Frame Relay

Frame Relay is a virtual – circuit technology that provide low level (Physical and data link layer) service in response to the following demands.

Higher Data Rate at lower Cost-  In the post many organizations used a Wan Technology such as leased line or x.25 to connect single computer.  That data rate was relatively low.  Today, most organization use high speed LAN and want to use WAN to connect this LANs.  One solution to use “T-Line”, but these line provide only point to point connections, no many too many.  Creating a Mash Network out of T-Lines is a very expensive.  For Example – To connect 6 LANS, we need 15 T-Lines.  On the other hand, we need only six-T-Lines to connect the same six LANs to a frame Relay Network.  Frame Relay provides the same type of service at lower cost.

               

            Although the Frame Relay originally was designed o provide a 1.544-Mbps data rate (equivalent to a T-1 Line) today most implementations can handle up to 44.376 Mbps(equivalent to a T-3 Line).

Virtual Circuits-  Frame Relay operates using virtual circuits as opposed to the actual circuits that leased Lines used.  These virtual circuits are what link together the thousand of devices connected o he providers “Cloud” There are two type of virtual circuits permanent and switched.

            Permanent virtual circuits (PVCs) are by far the most common type in use today.  What “permanent” means here is the Telco creates the mapping inside their gear and as long as you pay the bill, they will remain in place.

            Switched virtual circuits (SVCs) are more like a phone call.  The virtual circuit is established when data needs o be tansmitted, then  it’s taken down when the data transfer is complete.

Unguided Media

Unguided media transport  electromagnetic  waves without using a physical conductor this type of communication is often referred to as wireless communication.  Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them. Unguided signals can travel from the source to destination in several ways: ground propagation, sky propagation, and line-of-sight propagation.

In ground propagation, radio waves travel through the lowest portion of the atmosphere, hugging the earth.  These low-frequency signals emanate in all directions from the transmitting antenna and follow the curvature of the planet. Distance depends on the amount of power in the signal: The greater the distance.

In sky propagation higher- frequency radio waves radiate upward into the ionosphere (the layer of atmosphere where particle exist as ions) where they are reflected back to earth.  This type of transmission allows for greater distances with lower output power.

In line-or-sight propagation, very high-frequency signals are transmitted in straight lines directly from antenna to antenna. Antennas must be directional, facing each other, and either tall enough or close enough together not to be affected by the curvature of the earth, line-of-sight propagation is tricky because radio transmissions cannot be completely focused.

SIGNAL

Analog data-   Analog data is human voice.  When somebody speaks, a continuous wave is created   in the air.  This can be captured by a microphone and converted to the analog signal.

Digital data-   Digital data is data stored in memory of the computer in the form of 0s to 1s.  It is usually converted to a digital signal.  When it is transferred from one position to another position.

Analog and digital Signal-   Signal can be analog and digital.  Analog signal can have any value in range.  Digital signals can have only a limited number of value.

                              

Periodic Signals-   A periodic signal consists of a continuously repued pattern.  The period of signal (T) is expressed in seconds.

                                      

                                                  Example of Periodic and aperiodic signal

Aperiodic Signals-   An aperodic or nonperiodic signal has no repetitive pattern.

Amplitude-   Amplitude refer to height of signal.  The unit for amplitude depend on the type of the signal.  For electrical signal, the unit is normally volts ampere or watts.

Sound level	Type of Sound
40db	normal speech
90db	lawn mowers
110db	shotgun blast
120db	jet engine taking off
120db+	rock concerts

Frequency-  The frequency of a periodic function is the number of complete cycles that can o cccur per second,  Frequency is denoted with a lower-case f.  It is defined in terms of the period, as follows:

Period of frequency-   Period refers to the amount of time in seconds, a signal needs to complete one cycle.  Frequency refer to the number of period in  one second.

Unit of Period-   Period is expressed in seconds the communication industry uses five unit to measure period second (s) millisecond, microsecond, nanosecond and picoseconds.

Unit of Frequency-   Frequency is hertz, after the German Physicist Heinrich Rudolf Hertz.  The communications industry uses five units to measure frequency. Hertz, Kilohertz, Megaherth, Gigahertz and Terahertz.

Unit of Frequency-  

Frequency	1 mHz (10−3)	1 Hz (100)	1 kHz (103)	1 MHz (106)	1 GHz (109)	1 THz (1012)
Period (time)	1 ks (103)	1 s (100)	1 ms (10−3)	1 µs (10−6)	1 ns (10−9)	1 ps (10−12)

Digital Signal-   In addition to being represented by an analog signal, data can also be represented by a digital signal.

