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service function chain                                            C. Xie
Internet-Draft                                                    Q. Sun
Intended status: Standards Track                           China Telecom
Expires: September 10, 2015                                      W. Meng
                                                                 C. Wang
                                                         ZTE Corporation
                                                           B. Khasnabish
                                                            ZTE TX, Inc.
                                                           March 9, 2015


             service function chain Use Cases in Broadband
                  draft-meng-sfc-broadband-usecases-03

Abstract

   This document discusses about service function chain use cases in
   different scenarios of broadband network.  The document provides
   analysis of different solutions and also describes the feasible
   deployment scenarios corresponding to each solution.

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 10, 2015.

Copyright Notice

   Copyright (c) 2015 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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Convention and Terminology . . . . . . . . . . . . . . . . . .  5
   3.  Use cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Internet Access from Homes . . . . . . . . . . . . . . . .  6
       3.1.1.  Native IPv4 Network or Native IPv6 Network . . . . . .  6
       3.1.2.  IPv4/IPv6 Coexist Network  . . . . . . . . . . . . . .  7
     3.2.  Internet Access from Enterprises . . . . . . . . . . . . . 11
     3.3.  Internet Access from Campuses  . . . . . . . . . . . . . . 12
     3.4.  Added-value Service Access . . . . . . . . . . . . . . . . 12
       3.4.1.  Destination Address Accounting(DAA)  . . . . . . . . . 13
       3.4.2.  IPTV . . . . . . . . . . . . . . . . . . . . . . . . . 14
       3.4.3.  VoIP/MoIP  . . . . . . . . . . . . . . . . . . . . . . 16
   4.  Considerations . . . . . . . . . . . . . . . . . . . . . . . . 17
     4.1.  Service Function Chain Symmetry  . . . . . . . . . . . . . 17
     4.2.  Deploying consideration  . . . . . . . . . . . . . . . . . 17
       4.2.1.  Standalone mode  . . . . . . . . . . . . . . . . . . . 17
       4.2.2.  Directly connecting mode . . . . . . . . . . . . . . . 19
     4.3.  Pool consideration . . . . . . . . . . . . . . . . . . . . 21
     4.4.  NAT traversal  . . . . . . . . . . . . . . . . . . . . . . 21
     4.5.  Unify home router  . . . . . . . . . . . . . . . . . . . . 21
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   7.  Normative References . . . . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25



















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1.  Introduction

   The object of SFC is trying to unload services from legacy devices in
   traditional network and deal with such services through corresponding
   service functions which are topologically independent from physical
   devices.

   As increasingly large number of customers, the possibility of
   deployment SFC in broadband network seems emergency.  And this
   document aims to illustrate the possibly typical and unified service
   function chains in Broadband Networks and analyze the possible
   deployments of diverse service function chains in broadband network.

   In figure 1, here outlines the possible SFC deployment architecture
   in Broadband Networks.  This architecture tries to simplify and unify
   the services in CPEs and unloads the services from CPEs to the SFCs
   in Access Networks to achieve virtual CPE functions.  And as well,
   extracts the services in BNASs and offloads the services from BNASs
   to the SFCs in Barrier Networks to accomplish virtual BNAS functions.
   As a result of that, the Internet Service Provider can manage and
   maintain the whole Broadband Networks more flexibly.






























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                 +-----------+       +-----------+
                 |    Host1  |  ...  |    HostN  |
                 +-----+-----+       +-----+-----+
                       |                   |
                 +-----+-----+       +-----+-----+
                 | classifer |       | classifer |
                 +-----+-----+       +-----+-----+
                       |                   |
                       |---------|---------|
                                 |
                         +-------+---------+
                         |    SFCs/vCPEs   |
           .             +-------+---------+          .
           .                     |                    .
   +-------|---------+   +-------|---------+  +-------|---------+
   |switch/classifier|   |switch/classifier|  |switch/classifier|  ...
   +-------|---------+   +-------|---------+  +-------|---------+
           |                     |                    |
           +---------------------|--------------------+
                                 |
                          +------+------+
                          | SFCs/vBNASs |
                          +------+------+
                                 |
                         --------|--------
                       /         |         \
                      |       Internet      |
                       \         |         /
                         --------|--------

              Figure 1: SFC Architecture of Broadband Network




















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2.  Convention and Terminology

   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].

