What is a Network? CS 352 Internet Technology. What is Internet Technology? Why Networks?

Transcription

1 What is a? CS 352 Internet Technology Badri Nath Dept. of Computer Science Rutgers University Carrier of information between 2 or more entities Interconnection may be any medium capable of communicating information: copper wire Lasers (optic fibre) Microwave Cable (coax) satellite link Wireless link (cellular, , bluetooth) Examples: Ethernet, , cable modem Why s? Availability of Resources Resources become available regardless of the user s physical location Load Sharing Jobs processed on least crowded machine High Reliability Alternative source of supply (multiple copies) Human-to-Human Communication e.g., Telephone (Voice-over IP) What is Internet Technology? What is an internet? of networks What is the Internet? A global internet based on the IP protocol to network adopt a common language To what does Internet technology refer? Architecture, protocols and services

2 Sample Internet s Electronic mail, Instant messaging Remote terminal File transfer Chat groups File sharing Resource distribution World Wide Web, blog Streaming media, VOIP Video conferencing Games Impact of the Net on People Access to remote information HW assignments from my server Stock quotes from financial web site Corporate video, news clips, virtual tours Virtual tours of homes, tourist spots Person to person and group communication , collaborative tools (chat groups), blogs Interactive entertainment MTV online, Audio juke box, music (napster?), video clips Impact of the Net on Society The good Access to information (i-commerce), e- commerce, incredible productivity tool The bad gossip, too much information, chat room, net addicts The ugly Fraud, pornography, threatening But, it is just a mirror of society Internet Players Users, people who use the applications Everyone (mom and pop, kids) get something done (hopefully useful) Designers You: protocol design and implementation performance, cost and scale Service Providers Administrators and ISPs ( Management, revenue, deployment Market/business models for the Internet Consumer to consumer (ebay), Business to consumer (amazon, orbitz), Business to business (Freemarket, ARIBA), Consumer to business (hotjobs, monster), Govt to C, Govt to B etc PtoP : napster or peer to peer

3 Internet service providers (ISPs) Peering ISPs Have a mutual relationship about forwarding traffic of each others customers (no $ involved) Transit ISPs Provides access to all reachable customers ($$ involved) Tier3 local ISPs Tier2- regional ISPs Tier1 global ISPS (MCI, ATT) ISP1 Peering Peering Vs transit ISP1 Peering ISPs carry each others traffic Share resources Transit ISPS provide service to its customers. Involves money (global crossing, MCI. ATT) provider Transit Customer Components of an Internet Types of s in an Internet Links Communication links for transmission Host Computer running applications of end user Router Computer for routing packets from input line to another output line Gateway A router directly connected to two or more networks Firewall A ingress router that enforces policy on which packets to allow into the network Local area networks Privately owned, within building High speed, broadcast, Ethernet 2 to 100 Mbps Wide area networks Spans a large area Point-to-point, high speed fiber or trunk lines Long delays but very high speed links

4 Types of s (cont d) Historical perspective Wireless networks Hosts connected by infrared or radio links Local area and wide area Satellite networks Late 1960 s: ARPAnet (4 nodes) Early 1970 s: Aloha net, ethernet, multiple access problem Mid-to-late 1970 s: TCP/IP, 4.2BSD 1980 s to early 1990 s: early internet growth, & file transfer dominant, NSFNET Mid 1990s: NSFnet handed over to commercial service providers, WWW explodes Late 90s, business models using the internet; dot-com boom and bust Future: Embedded networks, 5 to 10 billion devices waiting to be networked, media convergence. RFID tags Internet Hosts Growth WWW Growth Log scale Source: 170 million web hosts-today 1-Jan-95 1-Jul-95 1-Jan-96 1-Jul-96 1-Jul-97 1-Jan-98 1-Jul-98 1-Jan-99 7/1/199 1-Jan-00 1-Jul-00 1-Jan-01 2-Jul-02 3-Jan-03 Hosts 46 million web sites-today Log scale WWW lsource: Jul-93 Jul-94 Jul-95 Jul-96 Jul-97 Jul-98 Jul-99 Jul-00 Jul-01 Jul-02 Jul-03 Jul-04

