Download Signaling Compression

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]
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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
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53. ACK
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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, … ???
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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?
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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
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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
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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?
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Profiles
• Could combine
– One protocol
with
– One or more compression algorithms
(plugged in like ROHC profiles)
 future extensibility!
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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
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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
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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)
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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!
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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?
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