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Network Working Group                                             J. You
Internet-Draft                                                  C. Xiong
Intended status: Informational                                    Huawei
Expires: April 21, 2016                                 October 19, 2015


   The Effect of Encrypted Traffic on the QoS Mechanisms in Cellular
                                Networks
               draft-you-encrypted-traffic-management-00

Abstract

   This document provides a detailed description of the QoS mechanisms
   of the 3GPP network and why encrypted IP traffic makes current QoS
   management mechanisms almost useless.  Finally, we propose some ideas
   to solve this conflict to allow QoS mechanisms to be applied to
   encrypted IP traffic whilst maintaining the confidentiality of the IP
   traffic.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

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
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   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 April 21, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Abbreviations and acronyms  . . . . . . . . . . . . . . .   3
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  The Influence of Encryption on the QoS Management . . . . . .   4
     3.1.  IPsec/VPN Tunnel-based IP Layer Encryption Effect . . . .   5
     3.2.  IMS/SIP Session Service Encryption Effect . . . . . . . .   6
     3.3.  HTTP Encryption Effect  . . . . . . . . . . . . . . . . .   6
   4.  Potential Co-operative Information between Application and
       Network . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Application to Network  . . . . . . . . . . . . . . . . .   7
     4.2.  Network to Application  . . . . . . . . . . . . . . . . .   8
   5.  Potential Bandwidth Optimization Methods  . . . . . . . . . .   8
     5.1.  Intelligent Heuristic Method  . . . . . . . . . . . . . .   8
     5.2.  Legacy Protocol Extension . . . . . . . . . . . . . . . .   9
     5.3.  New Substrate Protocol  . . . . . . . . . . . . . . . . .   9
   6.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Encryption of internet traffic is to prevent pervasive monitoring and
   protect customer privacy.  Historically, Secure Sockets Layer (SSL) /
   Transport Layer Security (TLS) were earlier used in financial
   services to encrypt a subset of Internet traffic, especially
   financial transactions.  However, the shift away from unencrypted
   traffic towards encrypted traffic is accelerating in recent years
   [I-D.mm-wg-effect-encrypt] due to concerns about privacy.  Google
   offered end-to-end encryption for Gmail since 2010, and switched all
   searches over to HTTPS in 2013.  YouTube traffic is carried via HTTPS
   (or QUIC) since 2014.  Also, the Snowden revelations [RFC7258]
   [RFC7624] seem to cause an upward surge in encrypted traffic.  A



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   large number of operators began requiring encryption for all XMPP
   traffic in May 2014 [XMPP].

   However, the prevalence of encryption impacts current network
   services, such as policy control, load balancing, etc.  The network
   services may be less efficient or totally unavailable in the case of
   fully encrypted traffic.  QoS handling is the most important part of
   the 3GPP radio resource management. 3GPP networks have limited radio
   and transmission resources and need to strictly schedule the
   utilization of radio and transmit resources using different
   granularity of bearers to provide and ensure Quality of Service (QoS)
   for the IP traffic.  Different bearers with different QoS parameters
   will provide different QoS handling for the IP flows on each bearer.
   Different IP flows can share the same bearer; IP flows on the same
   bearer will receive the same QoS handling of the 3GPP network.  With
   this binding mechanism, the 3GPP network can provide any IP flow with
   its required QoS handling.  Therefore, the 3GPP network firstly needs
   to know the IP flow information and its QoS requirements.  If this
   information is unknown, possibly as a result of encryption applied to
   the IP flow, the 3GPP network will discard this IP flow or handle the
   IP flow with default QoS.

2.  Terminology

2.1.  Abbreviations and acronyms

      AF: Application Function

      ARP: Allocation and retention priority

      EPS: Evolved packet System

      IMS: IP Multimedia Subsystem

      PCRF: Policy and Charging Rules Function

      QCI: QoS Class Identifier

      QoS: Quality of Service

      SDF: Service Data Flow

      SIP: Session Initiation Protocol

      SLA: Service-Level Agreement

      URL: Uniform/Universal Resource Locator




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2.2.  Definitions

   This section contains definitions for terms used frequently
   throughout this document.  However, many additional definitions can
   be found in [3GPP 23.203]

      ARP: The Allocation and Retention Priority for the service data
      flow consisting of the priority level, the pre-emption capability
      and the pre-emption vulnerability.

      IP CAN bearer: An IP transmission path of defined capacity, delay
      and bit error rate, etc.

      GBR bearer: An IP CAN bearer with reserved (guaranteed) bitrate
      resources.

