Transcript Chapter 1
Chapter 1 Read (again) chapter 1 Why use networks? Resource sharing Reliability Cost CSC-3352 Computer Communications Chapter I 2 Network Hardware: Type of Transmission Broadcast Multicasting Point-to-point CSC-3352 Computer Communications Chapter I 3 Network Hardware: Metropolitan Area Networks (MANs) On the level of a city There are no switching elements Example: Distributed Queue Dual Bus (DQDB) standardized under 802.6 Source Hosts Source CSC-3352 Computer Communications Chapter I 4 Network Hardware: Wide Area Networks (WANs) Large Geographical area Switching elements (p.s. nodes, I.S, or Data switching exchanges, router) CSC-3352 Computer Communications Chapter I 5 Network Hardware: Topologies Main characteristics? CSC-3352 Computer Communications Chapter I 6 Network Hardware: Wireless Networks Wireless does not mean mobile, and mobile does not mean wireless Wavelan, Cellular Digital Packet Data (CDPD) 802.11 CSC-3352 Computer Communications Chapter I 7 Network Hardware: The OSI Reference Model What is it? Who created it? Why was it created? What is it used for, today? CSC-3352 Computer Communications Chapter I 8 Network Software: Protocol Hierarchy or Layered Design Host 1 Layer 3 protocol Layer 3 Host 2 Layer 3 Layer 2/3 Interface Layer 2 protocol Layer 2 Layer 2 Layer 1/2 Interface Layer 1 protocol Layer 1 Layer 1 Physical Medium CSC-3352 Computer Communications Chapter I 9 OSI - The Model A layer model Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers CSC-3352 Computer Communications Chapter I 10 OSI as Framework for Standardization CSC-3352 Computer Communications Chapter I 11 Network Hardware: The OSI Reference Model Host A Application Interface Presentation Interface Session Interface Transport Interface Network Interface Data link Interface Physical CSC-3352 Computer Communications Application Protocol Presentation Protocol Session Protocol Transport Protocol Network Protocol Data link Protocol Physical Protocol Chapter I Host B Application Presentation Session Transport Network Data link Physical 12 Network Hardware: The OSI Reference Model Host A Application Interface Application Protocol (End to End layer) Presentation Protocol (End to End layer) Presentation Interface Presentation Session Protocol (End to End layer) Session Interface Transport Session Transport Protocol (End to End layer) Interface Network Protocol Network Interface Data link Protocol Data link Interface Physical Host B Application Physical Protocol Routing the packets over the net(s) CSC-3352 Computer Communications Chapter I Transport Network Data link Physical 13 The OSI Reference Model... CSC-3352 Computer Communications Chapter I 14 The OSI Reference Model... CSC-3352 Computer Communications Chapter I 15 The Physical Layer Transports raw bits, Defines the physical (electrical and mechanical) specifications Characteristics of transmission medium Signal levels Data rates etc. Example: RS232, V24, V35, X.21, ISDN... CSC-3352 Computer Communications Chapter I 16 The Data Link Layer Has 2 main functions Error detection and correction MAC (Medium Access Control) Examples:SLIP, PPP, Ethernet, HDLC, SDLC CSC-3352 Computer Communications Chapter I 17 The Network Layer Has 3 main functions addressing routing some congestion control Examples: IP CSC-3352 Computer Communications Chapter I 18 The Transport Layer It is an end-to-end layer, dealing with flow control congestion control may offer end-2-end reliability Examples: TCP, UDP. CSC-3352 Computer Communications Chapter I 19 The Session Layer - Used for : • session management • Synchronization CSC-3352 Computer Communications Chapter I 20 The Presentation Layer Concerned with “compatibility” (encoding) encryption (security purposes) CSC-3352 Computer Communications Chapter I 21 The Application Layer It is communication software directly accessible to the user Examples: FTP, Telnet, Network Virtual monitor, HTTP…. CSC-3352 Computer Communications Chapter I 22 Summary on OSI layers... The International Organization for Standardization (known as ISO, an abbreviation taken from its name in French) has devised a model for the design of communication protocols (known as the open systems interconnection (OSI) model). In this model each communicating entity has seven layers of protocol. The bottom layer (1) is known as the physical layer, and it essentially corresponds to the wire. The next layer (2) is known as the data link layer. It provides the means for putting data on the wire (and for taking it off). An example is ethernet. The next layer (3) is known as the network layer. Its primary responsibility is to see that the data travels to the intended destination (perhaps via a number of intermediate points). The next layer is known as the transport layer. Its job is to see to it that the data, which is transferred between machines by the network layer, reaches the desired party at the destination machine. The notion of a “connection” is maintained by this layer. The next layer is known as the session layer. This layer doesn’t really do very much (if anything); it is responsible for maintaining the notion of a “session.” Sessions might be in one-to-one correspondence with transport connections; there might be two successive sessions on the same connection; or one session might span multiple connections (e.g., the first connection was terminated due to a communication failure, the session continues as soon as communication is reestablished). The next layer is known as the presentation layer. Its job is to deal with the fact that different machines have different representations for data (i.e. it must somehow translate between data representations) and to deal with such concerns as compression or encryption of data. Finally, the application layer is where all other software resides. However, it has been discovered that there is “system software” that logically fits above the presentation layer. The only place to put it is in the application layer, so “real” application software sits on top of the application layer. The bottom three layers are sometimes known as the communications subnet. If our data must pass through a number of machines on their way to the destination, each intermediate machine has an implementation of these lower layers to forward the data on. CSC-3352 Computer Communications Chapter I 23 TCP/IP Protocol Suite Dominant commercial protocol architecture Specified and extensively used before OSI Developed by research funded US Department of Defense Used by the Internet CSC-3352 Computer Communications Chapter I 24 Telnet TCP UDP Telnet TCP UDP IP Ethernet Protocols CSC-3352 Computer Communications IP Ethernet Chapter I Application Transport Internet Services Physical link 25 OSI versus TCP/IP Application Transport Network Physical link CSC-3352 Computer Communications Chapter I 26 TCP/IP Protocol Architecture(1) Application Layer Communication between processes or applications End to end or transport layer (TCP/UDP/…) End to end transfer of data May include reliability mechanism (TCP) Hides detail of underlying network Internet Layer (IP) Routing of data CSC-3352 Computer Communications Chapter I 27 TCP/IP Protocol Architecture(2) Network Layer Logical interface between end system and network Physical Layer Transmission medium Signal rate and encoding CSC-3352 Computer Communications Chapter I 28 PDUs in TCP/IP CSC-3352 Computer Communications Chapter I 29 Some Protocols in TCP/IP Suite CSC-3352 Computer Communications Chapter I 30 Network Standardization What is it ? Why ? How is it done ? Who does it? CSC-3352 Computer Communications Chapter I 31 Big Standards Organization International standards ITU (International Telecom. Union) old CCITT ISO IEEE Internet Standards IAB IRTF, IETF CSC-3352 Computer Communications Chapter I 32 Conclusion You must be pretty familiar with: the layered view of a communication system know the function of each layer the mapping of communication protocols to the layers chapter 1 in textbook CSC-3352 Computer Communications Chapter I 33