Transcript chapter8.pps

WAN and Internet
Access
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Introduction
What is Wide Area Networking?
 How Internet access works
 Types of telecommunications services
 How to determine Internet access needs
 Steps in implementing a WAN connection
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What is Wide Area Networking?
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A WAN is a network that is created using the services of
the telephone company to connect LANs separated by
large geographical distances
WANs require the use of special WAN protocols and
devices
These protocols are usually part of a company’s Internet
access
WANs introduce a new level of complexity to
internetworking – such as coordinating with outside
organisations eg your telecommunications provider
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WANs (2)
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Characteristics are:
– Connections are low bandwidth, with speeds from 56kbps to
2Mbps
– A single Wan connection is shared by all devises on the LAN
(bottleneck) – sometimes a second link is installed for the sake of
redundancy
– WANs cover a large geographical area
– WAN technologies include Point-to-Point Protocol (PPP),
Asynchronous Transfer Mode (ATM), ISDN, DSL, dial-up access
and Frame Relay
– WAN devices include routers, modems and WAN switches
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How Internet access works
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Having set up the Internet at home you have
in effect established a WAN
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Internet Access at Home
Initiate Dialup Software
 Commands sent to modem
 ISP is dialled
 Modem uses ‘local loop’ – pair of copper
wires
 Signal goes to Local Exchange
 A Switch forwards the call to the often
distant ISP
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Internet Access at Home (2)
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Internet Access at Home (3)
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Between the Exchange and the IPS is a
multichannel trunk
Calls are multiplexed on that link
Calls are demultiplexed and separated to modems
in a bank
The user’s modem and the modem in the bank
handshake – a speed is established and data
transferred
High speed Internet connections for a company is
not too dissimilar to this
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Planning Internet Access
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How will the connection be used ?
How important is the connection to the company ?
What infrastructure already exists ?
Balance need for bandwidth, reliability of
connection, quality of service provider, quality of
telco, cost
Future Applications ?
– Video Conferencing/Streaming
– E-Commerce
– Virtual Private Network
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Telecommunications Services
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Circuit Switching
– ‘Creates’ channels as required
– Essentially for voice data
– Passive
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Packet Switching
– Transfer of data between two points over a shared
medium
– Sends packets across the network using the ‘best’ path
– Burst-like in nature – an efficient solution
– Cost is based upon usage
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WAN Technologies
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Point-to-Point Protocol
– Advantages
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Well tested and implemented
Offers excellent throughput
Supports most network protocols
Simple to implement
– Disadvantages
» Less flexible for rapidly expanding multiple sites
» ‘Expensive’
» Requires dedicated leased lines
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ISDN
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Touted as the solution to residential and SMEs in the ’80s as
a means of providing integrated data/voice
Due to costs has not been widely adopted
Advantages
– Runs on existing phone lines
– Supports voice, data and fax on one line
– Good for video conferencing
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Disadvantages
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Comparatively expensive
Only provides 128K – can go up in multiples
Less flexible for growth and cost than other WAN technologies
Not available everywhere
Can be ‘difficult’ to implement
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Digital Subscriber Line (DSL)
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‘New’ technology
Best option for Residential/SME customers
Asymmetrical DSL (ADSL) and Symmetrical DSL
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Now becoming affordable
Good download speeds
Runs over normal copper line
Data and voice can be simultaneous
Disadvantages
– ‘New’ means has yet to establish a reliability track record
– Not available everywhere –BT have introduced satellite broadband
(at a a price !)
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Data over Cable
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Standard – Data Over Cable System Interface Specification
(ITU-T J.112)
Known as cable-modem technology
Good Bandwidth/price ratio (cheap)
Provided by cable TV companies
Advantages
– Speeds up to 10Mbps
– Uses existing TV cable
– Cheap
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Disadvantages
– Not available in all areas
– Shared medium – speeds can drop
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Frame Relay
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Introduced in 1992
Communicates faster than X.25 (because it does not have
error correction)
Advantages
– Widely adopted, International
– High Capacity switched core offers scalability
– Flexible, allows expansion and growth
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Disadvantages
– Minimal error correction
– Connection-oriented service, can cause latency on slow links
– ‘Expensive’
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What To look Out For
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Do Research – Plan !
Read the small print – what do you get for your money
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ISP Setup Fee
Hardware Costs
Telecoms Installation Fee
Monthly/Annual Line Rental
No. of Fixed IP Addresses
Domain Name Service
Web Space
Email Addresses
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Moving To A New Service
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No current service – employees have no expectations
New Service (Transition)
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99% Uptime expected
No downtime apparent to clients
All services to be moved to new ISP
Resolve problems of Domain Name, email, Web etc
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Plan
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Establish contacts (names, phone, email) for all key
players
Plan with your account manager at the new ISP
How long will InterNIC take to fulfill Domain Name
Registrations
Order equipment well in advance, confirm delivery dates
Arrange check of new lines
Plan deployment of IP addresses
Install equipment – Check !
Submit new registration to InterNIC
Move to the new ISP outside office hours
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