28 Chapter 1 About the Passport 8672ATME Module209195-BThe VBR service provided by the 8672 module allows a previously idle channel toburst at a relatively high Peak Cell Rate (PCR) for a Maximum Burst Size (MBS)of ATM cells. If the channel exhausts its MBS, the module reduces the channel’srate to a Sustained Cell Rate (SCR). When the channel stops transmitting, itaccumulates credit towards another burst at PCR.The 8672 module also provides a UBR service for Transmitter channels. When aUBR channel is opened, there is no channel rate specified. All active UBRchannels are serviced in a round-robin queue. If no rate-shaped channel isscheduled for transmission, a single cell is sent from the channel at the head of theUBR queue.RFC 1483 SupportThe system software on the Passport 8672ATME Module supports theconfiguration of RFC 1483 LAN clients with multiprotocol encapsulation. RFC1483 supports standards-based methods of encapsulation that enable connectivitywith third-party ATM devices. Multiprotocol encapsulation provides thecapability to set up PVCs between Centillion ATM virtual ports (VPorts) andother clients based on LLC encapsulation. The current Centillion platform onlysupports bridged variations of RFC 1483.The Passport 8672ATME Module supports the following types of RFC 1483ELANs:• RFC 1483 bridged 802.3. The links can be set up within a single device orwith another switch. Multiple RFC 1483 links can be set up within oneELAN. Both LLC and NULL encapsulation are supported.• RFC 1483 routed IP and IPX. An RFC 1483 routed VLAN always containsonly one PVC, corresponding to a point-to-point link between routers. Thesoftware adds and removes the MAC header, as appropriate. Whenconfiguring an IP and IPX routed circuit, the ATM port must be the only portassigned to the VLAN.Physical descriptionThe Passport 8672ATME Module (Figure 1) is a single-slot module for thePassport 8600 Series chassis. Online LEDs indicate module operation.
