PPP Over AAL2

1. PPP Over AAL2 draft-buffam-avt-crtp-over-aal2-01.txt B. Thompson, B. Buffam, T. Koren Cisco Systems San Diego, December 2000

2. Status • CRTP over AAL2 Presented at AVT in Pittsburg draft-buffam-avt-crtp-over-aal2-00.txt Encapsulation Required a New AAL2 SSCS Needed Work in the ITU for New AAL2 SSCS • CRTP over AAL2 Presented in ITU T1S1 Encapsulation Modified to not Require New AAL2 SSCS I.366.1 or I.366.2 Frame Mode Application Modifications allowed Generalization to “PPP over AAL2” • CRTP over AAL2 Generalized to PPP over AAL2 Application of I.366.1 SSSAR Small, Long Packet CRC Added CRTP Packet Type >> PPP Payload Type

3. Status • PPP over AAL2 Presented in ITU SG13 Valid Application of I.366.1 SSSAR List of ITU Actions Determined Q.2630 Signaling Modifications to Identify Application Needed for Dynamic AAL2 SVC Creation New SSCF for This Type of Application Layer Below Application, Above I.366.1 SSSAR Defines use of I.366.1 UUI for Application Not Required for IETF Standardization No Action to be Taken Unless Draft Moves Forward in IETF • PPP over AAL2 Being Presented at PPPEXT in San Diego draft-buffam-avt-crtp-over-aal2-01.txt

4. Bandwidth Efficient Alternative to PPP over AAL5 Uses AAL2 instead of AAL5 for Link Layer Transport More Bandwidth Efficient for Small Packets Uses AAL2 CPS Function for Multiplexing Removes Cell Pad Overhead More Efficient than AAL5 when Average Packet Size < 440 Bytes RTP Voice Transport is Typical Application RTP (RFC 2508) Header Compression Reduces Packet Size Application of I.366.1 SSSAR SSSAR Provides Fragmentation/Reassembly for Long Packets CRC Added as Part of Application 2 Byte CRC for Short Packets 4 Byte CRC for Long Packets New I.366.1 SSCF will Provide CRC Functionality Use Separate AAL2 CIDs for Short/Long Packets Provides Link Fragmentation Interleave (LFI) for Short Packets PPP over AAL2

5. AAL2: SSCS and CPS P1 P2 P3 PPP Packets I.366.1 SSCS: Segmentation to CPS-packets CPS- packet header P1 CPS- packet header P2 CPS- packet header P3 CPS: Multiplex ATM HDR O S F CPS- packet header P1 CPS- packet header P2 ATM HDR O S F P 2 CPS- packet header P3 PAD 5 48 5 48

6. CID - Channel Identifier (8 bits) Identifies the substream within the AAL2 connection LI - Length Indicator (6 bits) UUI - User to User Indication (5 bits) Carries information between the SSCS HEC - Header Error Control (5 bits) AAL2 CPS Packet Header CPS- packet header P1 CID LI UUI HEC 3 bytes 8 6 5 5

7. PPP over AAL2 UUI Code Points

8. PPP over AAL2 - Short Packet PPP payload PPP Packet CPS-Packet CID1 LI UUI 2, 27 HEC PPP Prot ID PPP payload CRC CPS-header (3) CRC (2) CPS-Info Used for Packets <= 256 Bytes UUI code point 27 = Frame Mode Data, More to Come UUI code point 2 = Final Packet, 2 Byte CRC

9. PPP over AAL2 - Long Packet PPP payload PPP Packet CPS-Packet CID2 LI UUI 3, 27 HEC PPP Prot ID PPP payload CRC CPS-header (3) CRC (4) CPS-Info Used for Packets > 256 Bytes UUI code point 27 = Frame Mode Data, More to Come UUI code point 3 = Final Packet, 4 Byte CRC

10. Comparison with PPP over AAL5 • More Bandwidth Efficient for Small Packets • Removes Cell Pad Overhead AAL2 Timer_CU Determines Level of Cell PAD • AAL2 Overhead = 3 * Length / 64 (CID, LI, UUI, HEC) + Length / 48 (Start) + 2 (CRC) • AAL5 Overhead = 8 (AAL5 Trailer) + 24 (Cell PAD) • More Efficient than AAL5 when Ave Packet Size < 440 Bytes

11. Comparison with PPPMUX/AAL5 • PPPMUX/AAL5 Bandwidth Multiplexed Payloads Framed with AAL5; Cell Pad PPPMUX/AAL5 OverHead = 2 (PPPMUX Len, Prot ID) + 8 / SF (AAL5 Trailer) + 24 / SF (Cell PAD) SF = PPPMUX Samples / Frame • PPPMUX/AAL5 Delay PPPMUX Packets not sent/received until full AAL5 frame is available AAL2 Packets sent when ATM cell is filled AAL2 Packets received when ATM cell arrives • PPMUX/AAL5 Loss Single lost ATM cell causes loss of whole AAL5 Frame Lost ATM cell causes loss of AAL2 packets in cell

12. Issues / Additional Work • CRC Best CRC Algorithm Minimum CRC Length for Short Packets Are Two CRC Lengths Needed? 0 Byte CRC Option? • Optimized Encapsulations Could Save One Byte / Payload by Using Additional AAL2 UUI Values Represent Some PPP Payload Types with AAL2 UUI Values Removes PPP Payload Type Multi-Protocol Encapsulation over AAL2? Requires Definition of CRTP over AAL2?

13. PPP over AAL2 - Optimized Encapsulation PPP payload PPP Packet CPS-Packet CID2 LI UUI HEC PPP payload CRC CPS-header (3) CRC (2-4) CPS-Info

14. END

15. Protocol Stack +---+---+---+---+--+ + | Application A | | +---+---+---+---+--+ | | RTP | | +---+---+---+---+--+ +---+---+---+---+---+ Application | UDP | | Application B | | +---+---+---+---+--+ +---+---+---+---+---+ | | IP | | IP | | +---+---+---+---+--+ +---+---+---+---+---+ + | | +---------------+------------+ | | +---+---+---+---+---+--+ + | Compression Filter | | +---+---+---+---+---+--+ | | | | | +---------+-----------+ | | | | Compression | | Non-Compression | Interface V | Interface | +---+---+---+---+---+---+ | | | CRTP | | | +---+---+---+---+---+---+---+---+---+---+---+---+ Transport | PPP | | +---+---+---+---+---+---+---+---+---+---+---+---+ | | | +---+---+---+---+---+--+ | | Length Filter | | +---+---+---+---+---+--+ | | | +-----------------+----------------------+ | | | | +---+---+---+---+---+---+---+ +--+---+---+---+---+--+--+-+ | |Short Encapsulation (SSSAR)| |Long Encapsulation (SSSAR)| | +---+---+---+---+---+---+---+ +--+---+---+---+---+--+--+-+ | | | | | CID 1 | CID 2 | | | | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | | AAL2 CPS | | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | | ATM Layer | | | +---+---+---+---+---+---+---+---+---+---+---+---+---+---+ +