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Informing Science Challenges to Informing Clients: A Transdisciplinary Approach June 2001 Using Programmable Interfaces for Networks as the Key to Provide Quality of Service in the Internet Jairo A. Gutierrez Terence Wee University of Auckland, New Zealand National Computer Systems Pte Ltd, [email protected] Singapore [email protected] Abstract The growth of the Internet with its increasing levels of traffic, more ambitious applications and the convergence of communication technologies re- sults in poor quality of service. New technologies such as those discussed in this paper have been developed to aid in introducing quality of service to the Internet. However, those efforts may seem to be in vain due to the heterogeneous nature of IP-based networks. This paper suggests an inte- grated approach to provide end-to-end quality of service on the Internet based on the use of programmable interfaces. The need for dynamic modifi- cation of policies and configurations within IP routers and switches is already beginning to emerge and that functionality will help fulfill customers' demands for differentiated services. Keywords: Programmable networks, Quality of Service, Programming Interfaces, Multiple Protocol Label Switching (MPLS), Differentiated Services, Asynchronous Transfer Mode (ATM) Introduction • Compatibility with a wide range of routing proto- cols (Callon, R. et al, 1997) The objective of enabling the development of higher-level multimedia services with guaranteed quality of service • Resource reservation (QoS) on networks has prompted developments that at- tempt to accommodate these new application requirements. • Admission control Several architectures have been proposed, and a common basic functionality is emerging. Any new architecture that • Packet scheduling: including packet filtering and intends to satisfy the ever-growing need for bandwidth in classification the Internet while providing support for QoS guarantees, needs to concern itself with the following aspects (Zhang These aspects clearly call for routers with powerful fea- L., Deering S., Estrin D., Shenker S., Zappala D., 1993; tures that can be easily configured and modified in order to Biswas J. et al, 1998): support customers’ demands for differentiated services. • Flow management: identifying the traffic charac- Background teristics of a flow so that the network can specify the quality of service to be delivered to that flow The Internet is a phenomenon that has grown at an expo- nential rate, causing several new technologies to emerge to cope with the number of users of this global communica- Material published as part of this proceedings, either on-line or in tions network. TCP/IP was the protocol of choice because print, is copyrighted by the author with permission granted to the publisher of Informing Science for this printing. Permission to make of its simplicity and ability to find a route from a particular digital or paper copy of part or all of these works for personal or source to a particular destination. However, as the network classroom use is granted without fee provided that the copies are grows, there have been greater demands for additional ser- not made or distributed for profit or commercial advantage AND that copies 1) bear this notice in full and 2) give the full citation on vices and real-time applications to work over the Internet. the first page. It is permissible to abstract these works so long as Because TCP/IP is primarily a best-effort protocol, it is not credit is given. To copy in all other cases or to republish or to post on a server or to redistribute to lists requires specific permission able to provide the QoS that is required by real-time appli- from the author. cations and their users. To complement this deficiency, Programmable Interfaces for Networks other protocols such as Integrated Services (IntServ) and positioning of various building blocks for programmability Resource Reservation Protocol (RSVP), Differentiated of the network. This paper is a continuation of the above Services (DiffServ) and Multi-Protocol Label Switching effort, in order to realize the building blocks that support (MPLS) have been developed as well as the standards services on the Internet. The fundamental building blocks promoted by the IEEE P1520 Group. consist of a set of virtualized resources of the network ele- ments (routers and switches) structures in a fashion that The Integrated Services (IntServ) model is based on reser- make these resources available to multiple services on the vations-based traffic engineering assumptions. It reserves network and accessible through open and well defined in- resources explicitly using a dynamic signalling protocol terfaces for easy programming and fast and efficient ac- (RSVP) and employs admission control, packet classifica- cess. This paper explores the use of these virtualized re- tion, and intelligent scheduling to achieve a desired QoS sources to support