Chapter 1 Introduction A note on the use

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Chapter 1 Introduction A note on the use of these ppt slides: We’re making

Chapter 1 Introduction A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in Power. Point form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: v If you use these slides (e. g. , in a class) that you mention their source (after all, we’d like people to use our book!) v If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR All material copyright 1996 -2012 J. F Kurose and K. W. Ross, All Rights Reserved Computer Networking: A Top Down Approach 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 Modified By: Kazi Saeed Alam, Lecturer, CSE, KUET Introduction 1 -1

Computer Networks q q A computer network, often simply referred to as a network,

Computer Networks q q A computer network, often simply referred to as a network, is a collection of computers and devices connected in various ways in order to communicate and share resources. Usually, the connections between computers in a network are made using physical wires or cables Ø some connections are wireless, using radio waves or infrared signals Introduction 1 -2

Computer Networks q The purpose of a network is to share resources. A resource

Computer Networks q The purpose of a network is to share resources. A resource may be: Ø A file, folder, printer, disk drive Ø Or just about anything else that exists on a computer. The computers can be geographically located anywhere. q Networking is the term that describes the processes involved in designing, implementing, upgrading, managing and otherwise working with networks and network technologies. q Introduction 1 -3

What’s the Internet: “nuts and bolts” view PC server v millions of connected wireless

What’s the Internet: “nuts and bolts” view PC server v millions of connected wireless laptop smartphone computing devices: § hosts = end systems § running network apps v communication wireless links wired links § fiber, copper, radio, satellite § transmission rate: bandwidth v Packet router mobile network switches: forward packets (chunks of data) § routers and switches global ISP home network regional ISP institutional network Introduction 1 -4

What’s the Internet: “nuts and bolts” view v Internet: “network of networks” mobile network

What’s the Internet: “nuts and bolts” view v Internet: “network of networks” mobile network § Interconnected ISPs v protocols control sending, receiving of msgs § e. g. , TCP, IP, HTTP, Skype, 802. 11 v global ISP home network Internet standards regional ISP § RFC: Request for comments § IETF: Internet Engineering Task Force institutional network Introduction 1 -5

What’s the Internet: a service view v Infrastructure that provides services to applications: §

What’s the Internet: a service view v Infrastructure that provides services to applications: § Web, Vo. IP, email, games, e-commerce, social nets, … v mobile network global ISP home network regional ISP provides programming interface to apps § hooks that allow sending and receiving app programs to “connect” to Internet § provides service options, analogous to postal institutional network Introduction 1 -6

Internet vs WWW • Is the World Wide Web and the Internet the same

Internet vs WWW • Is the World Wide Web and the Internet the same thing? No. • The Internet is an interconnected network of thousands of networks and millions of computers which provides approximately 2. 56 billion people around the world with services such as e-mail, apps, newsgroups, shopping, research, instant messaging, music, videos, and news. • The World Wide Web, or Web for short, is one of the Internet’s most popular services providing access to billions of Web pages that contain text, multimedia content, services, and hyperlinks to Introduction 1 -7

What’s a protocol? human protocols: v v v “what’s the time? ” “I have

What’s a protocol? human protocols: v v v “what’s the time? ” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: v v machines rather than humans all communication activity in Internet governed by protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction 1 -8

What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection

What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http: //www. awl. com/kurose-ross 2: 00 <file> time Q: other human protocols? Introduction 1 -9

A closer look at network structure: v network edge: § § hosts: clients and

A closer look at network structure: v network edge: § § hosts: clients and servers often in data centers v access networks, physical media: wired, wireless communication links v network core: § interconnected routers § network of networks mobile network global ISP home network regional ISP institutional network Introduction 1 -10

Access networks and physical media Q: How to connect end systems to edge router?

Access networks and physical media Q: How to connect end systems to edge router? v v v residential access nets institutional access networks (school, company) mobile access networks keep in mind: v v bandwidth (bits per second) of access network? shared or dedicated? Introduction 1 -11

Access net: digital subscriber line (DSL) central office DSL splitter modem voice, data transmitted

Access net: digital subscriber line (DSL) central office DSL splitter modem voice, data transmitted at different frequencies over dedicated line to central office v v v telephone network DSLAM ISP DSL access multiplexer use existing telephone line to central office DSLAM § data over DSL phone line goes to Internet § voice over DSL phone line goes to telephone net < 2. 5 Mbps upstream transmission rate (typically < 1 Mbps) < 24 Mbps downstream transmission rate (typically < 10 Mbps) Introduction 1 -12

