an architectural framework for supporting distributed object based routing dhavy gantsou department...
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An Architectural Framework for Supporting Distributed Object
Based Routing
Dhavy Gantsou
Department of Computer ScienceUniversity of Valenciennes
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 ? 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 communicationSIGAda 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
Ada95 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
Ada95 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
SIGAda 2002, D. Gantsou
Class Router_ClassWith 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
Ada95 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_ObjectGeneric
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
Ada95 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_ManagerWith Router_Class, Common;
package Service_Manager is Pragma Remote_Call_Interface ;
type Router_Class_Ref is Access all Router_Class. 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
Ada95 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_RouterWith Router_Class, Virtual_DR , …;
package OSPF_Router is
Pragma Remote_Types ;
type OSPF_Router is new Router_Class.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