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Session_03 - UT D CS 6386 Telecommunication Software Design...

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Unformatted text preview: UT D CS 6386 Telecommunication Software Design Session 03 The Public Switched Data Networks PSDNs Credits: Some slides are from J. Kurose and W. Stallings Telephone Service Expenditures Average Annual Household Expenditures for Telephone Service as a percentage of Total Household Expenditures 1980 1985 1990 1995 2003 1.94% 1.94% 2.09% 2.19% 2.34% 2 http://www.fcc.gov/Bureaus/Common_Carrier/Reports/FCC-State_Link/IAD/ref05.pdf Source: FCC (May 2005) 1 Average Annual Household Telephone Expenditures Local Exchange Long Distance Wired subtotal Wireless Grand Total 1995 1996 1997 1998 1999 2000 2003 $358 359 379 398 402 416 441 $250 250 305 270 257 211 122 $608 609 684 668 659 627 563 $82 108 129 164 205 279 492 $690 717 813 832 864 906 1055 3 Source: FCC (May 2005) Broadband Access 4 2 Internet World Subscribers Forecast 5 What is The Internet ? Router Host Computer Host Backbone SLIP, PPP Host LAN or intranet Host ARP 6 3 Internet History 19611961-1972: Early packet-switching principles packet 1961: Kleinrock queueing theory shows effectiveness of packetpacket-switching 1964: Baran - packetpacketswitching in military nets 1967: ARPAnet conceived by Advanced Reearch Projects Agency 1969: first ARPAnet node operational 1972: ARPAnet demonstrated publicly NCP (Network Control Protocol) first host-host hostprotocol first e-mail program e ARPAnet has 15 nodes 7 Internet History 19721972-1980: Internetworking, new and proprietary nets 1970: ALOHAnet satellite network in Hawaii 1973: Metcalfe's PhD thesis proposes Ethernet 1974: Cerf and Kahn architecture for interconnecting networks late70's: proprietary architectures: DECnet, SNA, XNA late 70's: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn's internetworking principles: minimalism, autonomy no internal changes required to interconnect networks best effort service model stateless routers decentralized control define today's Internet architecture 8 4 Internet History 19801980-1990: new protocols, a proliferation of networks 1983: deployment of TCP/IP 1982: smtp e-mail eprotocol defined 1983: DNS defined for name-to-IPname-to-IP-address translation 1985: ftp protocol defined 1988: TCP congestion control new national networks: Csnet, BITnet, NSFnet, Minitel 100,000 hosts connected to confederation of networks 9 Internet History 1990's: commercialization, the WWW Early 1990's: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: WWW hypertext [Bush 1945, Nelson 1960's] HTML, http: Berners-Lee Berners 1994: Mosaic, later Netscape late 1990's: commercialization of the WWW Late 1990's: est. 50 million computers on Internet est. 100 million+ users backbone links running at 1 Gbps 10 5 Internet Traffic in the US 100 Pbps 10 Pbps 1 Pbps 100Tbps 10Tbps 1Tbps New Measurements Voice Crossover: August 2000 Projected at 4/Year 100Gbps 10Gbps 1Gbps 100Mbps 10Mbps 1Mbps ARPA & NSF Data to 96 2.8/Year 4/Year 100Kbps 10Kbps 1Kbps 100 bps 10 bps 1970 1975 1980 1985 1990 1995 2000 2005 2010 11 Source: Roberts et al., 2001 A Communications Model Source Generates messages to be consumed by destination Transmitter Converts messages into signals convenient for networks Networks Transmission and exchange systems Carries, switches and routes messages Receiver Converts received signal back to messages Destination Consumes messages 12 6 Simplified Communications Model - Diagram networks 13 Simplified Communications Model for Dial-up Connections Dial- networks 14 7 Why Networking Point to point communications not usually practical Devices are too far apart Large set of devices would need impractical number of connections Solution is a communications network 15 Simplified Network Model networks 16 8 Wide Area Networks Large geographical area Rely in part on common carrier facilities Alternative technologies Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM) 17 Local Area Networks Smaller scope Building or small campus Usually owned by same organization as attached devices Data rates much higher (Gigabit/sec) Usually broadcast systems Now