Cisco Announces New Router Features for IBM Network:

Mixed-Media, Local Acknowledgement, LAN Manager Support

MENLO PARK, Calif., Jan. 13, 1992 -- A comprehensive set of features thatsupport internetworking in IBM environments -- including mixed-mediacommunication, local acknowledgement for token ring interfaces, and supportfor IBM's LAN Network Manager-- has been added to Cisco Systems' internetworkrouter/bridges.

The new features, available in March, comprise the third phase of Cisco's IBMinternetworking strategy, which was announced in January 1991.

Don Listwin, Cisco's marketing manager for IBM connectivity, said, "The trendwe recognized when we first defined our five-phase IBM strategy -- the mergingof parallel SNA and non-SNA networks in organizations to reduce costs andsupport -- is more pronounced today than ever. IBM environments have gonebeyond SNA to become multiprotocal, and beyond point-to-point connections toinclude LAN-based schemes with router backbones. Cisco has worked closelywith customers to adapt its original five-phase plan as these new environmentshave evolved."

Phase III adds five new features to Cisco's router/bridge software: SDLLC (TM)(SDLC-to-token ring conversion), local acknowledgement for token ringinterfaces, translational bridging between token ring interfaces,translational bridging between token rings and Ethernets, source-routetransparent (SRT) bridging, and support for IBM's LAN Network Manager.

SDLLC: SDLC-to-Token Ring Conversion

Cisco's new SDLLC feature permits communications between two IBM media, serial(with the synchronous data link control protocol, SDLC), and token ring (withthe LLC2 protocol). SDLLC protects the user's investment in serially-attachedIBM 3274 cluster controllers and other SDLC devices that are not upgradable tothe token ring capability found in newer SNA networks.

The CISCO router performs conversion between IBM hosts on token ring networksand IBM devices attached to serial lines, translating between LLC2 and SDLC.Thus a ring-attached IBM front-end processor and a serially-attached clustercontroller communicate with each other-- unaware that each is connected to adifferent medium running a different protocol. Cisco's remote source-routebridging software is also utilized when the two IBM machines are separated bya WAN backbone.

Cisco is "the first router vendor to implement SDLLC in software, " Listwinsaid. "SDLC-to-token ring conversion, which previously required a separatehardware unit costing $10,000 or more, now can be implemented for the price ona serial line."

Local Acknowledgement Eliminates Wide-Area Delays

LLC2, IBM's data-link protocol used in token ring networks, was designed toinsure reliable transmission of data across LAN media having minimal timedelays. But the advent of WAN backbones and remote source-route bridging hasmeant separating LANs by great distances, thus creating delays that are longerthan LLC2 allows for a response by the receiving host. Data transmissionsacross slow serial backbones, especially when they involve multiple hopsand/or X.25 networks, can result in multiple retransmissions and the ultimateloss of user sessions.

A unique "local acknowledgement" capability in CISCO router/bridges solvesthis problem. For example, when data is sent between two hosts separated by aWAN, the LLC2 session initiated by Host A terminates at the local router,which sends that host an acknowledgement within the prescribed time limit. ToHost A, the acknowledgement seems to come from Host B. The data is then sentover the WAN to host B.

An alternative to local acknowledgement is to change timing configurations onall networked nodes -- a complex and time-consuming process, especially inlarge internetworks.

Translational Bridging for Ethernet-Token Ring Communication

More and more, users are calling for linkages between Ethernet workstationnetworks and token ring PC networks. For routable protocols (e.g., TCP/IP,IPX, OSI), media translations can be performed. But bridging the nonroutableNetBIOS and SNA protocols raises problems, because Ethernet and token ringhave different bridging models -- "transparent" versus "source-route"bridging. The two network types also differ in other ways: e.g., token ringframes carry a routing information field (RIF), while Ethernet frames do not.IBM's solution has been a hardware unit called the 8209, a two-port bridgethat connects one Ethernet to one token ring by translating frames.

Cisco now incorporates 8209-like translational bridging functionality intorouter software, allowing mixed-media bridging between Ethernets and tokenrings with no changes to already installed bridges or end nodes. The routeracts as a gateway between the source-route-bridged token ring world and thetransparently bridged Ethernet world, either stripping the RIF from the framefor transmission to an Ethernet, or retrieving the RIF from cached data fortransmission to a token ring.

Source-Route Transparent Bridging: The Emerging Bridging Standard

Cisco also supports another means for bridging Ethernet and token ringnetworks: source-route transparent (SRT) bridging, based on the IBM-drivenannex to the IEEE 802.1D standard.

"SRT extends Ethernet's transparent bridging model to token rings,"Listwin said, providing a single bridging algorithm for both types ofnetwork and eliminating the bridging software overhead in PCs. A majorbenefit of SRT is that it will allow true standards-based interoperabilityin large installations having a mix of Ethernet and token ring LANs."

Cisco is the only router vendor to support both bridging methods --translational and source-route transparent -- in its router/bridge products.Both can be freely intermixed on router interfaces and use concurrently withmultiprotocol routing.

Cisco Routers Gain Link to LAN Network Manager

LAN Network Manager (LNM) , IBM's PC-based software for managing a group ofsource-route bridged token rings, now links to a Cisco router, monitoring andmanaging any token ring connected to that router.

Cisco has implemented bridging support for the LNM proprietary protocolthatruns atop an LLC2 connection to gather data from token rings in a bridgednetwork. Configuring the router as a source-route bridge automatically allowsthis nonroutable protocol to reach across the router to collect such data fromrings on the other side. In addition, information from these rings now has apath through LNM to Netview, IBM's SNA network management system.

"The network administrator can now manage the backbone-attached part ofhis network using familair LNM tools, rather than learning new SNMP tools,"Listwin said.

As with an IBM bridge, the Cisco router equipped with LNM support keeps trackof current token ring logical configurations and reports changes to LNM,monitors errors reported by any station on the ring and whether or not thering is functional, ensures that all stations on the ring are using consistentreporting parameters, and reports when a new station joins the ring.

Pricing /Availability

The five new IBM internetworking features will be available in March 1992 aspart of the bridging software option for Cisco routers.

Cisco Systems, Inc., is the leading supplier of high-performance, multimediaand multiprotocol internetworking products, including routers, bridges,terminal servers, and network management software. Cisco technology can beused to build enterprise-wide networks linking an unlimited number ofgeographically dispersed LANs. Cisco is publicly traded over the counterunder the NASDAQ symbol CSCO.