CS5008: Internet Computing

Transcription

1 CS5008: Internet Computing Lecture 6: Protocols and Standards A. O Riordan, latest revision 2015 Some slides from Fitzgerald and Dennis, 2010

2 Networking Protocols A networking protocol is a set of rules which is used by computers to communicate with each other across a network. defines how messages are sent and received. Networking protocols may also define: media access flow control handle data with efficient pace segmentation breaking messages into smaller units of transmission addressing and routing connection establishment and termination how to start and end a message format of message detecting and dealing with loss and security. 2

3 Layering In modern protocol design, protocols are layered: set of cooperating protocols in a stack instead of a single protocol each layer only uses the functions of the layer below, and only exports functionality to the layer above this abstraction layer is a way of hiding the implementation details of a particular set of functionality protocol stacks can be implemented either in hardware or software, or a mixture of both The two most important (layered) network protocol models are ISO s OSI model DARPA/Internet model 3

4 Open Systems Interconnection (OSI) Model Created in 1984 as a framework for computer network standards for open systems Standardized by International Standards Organization (ISO) and ITU-T X.200-series recommendation Design evolved from experiences with the CYCLADES network Consists of seven layers Doesn t specify actual programming interface 4

5 OSI Reference Model 5

6 Layers of OSI Model 7: Application Layer set of utilities used by application programs 6: Presentation Layer formats data for presentation to the user and provides data interfaces, data compression and translation 5: Session Layer initiates, maintains and terminates each logical session between sender and receiver, e.g. session ids, logins 4: Transport Layer deals with issues such as segmenting the message for network transport, and maintaining the logical connections between sender and receiver 3: Network Layer deals with data transfer and routing 2: Data Link Layer deals with message delineation, flow control, error control and network medium access control 1: Physical Layer defines how individual bits are formatted to be transmitted through the network covers mechanical and electrical characteristics 6

7 DARPA/ Internet Model/ TCP/IP stack Created by (D)ARPA originally in 1970s to solve the problem of internetworking Based on Transmission Control Protocol/ Internet Protocol (TCP/IP) Widely adopted from circa 1984 Consists of 4/5 layers TCP/IP not as rigidly layered; TCP/IP emphasizes architectural principles over layering End-to-end Principle: communications protocol operations should be defined to occur at the end-points of a communications system (End-to-End Arguments in System Design, Saltzer, J. et al., ACM Transactions on Computer Systems,1984) Robustness Principle: implementation must be conservative in its sending behaviour and liberal in receiving behaviour (RFC 761 and RFC 791) 7

8 DARPA 4 Layer Model Application Layer application program interface Transport/ Host-to-host Layer responsible for establishing end-to-end connections, translates domain names into numeric addresses and segmenting messages Internet Layer IP addressing and routing Network Interface Layer much the same as Data Link layer in OSI model OSI vs. Internet/ DARPA Note: sometimes presented as consisting of 5 layers (e.g. in Stallings and Tanenbaum textbooks) with extra beign the physical layer. 8

9 Protocol Responsibility Protocol has sets of rules to define how to communicate at each layer and how to interface with adjacent layers in terms of the protocol data unit (PDU) PDU consists of user-data and protocol control info, usually a header Layer N+1 Layer N peer protocol Layer N+1 Layer N Layer N-1 Layer N-1 sender receiver 9

10 Message Transmission Using Layers sender receiver Applications Applications A receiving layer wraps incoming message with an envelope adding layer related addressing information A receiving layer removes the layer related envelope and forwards the message up Note: This diagram is Copyright John Wiley & Sons, Inc 10

11 PDUs Message Transmission Example message/ request segment packet/ datagram frame bit/ energy Note: This diagram is Copyright John Wiley & Sons, Inc

12 Initial TCP/IP Protocols 12

13 TCP/IP Protocols Today 13

14 Networking Standards Provide an agreed way for hardware and/or software systems (possibly from different companies) to communicate Help promote competition (prevent monopolies) and decrease the price Types of Standards formal standards developed by an industry or government standardsmaking body, e.g. ISO de-facto standards emerge in the marketplace and widely used; lack official backing by a standards-making body 14

15 Networking Standardization Bodies I ISO (International Organization for Standardization) technical recommendations for data communication interfaces composed of national standards orgs. based in Geneva, Switzerland ITU-T (International Telecommunications Union Telecom Group) technical recommendations about telephone, telegraph and data communications interfaces composed of representatives from each country in UN based in Geneva, Switzerland 15

16 Networking Standardization Bodies II IEEE (Institute of Electrical and Electronic Engineers) professional society; develops LAN/MAN standards IEEE 802 based in New York, USA ECMA International international, non-profit standards organization standard for medium access control (MAC) and physical layer (PHY) for wireless networks based in Geneva, Switzerland Internet Society, IETF, etc. covered later 16