      Non-GBR bearer: An IP CAN bearer with no reserved (guaranteed)
      bitrate resources.

      QoS class identifier: A scalar that is used as a reference to a
      specific packet forwarding behavior (e.g. packet loss rate, packet
      delay budget) to be provided to a SDF.

      QoS: It contains the QoS class identifier and the data rate for a
      service data flow.

      Service data flow: An aggregate set of packet flows that matches a
      service data flow template.

      Service data flow template: The set of service data flow filters
      that contains a set of packet flow header parameter values/ranges
      used to identify one or more of the packet flows.

3.  The Influence of Encryption on the QoS Management

   EPS provides different levels of QoS guarantee for IP services.  Any
   IP service can be identified by one or more Service Data Flows (SDFs)
   of the transfer data.  A SDF can be identified by one or more IP Flow
   Filters, and a SDF is transferred through an EPS bearer.  By
   implementing the QoS of EPS bearer, it can realize the QoS of SDF,
   and realize the QoS of IP services.  The EPS bearer is one type of
   logical transport channel between the UE to Packet Gateway (PGW).

   In general, if the cellular network cannot know the SDF of one IP
   service in advance or the content type of the transmission data and
   its QoS requirements, the SDF of the IP service is usually mapped to
   the Default Bearer with the Default QoS or is mapped to a poor ARP
   (Allocation and retention priority) dedicated EPS (Evolved packet



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   System) Bearer with default QCI or is discarded because of the
   unknown service information of the SDF based on the predefined
   operators rules.

   Through our analysis of impacted services in the case of encrypted
   traffic, we find that the impacted services can be categorized into
   three types based on the level of dependence to content visibility:

   A: Low-level dependence

      A service that is low-level dependent on the content visibility
      means the service can be effective providing with flow type (e.g.
      stream ID) rather than parsing the content itself.  The typical
      services of low-level dependence are IPsec/VPN tunnel, load
      balancing, etc.

   B: Middle-level dependence

      A service that is middle-level dependent on the content visibility
      means the service can be effective providing with access metadata
      (e.g. domain name, URI) besides flow type rather than parsing the
      content itself entirely.  Through the metadata different access
      features can be distinguished, thus appropriate actions could be
      enforced based on these features.  For example, illegal websites
      can be filtered.  The typical services of middle-level dependence
      are IMS/SIP service, parental controls, etc.

   C: High-level dependence

      A service that is high-level dependent on the content visibility
      means the service can be effective requiring analysis of content
      itself, even interaction procedure.  The typical services of high-
      level dependence are web acceleration, video caching, which
      usually requires user access behavior and detailed video content
      (e.g. encoding format).  In the case of encrypted traffic, this
      kind of service will not be available.

3.1.  IPsec/VPN Tunnel-based IP Layer Encryption Effect

   In this case, the internal real port number is invisible to cellular
   network and the tunnel-based IP traffic is usually mapped to the
   Default Bearer with Default QoS or to a dedicated EPS bearer with
   poor ARP and the same default QCI.  If the VPN is from a big
   customer, the special tunnel-based IP traffics are mapped to a
   special dedicated EPS bearer with special QoS according the
   predefined rules and SLA (Service-Level Agreement).  This might
   result in more dedicated EPS bearers with different QoS used to




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   transport the different tunneled-IP traffic with different QoS
   requirements.

3.2.  IMS/SIP Session Service Encryption Effect

   The cellular network can beforehand obtain the IP 5-tuple information
   of SDF of the voice, video and data parts and the content type of
   each SDF during the Offer/Answer signalling interaction if the
   signalling connection between the IMS/SIP UA (User Agent) and IMS/SIP
   server is plaintext without encryption.  Alternatively, the IMS/SIP
   Server or the AF (Application Function) in the server can actively
   tell the cellular network via the Rx interface to the PCRF (Policy
   and Charging Rule Function) [3GPP 23.203] all the voice, video and
   data SDF information even when the signalling connection is
   encrypted.  Even if the transmission of voice, video media above the
   transport layer is encrypted, such as using SRTP (Secure Real-time
   Transport Protocol), the cellular network can realize SDF detection
   and further can guarantee the SDF with the correct ARP and QoS
   control because the IP Flow information is known by the cellular
   network beforehand.

