Phase 3 Upgrade to T3 Network Completed

Following the successful deployment of serial interface cards on all T3 routers during May, hardware upgrades at regional sites using FDDI will begin in late August. These modifications will increase performance and enhance the stability of the network.

Since the completion of the May deployment, all of the backbone-connected midlevel networks not previously sending their traffic through the T3 network have been moved. Migration of the remaining agency networks and international interconnections is expected to be completed by the end of August and planning is underway to dismantle the older T1 backbone.

T3 interfaces improve performance

Between April 27 and May 23, the scheduled "Phase III" upgrade to the T3 network took place. All of the T3 adapters,  DSUs, RS/6000 planar boards, and cables were replaced with newer technology.

"The T3 network has been extremely reliable since November 1991," said Mark Knopper, manager of Internet Engineering at  Merit. "The RS/960 upgrade has enhanced network capacity such that the impact of moving the NSFNET traffic from T1 to T3 has been negligible."

The recent hardware upgrade is based upon an adapter technology known as RS/960 which supports on-card packet forwarding to other adapters connected across the IBM RS/6000 microchannel. The RS/6000 host is used as a network controller for route computation and network management. This technology supports up to five T3 interfaces per router. Packet rates over 10,000 pps with 200 bytes/packet and data throughput approaching 22.5 Mbps have been observed in routine testing on the independent ANS/Merit/IBM/MCI T3 test network, where the routers and circuits are configured similar to the production network.

Jordan Becker, Vice President for Network Services at ANS, which provides NSFNET backbone services under subcontract to Merit, noted that appraising router performance is not a straightforward task, and measurements of packets per second alone should not be used to evaluate the routers, or to compare them to other vendors' products:

"Approaching peak throughput on the T3 network requires carefully controlled conditions and applications that are specifically tuned to match the operating characteristics of the network," said Becker. "The performance that is currently observed by individual end users on the T3  network is generally more dependent on local access to the network rather than the high-speed backbone. However, some local networks can already access the backbone at more than 10 Mbps and technologies that achieve greater throughput in these cases are being tested.

Extensive monitoring of traffic loads

Merit's Knopper points out that the NSFNET engineering staff performs extensive monitoring of traffic loads and peaks,  routing table integrity, and other factors contributing to observed performance. "Any problems causing performance degradation are quickly identified and corrected. The staff  also assists regionals in identifying problem sources which occur external to the backbone," he stated.

Users should contact their network administrators if performance problems are suspected in any part of the Internet. "There is a high degree of communication among the various network engineers and problems can usually be resolved quickly when reported," Knopper said. "Merit engineering staff will be happy to assist with problems that are difficult to resolve at the local level," he added.

FDDI upgrade scheduled

The throughput that may be achieved by users of the T3 backbone will improve dramatically with the forthcoming FDDI upgrade which is scheduled to begin in August. The process will replace the older FDDI cards with RS/960 FDDI interfaces following extensive testing on the test network. The two-phase plan for the interface replacements reflects a conservative approach to upgrade deployment ensuring continued network stability.

Taken from The Link Letter, Vol. 5 No. 2, September/October 1992.