the functionality of Multi-Protocol La- (Trillium Digital Systems Inc., 1998). The Integrated Ser- bel Switching (MPLS). MPLS (Callon, R. et al, 1997) is vices model has two services categories, and they are taken merely as a case in point, to illustrate the principle of Guaranteed Delay and Controlled Load services. structuring the resources in a function independent fashion and then applying functions or algorithms upon these re- RSVP is a resource reservation set-up protocol designed sources in a disciplined manner. This paradigm represents a for an integrated service Internet. It is used by a host to shift from the traditional approach of each function, proto- request specific qualities of service from the network for col or algorithm being developed in an independent fash- particular application data streams or flows. RSVP is also ion, thereby leading to an immense number of interactions used to establish and maintain state information in all between functions that must be considered individually. nodes along a flow so as to provide the requested service. However, RSVP itself is not a routing protocol, but instead Multi-Protocol Label Switching it is considered a signalling protocol similar to that used in ATM networks. MPLS, used with or without RSVP (Zhang L. et al, 1993; Baker F., Krawczyk J., Sastry A., 1998), fits within the The Differentiated Services (DiffServ) model is based on framework of Integrated Services (Braden R., Clark D., reservation-less traffic engineering assumptions. It classi- Shenker S., 1994). Before suggesting detailed interfaces for fies packets into a small number of service types and uses IP routers or switches it is necessary to understand the ba- priority mechanisms to provide adequate QoS to the traffic. sic operations of this proposed standard. The roots of No explicit resource reservation or admission control is MPLS originated from technologies such as IP switching, employed, although network nodes do have to use intelli- developed by Ipsilon Networks Inc. (Sunnyvale, Califor- gent queuing mechanisms to differentiate traffic (Trillium nia), and tag switching, developed by Cisco Systems Inc. Digital Systems Inc., 1998). (San Jose, California). Thus, Multi-Protocol Label Switch- ing is the use of fixed length labels to decide packet han- MPLS stands for Multi-Protocol Label Switching, and it is dling (Xiao X., and Ni L.M., 1999). An MPLS router, a protocol that assigns a particular FEC (Forwarding called the label-switch router (LSR), examines only the Equivalence Class) to a particular packet as it enters the label in forwarding the packet. MPLS also needs a proto- network. The FEC to which the packet is assigned is en- col to distribute labels to set-up label-switched paths coded as a short fixed length value known as a "label". (LSPs). The protocol used to distribute labels is known as Once a packet is assigned to a FEC, no further header the label distribution protocol (LDP). Whether a generic analysis is done by subsequent MPLS capable routers and LDP should be created or RSVP should be extended for all forwarding is driven by the labels (Rosen E. C., this purpose is an issue that is yet to be decided (Xiao X., Viswanathan A., Callon A., 1999). and Ni L.M., 1999). MPLS can also be piggybacked by routing protocols. A LSP is similar to an ATM virtual cir- In the IEEE P1520 standardization project (Working Group cuit (VC) and is unidirectional from the sender to the re- on IEEE P1520, 2000) it is the objective to allow routers ceiver. MPLS LSRs use the protocol to negotiate the se- and switches to be programmable by third parties that will mantics of how each packet with a particular label from its have access to the scheduling mechanisms and policies of peer is to be handled. Therefore, when a packet enters an the router, thereby allowing a greater degree of flexibility MPLS domain, it is classified and routed at the ingress and freedom for service provisioning. In line with this the LSR. MPLS headers are then inserted to the packet. When IP Sub Working Group (SWG) of P1520 has written a a LSR receives a labelled packet, it will use the label as the white paper and an architectural framework document in index to look up the forwarding table. This is faster than (Working Group on IEEE P1520, 2000) that depicts the the processes of parsing the routing table in search of the 236 Jairo A. Gutierrez and Terence Wee longest match done in IP routing. The packet is processed • Analyzes the network-layer header as specified by the forwarding table entry. The outgoing label then replaces the incoming label, and the packet is • Performs applicable network-layer services (such switched to the next LSR. Inside an MPLS domain, packet as security, bandwidth management, etc) forwarding, classification and QoS service is determined by the labels and the COS (Class of Service) fields. This • Selects a route for the packet from its routing ta- makes core LSRs simple.

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