New T-1 bundles bridge gap to T-3

A practical solution to this problem is to bundle readily available, inexpensive copper lines, thus forming a virtual multimegabit access path that has the high throughput and low latency of a single high-speed circuit and bandwidth equivalent to the aggregated lines. For example, four bundled lines would behave as one circuit with approximately four times the throughput and one-fourth the latency of a single line.

T-1 provides an excellent source of affordable and available copper lines because of its existing tariffs, guaranteed symmetrical transport, secure connectivity and ease of maintenance. However, established methods of bundling multiple T-1 circuits do not provide the cost-effective, high-performance, bandwidth-efficient means needed for large-scale deployment of a new multimegabit service.

This situation has driven the search for a new class of products able to break through the performance bottleneck of previous packet-based multilink solutions. To accomplish this breakthrough, the prospective products must bundle multiple T-1 circuits at wire speeds, using standards-based Multi-Link PPP (MLPPP) and Multi-Link Frame Relay (MFR) protocols.

For strong performance and low latency, these products need to segment packets into fragments and transport each fragment over a separate member of the T-1 bundle. At the other end of the link, the fragments will be reassembled after compensating for up to 128 msec of differential delay between the T-1s. The packet fragments must maximize the bandwidth available for customer IP traffic while avoiding the bandwidth inefficiencies associated with technologies such as Inverse Multiplexing over ATM. All T-1s in the bundle also must be highly efficient to provide truly plug-and-play performance, but the arrangement must not require load balancing or packet tuning.

The increased robustness available from a packet-based, multiple-link technology is critical for this new brand of bundled lines because the multilink virtual multimegabit access path must continue to operate reliably even if one of the links in the bundle is experiencing error, test or failure conditions. Removing the problem circuit from the bundle, decreasing the bundle bandwidth accordingly, and then reinstating the circuit once the anomaly has cleared will solve the reliability issue. Standards-based MLPPP and MFR protocols provide methods to ensure bundle recovery when individual circuits have problems, increasing overall network reliability.

To create a virtual multimegabit access path between an end user and a service provider point of presence requires multilink customer access and POP aggregation equipment. The equipment must fit seamlessly into the current network infrastructure to maximize its use while reducing overall deployment costs.

This next generation of multimegabit access products will enable ISPs to offer a new service, generate new revenue and differentiate themselves from competitors. ISPs will be able to layer services such as virtual private networks and quality-of-service agreements on top of this new service. The virtual multimegabit access path will let service providers offer business subscribers that have reached the limit of T-1 access a practical and affordable way to migrate to higher speeds without making the huge leap to T-3.