Chapter 1 Introduction Supplementery Slides BLM 431 Computer Networks Dr. Refik Samet 1
A Communications Model z Source ygenerates data to be transmitted z Transmitter y. Converts data into transmittable signals z Transmission System y. Carries data z Receiver y. Converts received signal into data z Destination y. Takes incoming data BLM 431 Computer Networks Dr. Refik Samet 2
Communications Tasks Transmission system utilization Addressing Interfacing Routing Signal generation Recovery Synchronization Message formatting Exchange management Security Error detection and correction Network management Flow control BLM 431 Computer Networks Dr. Refik Samet 3
Simplified Communications Model - Diagram BLM 431 Computer Networks Dr. Refik Samet 4
Key Communications Tasks z Transmission System Utilization z Interfacing z Signal Generation z Synchronization z Exchange Management z Error detection and correction z Addressing and routing z Recovery z Message formatting z Security z Network Management BLM 431 Computer Networks Dr. Refik Samet 5
Simplified Data Communications Model BLM 431 Computer Networks Dr. Refik Samet 6
Networking z Point to point communication not usually practical y. Devices are too far apart y. Large set of devices would need impractical number of connections z Solution is a communications network BLM 431 Computer Networks Dr. Refik Samet 7
Simplified Network Model BLM 431 Computer Networks Dr. Refik Samet 8
Wide Area Networks z Large geographical area z Crossing public rights of way z Rely in part on common carrier circuits z Alternative technologies y. Circuit switching y. Packet switching y. Frame relay y. Asynchronous Transfer Mode (ATM) BLM 431 Computer Networks Dr. Refik Samet 9
Circuit Switching z Dedicated communications path established for the duration of the conversation z e. g. telephone network BLM 431 Computer Networks Dr. Refik Samet 10
Packet Switching z Data sent out of sequence z Small chunks (packets) of data at a time z Packets passed from node to node between source and destination z Used for terminal to computer and computer to computer communications BLM 431 Computer Networks Dr. Refik Samet 11
Frame Relay z Packet switching systems have large overheads to compensate for errors z Modern systems are more reliable z Errors can be caught in end system z Most overhead for error control is stripped out BLM 431 Computer Networks Dr. Refik Samet 12
Asynchronous Transfer Mode z ATM z Evolution of frame relay z Little overhead for error control z Fixed packet (called cell) length z Anything from 10 Mbps to Gbps z Constant data rate using packet switching technique BLM 431 Computer Networks Dr. Refik Samet 13
Integrated Services Digital Network z ISDN z Designed to replace public telecom system z Wide variety of services z Entirely digital domain BLM 431 Computer Networks Dr. Refik Samet 14
Local Area Networks z Smaller scope y. Building or small campus z Usually owned by same organization as attached devices z Data rates much higher z Usually broadcast systems z Now some switched systems and ATM are being introduced BLM 431 Computer Networks Dr. Refik Samet 15
Protocols z Used for communications between entities in a system z Must speak the same language z Entities y. User applications ye-mail facilities yterminals z Systems y. Computer y. Terminal BLM 431 Computer Networks Dr. Refik Samet y. Remote sensor 16
Key Elements of a Protocol z Syntax y. Data formats y. Signal levels z Semantics y. Control information y. Error handling z Timing y. Speed matching y. Sequencing BLM 431 Computer Networks Dr. Refik Samet 17
Protocol Architecture z Task of communication broken up into modules z For example file transfer could use three modules y. File transfer application y. Communication service module y. Network access module BLM 431 Computer Networks Dr. Refik Samet 18
Simplified File Transfer Architecture BLM 431 Computer Networks Dr. Refik Samet 19
A Three Layer Model z Network Access Layer z Transport Layer z Application Layer BLM 431 Computer Networks Dr. Refik Samet 20
Network Access Layer z Exchange of data between the computer and the network z Sending computer provides address of destination z May invoke levels of service z Dependent on type of network used (LAN, packet switched etc. ) BLM 431 Computer Networks Dr. Refik Samet 21
Transport Layer z Reliable data exchange z Independent of network being used z Independent of application BLM 431 Computer Networks Dr. Refik Samet 22
Application Layer z Support for different user applications z e. g. e-mail, file transfer BLM 431 Computer Networks Dr. Refik Samet 23
Addressing Requirements z Two levels of addressing required z Each computer needs unique network address z Each application on a (multi-tasking) computer needs a unique address within the computer y. The service access point or SAP BLM 431 Computer Networks Dr. Refik Samet 24
Protocol Architectures and Networks BLM 431 Computer Networks Dr. Refik Samet 25
Protocols in Simplified Architecture BLM 431 Computer Networks Dr. Refik Samet 26