   The terms about SFC are defined in [I-D.ietf-sfc-problem-statement].

   The terms about CGN/DS-Lite/Lightweight 4o6/MAP/NAT64 are defined in
   [RFC6888]/[RFC6333]/ [I-D.ietf-softwire-lw4over6]/
   [I-D.ietf-softwire-map]/ [RFC6146].








































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3.  Use cases

   The following sections highlight some of the most common broadband
   network use case scenarios and are in no way exhaustive.

3.1.  Internet Access from Homes

   Figure 2 illustrates an abstract architecture of broadband network,
   including CPE sitting in home access network, BNAS as broadband access
   network gateway,CR located in bone network and the Internet.

      +---+      +------+        +-----+      +---------+
      |CPE|------| BNAS |--------| CR  |------| Internet|
      +---+      +------+        +-----+      +---------+

                Figure 2: Architecture of Broadband Network

   Also, the Broadband Forum(BBF) is developing a study document(SD-
   326), which aims to study market requirements and usecases for
   Flexible Service Chaining.  Except that, this document tries to
   develop more typical usecases in Broadband Networks.

3.1.1.  Native IPv4 Network or Native IPv6 Network

     ---------------------------------------------------------------------------->
                   +--- +   +-------+   +-----+   +----------+
                   |    |   |DPI/DFI|   | LB/ |   |URL Filter|---|
                |--| UM |---|  /Qos |---| FRR |---|  /FW/PC  |   |
                |  +----+ | +-------+ | +-----+ | +----------+   |
    +---+  +------+       |           |         |             +-----+     +---------+
    |CPE|--| BNAS-|-------|-----------|---------|-------------| CR  |-----| Internet|
    +---+  +------+                                           +-----+     +---------+

           Figure 3: Native IPv4 Network or Native IPv6 Network

   Figure 3 shows possible deployment of SFC in native IPv4 network or
   native IPv6 network.  As UM(users management) service, which is the
   main service of BNAS device in traditional network, consumes large
   memory and resources, it seems reasonable to decouple UM service from
   legacy BNAS device and treat it as a service node , which may include
   DHCP,AAA functions and some other functions related to users
   management.  And what's more, only users subscription messages
   (protocol messages) go through UM service.  Once a user is approved
   by UM service, the following data flow of this user go through the
   other service function chain which is assigned to this data flow.

   'BNAS-' means some functions have been unburdened from traditional
   BNAS,such as user management,Qos,Load Balance and so forth.



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   Given that SFC is applied in Broadband network, the main SFs may
   cover: User Management, DPI, DFI, Qos, Load Balance, Fast Reroute,
   URL Filter,Firewall,Parental Control and so forth.  And the possible
   order is not as strict as above.  The upstream/downstream traffic may
   go through different permutations and combination of these SNs.  For
   example:

   SFC1: UM

   This SFC stands for the process of subsribers's log-in and log-out.
   All the broadband subscribers's log-in messages and log-out messages
   need go through this SFC.  After approved by this SFC, then the users
   flow can access the Internet or other services through differentiated SFCs.

   SFC2: Qos

   This SFC shows some bandwidth restrictions or several priority-based
   schedules are applied to this approved subscriber.  Almost each home
   subscriber has a corresponding subscribed bandwidth, different
   services from a home have distinctive priority as well.  As a result,
   this is a basic SFC used in internet access from homes.

   SFC3: Qos--LB

   This SFC extends SFC2, which utilizes load balance to offload
   approved subscribers's flow from an overload path.  This is also a
   typical scenario in broadband network, especially in metropolitan
   area network.

