1. QoS control by means of COPS to Support SIP-based applications
S. Salsano, L. Veltri
IEEE Networks, March/April 2002
R 賈　立 R 黃文彬
R 陳育成 R 陳奕安

2. Contents Introduction
The COPS role for Dynamic DiffServ resource allocation
Definition of the COPS Interfaces
IP Telephony : A COPS Based QoS model
Implementation Testbed
conclusion
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3. What is QoS What is quality of service?
What does it take for the Internet to support QoS?
Existing Internet QoS architectures:
Integrated services, differentiated services, and MPLS overview.
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4. What is QoS User point of view: Relaxed definition:
Assurance of end-to-end service.
E.g. Guaranteed delay (VoIP), Guaranteed bandwidth (VPN)
Relaxed definition:
Service differentiation: different packets is treated differently.
end-to-end service guarantees may be achieved by provisioning.
e.g. only a small portion of high priority packets.
Existing IP networks only support best effort service. Adding service differentiation is non-trivial.
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5. What is QoS(Cont.) Applications that need QoS Common QoS parameters:
VoIP: bounded delay
VPN: bounded bandwidth
Video conferencing: bounded delay and bounded loss rate
Common QoS parameters:
delay/delay variation (jitter)
Bandwidth
error rate
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6. What is QoS(Cont.)
Per flow QoS guarantees and aggregate QoS guarantees
Statistical QoS guarantees .vs. deterministic QoS guarantees
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7. What is needed to support QoS
Between the network and its clients: Traffic contract. Traffic specification/desired QoS/supported QoS
At network edge:
Signaling and admission control
Packet classification/marking
Traffic shaping
Packet classification/marking and traffic shaping is also called traffic conditioning.
Traffic policing
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8. What is needed to support QoS
At routers:
classification and scheduling: FCFS won't work, need more advanced packet scheduling scheme (Fair Queuing)
Routing algorithm need to improve: find a path that satisfies QoS constraints (QoS/policy/constraint based routing).
Buffer management.
Traffic monitoring: find problems as early as possible
Traffic reshaping (at merge and fork points)
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9. QoS in the Internet: Do we really need it?
Alternative: buy excessive bandwidth
Everything is simple in the Internet without QoS, everything seems to be much harder in the Internet with QoS support.
What is the main problem?
Complexity and scalability of QoS mechanisms
Which is cheaper: higher network speed or network with QoS support.
Where is the balance?
A guess: Some form of QoS support will be there, per flow QoS guarantee may or may not ever be deployed.
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10. Intergrated Services (IntServ)
Trying to match the user demand by providing per flow QoS guarantees.
Signaling protocol: RSVP
IntServ is a reservation based approach
Main problem:
Router complexity (scalability)
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11. Differentiated Services (Diffserv)
Define per-hop behavior instead of end-to-end service model
Support a small number of forwarding classes at each router.
Forwarding class is encoded in the packet header.
Problems with DiffServ:
end-to-end service guaranteed is hard to maintain.
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12. Multi-Protocol Label Switching (MPLS):
Originally designed for IP over ATM
A short (fixed length) label is encoded for the packet header for packet forwarding
Allow Label switched path (LSP) to be setup (explicit routing).
allow datagram and virtual circuit to be coexisted in an IP network.
MPLS can be combined with IntServ and DiffServ to support QoS.