             For example, A “1” can be encoded as a positive voltage and a “0” as a zero voltage.

Bit Interval and Bit Rate-   Bit interval and bit rate are used to describe digital signals.

        The bit interval is the time required to send one single bit.

        The bit rate is the number of bit interval per second.  This means that the bit rae is the number of bits sent in one second usually expressed in bits per second (bps).  

           

Example of bit rate and bit interval

Problems of using Voice Channels for Digital Transmission
A digital signal is comprised of a number of signals. Specifically, the signal is represented as follows,

signal = f + f3 + f5 +f7 +f9 +f11 +f13 ....f(infinity)

This means a digital signal has a base frequency, plus another at three times the base frequency, plus another at five times the base frequency etc. f3 is called the third harmonic, f5 the fifth harmonic and so on. The third harmonic is one third of the amplitude of the base frequency (called the fundamental frequency), the fifth harmonic is one fifth the amplitude of the fundamental and so on.

In order to send a digital signal across a voice channel, the bandwidth of the channel must allow the fundamental plus third and fifth harmonic to pass without affecting them too much. As can be seen, this is what such a signal looks like, and is the minimum required to be correctly detected as a digital signal by the receiver.

Lets consider sending a 2400bps binary digital signal down a voice channel rated with a bandwidth of 3.1KHz. The base frequency of the digital signal is 1200Hz (it is always half the bit rate), so the fundamental frequency will pass through the channel relatively unaltered. The third harmonic is 3600Hz, which will suffer attenuation and arrive severely altered (if at all). The fifth harmonic has no chance of passing the channel.

In this case it can be seen that only the base frequency will arrive at the end of the channel. This means the receiver will not be able to reconstruct the digital signal properly, as it will require f3 and f5 for proper reconstruction. This results in errors in the detection process by the receiver. Baud Rate-The baud rate indicates the number of bits per second That are transmitted. For example: 300 baud means hat 300 bits are trans mitted each second (abbreviated 300bps).  Assuming asynchronous communication, which requires 10 bits per character, this translates to 30 characters per second (cps).  For slow rates (below 1200 baus), you can divide the baudby 10 o see how many characters per second are sent.

Type of Cable

10BASE2

The 10Base2 Ethernet standard uses thin coaxial (RG-58) cable.  10Base2 has a maximum length of 185 Meters (607feet) and because of its composition offers a fair amount of resistance to interference.  One of the more important is that it is limited to transfer speed of 10 Mbps.  This speed limitation reduces its effectiveness in many network environments.

10BASE5

The 10BASE5 standard uses the thick coaxial (RG-62) cable.  It is a transfer speed of 10Mbps and runs distance of 500 meter.  The 10BASE5 standard specifies a true bus topology, meaning that computer attached to the network cable itself using special cable and connectors it does no use additional networking equipment.

            10BASE5 network must be connected with a minimum distance of 2.5 meters between each other to prevent noise on the cable.

10BASE T

That a normal Ethernet network is one that operates at 10 Mbps and has  the name 10Base T.  Now-a-days more and more origination s are looking for even faster ways to connect there 3, 4 and 5 UTP cable and is limited to distance of hundred meters.

Fast Ethernet 100BASE T

100baseT is a 100 mbps networking standard based on  the principle of standard Ethernet.  A number of standard fall under the fast Ethernet banner; the most commonly implemented is 100BaseTX which use category 5(or higher)  UTP cabling.  The following sections describe he fast Ethernet standards.

10BASE FX

This is the standard of the running fast Ethernet over fiber optic cable.  Due to the cast of implementations this is the rarely used.  One of the largest advantages is its distance capabilities.  100BaseFX can reach an impressive10, 000 meters.

100BASE T4

100BASET4 can use category 3 4and 5 cable to reach speed of 100mbps with regards to distance limitation and other characteristics 100BASE T4  is comparable 100BASE TX.

100BASE TX

This is the fast Ethernet standard of choice on day network. 100BASETX is most often implemented with UTP cable, but it has been known to be used with STP.  100BASE TX operated at speed of 100 mbps and offers a maximum transmission

distance of 100 meters.  The difference between TX and T4 uses all four pairs of wire within the UTP cable TX only use two paired.

