Transcript
Networking Principles & Strategy
Integrated Services Digital Networks (ISDN)
Learning Objectives l l l l l
l World-wide network providing end-to-end digital communications supporting a wide range of services, to which users have access through a standard user interface l Signal includes data, voice, and still and moving images l On-demand availability
Discuss key Internet Access Technologies Introduce ISDN Introduce ADSL Introduce Cable Modems Indicate upcoming Internet Access Technologies
l ISDN concept has existed for more than 20 years, but has been surrounded by controversy, and implementation at national level has been slow l BT in UK has been pioneering and now offers ISDN nation-wide, but uptake has been slower than anticipated CI
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ISDN (2)
ISDN (3)
l ISDN terminal adapter / controller (the ISDN equivalent of a modem) should be used to connect to an ISDN network Ÿ ISDN terminal adapters /controllers are available as either expansion cards or stand alone units l A regular phone can be also attached through an ISDN adapter to be come an ‘ISDN phone’ l To connect an entire LAN to ISDN there are three options: Ÿ ISDN/LAN Gateway Ÿ ISDN/LAN Bridge/Router Ÿ ISDN/LAN Server
l ISDN offers both X.25 packet switching and traditional circuit switching (mainly for voice) l Twisted pair can be used for ISDN link from a residential or business subscriber to the main ISDN network l Stack Compression: Service provider controlled intermediate systems (such as routers) can offer real time compression of transferred data l Typically, network charges are irrespective of amount of data transferred Ÿ Charges are based on the call duration
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ISDN – Conceptual View
ISDN Channel Types and Options l Three channel types: B, H, D l B - 64 Kbps l H0 - 384 Kbps (=6B) l H11 - 1.544 Mbps (=23B+1D64) l H12 - 2.048 Mbps (=30B+1D64) l D - 16 & 64 Kbps (Control Data) l 2B64+D16=144 Kbps (Basic Service Option) l 23B64+D64=1.544 Mbps (North America and Japan) l 30 B64+D64=2.048 Mbps (Europe) CI
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Networking Principles & Strategy
Two Main Types of Services
Broadband ISDN (B-ISDN)
Basic Rate, or ISDN 2 l 2 Bearer channels, 64 Kbps l 1 Delta channel 16 Kbps l Available since 1991, 90% availability l Aimed at smaller users l One advantage of ISDN2 is it can be installed over existing telephones lines Primary Rate, or ISDN 30 l 30 Bearer channels, 64 Kbps l 1 Delta channel for dialing instructions l Has been available since mid 1980’s l Aimed at large users, although now offered at relaxed terms 47
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Broadband ISDN (B-ISDN) (2)
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ISDN Applications
l Three B-ISDN services are currently offered:
Ÿ Full duplex channel at 155.2 Mbps Ÿ Full duplex channel at 622.08 Mbps Ÿ Asymmetrical service with two simplex channels (Upstream: 155.2 Mbps, downstream: 622.08 Mbps)
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l Second generation set of standards for ISDN l Support for global, content rich, multiple participants communications Ÿ e.g. B-ISDN appropriate for video services such as video-on-demand l B-ISDN is a circuit-switched service that uses ATM (i.e. a packet based network protocol) to transfer data l Typical line rates: 155-600 Mbps Ÿ Only technology available for widespread support of such rates is optical fibre
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l Data transfer l Group 4 fax l Desktop and video conferencing l Teleworking l Accessing information services l Video surveillance l EPoS networks for retail sector l Graphics and CAD/CAM transfer l Incidental e-mail l ad hoc LAN to LAN connections CI
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Benefits of ISDN
Product Availability
l Cost savings l Increased flexibility for varying user patterns l Offers a wider range of services l Improved quality and reliability l Future oriented network
ISDN compatible products are now emerging l ISDN PC card l Group 4 fax l ISDN modem, linking ISDN and analogue Up to 8 devices (phone, fax, computer, video conferencing terminal) can be connected to ISDN2 and any 2 can communicate at any one time Standards CCITT recommendations for I-series
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Networking Principles & Strategy
Problems with ISDN
xDSL
l Relatively high initial setup costs l Need to be extra vigilant with running costs Ÿ Cost of each connection is only a phone call Ÿ However, difficult to control when calls are made Ÿ £10000 for three office business in 6 month period
l Digital Subscriber Line (xDSL): Family of encoding schemes which offers high transfer rates over conventional telephone lines Ÿ Duplex transfers are supported Ÿ Range from HDSL to VDSL l Asymmetric Digital Subscriber Line (ADSL)To be implemented in the UK in early 2000 Ÿ Faster downloads than uploads Ÿ Speeds up to 8 Mbps downstream (to the user) and up to 1 Mbps upstream l ADSL sends information in packets l ADSL delivers permanent, unmetered connection CI 414
§ More expensive than installing leased lines
Ÿ Need to configure involved servers in a very detailed fashion § e.g. increase the connection interval to the mail server
