OS Services And Networking Support Juan Wang Qi Pan Department of Computer Science Southeastern University August 1999

OS Services and Evolution n Typical OS Services Facilities for program creation Program execution Controlled access to I/O and files System access Error detection and response Accounting n OS evolves and expands to offer new services u In response to hardware upgrading and new types of hardware u in response to user demand u in response to the needs of system management

Why OS Services for Networking Support ? n Computer networks have revolutionize our use of computer. Almost Most computers are networking. n Network software is no longer regarded as an add- on for few users, but considered as essential as a text editor. n Many computer manufacturers package networking software as part of the basic OS. n In an information age, computer networks are becoming an integral part in the dissemination of information.

Networking Support Services n Management of network devices Network card, Modem n Access to files through networks File servers, Web pages n Access to network I/O devices Network printer, network scanner, network photocopier n Client/Server computing n Distributed process management n Network security

How Is Networking Support Provided by an OS? n Networking services has been supported by the evolution of distributed capabilities in the OS and support utilities. n Communications architecture provides support for a network of independent computers and distributed applications.

Protocol Architectures n A protocol architecture defines a set of layers and protocols. n A protocol architecture should provide a high degree of cooperation between two communicating systems n Protocol architectures u TCP/IP protocol architecture u OSI protocol architecture

TCP/IP Protocol Architecture Five independent layers: u Application Layer u Transport Layer u Network Layer u Data Link Layer u Physical Layer

n Physical layer u Defines the media, and physical aspects of the signals u Defines clocking and synchronization operations u Defines physical connectors n Data Link Layer u Supports the transfer of traffic over one link u May perform error detection and retransmission TCP/IP Protocol Architecture

n Network Layer u Performs IP packet forwarding and route discovery n Transport Layer u Supports end-to-end acknowledge of traffic u provides logic for assuring the reliability of data exchanged between hosts n Application Layer u Contains protocols for specific user applications u Contains end-user applications TCP/IP Protocol Architecture

Protocol Data Units in the TCP/IP Architecture TCP Header Network Header IP Header User data Application Byte Stream TCP Segment IP Datagram Network-Level Packet

OSI Protocol Architecture n Open Systems Interconnection n Developed by the International Organization for Standardization (ISO) n Consists of seven layers n Protocols are developed to perform the functions at each layer

OSI Layers Application Presentation Session Transport Network Data Link Physical

What’s a Network Protocol n A network protocol defines an agreement between the communicating parties on how communication is to proceed. n Peer entities should communicate based on network protocols known by each other.

Key Features of a Protocol n Syntax Concerns the format of the transferred data blocks. n Semantics Includes control information for coordination and error handling. n Timing Includes speed and sequencing.

Examples of Network Protocols n Application Layer FTP, SMTP, DNS n Transport Layer TCP, UDP n Network Layer IP, ICMP n Link Layer HDLC, PPP, Frame Relay n Physical Layer ISDN, ATM

Network and Internet n Network system for connecting computer using a single transmission technology n Internet set of networks connected by routers that are configured to pass traffic among any computers attached to networks in the set

Basic Elements of the Internet n Host The internet is an association of thousands user computers that communicate with each other through networks. A user computer is called a host. n Router (Gateway ) A router or gateway is a network device which performs the relaying functions between networks. It must decide next gateway to forward a datagram to.

A Simple Network n Individual computers are first connected to a LAN (Ethernet or Token Ring). One router device provides the TCP/IP connection between the LAN and the rest of the world.

Basic Networking Information for a Host n IP Address The IP address assigned to this host Example: n Subnet Mask The part of the IP address that distinguishes the network to which this host connects. Example: n Default Router The IP address of the router that connects this host to the rest of the world. Example:

IP Address, Mask and Routers

Network Management n Network manager or administrator is responsible for monitoring and controlling network hardware and software n Network management is a hard problem Internet is heterogeneous and large. n TCP/IP includes SNMP as network management protocol

Network Configuration n Protocol software requires configuration parameters. n Small, heterogeneous networks can use decentralized configuration. n IP uses server-based configuration BOOTP: Bootstrap protocol DHCP: Dynamic Host Configuration Protocol

Network security n Security is a problem because Internet is not owned by one entity n Organizations can use firewalls to prevent unauthorized access n Encryption and digital signatures can provide confidentiality and secure identification

Client/Server Computing n Client/server computing is the key to realize the potential of information systems and networks. n Client machines are generally single-user PCs or workstations with a highly user-friendly interface. n Each server provides a set of shared user services to the clients n The server enables many clients to share access to the same database and enables the use of a high- performance computer system to manage the database

Client/Server Computing n Involves splitting an application into tasks and putting each task on the platform where it can be handled most efficiently n Processing for the presentation on the user’s machine n Data management and storage on a server n Involves a network

Generic Client/Server Environment

How Far Will It Go? n Increasingly, computers function not in isolation but as part of computer networks. n Networking support has been regarded as basic OS services. More and more networking services will be integrated into major OS. Internet-related technologies (like Internet Explorer) have been included in Microsoft Windows OS.