Chapter_1 Introduction.pdf

Data Communications and Computer Networks 371CCS 1.1  Chapter 1 Part -1 Fundamental concepts of computer networks. 1.2 Topics discussed in this :section Components Data Representation Data Flow Components Figure 1.1 Five compo...

Data Communications and Computer Networks 371CCS 1.1  Chapter 1 Part -1 Fundamental concepts of computer networks. 1.2 Topics discussed in this :section Components Data Representation Data Flow Components Figure 1.1 Five components of data communication 5 1 2 3 4 1.3 Data Representation 1.1 1. Text 2. Number s 3. Images 4. Audio 5. Video Data flow  Simplex  Half-duplex  Full-duplex 1.4  NETWORKS1-2  A network is a set of devices (nodes) connected by communication links according to a particular topology.  A node can be a computer, printer, or any other end-device capable of sending and/or receiving data provided by other nodes in the network.  Physical Topologies: 1.5 Type of connections Point to point A dedicated link is provided between two devices Multipoint More than two specific devices share a single link 1.6  MESH Topology Every device has a dedicated point-to- point link to every other devices Dedicated Link carries traffic only between the two devices it connects A fully connected mesh network has n(n- 1)/2 physical channels to link n devices Every device on the network must have n-1 input/output (I/O) ports Advantage Less traffic, robust, secure, easy to maintain n(n-1)/2 physical duplex Disadvantage links Need more resource (cable and ports), expensive 1.7  STAR Topology Each device has a dedicated point-to-point link only to a central controller, usually called a hub. No direct traffic and link between devices Advantages Less expensive Easy to install and reconfigure Robustness Disadvantage Single point of failure 1.8  BUS Topology A multipoint topology All devices are linked through a backbone cable Nodes are connected to the bus cable by drop lines and taps. Drop line: A connection running between the device and the main cable Tap: A connector that splices into the main cable. Advantage: Ease of installation  Disadvantages: Difficult reconnection and fault isolation Broken or fault of the bus cable stops all transmission 1.9  RING Topology Each device is dedicated point-to-point connection only with the two devices on either side of it A signal is passed along the ring in the direction, from device to device, until it reaches its destination. Each device in the ring incorporates a repeater. Advantages Relatively easy to install and reconfigure Fault isolation is simplified Disadvantage Unidirectional traffic 1.10  Tree Topology Tree topologies integrate multiple topologies together Example: Tree topology integrates multiple star topologies together onto a bus Advantages: Point-to-point wiring for individual segments. Supported by several hardware and software venders. Disadvantages: Overall length of each segment is limited by the type of cabling used. If the backbone line breaks, 1.11 the entire segment goes down. Categories of Networks 1. Local Area Network (LAN) 2. Wireless Local Area Network (WLAN) 3. Metropolitan Area Network (MAN) 4. Wide Area Network (WAN) An isolated LAN connecting 12 computers to a hub in a closet 1.12 WANs: a switched WAN and a point-to-point WAN 1.13 Interconnection of Networks: internet A heterogeneous network made of four WANs and two LANs 1.14  PROTOCOLS AND STANDARDS1-3 Protocol: Set of rules for formatting and processing data. (synonymous with rules) Syntax → format of the data Semantics → meaning of each section Timing → when data should be sent and how fast. Standards are agreed-upon rules. Standards Organizations: International Standers Organization (ISO) International Telecommunication Union - Telecommunication Standards (ITU-T) American National Standards Institute (ANSI) Institute of Electrical and Electronics Engineers (IEEE) Electronic Industries Association (EIA) 1.15 Network ModelsOSI Model 1.16  LAYERED TASKS1-4 A network model is a layered architecture Task broken into subtasks Implemented separately in layers in stack Functions need in both systems Peer layers communicate 1.17  1-4.1 THE OSI MODEL The Open Systems Interconnection (OSI) model is the standard that covers all aspects of network communications from ISO. It was first introduced in the late 1970s. :Layered Architecture 1.18 Layered Architecture Each layer performs a subset of the required communication functions Each layer provides services to the next higher layer. Communication must move downward through the layers on the sending device and upward to the receiving device. Each layer in the sending device adds its own information to the message it receives from the layer just above it and passes the whole package to the layer just below it. At the receiving device, the message is unwrapped layer by layer, with each process receiving and removing the data meant for it. 1.19 The interaction between layers in the OSI model 1.20 Exchange Messages using the OSI model Encapsulation and unwrapping 1.21 Application Layer The application layer is responsible for providing services to the user. Functions Network virtual terminal (Remote log-in) File transfer and access Mail services Accessing the World Wide Web 1.22 Presentation Layer The presentation layer is responsible for translation, compression, and encryption.  Functions  Translation ( EBCDIC-coded text file  ASCII-coded file)  Encryption and Decryption  Compression 1.23 Session Layer The session layer is responsible for dialog control and synchronization.  Functions  Dialog control  Synchronization (checkpoints) 1.24 Transport Layer The transport layer is responsible for the delivery of a message from one process to another. (Reliable Process-to- process delivery( Functions Port addressing Flow control , Error control, and Connection control ( Connection- oriented or connection-less) Segmentation and reassembly 1.25 Network Layer The network layer is responsible for the delivery of individual packets from the original source host to the final destination host. ( Source-to-destination delivery( Functions Logical addressing. routing. 