Transcript IACT 424/924 The Design Process: Choosing Typologies and

IACT 424/924
The Design Process: Choosing
Typologies and Architectures
William Tibben
SITACS
University of Wollongong
23 September 2002
Overview
• Lecture first looks at why architectures are
important in the design process. Essentially deals
with the network from a logical aspects (Protocols,
name and addressing, etc)
• Then the lecture looks to why topologies are
important in the design process. Essentially deals
with the physical aspects of
– hardware provisioning and
– dimensioning
• Bandwidth
• Equal hops between network edges
In summary,
• Architectures and topologies are an essential
component of the design process.
• They provide:
– a method by which we can judge whether the proposed
system will the meet the needs that have been identified
– the network will be adequately provisioned in both
hardware and software
– An effective means to communicate to others what the
network consists
– A framework for ongoing network management and
fault rectification
Definitions-Architecture
Architecture: "A set of rules or outlines
needed to perform functions according to
user needs"
Communications Network Architecture:
"A set of design principles on the basis of
which a communications network is
designed and implemented to satisfy enduser needs over a period of time"
Definitions-Architecture cont’d
• A telecommunications network architecture is a
set of design principles used as a basis for the
designing and implementation of a network. It
simply describes ‘what’ will be built - it does not
say ‘how’.
• Architecture is a term applied to both the process
and the outcome of thinking out and specifying the
overall structure, logical components, and the
logical interrelationships of a network
Architectures-A Tool for Design
• A Network Architecture is an important element of
the design process and documentation
• For example how can one make sense of the
following list?
• HTTP, Frame Relay, Ethernet, PICT, TCP, IP, IPX, FTP
(File Transfer Protocol), MPEG, SMTP (Simple Mail
Transfer Protocol), Appletalk, UDP (User Datagram
Protocol), ICMP (Internet Control Monitoring Protocol),
Telnet, TIFF, NFS (Network File Server, SQL (Structured
Query language), DNS (Domain Name Server), JPEG
• Answer: By categorising these protocols and
applications according to the OSI Model
Architectures-A tool for Design
• The OSI Model is an example of an architecture that can
be used to map various protocols for better understanding.
Telnet, FTP, HTTP, SMTP, DNS
PICT, TIFF, JPEG, MPEG, MIDI Quicktime
NFS, SQL, X-Window System, Appletalk
TCP, UDP
IP, IPX, ICMP
Ethernet, Frame Relay, X.25
Architectures-Network
Management
• Implementing a network management
system is made possible by the use of an
architecture
• The architecture allows you monitor and
manage a complex network in a reliable and
consistent fashion
Network Management
• A network management system allows viewing of
the entire network as a unified architecture:
– With addresses and labels assigned to each network
element
– With specific attributes of each network element and its
connectivity known to the system
• The active elements of the network provide
regular feedback of status information to the
network control centre
Generic Architecture for Network Management
System
Source: Terplan, 1992, p. 77
Decentralised architectures
• There is a trend from centralised management
systems (as indicated by Terplan, previous slide)
to ones that give end-users greater control
• This gives departmental (local) level managers the
tools they need to maintain responsive networks,
systems and applications for their local end users
• This is done through SNMP (Simple Network
Management Protocol)
SNMP Architecture
(Terplan, 1992, p. 90)
SNMP
• Agent: local software program that stores
management related data and responds to a
manager’s request for data
• A manager is a software program that has the
ability to query agents by using various SNMP
commands
• Management Information Base (MIB): is a virtual
database of managed objects, accessible to an
agent and manipulated via SNMP to achieve
network management
Definition - Topology
• The physical arrangement of network nodes
and media within a network structure .
Examples of Topologies
•
•
•
•
Ring
Bus
Star
Tree, hierarchical, pyramid
(controversial)
Extended Star Topology
Topologies as a Design Aid
• Topologies are used in the design phase to
enable:
– The provision of hardware and network
bandwidth to all corporate functions
– The modularisation of the network into “bitesize” pieces.
Hardware and Bandwidth
Provisioning
Branch
Offices
Accounts
Marketing
Head Office
Network
Support
1 Gbps
links
Finance
Sales
Branch Office
100Mbps
link
Modularisation of the Network
The network can be layered in the following way
Core
High Speed Switching
Distribution
Access
Policy-based Connectivity
Local and Remote
Workgroup Access
Modularisation of the Network
Advantages
• Allows “measured” bandwidth allocation within
each layer
• Separate network elements can be associated with
specific facilities thereby promoting ease of
understanding(ie lower training costs).
