Transcript Requirements for Resource Priority Mechanisms for the Session

Requirements for Resource
Priority Mechanisms for the
Session Initiation Protocol
draft-ietf-ieprep-sip-reqs-01
Henning Schulzrinne
Columbia University
[email protected]
IEPREP/SIPPING working group
IETF 55 (November 2002, Atlanta)
Meta-Overview
• Protocol requirement document = input to
SIP(PING) WG
– SIP may (or may not) decide to enhance or modify
protocol based on these requirements
– there’s lots of information in SIP that most parties are
free to ignore, so hopefully not too hard 
• currently, in WG last call
– SIPPING group aware of last call
– no known WG open issues
Overview
• Priority in SIP-based systems, primarily for VoIP
systems that have gateways into a CSN
(including, but not limited to, the PSTN)
– needed for emergency telecommunications systems
• Resources:
–
–
–
–
–
gateway resources (trunks)
CSN resources away from the gateway
IP network resources -- out of scope
receiving end system resources (ACD)
SIP proxy resources (sometimes)
Network assumptions
• Full control
– all aspects of the protocol stack can be tuned
• Transparent
– forwards all valid IP packets
– can't modify network elements
• SIP/RTP transparent
– SIP calls go out
– but can't rely on anything else
• Restricted SIP
– no 'unknown' header fields, methods, body types, URI
schemes, …
– 3G networks
Requirements
• REQ-1: Not specific to one scheme or country
– not just GETS or US
• REQ-2: Independent of particular network architecture
– not just, say, 3GPP
•
•
•
•
•
REQ-3: Invisible to network (IP) layer
REQ-4: Mapping of existing schemes
REQ-5: No loss of information
REQ-6: Extensibility
REQ-7: Separation of policy and mechanism
– really, abstraction  don't try to provide detailed recipe
Requirements
• REQ-8: Request-neutral
– should work beyond INVITE
•
•
•
•
•
•
•
•
•
REQ-9: Default behavior
REQ-10: Address-neutral
REQ-11: Identity-independent
REQ-12: Independent of network location
REQ-13: Multiple simultaneous schemes
REQ-14: Discovery
REQ-15: Testing
REQ-16: 3PCC
REQ-17: Proxy-visible (added)
Security Requirements
•
•
•
•
•
•
•
•
•
•
•
•
SEC-1: More rigorous
SEC-2: Attack protection
SEC-3: Independent of mechanism
SEC-4: Non-trusted end systems
SEC-5: Replay
SEC-6: Cut-and-paste
SEC-7: Bid-down
SEC-9: Confidentiality
SEC-10: Anonymity
SEC-11: Denial-of-service
SEC-12: Minimize resource use by unauthorized users
SEC-13: Avoid amplification
Call routing
• Request destination may depend on
priority indication
– different gateways (e.g., not all IXCs support
GETS)
"9-1-1" calls
• Not related to 911/112 calls
• Also, if priority is desired, destination
already identifies such calls
– reduces mistakes or attempts to subvert
Changes since 00 edition
• Clarification of role in SIP proxies
• added network configurations and their
resources (CSN-to-IP, etc.)
• clarified network constraints:
– pre-configured for ETS
– transparent
– SIP/RTP transparent
– restricted SIP/RTP
• wordsmithed policy/mechanism discussion
Next steps
• IEPREP WGLC
• Residence time in SIPPING?
• As for History, discuss initial solutions in
SIPPING?
• Charter?
A survey of the solution space
Approach
Remarks
out-of-band indicator (RSVP, etc.)
•destination may not match – destination
may depend on indicator!
•doesn't work in SIP/RTP-transparent
networks
•too late in call
new SIP method
fails REQ-8
URI parameter (tel or SIP URI), e.g.,
CPC parameter
priority is property of call, not identifier or
property of person
Call-Info header
doesn't fit: not a URL
SIP body (e.g., SDP)
can't be used by proxies (REQ-17)
header + Accept-*
seems ok
caller preferences
might also be useful; sufficient?
Generalizing the problem
• Some properties are for instance, other for AOR!
– most seem of the instance kind (even language can
vary if secretary registers for user)
• Have three kinds of properties:
– caller or calling station properties
• "operator", "prison", "payphone"
• sip:[email protected] vs.
• sip:[email protected] – currently using JFK payphone
– callee or called station properties
• registration, caller preferences
– call properties
• Priority, resource priority