Buffer management and scheduling for TCP/IP over ATM-GFR

Today ATM technology is facing challenges from integrated service IP, IP switching, gigabit IP router and gigabit Ethernet. Although ATM is approved by the ITU-T as the standard technology in B-ISDN its survivability is still in question. Since ATM-UBR (unspecified bit rate) provides no service guarantee and ATM-ABR (available bit rate) is still unattainable for most users, many existing users have little or no incentives to migrate to ATM technology. The guaranteed frame rate (GFR) service is introduced to deal with this dilemma. The GFR can guarantee the minimum cell rate (MCR) with fair access to excess bandwidth. This paper studies various schemes to support the GFR. We have studied different discarding and scheduling schemes, and compared their throughput and fairness when TCP/IP traffic is carried. Through simulations, it is shown that only per-VC queueing with weighted round robin (WRR) can guarantee minimum cell rate. Among all the schemes that have been explored, we recommend DT-EPD (dynamic threshold-early packet discard) integrated with MCR+ (a WRR variant) to support the GFR service