  

CSMA/CD

When a device on a network want  to transmit to another device.  The first device  to check to see if the line is clear and then transmit.  The only problem is that two devices perform this action at the same time.  They will both line is clear and so will both attempt to transmit.

Ethernet can accept only one signal at a time.  So the two transmission with collide with each other.  These collisions damage the data packet on the network.  To avoid another collision each system will wait a period of time, known as the back off, before retransmitting the data.  If  data collide again the delay before retransmitting in increase and data is sent again.

The more device that are connected o an Ethernet network the more likely it is there will be collisions on the network this decrease in  performance has driven  improvements in the structures of Ethernet network, improvement include substation of older hubs with new high performance, Ethernet switches.

Ethernet Addressing

Ethernet Addressing-  Ethernet are the physical addressing of the device.  Every LAN card is identify as the Unicast  Ethernet  Address.  The LAN address are as per the IEEE standard.   The IEEE  802.3 standard the assigning the LAN Card.

IEEE assigning  OUI (Organization Uniquely Identification).

Ethernet Frame-   Ethernet frame are used by the data link layer to transfer the packet of the frame the data frame to network layer.  These are mode at the data link layer frame perform data security check and ensure the data is no corrupt.

Ethernet

ETHERNET

Ethernet is a physical and data link layer technology for local Area Network Ethernet was invented by Engineer Robert Metcalfe.

When first widely developed in the 1980’s Ethernet supported a maximum data rate to 100 mbps.  Today Gigabit technology further extends peak performance up to 1000 mbps.

OSI MODEL

OSI is the layer model for the network system designed by ISO .  OSI enable device to network to communicate with each other.

Application Layer-   The Application Layer is the top most layer of the OSI  model.  It provides network access to application and to users.  The application layer to provide service with which users can access all type of network  so application and user use these service to communicate with device and remote application.

Service- 

FTAM(File Transfer and Management)-  Using the application user can access file in a remote host it also enable the user manage file from remote host .

Mail Deliver Box-  Using the application email can be forwarded to another computer “Massage Handling Service” is the OSI protocol use for transfer mail over the internet.

Directory Service- Directory service is a source of information.    A about  such as people organization and file.

Network Virtual Terminal-   It is a software version  a physical terminal version Terminal using user can log on  the computer.  It is remotely connected on the network.

Protocol use in Application Layer- 

TCP-   A connection oriented protocol that is defined at the transport layer of the OSI reference model provide reliable delivery of data.

FTP-  The TCP/IP protocol used for transmitting files between network nodes .  It supports a brand range of file types and is defined in RFC959.

DHCP-   DHCP is used automatically configured a host during boot up on a TCP/IP network and also to change setting while the host is attached.

            This means that you can stored all the available IP address in a central data base along with information such as the subnet mask Gateways DNS server etc.

SMTP-   A protocol used on the internet to provide electronic mail Service.

DNS-   DNS is used to convert user friendly names to IP address.  They are two Zones in DNS.

 Device-  No Device use.

Presentation  Layer-  The Presentation Layer is sixth form the layer top the main function of this layer is the presentation of data.  There are situations when data sent from one system to another system has to be viewed in a different way.  Translation is the main function of the presentation layer the other function is rarely used.

Translation-     In a network there can be many type of computers, for example presentation layer is a mixed systems, we have two different type of systems, in the same network.  One is the MAC Machine and other is the UNIX machine.  Character set in both machine is different, but the presentation layer hide the different.

Compression-  This is an optional function, but it can be done by the presentation layer to improve performance.

Encryption-  We can use Presentation Layer encryption function to ensure security SSL is the one of the popular encryptions used in the Presentation layer.

Protocol-  RIP, SNMP AND DNS

Device-  Gateway

Session Layer-   It control the communication between the hosts the session layer is responsible to establish on connection to the user.

Service-

 Dialog Controller

Synchronization

Closing the Session

Dialog Box-   It allow to device to enter into dialog controller these dialog can take place in there in half duplex and full duplex.

Synchronization-  If the device  is sending he file 100 pages to ensure that these 100 pages without error they are greed link a sending data.

Closing the Session-  Ensure that the data transfer is completed before the session closed.

Protocol-  DNS, NETBIOS, SNTP, SMTP, FTP

Transport Layer-   Transport layer is responsible for source and the destination delivery the entire massage he transport layer ensure that the entire massage he arrived the destination at the computer.

Service- 

Segmentation and Reassembling

Connection Control

Error Control

Segmentation and Reassembling-  A Massage is delivered in to segment with each segment having a sequence number when they arrived that the destination with a sequence number. The transport layer Reassemble the massage.