   SFC4: Qos--LB--URL Filter

   Based on SFC3, this SFC gives extra restrictions to the content
   the approved subscriber wants to access.

   SFC5: Qos--Parental Control

   This is similar to SFC4,except there is no Load Balance.  Another
   difference is that SFC5 offers some restrictions to downstream
   traffic in terms of content.  SFC5 allows some legal or appropriate
   contents to flow to subscribers, while some illegal or inappropriate
   contents are blocking.

3.1.2.  IPv4/IPv6 Coexist Network

   As showed below in figure 4, the main difference between IPv4/IPv6
   native network and IPv4/IPv6 coexist network is whether there exists
   a NAT funtion.  Although in IPv4 native network, there maybe exist
   NAT44 function as a result of limited IPv4 address, we try to put



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   this scenario together with other IPv6 transition scenarioes in this
   section and discuss them in detail.

     ---------------------------------------------------------------------------->
                 +--- +   +-------+   +-----+   +----------+
                 |    |   |DPI/DFI|   | LB/ |   |URL Filter|---|
           |-----|NAT |---|  /Qos |---| FRR |---|  /FW/PC  |   |
           |     +----+ | +-------+ | +-----+ | +----------+   |
+---+  +------+         |           |         |             +-----+   +---------+
|CPE|--| BNAS-|---------|-----------|---------|-------------| CR  |---| Internet|
+---+  +------+                                             +-----+   +---------+

                    Figure 4: IPv4/IPv6 Coexist Network

   Whether NAT stands for NAT44 or NAT64 or NAT46 depends on the the
   Internet Server Provider.  It may be NAT44, which reflects the
   communication between IPv4 private customer and IPv4 public server.
   Or it may be NAT64, which means the communication between IPv6
   customer and IPv4 Server.  And where NAT is deployed is the
   preferance of the Internet Server Provider as well.  It may be
   besides BNAS,which stands for distributed deployment, or besides
   CR,which represents central deployment.

   Above figure 4 just gives a simple example of a possible deployment
   position in distributed deployment scenario.  Actually, there are
   some other complicated IPv6 transition scenarioes .  And this section
   tries to give some typical examples in IPv4/IPv6 coexist network, and
   conclude a feasible SFC architecture in IPv4/IPv6 coexist network.
   Also, in the following sections, the other SFs emphasized in section
   3.1.1 are not highlighted, just try to keep the diagram simple and
   suitable for the draft's specification.

3.1.2.1.  NAT44

   Figure 5 illustrates a simple NAT44 scenario how SF-NAT is deployed
   and how SF-NAT may work.















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                                 .
                                 :
                                 |
                 ............... |
              External realm     |
              ISP network-->     |-------------+
                                 |        ++---|----++
                                 |        | SF-NAT44 |
                                 |        ++---|----++
                                 |-------------+
                             ++--|----+
                 ........... |  BNAS-  |
             Internal realm  ++------++
                               |    |
              ISP network-->   |    |
                               |    |
                       ++------++  ++------++
                       |  CPE1  |  |  CPE2  |  etc.
                       ++------++  ++------++

                              Figure 5: NAT44

   In distributed broadband networks, SNs may be deployed beside BNAS.
   These SNs may contain or logically connect to SF-NAT and other
   service functions such as UM,QOS,Load Balance,etc.

   Here gives an example of possible SFC in IPv4/IPv6 coexist network,
   which combines NAT function with the service functions in native
   IPv4/IPv6 network.

   SFC6: Qos--NAT--LB--URL Filter

   SFC6 combines NAT function with SFC4, and represents the classical
   scenario in IPv4/IPv6 coexist network.  After customers have
   subscribed, apply subscriber-based Qos policy, then transform IPv4/
   IPv6 address into IPv4 address, and do five-tuple load balance for
   the outbound traffic.

   At last, monitor the outbound traffic and decide whether to permit
   them to the internet or block them.