some switched systems and ATM are being introduced 18 9 Why Network Architecture Error correction Signal regeneration ..... Framing Flow control Packetization ..... Error detection Decoding Encoding Stuffing Routing Networks are very complex and difficult to describe or design 19 What is Network Architecture Network architecture A structured way to describe and specify computer networks A set of layers and protocols Layering Built upon smaller and more manageable entities Manage complexity by using abstraction Protocols 20 Rules that govern interaction between peers 10 Layering Fundamental Idea Divide-and-conquer Divide-and Break a complex problem into smaller problems (e.g. subroutines) Solve individual (smaller) problems Combine into final solution This concept is applied to computer networks as layering Divided into multiple layers Abstraction of the next lower layer as a service provider 21 Layered Systems Each layer provides operation primitives and services to the higher layer Upper layer is built upon services provided by the next lower layer The interface between each pair of adjacent layers defines these primitives and services Layer interfaces should be clean and well-defined well- Peers in the same layer appear to be communicating using a particular protocol 22 11 Layered Network Architecture Host 1 Layer 5 Layer 4/5 interface Layer 4 Layer 3/4 interface Layer 3 Layer 2/3 interface Layer 2 Layer 1/2 interface Layer 1 Layer 1 protocol Layer 1 Layer 2 protocol Layer 2 Layer 3 protocol Layer 3 Layer 4 protocol Layer 4 Layer 5 protocol Host 2 Layer 5 Physical medium 23 Layer Protocol Design Issues Data transfer mode Simplex or duplex Half-duplex or full-duplex Halffull- Addressing identifying sender and receiver How to deal with errors Error detection Error correction Flow control Multiplexing and demultiplexing Routing Packetization .... 24 12 Service Abstraction Service abstraction is a crucial aspect for good layer design A layer provides well-defined services well Service primitive define what is the service Service interface (or access point) - how to use the service How the service is implemented is not a concern Service implementation can be changed easily without service disruption Service primitive and interface should be rarely changed 25 Service Primitives REQUEST Entity wants the lower layer to perform some operations CONFIRM The lower layer sends response to an earlier request INDICATION Entity is informed about an event by the lower layer RESPONSE Entity sends respond to an event Services can be either confirmed or unconfirmed confirmed: has all four primitives unconfirmed: has only request and indication primitives 26 13 Layer Specification Layer N+1 Service User Service User Layer N Service Provider Service Access Point (or Interface) Service Primitives 27 Layering Example User Post System User User P.Office Sort Ctr. User P.Office Sort Ctr. Transport System The postal service system is divided into three layers Example: Post office layer uses the services provided by sort center layer 28 14 What is a Protocol human protocol protocol Hi Hi Got the time? computer network TCP connection req. TCP connection reply. Get http://gaia.cs.umass.edu/index.htm 2:00 time <file> Set of rules for interaction between two communicating peers 29 Protocols Used for communications between entities in a system, or across systems through networks Entities must speak the same language Entities User applications e-mail facilities Systems Computer Terminal Remote sensor 30 15 Protocol Stack Layer 4 Layer 3 Layer 2 Layer 1 Layer 4 Layer 3 Layer 2 Layer 1 A set of layered protocols used by a system is called a protocol stack e.g. TCP/IP 31 GPRS Protocol Stacks Application IP/X.25 Relay Application IP/X.25 GTP SNDCP GTP SNDCP SNDCP LLC Relay LLC BSSGP RLC BSSGP UDP/ TCP IP L2 L1 UDP/ TCP IP L2 L1 RLC MAC Physical MAC Physical Network service L1bis Network Service L1bis MS Um BSS Gb SGNS Gn GGNS 32 16 Key Elements of a Protocol Syntax Data formats Signal levels Semantics Control information Error handling Timing Speed matching Sequencing 33 Message Two important concepts when discussing layering and protocols are messages and encapsulation Message is the basic