Networks in Operation

Computer Networks External Resources: Much of the complexity of modern networks arise from the huge quantity of distributed resources and the difficulties inherent in finding, accessing and managing those resources.

Network Software System Software must: Find requested resources on the network Negotiate resource access with distant resources allocation software Receive and deliver the resources to the requesting user or program Listen for resource requests Validate resource requests Deliver resources via the network

Network Software Operating Software Network Operating System (NOS) Server Operating System Transaction Processing Monitor (TP Monitor) Applications Systems DBMS Application Software

Network Operating Systems (NOS) Normally support both Ethernet and token passing Support WAN interfaces Supports WAN protocols including TCP/IP

Workstation Functions APPLICATION REDIRECTION NETWORK INTERFACE OPERATING SYSTEM CPU NIC

Client Functions Application execution Fat and thin clients Network access Network software and hardware (NIC) Application software maintenance Remote resources

Server NOS Software Manages central services and external interfaces Directory services Translation protocol

Server Functions Shared resources File and print services Application management Network operating system Access to the network Higher layer functions Security Backup and professional support

Network Operating Systems UNIX and LINUX Novell NetWare Microsoft Windows NT family Others: OS/390, Palm, etc.

UNIX 32 Bit Computer Operating System with networking built in Commonly a server environment Open platform system (all machines in some version) Virtual machine multi-tasking

LINUX Open architecture operating system Substantial free upgrades and special routines are available Developed by Linus Torvalds for the Intel Runs on a very wide range of platforms Supported by several 3rd party companies (e.g. Red Hat, Caldera)

Windows 2000/NT/XP 32 Bit Operating System with multitasking and multi-threading Built-in networking GUI interface Intel based

Novell NetWare Server operating system Includes global directory services Security and multi-environment functions mature Remote management IPX protocols vs. IP

OS/390 Mainframe The primary operating system used in IBM mainframes. OS/390 was originally the MVS/ESA operating system renamed and repackaged in 1996 with an extensive set of utilities. Enhancements in usability and workload balancing have made OS/390 stand apart from its MVS heritage.

Operating System Shipments in 1998

Client/Server Architecture An architecture in which the client (personal computer or workstation) is the requesting machine and the server is the supplying machine, both of which are connected via a network.

Centralized Architecture Not Scalable Low Bandwidth

Fat Client / File Server Scalability (server and client) Interoperability Needs bandwidth

Client / Server (fat client) Scalability (client) Interoperability Needs bandwidth

Three Tier Client / Server (fat client)

Web Network (thin client)

Client/Server Architecture Client May do some or all of the processing Requests services from the network Server Contains data and may contain programs Server downloads information (applications or data) to the client for operation

Basic Client/Server Component Model

Client/Server Components: Example

Client/Server Architectures SERVER PROCESSING CLIENT PROCESSING CENTRALIZEDSTAND-ALONE FAT SERVER FAT CLIENT

Client/Server Scalability Interoperability User buy-in Increased cost Multi-tier

One Tier System

Two Tier Client/Server

Three Tier Client/Server

Middleware Support of Connectivity

Middleware: Basic Services Client/Server Connectivity Platform Transparency Network Transparency and Isolation Application Tool Support API’s (Application Product Interfaces such as ODBC Open DataBase Connectivity) Language Support Database Management Support

Application Product Interface (API) Approaches Message Oriented Middleware (MOM) Remote Procedure Call (RPC) (NetWise, NobleNet, etc.) Database Access Middleware Distributed Transaction Processing (DTP) Monitors (Tuxedo, Encina, Top End, …) Object Request Broker (ORB ) (CORBA, OLE, OpenDOC, …)

Maintaining a Thread Versions of a server program for each client. Similar to the problems of multiprogramming in Operating Systems. Identifying a service  Service Identifier Identifying a client  Client and Server ID’s

Remote Procedure Call Approach Print roll Find students enrolled Print roll Client stub Server stub Find students enrolled Single Machine Client/Server ServerClient

RPC Sessions Distributes standard code modules Program functions distributed between client and server Stubs manage communication Client waits for response Session connected by: service port id’s + address’s

Message Oriented Sessions More complex than RPC Each message header contains enough data to route and process Messages are queued at client Client may process other actions

Middleware Support of Connectivity

TP Monitors (Transaction Processing Monitor) A control program that manages the transfer of data between multiple terminals and the application programs that serve them. In a distributed client/server environment, a TP monitor provides integrity by ensuring that transactions do not get lost or damaged. Examples of popular TP monitors are CICS, used on IBM mainframes and the UNIX- based Tuxedo and Encina products.

Application Software Distributed Computing Fat client and thin client Database Partitioning and replication Workgroup Meetingware and team support software Communications

Application Issues Interoperability (e.g. ODBC) OS support Multi-threaded or single threaded Network impact (e.g. chattiness) QoS demands Delivery: centralized, clien/server, web

Application Management Standards Supported Accepted Prohibited Version Control and Distribution License Management Virus detection and inoculation

Technologies Common WAN technologies.

ISDN Circuit Switched Data and Voice Service

Digital Subscriber Lines DSL uses packet switching technology that operates independent of the voice telephone system, allowing the telephone companies to provide the service and not lock up circuits for long calls.

Asynchronous Transfer Mode Cell switched Fast: Speeds up to 2488 Mbps Supports Quality of Service classes Used primarily as a backbone technology

ATM

ATM Traffic Classes (QoS)

Frame Relay Pricing Components Ports Maximum Bit Rate (56K, T1, etc.) Processing Committed Bit Rate Burst Rate (Discard Eligible)  Closed loop congestion control will not accept too high a load for the network  Open loop congestion control will discard excess packets if the network can’t process them

WAN Costs Circuit Charges Committed Bandwidth Peak Bandwidth Discard Priority Latency

Representative Prices per MB of traffic (Qwest, Dec. 98) Frame Relay Non-discard eligible4 cents Discard eligible3 cents ATM Constant bit rate2 cents Variable bit rate (real-time)1.2 cents Variable bit rate (non real-time).75 cents Available bit rate.55 cents Unspecified bit rate.4 cents

Representative Prices per port (Qwest, Dec. 98) 56 Kb Frame Relay$190 T-1 Frame Relay $1,595 T-3 Frame Relay $3,190

Networks