multiplexing to provide the illusion of multiple channels of data to travel over a single pair of wires.

Tuesday, January 20, 2009

Understanding Bridges

A bridge is an electronic device that is used to connects two LAN segments.Unlike a repeater,however a bridge is a digital device that uses the same network interface as a conventional computer and handles frames.The bridge listen to traffic on each segment in promiscuous mode.When it receives a frame from one segment,the bridge verifies that the frame arrived intact i.e there was no electrical interference on LAN during transmission and after that it forwards a copy of the frame to the other segment if necessary.Thus,two LAN segments behave connected by a bridge behave like a single LAN.A computer connected to either segment can send a frame to any of the other computers connected to the two segments.Because each segment supports standard network connections and uses the standard frame format that means computers do not know whether they are connected to a LAN or a bridged LAN.

When we compare bridges with LAN it is found that bridges are more useful and popular than repeaters because they help isolate problems.If two segments are connected by a repeater and lightning causes electrical interference on one of them,the repeater will propagate the interference to the other segment.In contrast if interference occurs on one of the two segments connected by a bridge,the bridge will receive an incorrectly formed frame,which the bridges simply discards the same way a conventional computer discards a frame that contains an error.Similarly,a bridge will not forward a collision from one segment to another.Thus,the bridge keeps problems on one segment from affecting the other.

Friday, January 16, 2009

Combining Switches and Hubs

From the last post it is clear that switching provides higher aggregate data rates in comparison to a hub,but the main drawback that occurred with the switched networks is the higher cost in comparison to hub.To overcome all these problems network administrator choose a compromise between the hub and the switched networks that means instead of connecting one computer to each port on a switch,the administrator connects the hub to each of the port of the switch and then connect each computer to one of the hubs.This result is very much closer to the conventional bridged LAN where each hub appears to be a single LAN segment, and the switch makes it appear that bridges connect all segments.The system also performs like a conventional bridged LAN where a computer must share a bandwidth with other computers connected to the same hub,communication can occur in parallel between a pair of computers attached to one hub and a pair of computers attached to another.

Thursday, January 15, 2009

Concept of Switching

In general,a network technology is called switched if the hardware includes an electronic device that connects to one or more computers and allows them to send and receive data from each other.More specifically,a switched LAN consisted of a single electronic device that transfers frames among many computers.As all we know that a switch resembles a hub,like a hub, a switch consists of a single box with multiple ports that each attach to a single computer.The main difference between a switch and a hub arises from the way the devices operates,a hub simulates a single shared medium while in the case of a switch it simulates a bridged LAN with one computer per segment.

If we talk about the chief advantage of using a switched LAN instead of a hub then the reason is same as that of using bridged LAN instead of a single segment.In the case of a hub a single segment is shared by all computers,that means at most two computers can communicate through hub at a time.Thus the maximum possible throughput of a hub system is R,the rate at which single computer can send data across a LAN segment.In the case of a switched LAN,each computer has a simulated LAN segment to itself that means the segment is busy only when a frame is being transferred to or from the computer.As a result,as many as one half of the computers connected to a switch can send the data at the same time(if they send to one of the computers that is not busy in sending).Thus,in this case the maximum throughput of a switch is RN/2 where R is the rate at which data transmits,and N is total number of computers that are connected to the switch.

Tuesday, January 13, 2009

Understanding Baud Rate and Framing Errors

As all we know that sending and receiving hardware are agreed on the length of the time the voltage will be held for each bit.Instead of specifying the time per bit,which is a small fraction of second,communication systems specify the number of bits that can be transferred in a second.For ex:some early RS-232 connections operated at 300 bits per second,19200 bits per second and 33600 bits per second are more common.Technically ,transmission hardware is rated in baud,the number of changes in the signal per second that the hardware generated.For the simple RS-232 scheme presented, the baud rate is exactly equal to the number of bits per second.Thus,9600 baud means 9600 bits per second.

To make RS-232 hardware more general,manufacturers usually design each piece of hardware to operate at variety of baud rates.The baud rate can be configured either manually by physically setting switches on the hardware when it is installed in a computer or automatically by device driver software in a computer.If the sending and receiving hardware are not configured to use the same baud rate,errors will occur because the receiver's timer will not wait an appropriate length of time for each bit.To detect errors,a receiver's measure the voltage for each bit multiple times and compares the measurements.If the voltage do not all agree or if the stop bit does not occur exactly at the time expected,the receiver reports an error.Such errors are known as framing errors.