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Signaling Compression: Overview and Questions Carsten Bormann [email protected] based on slides from: Hans Hannu Jan Christoffersson Mats Nordberg Signaling Compression [email protected] [email protected] [email protected] 1 ROHC WG chairs, 2001-08-05 Visited Network UE#1 Why? Home Network I-CSCF (Firewall) P-CSCF S-CSCF 1. INVITE 2. 100 Trying 3. INVITE 4. INVITE 5. 100 Trying 6. 100 Trying 7. Service Control 8. INVITE 9. 100 Trying • Minimize connection setup delay in complex 3GPP SIP interactions • Minimize bandwidth stealing for in-call usage of SIP • The point is not saving raw bandwidth (although it does help the network!) 12. 183 Session Progress 11. 183 Session Progress 10. 183 Session Progress 13. Authorize QoS Resources 14. 183 Session Progress 15. PRACK 16. PRACK 17. PRACK 18. PRACK 19. 200 OK 20. 200 OK 21. 200 OK 22. 200 OK 23. Resource Reservation 24. COMET 25. COMET 26. COMET 27. COMET 28. 200 OK 29. 200 OK 32. 180 Ringing 30. 200 OK 31. 200 OK 33. Service Control 34. 180 Ringing 35. 180 Ringing 36. 180 Ringing 37. PRACK 38. PRACK 39. PRACK 40. PRACK 41. 200 OK 42. 200 OK 43. 200 OK 45. 200 OK 44. 200 OK 46. Service Control 47. 200 OK 48. 200 OK 49. Approval of QoS Commit 49. 200 OK 50. ACK 51. ACK 52. ACK Signaling Compression 2 53. ACK ROHC WG chairs, 2001-08-05 What are the messages to be compressed? • SIP: – Largely a lock-step protocol – Essentially RFC822 (Text) – Can carry MIME payload • SDP: – v=2 m=audio etc. (Text) – Other MIME payloads are possible (SDPng!) • Either could be encrypted, possibly partially • RTSP (for streaming), also carrying SDP • DNS, RSVP, … ??? Signaling Compression 3 ROHC WG chairs, 2001-08-05 Why not IPCOMP (RFC2393)? • Yes, why not? • IPCOMP requires IPCA – need setup protocol (IKE?) • IPCOMP does not exploit inter-packet redundancies • Implementation issue: IPCOMP goes right into IP stack • May still be good enough, though: – Preloaded dictionary with SIP terms + LZSS 2.7:1 – Can use “manual configuration” using SRV – Or we could just steal IPCOMP’s framework? Signaling Compression 4 ROHC WG chairs, 2001-08-05 Contributions • ROGER, draft-hannu-rohc-roger-01.txt • SCRIBE, draft-liu-rohc-scribe-01.txt • UDPcomp, draft-rosenberg-rohc-sip-udpcomp-00.txt • EPIC, draft-price-rohc-signaling-epic-00.txt • TCCB, draft-ziyad-rohc-tccb-00.txt Signaling Compression 5 ROHC WG chairs, 2001-08-05 Signaling Compression: Components • 1) The protocol – Message handling, • E.g. Verification of correct decompression • E.g. Usage of previous messages in the compression process • E.g. Context state handling (dictionary/codebook handling), excluding algorithm-specific aspects • 2) The actual Compression Algorithm – What to save in the dictionaries/codebooks etc.. – Compressed message representation Movable boundary • E.g. Lempel-Ziv based representations Signaling Compression 6 ROHC WG chairs, 2001-08-05 End to end (above the IP level) or per-link (below IP)? • Reordering – Link often can exclude reordering, e2e can’t • Negotiation issue – Link has PPP etc., how to negotiate e2e? – SRV-records/URL/…? – Piggy-back on security negotiation? • Encapsulation issues • How to match forward and backward direction? • What is most efficient? Signaling Compression 7 ROHC WG chairs, 2001-08-05 Profiles • Could combine – One protocol with – One or more compression algorithms (plugged in like ROHC profiles) future extensibility! Signaling Compression 8 Movable boundary ROHC WG chairs, 2001-08-05 Focus of the contributions Contribution ROGER Protocol Comp. Algo x SCRIBE X X UDPcomp x x EPIC x TCCB x X X x Larger X - more focus Signaling Compression 9 ROHC WG chairs, 2001-08-05 Contribution specifics • Requires protocol knowledge to perform the actual compression – TCCB, EPIC (but falls back to ~ LZ) • Requires protocol knowledge for message handling – UDPcomp (uses application layer acks) • Can handle message reordering between compressor and decompressor – ROGER, SCRIBE, UDPcomp, (EPIC) • Well developed acknowledgement mechanism – ROGER, SCRIBE Signaling Compression 10 ROHC WG chairs, 2001-08-05 Other metrics of the contributions Contribution ROGER (any) Where in Stack? ROHC SCRIBE (any) ? UDPcomp (any) EPIC TCCB Signaling Compression Applicability Above UDP BNF (but falls (ROHC back) or above) SIP (RFC822) (Above UDP) 11 I-D EncumSize bered? (KB) 65 Yes 176 * Yes 27 31 Yes 62 Yes *) Not counting performance data ROHC WG chairs, 2001-08-05 Questions to the WG • Should it be done? – 3GPP wants it by R’5 (Dec 2001) • Should it be done here? – Will not be done in SIP WG any time soon! – Creation of new WG may take too long – Should not prejudice technical decision by WG choice • Discuss this in the light of the known solution space! Signaling Compression 12 ROHC WG chairs, 2001-08-05 Questions to the presenters • What is the specific point of your proposal? – Is it protocol or algorithm or both? – How do its characteristics influence the WG decision? • How would it work with the other proposals? – Possible protocol/algorithm combinations? Signaling Compression 13 ROHC WG chairs, 2001-08-05