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What is a Computer Network?  What is a Computer Network? A set of nodes (computers or electronic devices) which are connected together by communication links (communication pathway that transfer data from one device to another). This can mean t...

What is a Computer Network?  What is a Computer Network? A set of nodes (computers or electronic devices) which are connected together by communication links (communication pathway that transfer data from one device to another). This can mean two computers cabled together on the same desk, or thousands of computers across the world. The connections can be cables or wireless.  Network usages 1. Data Sharing 2. Software sharing 3. Hardware sharing 4. Personal Information Sharing 5. E-commerce 6. Person – to – Person Communication 7. Entertainment 8. Game Playing 9. Client – Server applications 10. Remote Communications 11. etc. Some Types of E-commerce Advantages of Computer Networks Enables users to share hardware like scanners and printers. This reduces costs by reducing the number of hardware items bought. Allows users access to data stored on others' computers. This keeps everyone up-to-date on the latest data Can share access to the Internet. Advantages of Computer Networks Can even let users run programs that are not installed on their own computers but are installed elsewhere in the network.  reduces the effort for networks administrators to keep programs configured correctly and saves a lot of storage space.  Important Definitions Data: information presented in whatever form is agreed upon by the parties creating and using the data. Data Communication: exchange of data between two devices via transmission medium (wire cable / link). Data Communication System: Made up of a combination of hardware (physical equipment) and software (programs) to facilitate for effective communication of data. Characteristics of a Data Communication System Delivery : System must deliver data to correct destination. Data must be received by only intended device or user. Accuracy: The system must deliver data accurately Timeliness: the system must deliver data in a timely manner. Data delivered later are useless. Jitter: Variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets.  Data Flow Path taken by data within a device, network, or organization, as it moves from its source to its destination (a data repository or a data user). Categorized by direction of flow: Simplex Half-duplex Full-duplex  Simplex Communication is unidirectional, one of the two devices on a link can transmit; the other can only receive (one-way street). Ex: keyboard (input), monitors (output)  Half-duplex Each station can both transmit and receive , but not at the same time. When one device is sending the other can receive and vice versa. (one-lane road with two direction).  Full-duplex Both stations can transmit and receive simultaneously. (two way street with traffic flowing in both directions at the same time). Ex: telephone network. Signals going in either direction share the capacity of the link in two ways: Either the link must contain two physically separate transmission paths one for sending and other for receiving. Capacity of the channel is divided between signals traveling in both direction  Performance Can be measured in many ways! – Transmit time: the amount of time required for a message to travel from one device to another. – Response time: the elapsed time between an inquiry and a response. Often evaluated by two networking metrics: throughput and delay.  What Is Bandwidth in Networking? The network bandwidth definition can be confusing, but basically, network bandwidth is defined as It’s a measure of how much data can be sent and received at a time. Bandwidth is measured in bits, megabits, or gigabits per second. It’s important to know bandwidth doesn’t actually increase the speed of a network, it just appears to make the network faster. You can increase a network’s bandwidth all you want, but all you’ll end up doing is increasing the amount of data that can be sent at one time, not increasing the transmission speed of said data. Bandwidth doesn’t change the speed at which packets are traveling. It’s similarly important to remember high bandwidth doesn’t necessarily equal high network performance. Substantial bandwidth won’t matter if data throughput is still being dragged down by latency, jitter, or packet loss.  Throughput Throughput measures how many packets arrive at their destinations successfully. For the most part, throughput capacity is measured in bits per second, but it can also be measured in data per second. The bandwidth of a network is given by the number of bits that can be transmitted over the network in a certain period of time. Depends on the network technology (hardware capabilities) and therefore is constant.  Throughput Notes: Throughput tells you how much data was transferred from a source at any given time. Bandwidth tells you how much data could theoretically be transferred from a source at any given time. How to Optimize Bandwidth? Are you using QoS settings? QoS or quality of service settings help networks support essential applications. With these settings, you can command traffic policies to prioritize certain types of traffic, so the most important applications don’t have to compete for bandwidth when they need it. Are you using cloud-based applications? Running applications in the cloud is an easy way to improve network performance. By outsourcing some of your traffic to public and private cloud networks, you can relieve some of the pressure on your own network. This also reduces your monitoring burdens and heightens the performance of your more regularly-used applications.  How to Optimize Bandwidth? Have you eliminated all non-essential traffic? No employee should be denied the odd YouTube video every now and then, but you’d be surprised at how much non-essential traffic goes on in even the most productive work environments. Block certain traffic during business hours to make sure your precious bandwidth is only being used for essential operations. Are you conducting backups and updates at the right time? Backups and network updates take up a massive amount of bandwidth and often require the shutdown of some network functions. Running these operations can really cut into network performance and increase latency. It may sound obvious, but you have to strategically schedule your maintenance. Backups and updates should be done outside of normal working hours to ensure the network is free for use when employees really need it.  Delay Also known as latency. corresponds to how long it takes a message to travel from one end of a network to the other. Latency is measured strictly in terms of time. Effected by number of users and hence may change from time to time. Factors Affecting Performance Type of transmission media, Capabilities of connected H.W and the efficiency of software. Number of user  *Design Issues Reliability: – Network must operate correctly although it is made up of a collection of components that are themselves unreliable. – Accuracy of delivery is measured by: 1. Frequency of failures 2. Time it takes to recover from a failure 3. The network’s robustness in a catastrophe. Error Detection: – It typically uses codes to locate the erroneously transmitted bit(s) and request re-transmission. Error Correction – Correct messages is recovered from the possibly incorrect bit(s) that were originally received.  *Design Issues Routing: – Finding a working path through a network. Protocol Layering: – Networks grow larger over time and new designs emerge that need to connected to the existing networks. – Therefore, there is essential requirement to divide the networking software into a list of layers. Each layer serves some devices or software.  *Design Issues (cont.) Congestion: – The problem may occur when the network is oversubscribed because to many computers want to send too much traffic and the network will not be able to deliver them all. – Overloading problem of the network. – One strategy is for each computer to reduce its demand. Quality of Service – Additional Resources (other than Bandwidth), – Real-time delivery (for applications that require high throughput), – Live Video,  *Design Issues (cont.) Network Security – How good is the network against different kinds of threats Eavesdropping, Confidentiality, Authentication, Integrity, etc.  *Design Issues (cont.) Eavesdropping attacks happen when cyber criminals or attackers listen in to network traffic traveling over computers, servers, mobile devices and Internet of Things (IoT) devices. Network eavesdropping, also known as network snooping or sniffing, occurs when malicious actors exploit insecure or vulnerable networks to read or steal data as it travels between two devices. Eavesdropping is most common for wireless communication. Confidentiality – ensures that sensitive information are accessed only by an authorized person and kept away from those not authorized to possess them. It is implemented using security mechanisms such as usernames, passwords, access control lists (ACLs), and encryption. It is also common for information to be categorized according to the extent of damage that could be done should it fall into unintended hands. Security measures can then be implemented accordingly.  *Design Issues (cont.) authentication is the process that confirms a user’s identity and provides access to sensitive information. Traditionally, this is done through a username and password. The user enters their username, which allows the system to confirm their identity. This system relies on the fact that (hopefully) only the user and the server know the password. The website authentication process works by comparing the user’s credentials with the ones on file. If a match is found, the authentication process is complete, and the individual can be pushed through to the authorization process.  *Design Issues (cont.) Network Security Authentication, Integrity – ensures that information are in a format that is true and correct to its original purposes. The receiver of the information must have the information the creator intended him to have. The information can be edited by authorized persons only and remains in its original state when at rest. Integrity is implemented using security mechanism such as data encryption and hashing. Note that the changes in data might also occur as a result of non-human-caused events such as an electromagnetic pulse (EMP) or server crash, so it’s important to have the backup procedure and redundant systems in place to ensure data integrity.  *Design Issues (cont.) Network Security – How good is the network against different kinds of threats Eavesdropping, Confidentiality, Authentication, Integrity, etc.  Security Many issues at the different layers! Examples: – Protecting data from unauthorized access. – Protecting data from damage. – Implementing policies and procedures for recovery from breaches and data losses.  Connection-Oriented Versus Connectionless Service Layers can offer two different types of service to the layers above them: – Connection-oriented, and – Connectionless  Connection-Oriented Service Modeled after telephone system: – Pickup-the-phone – Dial the number – Talk – Hang-up Service User: – Establishes a connection, – Uses a connection (sender pushes objects in at one end and the receiver takes them out at the other end). – In some cases when connection is established, the sender, receiver, and a subnet conduct a negotiation about the parameters to be used: Maximum message size, Quality of service required,  Connectionless Service Modeled after a postal system: – Each message carries the full destination address, and – Each one is routed through the intermediate nodes inside the system independent of all the subsequent messages. Different Names for Messages: – Store-and-forward switching: Packet, a message, is processed in full before sending it on the next node. – Cut-through-switching: when the onward transmission of a message at a node start before it is completely received. Each kind of the Service can be further characterized by its reliability: – A reliable service is implemented by having the receiver acknowledge the receipt of each message. – Acknowledgment service introduces overhead and delays.  *Connection-Oriented Service Reliable connection-oriented service: – Message Sequences, and – Byte Streams Message Sequences: – Message boundaries are preserved. – Example: Two 1024 byte messages are sent, the arrive as two distinct 1024-byte messages; Never as one 2048-byte message. Byte Streams: – Message is send as a stream of bytes with no concepts of message boundaries. – Example: When a 2048-byte message arrives at the receiver there is no way to tell if they were sent as One 2048-byte message, Two 1024-byte message, or 2048 1-byte messages. *Connection-Oriented Versus Connectionless Service Six different types of service. Reliable vs. Unreliable Communication Why would one prefer unreliable communication vs. reliable one? 1. Reliable communication may not be available: Ethernet. Packets can be damaged. It is up to higher levels of protocol to recover from this problem. Many reliable services are built on top of the unreliable service. 2. The delays for providing reliable service are not acceptable: Real time applications such as multimedia.  Service Primitives (1) Six service primitives that provide a simple connection-oriented service  *Difference between Connection-oriented and Connection-less Services: CONNECTION-LESS CONNECTION-ORIENTED # SERVICE SERVICE Connection-less service is Connection-oriented service is 1 related to the postal system. related to the telephone system. In connection-less Service, In connection-oriented Service, 2 Congestion is possible. Congestion is not possible. Connection-less Service does Connection-oriented Service gives the 3 not give the guarantee of guarantee of reliability. reliability. In connection-less Service, In connection-oriented Service, 4 Packets do not follow the same Packets follow the same route. route.  Type of Connections For communication to occur, two devices must be connected in someway to the same link at the same time. Two possible connections: – Broadcast – Point-to-point – Multipoint  Network Hardware – Broadcast Communication channel shared by all machines Packets send by any machine are received by all the others. Wireless network is a common example of a broadcast link Broadcast systems usually also allow the possibility of addressing a packet to all destinations. – Point-to-point Connect individual pairs of machines Packets (short messages) may have to visit one or more intermediates machines. Multiple routes of different lengths are possible. Finding good ones is important. Unicasting – transmission with exactly one sender and exactly one receiver.  Physical Structures: Type of connection 1. Point –to-point Dedicated link between two devices. Most of them uses an actual length of wire or cable to connect the two ends but other options ,such as microwave satellite are possible.  Physical Structures: Type of connection 2. Multipoint Is one in which more than two specific devices share a single link  Links Each node needs one interface for each link. point-to-point(a) multiple-access(b) Geographical coverage and scalability are limited. 1/18/2006 CSCI 363 Computer Networks 42  Physical Topology Two or more links for a topology. – The topology of a network refers to the geometric representation of the relationship of all the links and linking devices (nodes) to one another. The term physical topology refers to the way in which a network is laid out physically.  Physical Topology The way in which a network is laid out physically.  Mesh Topology Every device has a dedicated point-to-point link with every other device on the network. How many links do we need in a network with N nodes? – Half duplex - Full duplex link carries traffic only between the two devices. Fully connected mesh topology (for five devices) Every device has a dedicated point-to-point link to every other devices Fully connected mesh network has n(n-1)/2 physical connection to link n devices. Every device on the network must have n-1 input/output (I/O) ports  Advantages of a Mesh topology Privacy or security (every message travels along a dedicated line, only the intended recipient sees it. Physical boundaries prevents other user from gaining access the message Eliminating the traffic problems The use of dedicated links guarantees that each connection can carry its own data load; that can occur when links must be shared by multiple devices.  Advantages of a Mesh topology A mesh is robust. If one link becomes unusable, it does not incapacitate the entire system. Fault identification and fault isolation easy. This enables the network manager to discover the precise location of fault and aids in finding its cause and solution.  Disadvantages of a Mesh topology Related to the amount of cabling devices and the amount of I/O ports required: – Every device must be connected to every other device, installation and reconnection are difficult – The sheer bulk of the wiring can be greater than the available space can accommodate. – The H.W required to connect each link (I/O ports and cable) expensive. Disadvantages of a Mesh topology So a mesh topology is usually implemented in a limited fashion( as a backbone connecting the main computers of a hybrid network that can include several other topology  Star topology Each device has a dedicated point-to-point link only to a central controller (hub) Unlike a mesh , a star topology does not allow direct traffic between devices, if one device want to send data to another , it send it to the hub, which send it to other device  The star pattern connects everything to a host computer, a network switch, or a network hub, which handles the network tasks. All communications between computers go through the host/switch/hub.  