ECN Based Admission Control for Inter-Provider QoS

Transcription

1 ECN Based Admission Control for Inter-Provider QoS Kwok Ho Chan, Jozef Babiarz CTO Office, Nortel Networks January 28,

2 Overview > Provide session admission control for real-time inelastic flows like voice, video and multimedia end-to-end including across inter-provider links. > Use per service class Explicit Congestion Notification (ECN) marking to notify the end-system (or proxy) of congestion level along the path that the session/flow will take. > During session setup, end-system (or proxy) perform verification of path status (verify connectivity and congestion level), i.e., for VoIP, end-system (or proxy) sends early media or RTP probes, ECN-capable routers mark ECN bits of EF packets based on congestion or traffic level they measure. > Application running in the end-system or network server makes the decision to admit or not admit the new session based on ECN marking. 2

3 Defined SLAs for End-to-End Service Customer A Application Provider Service Agreement Communication Server CS Service Agreement SP A SP B SP C Customer B QoS Access SLA QoS Transport SLA QoS Transport SLA Customer A has SLA with SP A for access and transport using Telephony service class and service agreement with Application Provider Customer B has SLA with SP C for access and transport using Telephony service class and service agreement with Application Provider SP A has SLA with SP B for transport using Telephony service class SP C has SLA with SP B for transport using Telephony service class Application Provider has agreement with SP A to use Telephony service class QoS Access SLA 3

4 Admission Control Communication Server Terminal A CS Signaling or Control ECN Capable ECN Capable SP A SP B SP C Terminal B QoS Transport SLA QoS Transport SLA On reception of call request message from Terminal A : 1. Terminal B, generates and sends RTP Request probe packets to Terminal A 2. If rate in the Telephony service class > than a, ECN bit 7 set to 1 3. Upon receiving Request probe packets, Terminal A replies with RTP Response probe packets to Terminal B, echoing the received ECN bits in probe payload 4. If rate in Telephony service class > than a, ECN bit 7 set to 1 5. If Response probe packets ECN= 00 Terminal B will start alerting the user (Ring phone) 4

5 SLA Bandwidth Diagram for ECN SAC BW = 100% BW available for other services if voice is not using it BW assigned for other services BW borrowed from other services BW reserved & guaranteed for VoIP 2nd Traffic Level (ECN 11 ) 1st Traffic Level (ECN 01 ) Other Traffic Voice Traffic Minimum delta is one call time All calls are admitted Only higher priority or emergency calls are admitted 5

6 Status > Extensions to ECN for use with Real-Time inelastic traffic like VoIP, video and multimedia streaming applications are proposed in IETF Planning to update the above draft to include ECT(0) marking Companion draft to define generic RTP probe format (March IETF) Framework draft explaining how ECN mechanism is used for admission control of VoIP. (March IETF?) > For more information please contact Joe Babiarz Kwok Chan 6

7 Backup Slides 7

8 End to End Session Admission Control Using ECN Marker and RTP Probe Jozef Babiarz Oct. 21, 2004

9 Session Admission Control > Session admission control (SAC) is a mechanism to block new real-time inelastic flows like voice and videoconferencing when the network resources are at capacity and the admission of additional flows would degrade the service quality to established users. > ECN SAC is a probe based approach during session (call) setup to determine if there is sufficient bandwidth for a new session to be admitted. > The ECN SAC concept can also be extended and used to control admission control of priority sessions (i.e., E911, etc.) as well for session preemption. (Note covered in this presentation). 9

10 Key Features of ECN SAC Probing verifies Connectivity path between the two end points Availability of bandwidth along the path end-to-end in the IP network Measures total round trip delay (RTT) Works for all real-time flows VoIP Video conferencing Video and audio streaming applications Can be used with any signaling method SIP, H.323, MGCP, H.248, UNISTIM, ASPEN, etc. Only VoIP SIP scenarios are discussed in this presentation 10

11 DiffServ Field & Explicit Congestion Notification DSCP ECN Explicit Congestion Notification (ECN) bits 6 & Version HLen DS field Length Identification Flags Fragment offset TTL Protocol Header checksum Source address Destination address Data IP Header The DiffServ (DS) Field is an 6-bit field in the IP header and is defined in RFC The first six bits contain the DiffServ Code Points (DSCP). - The two least significant bits (LSBs) of the DiffServ Field (bits 6 & 7) are used for Explicit Congestion Notifications (ECN). RFC 3168 defines the incorporation of ECN and usage for TCP flows. 11

12 Architecture Telephony Service Expedited Forward (EF) PHB used for VoIP Packet marking for VoIP (IP telephony) EF DSCP is used for VoIP payload EF DSCP is used for probe packets sent during call setup CS5 DSCP is used for SIP signaling ECN bits are used to explicitly convey status of bandwidth usage end-to-end in the network for packets in the Telephony service class (in both directions) Video Conferencing Service CS4 DSCP is used for inelastic flows Probe packets marked with CS4 DSCP are sent during session setup etc. 12