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13. Comparison of IntServ and DiffServ
Coordination for service differentiation
End-to-End
Local (per-Hop)
Scope of service differentiation
A Unicast or Multicast path
Anywhere in a Network or a specific path
Scalability
Limitation by the number of flows
Limited by the number of classes of service
Network Accounting
Based on flow characteristics and QoS requirement
Based on class usage
Network Management
Similar to circuit Switching network
Similar to existing IP networks
Interdomain deployment
Multilateral Agreements
Bilateral Agreements
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14. COPS Definition Common Open Policy Service protocol
IETF RAP working group
To support policy control in an IP QoS environment
Policy servers v.s. policy clients
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15. The COPS Role for Dynamic DiffServ Resource Allocation
COPS protocol
A simple query
Response protocol that allows policy servers (PDPs, Policy Decision Point ) to communicate policy decisions to network devices (PEPs, Policy Enforcement Point )
To support multiple types of policy clients
Uses to TCP to provide reliable exchange of messages
Provides the means
To establish and maintain a dialogue between the client and the server
To identify the requests
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16. The COPS Role for Dynamic DiffServ Resource Allocation(2)
Two main model
Outsourcing model
Provisioning model
Events
Bandwidth broker (policy decision point)
Query (2)
Notifications
Trigger Events (1)
Bandwidth broker (policy decision point)
Response (3)
Configuration commands
Edge router (policy enforcement point)
Edge router (policy enforcement point)
Trigger events generate queries and responses
Trigger events, notifications, and configuration commands are asynchronous
Outsourcing and provisioning models in COPS
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17. The COPS Role for Dynamic DiffServ Resource Allocation(3)
The dynamic scenario for DiffServ QoS
An admission control framework
To use server to control the admission of traffic within a DiffServ domain  Bandwidth Broker
The use of COPS for the communication between the edge device and the BB
COPS extensions for DiffServ resources allocation under outsourcing model
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18. The COPS Role for Dynamic DiffServ Resource Allocation(4)
Signaling mechanism
The QoS client to make resource reservation requests to the network
RSVP
End-to-end protocol to support multicast sessions spanning the whole Internet with receiver-oriented reservations
More complex
The European IST project AQUILA
More systematic approach to address this problem
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19. The COPS Role for Dynamic DiffServ Resource Allocation(5)
Bandwidth broker
QoS client (H323 gatekeeper,SIP server…)
PDP
PEP
COPS
PDP
PEP
QoS-enabled network
COPS
Edge router
COPS support to dynamic DiffServ-based IP QoS
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20. Definition of the COPS Interface
The extension of COPS
For dynamic DiffServ QoS scenario
COPS-DRA : DiffServ Resource Allocation
COPS-ODRA : Outsourcing DRA
Based only on the outsourcing model
For flexibility and efficiency
In combination with providing model
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21. Definition of the COPS Interface
The PEP always explicitly asks the PDP/BB for a given amount of resources
For scalability
Per-flow state is not stored in PDP/BB
Resource allocation requests are properly aggregated
Aggregate state information is kept in PDP/BB
Provisioning model
More scalable
Inflexibility : difficult to handle modification of config.
Not explicitly customized to handle dynamic DiffServ QoS
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22. Definition of the COPS Interface
Requirements for a combined model
The capability of provisioning resource to local nodes, in order to avoid high signaling burden
Easy for the local node to request the modification of the provisioned resource
Possible to handle specific requests under the outsourcing model
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23. Definition of the COPS Interface
Three components of the reserv. Requests
The scope and amount of reservation
Where the reservation applies
How much bandwidth
The type of requested service
Possibly including a set of QoS parameters
The flow identification
To which IP flow or aggregate of flows the reservation applies
More complex scenarios may require more parameters
Ex : timing
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24. Definition of the COPS Interface
Bandwidth broker
(1)
PDP
(4)
(2)
PDP
PEP
PEP
PDP
(3)
(5)
(6)
QoS-enabled network
An example information exchange using COPS-DRA
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25. IP telephony : A COPS Based QoS model
SIP protocol
Defined within the IETF
Initiate voice, video, and multimedia sessions
Candidate for call setup signaling in IP telephony
IntServ-based approaches
Client is customized for specific QoS mechanism.
Terminal has to implement SIP and QoS reservation protocol.
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26. IP telephony : A COPS Based QoS model
The main idea
To eliminate the need for a specific QoS protocol in the terminals
To use SIP as the sole call setup protocol
All the QoS-related functions can be moved from the terminal to local SIP proxy servers
To relieve the terminals of unneeded complexity and preserving backward compatibility
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27. Q-SIP Architecture No specific QoS protocol required.
Terminal implementation is simplified.
