Interactions of Link-Layer and Transport Protocols

Maintained by Pasi Sarolahti and Sally Floyd.

Table of Contents:

Related Web Pages:

• References on Layering and the Internet Architecture
• TCP and other Transport Protocols over X
• Other Changes Proposed to TCP, including Reordering, Corruption, Link Outages and Intermittently-Connected Paths,
• Cross-Layer Protocol Engineering for Wireless Mobile Networks: Part 1
  IEEE Communications Magazine, Vol.43 No.12, December 2005.
  " Of late, there has been an avalanche of cross-layer design proposals for wireless networks."
• Cross-Layer Protocol Engineering for Wireless Mobile Networks: Part 2
  IEEE Communications Magazine, Vol.44 No.1, January 2006.
  " Applications using traditional protocol stacks (e.g., TCP/IP) from wired networks do not function efficiently in mobile wireless environments. This is primarily due to the layered architecture and implementation of protocol stacks. One mechanism to improve the efficiency of the stack is cross-layer feedback, that is, making information from within one layer available to another layer of the stack."

IETF History in this Area

• TCP Over Satellite Working Group (tcpsat)
  This working group produced two RFCs.
• Performance Implications of Link Characteristics Working Group (pilc)
  This working group produced seven RFCs.
• Triggers for Transport BOF (trigtran) (November 2002, March 2003)
  Expired drafts:
  draft-dawkins-trigtran-probstmt: "When transport protocols are deployed over a path including a wireless sub-network, a wireless access device now has significantly better knowledge of the wireless portion of the connection path characteristics than one or both endpoints... This document will set the framework for investigation of whether this special knowledge from wireless access devices can be useful to endpoint transports."
  draft-dawkins-trigtran-linkup: "This document codifies the "Link Up Notification" for TCP."
• Access Link Intermediaries Assisting Services BOF (alias) (July 2003 )
  "This BoF investigates further work in support of transport intermediaries that provide assistance to access links, including (but not exclusively) wireless links, primarily in the areas of security protocol interaction with transport intermediaries and response to changing link conditions."
• RFC 3077: A Link-Layer Tunneling Mechanism for Unidirectional Links
• Architectural Implications of Link Indications, B. Aboba, internet-draft, work in progress, 2007.
  "This document describes the role of link indications within the Internet Architecture. While the judicious use of link indications can provide performance benefits, inappropriate use can degrade both robustness and performance."
• Combined Fixes for TCP over Dynamic Paths, presentation at the TCPM working group, July 2006.
  "Basic Idea: Have TCP respond to generic connectivity-change indications from lower-layers."
• Cross-layer Indications for Transport Protocols, P. Sarolahti, S. Floyd, and M. Kojo, Internet-draft draft-sarolahti-tsvwg-crosslayer-01.txt, work in progress, March 2007.

End-to-End Performance Enhancements

• A. Singh, A. Konrad, and A.D. Joseph. Performance Evaluation of UDP Lite for Cellular Video. In Proceedings of NOSSDAV'01, June 2001.
  Discusses using RTP over UDP lite as transport for transmitting MPEG-4 or H.263+ video stream in GSM network. UDP lite is compared to regular UDP in reliable and non-reliable GSM mode. Non-reliable GSM mode reduces the delay in delivering datagrams and UDP lite reduces the loss rate of datagrams. As a end result, it is concluded that UDP lite results in best perceived image quality when the codec is resilient to some amount of errors.
• S. Cen, P.C. Cosman, and G.M Voelker. End-to-End Differentiation of Congestion and Wireless Losses. IEEE/ACM Transactions on Networking, 11(5), October 2003.
  Compares different schemes of separating congestion losses from wireless losses at the end host. In addition to existing solutions, authors propose a new solution and present a hybrid scheme that heuristically switches between different algorithms.
• M. Allman, W. Eddy, S. Ostermann. Estimating Loss Rates With TCP. ACM Performance Evaluation Review, 31(3), December 2003.
  This paper introduces mechanisms for estimating the real loss rate of packets at the TCP sender with TCP Reno and with SACK option. Simply counting the number of retransmissions often gives wrong results because TCP senders do spurious retransmissions for various reasons. The paper identifies some of the reasons for unnecessary retransmissions.

