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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force G. Chen 3 Internet-Draft H. Deng 4 Intended status: Informational China Mobile 5 Expires: September 8, 2011 March 7, 2011 7 Problem Statement of Long-lived TCP Connection 8 draft-chen-long-lived-connection-ps-00 10 Abstract 12 This memo describes issues encountered by a long-lived TCP 13 connection. Long-lived TCP connections are served for several 14 applications, which are quite popularly used in our daily life, such 15 as chat and messaging(MSN, Skype). Others are computer-to-computer 16 communications, which are also demanding at long-lived TCP 17 connection. Issues such as network resources consumption happen when 18 there are frequent keepalive message has been transmitted 19 periodically. Moreover, other issues are occurring during long TCP 20 connection, such as TCP congestion, TCP connection recovery. 21 Depending on raised issues, protocol optimization could be considered 22 to optimize network quality. 24 Status of this Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on September 8, 2011. 41 Copyright Notice 43 Copyright (c) 2011 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 This document may contain material from IETF Documents or IETF 57 Contributions published or made publicly available before November 58 10, 2008. The person(s) controlling the copyright in some of this 59 material may not have granted the IETF Trust the right to allow 60 modifications of such material outside the IETF Standards Process. 61 Without obtaining an adequate license from the person(s) controlling 62 the copyright in such materials, this document may not be modified 63 outside the IETF Standards Process, and derivative works of it may 64 not be created outside the IETF Standards Process, except to format 65 it for publication as an RFC or to translate it into languages other 66 than English. 68 Table of Contents 70 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 71 2. Traffic Features of Long-lived TCP Connection . . . . . . . . . 4 72 3. Problems caused by Long-Lived TCP Connection . . . . . . . . . 5 73 3.1. Keepalive issues . . . . . . . . . . . . . . . . . . . . . 5 74 3.2. TCP Congestion Issues . . . . . . . . . . . . . . . . . . . 5 75 3.3. TCP connection Recovery Issues . . . . . . . . . . . . . . 6 76 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 77 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 78 6. Normative References . . . . . . . . . . . . . . . . . . . . . 6 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 81 1. Introduction 83 Traffic in the Internet is a complex mix of effects from protocols, 84 different application characteristics, and user behaviors. 85 Understanding traffic is essential for network protocol optimization 86 and quality improvement. This memo describes issues encountered by a 87 long-lived TCP connection. Long-lived TCP connection is served for 88 several applications, which are quite popularly used in our daily 89 life, such as chat and messaging(MSN, Skype). Others are computer- 90 to-computer communications. Such traffic is growing due to automated 91 control and sensing, online backup, and distributed processing in the 92 cloud and across distributed data centers. This kind applications 93 are demanding at long-lived TCP connection. 95 The long-lived TCP connections have impacts on normal network 96 behavior.Issues such as network resources consumption happen when 97 there are frequent keepalive message has been transmitted 98 periodically. Moreover, long TCP connection will lead to others 99 issues, such as TCP congestion, TCP connection recovery. Depending 100 on raised issues, protocol optimization could be considered to 101 optimize the network quality. 103 2. Traffic Features of Long-lived TCP Connection 105 The traffic features of long-lived TCP depends on specific 106 applications usages characteristics. 108 In some cases, TCP is not able to fully utilize the transport or 109 network layer resources because the application does not produce data 110 fast enough. The application is producing small amounts of data at a 111 relatively constant rate for the TCP layer. This results in small 112 bursts of packets, in the extreme case a single packet of size less 113 than the maximum segment size of the connection. Typical examples 114 are live streaming applications such as Skype that transfer data over 115 TCP at a constant rate of 32 Kbit/s. Also, applications that use 116 permanent TCP connections and send keep-alive packets during inactive 117 periods, fall in this category (BitTorrent exhibits this behavior 118 during choke periods). 120 In some scenarios, application is producing data in bursts separated 121 from each other by idle periods. An example of such behavior is web 122 browsing with persistent HTTP connections. The user clicks on a link 123 to load a web page, causing a transfer period, reads the page, 124 causing an idle period, and clicks on another link, causing another 125 transfer period. 127 From duration point of view, hour time-scales are dominated by web 128 (HTTP, HTTPS, ports 80 and 443) destinations.Day-long flows contain 129 background traffic, with computer-driven but human initiated 130 protocols like chat and messaging. Week-long flows are almost all 131 computer-to-computer protocols that run without human involvement, 132 such as time synchronization (ntp) and multicast control (sd, pim, 133 sapv1). 135 3. Problems caused by Long-Lived TCP Connection 137 This section describes possible problems caused by long-lived TCP 138 connection. 140 3.1. Keepalive issues 142 Keepalive is to prevent inactivity from disconnecting the channel. 143 It's a very common phenomenons, when you are behind a NAT proxy or a 144 firewall, you could be disconnected without a reason. This behavior 145 is caused by the connection tracking procedures implemented in 146 NAT/FW, which keep track of all connections that pass through them. 147 Because of the physical limits of these machines, they can only keep 148 a finite number of connections in their memory. The most common and 149 logical policy is to keep newest connections and to discard old and 150 inactive connections first. 152 Frequent TCP keepalive message will help to constantly maintain 153 mapping records in NAT/FW, and eliminate interruptions of TCP 154 connections. However, it will cause significant network resource 155 consumption, especially, in wireless environment. The dedicated air 156 channel resource need to be assigned to each keepalive signaling. 157 The numerous keepalive messages might cause air resource depletion, 158 and degrade other application performance. Currently, PCP [PCP] is a 159 way to optimize this situation. 161 3.2. TCP Congestion Issues 163 When long-lived TCP connections produce data in bursts, it mostly 164 operates in congestion avoidance phase probing for bandwidth with 165 larger windows, they produce larger packet bursts. TCP connections 166 with large window sizes are more tolerant of packet loss than those 167 with small windows. While long-lived TCP flows may recover from 168 multiple packet losses in one round-trip time (RTT), short-lived TCP 169 flows may have to wait for a timeout period to recover from a single 170 packet loss. It is observed that long-lived TCP flows may completely 171 shut off short-lived TCP flows. This causes performance problems for 172 short-lived TCP flows, which generally carry interactive/delay 173 sensitive data. 175 3.3. TCP connection Recovery Issues 177 TCP was not initially designed to cope with some of the extreme 178 conditions which cause frequent disconnections. In this sceanrio, 179 TCP connection will try to re-transmit to re-establish TCP 180 connection. It will cause bad user experiences and network 181 consumptions. 183 4. IANA Considerations 185 This memo includes no request to IANA. 187 5. Security Considerations 189 TBD 191 6. Normative References 193 [PCP] Wing, D., "Pinhole Control Protocol (PCP)", 194 draft-ietf-pcp-base-06.txt (work in progress), February 2011. 196 Authors' Addresses 198 Gang Chen 199 China Mobile 200 53A,Xibianmennei Ave., 201 Xuanwu District, 202 Beijing 100053 203 China 205 Email: chengang@chinamobile.com 207 Hui Deng 208 China Mobile 209 53A,Xibianmennei Ave. 210 Beijing 100053 211 P.R.China 213 Phone: +86-13910750201 214 Email: denghui02@gmail.com