   If the cellular network cannot obtain prior SDF information on the
   voice, video and data part of the session because the signalling
   connection is encrypted and the server/AF does not provide the SDF
   information, if the voice and video use different IP flows, the
   cellular network still can identify the SDF type through using
   intelligent heuristic algorithms which can identify the difference
   content type by the transmission span of two successive packets,
   packet size and other information.  After the cellular network
   identifies the SDF information of voice, video and other (data)
   parts, the cellular network can realize the corresponding QoS control
   and ARP and ensure the whole session's QoS.

3.3.  HTTP Encryption Effect

   Currently HTTP 1.1 is the most widely used service/application
   protocol and it is expected to be widely replaced by HTTP 2 in the
   near future.  HTTP supports transport of various types of data in a
   single TCP connection.  Due to a single TCP connection corresponding
   to a single SDF, and different types of data and services are
   transmitted on the same TCP connection, the result is traditional
   SDF-based mapping SDFs transmitting different types of content/data
   to different EPS Bearers with different QoS and ARP no longer works
   well or is applicable for the cellular network.  Instead, cellular
   network operators evolve and adopt new types of QoS-related
   acceleration technologies to realize and improve the user's
   experience.  Therefore, Mobile CDN technology, Mobile Video
   Optimization technology, Mobile Web Optimization, Anti-Virus, Anti-



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   Spoofing, Parent Control technology and all kinds of value-added
   technologies emerge and are widely used.  These technologies can
   reduce the transport cost of cellular network and at the same time
   can greatly improve mobile user video and web browsing experience.

   When HTTP2 and HTTP1.1 use TLS to encrypt the TCP connection, the
   widely used Web acceleration and value-added technologies no longer
   work well.  The usual result is the HTTPS connection is mapped to the
   Default Bearer with Default QoS or dedicated EPS bearer with default
   QCI and poor ARP.  Therefore, there is no guarantee for the different
   services provided by HTTPS websites.  One exception is if there is a
   SLA/cooperation agreement, then the cellular network can map the TCP
   connection of the HTTPS website to a dedicated EPS bearer with
   special QoS, then the QoS for the HTTS website may be improve
   respectively with the special dedicated EPS Bearer and the specific
   QoS.

4.  Potential Co-operative Information between Application and Network

4.1.  Application to Network

   A SDF is mapped to a specific QoS EPS Bearer, and SDFs associated
   with different IP services can be mapped to the same EPS Bearer with
   the same QoS parameters (namely QCI (QoS Class Identifier) and ARP
   (Allocation and retention priority)) [PCC].

   So application could provide the service level (i.e. per SDF) QoS
   parameters such as QCI and APR to indicate how certain service/
   application traffic shall be treated in the operator's network.  For
   example, given that the categories in table 1 map to GBR and non-GBR
   resources, with a priority level, it seems cleaner to reveal just the
   resource type and priority.  This also seems possible to encode in a
   space similar to the QCI.


















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    Table 1: Standardized QCI characteristics
   +------+----------------+-----------------+
   | QCI  | Resource Type  | Priority Level  |
   +------+----------------+-----------------+
   |  1   |                |        2        |
   +------+                +-----------------+
   |  2   |                |        4        |
   +------+                +-----------------+
   |  3   |                |        3        |
   +------+    GBR         +-----------------+
   |  4   |                |        5        |
   +------+                +-----------------+
   |  65  |                |        0.7      |
   +------+                +-----------------+
   |  66  |                |        2        |
   +------+----------------+-----------------+
   |  5   |                |        1        |
   +------+                +-----------------+
   |  6   |                |        6        |
   +------+                +-----------------+
   |  7   |                |        7        |
   +------+                +-----------------+
   |  8   |   Non-GBR      |        8        |
   +------+                +-----------------+
   |  9   |                |        9        |
   +------+                +-----------------+
   |  69  |                |        0.5      |
   +------+                +-----------------+
   |  70  |                |        5.5      |
   +------+----------------+-----------------+

4.2.  Network to Application

   The network could provide the application with the real time
   information about the throughput estimated to be available at the
   radio downlink interface between a UE and the base station the UE
   connects to, which is discussed in
   [I-D.flinck-mobile-throughput-guidance].

5.  Potential Bandwidth Optimization Methods

5.1.  Intelligent Heuristic Method

   By collection and convergence of the information of packet interval,
   packet size, port number, protocol type etc, the intelligent
   heuristic algorithm can guess correctly some the types of the content
   of the packet transmission as mentioned in previous chapter of IMS/
   SIP session type communication.



