FUNCTIONAL REQUIREMENTS OF PEER-TO-PEER OPTICAL NETWORKING Jing Wu (1), J. Michel Savoie (1), Bill St. Arnaud (2) 1 : Communications Research Centre Canada, 3701 Carling Avenue, Ottawa, Ontario, Canada K2H 8S2 {jing.wu, michel.savoie}@crc.ca 2 : Canarie Inc.,
[email protected] Abstract Four key functional requirements are identified in peer-to-peer optical networking: resource discovery and inter-domain routing protocol, symmetric inter-domain signaling mechanism, autonomous blocking control, and data plane or physical layer internetworking. Introduction Transport networks such as optical backbone networks are built based on the client-service provider network architecture from the beginning [1]. With the development and deployment of new generation transport network equipment and the deregulation on communications, it is now possible for some client domains to build a private transport network among themselves using the peer-to-peer network architecture [2]. With this architecture, client domains may be able to exchange traffic more efficiently by directly peering to each other at the physical layer. Compared to relying on a service provider to connect them by using permanent or semi-permanent SONET connections or lightpaths, they have more control on the connectivity among themselves and thus more flexibility, which enables some innovative applications. The architecture of peer-to-peer optical networking would be that multiple optical network domains connected together equally control the links among them without centralized control and mutually provide transit service to each other based on an open access policy. The difference between the peer-to-peer network architecture and the peer model needs to be clarified. The peer model is proposed as a control model in the client-service provider network architecture [3]. It suggests intra-domain control protocols such as routing protocols and signaling protocols to be extended beyond the boundary of a service provider’s domain and to be used as a unified method to control both intra-domain and inter-domain network resources. It is in parallel with the overlay model, where a client domain requests connections to reach another client domain only through their service provider’s cloud by the means of the well defined Optical User Network Interface (O-UNI). Regardless of whether the peer model or the overlay model is used, the client-service provider network architecture is asymmetric in terms of the control of network resources. Compared to the client-service provider network architecture, the peer-to-peer network architecture has two key features. Firstly, each domain not only receives transport services from other domains but also contributes new transport services to other domains. Secondly, a link between two domains is equally controlled by both of them as opposed to being controlled as an access link, where a service provider plays an active role while a client domain plays a passive role. Functional Requirements of Peer-To-Peer Optical Networking Peer-to-peer optical networking has some unique functional requirements. During the establishment of
an end-to-end connection, each segment of the connection between domains is set up on a peer-topeer basis. Both domains connecting to an interdomain link have equal authority in terms of its control. Central guiding intelligence and arbitration of conflicts are necessary. But day-to-day management and per connection control should be decentralized. Resource discovery and inter-domain routing protocol Unlike inter-domain routing in the Internet, where only logical connectivity information (i.e. reachability information) is disseminated, peer-to-peer optical networking requires additional information such as availability information (i.e. idle or occupied) of channels or wavelengths to be disseminated dynamically. This can be explained by the difference between the packet-switched nature of the Internet and the circuit-switched nature in peer-to-peer optical networking. In SONET technology based networks, the availability information can be aggregated into the number of available channels at a specific data rate. In WDM technology based networks, some wavelength assignment schemes need the availability information of every wavelength channel on all links. The scalability issue has to be considered. The capability of interacting with an intra-domain routing protocol is another functional requirement of an inter-domain routing protocol. This interaction is a two-way process. On the one hand, a mechanism needs to be introduced to make inter-domain routing information learnt from outside of a domain, carried within the domain to related nodes. On the other hand, a mechanism is required to inject intra-domain routing information into inter-domain routing protocols. As in the Internet, the dissemination of internal topology of optical networks to external nodes is strictly controlled but only at an abstract level. However, how to abstract the internal topology information of an optical network needs further study. Symmetric inter-domain signaling mechanism Because peer-to-peer optical networking operates in a connection-oriented mode, a signaling mechanism is required to establish, terminate or maintain connections. This is a different functional requirement than in the Internet, which operates in a connectionless mode. Generalized MPLS (GMPLS) acts as an intra-domain signaling mechanism in the control of optical networks [4]. O-UNI signaling is used between a client domain and its service provider and operates in an asymmetric mode [5]. Since under peer-to-peer optical networking all domains can operate both as clients and as service providers, and propagate connection requests when needed, a new symmetric signaling mechanism is required. When a domain initiates or carries over from another