QoS Access Point
QoS Access Point
COPS/Other
Client network
COPS/Other
Client network
SIP
SIP
Q-SIP
SIP terminal
Q-SIP proxy server
Q-SIP proxy server
SIP terminal
QoS SIP architecture
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28. Asymmetric Q-SIP Architecture
Variant scenarios
QoS Access Point
QoS Access Point
Client network
COPS/Other
COPS/Other
Client network
SIP
SIP
Q-SIP
Q-SIP proxy server
Q-SIP terminal
SIP proxy server
SIP terminal
QoS SIP architecture
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29. A Q-SIP Architecture using COPS Based QoS model
Bandwidth Broker(BB)
PDP
Qos signaling (COPS)
COPS-DRA
Qos-enabled network
Client network
PDP
PEP
PEP
PDP
Client network
COPS-DRA
COPS-DRA
Access edge router
Access edge router
SIP
SIP
Q-SIP
SIP terminal
SIP terminal
Q-SIP proxy server
Q-SIP proxy server
QoS SIP architecture
Application signaling (SIP)
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30. A COPS Based QoS model QoS SIP architecture The edge routers
Implement all mechanisms needed to perform admission control decision and policing function
COPS protocol
Used to make QoS reservation requests to the QoS access points
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31. A COPS Based QoS model(Cont.)
SIP server
To exchange message between the clients
To add QoS related information in the SIP messages
To negotiate QoS parameters among them
Interact with the network QoS mechanisms
Q-SIP
Enhanced SIP ( QoS-enable SIP server )
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32. Message Flow DiffServ network INVITE INVITE(With QoS-Info) INVITE
Called user Q-SIP server
SIP terminal
Called user ER
Bandwidth broker
INVITE
INVITE(With QoS-Info)
INVITE
180 ringing
180 ringing
180 ringing
200 OK
Cops REQ
Cops REQ
Cops DEC
Cops DEC
(With QoS-Info)200 OK
Cops REQ
Cops REQ
Cops DEC
Cops DEC
200 OK
ACK
ACK
ACK
<Traffic stream>
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33. QoS Info recorded in Q-SIP
QoS info. is inserted into new INVITE messages or 200 OK response message:
QoS-Info: <qos-param> *(;<qos-param>)
Same info can also be carried by “Record-Route” header.
Example of QoS-Info:
QoS-Info: qos-domain=coritel.it; er-ingress= ; qos-mode=unidirectional
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34. QoS Info recorded in Q-SIP(Cont.)
<qos-mode>
Either “unidirectional” or “bidirectional”
<er-ingress> & <er-egress>
The edge router on caller/callee side
<qos-domain>
Identify the domain where resource reservation is done
<caller-media-addr> & <caller-media-port>
Caller address
<other>
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35. Implementation Testbed
The overall testbed scenario
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36. Implementation Testbed
the QoS and call setup aspects
two Ethernet based client networks
Based on Linux OS
COPS clients/servers
A DiffServ core network
Two ERs & one core router
PDP/BB
Access network
One SIP terminal & one Q-SIP server
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37. Implementation Testbed
Q-SIP server, ER, and BB internal architecture
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38. Conclusions Signaling mechanism
Resource admission control within DiffServ
Resource requests to a QoS provider
QoS-aware call setups for SIP-based applications
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39. Conclusions (Cont.) Resource admission control within DiffServ
PEP (Edge Router)
Handles resource & policy enforcement
PDP (Bandwidth Broker)
Handles resource allocation pecisions
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40. Conclusions (Cont.) Resource requests to a QoS provider
PEP (SIP proxy server)
Asks for QoS reservation
PDP (edge router)
Typically edge routers of the DiffServ network
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41. Conclusions (Cont.) QoS-aware call setups for SIP-based applications
Integrating the SIP signaling with DiffServ QoS mechanisms
Preserving backward compatability.
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42. Reference
S. Salsano, L. Veltri, Qos Control by Means of COPS to Support SIP-Based Applications
X. Xiao, L. M. Ni, Internet QoS: A Big Picture
S. Mallenius, The COPS (Common Open Policy Service) Protocol
S. Salsano, L. Veltri, SIP Extensions for QoS support, <draft-veltri-sip-qsip-01.txt>
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