Understanding Computer Communication Systems: Layered Models and IP Addressing, Slides of Web Application Development

Download Understanding Computer Communication Systems: Layered Models and IP Addressing and more Slides Web Application Development in PDF only on Docsity! Important Elements of an internet Hosts – devices which attach to networks. Generally computers but may be embedded computers e.g. printers, printer servers, routers, etc Networks – entities which provide communication capabilities to hosts. Internetworking Device – a special entity allowing information to travel from one network to another. Networking Protocols – rules of communication between hosts. Internetworking Protocols – special protocols allowing internetworking capabilities Docsity.com Layered Models  Divide and Conquer approach  Benefits of the layered model approach to understanding and design of computer communication systems  Layered means that related communication tasks are grouped together and implemented as a module or layer  Each layer communicates with only the adjacent layers  Each layer communicates with the corresponding layer in the other system Docsity.com Application layer (Presentation process)  Presentation – Provides independence to the application process from differences in data representation (syntax) such as Handles conversion between ASCII and EBCDIC  It formats the data to be presented to the Application Layer. It can be viewed as the translator for the network  It provides a common representation for data that can be used between application processes - Encoding data - Compressing data to reduce the number of bits transmitted - Encrypting data for privacy and authentication Docsity.com Application Layer (Session Process)  Session – Establishes, manages, and terminates connections (sessions) between application processes  Responsible for check pointing and recovery  It provides the means for two application layer entities to synchronize and manage their data exchange. It sets up a communication channel between two Application - or – Presentation layer entities for the duration of the network transaction, manages the communication, and terminates the connections. Docsity.com Transport Layer  The Transport Layer forms the interface between the higher application-oriented layers and underlying network- dependent protocol layers. It provides the session layer with reliable message transfer facilities  Transport Layer Provides reliable, transparent transfer of data between end points; provides end-to-end (host-to- host) error recovery and flow control  Example TCP, UDP Docsity.com Network Interface Layer • Contains the following layer functions: – Data link – Physical Docsity.com Datalink  Data Link – Provides for the reliable transfer of information across the physical link; sends blocks of data (frames) with necessary synchronization, error control, and flow control  Example HDLC, SDLC, PPP Docsity.com Datalink  The primary purpose of the Data Link functions is to provide error-free transmission of information between two end stations ‘’edge nodes’’ attached to the same physical cable or media. This then allows the next higher layer to assume virtually error-free transmission over the physical on the network media. It then manages how the flow process of the bit steam takes place to include the following: - Creates and recognizes frame boundaries - Checks received messages for integrity - Manages channel access and flow control - Ensures correct sequence and transmitted data - Detects and possibly corrects errors that occur in the Physical Layer without using the functions of the upper layers - Provides flow-control techniques to ensure that link buffer capacity is not exceeded Docsity.com End Systems and Intermediate Systems  Many times direct physical connection is not practically possible between a pair of devices – End Systems or ES in ISO jargon  Communications happens through the service of intermediates  These intermediates are called Intermediate Systems or IS  Intermediate systems may not process information at all layers  Examples of intermediate systems – repeaters, bridges, switchers, routers, gateways Docsity.com Problems with Layering  Inefficiency – each layer introduces overhead  Restrictive – layer N may need access to lower layers than N – 1  Redundancy – of functions such as flow control error handling, addressing, packetizing, and encapsulation between layers Docsity.com Internet Model – TCP/IP Roughly five layers (originally four)  Application layer (TELNET, FTP, SMTP, …)  Host-to-host, or transport layer (TCP, UDP)  Internet layer (IP)  Network access layer (PPP)  Physical layer (Fiber, UTP, Coax, Wireless) Docsity.com IP provides several services • Addressing: IP headers contain 32-bit addresses which identify the sending and receiving hosts. These addresses are used by intermediate routers to select a path through the network for the packet. • Fragmentation: IP packets may be split, or fragmented, into smaller packets. This permits a large packet to travel across a network which can only handle smaller packets. IP fragments and reassembles packets transparently. • Packet timeouts: Each IP packet contains a Time To Live(TTL) field, which is decremented every time a router handles the packet. If TTl reaches zero, the packet is discarded, preventing packets from running in circles forever and flooding a network. Docsity.com IP provides several services • Types of service: IP supports traffic prioritization by allowing packets to be labeled with an abstract type of service. • Options: IP provides several optional features, allowing a packet’s sender to set requirements on the path it takes through the network (source routing), trace the route a packet takes (record route), and label packets with security features. Docsity.com IP datagram or packet format Docsity.com The Dotted Decimal Notation • IP addresses are usually represented in a dotted decimal form (as the decimal representation of four 8-bit values concatenated with dots) • For example 128.2.7.9 is an IP address with 128.2 being the network number and 7.9 being the host number Docsity.com IP Addresses Example • The decimal format of the IP address is 128.2.7.9 • IP address is made of four groups of decimal numbers between 0 - 255 separated by dots. Docsity.com Parts of an IP Address • A part of the address designates the network numbers, and the remaining part designates the host number. So , we may say an IP address has the format NETWORK HOST • The network number part of the IP address is centrally administered by the Internet Network Information Centre (the InterNIC) and is unique throughout the Interne • IP address = < network number > <host number > Docsity.com