In the "early days" of the Internet, organisations (eg, universities) which desired Internet access purchased a "leased line" telecommunications service, allowing them to "co-operatively" connect their campus LAN to another university's LAN which already had Internet access. In Australia, circa 1991, the original AARNet (Australian Academic and Research Network) was structured in (approximately) this way.
"Leased line" is a generic term for a permanently-available point-to-point data link. The name derives from the ancient technology of renting a permanently connected "phone line" plus the necessary modems at each end.
Historically, it's interesting to note that the profitability of these "basic telecommunications services" has been in continuous decline for at least two decades: in other words, it's become less and less profitable for the major Telcos to provide just these services.
The number of B channels can be increased in multiples of 10.
The NT2 (typically a PABX) connects to a special OnRamp NT1, at a point called the T interface. An S interface can be provided on the customer side of the NT2.
Note that in the USA and Japan, the primary rate service is instead 20B+D over a 1.544 Mbps ( called a T1) bearer.
Where all of the available B channels are dedicated as a "leased line" point-to-point data service, users refer to an E1 (2Mbps) or T1 connection speed.
Such links are called "semi permanent" because they are not a "fixed" physical link within the ISDN network but a permanent call set up by the ISDN terminal equipment.
In its more recent OnRamp products, Telstra currently offers its OnRamp Xpress service. This is similar to a SPC, but charging is significantly more complicated! OnRamp Xpress charging is based on the idea of a monthly capped charge. Example:
A business purchases an OnRamp Xpress service to connect permanently to another local business:
| On Ramp 2 | $50 per month |
| Xpress 1 Plan Fee | $90 per month |
| Xpress 1 limited cap | $135 per month |
| Total Xpress charges | $275 per month |
It is based on a model whereby either LAN frames or, more commonly, higher-layer packets (such as IP datagrams) are transported through the frame relay network in a "point-to-point" manner using "permanent virtual circuits" (PVCs) to define the two endpoints, eg:
Note that frame relay standards also allow for "switched virtual circuits", but these are not (yet?) available in Australia.
Internally, the frame relay network is engineered on the basis that not all nodes will continuously attempt to transmit at their full port speed all of the time. In fact, each port is only guaranteed reliable service at an agreed "Committed Information Rate" (CIR). This is typically less than half of the actual port speed in bps.
The charge for a frame relay PVC is mainly based on the agreed CIR, and to a lesser extent on the actual port speed. To minimise the cost, some providers even allow a CIR of 0 bps.
It is possible for a frame relay user to transmit up to the port speed -- in other words, continuously. However, the network is engineered so that reliable frame delivery becomes less and less probable as the average offered data rate rises above the CIR: ultimately, the network is permitted to drop frames.
The business model for an independent retail ISP is that they have a "leased line" (eg, ISDN or frame relay) connection to another (usually larger) organisation which in turn has a connection to the various "backbone" ISPs -- ie, an organisation which is "better connected". In turn, the retail ISP provide a number of modem (or ISDN) dial-in lines which are shared amongst their retail customers. The business is based on balancing the various "backend" telcommunications services costs against a sustainable retail customer service and charging regime.
The term "point-of-presence" (POP) is used to define a geographical area where an ISP provides local-call ISP dial-in service.
For anyone contemplating setting up a retail ISP business, it's perhaps sobering to realise (see next slide) that the major "wholesale" ISPs usually also have a "retail" (or dial-in) product as well -- this leaves a relatively small "niche" for a local "ma-and-pa" operation to succeed. The fact that many have survived is testament to their obvious commitment to end-user service.
For example, Telstra Big Pond is now an (independent?) Australia-wide wholesale ISP, selling permanent links to many retail ISPs, and simultaneously competing with them in the retail market. Subtlety: in order to establish a permanent link to an ISP, a user has to negotiate with both the ISP (for Internet service) and a telco (usually Telstra) for an "access method", or physical "leased line".
On interesting observation on the Telstra (and C&W Optus) Internet (IP) services is that charging is based on volume of data received. This has some interesting implications...
In our universities, the Australian Vice Chancellors have contracted C&W Optus to provide Internet service to AARNet, the network of Australian universities. C&W Optus charges AARNet $120 per gigabyte for Australian traffic, and $180 per gigabyte for International traffic. Telstra is rumoured to charge a flat $190 per gigabyte, depending on which "plan" you choose.
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