Access net: cable network cable headend … cable splitter modem V I D E

Access net: cable network cable headend … cable splitter modem V I D E O V I D E O D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 Channels frequency division multiplexing: different channels transmitted in different frequency bands Introduction 1 -13

Access net: cable network cable headend … cable splitter modem data, TV transmitted at

Access net: cable network cable headend … cable splitter modem data, TV transmitted at different frequencies over shared cable distribution network v v CMTS cable modem termination system ISP HFC: hybrid fiber coax § asymmetric: up to 30 Mbps downstream transmission rate, 2 Mbps upstream transmission rate network of cable, fiber attaches homes to ISP router § homes share access network to cable headend § unlike DSL, which has dedicated access to central Introduction 1 -14 office

Access net: home network wireless devices to/from headend or central office often combined in

Access net: home network wireless devices to/from headend or central office often combined in single box cable or DSL modem wireless access point (54 Mbps) router, firewall, NAT wired Ethernet (100 Mbps) Introduction 1 -15

Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet switch v

Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet switch v v v institutional mail, web servers typically used in companies, universities, etc 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps transmission rates today, end systems typically connect into Ethernet switch Introduction 1 -16

Wireless access networks v shared wireless access network connects end system to router §

Wireless access networks v shared wireless access network connects end system to router § via base station aka “access point” wireless LANs: § within building (100 ft) § 802. 11 b/g (Wi. Fi): 11, 54 Mbps transmission rate wide-area wireless access § provided by telco (cellular) operator, 10’s km § between 1 and 10 Mbps § 3 G, 4 G: LTE to Internet Introduction 1 -17

Types of Computer Networks n Networks are classified depending on the geographical area covered

Types of Computer Networks n Networks are classified depending on the geographical area covered by the network Computer Networks Local Campus Metropolitan Wide Area Network (LAN) (CAN) (MAN) (WAN) Introduction 18

Local Area Network (LAN) n n Covers a small area Connects computers and workstations

Local Area Network (LAN) n n Covers a small area Connects computers and workstations covering a local area like, office or home Introduction 2 -19

Local Area Network (LAN) n n Advantages of LAN: q Improves productivity due to

Local Area Network (LAN) n n Advantages of LAN: q Improves productivity due to faster work q Provides easy maintenance q New systems can be installed and configured easily Disadvantages of LAN: q Limited number of systems can only be connected q Cannot cover large area q Network performance degrades as number of users exceeds Introduction 2 -20

Personal Area Network (PAN) n n n One type of LAN, connecting devices close

Personal Area Network (PAN) n n n One type of LAN, connecting devices close to one person Covers few ranges (10 meters) Used for personal tasks Introduction 2 -21

Campus Area Network (CAN) n n Made up of multiple LANs within limited area

Campus Area Network (CAN) n n Made up of multiple LANs within limited area Connects different LANs in a campus or institution Introduction 2 -22

Metropolitan Area Network (MAN) v v v Interconnects networks within a city Supports data

Metropolitan Area Network (MAN) v v v Interconnects networks within a city Supports data and voice transmission Larger than LAN & PAN but smaller than WAN Introduction 2 -23

Wide Area Network (WAN) v Covers a wide geographical area which includes multiple computers

Wide Area Network (WAN) v Covers a wide geographical area which includes multiple computers or LANs e. g. Internet Introduction 2 -24

Comparison of Networks LAN CAN MAN WAN Connects computers and workstations in office or

Comparison of Networks LAN CAN MAN WAN Connects computers and workstations in office or home. Connects two or more LANs within a campus. Interconnects Connects networks in a town or geographically a city. separated LANs. Covers a local area of Covers privately 1 Km. owned campus with an area of 5 to 10 Kms. Covers larger area Spans large than LAN but smaller geographical area than WAN with more than 100 Kms. an area of 2 to 100 Kms. Data Transmission Rate – 10/100 Mbps Data Transmission Rate – Variable Data Transmission Rate - Variable Data Transmission Rate – 64 Kbps or 2 Mbps Uses IEEE 802 standard. Low cost ____ Uses IEEE 802 standard. High cost (Repetitive) Uses ITU standard. High cost (Repetitive) Introduction 2 -25

Virtual Private Network (VPN) v A virtual private network (VPN) is a computer network

Virtual Private Network (VPN) v A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e. g. , the Internet) instead of by physical wires. Introduction 2 -26

Network Topology v v The network topology defines the way in which computers, printers,