Link Layer based Performance Enhancements

• H. Balakrishnan, S. Seshan, and R.H. Katz. Improving Reliable Transport and Handoff Performance in Cellular Wireless Networks. ACM Wireless Networks, 1(4), December 1995.
  Describes Snoop agent that caches unacknowledged TCP data at the wireless base station and makes local retransmission over wireless link while masking the wireless losses from the real fixed sender. Additionally, the paper presents a solution supporting handoffs by using IP multicast.
• R. Ludwig and B. Rathonyi. Link-layer Enhancements for TCP/IP over GSM. In Proceedings of IEEE Infocom '99, March 1999.
  Proposes Quickstart-PPP that reduces the number of round-trips required in the PPP handshake. Additionally, the paper discusses the possibility of making the link flow-adaptive by using different reliability mode for TCP and UDP packets.
• J. Scott, G. Mapp. Link Layer Based TCP Optimisation for Disconnecting Networks. In ACM SIGCOMM Computer Communication Review, 33(5), October 2003.
  This paper presents a link-layer enhancement for improving TCP performance on link disconnections. When link comes back up after disconnection, link layer protocol retransmits the last packet to kick start the TCP transfer. This avoids the delay related to TCP retransmission timeout. Different variants of packet retransmission are compared. This scheme could also be seen as one kind of implicit link layer trigger.
• T. Duke, T. Henderson, and J. Meegan, Experience with "Link-Up Notification" over a Mobile Satellite Link, CCR, V.34 N.3, pp. 93-104, July 2004.

Cross-Layer Communication Mechanisms

• B.S. Bakshi, P. Krishna, N.H. Vadiya, and D.K. Pradhan. Improving Performance of TCP over Wireless Networks. In Proceedings of the 1997 International Conference on Distributed Computer Systems, Baltimore, May 1997.
  The paper studies TCP Tahoe performance over simulated wireless links. In addition to varying the packet MTU, the effect of explicit feedback mechanisms are studied. The paper observes spurious reransmission timeouts due to persistently reliable wireless link. In addition to discussing use of ICMP Source Quench to hold the sender when link goes to bad state, the paper presents Explicit Bad State Notification that makes the sender cancel the present retransmission timer and and restart a new one. Thus many retransmission timeouts are avoided. EBSN is sent by the base station after every unsuccesful attempt to transmit a packet over wireless link.
• H. Balakrishnan, V.N. Padmanabhan, S. Seshan, and R.H. Katz. A Comparison of Mechanisms for Improving TCP Performance over Wireless Links. IEEE/ACM Transactions on Networking, 5(6):756-769, December 1997
  This paper compares various end-to-end, split connection, and link-layer based mechanisms for improving TCP performance over wireless link. Additionally, an explicit loss notification mechanism is presented. The receiver checks the correctness of a packet, and if it is corrupted, an ELN is sent with a duplicate acknowledgement. Use of ELN improves the performance over the baseline TCP Reno.
• K. Chandran, S. Raghunathan, S. Venkatesan, and R. Prakash. A Feedback-Based Scheme for Improving TCP Performance in Ad-Hoc Wireless Networks. Proceedings of the 18th International Conference on Distributed Computing Systems (ICDCS), Amsterdam, May 1998.
  Presents TCP-F protocol that delivers explicit route failure notification to TCP sender when a route failure in Ad-Hoc network occurs. When the TCP sender gets a route failure notification, it stops sending new packets, and freezes its timers and other TCP state. The sender then waits for route re-establishment notification or route failure timer to expire in order to continue transmission from the frozen state sending activity and waits for a route failure timer before continuing the connection.
• H. Balakrishnan and R.H. Katz. Explicit Loss Notification and Wireless Web Performance. Proceedings of IEEE Globecom Internet Mini-Conference, Sydney, Australia, November 1998.
  This paper extends the ELN mechanism presented above by combining a Snoop agent at the wireless base station that is also capable of making ELN markings. The paper also discusses a bit different set of TCP transfer scenarios than the earlier paper of the same authors.
• S. Goel and D. Sanghi. Improving TCP Performance over Wireless Links. In Proceedings of TENCON'98, pages 332-335. IEEE, December 1998.
  Suggests using ICMP messages for informing the sender about failure to transmit a packet on wireless link. ICMP-DEFER message is used to indicate that link layer retransmissions are in progress and the sender should defer making TCP retransmissions. When receiving the ICMP-DEFER message, the sender restarts TCP RTO. Additionally, ICMP-RETRANSMIT is sent from wireless basestation to indicate that TCP sender should retransmit a packet, i.e. the wireless base station is not doing any more local retransmissions.
• G. Holland and N.H. Vaidya. Analysis of TCP Performance over Mobile Ad Hoc Networks. In Proceedings of the Fifth International Conference on Mobile Computing and Networking, pages 219-230. ACM/IEEE, Seattle, August 1999.
  The paper describes Explicit Link Failure Notification used in the context of Ad-Hoc networks. ELFN is sent when link or route failure in Ad-Hoc network is detected. Using ICMP host unreachable and DSR routing protocols "route failure" messages to deliver the ELFN notification were studied.
• R. Krishnan, M. Allman, C. Partridge, J.P.G. Sterbenz. Explicit Transport Error Notification (ETEN) for Error-Prone Wireless and Satellite Networks. Technical Report No. 8333, BBN Technologies, March 2002.
  Discusses different types of Explicit Transport Error Notifications: Backward ETEN, Forward ETEN and Cumulative ETEN that indicates the probability of corruption error on the network path to the transport end hosts. The report evaluates ETENs with TCP Reno and SACK, and compares TCP Westwood performance to ETEN schemes. It also discusses security issues involved with ETENs.
• A. Gurtov and R. Ludwig. Lifetime Packet Discard for Efficient Real-Time Transport over Celullar Links. In ACM Mobile Computing and Communications Review, 7(4):32--45, October 2003.
  Proposes use of IP options to indicate maximum lifetime for packets in real-time protocols that do not require definite reliablity from the link layer. Instead of persistently retransmitting a packet, a link-layer can discard the packet if its lifetime in IP option is exceeded. Additionally, the paper presents Headercasting, i.e. transmitting the headers for packets after being discarded in the network. The receiver can send feedback to sender based on the header, and this helps to avoid unnecessary congestion control after packets have been discarded due to lifetime expiration.
• Y. Swami and K. Le. Lightweight Mobility Detection and Response (LMDR) Algorithm for TCP. Internet Draft "draft-swami-tcp-lmdr-02.txt", March 2004. Work In Progress.
  A proposal of using a bit in TCP header to indicate that an end host has moved to different subnet. The other end can then use this information in adjusting its congestion control parameters. This method does not require support from intermediate hosts, but uses local information from lower protocol layers to adjust transport protocol state.
• A.Gurtov and J. Korhonen. Effect of Vertical Handovers on Performance of TCP-Friendly Rate Control. ACM MCCR, 2004.
  Discusses the TFRC performance on vertical handovers between GPRS, WLAN and UMTS. TFRC is observed to adapt slowly on suddenly changing network conditions. The paper proposes Explicit Handover Notification to allow resetting the TFRC congestion control state for the new conditions after the handover.
• M. Welzl Passing Corrupt Data Across Network Layers: An Overview of Recent Developments and Issues. EURASIP Journal on Applied Signal Processing, 2005, Issue 2.
  An overview of transport protocols such as UDP Lite and DCCP that are designed to allow link layers to pass corrupt data to network layers and above. The paper includes a discussion of possible mechanisms for transport protocols to inform link layers that corrupted packets should be passed up to higher layers.

