ICS 153 Introduction to Computer Networks Inst: Chris Davison cbdaviso@uci.edu 1
ICS 153 Introduction to Computer Networks Course Goals Understand the basic principles of computer networks Design Architecture Understand the Internet and its protocols 2
ICS 153 Introduction to Computer Networks Homework: Chapter 1 Problems: 2, 3 5, 11, 13, 15, 18, 21, 22, 25 3
What is a Computer Network? Interconnected collection of autonomous computers Interconnection may be: copper (Twisted Pair) lasers (Fiber Optics) microwave satellite Examples: Internet, Ethernet, DDN 4
Use of Computer Networks Availability of Resources - Resources become available regardless of the user s physical location Load Sharing - Jobs processed on the least crowded machine High Reliability - File and processor redundancy Human-to-Human Communication - Telephone - Long distance education and collaboration 5
Use of Computer Networks Save money - PC networks are inexpensive and powerful. - Companies are adapting the client/server model. 6
Client / Server Model Client/server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the server, which fulfills the request. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations 7
Client / Server Model "Fat" client Is one in which most of the application resides on and runs on the user workstation Thin client Is one where most of the application resides on and runs on one or more server computers 8
Computer Network Applications Electronic mail Remote terminal File transfer World wide web File sharing Resource distribution Video conferencing Talk / chat Games 9
Network Classifications Classification based on transmission technology: Broadcast vs. Point to point networks - Broadcast networks use one communication channel that is shared by all the machines. Packets are sent to the shared channel and are listened to by all machines. - Point to point network packets are routed to their destination. 10
Network Classifications cont. Classification based on scale - Data Flow : Same circuit board - Multicomputer : same system, processors communicate over high speed busses - PAN: small area - LAN: Room, Building, Campus - MAN: City -WAN: Country, Continent - Internet: Global 11
Definitions: Speak the LANguage Network: Interconnected collection of autonomous computers Host: machine running user application Subnet: Communication subnet carries messages between hosts Channel: Logical Line of communication (circuit) Topology: Network Configuration 12
Possible Topologies 13
Network Software Layers: Networks are organized in levels to reduce design complexity. Protocols: Rules and conventions of a specific layer (layer n) Network Architecture: a set of layers and protocols Protocol Stack: list of protocols (1 per layer) used by a system. 14
Network Software Interface: defines the functions that a lower layer performs for an upper layer Each layer provides a set of specific, well defined functions 15
Network Software 16
Design Issues Addressing Data transfer Error control Sequencing Flow control Message size Routing 17
Services Service: function a layer provides to the higher layers Connection-orientated Service Connectionless Service Both are judged by their Quality of Service : - Reliable vs. Unreliable 18
Services Services Formally specified by primitives (operations) Primitives tell the Service to do something Request Indication Response Confirm -Primitives make use of negotiation to establish communication parameters Window Size 19
Service vs. Protocol Service: set of operations that one layer provides to another. - Specified by Primitives (operations) Protocol: set of rules governing the messages exchanged between peers within a layer. Peers negotiate communication parameters. 20
Standardization Given various layers and protocols; standardization becomes necessary. 21
Standards Making Organizations ISO = International Standards Organization ITU = International Telecommunication 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... many more 22
Why so many Standards Orgs? Multiple standards Different areas of emphasis 23
IEEE 802 Working Groups Standardized many networks 24
Different Layering Architecture ISO OSI 7-layer architecture TCP/IP 4-layer architecture Novell NetWare IPX/SPX 4 layer architecture 25
Why Layer? Network communication is very complex Testing and maintenance is simplified Easy to replace a single layer with a different version 26
OSI 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 27
OSI Model Concepts: Services - Defines what the layer does not how it works Interfaces -Defines how to access a layer e.g. parameters and results Protocols -As long as the layer works any protocol necessary can be used. 28
OSI Model 29
TCP/IP s Design Principles ad hoc: the protocols came first and the layering model came later TCP/IP specifically designed for the Internet TCP/IP model doesn t describe other protocols well 30
TCP/IP Model 31
OSI Layer 1: Physical Functions: Layer - Transmission of a raw bit stream - forms the physical interface between devices Issues: -Which modulation technique? -How long will a bit last? - Half- or full-duplex transmission? - How many pins does the network connection have? - How is a connection set up or torn down? 32
OSI Layer 2: Data Link Functions: Layer -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. 33
OSI Layer 3: Network Functions: Layer - Responsible for routing decisions: Fixed routing vs. dynamic routing Performs congestion control A bottleneck on a subnet is a result of congestion. 34