Advantages of a Star topology 1.Easy to install and reconfigure and less expensive – each device need only one link and I/O port to connect it to any other devices.) 2.Robustness: – if one link fails, only that link affected and other links remain active. 3.identification and fault isolation Disadvantages of a Star topology The dependency of the whole topology on one single point, the hub. If the hub goes down, the whole system is dead.  Tree topology : is a variation of star - Not every device plugs directly into the central hub. The majority of devices connect to secondary hub that in turn is connected to the central hub.  Tree topology : is a variation of star The advantages and disadvantages of tree topology are generally the same as those of star. - The addition of secondary hubs bring more advantage: allows for more devices to be attached to a single central hub, therefore increase the distance a signal can travel between devices.  Bus topology Bus topology (line topology) is a Multipoint connection where each computer and network device is connected to a single cable or backbone to link all the devices in a network.  The bus pattern connects a computer to the same communications line. Communications goes both directions along the line. All the computers can communicate with each other without having to go through the server or any other machine.  Bus topology Notes:  There is a limit on the number of taps a bus can support and on the distance between those taps.  As a signal travels along the Advantages of a Bus topology  Ease of insulation  Use less cabling than mesh or star.  It works well when you have a small network. Disadvantages of a Bus topology 1. A fault in bus cable (break) stops all transmissions even between devices on the same side of the problem. The damaged area reflects signals back the direction of origin, creating noise in both directions 2. Reconnection It can difficult to add new devices (adding more require modification or replacement of the backbone).  Disadvantages of a Bus topology 1. A fault in bus cable (break) stops all transmissions even between devices on the same side of the problem. The damaged area reflects signals back the direction of origin, creating noise in both directions. 2. It can be hard to troubleshoot individual device issues. 3. Bus topology is not great for large networks.  Ring Topology Each device has a dedicated point-to- point connection only with the two devices on either side of it A signal is passed along the ring in one direction from device until it reaches its destination.  The ring pattern connects the computers and other devices one to the other in a circle. There is no central host computer that holds all the data. Communication flows in one direction around the ring.  Ring Topology Each device in the ring incorporate as repeater Repeater is a device used to regenerates the signal  it receives a weakened signal, creates a copy, bit for bit, at the original strength  Ring Topology Advantages: Easy to install and reconfigure. Each device is linked only to its immediate neighbors. To add or delete a device requires hanging only 2 connections Fault isolation is simplified : A signal is circulating at all times (token) if one device does not receive a signal within specified period, it can issue an alarm. The alarm alerts the network operator to the problem and its location. Disadvantages Unidirectional traffic. A break in the ring (such as disabled station) can disable the entire network. This can be solved by use dual ring  A hybrid topology A hybrid topology is a type of network topology that uses two or more differing network topologies.  These topologies can include a mix of bus topology, mesh topology, ring topology, star topology, and tree topology.  The choice to use a hybrid topology over a standard topology depends on the needs of a business, school, or the users.  The number of computers, their location, and desired network performance are all factors in the decision. A hybrid topology: a star backbone with three bus networks  Network Categories Network category is determined by its size, ownership, the distance it cover and its physical architecture. Therefore, according to geographical distance, networks can be classified into: 1. Personal Area Networks (PANs) 2. Local Area Networks (LANs) 3. Metropolitan Area Networks (MANs) 4. Wide Area Networks (WANs) 5. The Internet Network Categories  Personal Area Network Bluetooth PAN (Personal Area Network) configuration A personal area network, or PAN, is a computer network that enables communication between computer devices near a person. PANs can be wired, such as USB or FireWire, or they can be wireless, such as infrared, ZigBee, Bluetooth and ultrawideband, (UWB). The range of a PAN typically is a few meters. Examples of wireless PAN, or WPAN, devices include cell phone headsets, wireless keyboards, wireless mice, printers, bar code scanners and game consoles.  Home Computer Networks (HANs)  Home Area Network (HAN) is a network in a user’s home where all the laptops, computers, smartphones, and other smart appliances and digital devices are connected into a network.  This facilitates communication among the digital devices within a home which are connected to the Home network. Home Area Network may be wired or wireless.  Mostly wireless network is used for HAN.  One centralized device is there for the function Network Address Translation (NAT).  This Home Area Network enables communication and sharing of resources between the smart devices over a network connection.  Local Area Networks  A local area network (LAN) is a collection of devices connected together in one physical location where the computers are relatively close together.  So LANs would be within the same office, a single building, or several buildings close together.  A LAN can be small or large, ranging from a home network with one user to an enterprise network with thousands of users and devices in an office or school. Local Area Networks Wireless and wired LANs. (a) IEEE 802.11 or WiFi. (b) Switched Ethernet (802.3).  Important terminology related to LAN Switched Ethernet Switch: Hardware that connects two devices point-to-point A Switch has multiple ports Physical vs. Virtual LAN – VLAN Note that LAN stands for Local Area Network is a group of network devices which allow the communication between connected devices. On the other hand VLAN stands for Virtual Local Area Network which is used to enhance the performance of LANs (Local Area Networks). The main difference between LAN (Local Area Network) and VLAN (Virtual Local Area Network) is that LAN work on single broadcast domain on the other hand VLAN works on multiple broadcast domain and In local are network, the Packet is advertised to each device while In virtual local area network, packet is send to specific broadcast domain  Important terminology related to LAN Dynamic vs. Static Channel Allocation Static Allocation: Each device is allocated its time slot weather or not it uses it. Dynamic methods allow changing the time allocation scheme. Dynamic Allocation Centralized where the channel allocation is managed by a central device. Decentralized where there is no central device manages the channel allocation process. That is, each device know the channel according to specific procedure known by all other devices.  LAN ( Local Area Network) Traditionally LAN have data rates in the 4 to 16 Mbps. Today Speed can reach to 100Mbps or 1000MBps (1G).  MAN (Metropolitan Area Network) Owned by private company or it may be a service provided by public company ( such as local tel.-company) Extended over an entire city. May be single network such as a cable television network, or it may be connected number of LANs into a large network so that resources may be shared LAN-TO- LAN.  MAN (Metropolitan Area Network) Examples:  Company can use MAN to connect the LANs in all its offices throughout the city.  A part of the telephone line network that can provide DSL line to the customer.  Wide Area Network A WAN is a Wide Area Network, which would be all networks too large to be LANs. A WAN would be most useful for large companies with offices or factories in widely separated areas, like Microsoft, IBM, Ford, AT&T, etc.  Network Configuration Broadcasting: in computer network is a group communication, where a sender sends data to receivers simultaneously. This is an all − to − all communication model where each sending device transmits data to all other devices in the network domain. The ways of operation of broadcasting may be −A high level operation in a program, like broadcasting in Message Passing Interface. A low level networking operation, like broadcasting on Ethernet.  