Mid Boxes

• N. Freed. Behavior of and Requirements for Internet Firewalls RFC 2979, October 2000.
  Describes characteristics of firewalls and lists some common types of firewalls. The RFC gives requirements for firewalls and their transparency. Examples of how firewalls should handle some specific types of network traffic are given. Additionally, some guidelines for application designers about dealing with firewalls are given.
• J. Border, M. Kojo, J. Griner, and G. Montenegro. Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations. RFC 3135, June 2001.
  This RFC discusses the different types of proxies that are known to be used to improve performance especially on environments with wireless links. The document describes mechanisms used in proxies and gives specific examples of proxies. Implications and disadvantages of having proxies in the communication path are also discussed.
• S. Floyd. Inappropriate TCP Resets Considered Harmful. RFC 3360, August 2002.
  The document was motivated by some firewalls that send TCP Resets to the TCP source when rejecting TCP segments. The document lists the events that have been observed to trigger sending a TCP RST at firewall. It gives a specific example regarding Explicit Congestion Notification (ECN), where the presence of ECN bits in TCP header causes a firewall to send RST back to the sender. Finally, the document more generally discusses the problems that broken firewalls cause for TCP development an proposes alternative solutions to be applied at midboxes instead of sending TCP RST packets.

Security

• R. Braden, D. Clark, S. Crocker, and C. Huitema. Report of IAB Workshop on Security in the Internet Architecture. RFC 1636, June 1994.
  The workshop discussed various aspects on security, such as issues on firewalls, QoS forwarding, authentication schemes. Even though the document is ten years old, it provides a useful list of topics worth reviewing also today.

