Transcript Document
ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 6. Network Model 1 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Why Network Protocol Models? • Network communication is an extremely complex task • Need cooperative efforts from all nodes involved • A standard model helps to describe the task of a networking product or service • Also help in troubleshooting by providing a frame of reference 2 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Who define Network Model? • Need non-profit making organizations • ISO - International Standards Organization e.g. OSI, MPEG-1, 2, 4, etc. (http://www.iso.ch/) • IEEE - Institute of Electrical & Electronic Engineers e.g IEEE 802, IEEE 754, etc. (http://www.ieee.org) • ITU - International Telecommunication Union e.g. V.34, H.323, H.324, etc. (http://www.itu.int) 3 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model The OSI 7-layer Model • OSI - Open Systems Interconnection • Defined in 1984 and become an international standard 4 All People Seem Away To Throw Need Data Not Do Processing Please Pizza Sausage ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Layered Architecture • Layering specifies different level of functions and services • Each layer works with the layer below and above it • Each layer provides services to next layer • Shield the upper layer from the details of actual implementation 5 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Relationship of OSI layers Virtual Communication Physical Communication 6 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Protocols in a layered architecture • Network communication is possible only if machines speaking the same languages (protocols) • Since each layer work independently, each layer speaks different languages (protocols) • Lead to the concept of a Protocol Stack • Network communication is possible only if the Protocol Stacks on two machines are the same 7 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model • To identify the language (protocol) of each layer, identifier (header and trailer) are added to data 8 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 1. Physical Layer Example protocols: Ethernet, Token Ring (Physical part) Appl. Appl. Pres. Pres. Sess. Sess. • Max/min electrical voltage? Tran. Tran. • Responsible for transmitting bits from one computer to another Netw. Netw. Data. Data. Phys. Phys. • Define how cable is attached to the Network Adapter Card • How many pins in the connector? • The impedance? 9 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 2. Data Link Layer Example protocols: Ethernet, Token Ring • Make data frames Frame • Provide error-free frame transfer by acknowledgment and retransmission 10 Appl. Appl. Pres. Pres. Sess. Sess. Tran. Tran. Netw. Netw. Data. Data. Phys. Phys. ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 11 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 3. Network Layer Example protocols: IP, IPX • Logical address to physical address translation For TCP/IP running on Ethernet Logical address: IP address 158.132.148.99 Physical address: Ethernet address 00 00 E2 15 1A CA • Determine the route from source to destination computer 12 Appl. Appl. Pres. Pres. Sess. Sess. Tran. Tran. Netw. Netw. Data. Data. Phys. Phys. ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 13 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 4. Transport Layer Example protocols: TCP, SPX, NWLink • Ensure packets are delivered error free, in sequence Appl. Appl. • Translate between packets and message Pres. Pres. Sess. Sess. Receiving Sending Tran. Tran. Netw. Netw. Data. Data. Phys. Phys. 1 14 3 2 2 3 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 5. Session Layer Example application program: Winsock, UNIX Socket • Establishment, maintaining and release of session Appl. Appl. Pres. Pres. • Provide dialog management Sess. Sess. • Regulate which side transmit, Tran. when, for how long (Sync.) Netw. Tran. • Provide synchronization between user tasks 15 Netw. Data. Data. Phys. Phys. ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model What is a Session? A. Consecutive sessions on a transport layer connection 1 2 3 C. Both 1 16 2 3 B. Consecutive sessions on a multiple transport layer connections 1 2 3 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 6. Presentation Layer Example application program: redirector (NT), SSL • Translate data from Application Layer to the format suitable for session layer (the network) • Provide data encryption, compression • Changing or converting character set, graphic, and file format 17 Appl. Appl. Pres. Pres. Sess. Sess. Tran. Tran. Netw. Netw. Data. Data. Phys. Phys. ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model 7. Application Layer Example protocols: FTP, Telnet, HTTP • Entry point for application to access network Appl. Appl. Pres. Pres. • Directly support user applications Sess. Sess. Tran. Tran. Netw. Netw. Data. Data. Phys. Phys. • E.g. File transfer, email • General capabilities: Network access, flow control, Error recovery 18 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Example: File Transfer • The most traditional network task • Implemented by a simple Application Layer protocol called FTP FTP Client FTP Server PictureTel Network 19 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Utility: WS_FTP 20 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model PictureTel WS_FTP FTP Client FTP FTP Layers 5-7 Layers 5-7 Layer 4 TCP TCP Layer 4 Layer 3 IP IP Layer 3 Ethernet Ethernet Layers 1,2 21 FTP Server Layers 1,2 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model The 802 Project Model • IEEE launched the Project 802 in 1980 February • Predate the ISO standard, but the development was performed in roughly the same time • Objective: To clearly define the network standards for different kind of physical components of a network - the interface card and the cabling • Enhance the Data Link and Physical layers of the OSI model 22 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model IEEE 802 Categories 802.1 802.3 802.4 802.6 Internetworking 802.2 Logical Link Control (LLC) Carrier-Sense Multiple Access with Collision Detection (CSMA/CD) LAN (Ethernet) Token Bus LAN 802.5 Token Ring LAN Metropolitan Area Network (MAN) 802.7 Broadband Technical Advisory Group 802.8 802.9 802.10 802.12 Fiber-Optic Technical Advisory Group Integrated Voice/Data Networks Network Security 802.11 Wireless Networks Demand Priority Access LAN, 100 BaseVG-AnyLAN 23 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Enhancements to the OSI Model • Divide the Data Link layer into 2 sub-layers • Logical Link Control Sub-layer • Define the use of service access points (SAPs) as an interface for higher layer to Data Link layer • Media Access Control Sub-layer • Directly interface with the network card • For delivering error-free data communications 24 ENG224 INFORMATION TECHNOLOGY – Part I 6. Network Model Logical Link 802.1 Control 802.2 (LLC) Media Access Control (MAC) 25 802.3 802.4 802.5 802.12