domain a connection request to a second domain, they will temporarily form a client-service provider relationship in which the first domain is a client. The signaling entity in the first domain will act in a client mode to send connection requests to the second domain. And the signaling entity in the second domain will act in a service provider mode to receive connection requests and to send back success confirmation or error notification. Most importantly, the signaling mechanism needs to handle another type of cases where the second domain initiates connection requests to the first domain, where the first domain acts as a temporary service provider. The inter-domain signaling mechanism designed to support peer-to-peer optical networking needs to interwork with intra-domain signaling mechanisms. Signaling messages need to be translated back and forth between the inter-domain signaling entity and the intra-domain signaling entity at border optical switches or SONET ADMs. Security and authentication mechanisms need to be implemented to protect domains. Autonomous blocking control Managing shared network resources is quite different from managing private resources. Using shared network resources in a distributed mode needs to solve possible contention. In the Internet, contentions occur as network congestion and are solved by upper layer flow control mechanisms such as TCP flow control. In optical networks, contentions occur as network blocking where a connection request arrives at a link with no available resource. A distributed blocking control mechanism is required to coordinate the requests on shared network resources. Because in peer-to-peer optical networking every domain has equal authority, the blocking control mechanism has to operate in an autonomous mode. The autonomous blocking control should be based on the assumption that each of the participating domains can set their own policies while the network as a whole functions through the cooperation and goodwill of the community. Internet experience has shown that three major strategies are effective to build cooperative relationships and handle potential contentions. Either systems are designed that do not require cooperation to function correctly, or some incentives are created for cooperation by rewarding proper behavior, or usage are audited so that misbehavior can be punished. These strategies are also applicable to the design of an autonomous blocking control mechanism in peer-to-peer optical networking. When there are sufficient network resources to fulfill all potential requests, no blocking control mechanism is required and the peer-to-peer network architecture functions correctly without much cooperation. In practice, at an early stage peer-to-peer optical networking can possibly operate in this mode, providing minimal quality of service and encouraging usage. When network resources cannot satisfy all requests or a sort of quality of service is required, blocking control has to be introduced. Because there is no central control, an autonomous blocking control is necessary. An autonomous blocking control mechanism is a way for individual peers to manage
shared resources without a central coordinator. When blocking happens in a link, all the connections that go through this link should be notified. Then they should back off their usage on this link. With autonomous blocking control, not only do individual connections optimize their bandwidth usage, the whole network can operate efficiently. By design an autonomous blocking control scheme and more importantly by enforcing its deployment in every domain, polite and self-disciplined behaviors will be observed in the whole network. As a result, each domain may expect some quality of service. Although no central control is used in peer-to-peer optical networking, every domain should audit and log network operations from its local point of view. If any significant misbehavior is observed, a central administrative committee or board will arbitrate and issue appropriate punishments. Data plane or physical layer internetworking In peer-to-peer optical networking, all peer domains are considered equals, but they may not share the same capability in the data plane or physical layer. Edge nodes in peer domains may have different transmission or switching capabilities. Some domains are only able to make fibre crossconnect. Some are able to perform individual wavelength switching or wave-band switching. Some can perform time slot switching or add/drop time slots in SONET frames at one or more specific data rates. In order to internetwork peer domains with heterogeneous technologies in the data plane or physical layer, the control information carried in either inter-domain routing protocols or inter-domain signaling protocols or both needs to be enhanced. Conclusions In peer-to-peer optical networking, multiple optical network domains connected together equally control the links among them without centralized control and mutually provide transit service to each other based on an open access policy. It is a new architecture for building optical networks among some domains with mutual agreement and benefits. So far its potentials have not been explored yet. This paper identifies its architectural aspects, as well as its functional requirements. Both domains connecting to an inter-domain link have equal authority in terms of its control. Central guiding intelligence and arbitration of conflicts are necessary. But day-to-day management and per connection control should be decentralized. Specifically, four key functional requirements are identified: resource discovery and inter-domain routing protocol, symmetric inter-domain signaling mechanism, autonomous blocking control, and data plane or physical layer internetworking. References 1 A.A.M. Saleh, et al. Journal of Lightwave Technology. Vol.17, No.12 (1999) pp.2431-2448. 2 B.S. Arnaud. “Proposed CA*net 4 Network Design and Research Program.”http://www.canet3.net/library/papers/CAnet4_Design_D ocument.doc 3 B. Rajagopalan, et al. IEEE Communications Magazine. Vol.38, No.9 (2000) pp.94-102. 4 A. Banerjee, et al. IEEE Communications Magazine. Vol.39, No.7 (2001) pp.144-151. 5 O. Aboul-Magd, et al. “User Network Interface (UNI) 1.0 Signaling Specification.” Optical Internetworking Forum (OIF), 2001.