Network Configuration Broadcasting is shown in the following figure  Advantages of Broadcasting  Broadcast helps to attain economies of scale when a common data stream needs to be delivered to all, by minimizing the communication and processing overhead.  It ensures better utilization of resources and faster delivery in comparison to several unicast communication.  Disadvantages of Broadcasting  Broadcasting cannot accommodate a very large amount of devices.  Also it does not allow personalization of the messages according to the individual preferences of the devices.  Network Configuration Switching: In contrast to broadcasting, where sender can send data to all receivers, switching depends on dividing the whole network to small networks connected by switching elements or devices (either switches or routers). Each one can forward data to intermediate nodes inside the system independent of all the subsequent. Therefore, the data is directed to a specific machine, not all machines. Note: Switching elements, or just switches, are specialized computers that connect two or more transmission lines. When data arrive on an incoming line, the switching element must choose an outgoing line on which to forward them. These switching computers have been called by various names in the past; the name router is now most commonly used.  Network Configuration When the intermediate nodes receive a message in full before sending it on to the next node, this is called store- and-forward switching. The alternative, in which the onward transmission of a message at a node starts before it is completely received by the node, is called cut- through switching. Normally, when two messages are sent to the same destination, the first one sent will be the first one to arrive. However, it is possible that the first one sent can be delayed so that the second one arrives first.  Network Configuration Circuit Switching in Computer Network  A dedicated path/circuit is established between sender and receiver provides a guaranteed data rate.  In circuit switching network resources (bandwidth) are divided into pieces and bit delay is constant during a connection.  Data can be transmitted without any delays once the circuit is established.  Telephone system network is one of the example of circuit switching.  Network Configuration Advantages of Circuit Switching: Circuit Switching has the following advantages : 1. The main advantage of circuit switching is that a committed transmission channel is established between the computers which give a guaranteed data rate. 2. In-circuit switching, there is no delay in data flow because of the dedicated transmission path.  Network Configuration Disadvantages of Circuit Switching: Circuit Switching has the following disadvantages : 1. It takes a long time to establish a connection. 2. More bandwidth is required in setting up dedicated channels. 3. It cannot be used to transmit any other data even if the channel is free as the connection is dedicated to circuit switching.  Network Configuration Packet Switching and Delays in Computer Network  Packet switching is a method of transferring the data to a network in form of packets.  In order to transfer the file fast and efficient manner over the network and minimize the transmission latency, the data is broken into small pieces of variable length, called Packet.  At the destination, all these small-parts (packets) has to be reassembled, belonging to the same file.  A packet composes of payload and various control information. No pre-setup or reservation of resources is needed.  Network Configuration Packet Switching and Delays in Computer Network  Packet Switching uses Store and Forward technique while switching the packets; while forwarding the packet each hop first store that packet then forward.  This technique is very beneficial because packets may get discarded at any hop due to some reason.  More than one path is possible between a pair of source and destination.  Each packet contains Source and destination address using which they independently travel through the network. In other words, packets belonging to the same file may or may not travel through the same path.  If there is congestion at some path, packets are allowed to choose different path possible over existing network.  Network Configuration Packet Switching and Delays in Computer Network Packet-Switched networks were designed to overcome the weaknesses of Circuit-Switched networks since circuit-switched networks were not very effective for small messages.  Network Configuration Advantage of Packet Switching over Circuit Switching : 1. More efficient in terms of bandwidth, since the concept of reserving circuit is not there. 2. Minimal transmission latency. 3. More reliable as destination can detect the missing packet. 4. More fault tolerant because packets may follow different path in case any link is down, Unlike Circuit Switching. 5. Cost effective and comparatively cheaper to implement.  Network Configuration Disadvantage of Packet Switching over Circuit Switching : 1. Packet Switching don’t give packets in order, whereas Circuit Switching provides ordered delivery of packets because all the packets follow the same path. 2. Since the packets are unordered, we need to provide sequence numbers to each packet. 3. Complexity is more at each node because of the facility to follow multiple path. 4. Transmission delay is more because of rerouting. 5. Packet Switching is beneficial only for small messages, but for bursty data (large messages) Circuit Switching is better.  Network Configuration Modes (types) of Packet Switching : 1.Connection-oriented Packet Switching (Virtual Circuit) :  Before starting the transmission, it establishes a logical path or virtual connection using signaling protocol, between sender and receiver and all packets belongs to this flow will follow this predefined route.  Virtual Circuit ID is provided by switches/routers to uniquely identify this virtual connection.  Data is divided into small units and all these small units are appended with help of sequence number.  Overall, three phases takes place here- Setup, data transfer and tear down phase.  Network Configuration Phases of Virtual Circuit Packet Switching  Network Configuration Modes (types) of Packet Switching :  Network Configuration Delays in Packet switching : 1. Transmission Delay 2. Propagation Delay 3. Queuing Delay 4. Processing Delay  Network Configuration Differences between Virtual Circuits and Datagram Networks Computer networks that provide Connection-oriented service are called Virtual Circuits while those providing connection-less services are called as Datagram networks. For prior knowledge, the Internet which we use is actually based on Datagram network (connection-less) at the network level as all packets from a source to a destination do not follow the same path. Let us see what are the highlighting differences between these two hot debated topics here:  Network Configuration Virtual Circuits: 1. It is connection-oriented, meaning that there is a reservation of resources like buffers, CPU, bandwidth, etc. for the time in which the newly setup VC is going to be used by a data transfer session. 2. The first sent packet reserves resources at each server along the path. Subsequent packets will follow the same path as the first sent packet for the connection time. 3. Since all the packets are going to follow the same path, a global header is required. Only the first packet of the connection requires a global header, the remaining packets generally don’t require global headers.  Network Configuration Virtual Circuits: 4. Since all packets follow a specific path, packets are received in-order at the destination. 5. Virtual Circuit Switching ensures that all packets successfully reach the Destination. No packet will be discarded due to unavailability of resources. 6. From the above points, it can be concluded that Virtual Circuits are a highly reliable method of data transfer. 7. The issue with virtual circuits is that each time a new connection is set up, resources and extra information have to be reserved at every router along the path, which becomes problematic if many clients are trying to reserve a routers resources simultaneously. 8. It is used by the ATM (Asynchronous Transfer Mode) Network, specifically for Telephone calls.  Network Configuration Datagram Networks : 1. It is a connection-less service. There is no need for reservation of resources as there is no dedicated path for a connection session. 2. All packets are free to use any available path. As a result, intermediate routers calculate routes on the go due to dynamically changing routing tables on routers. 3. Since every packet is free to choose any path, all packets must be associated with a header with proper information about the source and the upper layer data. 4. The connection-less property makes data packets reach the destination in any order, which means that they can potentially be received out of order at the receiver’s end.  