Broadband Internet Access Solutions Lecture 12

Definition Broadband can be defined as transferring multiple channels of (data) over a single link. A form of multiplexing In contrast baseband transmission only allows a single signal at a time on any link.

Possible Broadband Selections Always on? Shared>500Kb DSL avail? Service guaranteed Satellite or ISDN DSL via Modem Cable avail? Cable ISDNLeased Line DSL ISDN available? ISDN No Yes No

Location/Availability 97% of UK population has access to ADSL (BT claim) Increasing to 99.6% Cable has limited availability Leased Line cost can be excessive Satellite has severe cost /upload problems

Cable Utilise Fibre Optic Technology Lower Contention Costs are lower than DSL Geographic problems –limited access Offers a stable and reliable access technology Down traffic to consumer easier than getting upstream traffic from consumer

Cable broadband

DSL – Digital Subscriber Lines DSL offers the ability to access Broadband over existing copper cables DSL uses the unused bandwidth on current telephone lines Up to 2MHz is available on current telephone lines – up to 3Km distance

DSL 2 MHz minus the telephone bandwidth leaves 1.5 MHz for data. Most current solutions offer up to 2Mbps downlink with 256 kbps uplink. Contention Ratio is a problem – 10:1 is good 20:1 is adequate and up to 50:1 is acceptable.

DSL Exchange Up to 3Km Telephone DSL or ADSL Modem DSL technology uses the same physical cable for telephone and data transmission

ADSL or SDSL? Asymmetric or symmetric? ADSL allows voice and data on the cable at the same time Different upload and download speeds 256kbps, 512kbps, 1024 kbps (= 1 Mbps), and 2 Mbps kbps. (download) 256 kbps (upload) SDSL No simultaneous voice use Same upload and download speed 256kbps, 512kbps, 1024 kbps, 2048 kbps (both ways) Up to 8 Mbps available soon

Useful information News about broadband BT wholesale broadband Internet service providers association

ISDN Fully digital, integrates voice and data over a common digital technology. Requires an ISDN line and a terminal adapter (TA) ISDN2 – or basic rate interface offers 2 x 64kbits for data or voice 1 x D channel for control

Leased Line Traditional route for Business to have always-on Internet connectivity Leased lines are expensive Contention ratio is of course 1:1 This is a major attraction over DSL System set up is a non-trivial task

Leased Line Designing using leased line techniques requires skills in WAN technologies Leased lines can either use Digital Signalling level channels (DSO) Synchronous Optical Networking(Sonet) This offers a range of speed from 64 kbits/sec Up to 10 Gbits/sec

Leased Line rates Line TypeCapacity DS064 Kbits/sec DS Mbits/sec DS Mbits/sec DS Mbits/sec DS Mbits/sec OC Mbits/sec OC Mbits/sec OC Mbits/sec OC-482, Mbits/sec OC-19210GBits/sec

Satellite Location is a major problem for a broadband connection Need to be near an exchange Satellite theoretically removes the need for any physical cabling Customer Premises Satellite Interface (CPSI) is a new open standard which avoids buying a unique decoder from each supplier.

Satellite access Al-Chalabi and Stewart (Chaltel Ltd) -2001

Two-way Satellite Typical speeds – 1Mbps download 256k upload Higher speeds available

Satellite footprint

One-way satellite Current system require two connections A coaxial feed from the receiver disk A telephone connection The use of a tunnelling protocol allows the phone link to identify the consumers request to the ground station and hence onto the satellite downlink.

Satellite Latency Latency on such a system is very high 0.25 seconds for the 35,000 km link to the satellite 56 kbps maximum on the phone link. basic browsing not ideal for serious users of multimedia.

Questions left unanswered Broadband – what technology will be used in the future? Unbundling the local loop! Will this enhance the adoption of DSL technology What is the impact on all this for Multimedia?

Conclusions Broadband is needed for more utilisation of multimedia on the Internet. Consumers or Business influence on the technology adoption for broadband very limited. It is probable that it will be Broadband Service Providers and the Infrastructure Providers that will have the most influence.