1. 1 Transport of AAL1 Frames over PSN draft-davari-pwe3-aal12-over-psn-01.txt Shahram Davari Senior Product Research Engineer PMC-Sierra March 2003

2. 2 PMC-Sierra Changes Made to PDU mode in ATM Encap draft l Removed the requirement to reassemble fragments at the egress PE -Replaced FRAG bits with UU-bit l This change improves the PDU mode -By not re-ordering the OAM cells -By not introducing excess delay -By not requiring reassembly buffer l This change actually made PDU mode applicable to other AAL types

3. 3 PMC-Sierra Why is the Draft Informational? l It reuses the ATM transport modes of ATM Encap draft (Martini) -N:1 cell mode (mandatory), 1:1 cell mode and PDU mode (optional) l It does not introduce any new protocol -Except L&R bits for (PSN) failure indication, and -Packet loss handling due to congestion -Which should actually be added to ATM Encap draft

4. 4 PMC-Sierra Raised Issues & Proposed Solutions 1)How can we ensure correct AAL1 operation after packet loss? -Concatenate N cells per packet where N<8 -Can tolerate random packet loss -Replace the lost packets with pre-configured dummy packets -Optionally use interpolation to conceal packet loss -Requires detailed knowledge of customer traffic -ATM AIS generation at egress PE does not help.

5. 5 PMC-Sierra Raised Issues & Proposed Solutions 2)Won’t the ATM OAM transparency result in variable packet sizes, which is undesirable for AAL1 clock recovery? -Not for N:1 and 1:1 cell modes -Two choices for PDU mode: -Don’t send OAM cells -Delay OAM transmission until after transmission of a pre-configured fixed-size packet -May cause OAM cell mis-ordering

6. 6 PMC-Sierra Suggestion for Moving Forward l Add the proposed solutions to raised issues to the draft l Add PSN failure and packet loss handling to ATM encap draft l Accept this draft as an informational WG draft