13 Architecture (cont.) Flow Measurement is Performed Per Service Class (e.g., EF marked packets) On selected routers (ingress and/or egress ports) Measure the aggregated flow rate (token bucket or other method) Mark ECN bit if rate is exceeded No State Information is Kept in Router The table below summarizes the meaning of the ECN bits in the DS Field of IP Header from routers perspective Traffic Load Status in the Network Not Congested 1 st Traffic Level (1 st Level of Congestion) 2 nd Traffic Level (2 nd Level of Congestion) Bit Bit

14 SAC Procedure SIP Client A Communication Server ECN Capable Access link CS ECN Capable IP Network BW limited core link SIP Client B Access link On reception of call request message from Client A : Client B, generates and sends RTP Request probe packets to Client A If EF rate > than a, ECN bit 7 set to 1 Upon receiving Request probe packets, Client A replies with RTP Response probe packets to Client B, echoing the received ECN bits If EF rate > than a, ECN bit 7 set to 1 If Response probe packets ECN= 00 Client B will start alerting the user (Ring phone) 14

15 Link Bandwidth Diagram for ECN SAC BW = 100% BW available for other services if voice is not using it BW assigned for other services BW borrowed from other services BW reserved & guaranteed for VoIP 2nd Traffic Level (ECN 11 ) 1st Traffic Level (ECN 01 ) Other Traffic Voice Traffic Minimum delta is one call time All calls are admitted Only higher priority or emergency calls are admitted 15

16 Summary Probe packets provide information on Connectivity BW available along the path in both directions Round Trip Delay (RTT) IP end-point (SIP Client) examines this information and if parameters are met, session is admitted and alerting is done by the end-point Also, the end-point sends the obtained information to the communication server (B2BUA) via normal signaling Traffic Load Status in the Network Bit 6 Bit 7 Action taken by End-Point Not Congested 1 st Traffic Level (1 st Level of Congestion) 2 nd Traffic Level (2 nd Level of Congestion) Admit all calls Block admission of regular calls (Admit emergency or higher priority calls) Session preemption condition (if supported) Note: Forwarding BW of Telephony service class is configured to support normal calls + emergency calls 16

17 1. Client A includes a Require header field with the option tag ecn-probe in the initial INVITE request. Client A Network A Session Admission Control Session Admitted Scenario B2BUA 1 B2BUA 2 Network B Network C Client B 2. The presence of the option tag ecn-probe within the INVITE request prompts Client B to initiate a Request/Response Probe Packet transaction. INVITE SDP1 100 Trying INVITE SDP1 100 Trying RTP Request Probe INVITE SDP1 100 Trying 180 Ringing RTP Response Probe 180 Ringing 180 Ringing 200 OK 200 OK SDP 2 SIP SDP INVITE 2 Request 200 OK SDP 2 INVITE ACK sip: ;phone-context=barksdale.af.com@af.com;user=phone SIP/2.0 ACK ACK Via: SIP/2.0/TCP clienta. wrightpatterson.af.com:5060;branch=z9hg4bk74b43 Max-Forwards: 70 Media Route: <sip:b2bua1@ ;lr> From: John <sip: ; phone-context=wrightpatterson.af.com@af. com>;tag=9fxced76sl To: <sip: ;phone-context=barksdale.af.com@af.com> Call-ID: @af.com CSeq: 1 INVITE Contact: <sip: ;phone-context=wrightpatterson.af.com@ > Require: ecn-probe Resource-Priority: normal Content-Type: application/sdp Content-Length:

18 Session Admission Control Session Admitted Scenario - continued DSCP Version HLen DS field Length Identification Flags Fragment offset TTL Protocol Header checksum Source address Destination address RTP UDP IP B2BUA 1 B2BUA 2 Note: the ECN bit value of 00. Client A Network A Network B Network C Client B INVITE SDP1 100 Trying 180 Ringing 200 OK SDP 2 ACK INVITE SDP1 100 Trying RTP Request Probe RTP Response Probe 180 Ringing 200 OK SDP 2 ACK Media INVITE SDP1 100 Trying 180 Ringing 200 OK SDP 2 ACK 3. If the RTP Response Probe indicates that the level of congestion along the network path is below the predefined threshold then call processing proceeds as normal. 18

19 Session Admission Control - Session Blocked Scenario - Resource-Priority: Normal DSCP Version HLen DS field Length Identification Flags Fragment offset TTL Protocol Header checksum Source address Destination address 2. The 503 Response message prompts client A to provide the appropriate all circuits busy alerting to the associated user. Client A Network A INVITE SDP1 R-P: normal 100 Trying 503 Service Unavailable ACK RTP UDP IP B2BUA 1 B2BUA 2 Network B INVITE SDP1 R-P: normal 100 Trying RTP Request Probe RTP Response Probe 503 Service Unavailable ACK Network C INVITE SDP1 R-P: normal 100 Trying 503 Service Unavailable ACK Client B Note: the ECN bit value of If the ECN bit values in the RTP Response Probe indicate that the level of congestion between the two clients is above the predefined threshold, then Client B will send a 503 Service Unavailable response upstream to Client A. This action will terminate call setup. 19