Network Topology v v The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions. Introduction 2 -27

Star Topology v v v A star topology is established with a central connection

Star Topology v v v A star topology is established with a central connection point. Other Network devices are connected to this central point. The main benefit of a star network is that failure in any star network cable will only take down one computer’s network access but not the entire LAN. However, if the central node fails, the entire network will be down in a star network. Moreover, lots of wired connection is needed. Introduction 2 -28

Bus Topology v v v A common backbone wire is connected to all network

Bus Topology v v v A common backbone wire is connected to all network devices. It joins networks and central devices. If any network device wants to communicate with another network device, the device sends a broadcast message. All other devices will see the broadcast message but only the desired recipient will accepts and process the message. Required less wire but failure of the backbone cable will damage the whole network. Introduction 2 -29

Tree Topology v v A central ‘root’ node (top level of the hierarchy) is

Tree Topology v v A central ‘root’ node (top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy with a point-to-point physical link. Multiple star or bus network can be connected with a tree network. Introduction 2 -30

Mesh Topology v v v Every network device is connected to every other network

Mesh Topology v v v Every network device is connected to every other network device with a point-topoint connection. Can be Fully mesh or Partially mesh. Most expensive and difficult to maintain. Introduction 2 -31

Ring Topology v v Every network device is connected to two neighbor devices with

Ring Topology v v Every network device is connected to two neighbor devices with a point-to-point connection. All devices make a loop. If any cable or device is fail, the loop will break and also break down the entire ring network. Introduction 2 -32

Network Devices v v Network devices are components used to connect computers or other

Network Devices v v Network devices are components used to connect computers or other electronic devices together so that they can share resources. Devices used to set up Local Area Network(LAN) are the most common type of network devices. A LAN requires hub, switch, router…. Networking devices are also called Communicating devices. Introduction 2 -33

Network Devices q q q q NIC [Network Interface Card] Repeater Modem Bridge Hub

Network Devices q q q q NIC [Network Interface Card] Repeater Modem Bridge Hub Switch Router Introduction 2 -34

Network Interface Card[NIC] v v NIC provides the physical interface between computer and cabling.

Network Interface Card[NIC] v v NIC provides the physical interface between computer and cabling. It Prepares data, sends data and controls the flow of data. It can also receive and translate data into bytes for the CPU to understand. It has specific MAC address. It functions as a middleman between your computer and the data network by translating the computer data into electrical signals. Introduction 2 -35

Repeater v v A repeater (or regenerator) is an electronic device that operates on

Repeater v v A repeater (or regenerator) is an electronic device that operates on only the physical layer of the OSI model. A repeater installed on a link receives the signal before it becomes too weak or corrupted, regenerates the original pattern, and puts the refreshed copy back on the link. Introduction 2 -36

Repeater v v A repeater does not actually connect two LANS; it connects two

Repeater v v A repeater does not actually connect two LANS; it connects two segments of the same LAN. A repeater forwards every frame; it has no filtering capability Introduction 2 -37

Modem v v The word modem comes from “modulator-demodulator”. Modulation: digital information to analog

Modem v v The word modem comes from “modulator-demodulator”. Modulation: digital information to analog signals. Demodulation: analog signals back to useful digital information. An ISP(Internet Service Provider) is required to complete the connection to internet. Introduction 2 -38

Hubs v Hub is the most basic networking device that connects multiple computers or

Hubs v Hub is the most basic networking device that connects multiple computers or other network devices together. Unlike a network switch or router, a network hub has no routing tables or intelligence on where to send information and broadcasts all network data across each connection. Introduction 2 -39

Switch v v v A switch is a network device that connects network segments.

Switch v v v A switch is a network device that connects network segments. Populates MAC address table on the basis of source MAC address of the frame. Network switches are capable of inspecting data frames as they are received determining the source and destination device of that frame, and forwarding it appropriately. Data link layer or Layer 2 device. A vital difference between a hub and a switch is that all the nodes connected to a hub share the same bandwidth among themselves, while a device connected to a switch port has the full bandwidth to itself. Introduction 2 -40

Switch v v For example, if 10 nodes are communicating using a hub on

Switch v v For example, if 10 nodes are communicating using a hub on a 10 Mbps network, then each node may only get a portion of the 10 Mbps if other nodes on the hub want to communicate as well. But with a switch, each node could possibly communicate at the full 10 Mbps Introduction 2 -41