Connection Control-  There are two type of connection control.

 Connection Oriented

 Connection Less

Error Control-  Two type of Error Control.

Error Deduction

Error Correction

Protocol-   TCP & UDP

Device-   Gateway

Network Layer-  This is responsible for routing and logical addressing.  A Network layer is provide service such as assigning IP address for the delivering the packet.

Routing-  Routing is the selecting the best path for the packet.

 Service-

 Logical Addressing

Routing

Source of destination delivery

Logical Addressing-   The data link layer provide physical addressing which is useful of local Network When the packet is forward a device out of a network be required other addressing scheme o identify source and destination when we use 32 bit logical address.

Routing-   Routing is the process of where in a proper path define for the packet to reach destination routing.

There are two type of routing.

Static Routing

Dynamic Routing

Static Routing-   In a static routing he root o be forwarded by a packet its already sets by the network administration.

Dynamic Routing-   The route to be forwarded by a packet is decided at time of transmission of the packet.

Protocol- 

 IP

ARP

RARP

ICMP

Device-   Router

Source & Destination delivery-   Transfer from the source to its destination delivery.

Data Link Layer-  It handle data transfer between network layer and physical layer data unique data link layer its called as frame.

Service- 

Framing

Physical Addressing

Error Control

Exists Control

Flow Control

Protocol- 

HDLC

SDLC

Device- 

Bridge

Switch

Physical Layer-  It is responsible to transmit up bit over the physical medium.  A bi is a short of a binary digit, and is the smallest unit of information on the computer.  The bit can be either 0 to 1. 

Service- 

Encoding

Transmission Rate

Transmission Mode

Note-  No protocol working in Physical Layer.

Device-   Router and Hub

Data Link Layer For Ethernet-   Ethernet is data link layer responsible for physical source and destination addressing.   The packet in to frame for transmitting the network  layer.   

History Of Internet

How Did the Internet Begin- First time Internet beginning with the 1957 launching of Sputnik by the USSR.  The United State formed the “Advanced Research Projects Agency (ARPA)” within the Department of Defense, to lead the USA. in science an d technology applicable to the military. 

Stage I: The ARPAnet-   In 1968, Bolt, Beranak, and Newman(BBN) was contracted by ARPAnet.  The following we3re initial four sites connected:

University of California at Los Angeles—Network Measurements Center using a Xerox DSS 7:SEX

Standard Research Institute Network Information Center using an SDS940/Genie

University of California at Santa Barbara—Culler-Fried Interactive Mathematics using an AIBM 360/75:OS/MVT

University of Utah—Graphics using a DEC DPD-10/Tenex

The network was wired together using 50kbps circuits and was managed by information message processors (IMP) that run on Honeywell 516 minicomputers.  The protocol used to communicate between hosts was the network control protocol (NCP), which enable hosts running on  the same network to transfer data.

Protocols in a Network

A protocol is an agreement used for communication between two networked hosts.  The protocol defines how data should be packaged for transmission on the network so the receiving host can unpackage it on reception.  For two hosts to communicate on a network, they must be using the same protocol.

By1972 the ARPAnet had increased to 32 nodes.  Ray Tomlinson created an email program that enables a user to send personal messages across the network.  This application started moving the network away from its military roots.  Academic using he Arpanet began to use it to communicate with remote  colleagues.  Mailing list also started evolving at this time.  The Advance Research Project Agency (DARPA).

            In 1973, development began on the protocol suite now known as the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suit. 

            In 1976, two major networking developments occurred.   Bob Metcalf of Xerox developed Ethernet, which allowed for the development of local area networks (LANs).  The other major development was the implementation of SATNET, the Atlantic packet satellite network that linked the United States with Europe.

“Internet” Verses “Internet”
In 1982, the term internet was defined as a connected  of separate networks using the TCP/IP protocol suite.  The internet was defined as connected TCP/IP INTERNETS.  This book continues his distinction, using the term internet to refer to the global network.

Stage II NSFNET   

In 1985, the National Science Foundation Began deploying new T1 lines at 1.544Mbps for the next generation of the ARPAnet, known as the NSFNET.

            With the movement toward the NSFNET, the National Science Foundation introduced two enhancements to the TCP/IP protocol.   The Network News Transfer Protocol(NNTP) was introduced to increase Usenet News performance, and Mail Exchanger (MX) records were developed for use with DNS servers.