OSI Layer 4: Transport Layer Functions - Hide the details of the network from the session layer -Example: If we want to 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 - Provides end-to-end flow control - Performs packet retransmission when packets are lost by the network - Establishes and deletes connections across the network 35
OSI Layer 5:Session Layer May perform synchronization and token management between several communicating applications Groups several user-level connections into a single session 36
OSI Layer 6: Presentation Layer Performs specific functions that are requested regularly by applications: - Encryption - ASCII to Unicode, Unicode to ASCII 37
OSI Layer 7: Application Layer Application layer protocols are application dependent Implements communication between two applications of the same type: - FTP -SMTP (email) 38
TCP/IP Layer 1: Host to Network Packaged in frames - Has a Frame header that includes address and control information. -Has a frame trailer that is used for error detection. 39
TCP/IP Layer 2: Internet Layer Network layer functions Routes data between hosts Connectionless Every packet routed independently Does not guarantee reliable or in-sequence delivery 40
TCP/IP Layer 3: Transport Layer Allow Peer entities on the source and destination systems to converse Two end-to-end Protocols: TCP Transmission Control Protocol reliable connection-oriented UDP User Datagram Protocol unreliable connectionless 41
TCP/IP Layer 4: Application Layer Contains all the higher-level protocols TELNET DNS HTTP 42
TCP/IP vs. OSI 43
TCP/IP vs. OSI Model TCP/IP model was created AFTER the protocols OSI was devised BEFORE the protocols TCP/IP is widely implemented OSI is structured Neither are perfect 44
Example PC Networks Novell NetWare - Uses IPX - Native TCP/IP with version 5 Microsoft Windows - Uses NetBEUI - Support a variety of other protocols including TCP/IP Linux - Uses TCP/IP 45
Example Networks ARPANET - Advanced Research Projects Agency (US Government) -Packet switched network consisting of a subnet and host computers. - Subnet was Honeywell minicomputers (Interface Message Processors) connected by transmission lines. - Precursor to the Internet. 46
Example Networks Internet - Collection of hosts and networks (NASA, IBM, ANSNET, ARPANET, etc.) tied together and 1. using the TCP/IP protocol stack 2. having an IP address 3. having the ability to send IP packets to other machines on the Internet. 47
Example Data Communication Services Leased Line Company buys an entire circuit from a service provider. Has full access to the entire bandwidth of that circuit Expensive 48
SMDS Example Data Communication Services - Switched Multimegabit Data Service - Standard Operating speed is 45Mbps - Broadband (high speed, multi-channel), connectionless, switched service - Delivery is not guaranteed -Inexpensive alternative to leased lines 49
Example Data Communication Services Frame Relay - Inexpensive alternative to a leased line. - Connection orientated virtual leased line -Operates at 1.5 MBPS - Priced right for companies who need connectivity 50
Example Data Communication Services B-ISDN and ATM - Broadband Integrated Services Digital Network - High speed, connection orientated communication service - ITU-T standards supporting integrated high-speed transmission, switching and multiplexing of data, audio and video. - Wide area service based on ATM technology ATM - Asynchronous Transfer Mode - Not a money machine! - Transmits all information in small 53 byte cells. 5 bytes for header and 48 bytes for payload. -Connection orientated but delivery is not guaranteed -Operates at 155Mbps (OC3)and 622 Mbp (OC12) and higher. 51
ATM Reference Model 52
Example Data Communication Services ATM Reference Model - 3 Dimensional Model: 3 Layers High and 3 Layers Deep 1. Physical Layer - Cells can be sent by themselves or tunneled - Independent of the transmission media - Voltage, Bit timing 2. ATM Layer - Cells and cell transport - Defines the layout of an ATM cell - Performs congestion control - Establishment and teardown of virtual circuits 3. (AAL) ATM Adaptation Layer - Segments large packets into cells, transmits the cells, and reassembles the packet. 53
Example Data Communication Services ATM Reference Model cont. -3 Dimensional Model 1a. User Plane - Data transport, flow control, error correction, and other user functions 1b. Control Plane - Concerned with connection management 2. Layer Management -Resource management and interlayer coordination 3. Plane Management - Resource management and interlayer coordination 54
Example Data Communication Services ATM Reference Model cont. 1. Physical Layer Sublayers - PMD: Physical Medium Dependant Sublayer Interfaces with the physical medium (cable) -TC: Transmission Convergence Sublayer Performs conversions from bits to cells and vice versa. Provides the interface between the the PMD and the ATM layer. 2. AAL Layer Sublayers - SAR: Segment and Reassembly sublayer Breaks packets into cells and vice versa - CS: Convergence Sublayer Provides the standard interface Makes it possible to offer multiple services 55
ATM News Example Data Communication Services Marconi (Formerly FORE Systems) 10Gbps ATM switch ICS Graduate ATM Network All fiber OC3 feed into CalREN-2 CalREN-2 is California s feed into vbns (very high performance Backbone Network Service) www.calren2.net www.vbns.net 56
Metric Units of Measurement Most Disk drives are in MegaBytes (2^20 = 1,048,576) Speed is measured in Megabits (10^6 = 1,000,000) 57