1.26 Network Layer Source-to-destination delivery. Example: We want to send data from a node with network address A and physical address 10, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only. What we need use are universal address (network address) that can pass through the LAN boundaries. 1.27 Data Link Layer The data link layer is responsible for moving frames from one hop (node) to the next. Functions Framing Physical addressing Flow control Error control Access control 1.28 Data Link Layer Node to node delivery in the same local LAN. Example : Anode with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. 1.29 Physical Layer The physical layer is responsible for movements of individual bits from one hop (node) to the next. Functions Representation of bits Data rate Synchronization of bits Physical topology (mesh, star, ring or bus) Transmission mode ( simplex, half-duplex or duplex) 1.30  Summary of layers OSI Model Data Layer Function unit User 7. Application Network process to application support Data 6. Presentation Data representation and encryption layers 5. Session Inter-host communication Sender Receiver User Segment 4. Transport End-to-end connections and reliability Networ k Path determination and logical Packet 3. Network Network addressing support Frame 2. Data Link Physical addressing layers Bit 1. Physical Media, signal and binary transmission 1.31 Network Models TCP/IP Model 1.32 TCP/IP PROTOCOL SUITE 1-4.2  The layers in the TCP/IP protocol suite do not exactly match those in the OSI model.  The original TCP/IP protocol suite was defined as having four layers: host- to-network, internet, transport, and application.  However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of four layers: link, network, transport, and application. 1.33  TCP/IP and OSI model TCP/IP Model OSI Model 1.34 Relationship of layers and addresses in TCP/IP 1.35  Addresses 1-5 Physical Address (MAC): known also as the MAC address. It is the address of a node as defined by its LAN. It is included in the frame used by data link layer. Physical addresses are imprinted on the NIC. Most local-area networks (Ethernet) use a 48-bit (6-byte) physical address written as 12 hexadecimal digits. Example: 07:01:02:01:2C: 4B A 6-byte (12 hexadecimal digits) physical address. 1.36 Addresses Logical Address (IP):  IP addresses are necessary for universal communications that are independent of physical network.  No two host address on the internet can have the same IP address  IP addresses in the Internet are 32-bit address that uniquely define a host. remain the same. 1.37  Addresses Port address: Port address is a 16-bit address represented by one decimal number ranged from (0-65535) to choose a process among multiple processes on the destination host.  Destination port number is needed for delivery.  Source port number is needed for receiving a reply as an acknowledgments. Example: 753 The physical addresses change from hop to hop, but the logical and port addresses usually remain the same. 1.38 Chapter 1 Part-2 Computer Networking: A Top Down Approach 7th edition Jim Kurose, Keith Ross Pearson/Addison Wesley April 2016 39-1 Chapter 1: roadmap 1.1 what is the Internet? 1.2 network edge  end systems, access networks, links 1.3 network core  packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 40-1 What’s the Internet: view PC  billions of connected mobile network server computing devices: wireless hosts = end global ISP laptop smartphone systems running network home apps  communication network regional ISP wireless links links Wber, copper, wired links radio, satellite transmission rate: bandwidth  packet switches: router forward packets institutional (chunks of data) network routers and switches 41-1 What’s the Internet: view mobile network  Internet: “network of networks” global ISP Interconnected ISPs  Protocols control sending, receiving of messages home e.g., TCP, IP, HTTP, Skype, network regional ISP 802.11  Internet standards RFC: Request for comments IETF: Internet Engineering Task Force institutional network 42-1 What’s the Internet: a service view mobile network  infrastructure that provides services to global ISP applications: Web, VoIP, email, home games, e-commerce, network regional ISP social nets, …  provides programming interface to apps hooks that allow sending and receiving app programs to institutional network “connect” to Internet provides service 43-1 options, analogous to postal service A closer look at network structure:  network edge: mobile network hosts: clients and servers global ISP servers often in data centers home  access networks, network regional ISP physical media: wired, wireless communication links  network core: interconnected routers institutional network of network networks 44-1 Access networks and physical media Q: How to connect end systems to edge router?  residential access nets  institutional access networks (school, company)  mobile access networks keep in mind:  bandwidth (bits per second) of access network?  shared or dedicated? 45-1 Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers  typically used in companies, universities, etc.  Users have 100 Mbps or 1Gbps access ,servers may have 1Gbps or 10Gbps transmission rates  today, end systems typically connect into Ethernet switch 46-1 Wireless access networks(WiFi)  shared wireless access network connects end system to router via base station - “access point” wireless LANs: wide-area wireless access  within building (100 ft.)  provided by telco (cellular)  802.11b/g/n (WiFi): 11, operator, 10’s km 54, 450 Mbps  between 1 and 10 Mbps transmission rate  3G, 4G: LTE to Internet to Internet 47-1 Internet structure: network of networks  End systems connect to Internet via access ISPs (Internet Service Providers) Can provide either wired or wireless connectivity, using DSL, Cable, WiW and Cellular residential, company and university ISPs  Access ISPs in turn must be interconnected. so that any two hosts can send packets to each other. 