Protocol Data Units (PDU) z At each layer, protocols are used to communicate z Control information is added to user data at each layer z Transport layer may fragment user data z Each fragment has a transport header added y. Destination SAP y. Sequence number y. Error detection code z This gives a transport protocol data unit BLM 431 Computer Networks Dr. Refik Samet 27
Network PDU z Adds network header ynetwork address for destination computer y. Facilities requests BLM 431 Computer Networks Dr. Refik Samet 28
Operation of a Protocol Architecture BLM 431 Computer Networks Dr. Refik Samet 29
TCP/IP Protocol Architecture z Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) z Used by the global Internet z No official model but a working one. y. Application layer y. Host to host or transport layer y. Internet layer y. Network access layer y. Physical layer BLM 431 Computer Networks Dr. Refik Samet 30
Physical Layer z Physical interface between data transmission device (e. g. computer) and transmission medium or network z Characteristics of transmission medium z Signal levels z Data rates z etc. BLM 431 Computer Networks Dr. Refik Samet 31
Network Access Layer z Exchange of data between end system and network z Destination address provision z Invoking services like priority BLM 431 Computer Networks Dr. Refik Samet 32
Internet Layer (IP) z Systems may be attached to different networks z Routing functions across multiple networks z Implemented in end systems and routers BLM 431 Computer Networks Dr. Refik Samet 33
Transport Layer (TCP) z Reliable delivery of data z Ordering of delivery BLM 431 Computer Networks Dr. Refik Samet 34
Application Layer z Support for user applications z e. g. http, SMPT BLM 431 Computer Networks Dr. Refik Samet 35
TCP/IP Protocol Architecture Model BLM 431 Computer Networks Dr. Refik Samet 36
OSI Model z Open Systems Interconnection z Developed by the International Organization for Standardization (ISO) z Seven layers z A theoretical system delivered too late! z TCP/IP is the de facto standard BLM 431 Computer Networks Dr. Refik Samet 37
OSI Layers z Application z Presentation z Session z Transport z Network z Data Link z Physical BLM 431 Computer Networks Dr. Refik Samet 38
OSI v TCP/IP BLM 431 Computer Networks Dr. Refik Samet 39
Standards z Required to allow for interoperability between equipment z Advantages y. Ensures a large market for equipment and software y. Allows products from different vendors to communicate z Disadvantages y. Freeze technology y. May be multiple standards for the same thing BLM 431 Computer Networks Dr. Refik Samet 40
Standards Organizations z Internet Society z ISO z ITU-T (formally CCITT) z ATM forum BLM 431 Computer Networks Dr. Refik Samet 41
Further Reading z Stallings, W. Data and Computer Communications (6 th edition), Prentice Hall 1999 chapter 1 z Web site for Stallings book ywww. shore. net/~ws/DCC 6 e. html z Web sites for IETF, IEEE, ITU-T, ISO z Internet Requests for Comment (RFCs) z Usenet News groups ycomp. dcom. * ycomp. protocols. tcp-ip BLM 431 Computer Networks Dr. Refik Samet 42
Networking Configuration BLM 431 Computer Networks Dr. Refik Samet 43
Service Primitives and Parameters z Services between adjacent layers expressed in terms of primitives and parameters z Primitives specify function to be performed z Parameters pass data and control info BLM 431 Computer Networks Dr. Refik Samet 44
Primitive Types REQUEST A primitive issued by a service user to invoke some service and to pass the parameters needed to specify fully the requested service INDICATION A primitive issued by a service provider either to: indicate that a procedure has been invoked by the peer service user on the connection and to provide the associated parameters, or notify the service user of a provider-initiated action RESPONSE A primitive issued by a service user to acknowledge or complete some procedure previously invoked by an indication to that user CONFIRM A primitive issued by a service provider to acknowledge or complete some procedure previously invoked by a request by the service user BLM 431 Computer Networks Dr. Refik Samet 45
Timing Sequence for Service Primitives BLM 431 Computer Networks Dr. Refik Samet 46
Networking z Point to point communication not usually practical y. Devices are too far apart y. Large set of devices would need impractical number of connections z Solution is a communications network y. Wide Area Network (WAN) y. Local Area Network (LAN) BLM 431 Computer Networks Dr. Refik Samet 47
Wide Area Networks z Large geographical area z Crossing public rights of way z Rely in part on common carrier circuits z Alternative technologies y. Circuit switching y. Packet switching y. Frame relay y. Asynchronous Transfer Mode (ATM) BLM 431 Computer Networks Dr. Refik Samet 48
Circuit Switching z Dedicated communications path established for the duration of the conversation z e. g. telephone network BLM 431 Computer Networks Dr. Refik Samet 49