   After the first packet of an outbound flow has been processed by this
   SFC, this SFC can do SFP optimization to bypass NAT service function
   to improve the experience of this subscriber.  Then, for the
   following packets of this outbound flow, the SFF connects to NAT
   service function can forward them according to the forwarding table
   which is derived from the NAT service function.




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   As for the inbound flow of this subscriber, there exists an open
   issue: how the inbound flow is steered to the same NAT service
   function or the same SFF which connects to the same NAT service
   function.

3.1.2.2.  DS-Lite

   Figure 6 describes a scenario of DS-lite, which completes IPv4
   communication between IPv4 private customer and IPv4 server across
   IPv6 network through tunnels.  And the main principle of DS-Lite is
   to encapsulate IPv4 packets in IPv6 Header and forward this IPv4-in-
   IPv6 packets to CGN device and enforce NAT function in CGN device.
   Generally, CGN device resides in BNAS device.

                     +-----------+
                     | IPv4 Host |
                     +-----+-----+
                           |
                 +---------|---------+
                 |       CPE-        |
                 +---------|---------+
                           +-----------------+
                           |           +-----|--------+
                           |           | SF-Dslite-Enc|
                           |           +-----|--------+
                           +-----------------+
                          |||
                          |||<-IPv4-in-IPv6 softwire
                          |||
                 +--------|||--------+
                 |        BNAS-       |
                 +--------|||--------+
                           +----------------------+
                           |           +----------|----------+
                           |           |     SF-Dslite-Dec   |
                           |           |        SF-NAT       |
                           |           +----------|----------+
                           +-----------------+
                           |
                           |
                   --------|--------
                 /         |         \
                |  IPv4 Internet     |
                 \         |         /
                   --------|--------


                             Figure 6: DS-Lite



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   SFC7: Dslite-Enc---Dslite-Dec---NAT---LB---URL Filter

   When the outbound flow are received by the CPE, the CPE sends them to
   a specific classifier which determines the flow should be forwarded
   directly or dealed with DS-Lite process. if the flow should be dealed
   with DS-Lite process, then the classifier sends the datagram within
   service header encapsulation to Softwire-SN which contains SF-Dslite-
   Encapsulation instance.  In this instance, it fulfils DS-Lite
   encapsulate and then encapsulates overlay header and forwards this
   flow to nexthop in the traditional network.

   Next, the BNAS- receives the processed flow, the BNAS- sends them to
   a classifier and finds they are legal flow and need to be dealed with
   DS-Lite process. then, this flow are forwarded to SF-Dslite-
   Decapsulation to decapsulate DS-Lite encapsulation.  And as well,
   forwarded to SF-NAT to create and maintain the NAT mapping table for
   DS-Lite subscriber.  SF-Dslite-decapsulation and SF-NAT can reside in
   one service function or two different service functions.  After that,
   completes the subsequent SFs.

   In other words, BNAS-,itself, would decouple DS-lite-related
   functions to specific service function(s).  What!_s more, if SFP
   optimization function is enabled, BNAS- acts as SFF which connectes
   to SF-NAT, and derives the NAT/forwarding table from SF-NAT and
   bypasses SF-NAT to improve the experience of this subscriber.

   If deploy SFC7 in this scenario, there also exists a consideration:
   how to address the relationship between the access side SFC domain
   and the network side SFC domain.  If they are deployed in two
   different SFC domain, how to cooperate between the SF-Dslite-
   Encapsulation service function and SF-Dslite-Decapsulation service
   function.  On the other hand, if they are deployed in one big SFC
   domain, it seems more feasible to carry out this SFC7.