48-1 Internet structure: network of networks Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement.access … access net access net … net access access net net access access net net … … global access net ISP access net access net access net access net access … net access access … net access net net 49-1 Internet structure: network of networks But if one global ISP is viable business, there will be competitors …. access … access net access net … net access access net net access access net net ISP A … … access net ISP B access net access net ISP C access net access net access … net access access … net access net net 50-1 Internet structure: network of networks But if one global ISP is viable business, there will be competitors …. which must be interconnected Internet exchange point access access … access net net … net access access net net access IXP access net net ISP A … … access net IXP ISP B access net access net ISP C access net access net peering link access … net access access … net access net net 51-1 Internet structure: network of networks … and regional networks may arise to connect access nets to ISPs access … access net access net … net access access net net access IXP access net net ISP A … … access net IXP ISP B access net access net ISP C access net access net regional net access … net access access … net access net net 52-1 Internet structure: network of networks … and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users access … access net access net … net access access net net access IXP access net net ISP A … … Content provider network access net IXP ISP B access net access net ISP C access net access net regional net access … net access access … net access net net 53-1 Internet structure: network of networks Tier 1 ISP Tier 1 ISP Google IX IX IX P P P Regional ISP Regional ISP access access access access access access access access ISP ISP ISP ISP ISP ISP ISP ISP  at center: small # of well-connected large networks “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage content provider network (e.g., Google): private network that connects it data centers to Internet, often bypassing 54-1 tier-1, regional ISPs Host: sends packets of data host sending function:  takes application message two packets,  breaks into smaller L bits each chunks, known as packets, of length L bits 2 1  transmits packet into R: link transmission rate access network at host transmission rate R link transmission rate, aka link capacity, or link time needed to bandwidth packet L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) 55-1 Network Performance-Loss and Delay packets queue in router bufers  packet arrival rate to link (temporarily) exceeds output link capacity  packets queue, wait for turn packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers 56-1 Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal dqueue: queueing processing delay  When packet arrives at  time waiting at router A, router A output link for examines the packets transmission header and direct the  depends on packet to the outbound 57-1 link, and if link is busy congestion level of Four sources of packet delay transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dtrans: transmission dprop: propagation delay: delay:  Time required to propagate from  L: packet length (bits) the beginning of the link to dtrans and  R: link bandwidth dprop router B (bps)  s: propagation speed on the  dtrans = L/R very different physical medium of the link (2.108 m/sec to 3.108 m/sec)  dprop = d/s(Distance between 58-1 two router divided by Caravan analogy 100 km 100 km ten-car toll toll caravan booth booth  cars “propagate” at  time to “push” 100 km/hr entire caravan  toll booth takes 12 sec through toll booth to service car (bit onto highway = transmission time) 12*10 = 120 sec  car ~ bit; caravan ~  time for last car to packet propagate from 1st  Q: How long until to 2nd toll both: caravan is lined up 100km/(100km/hr) before 2nd toll booth? = 1 hr  A: 62 minutes 59-1 Packet loss  queue (aka bufer) preceding link in bufer has Wnite capacity  packet arriving to full queue dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not at all buffer (waiting area) packet being transmitted A B packet arriving to full buffer is lost 60-1  Throughput  throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at which host receives the Wles average: rate over longer period of time(F/T bits/sec) server, with server sends link capacity pipe that can carry link capacity pipe that can carry Wle ofbits F bits nuid at rate Rs bits/sec nuid at rate Rc bits/sec to(nuid) send into to client pipe Rs bits/sec) Rc bits/sec) 61-1 Throughput (more)  Rs < Rc The bits transmitted by the server will Oow through the router and arrive at the client Rs bits/sec Rc bits/sec  Rs > Rc Router will not be able to forward bits as quickly as it receives them. Rs bits/sec Rc bits/sec bottleneck link onlink end-end path that constrains end-end throughput 62-1 Internet protocol Layering  application: supporting network applications FTP, SMTP, HTTP application  transport: process-process data transfer transport TCP, UDP  network: routing of network datagrams from source to destination link IP, routing protocols  link: data transfer between physical neighboring network elements Ethernet, 802.111 (WiFi), PPP  physical: bits “on the wire” 63-1  message M source application Encapsulation segment Ht M transport datagram Hn Ht M network frame Hl Hn Ht M link physical link physical switch destination Hn Ht M network M application Hl Hn Ht M link Hn Ht M Ht M transport physical Hn Ht M network Hl Hn Ht M link router physical 64-1