72 CHAPTER 1: ATM AND DSL INTERFACE CONFIGURATIONlow transmission cost feature of DSL. So far, DSL technologies have been widelyadopted for broadband accessing.ATM interfaces available for the low-end and mid-range routersSo far, the low-end and mid-range routers can provide the following ATMinterfaces:■ IMA-E1/T1■ ATM E3/T3■ ATM 25.6 Mbps■ ATM OC-3c/STM-1 based on SONET/SDH■ ATM ADSL based on the ADSL technology■ ATM GSHDSL based on the GSHDSL technologyThese interfaces support IPoA, IPoEoA, PPPoA, and PPPoEoA. For moreinformation about them, refer to “ATM Configuration” on page 127.ATM interface featuresThe ATM interfaces support:■ Nonreal-time variable bit rate (nrt_VBR)■ Real-time variable bit rate (rt_VBR)■ Constant bit rate (CBR)■ Unspecified bit rate (UBR)■ Permanent virtual circuit (PVC)■ Per-VC traffic shaping■ User-to-network Interface (UNI)■ RFC1483 Multiprotocol Encapsulation over ATM Adaptation Layer 5■ RFC1577 Classical IP and ARP over ATM■ F5 end to end loopback OAM■ ATM adaptation layer 5 (AAL5)IMA-E1/T1 InterfaceConfigurationThis section covers these topics:■ “Overview” on page 72■ “Configuring an ATM E1/T1 Interface” on page 73■ “Configuring an IMA Group” on page 73■ “ATM IMA-E1/T1 Interface Configuration Example” on page 74■ “Troubleshooting ATM IMA-E1/T1 Interfaces” on page 75Overview Inverse multiplexing for ATM (IMA) technology distributes an ATM cell stream overmultiple low-speed links on a cell by cell basis and reassembles the cells into theoriginal stream at the far end. It is a cheap way for you to transmit high-speedATM cell streams over low-speed links while allowing for great flexibility.