5 Rutgers Intranetwork Rutgers Internet Connections Camden CAC OC3 OC12 Cook/Douglass OC3 Busch OC12 OC3 Info provided by Michael Mundrane OC12 OC3=155Mbps OC12=622Mbps Livingston Newark EsNet T1 2 T1 BBN Planet network Busch OC3 Newark T3 AlterNet OC3 T1=1.544 mbps T3=44.7 mbps OC3= mbps vbns Course Goals Course Work Understand the basic principles of computer networks Understand the Internet and its protocols Understand the key design principles used to build the Internet Quizzes (5%) during recitations Programming Assignments + written homeworks (30%) Two Midterms (30%) Final (35%)

6 Honor code All work submitted must be your own Severe consequences for violating the above Please turn off cell phones in class Some Definitions : Collection of interconnected machines Host: Machine running user application Subnet: Subset of the network, responsible for carrying messages between hosts Channel: Logical line of communication Topology: configuration Router: Process packets and routes packets towards the destination Protocol: Rules of communication 1. How Do Computers Communicate? With 1 s and 0 s Computers only deal with 1 s and 0 s So do networks How do we transmit 1 s and 0 s in a network? Transmission See Tanenbaum Fig. 2-18, pp. 110

7 (1) Circuit Switching Switching Schemes (2) Message Switching (Store-and-Forward) Circuit Switching Provides service by setting up the total path of connected lines from the origin to the destination Example: Telephone network (3) Packet Switching (Store-and-Forward) Circuit Switching (cont d) 1. Control message sets up a path from origin to destination 2. Return signal informs source that data transmission may proceed 3. transmission begins 4. Entire path remains allocated to the transmission (whether used or not) 5. When transmission is complete, source releases the circuit Propagation Delay Time Transmission Time Circuit Switching (cont d) Call request signal Transmission Delay Call accept signal A B C D IMPs

8 Message Switching Message Switching (cont d) Each message is addressed to a destination When the entire message is received at a router, the next step in its journey is selected; if this selected channel is busy, the message waits in a queue until the channel becomes free Thus, the message hops from node to node through a network while allocating only one channel at a time Analogy: Postal service Time Header Msg Msg Queueing Delay Transmission Delay Msg A B C D IMPs Packet Switching Packet Switching (cont d) Messages are split into smaller pieces called packets These packets are numbered and addressed and sent through the network one at a time Pipelining Header Pkt 1 Pkt 2 Time Pkt 3 Pkt 1 Transmission Delay Pkt 2 Pkt 3 Pkt 1 Pkt 2 Pkt 3 A B C D IMPs

9 Comparisons (1) Header Overhead Circuit < Message < Packet (2) Transmission Delay Short Bursty Messages: Packet < Message < Circuit Long Continuous Messages: Circuit < Message < Packet Protocols Building blocks of a network architecture Each protocol object has two different interfaces service interface: operations on this protocol peer-to-peer interface: messages exchanged with peer Term protocol refers to both the specification and implementation of the module ISO/OSI Architecture Why ing? End host Presentation Session End host Presentation Session communication is very complex Testing and maintenance is simplified Easy to replace a single layer with a different version link link link link One or more nodes within the network

10 Standards Making Organizations Protocols An Overview ISO = International Standards Organization ITU = International Teletraffic Union (formerly CCITT) ANSI = American National Standards Institute IEEE = Institute of Electrical and Electronic Engineers IETF = Internet Engineering Task Force ATM Forum = ATM standards-making body...and many more Why So Many Standards Organizations? Multiple standards Different areas of emphasis Different ing Architectures ISO OSI 7- Architecture TCP/IP 4- Architecture Novell NetWare IPX/SPX 4- Architecture

11 ISO OSI ing Architecture Host A Host B Protocol Presentation Presentation Protocol Presentation Session Session Protocol Session Protocol ISO s Design Principles A layer should be created where a different level of abstraction is needed Each layer should perform a well-defined function The layer boundaries should be chosen to minimize information flow across the interfaces The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity, and small enough that the architecture does not become unwieldy Link Link Link Link Router Router Presentation Session Link General Protocol Functions AH PH SH TH NH DH Header encapsulation and stripping DT 1: Functions: Transmission of a raw bit stream Forms the physical interface between devices Issues: Which modulation technique (bits to pulse)? How long will a bit last? Bit-serial or parallel transmission? Half- or Full-duplex transmission? How many pins does the network connector have? How is a connection set up or torn down? PH