3.2.  Internet Access from Enterprises

 ------------------------------------------------------------------------------------>
                                   +-------+   +-----+   +----------+
                                   |DPI/DFI|   | LB/ |   |URL Filter|---|
 +-----+                      |----|  /Qos |---| FRR |---|  /FW/PC  |   |
 |host1|--|  +----------+     |    +-------+ | +-----+ | +----------+   |
 +-----+  |  |URL Filter|  +-----+           |         |             +-----+   +---------+
          ---|  /FW/PC  |--| SR- |-----------|---------|-------------| CR  |---| Internet|
 +-----+  |  +----------+  +-----+                                   +-----+   +---------+
 |host2|--|
 +-----+

                Figure 7: Internet access from enterprises



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   Internet access from enterprises is another network service.  They
   lease some ports or even some devices from Internet Server Providers.
   In addition to internal s service functions which are situated in the
   internal enterprise network, there maybe deploy many external ISP's
   service functions which are sitted on the way to the internet. And
   what's more, there maybe deploy IPsec along with VPN users for the
   sake of the security of enterprise network.

   Internal service functions may include: Firewall, NAT function, etc.

   As for external service functions deployed by ISP, typical service
   functions are VPN, like L2VPN,L3VPN,IPsec,IPsec VPN etc.
   Conventionally, there is a NAT function residing on SR, converting
   VPN traffic to public traffic to access the internet.

   In some cases, service providers need to assign differentiated
   services to VPN users.  In other words, different VPN users may go
   through differentiated SFC.  But, VPN traffic are all encapsulated in
   outer MPLS header or some other transport headers, how the public
   network elements classify them to different SFCs?  At this time,
   there maybe need create a mapping between VPN ID/VPN Name and
   corresponding SFC on the service provider edge device.

   Other external service functions involved in Internet access from
   enterprise network maybe similar to home network, for example,
   DPI,DFI,Qos,Load Balance, URL Filter,Firewall,Parental Control and so
   on.

   SFC8: URL Filter--FW---NAT---Qos---Load Balance----FW

   Here, you may see two FW functions.  One is in the inner of
   enterprise, which represents the URL constrains from the perspective
   of enterprise.  While the other one is sitted in the ISP network, out
   of the inner enterprise, and stands for the URL restrictions from the
   standpoint of ISP.

3.3.  Internet Access from Campuses

   TBD

3.4.  Added-value Service Access

   To promote their primary service, ISP try to provide value-added
   services to add value to the standard service offering.  Here maybe
   focus on some significant value-added services in broadband network
   such as IPTV,VOIP,etc.





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3.4.1.  Destination Address Accounting(DAA)

   Figure 8 illustrates a possible deployment of DAA funtion in
   broadband network.


    +-----+
    |host1|--|
    +-----+  | +-------+   +----------+      +-----+   +---------+
             --|  CPE  |---| BRAS+DAA |------| CR  |---| Internet|
    +-----+  | +-------+   +----------+      +-----+   +---------+
    |host2|--|
    +-----+


               Figure 8: DAA Deployment in broadband network

   In this diagram, DAA assists BRAS to accomplish finer-granularity
   outbound filter or/and inbound filter based on destination IP
   address.  But,in central deployment scenario of DS-Lite, there is a
   IPv4-in-IPv6 tunnel from CPE to CR.  As a result of that, BRAS cannot
   identify the true IPv4 destination address in this IPv4-in-IPv6
   packets.  And then, BRAS cannot enforce DAA function to manage the
   subscriber more flexibly.

   SFC9: DAA----Dslite-Enc----Dslite-Dec----NAT

























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          +-----------+       +-----------+
          |    Host1  |       |    Host2  |
          +-----+-----+       +-----+-----+
                |                   |
          +-----|-----+       +-----|-----+
          |   CPE2-   |       |   CPE2-   |
          +-----|-----+       +-----|-----+
                |                   |
                |---------|---------|
                          |
                  +-------|---------+
                  |    SF-DAA       |
                  +-------|---------+
                          |
                  +-------|---------+
                  | SF-Dslite-Enc   |
                  +-------|---------+
                          |
                         |||
                         |||<--softwire
                         |||
                +--------|||--------+
                |        CR         |
                +--------|||--------+
                          +----------------------+
                          |           +----------|-----+
                          |           | SF-Dslite-Dec  |
                          |           |   SF-NAT       |
                          |           +----------|-----+
                          +----------------------+
                          |
                          |
                  --------|--------
                /         |         \
               |       Internet      |
                \         |         /
                  --------|--------


         Figure 9: DAA + Softwire Deployment in broadband network

3.4.2.  IPTV

   Figure 10 illustrates a possible deployment of IPTV network via SFC.