Packet Switching z Data sent out of sequence z Small chunks (packets) of data at a time z Packets passed from node to node between source and destination z Used for terminal to computer and computer to computer communications BLM 431 Computer Networks Dr. Refik Samet 50
Frame Relay z Packet switching systems have large overheads to compensate for errors z Modern systems are more reliable z Errors can be caught in end system z Most overhead for error control is stripped out BLM 431 Computer Networks Dr. Refik Samet 51
Asynchronous Transfer Mode z ATM z Evolution of frame relay z Little overhead for error control z Fixed packet (called cell) length z Anything from 10 Mbps to Gbps z Constant data rate using packet switching technique BLM 431 Computer Networks Dr. Refik Samet 52
Local Area Networks z Smaller scope y. Building or small campus z Usually owned by same organization as attached devices z Data rates much higher z Usually broadcast systems z Now some switched systems and ATM are being introduced BLM 431 Computer Networks Dr. Refik Samet 53
LAN Configurations z Switched y. Switched Ethernet x. May be single or multiple switches y. ATM LAN y. Fibre Channel z Wireless y. Mobility y. Ease of installation BLM 431 Computer Networks Dr. Refik Samet 54
Metropolitan Area Networks z MAN z Middle ground between LAN and WAN z Private or public network z High speed z Large area BLM 431 Computer Networks Dr. Refik Samet 55
Protocols and Architecture Characteristics z Direct or indirect z Monolithic or structured z Symmetric or asymmetric z Standard or nonstandard BLM 431 Computer Networks Dr. Refik Samet 56
Direct or Indirect z Direct y. Systems share a point to point link or y. Systems share a multi-point link y. Data can pass without intervening active agent z Indirect y. Switched networks or y. Internetworks or internets y. Data transfer depend on other entities BLM 431 Computer Networks Dr. Refik Samet 57
Monolithic or Structured z Communications is a complex task z To complex for single unit z Structured design breaks down problem into smaller units z Layered structure BLM 431 Computer Networks Dr. Refik Samet 58
Symmetric or Asymmetric z Symmetric y. Communication between peer entities z Asymmetric y. Client/server BLM 431 Computer Networks Dr. Refik Samet 59
Standard or Nonstandard z Nonstandard protocols built for specific computers and tasks z K sources and L receivers leads to K*L protocols and 2*K*L implementations z If common protocol used, K + L implementations needed BLM 431 Computer Networks Dr. Refik Samet 60
Use of Standard Protocols BLM 431 Computer Networks Dr. Refik Samet 61
Functions z Encapsulation z Segmentation and reassmebly z Connection control z Ordered delivery z Flow control z Error control z Addressing z Multiplexing z Transmission services BLM 431 Computer Networks Dr. Refik Samet 62
Encapsulation z Addition of control information to data y. Address information y. Error-detecting code y. Protocol control BLM 431 Computer Networks Dr. Refik Samet 63
Segmentation (Fragmentation) z Data blocks are of bounded size z Application layer messages may be large z Network packets may be smaller z Splitting larger blocks into smaller ones is segmentation (or fragmentation in TCP/IP) y. ATM blocks (cells) are 53 octets long y. Ethernet blocks (frames) are up to 1526 octets long z Checkpoints and restart/recovery BLM 431 Computer Networks Dr. Refik Samet 64
Why Fragment? z Advantages y. More efficient error control y. More equitable access to network facilities y. Shorter delays y. Smaller buffers needed z Disadvantages y. Overheads y. Increased interrupts at receiver y. More processing time BLM 431 Computer Networks Dr. Refik Samet 65
Connection Control z Connection Establishment z Data transfer z Connection termination z May be connection interruption and recovery z Sequence numbers used for y. Ordered delivery y. Flow control y. Error control BLM 431 Computer Networks Dr. Refik Samet 66
Connection Oriented Data Transfer BLM 431 Computer Networks Dr. Refik Samet 67
Ordered Delivery z PDUs may traverse different paths through network z PDUs may arrive out of order z Sequentially number PDUs to allow for ordering BLM 431 Computer Networks Dr. Refik Samet 68
Flow Control z Done by receiving entity z Limit amount or rate of data z Stop and wait z Credit systems y. Sliding window z Needed at application as well as network layers BLM 431 Computer Networks Dr. Refik Samet 69
Error Control z Guard against loss or damage z Error detection y. Sender inserts error detecting bits y. Receiver checks these bits y. If OK, acknowledge y. If error, discard packet z Retransmission y. If no acknowledge in given time, re-transmit z Performed at various levels BLM 431 Computer Networks Dr. Refik Samet 70
Addressing z Addressing level z Addressing scope z Connection identifiers z Addressing mode BLM 431 Computer Networks Dr. Refik Samet 71
