Open Issue: Inside Open Issue: Inside versus Outside the versus Outside the Network Network

3.5.1 Open Issue: Inside Open Issue: Inside versus Outside the versus Outside the NetworkNetwork

Perhaps the larger question we should be asking is how much can we expect from the network and how much responsibility will ultimately fall to the end hosts? The emerging reservation-based strategies certainly have the advantage of providing for more varied qualities of service than today’s feedback-based schemes; being able to support different qualities of service is a strong reason to put more functionality into the network’s routers. Does this mean that the days of TCP-like end-to-end congestion control are numbered? This seems very unlikely. TCP and the applications that use it are well entrenched, and in many cases have no need of much more help from the network.

Furthermore, it is most unlikely that all the routers in a worldwide, heteroge- neous network like the Internet will implement precisely the same resource res- ervation algorithm. Ultimately, it seems that the endpoints are going to have to look out for themselves, at least to some extent. The end-to-end principle argues that we should be very selective about putting additional functionality inside the network. How this all plays out in the next few years, in more areas than resource allocation, will be very interesting indeed.

In some sense, the Differentiated Services approach represents the middle ground between absolutely minimal intelligence in the network and the rather

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significant amount of intelligence (and stored state information) that is required in an Integrated Services network. Certainly most Internet service providers have balked at allowing their customers to make RSVP reservations inside the providers’ networks. One important question is whether the Differentiated Services approach will meet the requirements of more stringent applications. For example, if a service provider is trying to offer a large-scale telephony service over an IP network, will Differentiated Services techniques be adequate to deliver the quality of service that traditional telephone users expect? It seems likely that yet more QoS options, with varying amounts of intelligence in the network, will need to be explored.

3.6

3.6 FURTHER READING FURTHER READING

The recommended reading list for this chapter is long, reflecting the breadth of interesting work being done in congestion control and resource allocation. It includes the srcinal papers introducing the various mechanisms discussed in this chapter. In addition to a more detailed description of these mechanisms, including thorough analysis of their effectiveness and fairness, these papers are must reading because of the insights they give into the interplay of the various issues related to congestion control. In addition, the first paper gives a nice overview of some of the early work on this topic, while the last is considered one of the seminal papers in the development of QoS capabilities in the Internet.

Clark, D., S. Shenker, and L. Zhang, “Supporting Real-Time Applications in an Integrated Services Packet Network: Architecture and Mechanism.” Proceedings of the SIGCOMM ’92 Symposium, pp. 14–26, August 1992.

Demers, A., S. Keshav, and S. Shenker, “Analysis and Simulation of a Fair Queuing Algorithm.” Proceedings of the SIGCOMM ’89 Symposium, pp. 1–12, September

1989.

Floyd, S., and V. Jacobson, “Random Early Detection Gateways for Congestion Avoidance.” IEEE/ACM Transactions on Networking1(4):397–413, 1993.

Gerla, M., and L. Kleinrock, “Flow Control: A Comparative Survey.” IEEE Transactions on CommunicationsCOM-28(4):553–573, 1980.

Jacobson, V., “Congestion Avoidance and Control.” Proceedings of the SIGCOMM ’88 Symposium, pp. 314–329, August 1988.

Parekh, A., and R. Gallager, “A Generalized Processor Sharing Approach to Flow Control in Integrated Services Networks: The Multiple Node Case.” IEEE/ACM Transactions on Networking2(2):137–150, 1994.

Beyond these recommended papers, there is a wealth of other valuable mate- rial on resource allocation. For starters, two early papers set the foundation for using power as a measure of congestion-control effectiveness:

Jaffe, J. M., “Flow Control Power Is Nondecentralizable.” IEEE Transactions on Commu- nications COM-29(9), 1981.

Kleinrock, L., “Power and Deterministic Rules of Thumb for Probabilistic Problems in Computer Communications.” Proceedings of the International Conference on Com- munications, 1979.

A thorough discussion of various issues related to performance evaluation, including a description of Jain’s fairness index can also be found in Jain, R., The Art of Computer Systems Performance Analysis: Techniques for Experimen- tal Design, Measurement, Simulation, and Modeling . John Wiley & Sons, 1991.

More details about TCP Vegas can be found in Brakmo, L. S., and L. L. Peterson, “TCP Vegas: End-to-End Congestion Avoidance on a Global Internet.” IEEE Journal of Selected Areas in Communications (JASC) 13(8), 1995. Similar congestion- avoidance techniques can be found in Wang, Z., and J. Crowcroft, “Eliminating Periodic Packet Losses in 4.3-Tahoe BSD TCP Congestion Control Algorithm.” Communications Review 22(2), 1992. This paper gives an especially nice over- view of congestion avoidance based on a common understanding of how the network changes as it approaches congestion. Some issues with and proposed modifications to the RED algorithm including “Flow RED” (FRED) are described in Lin, D., and R. Morris, “Dynamics of Random Early Detection.” Proceedings of the SIGCOMM ’97 Symposium, 1997.

The proposed ECN standard is spelled out in Ramakrishnan, K., S. Floyd, and D. Black, “The Addition of Explicit Congestion Notification (ECN) to IP.” RFC 3168 , IETF, 2001. Efforts to generalize this idea in the form of active queue man- agement are put forth in many sources including Katabi, D., M. Handley, and C. Rohrs, “Congestion Control for High Bandwidth-Delay Product Networks.” Pro- ceedings of the ACM SIGCOMM ’02, 2002. This paper introduces XCP, one of the proposed new transport protocols that tackles the issue of improving on TCP’s throughput in high bandwidth-delay product networks.

There is a considerable body of work on packet scheduling that has extended the srcinal fair queuing and processor sharing papers just cited. Excellent exam- ples include the following.

Bennett, T., and H. Zhang, “Hierarchical Packet Fair Queuing Algorithms.” Proceedings of the SIGCOMM ’96 Symposium, 1996.

Goyal, P., H. Vin, and H. Chen, “Start-Time Fair Queuing: A Scheduling Algorithm for Inte- grated Services Packet Switching Networks.” Proceedings of the SIGCOMM ’96 Sympo- sium,1996.

Stoica, I., and H. Zhang, “A Hierarchical Fair Service Curve Algorithm for Link-Sharing and Priority Services.” Proceedings of the SIGCOMM ’97 Symposium, 1997.

Many additional articles have been published on the Integrated Services archi- tecture, including:

Clark, D., “Internet Cost Allocation and Pricing.” In Internet Economics edited by L. Knight and J. Bailey, MIT Press, 1997: the first paper to address the topic of Differentiated

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Services. It introduces the RIO mechanism as well as the overall architecture of Differ- entiated Services.

Clark, D., and W. Fang, “ Explicit Allocation of Best-Effort Packet Delivery Service.” IEEE/ ACM Transactions on Networking 6(4), 1998: follow-on paper that presents some

simulation results.

RFC 1633—Integrated Services in the Internet Architecture: An Overview, R. Braden, D. Clark, and S. Shanker, IETF, 1994: provides an overview of Integrated Services. RFC 2475 —An Architecture for Differentiated Services, S. Blake et al., IETF, 1998: defines

the Differentiated Services architecture.

RFC 3246— An Expedited Forwarding PHB (Per-Hop Behavior), B. Davie, et al., IETF, 2002: defines the EF per-hop behavior.

Zhang, L. et al., “RSVP: A New Resource Reservation Protocol.” IEEE Network, 1993: pro- vides a description of RSVP.

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