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      <----------------------------------------------------
      +----+
      |STB1|-------|
      +----+       |
                   |
      +----+   +-------+    +------+
      |STB2|---| BNAS1-|----| Qos1 |---------|
      +----+   +-------+    +------+         |
                   |                         |
      +----+       |                         |
      |STB3|-------|                         |
      +----+                                 |
                                          +---------+     +-----+
      +----+                              | DPI/DFI |-----| CDN |
      |STB4|-------|                      +---------+     +-----+
      +----+       |                         |
                   |                         |
      +----+   +-------+    +------+         |
      |STB5|---| BNAS2-|----| Qos2 |---------|
      +----+   +-------+    +------+
                   |
      +----+       |
      |STB6|-------|
      +----+

                      Figure 10: IPTV network via SFC

   IPTV is a IP multicast service, in which multi-subscribers should
   receive the same traffic from the multicast source like Content
   Distribution Network.  Supposed there are six IPTV subscribers, from
   STB1 to STB6, they are located in different districts and they all
   need to receive traffic from Program 1.  A possible SFC abstract here
   is :

   SFC10: DPI--Qos1

           |---Qos2

   In SFC10, as for the inbound traffic, there are two different
   outputs, Qos1 and Qos2.  Firstly, traffic from multicast source go
   through DPI, which used for detecting whether the multicast traffic
   are legal or unmalicious.  After that, legal traffic propagate to
   different Qos, and next, each goes through different BNAS- to
   different STB subscirbers separately.







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3.4.3.  VoIP/MoIP

   TBD
















































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4.  Considerations

4.1.  Service Function Chain Symmetry

   A complete end-to-end access in broadband network should consist of a
   set of service function instances in a specific order.

4.2.  Deploying consideration

4.2.1.  Standalone mode

   In broadband networks, service function components are hanging next
   to routers such as CPEs/BNASs/CRs.  All traffics would be received
   and steered by routers.  Routers send the traffic to classifier in
   which traffic that matches classification criteria is forwarded along
   a given SFP to realize the specifications of an SFC.





















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                         +-----------+
                         |    Host   |
                         +-----+-----+
                               |
                               |
                     +---------|---------+    +-------------------+
                     |                   |    |    -------------  |
                     |        CPE        ----->   |    SFP      | |
                     |                   <-----   --------------  |
                     +---------|---------+    +-------------------+
                               |
                               |
                       --------|-------
                     /         |         \
                    |   ISP core network  |
                     \         |         /
                       ------- | -------
                               |
                               |
                     +---------|---------+    +-------------------+
                     |                   |    |    -----------    |
                     |       BNAS        |---->   |   SFP     |   |
                     |                   <----|    -----------    |
                     +---------|---------+    +-------------------+
                               |
                               |
                       --------|--------
                     /         |         \
                    |       Internet      |
                     \         |         /
                       --------|--------


                        Figure 11: Standalone mode

   Take DS-Lite CGN for example.

   Outbound traffic:

   In the example shown in Figure X, a datagram received by the CPE from
   the host at address 10.0.0.1, using TCP DST port 10000, will be
   translated to a datagram with IPv4 SRC address 192.0.2.1 and TCP SRC
   port 5000 in the Internet.

   When the datagram 1 is received by the CPE, the CPE sent it to a
   specific classifier which determines the datagram should be forwarded
   directly or dealed with DS-Lite process.  Then the classifier sends
   the datagram within service header encapsulated to the first element



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   of SFP.  SF-SOFTWIRE encapsulates the datagram in another datagram
   (datagram 2) and forwards it BACK to CPE over the softwire.  The
   datagram 2 would be sent to the Dual-Stack Lite carrier-grade NAT by
   CPE.