Addressing level z Level in architecture at which entity is named z Unique address for each end system (computer) and router z Network level address y. IP or internet address (TCP/IP) y. Network service access point or NSAP (OSI) z Process within the system y. Port number (TCP/IP) y. Service access point or SAP (OSI) BLM 431 Computer Networks Dr. Refik Samet 72
Address Concepts BLM 431 Computer Networks Dr. Refik Samet 73
Addressing Scope z Global nonambiguity y. Global address identifies unique system y. There is only one system with address X z Global applicability y. It is possible at any system (any address) to identify any other system (address) by the global address of the other system y. Address X identifies that system from anywhere on the network z e. g. MAC address on IEEE 802 networks BLM 431 Computer Networks Dr. Refik Samet 74
Connection Identifiers z Connection oriented data transfer (virtual circuits) z Allocate a connection name during the transfer phase y. Reduced overhead as connection identifiers are shorter than global addresses y. Routing may be fixed and identified by connection name y. Entities may want multiple connections - multiplexing y. State information BLM 431 Computer Networks Dr. Refik Samet 75
Addressing Mode z Usually an address refers to a single system y. Unicast address y. Sent to one machine or person z May address all entities within a domain y. Broadcast y. Sent to all machines or users z May address a subset of the entities in a domain y. Multicast y. Sent to some machines or a group of users BLM 431 Computer Networks Dr. Refik Samet 76
Multiplexing z Supporting multiple connections on one machine z Mapping of multiple connections at one level to a single connection at another y. Carrying a number of connections on one fiber optic cable y. Aggregating or bonding ISDN lines to gain bandwidth BLM 431 Computer Networks Dr. Refik Samet 77
Transmission Services z Priority ye. g. control messages z Quality of service y. Minimum acceptable throughput y. Maximum acceptable delay z Security y. Access restrictions BLM 431 Computer Networks Dr. Refik Samet 78
OSI - The Model z A layer model z Each layer performs a subset of the required communication functions z Each layer relies on the next lower layer to perform more primitive functions z Each layer provides services to the next higher layer z Changes in one layer should not require changes in other layers BLM 431 Computer Networks Dr. Refik Samet 79
The OSI Environment BLM 431 Computer Networks Dr. Refik Samet 80
OSI as Framework for Standardization BLM 431 Computer Networks Dr. Refik Samet 81
Layer Specific Standards BLM 431 Computer Networks Dr. Refik Samet 82
Elements of Standardization z Protocol specification y. Operates between the same layer on two systems y. May involve different operating system y. Protocol specification must be precise x. Format of data units x. Semantics of all fields xallowable sequence of PCUs z Service definition y. Functional description of what is provided z Addressing y. Referenced by SAPs BLM 431 Computer Networks Dr. Refik Samet 83
OSI Layers (1) z Physical y. Physical interface between devices x. Mechanical x. Electrical x. Functional x. Procedural z Data Link y. Means of activating, maintaining and deactivating a reliable link y. Error detection and control y. Higher layers may assume error free transmission BLM 431 Computer Networks Dr. Refik Samet 84
OSI Layers (2) z Network y. Transport of information y. Higher layers do not need to know about underlying technology y. Not needed on direct links z Transport y. Exchange of data between end systems y. Error free y. In sequence y. No losses y. No duplicates BLM 431 Computer Networks y. Quality of service Dr. Refik Samet 85
OSI Layers (3) z Session y. Control of dialogues between applications y. Dialogue discipline y. Grouping y. Recovery z Presentation y. Data formats and coding y. Data compression y. Encryption z Application y. Means for applications to access OSI environment BLM 431 Computer Networks Dr. Refik Samet 86
Use of a Relay BLM 431 Computer Networks Dr. Refik Samet 87
TCP/IP Protocol Suite z Dominant commercial protocol architecture z Specified and extensively used before OSI z Developed by research funded US Department of Defense z Used by the Internet BLM 431 Computer Networks Dr. Refik Samet 88
TCP/IP Protocol Architecture(1) z Application Layer y. Communication between processes or applications z End to end or transport layer (TCP/UDP/…) y. End to end transfer of data y. May include reliability mechanism (TCP) y. Hides detail of underlying network z Internet Layer (IP) y. Routing of data BLM 431 Computer Networks Dr. Refik Samet 89
TCP/IP Protocol Architecture(2) z Network Layer y. Logical interface between end system and network z Physical Layer y. Transmission medium y. Signal rate and encoding BLM 431 Computer Networks Dr. Refik Samet 90
PDUs in TCP/IP BLM 431 Computer Networks Dr. Refik Samet 91
Some Protocols in TCP/IP Suite BLM 431 Computer Networks Dr. Refik Samet 92
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