Using Prioritized Network Traffic to Achieve End-to-End Predictability

Transcription

1 Using Prioritized Network Traffic to Achieve End-to-End Predictability BBN Technologies OOMWorks LLC Cambridge, MA Metuchen, NJ Craig Rodrigues Yamuna Krishnamurthy Irfan Pyarali Pradeep Gore Real-Time and Embedded Distributed Object Computing June 15-18, 2002 Arlington, Virginia, USA

2 Managed Behavior for Computational Resources In order to preserve end-to-end Quality of Service (QoS) requirements, different technologies must be used to manage the behavior of computational resources Processor Resources RT-CORBA Network Resources RSVP DiffServ

3 Talk Outline Real-Time CORBA (RTCORBA) Overview RSVP and Diffserv Overviews Diffserv enhancements to RTCORBA middleware

4 Real-time CORBA Overview RT-CORBA adds QoS control to regular CORBA to improve the application predictability Bounding priority inversions Managing resources end-to-end Policies & mechanisms for resource configuration/control in RT-CORBA include: Processor Resources Thread pools Priority models Portable priorities Communication Resources Protocol policies Explicit binding Memory Resources Request buffering IDL STUBS Client ORB CORE Explicit Binding OBJ REF End-to-End Priority Propagation in args operation() out args + return Scheduling Service Standard Synchronizers Portable Priorities Object (Servant) IDL SKEL Thread Pools Object Adapter GIOP These capabilities address some (but by no means all) important real-time application development challenges Protocol Properties

5 Preserving Priorities End-to-End RT-CORBA preserves end-to-end priorities by: Mapping importance of activities to corresponding OS priorities Propagating priorities across the network as activity spans multiple hosts However, RT-CORBA specification is less explicit about: Communication transport and underlying network Unless this behavior is carefully considered and modeled: In-transit activities will be affected by network idiosyncrasies End-to-end predictability in the system difficult to achieve

6 What is RSVP? Resource Reservation Protocol, specified in IETF RFC 2205 QoS properties are requested by an out-of-band signalling protocol Can be used to request a reserved bandwidth between a sender and receiver host Information about the reservation is stored in each intermediate router: soft-state

7 Problems with RSVP Protocol is very complex to implement much complexity due to anticipated use-cases of large scale multicast trees; multicast not widely used Storing reservation per-flow reservation state is costly some work being done into looking reservations for aggregate flows Microsoft implemented RSVP in Win2K, disabled it in WinXP equipment vendors have less incentive to implement it

8 Problems with RSVP (continued) IETF Next Steps in Signaling (NSIS) Working group realized that RSVP has it shortcomings, but a signaling protocol for QoS is useful developing new signaling mechanism ( RSVP Lite?) specification due end of 2002 Maybe worth looking at in future, but right now industry seems to be moving away RSVP

9 Solution: Differentiated Services Use Differentiated Services to prioritize the RT-CORBA network traffic Differentiated Services (Diffserv) architecture provides different types or levels of service for network traffic Diffserv Code Points (DSCP) are added to data packet headers to specify the expected type of service Diffserv enabled routers and network elements use DSCP codepoints to differentiate the network traffic We are enhancing the existing TAO ORB's real-time implementation by making it Diffserv aware

10 What is Diffserv? IP Datagram Header Version (4-bits) Header Length (4-bits) Diffserv Field (8-bits) Total Length (16-bits) Identification (16-bits) Flags (3-bits) Fragment offset (13-bits) TTL (8-bits) Protocol (8-bits) Checksum (16-bits) Source Address (32-bits) Destination Address (32-bits) Diffserv field: 6 bits of Diffserv Codepoint, 2 bits ECN Each DSCP (0-63) specifies a Per-Hop-Behavior (PHB), which is a type of router-level QoS (RFC 2475)

11 Diffserv QoS Enhancements to the TAO ORB Provided an efficient and flexible way of setting the DSCP codepoints in the ORB data packets Done by extending the ORB protocol properties Setting the DSCP codepoint in the message sent and the reply received Provided a mechanism to map the RT-CORBA priorities to the Diff-Serv network priorities Diffserv CodePoint = EF Diffserv CodePoint = EF Client QNX priority = 16 Service Context priority = 100 Router Middle-tier Server Service Context priority = 100 LynxOS priority = 128 Router Server Solaris priority = 136