Bridges v v Bridges operate in both the physical and the data link layers

Bridges v v Bridges operate in both the physical and the data link layers of the OSI model. Bridges can divide a large network into smaller segments. They contain logic that allows them to keep the traffic on each segment separate. When a frame (or packet) enters a bridge, the bridge not only regenerates the signal but checks the destination address and forwards the new copy only to the segment the address belong. Introduction 2 -42

Bridges v v v A bridge operates in both the physical and the data

Bridges v v v A bridge operates in both the physical and the data link layers. As a physical layer device, it regenerates the signal it receives. As a data link layer device, the bridge can check the physical (MAC) address (source and destination) contained in the frame. A bridge has filtering capability. It can check the destination address of a frame and decide if the frame should be forwarded or dropped. If the frame is to be forwarded, the decision must specify the port. A bridge does not change the physical (MAC) addresses in a Introduction 2 -43 frame.

Routers v v v Routers are highly intelligent devices that have access to network

Routers v v v Routers are highly intelligent devices that have access to network layer addresses and contain software that enables them to determine which of several possible paths between those addresses is the best for a particular transmission. Routers operate in the physical, data link, and network layers of the OSI model. Router connects networks whereas bridges connect network segments. Introduction 2 -44

Routers v v Routers relay packets among multiple interconnected networks. They route packets from

Routers v v Routers relay packets among multiple interconnected networks. They route packets from one network to any of a number of potential destination networks on an internet. However, they are slower than bridges because they are more intelligent devices. They analyze every packets causing packet -forwarding delays. They are also expensive. Introduction 2 -45

Gateways v v Gateways potentially operate in all seven layers of the OSI model.

Gateways v v Gateways potentially operate in all seven layers of the OSI model. A gateway is a protocol converter. A router by itself transfers, accepts, and relays packets only across networks using similar protocols. A gateway can accept a packet formatted for one protocol (e. g. Apple. Talk) and convert it to a packet for another protocol (e. g. TCP/IP). A gateway is generally software installed within a router. The gateway understands the protocols used by each network linked into the router and is therefore able to translate from one to another. Introduction 2 -46

Networking Media v Networking media can be defined simply as the means by which

Networking Media v Networking media can be defined simply as the means by which signals (data) are sent from one computer to another (either by cable or wireless means). Introduction 2 -47

Communication Architecture v Strategy for connecting host computers and other communicating equipment. v Defines

Communication Architecture v Strategy for connecting host computers and other communicating equipment. v Defines necessary elements for data communication between devices. v A communication architecture, therefore, defines a standard for the communicating hosts. v A programmer formats data in a manner defined by the communication architecture and passes it on to the communication software. v Separating communication functions adds flexibility, for example, we do not need to modify the entire host software to include more communication devices. v Layer architecture simplifies the network design. § It is easy to debug network applications in a layered architecture network. Introduction 2 -48

Layer Architecture Layer architecture simplifies the network design. It is easy to debug network

Layer Architecture Layer architecture simplifies the network design. It is easy to debug network applications in a layered architecture network. The network management is easier due to the layered architecture. Computer Network layers follow a set of rules, called protocol. The protocol defines the format of the data being exchanged, and the control and timing for the handshake between layers. Introduction 2 -49

OSI Reference Model The OSI model is now considered the primary Architectural model for

OSI Reference Model The OSI model is now considered the primary Architectural model for inter-computer communications. It describes how information or data makes its way from application programmes (such as spreadsheets) through a network medium (such as wire) to another application programme located on another network. The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems. This separation into smaller more manageable functions is known as layering. Introduction 2 -50

OSI Reference Model The process of breaking up the functions or tasks of networking

OSI Reference Model The process of breaking up the functions or tasks of networking into layers reduces complexity. Each layer provides a service to the layer above it in the protocol specification. Each layer communicates with the same layer’s software or hardware on other computers. The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end through the network. The upper 3 layers of the OSI model (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services to the applications. Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit. Introduction 2 -51

OSI Model v v 1. 2. 3. Open System Interconnection Model is description for

OSI Model v v 1. 2. 3. Open System Interconnection Model is description for layered communications and computer network protocol design 7 Layers Physical Layer - defines the relationship between a device and a physical medium. This includes layout of pins, voltages, cable specifications, and more Data Link Layer - provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors Network Layer – determine logical path for transferring data sequences from a source to a destination via one or more networks Introduction 2 -52

