Internet Engineering Task Force G. Chen Internet-Draft H. Deng Intended status: Informational China Mobile Expires: September 8, 2011 March 7, 2011 Problem Statement of Long-lived TCP Connection draft-chen-long-lived-connection-ps-00 Abstract This memo describes issues encountered by a long-lived TCP connection. Long-lived TCP connections are served for several applications, which are quite popularly used in our daily life, such as chat and messaging(MSN, Skype). Others are computer-to-computer communications, which are also demanding at long-lived TCP connection. Issues such as network resources consumption happen when there are frequent keepalive message has been transmitted periodically. Moreover, other issues are occurring during long TCP connection, such as TCP congestion, TCP connection recovery. Depending on raised issues, protocol optimization could be considered to optimize network quality. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 8, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Chen & Deng Expires September 8, 2011 [Page 1] Internet-Draft Long-lived-connection March 2011 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Chen & Deng Expires September 8, 2011 [Page 2] Internet-Draft Long-lived-connection March 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Traffic Features of Long-lived TCP Connection . . . . . . . . . 4 3. Problems caused by Long-Lived TCP Connection . . . . . . . . . 5 3.1. Keepalive issues . . . . . . . . . . . . . . . . . . . . . 5 3.2. TCP Congestion Issues . . . . . . . . . . . . . . . . . . . 5 3.3. TCP connection Recovery Issues . . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Chen & Deng Expires September 8, 2011 [Page 3] Internet-Draft Long-lived-connection March 2011 1. Introduction Traffic in the Internet is a complex mix of effects from protocols, different application characteristics, and user behaviors. Understanding traffic is essential for network protocol optimization and quality improvement. This memo describes issues encountered by a long-lived TCP connection. Long-lived TCP connection is served for several applications, which are quite popularly used in our daily life, such as chat and messaging(MSN, Skype). Others are computer- to-computer communications. Such traffic is growing due to automated control and sensing, online backup, and distributed processing in the cloud and across distributed data centers. This kind applications are demanding at long-lived TCP connection. The long-lived TCP connections have impacts on normal network behavior.Issues such as network resources consumption happen when there are frequent keepalive message has been transmitted periodically. Moreover, long TCP connection will lead to others issues, such as TCP congestion, TCP connection recovery. Depending on raised issues, protocol optimization could be considered to optimize the network quality. 2. Traffic Features of Long-lived TCP Connection The traffic features of long-lived TCP depends on specific applications usages characteristics. In some cases, TCP is not able to fully utilize the transport or network layer resources because the application does not produce data fast enough. The application is producing small amounts of data at a relatively constant rate for the TCP layer. This results in small bursts of packets, in the extreme case a single packet of size less than the maximum segment size of the connection. Typical examples are live streaming applications such as Skype that transfer data over TCP at a constant rate of 32 Kbit/s. Also, applications that use permanent TCP connections and send keep-alive packets during inactive periods, fall in this category (BitTorrent exhibits this behavior during choke periods). In some scenarios, application is producing data in bursts separated from each other by idle periods. An example of such behavior is web browsing with persistent HTTP connections. The user clicks on a link to load a web page, causing a transfer period, reads the page, causing an idle period, and clicks on another link, causing another transfer period. From duration point of view, hour time-scales are dominated by web Chen & Deng Expires September 8, 2011 [Page 4] Internet-Draft Long-lived-connection March 2011 (HTTP, HTTPS, ports 80 and 443) destinations.Day-long flows contain background traffic, with computer-driven but human initiated protocols like chat and messaging. Week-long flows are almost all computer-to-computer protocols that run without human involvement, such as time synchronization (ntp) and multicast control (sd, pim, sapv1). 3. Problems caused by Long-Lived TCP Connection This section describes possible problems caused by long-lived TCP connection. 3.1. Keepalive issues Keepalive is to prevent inactivity from disconnecting the channel. It's a very common phenomenons, when you are behind a NAT proxy or a firewall, you could be disconnected without a reason. This behavior is caused by the connection tracking procedures implemented in NAT/FW, which keep track of all connections that pass through them. Because of the physical limits of these machines, they can only keep a finite number of connections in their memory. The most common and logical policy is to keep newest connections and to discard old and inactive connections first. Frequent TCP keepalive message will help to constantly maintain mapping records in NAT/FW, and eliminate interruptions of TCP connections. However, it will cause significant network resource consumption, especially, in wireless environment. The dedicated air channel resource need to be assigned to each keepalive signaling. The numerous keepalive messages might cause air resource depletion, and degrade other application performance. Currently, PCP [PCP] is a way to optimize this situation. 3.2. TCP Congestion Issues When long-lived TCP connections produce data in bursts, it mostly operates in congestion avoidance phase probing for bandwidth with larger windows, they produce larger packet bursts. TCP connections with large window sizes are more tolerant of packet loss than those with small windows. While long-lived TCP flows may recover from multiple packet losses in one round-trip time (RTT), short-lived TCP flows may have to wait for a timeout period to recover from a single packet loss. It is observed that long-lived TCP flows may completely shut off short-lived TCP flows. This causes performance problems for short-lived TCP flows, which generally carry interactive/delay sensitive data. Chen & Deng Expires September 8, 2011 [Page 5] Internet-Draft Long-lived-connection March 2011 3.3. TCP connection Recovery Issues TCP was not initially designed to cope with some of the extreme conditions which cause frequent disconnections. In this sceanrio, TCP connection will try to re-transmit to re-establish TCP connection. It will cause bad user experiences and network consumptions. 4. IANA Considerations This memo includes no request to IANA. 5. Security Considerations TBD 6. Normative References [PCP] Wing, D., "Pinhole Control Protocol (PCP)", draft-ietf-pcp-base-06.txt (work in progress), February 2011. Authors' Addresses Gang Chen China Mobile 53A,Xibianmennei Ave., Xuanwu District, Beijing 100053 China Email: chengang@chinamobile.com Hui Deng China Mobile 53A,Xibianmennei Ave. Beijing 100053 P.R.China Phone: +86-13910750201 Email: denghui02@gmail.com Chen & Deng Expires September 8, 2011 [Page 6]