12 RTCORBA IDL Modification local interface TCPProtocolProperties : ProtocolProperties { attribute long send_buffer_size; attribute long recv_buffer_size; attribute boolean keep_alive; attribute boolean dont_route; attribute boolean no_delay; attribute boolean enable_network_priority; };

13 Initialize Protocol Properties //Set the tcp protocol protperties RTCORBA::TCPProtocolProperties_var tcp_properties = rt_orb->create_tcp_protocol_properties (send_buffer_size, recv_buffer_size, 1, // keep_alive 0, // dont_route 1, // no_delay enable_network_priority);

14 Client Side Initializing the Policy List RTCORBA::ProtocolList protocols; protocols.length (1); protocols[0].protocol_type = 0; protocols[0].transport_protocol_properties = RTCORBA::ProtocolProperties::_duplicate (tcp_properties.in ()); protocols[0].orb_protocol_properties = RTCORBA::ProtocolProperties::_nil (); CORBA::PolicyList policy_list; policy_list.length (1); policy_list[0] = rt_orb->create_client_protocol_policy (protocols);

15 Client Side - Change Transport Protocol Policy ORB Level object = orb->resolve_initial_references ("ORBPolicyManager"); CORBA::PolicyManager_var policy_manager = CORBA::PolicyManager::_narrow (object.in () ); policy_manager->set_policy_overrides (policy_list, CORBA::SET_OVERRIDE );

16 Client Side - Change Transport Protocol Policy Thread Level orb->orb_core () >policy_current().set_policy_overrides (policy_list, CORBA::SET_OVERRIDE); Object Level CORBA::Object_var object = server->_set_policy_overrides (policy_list, CORBA::SET_OVERRIDE); server = Test::_narrow (object.in () );

17 Server Side - Initializing the Policy List RTCORBA::ProtocolList protocols; protocols.length (1); protocols[0].protocol_type = 0; protocols[0].transport_protocol_properties = RTCORBA::ProtocolProperties::_duplicate (tcp_properties.in ()); protocols[0].orb_protocol_properties = RTCORBA::ProtocolProperties::_nil (); poa_policy_list[1] = rt_orb->create_server_protocol_policy (protocols );

18 Server Side Set Policy on the POA //Create POA with Diffserv enabled PortableServer::POA_var poa_with_ds = root_poa->create_poa ("POA_WITH_DS", poa_manager.in (), poa_policy_list);

19 RTCORBA to Network Priority Mapping Added a pluggable RTCORBA to Network Priority Mapping framework Similar to the RTCORBA to Thread Priority Mapping framework RTCORBA IDL modification: typedef short NetworkPriority; native NetworkPriorityMapping; The framework allows the user to implement their own mapping algorithms and plug it in using the ACE Service Configurator

20 Potential Use Case for RT-CORBA/Diffserv JTIDS Network ISR Constellation Air Operations Center Air Defense System Integrator With JCPI TADIL & Intel Feeds UAV PPLI STU III Back-Up Predator Squadron Operations Center ADSI with JCPI & PowerScene Equipped Nellis ISAFAF Fiber Optical Link Primary UAV Precise Position Location Information Prioritized Data Feeds PPLI Source: UAV Battlelab, Eglin Air Force Base U.S. Air Force GCS #1 GCS #2 GCS #3 GCS #4

21 Summary End-to-end QoS requires resource management of CPU and network resources RT-CORBA today primarily manages CPU resources Our enhancement allows RT-CORBA middleware to manage network resources using Diffserv, which is priority based Other services like CORBA CCM and RT- Notification can greatly benefit from this enhancement

22 Obtaining Software Contacts: Craig Rodrigues, Yamuna Krishnamurthy,

23 Further References Protocol Selection and Explicit Binding, Schmidt & Vinoski An Architectural for Differentiated Services, RFC