Network Configuration Datagram Networks : 5. Datagram networks are not as reliable as Virtual Circuits. 6. The major drawback of Datagram Packet switching is that a packet can only be forwarded if resources such as the buffer, CPU, and bandwidth are available. Otherwise, the packet will be discarded. 7. But it is always easy and cost-efficient to implement datagram networks as there is no extra headache of reserving resources and making a dedicated each time an application has to communicate. 8. It is generally used by the IP network, which is used for Data services like the Internet.  Network Configuration Difference between Circuit Switching and Packet Switching Circuit Switching Packet Switching In circuit switching there are 3 phases: i) Connection Establishment. In Packet switching directly data ii) Data Transfer.. transfer takes place.iii) Connection Released In Packet switching, each data unit In circuit switching, each data unit know just know the final destination the entire path address which is provided by address intermediate path is decided.the source.by the routers In Packet switching, data is In Circuit switching, data is processed at processed at all intermediate node source system only.including source system Delay between data units in circuit Delay between data units in packet.switching is uniform.switching is not uniform Resource reservation is the feature of circuit There is no resource reservation switching because path is fixed for data because bandwidth is shared among.transmission.users.Circuit switching is more reliable.Packet switching is less reliable  Network Configuration Difference between Circuit Switching and Packet Switching Circuit Switching Packet Switching Wastage of resources are more in Less wastage of resources as compared Circuit Switching to Circuit Switching.It is not a store and forward technique.It is a store and forward technique Transmission of the data is done not only Transmission of the data is done by the by the source, but also by the.source.intermediate routers Congestion can occur during connection Congestion can occur during data establishment time, there might be a transfer phase, large number of packets case will requesting for channel the.comes in no time.channel is already occupied Circuit switching is not convenient for Packet switching is suitable for handling.handling bilateral traffic.bilateral traffic In Circuit switching, charge depend on In Packet switching, charge is based on time and distance, not on traffic in the the number of bytes and connection.network.time Recording of packet is never possible in While recording of packet is possible in.circuit switching.packet switching Computer Networks Devices , Reference Models , and Protocols  Network Connecting Devices 1. Repeater – A repeater operates at the physical layer. Its job is to regenerate the signal over the same network before the signal becomes too weak or corrupted so as to extend the length to which the signal can be transmitted over the same network. An important point to be noted about repeaters is that they do not amplify the signal. When the signal becomes weak, they copy the signal bit by bit and regenerate it at the original strength. It is a 2 port device.  Network Devices 2. Hub – A hub is basically a multiport repeater. A hub connects multiple wires coming from different branches, for example, the connector in star topology which connects different stations. Hubs cannot filter data, so data packets are sent to all connected devices. In other words, collision domain of all hosts connected through Hub remains one. Also, they do not have intelligence to find out best path for data packets which leads to inefficiencies and wastage. Hub works in physical layer.  Network Devices Types of Hub Passive Hub :- These are the hubs which collect wiring from nodes and power supply from active hub. These hubs relay signals onto the network without cleaning and boosting them and can’t be used to extend the distance between nodes. Active Hub:- These are the hubs which have their own power supply and can clean, boost and relay the signal along with the network. It serves both as a repeater as well as wiring center. These are used to extend the maximum distance between nodes. Intelligent Hub :-A network device that performs a variety of processing functions, including network management, bridging, routing and switching in  Network Devices 3. Bridge – A bridge operates at data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2 port device.  Network Devices 4. Switch – A switch is a multiport bridge with a buffer and a design that can boost its efficiency (a large number of ports imply less traffic) and performance. A switch is a data link layer device. The switch can perform error checking before forwarding data, that makes it very efficient as it does not forward packets that have errors and forward good packets selectively to correct port only * Switches at the forward same data network. packets based on Intheir other words, MAC switch divides collision domain of addresses. hosts, but broadcast domain remains same.  Network Devices 5. Routers – A router is a device like a switch that routes data packets based on their IP addresses. Router is mainly a Network Layer device. Routers normally connect LANs and WANs together and have a dynamically updating routing table based on which they make decisions on routing the data packets. Routers divide broadcast domains of hosts connected through it. https://www.youtube.com/watch? time_continue=3&v=ZvWn5xBflUs&feature=emb_title  Network Devices 6. Gateway – A gateway, as the name suggests, is a passage to connect two networks together that may work upon different networking models. They basically work as the messenger agents that take data from one system, interpret it, and transfer it to another system. Gateways are also called protocol converters and can operate at any network layer. Gateways are generally more complex and intelligent than switch or router.  Network Devices Differences between Routers and Bridges  Network Devices Comparison between Switches, Routers, and Gateways  Network Devices 7. Brouter – It is also known as bridging router is a device which combines features of both bridge and router. It can work either at data link layer or at network layer. Working as router, it is capable of routing packets across networks and working as bridge, it is capable of filtering local area network traffic.  Network Devices Advantages of Brouter in Networking 1. It works on Both LAN and WAN 2. NAT can be configured which hides the real IP Address of your internal network (for security issues). 3. Supports packet filtering. 4. Supports packet Switching. 5. Can be used to separate a LAN into segments. 6. Allows you to set the best path for data Disadvantages packets. of Brouter in 7. Reduce network traffic. Networking 1. It is more expensive then hub, switch and router.  Network Devices 8. Modem – The acronym modem is a shortened form of modulator-demodulator. In simple language, a Modem is the device that is used to connect a pc with the Internet. Technically, it is the device that enables the digital data to be transmitted over the telecommunication lines (analogue data). A Telephone companies use entirely different data transmission technology from the technology that a PC uses for the data transmission. A modem understands both technologies. It changes the technology that a  Network Devices Modem  Network Devices 9. Proxy – Proxy is used to hide the internal network from external world.  It can be a dedicate device or can be an application software.  Once it is configured, all communication goes through it.  Therefore, external devices cannot access the internal devices directly.  Hence, they cannot tamper (change and corrupt) with the internal devices.  Proxy servers allow to hide, conceal and make your network id anonymous by hiding your IP address.  Proxy server is an intermediary server  Network Devices Proxy servers offers the following basic functionalities: 1. Firewall and network data filtering. 2. Network connection sharing. 3. Data caching.  Network Devices 10. Transceiver: 1. Transceiver is a small device that has the capability of receiving and sending both types of signals; analog and digital. Usually, it is inbuilt in network interface card. 2. It is also available as an individual device. It detects the type of signal from the network wire and converts the passing signal accordingly. 3. For example, a transceiver is attached with a device that transmits signal in digital form. Now suppose, this device is connected with the network wire that uses analog form for data transmission. In this case, transceiver converts digital signals in the analog signals before placing them in the network wire. 4. It can performs modem functions.  