12 2: Link Functions: Provides reliable transfer of information between two adjacent nodes Creates frames, or packets, from bits and vice versa Provides frame-level error control Provides flow control In summary, the data link layer provides the network layer with what appears to be an errorfree link for packets 3: Functions: Responsible for routing decisions Dynamic routing Fixed routing Performs congestion control 4: Functions: Hide the details of the network from the session layer Example: If we want replace a point-to-point link with a satellite link, this change should not affect the behavior of the upper layers Provides reliable end-to-end communication first end-to-end layer (cont d) Host A Protocol Presentation Presentation Protocol Session Session Protocol Protocol Host B Presentation Session Link Link Link Link Router Router

13 (cont d) Functions (cont d): Perform end-to-end flow control Perform packet retransmission when packets are lost by the network 5: Session May perform synchronization between several communicating applications Groups several user-level connections into a single session 6: Presentation Performs specific functions that are requested regularly by applications Examples: encryption ASCII to Unicode, Unicode to ASCII LSB-first representations to MSB-first representations 7: layer protocols are applicationdependent Implements communication between two applications of the same type Examples: FTP HTTP SMTP ( )

14 Internet Architecture TCP/IP ing Architecture Defined by Internet Engineering Task Force (IETF) Hourglass Design vs Protocol (FTP, HTTP) FTP HTTP NV TFTP TCP IP UDP NET 1 NET 2 NET n Internet/ Host-to to-net A simplified model The network layer Hosts drop packets into this layer, layer routes towards destination- only promise- try my best The transport layer reliable byte-oriented stream TCP/IP ing Architecture (cont d) Internet Design Principles IP Host B Host-to- Net Protocol Protocol (TCP) IP Host-to- Host-to- Net Net IP Host A Host-to- Net Scale Protocols should work in networks of all sizes and distances Incremental deployment New protocols need to be deployed gradually Heterogeneity Different technologies, autonomous organizations End-to-end argument ing functions should be delegated to the edges; application knows best

15 Some Definitions Measuring a s Performance A Brief Introduction Packet length: size of a packet (units = bits or bytes) Channel speed: How fast the channel can transmit bits (units = bits/second) Packet transmission time: amount of time to transmit an entire packet (units = seconds) Propagation delay: Delay imposed by the properties of the link. Depends on the link s distance (units = seconds) A Example 500 m packet length = 1500 bytes channel capacity = 10 Mbps propagation delay factor = 5 µsec/km 1. How long does it take a single bit to travel on the link from A to B? 2. How long does it take A to transmit an entire packet onto the link? B Digression: Units Bits are the units used to describe an amount of data in a network 1 kilobit (Kbit) = 1 x 10 3 bits = 1,000 bits 1 megabit (Mbit) = 1 x 10 6 bits = 1,000,000 bits 1 gigabit (Gbit) = 1 x 10 9 bits = 1,000,000,000 bits Seconds are the units used to measure time 1 millisecond (msec) = 1 x 10-3 seconds = seconds 1 microsecond (µsec) = 1 x 10-6 seconds = seconds 1 nanosecond (nsec) = 1 x 10-9 seconds = seconds Bits per second are the units used to measure channel capacity/bandwidth and throughput bit per second (bps) kilobits per second (Kbps) megabits per second (Mbps)

16 Propagation Delay 1. How long does it take a single bit to travel on the link from A to B of length 500 m with a prop. delay factor = 5 msec/km? Packet Transmission Time 2. How long does it take A to transmit an entire packet onto the link? Relevant information: packet length = 1500 bytes channel capacity = 10 Mbps Another way to ask this question: If it takes a signal 5 µsec to travel 1 kilometer, then how long does it take a signal to travel 500 meters? 5 µsec 1000 m = t 500 m Solving for t t = 2.5 µsec Another way to ask this question: If the link can transmit 10 million bits in a second, how many seconds does it take to transmit 1500 bytes (8x1500 bits)? 10 Mbits = 1 sec 1500 x 8 bits t Solving for t t = sec (or 1.2 msec) Analogy Message switching vs Packet switching Think of a transmission link as a water pipe 1. The thicker the pipe, the more water it can carry from one end to the other 2. Water is carried from one end of the pipe to the other at constant speed, no matter how thick the pipe is Water = bits Thickness of the pipe = Channel capacity or speed Speed of water through the pipe = Propagation delay Link speed is 1.5 Mbps. (ignore prop delay) Packet size is 1.5 Kbps, file size is 7.5 Mbits Find total time to transfer the entire file under the two switching techniques