l Has already lost momentum partly due to unsuccessful pricing policies
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Digital Subscriber Line (2)
Digital Subscriber Line l Digital Subscriber Line (DSL) is one of the most promising technologies now being implemented to significantly increase the data rates over traditional telephone lines l Historically, voice telephone circuits have had only a limited capacity for data communications because they were constrained by the 4 kHz bandwidth voice channel l Most local loop telephone lines actually have a much higher bandwidth and can therefore carry data at much higher rates
l DSL services are quite new and not all common carriers offer them l Two general categories of DSL services have emerged in the marketplace Ÿ Symmetric DSL (SDSL) provides the same transmission rates (up to 128 Kbps) in both directions on the circuits Ÿ Asymmetric DSL (ADSL) provides different data rates to (up to 640 Kbps) and from (up to 6.144 Mbps) the carrier’s end office. § It also includes an analogue channel for voice transmissions
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ADSL (2)
ADSL l ADSL networks are set up so that every connection is private Ÿ Bandwidth does not decrease as number of users increases l ADSL uses radio frequencies for simultaneous transmission Ÿ Over 250 separate radio channels capable of transmitting simultaneously Ÿ Frequencies used are much higher than humans can hear § Voice channel left free; Telephone call is possible with simulta neous data transmission
l More susceptible to intensive and frequent attacks since it is permanent on Ÿ Packets designed to crash PCs, activate trojan horses, to exploit security weaknesses in Windows etc. CI
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l High levels of security should be implemented from the outset l ADSL could be used for: videophones, high-quality music online, software upgrades, browsing e-commerce sites etc. Ÿ Value added services have been announced l Kingston Communications to offer first commercial UK ADSL service Ÿ Digital television, Video On Demand (VOD), fast Internet access etc. l ADSL Modems necessary to maintain connection DL: The Operation of ADSL Based Networks - K Drive CI
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Networking Principles & Strategy
Customer Premises DSL Modem
Local Carrier End Office Main Distribution Frame
Line Splitter
Voice Telephone Network
ADSL Data Rates
Local Loop
Type
Maximum Length of Local Loop
Maximum Downstream Rate
Maximum Upstream Rate
Hub
Telephone
Computer
Computer
Customer Premises
ATM Switch
DSL Access Multiplexer
ISP POP
T1
18,000 feet
1.5 Mbps
384 Kbps
E1*
16,000 feet
2.0 Mbps
384 Kbps
T2
12,000 feet
6.1 Mbps
384 Kbps
E2*
9,000 feet
8.4 Mbps
640 Kbps
ISP POP
ISP POP
* E1 and E2 are the European standard services similar to T1 and T2 services in North America
ISP POP Customer Premises
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Very High Rate Digital Subscriber Line (VDSL)
Anticipated VDSL Data Rates
l VDSL is a high-speed member of the DSL family, designed for local loops of 1000 feet or less. l Its three FDM channels are:
Type
Ÿ 4 KHz analogue voice channel Ÿ Upstream digital 1.6 Mbps channel Ÿ Downstream digital 52 Mbps channel
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Maximum Length of Local Loop
Maximum Downstream Rate
Maximum Upstream Rate
1/4 OC-1
4,500 feet
12.96 Mbps
1.6 Mbps
1/2 OC-1
3,000 feet
25.92 Mbps
2.3 Mbps
OC-1
1,000 feet
51.84 Mbps
2.3 Mbps
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Upcoming Access Technologies Cable Modems l One potential competitor to xDSL is the cable modem Ÿ In essence, cable modems are used to provide a digital service offered by cable television companies Ÿ The service offers an upstream rate of 1.5-10 Mbps and a downstream rate of 2-30 Mbps l Few cable companies offer downstream services only, with upstream communications using regular telephone lines
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l Fixed and mobile wireless access technologies becoming more and more popular Ÿ Fixed solutions usually involve the use of dish-based microwave technologies Ÿ Mobile solutions make use of cell phone technologies and the wireless application environment (WAE) l Passive Optical Networking (PON) Ÿ PON, also called Fibre to the Home will unleash the potential of optical fibre communications to end users Ÿ With Wavelength Division Multiplexing hundreds or thousand of channels are possible Ÿ Passive optical doesn’t require electricity to split signals into channels, lowering thus the cost, but limiting its maximum distance (10miles maximum) CI 424
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Networking Principles & Strategy
Upcoming Access Technologies (2) l Ethernet to the Home Ÿ Gives home users 10BaseT or 100BaseT connections Ÿ Yipes.com has already implemented this service in several large US cities Ÿ The common carrier installs TCP/IP routers with 10BaseT or 100BaseT connections into a customer’s network and an Ethernet fibre on the other side to move the traffic from the router into the carrier's Ethernet MAN (and then onto the Internet)
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