Network Devices 11.Network Interface Card (NIC) 1. In the list of the networking devices, NIC stands on the first place. Without NIC , networking cannot be done. 2. This is also known as network adapter card, Ethernet Card and LAN card. 3. NIC allows a networking device to communicate with the other networking device. 4. NIC converts the data packets between two different data transmission technologies. 5. A PC uses parallel data transmission technology to transmit the data between its internal parts while the media that provides connectivity between different PCs uses serial data transmission technology. 6. A NIC converts parallel data stream into the  Network Devices 11.Network Interface Card (NIC) Typically all modern PCs have the integrated NICs in the motherboards. If additional NICs are required, they are also available as add-on devices separately. For desktop or server system, they are available in the adapter form which can be plugged into the available slots of the motherboard. For laptop or other small size devices, they are available in the PCMCIA (Personal Computer Memory Card International Association) card form which can be inserted into the PCMCIA slot.  Network Devices 11.Network Interface Card (NIC)  Network Devices 12. Splitter 1. DSL Modem Splitter Adapter separates (Filters) signals coming from telephone company to data signals to be used in computers networks and voice signals on telephone line. 2. Filter is used also to eliminate interference on voice line caused by DSL signal. 3. One RJ11 at one end for line; Two RJ11 at the other end for phone and DSL modem.  Network Reference Models Network reference models are platforms to ensure a reliable communication between network devices either computers, switches or routers. Each reference model decompose the networking functionalities to different tasks. To simplify the communicating process, each task is Weachieved by a two will consider partbasic (layer) of the models reference reference in model. this course. 1- The Open Systems Interconnection (OSI) which is considered as a conceptual model to show the basic functionalities of the different parts. This model is regarded as main constitution of the other reference models. It is an explanatory and educational model. This model consists of 7 layers. 2- The other model is Transmission Control  OSI Reference Model -1 In this section we explain OSI reference As model. before, OSI reference we mentioned model consists of 7 layers starting with the closest one to the user and ending with the closest one to the transmission media. These layers are named. The Application Layer (Closed to user), The Presentation Layer, The Session Layer, The Transport Layer, The Network Layer, The Data Link Layer, The Physical Layer. Each layer of these layers has a set of protocols and is assigned a specific task. OSI Reference Model -1  Application Layer This is the only layer that 1- Application Layer directly interacts with data from the user. 2- Presentation layer Functions: This layer provides specific jobs to the 3- Session layer applications used by users to make these applications useful and 4- Transport layer reliable for users. These applications can be (for example) mailing, Web 5- Network layer browsing, Streaming, chatting, video conferencing, telecommunication, 6- Data Link layer database, etc. The protocols used in this layer are: HTTP (Hyper 7- Physical layer Text Transfer Protocol),  Application Layer 1- Application Layer Common Protocols: 2- Presentation layer 1. DHCP : Dynamic Host Configuration Protocol to dynamically assigns an IP 3- Session layer address and other network configuration parameters to each device on a network so 4- Transport layer they can communicate with other IP networks 2. DNS A Domain Name 5- Network layer System to resolve URL of a web page to an IP address. 3. FTP : File Transfer 6- Data Link layer Protocol to send and receive data files 4. HTTP : Hypertext 7- Physical layer Transfer Protocol to fetch  Application Layer 1- Application Layer Common Protocols: 2- Presentation layer 6. SSH : Secure Shell to operate network services securely over an 3- Session layer unsecured network 7. TELNET : allows a user to communicate with a 4- Transport layer remote device (Logging In). 5- Network layer 8.RSS : Really Simple Syndication to publish regular updates of web- 6- Data Link layer based content. Common Devices: 9. PCs 7- Physical layer 10. Servers  Presentation layer This layer is primarily 1- Application Layer responsible for preparing data so that it can be used by the application layer. The 2- Presentation layer presentation layer is responsible for translation, encryption, and compression 3- Session layer of data Functions: 1.Data Translation: to 4- Transport layer translate the data format in one machine to a format recognized by the network 5- Network layer ASCII to EBCDIC or vice versa. 2. Data Encryption: to 6- Data Link layer securely send data through the network 3.Data compression: to 7- Physical layer powerfully uses the available bandwidth.  Presentation layer 1- Application Layer Common Protocols: 1.XDR : External Data 2- Presentation layer Representation , useful for transferring data between different 3- Session layer computer architectures to XDR format. 2. TLS: Transport Layer 4- Transport layer Security , is a cryptographic protocol that provides end-to-end 5- Network layer communications security over networks. 3. SSL: Secure Sockets 6- Data Link layer Layer , provide security to the data that is transferred between web browser and server. 7- Physical layer Common  Session layer 1- Application Layer This is the layer responsible for starting, 2- Presentation layer managing and terminating connections 3- Session layer between applications. Functions: 4- Transport layer 1.Setting up conversations, exchanges, and dialogues between the applications at 5- Network layer each end. 2.Coordinating conversations, exchanges, and dialogues 6- Data Link layer between the applications at each end. 3.Terminating conversations, 7- Physical layer exchanges, and dialogues between the applications at  Session layer 1- Application Layer Common Protocols: 2- Presentation layer Remote procedure call protocol (RPC) : is a protocol that one program 3- Session layer can use to request a service from a program located in 4- Transport layer another computer on a network without having to understand the network's 5- Network layer details. Point-to-Point Tunnelling Protocol (PPTP) : used for 6- Data Link layer connecting to virtual private networks Session Control Protocol 7- Physical layer (SCP) : to provide a  Session layer 1- Application Layer Common Protocols: 2- Presentation layer Session Description Protocol (SDP): used for creating, modifying, and 3- Session layer terminating sessions such as Internet multimedia Session Announcement 4- Transport layer Protocol (SAP): is used for multicast data session broadcasts and participant 5- Network layer communication requirements. Password Authentication Protocol (PAP):PAP is used 6- Data Link layer by PPP (point to point protocol) links to validate users. PAP authentication 7- Physical layer requires the calling device to enter the username and  Transport layer 1- Application Layer This is the layer responsible for end-to-end communication between the 2- Presentation layer two devices. Functions: 3- Session layer 1. Breaking Data up into chunks called segments before sending it to Network layer (and 4- Transport layer reassemble them again at the other side before sending to Session Layer). 5- Network layer 2.Flow control and error control for inter-network communications. 3.Performing error control on 6- Data Link layer the receiving end by ensuring that the data received is complete, and requesting a 7- Physical layer retransmission if it isn’t for  Transport layer 1- Application Common protocols: 1.Transmission Control Protocol (TCP). Layer CP is a connection-oriented protocol 2- Presentation 2.User Datagram Protocol (UDP). UDP layer is a connectionless protocol. 3.Datagram Congestion Control 3- Session layer Protocol (DCCP). DCCP is a minimal, general-purpose transport protocol that provides two main functions: (1) 4- Transport layer the establishment, maintenance and disassemble of an unreliable packet flow and (2) congestion 5- Network layer control of that packet flow. 4.RSVP Resource Reservation Protocol is a protocol used to reserve 6- Data Link layer network resources and enable running Internet applications to gain quality of service (QoS). 7- Physical layer Common Devices:  Network layer The network layer is 1- Application Layer responsible for facilitating data transfer between two 2- Presentation layer different networks. Functions: 3- Session layer 1. Breaks up (and Reassembling) segments from the 4- Transport layer transport layer into smaller units, called packets. 5- Network layer 2.Routing , that is fining the best physical path for the data to reach its destination. 