unit for information exchange between peer (PDU Protocol Data Unit) a message is consisted of a header portion and a data portion The header contains protocol control information used by the remote peer 34 17 Encapsulation When layer N accepts a message from layer N+1, it adds the protocol control information to the header encapsulates the whole message into the data portion When the remote peer receives the message, it strips of the header portion delivers only the data portion to the N+1 layer 35 Network Architecture Example FTP Task of communication broken up into modules For example file transfer task could be divided into three modules File transfer application Communication service module Network access module 36 18 Simplified File Transfer Architecture 37 A Three Layer Model Network Access Layer Transport Layer Application Layer 38 19 Network Access Layer Exchange of data between the computer and the network Sending computer provides address of destination May invoke levels of service Dependent on type of network used (LAN, packet switched etc.) 39 Transport Layer Reliable data exchange Independent of network being used Independent of application 40 20 Application Layer Support for different user applications e.g. e-mail, file transfer e- 41 Addressing Requirements Two levels of addressing required Each computer needs unique network address Each application on a (multi-tasking) (multicomputer needs a unique address within the computer The service access point or SAP 42 21 Protocol Architectures and Networks 43 Protocols in Simplified Architecture 44 22 TCP/IP Protocol Architecture Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) Used by the global Internet No official model but a working one Application layer Host to host or transport layer Internet layer Network access layer Physical layer 45 Physical Layer Physical interface between data transmission device (e.g. computer) and transmission medium or network Characteristics of transmission medium Signal levels Data rates etc. 46 23 Network Access Layer Exchange of data between end system and network Destination address provision Invoking services like priority 47 Internet Layer (IP) Systems may be attached to different networks Routing functions across multiple networks Implemented in end systems and routers 48 24 Transport Layer (TCP) Reliable delivery of data Ordering of delivery 49 Application Layer Support for user applications e.g. http, SMPT, ftp, POP3 etc... 50 25 TCP/IP Protocol Architecture Model networks 51 Operation of TCP and IP IP implemented in end systems and routers, relaying data between hosts TCP implemented only in end systems, assuring reliable delivery of blocks of data Each host on subnetwork has unique IP address Each process on each process has unique IP port number 52 26 TCP/IP Concepts 53 PDUs in TCP/IP Networks 54 27 IP and TCP Header 55 TCP/IP Configuration Example 56 28 Internet Protocols HTML SMTP POP, IMAP RT Data Signalling Protocols (e.g. ISUP) FTP TCP IP HTTP DNS RTP UDP SCTP OSPF BGP ICMP ARP RIP SLIP PPP LAN-protocols, ATM, PSTN/ISDN, PLMN ... 57 Internet Protocols Summary 58 29 ClientClient-Server Paradigm Host Client Request Response Host Server 59 How Internet Handles Web Browsing ? (1) User terminal (Client) Send me HTML page HTML page source (Server) HTTP TCP IP PPP Internet service provider's PoP IP PPP ATM HTTP TCP IP ATM 60 30 How Internet Handles Web Browsing ? (2) User terminal (Client) DNS replies ... UDP IP HTML page source (Server) Contact DNS ... UDP IP PPP UDP IP PPP ATM HTTP TCP IP ATM 61 How Internet Handles Web Browsing ? (3) User terminal (Client) HTML page source (Server) HTTP TCP IP PPP Three-way handshaking IP PPP ATM HTTP TCP IP ATM 62 31 How Internet Handles Web Browsing ? (4) User terminal (Client) Request Reply IP PPP ATM HTML page source (Server) HTTP TCP IP PPP HTTP TCP IP ATM 63 How Internet Handles Web Browsing ? (5) User terminal (Client) HTML page source (Server) HTTP TCP IP PPP Two-way handshaking IP PPP ATM HTTP TCP IP ATM 64 32 How Internet Handles Web Browsing ? (6) User terminal (Client) HTML page source (Server) HTTP TCP IP PPP PPP IP ATM HTTP TCP IP ATM 65 33 ...
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