OSI Model 4. 5. 6. 7. Transport Layer - The Transport Layer controls the

OSI Model 4. 5. 6. 7. Transport Layer - The Transport Layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control Session Layer - controls the connections between computers. It establishes, manages and terminates the connections between the local and remote application Presentation Layer - provides independence from differences in data representation (e. g. , encryption) by translating from application to network format, and vice versa Application Layer - interacts with software applications that implement a communicating component Introduction 2 -53

OSI Reference Model: 7 Layers Introduction 2 -54

OSI Reference Model: 7 Layers Introduction 2 -54

Physical Layer Provides physical interface for transmission of information. Defines rules by which bits

Physical Layer Provides physical interface for transmission of information. Defines rules by which bits are passed from one system to another on a physical communication medium. Covers all - mechanical, electrical, functional and procedural - aspects for physical communication. Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications. Introduction 2 -55

Data Link Layer Data link layer attempts to provide reliable communication over the physical

Data Link Layer Data link layer attempts to provide reliable communication over the physical layer interface. Breaks the outgoing data into frames and reassemble the received frames. Create and detect frame boundaries. Handle errors by implementing an acknowledgement and retransmission scheme. Implement flow control. Supports points-to-point as well as broadcast communication. Supports simplex, half-duplex or full-duplex communication. Introduction 2 -56

Network Layer Implements routing of packets through the network. Defines the most optimum path

Network Layer Implements routing of packets through the network. Defines the most optimum path the packet should take from the source to the destination Defines logical addressing so that any endpoint can be identified. Handles congestion in the network. Facilitates interconnection between heterogeneous networks (Internetworking). The network layer also defines how to fragment a packet into smaller packets to accommodate different media. Introduction 2 -57

Transport Layer Purpose of this layer is to provide a reliable mechanism for the

Transport Layer Purpose of this layer is to provide a reliable mechanism for the exchange of data between two processes in different computers. Ensures End to End reliable communication - that the data units are delivered error free. delivered in sequence. no loss or duplication Provides connectionless or connection oriented service. Provides for the connection management. Multiplex multiple connection over a single channel. Introduction 2 -58

Session Layer provides mechanism for controlling the dialogue between the two end systems. It

Session Layer provides mechanism for controlling the dialogue between the two end systems. It defines how to start, control and end conversations (called sessions) between applications. This layer requests for a logical connection to be established on an end-user’s request. Any necessary log-on or password validation is also handled by this layer. Session layer is also responsible for terminating the connection. This layer provides services like dialogue discipline which can be full duplex or half duplex. Session layer can also provide check-pointing mechanism such that if a failure of some sort occurs between checkpoints, all data can be retransmitted from the last checkpoint. Introduction 2 -59

Presentation Layer Presentation layer defines the format in which the data is to be

Presentation Layer Presentation layer defines the format in which the data is to be exchanged between the two communicating entities. Also handles data compression and data encryption (cryptography). Introduction 2 -60

Application Layer Application layer interacts with application programs and is the highest level of

Application Layer Application layer interacts with application programs and is the highest level of OSI model. Application layer contains management functions to support distributed applications. Examples of application layer are applications such as file transfer, electronic mail, remote login etc. Introduction 2 -61

OSI in Action A message begins at the top application layer and moves down

OSI in Action A message begins at the top application layer and moves down the OSI layers to the bottom physical layer. As the message descends, each successive OSI model layer adds a header to it. A header is layer-specific information that basically explains what functions the layer carried out. Conversely, at the receiving end, headers are striped from the message as it travels up the corresponding layers. Introduction 2 -62

TCP/IP v TCP stands for Transmission Control Protocol TCP software breaks messages into packets,

TCP/IP v TCP stands for Transmission Control Protocol TCP software breaks messages into packets, hands them off to the IP software for delivery, and then orders and reassembles the packets at their destination v IP stands for Internet Protocol IP software deals with the routing of packets through the maze of interconnected networks to their final destination Introduction 2 -63

Networking Protocol: TCP/IP Introduction 2 -64

Networking Protocol: TCP/IP Introduction 2 -64

OSI & TCP/IP Models Introduction 2 -65

OSI & TCP/IP Models Introduction 2 -65

TCP/IP Model Application Layer Application programs using the network Transport Layer (TCP/UDP) Management of

TCP/IP Model Application Layer Application programs using the network Transport Layer (TCP/UDP) Management of end-to-end message transmission, error detection and error correction Network Layer (IP) Handling of datagrams : routing and congestion Data Link Layer Management of cost effective and reliable data delivery, access to physical networks Physical Layer Physical Media Introduction 2 -66

End of Chapter 1 Introduction 2 -67

End of Chapter 1 Introduction 2 -67