6- Data Link layer 3. Creating logical paths ( known as virtual circuits, for transmitting 7- Physical layer data from node to node).  Network layer 1- Application Layer Common Protocols: 1. IP (IPv4 - IPv6): Internet 2- Presentation layer Protocol (IP) – a set of rules that dictate how data should be delivered over the public network 3- Session layer (Internet). 2.ICMP - IGMP : The Internet Control Message Protocol (ICMP) 4- Transport layer is a network layer protocol used by network devices to diagnose network 5- Network layer communication issues. ICMP is mainly used to determine whether or not data is reaching 6- Data Link layer its intended destination in a timely manner. 7- Physical layer  Network layer 1- Application Layer Common Protocols: 3. IPSec: IPsec (Internet Protocol 2- Presentation layer Security) is a framework that helps us to protect IP traffic on the network layer. 3- Session layer 4. IPX/SPX: Short for Internet Packet Exchange/Sequential Packet Exchange, IPX/SPX is a 4- Transport layer local area network communications protocol developed by Novell. It 5- Network layer exchanges information between network clients, applications, and network peripherals. 6- Data Link layer Common Devices Routers. 7- Physical layer Layers 3 Switches.  ***Data Link layer 1- Application Layer 2- Presentation layer The Data Link Layer 3- Session layer provides node-to-node data transfer (between two directly connected 4- Transport layer nodes in the same network). The data link consists of 5- Network layer two sublayers: the Media Access Control (MAC) sublayer and the Logical Link Control (LLC) 6- Data Link layer sublayer. The MAC sublayer controls device interaction. The LLC 7- Physical layer sublayer deals with  Data Link layer 1- Application Functions: Layer 1.Error correction. 2- Presentation 2.Error Detection. 3.Flow control. layer 4.Framing. 5. Media Access Control. 3- Session layer 6.Physical Addressing Common Protocols: Point To Point Protocol (PPP) : is 4- Transport layer used for basic data encapsulation and transmission across a 5- Network layer network High-Level Data Link Control (HDLC): is a bit oriented protocol 6- Data Link layer that supports both half-duplex and full-duplex communication over point to point & multipoint 7- Physical layer link. ARP : Address Resolution  Data Link layer 1- Application Layer 2- Presentation layer 3- Session layer 4- Transport layer 5- Network layer Devices operate at this layer are: Layer 6- Data Link layer switches (switching 2 hubs) bridges. 7- Physical layer Modems.  Physical layer 1- Application Layer Physical layer is 2- Presentation layer responsible for represent the electrical and 3- Session layer physical representation of the system. This can include everything from the 4- Transport layer cable type, radio frequency link (as in an 802.11 wireless systems), as well as the 5- Network layer layout of pins, voltages and other physical requirements. When a networking problem 6- Data Link layer occurs, many networking pros go right to the physical layer to check that all of the 7- Physical layer cables are properly  Physical layer 1- Application Layer Functions: 2- Presentation 1. Signaling. 2. Timing. layer 3. Cables connection checking. 3- Session layer Devices operate at this 4- Transport layer layer are: Cables. Repeaters. 5- Network layer NIC. Protocols: 6- Data Link layer Ethernet Protocol 7- Physical layer The following figure summarize the main functions, elementary data unit names, and devices of OSI reference model. OSI reference Model TCP/IP reference Model Mapping OSI to TCP/IP reference models  TCP/IP reference Model Application Layer of TCP/IP protocol suite is concerned mainly with human interaction and the implementation of Application Layer software applications and related protocols. It combines the functionalities of the session layer, the Transport Layer presentation layer and the application layer of the OSI model Functions: Internet Layer 1. It helps users to use the services of the network. 2. It is used to develop network-based applications. Link Layer 3. It provides user services like user login, naming network devices, formatting TCP/IP reference Model Protocols: 1. Hypertext Transfer Protocol (HTTP) Application Layer 2. Simple Mail Transfer Protocol (SMTP) 3. Dynamic Host Configuration Protocol Transport Layer (DHCP) 4. Domain Name System (DNS) 5. Simple Network Management Protocol Internet Layer (SNMP) 6. File Transfer Protocol (FTP), uses TCP 7. Trivial File Transfer Link Layer Protocol (TFTP) , uses UDP. Common Devices  TCP/IP reference Model The transport layer is responsible for error-free, end- to-end delivery of data from the source host to the Application Layer destination host. It corresponds to the transport layer of the OSI model. Transport Layer The functions of the transport layer are Functions: 1. It facilitates the Internet Layer communicating hosts to carry on a conversation. 2. It provides an interface for the users to the underlying network. Link Layer 3. It can provide for a reliable connection. It can also carry out error checking, flow control, TCP/IP reference Model Protocols: 1. Transmission Control Protocol, TCP − It is a reliable connection- Application Layer oriented protocol that transmits data from the source to the destination Transport Layer machine without any error. 2. User Datagram Protocol, UDP − It is a message- oriented protocol that provides a simple Internet Layer unreliable, connectionless, unacknowledged service. 3. Stream Control Transmission Protocol, SCTP − It combines the Link Layer features of both TCP and UDP. It is message oriented like the UDP, which providing the  TCP/IP reference Model The Internet layer is responsible for logical transmission of data packets over the internet. Application Layer It can be compared to the network layer of the OSI model. Transport Layer The functions of the transport layer are : Functions: 1. It transmits data packets Internet Layer to the link layer. 2. It routes each of the data packets independently from the source to the Link Layer destination, using the optimal route. 3. It reassembles the out- of-order packets when TCP/IP reference Model Protocols: 1. Internet Protocol, IP − It is a connectionless and Application Layer unreliable protocol that provides a best effort delivery service. It transports data packets Transport Layer called datagrams that travel over different routes across multiple nodes. 2. Address Resolution Protocol, ARP −This Internet Layer protocol maps the logical address or the Internet address of a host to its physical address, as printed in the network Link Layer interface card. 3. Reverse Address Resolution Protocol, RARP − This is to find the TCP/IP reference Model Application Layer Protocols: Transport Layer 4. Internet Control Message Protocol, ICMP − It monitors sending the queries as well as the error Internet Layer messages. 5. Internet Group Message Protocol, IGMP −It allows the transmission of a message to a group of Link Layer recipients simultaneously. Common Devices Routers Brouters  TCP/IP reference Model The link layer (Sometimes referred to as Network access Application Layer layer) is the lowest layer of the TCP/IP model and is concerned with the physical transmission of data. It is also called a network Transport Layer interface layer or link layer. It can be considered as the combination of physical layer and data link layer of the OSI model. Internet Layer The functions of the transport layer are Functions: 1. It defines how bits are to be encoded into optical or Link Layer electrical pulses. 2. It accepts IP packets from the network layer and encapsulates them into  TCP/IP reference Model Functions: 4. It states the transmission mode, i.e. Application Layer simplex, half duplex or full duplex 5. It states the topology of the network, i.e. bus, Transport Layer star, ring etc. Common Protocol Ethernet Internet Layer Frame Relay DSL ATM SONET Link Layer Common Devices 1. Hubs 2. Repeaters 3. NICs  ‫‪The TCP/IP Reference Model‬‬ ‫هام جدا‪ :‬المطلوب معرفة ما تشير اليه االختصارات‬ ‫‪.‬وفائدة كل بروتوكول وفي أي طبقة يكون‬ Computer Networks Transmission Media  Transmission Media Wirele Wired ss Microwav Radio Light Infrared Twisted Pair Coaxial Fiber e Serial Transmiss Transmiss Transmiss Cable Cable Optics Transmiss ion ion ion ion TRANSMISSION MEDIA When we decide to select a specific transmission media, we have to consider the following criteria: 1.Cost of installation of transmission medium 2.Connectivity 3.Topology constraints 4.Distance coverage 5.Environmental constraints Magnetic Media is the simplest and most trivial transmission media. It is used as saving the data on external storage and the employer moves from one location to another with the data. It may be has huge bandwidth but has low speed.  