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
REDIRECTION
APPLICATION
OPERATING
SYSTEM
CPU
NETWORK
INTERFACE
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
80386
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
OS/2: 3.0%
Linux: 17.2%
Others: 2.4%
Windows NT: 35.8%
Unix: 17.4%
Netware: 24.2%
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
FAT CLIENT
FAT SERVER
SERVER PROCESSING
CLIENT PROCESSING
CENTRALIZED
STAND-ALONE
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
Single
Machine
Find
students
enrolled
Print roll
Client/Server
Server
Client
Find
students
enrolled
Server
stub
Print roll
Client
stub
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 UNIXbased 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)
Constant Bit Rate (CBR) Real time voice & video
Variable Bit Rate – real
time (rt-VBR)
Variable Bit Rate – non
real time (nrt-VBR)
Available Bit Rate (ABR)
Unspecified Bit Rate
(UBR)
Compressed video &
LAN
LAN internetworking
Non mission critical
bursty Traffic
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 Charges
Committed Bandwidth
Peak Bandwidth
Discard Priority
Latency
Representative Prices
per MB of traffic (Qwest, Dec. 98)
Frame Relay
Non-discard eligible
Discard eligible
4 cents
3 cents
ATM
Constant bit rate
Variable bit rate (real-time)
Variable bit rate (non real-time)
Available bit rate
Unspecified bit rate
2 cents
1.2 cents
.75 cents
.55 cents
.4 cents
Representative Prices
per port (Qwest, Dec. 98)
56 Kb Frame Relay
T-1 Frame Relay
$1,595
T-3 Frame Relay
$3,190
$190
Networks