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 networkNegotiate resource access with distant resources allocation softwareReceive and deliver the resources to the requesting user or programListen for resource requestsValidate resource requestsDeliver 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 passingSupport WAN interfacesSupports WAN protocols including TCP/IP

Workstation Functions

APPLICATION REDIRECTION

NETWORKINTERFACE

OPERATINGSYSTEM

CPU NIC

Client Functions

Application executionFat and thin clients

Network accessNetwork software and hardware (NIC)

Application software maintenanceRemote resources

Server NOSSoftware

Manages centralservices and externalinterfaces•Directory services•Translation protocol

Server Functions

Shared resourcesFile and print services

Application managementNetwork operating systemAccess to the networkHigher layer functions

SecurityBackup and professional support

Network Operating Systems

UNIX and LINUXNovell NetWareMicrosoft Windows NT familyOthers: OS/390, Palm, etc.

UNIX

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

LINUX

Open architecture operating systemSubstantial free upgrades and special routines are availableDeveloped by Linus Torvalds for the Intel 80386Runs on a very wide range of platformsSupported by several 3rd party companies (e.g. Red Hat, Caldera)

Windows 2000/NT/XP

32 Bit Operating System with multitasking and multi-threadingBuilt-in networkingGUI interfaceIntel based

Novell NetWare

Server operating systemIncludes global directory servicesSecurity and multi-environment functions matureRemote managementIPX 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

Windows NT: 35.8%

Netware: 24.2%

Unix: 17.4%

Linux: 17.2%

OS/2: 3.0%Others: 2.4%

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

ClientMay do some or all of the processingRequests services from the network

ServerContains data and may contain programsServer 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

CENTRALIZED STAND-ALONE

FAT SERVER FAT CLIENT

Client/Server

ScalabilityInteroperabilityUser buy-inIncreased costMulti-tier

One Tier System

Two Tier Client/Server

Three Tier Client/Server

Middleware Support of Connectivity

Middleware: Basic Services

Client/Server ConnectivityPlatform TransparencyNetwork Transparency and IsolationApplication Tool Support API’s (Application Product Interfaces such

as ODBC Open DataBase Connectivity)

Language SupportDatabase Management Support

Application Product Interface (API) Approaches

Message Oriented Middleware (MOM)Remote Procedure Call (RPC)(NetWise, NobleNet, etc.)

Database Access MiddlewareDistributed 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

Clientstub

Serverstub

Find students enrolled

SingleMachine

Client/ServerServer Client

RPC Sessions

Distributes standard code modulesProgram functions distributed between client and serverStubs manage communicationClient waits for responseSession connected by:

service port id’s + address’s

Message Oriented Sessions

More complex than RPCEach message header contains enough data to route and processMessages are queued at clientClient 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 supportMulti-threaded or single threadedNetwork impact (e.g. chattiness)QoS demandsDelivery: centralized, clien/server, web

Application Management

Standards Supported Accepted Prohibited

Version Control and DistributionLicense ManagementVirus 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 switchedFast: Speeds up to 2488 MbpsSupports Quality of Service classesUsed primarily as a backbone technology

ATM

ATM Traffic Classes (QoS)

Constant Bit Rate (CBR) Real time voice & video

Variable Bit Rate – realtime (rt-VBR)

Compressed video &LAN

Variable Bit Rate – nonreal time (nrt-VBR)

LAN internetworking

Available Bit Rate (ABR) Non mission criticalbursty Traffic

Unspecified Bit Rate(UBR)

No guarantee, e-mail,bulk file transfers

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 ChargesCommitted BandwidthPeak BandwidthDiscard PriorityLatency

Representative Prices per MB of traffic (Qwest, Dec. 98)

Frame RelayNon-discard eligible 4 centsDiscard eligible 3 cents

ATMConstant bit rate 2 centsVariable bit rate (real-time) 1.2 centsVariable bit rate (non real-time) .75 centsAvailable bit rate .55 centsUnspecified bit rate .4 cents

Representative Prices per port (Qwest, Dec. 98)

56 Kb Frame Relay$190T-1 Frame Relay$1,595T-3 Frame Relay$3,190

Networks