Twisted Pair Cable A twisted pair cable is made of two plastic insulated copper wires twisted together to form a single media. Out of these two wires, only one carries actual signal and another is used for ground reference. The twists between wires are helpful in reducing noise (electro-magnetic interference) and crosstalk.  Twisted Pair Cable There are two types of twisted pair cables: 1. Unshielded Twisted Pair (UTP) Cable: UTP or Unshielded Twisted Pair cable is used on Ethernet 10BaseT and can also be used with Token Ring. It uses the RJ line of connectors (RJ45, RJ11, etc.) The following summarizes the features of UTP cable: 1. Speed and throughput—10 to 1000 Mbps 2. Average cost per node—Least expensive 3. Media and connector size—Small 4. Maximum cable length—100 m (short)  Twisted Pair Cable Unshielded Twisted Pair (UTP) Cable  The following table shows different twisted pair categories and corresponding transfer.rate UTP Category Purpose Frequency Transfer Rate Category 1 Voice Only Category 2 Data 4 MHz 4 Mbps Category 3 Data 16 MHz 10 Mbps Category 4 Data 20 Mbps 16 Mbps Category 5 Data 100 MHz 100 Mbps Category 5e Data 100 MHz 1 Gbps Category 6 Data 250 MHz Upto 10 Gbps Category 6a Data 500 MHz Upto 10 Gbps Category 7 Data 600 MHz Upto 10 Gbps Category 7a Data 1 GHz (1000 MHz) 40 to 100 Gbps Category 8 Data 2 GHz (2000 MHz) 25 to 40 Gbps  Twisted Pair Cable 2. Shielded Twisted Pair (STP) Cable : STP or Shielded Twisted Pair consists of 4 pairs of wires. Each pair of wires is wrapped in a metallic foil. The four pairs of wires then are wrapped in an overall metallic braid or foil and is used with the traditional Token Ring cabling or ICS - IBM Cabling System. It requires a custom connector. IBM STP (Shielded Twisted Pair) has a characteristic impedance of 150 ohms. The following summarizes the features of STP cable: 1. Speed and throughput—10 to 100 Mbps 2. Average cost per node—Moderately expensive 3. Media and connector size—Medium to large 4. Maximum cable length—100 m (short)  Coaxial Cable Coaxial cable has two wires of copper. The core wire lies in the center and it is made of solid conductor. The core is enclosed in an insulating sheath. The second wire is wrapped around over the sheath and that too in turn encased by insulator sheath. This all is covered by plastic cover. The coaxial cable represents a more historic form of transmission medium that may today be limited in usage within the enterprise network. As a transmission medium, the coaxial cable comprises generally of two standards, the 10Base2 and 10Base5 forms, that are known as Thinnet or Thinwire, and Thicknet or Thickwire respectively.  Coaxial Cable Standar Cables Maximum Transmission Distance Connectors d Thin 10Base2 185m BNC coaxial Thick 10Base5 500m Type N coaxial Copper coaxial cabling commonly used to support users as part of a shared network  Optical fiber Cabling Fiber Optic works on the properties of light. When light ray hits at critical angle, it tends to refracts at 90 degree. This property has been used in fiber optic. The core of fiber optic cable is made of high quality glass or plastic. From one end of it light is emitted, it travels through it and at the other end light detector detects light stream and converts it to electric data. Fiber Optic provides the highest mode of speed. It comes in two modes: Single mode fiber and second is multimode fiber. 1. Single mode fiber can carry a single ray of light. Single mode fiber has higher speeds and reach long distances. 2. Mltimode is capable of carrying multiple beams of light. Mltimode reduces the risk of signal interference from dust  Optical Fiber Cabling Fiber Optic can be generated using LED ( Light-Emitting Diodes) or SEMICODUCTOR LASER. The difference between them is shown below  Serial Cable Serial Cables support reliable transmission between devices (router to pc, for example), during which time many evolutions of the standard have taken place. The serial connection is designed to support the transmission of data as a serial stream of bits. The common standard implemented is referred to as (Recommended Standard) RS-232 but it is limited somewhat by both distance and speed Other serial standards have the capability to achieve much greater transmission ranges, such as is the case with the RS-422 and RS-485 standards that span distances of up to 4900ft (1200 meters). StandardS Speed RS-232 Standards define up to 20000bps, but can reach 1Mbit/s RS-422 100Kbit/s ~ 10Mbit/s+  Wireless communication In wireless communications, wireless signals are spread over in the air and are received and interpreted by appropriate antennas. When an antenna is attached to electrical circuit of a computer or wireless device, it converts the digital data into wireless signals and spread all over within its frequency range. The receptor on the other end receives these signals and converts them back to digital data. A little part of electromagnetic spectrum can be used for wireless transmission.  Radio Transmission 1. Radio frequency is easier to generate, 2. Because of its large wavelength it can penetrate through walls and structures alike. 3. Radio waves can have wavelength from 1mm – 100,000km and have frequency ranging from 3Hz (Extremely Low Frequency) to 300 GHz (Extremely High Frequency). 4. Radio waves at lower frequencies can travel through walls whereas higher RF can travel in straight line and bounce back. 5. The power of low frequency waves decreases sharply as they cover long distance. High frequency radio waves have more power. 6. Lower frequencies such as VLF, LF, MF bands can travel on the ground up to 1000 kilometers, over the earth’s surface. ok  Radio Transmission 6. Radio waves of high frequencies are prone to be absorbed by rain and other obstacles. They use ionosphere of earth atmosphere. High frequency radio waves such as HF and VHF bands are spread upwards. When they reach Ionosphere, they are refracted back to the earth. Some of the areas of applications of radio waves 1. Broadcasting and multicasting. 2. Fixed and mobile radio communications. 3. AM and FM radio. 4. Television. 5. Marine communication. 6. Wireless computer networks. 7. Cordless phones. 8. Bluetooth, UWB, Wi-Fi, and WiMAX communications technologies use broadcast radio signals.  Microwave Transmission 1. Electromagnetic waves above 100MHz. 2. Travel in a straight line. 3. Sender and receiver must be aligned to be strictly in line-of-sight. 4. Microwaves have higher frequencies and do not penetrate wall like obstacles. 5. Microwave transmission depends highly upon the weather conditions and the frequency it is using. 6. Microwaves are widely used for point-to- point communications because their small wavelength allows conveniently- sized antennas to direct them in narrow beams. 7. Frequency ranging from 300MHz to 300GHz Microwave Transmission Satellite Microwave Used for long distances Terrestrial Microwave  Microwave Transmission Applications 1. Long distance telephone communication. 2. Cellular phones. 3. Television networks. 4. Satellites. 5. Wireless LANs.  Infrared Transmission 1. Electromagnetic waves above 100MHz. 2. Travel in a often straight line. 3. Sender and receiver must be often aligned to be strictly in line-of-sight. 4. Infrared wave is used for very short range communication purposes such as television and its remote control device. 5. Because of high frequency range, Infrared cannot cross wall-like obstacles.  Infrared waves applications in 1. communications Remote controls for television, stereos and other home appliances. 2. Wireless LANs. 3. Some mobile computers and devices, such as a mouse, printer, and smart phone, often have an IrDA (Infrared Data Association) port that enables the transfer of data from one device to another using infrared light waves. 4. Wireless modem, keyboard, mouse, printer etc. 5. Fire detectors. 6. Night vision systems. 7. Intrusion detection systems. 8. Motion detectors.  Visible Light Transmission 1. This is achieved by means of LASER. 2. Because laser transmission is unidirectional, at both ends of communication the laser and the photo-detector needs to be installed. 3. Travel in a often straight line. 4. Laser works as Tx (transmitter) and photo-detectors works as Rx (receiver). 5. Lasers cannot penetrate obstacles such as walls, rain, and thick fog. 6. Additionally, laser beam is distorted by wind, atmosphere temperature, or variation in temperature in the path. Visible Light Transmission  Visible Light applications in communications Potential applications of Visible Light Communications VLC include 1. Li-Fi ( light fidelity) light based Wi-Fi (wireless fidelity of speed from can reach to 300-450 Mbps) uses visible light for communication to provide high speed internet up to 10G bps Wireless LANs. 2. Used in vehicular communication for lane change warning, pre-crash sensing and traffic signal violation warning to avoid accidents. 3. Used in areas that are sensitive to electromagnetic waves, such as aircrafts and hospitals where the radio signals interfere with the waves of other machines.