kozel@milano.cisco.com (Edward R. Kozel) (09/24/90)
PRIORITY QUEUING FEATURE LETS CISCO ROUTERS IMPROVE SERVICE ON LOW-BANDWIDTH SERIAL LINES MENLO PARK, Calif., Sept.18, 1990 -- Cisco Systems has added to its internetwork router/bridges a software feature that lets users assign priorities to classes of data sent over a network, thereby maximizing service on low-bandwidth congested serial interfaces. Cisco's new "priority output queuing" feature is a mechanism for prioritizing datagrams, typically classified by protocol (e.g., TCP, DECnet, AppleTalk, bridging) or sub-protocol (Telnet, FTP, LAT, electronic mail) type. It is designed as a flexible way to let the user specify the data types most important to his application (e.g., TCP/IP, over DECnet, terminal traffic over file transfer) and ensure that those types are transmitted first over an interface. Cisco, whose router products also support concurrent bridging, is the first vendor to offer priority queuing for both routed and bridged protocols. According to Doug Tsui, manager of product marketing, priority output queuing addresses the problem of heavily loaded, low-bandwidth serial interfaces, generally 56 Kbps or slower. "The serial lines linking wide-area multi-purpose networks often get bogged down with large numbers of file transfers occurring simultaneously with interactive terminal traffic such as Telnet or LAT sessions," Tsui said. "Not only is response time for terminal traffic traditionally low, but in the case of LAT, for example, there is a maximum timeout of 255 milliseconds; if an acknowledgement isn't received by then, the session terminates. Priority output queuing solves this problem by letting the user give LAT priority over all other traffic." Priority queuing addresses operational as well as technical issues, Tsui said. "Suppose a company has set up a multiprotocol WAN. Department A, the company's R&D lab using TCP/IP, has bought and installed all the routing equipment, and wants to ensure that its critical design data have top priority on available bandwidth. Priority queuing in effect establishes grades of service, 'favoring' TCP/IP packets so they get switched before DECnet packets from another department." Tsui noted that priority queuing is especially useful in international networks, where bandwidth is often most expensive. Priority output queuing works by classifying datagrams according to various criteria and queuing them on one of four output queues. When the router is ready to transmit a datagram, it scans the priority queues in order, from highest to lowest, to find the highest-priority datagram. When that datagram has been transmitted, the queues are scanned again. Priority output queuing will be available as a standard feature (no extra cost) with cisco routers shipped beginning in November. Existing units can be upgraded under cisco's software maintenance program. [boilerplate deleted....]