Computer Networks CS321

Transcription

1 Computer Networks CS321 Dr. Ramana I.I.T Jodhpur Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 1 / 22

2 Outline of the Lectures 1 Introduction OSI Reference Model Internet Protocol Performance Metrics 2 Packet Switching Technologies Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 2 / 22

3 Introduction Key elements of a Network Standalone Mainframe Router Wide Area Network (e.g. ATM) Local Area Network Router Router Ethernet switch Wide Area Network (e.g. ATM) Router Local Area Network Ethernet switch Information server LAN PCs and workstations Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 3 / 22

4 Layered Architecture Introduction Layer 7 (Application) Service to Layer N+1 Total Communication Function Decompose (modularity, information-hiding) Layer N Layer N entity Service from Layer N 1 Protocol with peer Layer N Layer 1 (Physical) OSI-wide standards (e.g., network management, security) Figure 2.8 The OSI Architecture as a Framework for Standardization Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 4 / 22

5 OSI Reference Model Introduction OSI Reference Model Application Provides access to the OSI environment for users and also provides distributed information services. Presentation Provides independence to the application processes from differences in data representation (syntax). Session Provides the control structure for communication between applications; establishes, manages, and terminates connections (sessions) between cooperating applications. Transport Provides reliable, transparent transfer of data between end points; provides end-to-end error recovery and flow control. Network Provides upper layers with independence from the data transmission and switching technologies used to connect systems; responsible for establishing, maintaining, and terminating connections. Data Link Provides for the reliable transfer of information across the physical link; sends blocks (frames) with the necessary synchronization, error control, and flow control. Physical Concerned with transmission of unstructured bit stream over physical medium; deals with the mechanical, electrical, functional, and procedural characteristics to access the physical medium. The OSI Layers Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 5 / 22

6 Introduction OSI Reference Model (Cont.) Physical Layer Physical characteristics of interfaces and media Representation of bits Data rate - number of bits per second Synchronization between sender and receiver Line configuration - point-to-point or multi-point Physical topology - bus/star/ring/mesh Transmission mode - simplex/half duplex/duplex Data Link Layer Framing Physical addressing - local address Flow control Error control Access control Network Layer Logical addressing - global address Forwarding Routing Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 6 / 22

7 Introduction OSI Reference Model (Cont.) Transport Layer Service-point addressing Segmentation and reassembly Connection control Flow control Error control Session Layer Dialog Control Synchronization Presentation Layer Translation Encryption Compression Application Layer Enabling users to access the network services/resource Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 7 / 22

8 Introduction OSI Reference Model (Cont.) Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 8 / 22

9 Introduction OSI Reference Model ISO OSI Protocol Stack Visit for more details on the OSI Reference Architecture (Cont.) 7: Application Application services (SIP, FTP, HTTP, Telnet, ) 6: Presentation Data translation (MIME) Encryption (SSL) Compression 5: Session Dialog control Synchronization 4: Transport Reliable (TCP) Real-time (RTP) 3: Network Source-to-destination (IP) Routing Address resolution 2: Link 1: Physical MAC Wireless link (WiFi) Wired link (Ethernet) Radio spectrum Infrared Fiber Copper Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 9 / 22

10 Introduction OSI Reference Model (Cont.) Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

11 Introduction OSI Reference Model (Cont.) Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

12 TCP/IP Protocol Stack Introduction Internet Protocol OSI TCP/IP Application Presentation Application Session Transport Network Data Link Physical Transport (host-to-host) Internet Network Access Physical A Comparison of the OSI and TCP/IP Protocol Architectures Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

13 Introduction Internet Protocol (Cont.) MIME BGP FTP HTTP SMTP TELNET SNMP TCP UDP ICMP IGMP OSPF RSVP IP BGP = Border Gateway Protocol FTP = File Transfer Protocol HTTP = Hypertext Transfer Protocol ICMP = Internet Control Message Protocol IGMP = Internet Group Management Protocol IP = Internet Protocol MIME = Multipurpose Internet Mail Extension OSPF = Open Shortest Path First RSVP = Resource ReSerVation Protocol SMTP = Simple Mail Transfer Protocol SNMP = Simple Network Management Protocol TCP = Transmission Control Protocol UDP = User Datagram Protocol Some Protocols in the TCP/IP Protocol Suite Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

14 Introduction Internet Protocol (Cont.) User data Application byte stream TCP header TCP segment IP header IP datagram Network header Network-level packet Protocol Data Units (PDUs) in the TCP/IP Architecture Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

15 Introduction Performance Metrics Data Rate : Number of bits per second Throughput: Amount of data transmitted over time Latency = Transmission Time + Propogation Time + Queuing Time Transmission Time: Time to emit the data on to medium = DataSize DataRate Propgation Time: Time taken to propagate bits from the Distance transmitter to the receiver = SpeedOfLight Speed of Light in Vacuum m/s Speed of Light in Copper m/s Speed of Light in Fiber m/s Round Trip Time is roughly 2 Latency BDP (Bandwidth Delay Product) aka Data Rate Latency Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

16 Packet Switching Technologies Switching Technologies (a) Circuit switching (b) Virtual circuit packet switching (c) Datagram packet switching Call request signal propagation delay User data processing delay Call accept signal Acknowledgement signal Call request packet Pkt1 Pkt2 Pkt3 Pkt1 Pkt2 Pkt3 Pkt1 Pkt2 Call accept packet Pkt1 Pkt2 Pkt3 Pkt1 Pkt2 Pkt3 Pkt1 Pkt2 Pkt3 Pkt3 Acknowledgement packet link link link Nodes: Figure Event Timing for Circuit Switching and Packet Switching Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

17 Packet Switching Technologies Virtual Circuit (VC) Switching Mainframe Personal computer C Server B D Personal computer Personal computer A Packet-Switching Network E Personal computer Solid line = physical link Dashed line = virtual circuit Figure The Use of Virtual Circuits F Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

18 Packet Switching Technologies (Cont.) (a) 3 (b) 1 (c) (d) (e) Figure Packet Switching: Virtual-Circuit Approach Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

19 2 1 Packet Switching Packet Switching Technologies (a) 3 (b) (c) (d) (e) Figure 10.9 Packet Switching: Datagram Approach Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

20 Packets on VC Packet Switching Technologies Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

21 Packet Switching Technologies (Cont.) Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS / 22

22 Packet Switching Technologies Large vs Short Packet Sizes (a) 1-packet message (b) 2-packet message (c) 5-packet message (d) 10-packet message Header 1 1 Data 2 1 Data Data Data Data Data Data Data 2 X a b Y 10 X a b Y X a b Y Data X a b Y Dr. Ramana ( I.I.T Jodhpur Figure ) Effect Computer of Packet Networks Size CS321 on Transmission Time 22 / 22