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   This method can be implemented in the mostly widely deployed Apache
   and or nginx HTTP Server package without destroying any current
   protocols.  This method requires the OTT to deploy the modified
   Apache/nginx HTTP Server and an intelligent heuristic algorithm
   running in the cellular network to identify the dynamically changed
   content type of the encrypted HTTPS connection.

5.2.  Legacy Protocol Extension

   Regarding to the low-level dependence services, existing protocols
   could be extended in order to carry flow type, for example, enhancing
   TLS header.

   A new TCP option to identify the encrypted content type has certain
   feasibility, but it may have problems when passing through some
   existing middleboxes.

   For DSCP method, it requires OTTs to set the right DSCP field of
   outer IP packet corresponding to different content types in the
   encrypted TLS connection.  But the DSCP value may be modified by the
   routers from the OTT to the cellular network.

5.3.  New Substrate Protocol

   New substrate protocols over existing transport layers, such as UDP,
   TCP, are considered to carry flow information in order to make
   middle-level dependence service effective.

   Developing UDP-based substrate protocols to enable transport
   evolution is a hot topic in IETF recently.  The QUIC protocol from
   Google falls into this space; however, QUIC is not aiming to solve
   the encrypted traffic management.  One major issue with UDP-based
   substrate is middleboxes may block UDP or limit rate.  SPUD-like
   [I-D.hildebrand-spud-prototype] UDP-based substrate could be a
   potential method to allow traffic management while using transport
   protocols.  How middleboxes trust the information exposed by the
   endpoints should be considered.

   However today's Internet is full of middleboxes that may interfere
   with the information sent in IP packets and TCP segments.  "Is it
   still possible to extend TCP?"  [ExtendTCP] shows the limitation
   imposed on TCP extensions by middleboxes behaviors, such as TCP
   options removed or updated, the source and destination port numbers
   translated by NATs.  Though we can still extend TCP to support
   middle-level dependence services, extensions are very constrained as
   it needs to take into account middleboxes behaviors.





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6.  Conclusion

   In this draft the importance of QoS in the cellular network service
   is discussed and the basic QoS management concept in the EPS system
   is described.  Regarding to the low/middle-level dependence services,
   the challenges for potential traffic management methods for encrypted
   traffic are analyzed.  Furthermore, possible IETF standardization
   work (i.e. legacy protocol extensions and new substrates) is explored
   in order to solve the conflict between user privacy and traffic
   management.

7.  Acknowledgement

   The editors would like to thank Ted Hardie and Dan Druta for their
   useful comments.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <http://www.rfc-editor.org/info/rfc7258>.

   [RFC7624]  Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
              Trammell, B., Huitema, C., and D. Borkmann,
              "Confidentiality in the Face of Pervasive Surveillance: A
              Threat Model and Problem Statement", RFC 7624,
              DOI 10.17487/RFC7624, August 2015,
              <http://www.rfc-editor.org/info/rfc7624>.

8.2.  Informative References

   [ExtendTCP]
              Honda, M., Nishida, Y., Raiciu, C., Greenhalgh, A.,
              Handley, M., and H. Tokuda, "Is it Still Possible to
              Extend TCP", IMC'11 Page(s): 2-4, November 2011.

   [I-D.flinck-mobile-throughput-guidance]
              Jain, A., Terzis, A., Flinck, H., Sprecher, N.,
              Swaminathan, S., and K. Smith, "Mobile Throughput Guidance
              Inband Signaling Protocol", draft-flinck-mobile-
              throughput-guidance-03 (work in progress), September 2015.



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   [I-D.hildebrand-spud-prototype]
              Hildebrand, J. and B. Trammell, "Substrate Protocol for
              User Datagrams (SPUD) Prototype", draft-hildebrand-spud-
              prototype-03 (work in progress), March 2015.

   [I-D.mm-wg-effect-encrypt]
              Moriarty, K. and A. Morton, "Effect of Ubiquitous
              Encryption", draft-mm-wg-effect-encrypt-02 (work in
              progress), July 2015.

   [PCC]      "3GPP TS 23.203, "Policy and charging control
              architecture"", 2015.

   [XMPP]     ""XMPP switches on mandatory encryption"
              (http://lwn.net/Articles/599647/)", May 2014.

Authors' Addresses

   Jianjie You
   Huawei
   101 Software Avenue, Yuhuatai District
   Nanjing,  210012
   China

   Email: youjianjie@huawei.com


   Chunshan Xiong
   Huawei
   No.3, Xin-Xi Rd., Haidian District
   Beijing,  100085
   China

   Email: sam.xiongchunshan@huawei.com

















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