• Improved fault isolation. (Too many
interconnections create complexity where a
change to one part of the network can have effects
in other parts)
Modularisation of the Network
Advantages
Naming and addressing schemes assume a
hierarchy
e.g
UoW IP address is 130.130.0.0
SITACS Staff IP group no. is 130.130.64.0
My PC’s IP address is 130.130.64.152
Core Layer - Backbone
•
•
•
•
•
Generally talking about WAN
High Speed
High Reliability
Redundancy
Low latency
– Time between service request and the service being
granted
– Delay between the receipt of a frame and the time it is
forwarded on
• Minimal packet manipulation (filtering)
Core Layer - Backbone
WAN
Dedicated
Lease lines:
T1/E1
T3/E3
(Point to Point
Protocol)
Switched
Circuit
switched
Packet/cell
switched
Dial-up modem
(ISDN
ADSL)
(X.25
Frame Relay
ATM)
Diameter
The number of router hops between router
edges is described in terms of diameter
1. The number of router hops from endstation to end-station across the backbone
should be equal
2. The distance from any end station to a
server should be consistent
Distribution Layer – Policy
Based Connectivity
• Interface between LANs and WAN
• Interface between LANs,VLANs
• Information Access Policy is enabled
– Who is allowed access to what
• Demarcation between static and dynamic
routing
Distribution Layer – Policy
Based Connectivity
• Security is deployed
– Who is allowed access to what
– Protection from non-authorised external traffic
• Router can filter traffic on the basis of source and
destination address
• Filtering in specific input and out ports of router
• Hiding internal network numbers
• Static routing
Firewall
(Teare, 1999, p. 103)
Access Layer
• User access to LANs
• Switched and shared bandwidth networks
(eg Ethernet)
• Microsegmentation of LANS occurs at
Access layer to limit collision domains and
enable high bandwidth provision to specific
groups
Redundancy
• Redundancy should be designed into your network
if your business relies on critical systems or
provides critical services.
• Router redundancy
– Hot Standby Router Protocol (HSRP) is a CISCO
protocol that enables IP workstations to keep using the
internetwork should its default router fail. Essentially is
a system where 2 or more routers communicate with
each other using HSRP. Should one fail the other router
takes over it load
Server Redundancy
• Server Redundancy
– Mirrored file servers should be used for critical
systems such as brokerage firms
– Servers should be on separate networks and
power supplies
Route Redundancy
• Route Redundancy can be achieved by
using a full mesh or partial mesh
architecture
• Full mesh is where every router is
connected to each other
– The number of links required make it an
expensive solution
– There is considerable overhead because of the
number of routing table updates that must occur
Route Redundancy
• Partial mesh is a more practical solution
Headquarters
1.5Mbps
Regions
64kbps
Branches
Media Redundancy
• Redundant links are most relevant to WANs
• Can be a different technology – Leased line
backed up by ISDN or dial up modem
• Investigate that your back up lines are not
susceptible to the same failures that your primary
path is.
Some Important Questions
• Does your company have a central office
with many branches?
– If yes, you need to be looking at hierarchical
topologies with an emphasis on WAN
technologies
– You should be looking at route redundancy to
ensure an alternative path should a WAN link
fail.
Some Important Questions
• Is it a small company that uses high
bandwidth applications (multimedia
applications as opposed to finance data)?
– If yes, you need to have high bandwidth LANs.
If this data needs to be transferred to other
places you are also looking at installing high
speed WAN links)
– Once again, hierarchical topologies are a must
to ensure bottlenecks do not emerge in use.
Some Important Questions
• Does your company rely on real time access
to critical data (eg Web CT or stock market
information)?
• If yes, you should be looking at installing
redundancy within your topology
Some Important Questions
• Does you company require on online
presence that represents an attractive site for
hackers?
• You need to consider installing security
such as a firewall.
References
• Awyzio, G. IACT 302-1999 and IACT 424-2002 Lecture Notes,
University of Wollongong
• Cisco, 2001, Cisco Academy Networking Program: Second Year
Companion Guide, Cisco Press Indianapolis.
• Teare, D. 1999, Designing Cisco Networks, Cisco Press Indianapolis.
• Terplan, C. 1992, Communications Network Management, 2nd ed.
Prentice Hall Communication Series, Englewood Cliffs, New Jersey,
USA.
• TechTarget Enterprises, 2002, Architecture-A Whatis definition,
Available from: http://www.whatis.techtarget.com. Accessed 3
September 2002.