Router Performance & Hardware Protocol Processing

• V. Srinivasan, G. Varghese, S. Suri, Marcel Waldvogel. Fast Scalable Algorithms for Level Four Switching. In Proceedings of ACM SIGCOMM '98, Vancouver, Canada, August 1998.
  Discusses efficiency of lookup algorithms in layer 4 switches, that use additional information such as transport protocol and port numbers in network switches or routers. This information can be used for example in routing decisions or firewall filtering. The paper presents two algorithms for efficient lookup of routing filters. The paper also demonstrates experimental results when applying the lookup algorithms on Pentium class machine.
• I. Hadzic and J. M. Smith. Balancing Performance and Flexibility with Hardware Support for Network Architectures. ACM Transactions on Computer Systems, 21(4), November 2003.
  Presents The Programmable Protocol Processing Pipeline (P4) for accelerating protocol processing functions on hardware. P4 can be reconfigured in real-time locally or remotely, and thus it is able to flexibly adapt on changing conditions. The paper presents on example application of Forward Error Correction where the P4 node monitors the bit error rate and applies FEC only when the error rate exceeds a certain level.

Radicalities

• D. L. Tennenhouse and D. J. Wetherall. Towards an Active Network Architecture. ACM SIGCOMM Computer Communication Review, 26(2), April 1996.
  Rather than presenting any analytical or experimental results, this paper discusses various topics regarding Active Networks and lays foundation on future work on more intelligent network. Different types of active networking are discussed and some threads for future work are given.
• D. Katabi, M. Handley, and C. Rohrs. Congestion Control for High Bandwidth-Delay Product Networks. In Proceedings of ACM SIGCOMM 2002, Pittsburgh, PA, USA, August 2002.
  Paper presents Explicit Control Protocol (XCP) that extends the idea of ECN by allowing the routers to report the degree of congestion in the network in feedback packets. With the new control protocol the utilization control is separated from fairness control at the routers, and most of the congestion-related packet losses are avoided.
• R. Braden, T. Faber, M. Handley. From Protocol Stack to Protocol Heap - Role-Based Architecture. In ACM SIGCOMM Computer Communication Review, 33(1), January 2003. (Proceedings of HOTNETS-1 Workshop).
  This paper presents a new architecture for network protocols. Instead of layering the protocols, this paper proposes a more flexible way of organizing different protocols used in (Internet) communication.

End-to-End Principle & Congestion Control

• V. Jacobson and M.J. Karels. Congestion Avoidance and Control. Slightly revised from ACM Computer Communication Review: Proceedings of the SIGCOMM '88, Stanford, CA, August, 1988.
  The Congestion Control paper. Introduces congestion window, slow start, congestion avoidance and discusses the round-trip time estimation.
• S. Floyd and K. Fall. Promoting the Use of End-to-End Congestion Control in the Internet. IEEE/ACM Transactions on Networking, 1(4), August 1999.
  Discusses the negative effects of not being responsive to congestion, identifies different forms of congestion collapse, and suggests incentives employed at routers to encourage end hosts to apply a proper congestion control. The paper proposes methods for identifying flows that are not TCP-friendly, unresposive flows, and flows that use disproportionate share of bandwidth, and how to deal with such flows. Additionally per-flow scheduling algorithms at routers are discussed.
• S. Floyd. Congestion Control Principles. RFC 2914, September 2000.
  This RFC discusses various issues regarding end-to-end congestion control. It describes the history and the problems that lead to present congestion control requirements. The document gives guidelines for authoring standards and implementations to follow the congestion control principles.

Quality of Service

• T. Aimoto and S. Miyake. Overview of DiffServ Technology: Its Mechanism and Implementation. IEICE Transaction on Information and Systems, Vol. E83-D, No. 5, pp. 957--964, 2000.
  Gives on overview of DiffServ, including discussion of techniques on gigabit routers to support DiffServ, and management of DiffServ policies in the network.
• L. Breslau, E.W. Knightly, S. Shenker, I. Stoica, H. Zhang. Endpoint Admission Control: Architectural Issues and Performance. In Proceedings of ACM SIGCOMM 2000, August 2000, Stockholm, Sweden.
  Endpoint admission control mechanisms try to ensure a requested quality of service by probing the network from the end hosts. This kind of mechanisms would avoid the scalability problems of Integrated Services, because they do not require state at the routers. This paper discusses architectural and performance issues of different approaches for Endpoint admission control. The paper concludes that although out-of-band probing often results in better loss rate, it is not always superior to in-band signaling. The identified disadvantages of endpoint admission control techniques are the substantial delay they cause on connection setup, the problems related to misuse of endpoint admission control mechanisms, and the open issues regarding deployment of endpoint admission control techniques.

Other Pointers to Literature

• S. Floyd. TCP and Changes.
  Papers describing changes to TCP to improve its performance for various kinds of network conditions, or to meet other specific requirements.
• S. Floyd. TCP and other Transport Protocols over X.
  Papers analysing Transport Performance over a specific link or network technology.

To be added:

• Papers by Hans Kruse, including Protocol Interactions
• Papers by Yongguang Zhang