An Architectural Framework for Supporting Distributed Object Based

An Architectural Framework for Supporting Distributed Object Based Routing Dhavy Gantsou Department of Computer Science University of Valenciennes France Dhavy. gantsou@univ-valenciennes. fr SIGAda 2002, D. Gantsou

Basic networking terminology and concepts: Protocol ? In general A set of rules that govern all activity involving two or more entities that exchange messages in order to accomplish a task SIGAda 2002, D. Gantsou

Basic networking terminology and concepts: Routing protocol ? Activity = transmitting data (packets) from a host (sender) to a remote host (receiver). Task = routing Communicating entities = software components of hosts and devices performing routing (routers ). SIGAda 2002, D. Gantsou

Basic networking terminology and concepts: Routing ? Route computing. Involves: • Exchange of update messages (routing tables) only between neighboring routers • Use of received routing tables to dynamically determine the best path that a packet should take to reach its destination. SIGAda 2002, D. Gantsou

Basic networking terminology and concepts: Routing ? Route computing. Requires : • Coherent route maintenance (route insertion, change, and deletion), may be periodic • Real-time inter-router communication. Receiving update messages at wrong time leads to instabilities SIGAda 2002, D. Gantsou

Basic networking terminology and concepts: Routing ? R 7 R 3 R 1 R 5 R 4 R 2 R 6

Basic networking terminology and concepts: Routing ? cont. Route lookup • Forwarding packets received on an input network interface to an appropriate output interface for transmission across the Internet. SIGAda 2002, D. Gantsou

Basic networking terminology and concepts: Routing protocols issues Implement multiple algorithms that : • execute concurrently • interact to achieve a common goal Require real-time communication SIGAda 2002, D. Gantsou

Basic networking terminology and concepts: networking domain specific issues Co-existence of two alternative data representation, due to exchanges of data among hosts having different byte-ordering. Packets loss implying retransmission Data error involving retransmission Retransmission requiring timer management Varying and complicated message formats, Asynchronous communication SIGAda 2002, D. Gantsou

Basic networking terminology and concepts: Concluding remark Given the issues that they raise, routing protocols belong to the domain of large-scale, real-time applications How to implement routing software ? SIGAda 2002, D. Gantsou

Routing software implementation: Designs Conventional (monolithic) Distributed object based A poor choice of technology can make the implementation tedious and difficult SIGAda 2002, D. Gantsou

Conventional design For single processor targets Uses C and C++ Extensive use of operating system features for implementing real-time functionality Widely used by network designers May be for historical and business reasons SIGAda 2002, D. Gantsou

Conventional design cont. Needs specific procedures for performing: • network byte-ordering • mapping between the logical view and realistic messages Not suitable for the implementation of next generation Internet’s architecture SIGAda 2002, D. Gantsou

Ada 95 technology based Prototype Uses GLADE features to perform data representation operations Consists on four major classes: • Router_Class • Shared_Object • Service_Manager • OSPF_Router SIGAda 2002, D. Gantsou

Ada 95 technology based Prototype Router_Class : An abstract (virtual) class specifying the behavior of communicating entities (routers) Subclasses derived from Router_Class must provide real methods (operations) performing the functionality of the routers

Class Router_Class With common, common_types; package Router_Class is pragma Remote_Types ; type Router_Class is abstract tagged limited private ; procedure Update (Router : Access router_Class; Message : Common. Message_Type) is abstract ; private type Router_Class is abstract tagged limited null record ; end Router_Class ; SIGAda 2002, D. Gantsou

Ada 95 technology based Prototype Shared_Object : A class implementing concurrent query and/or modify methods that are inherent to the OSPF DR (designated router) concept. A single member of a set of OSPF routers, which is elected by its neighbors to serve as central point of contact for routing information exchange SIGAda 2002, D. Gantsou

Class Shared_Object Generic type For_Multiple_Inheritence is tagged limited private ; package Virtual_DR is pragma Shared_Passive ; type Shared_Object is new For_Multiple_Inheritence with private ; procedure Insert (DR : Access Shared_Object ; Msg : Common. Message_Type; Where: Natural ) ; private type Shared_Object is new For_Multiple_Inheritence with null record ; end Virtual_DR ; SIGAda 2002, D. Gantsou

package body Virtual_DR is protected Acces_Control is private end protected Acces_Control ; protected body Acces_Control is end protected Acces_Control ; procedure Insert (DR : Access Shared_Object ; Msg : Common. Message_Type; Where: Natural ) is end Insert ; end Virtual_DR ; SIGAda 2002, D. Gantsou

Ada 95 technology based Prototype Service_Manager : provides methods that enable: • to register distributed objects • clients (objects requiring services) to find and retrieve references of distributed objects providing remote services (server) SIGAda 2002, D. Gantsou

Class Service_Manager With Router_Class, Common; package Service_Manager is Pragma Remote_Call_Interface ; type Router_Class_Ref is Access all Router_Class’Class ; type Remote_Router_Reference is record Router_Ref: Router_Class_Ref ; Router_Id : Common. Address ; end record ; procedure Registry (Router : Access Router_Class_Ref; Router_ID: Common. Address ; Host : Common. Host_Name) ; function Give_Router_Reference(Key : Natural) return Router_Class_Ref ; end Service_Manager ; SIGAda 2002, D. Gantsou

package body Service_Manager is protected Synchro_Ref_Acces is procedure Registry (Router : Access Router_Class_Ref; Router_ID: Common. Address ; Host : Common. Host_Name) ; function Give_Router_Reference(Key : Natural) return Router_Class_Ref ; private Router_Reference : Router_Reference_List ; end Synchro_Ref_Acces ; protected body Synchro_Ref_Acces is procedure Registry (Router : Access Router_Class_Ref; Router_ID: Common. Address ; Host : Common. Host_Name) is end Synchro_Ref_Acces ; procedure Registry (Router : Access Router_Class_Ref; Router_ID: Common. Address ; Host : Common. Host_Name) is begin Synchro_Ref_Acces. Registry(Router, Router_ID, Host) ; end Service_Manager ; SIGAda 2002, D. Gantsou

Ada 95 technology based Prototype Ospf_Router : a class implementing methods that perform the functionality of a router running the Open Shortest Path First(OSPF) protocol. • Provides methods that perform : - basic routing functionality - OSPF specific services such as the designated router concept (Class Shared_Object) • Must inherit methods from Router_Class and Shared_Object (multiple inheritance ) SIGAda 2002, D. Gantsou

Class OSPF_Router With Router_Class, Virtual_DR , …; package OSPF_Router is Pragma Remote_Types ; type OSPF_Router is new Router_Class with record end record ; package VDR is new Virtual_DR (OSPF_Router) ; type DR is new VDR. Shared_Object with null record ; procedure Update (Router : Access OSPF_Router ; Message : Common. Message_Type) ; end OSPF_Router ; SIGAda 2002, D. Gantsou

With Ada. Real_Time, Service_Manager, …; package body OSPF_Router is Local_Router : Aliased OSPF_Router ; Local_DR : Aliased DR ; package VDR is new Virtual_DR (OSPF_Router) ; type DR is new VDR. Shared_Object with null record ; procedure Update (Router : Access OSPF_Router ; Message : Common. Message_Type) is begin Insert. (Local_DR’Acces, Message, Hash(Service_Manager. Give_Router_Reference(Message. Source_Message))) ; end Update ; declare begin Service_Manager. Registry(Local_Router’Access, Host_ID , Host_Name) ; end OSPF_Router ; SIGAda 2002, D. Gantsou

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