   When the BNAS receives datagram 2, the BNAS sends it to a classifier
   and find it need to be dealed with DS-Lite process.  Then the
   classifier send the datagram within service header encapsulated to
   the first element of SFP.

   SF-SOFTWIRE decapsulates the datagram 2 to datagram 1 and forwards it
   SF-NAT, which determines from its NAT table that the datagram
   received on the softwire with TCP SRC port 10000 should be translated
   to datagram 3 with IPv4 SRC address 192.0.2.1 and TCP SRC port 5000.

   The translated datagram would be also sent back to BNAS for next
   forwarding.

   Inbound traffic:

   Figure x shows an inbound message received at the classifer.  When
   the BNAS receives datagram 1, the BNAS sends it to a classifier.
   Then the classifier sends the datagram within service header
   encapsulated to the first element of SFP.  SF- NAT looks up the IP/
   TCP DST information in its translation table.  In the example in
   Figure 3, the NAT changes the TCP DST port to 10000, sets the IP DST
   address to 10.0.0.1, and it will be sent back to BNAS to forwards the
   datagram to the softwire.  The SF-SOFTWIRE of the CPE decapsulates
   the IPv4 datagram inbound softwire datagram and forwards it to the
   host.

4.2.2.  Directly connecting mode

   There is another mode to deploy service function components.  In
   broadband home networks, service function components are directly
   connected to the network.  They are connected straight to a BNAS or
   Routers.

   Under this scenario, it seems like more costly than standalone mode
   during transition period.











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                      |  +-----------+
                     out |    Host   |
                      |  +-----+-----+
                      v        |
                     +---------|---------+     +-------------+
                     |                   |-out->classifier A |
                     |                   |     +------|------+
                     |        CPE        |            |
                     |                   |            |
                     |                   |           out
                     +---------/\--------+            |
                               ||                     |
                               +<===== in =====+------v------+
                                               |             |
                                               |     SFP  A  |
                                               |             |
                               +<----- out-----+------/\-----+
                               |                      ||
                     +---------v---------+            ||
                     |                   |            ||
                     |                   |            ||
                     |       BNAS        |            ||
                     |                   |     +------||-----+
                     |                   |==in=>classifier B |
                     +---------|---------+     +-------------+
                       --------|--------   /\
                     /         |         \ ||
                    |    METRO NETWORK   | in
                     \         |         / ||
                      ---------^--------
                               .
                               .
                     +---------+---------+
                     |                   |
                     |                   |    +-------------+
                     |         CR        |    |    SFP N    |
                     |                   |    +-------------+
                     |                   |
                     +-------------------+


                    Figure 12: Directly connecting mode

   Take NAT44 for example.

   Outbound traffic:

   For directly connecting mode, the difference in dealing with traffic



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   is whether the network steer the traffic loopback.  That means
   service function node could send datagrams directly to the next hop.

   For example, when the outbound datagram is received by the BNAS and
   processed by classifer A and SF-NAT which forward the processed
   datagram straight next to router.

   Inbound traffic:

   It is quite similar with the process of dealing with outbound
   traffic. when the inbound datagram is received by the router and
   processed by classifer B and SF-NAT which forward the processed
   datagram straight next to NAT BNAS.

4.3.  Pool consideration

   In traditional networks, pools are configured in router one by one.
   Pool configuration means these IP addresses in each pool MUST be
   advertised for creating forward routing path to ensures that the
   message is routed to the correct target, especially to inbound
   traffic.  Thus, pool location is a problem we must face to in SFC
   framework.

   In standalone mode shown in figure 6, pool could be configured in the
   classifier beside gateway and advertised by the gateway itself.  The
   classifier would assign IP addresses to service functions for
   creating mapping table.  Both-bound traffic should be forward to
   gateway first and then for NAT treatment in relative service function
   components.

   In Directly connecting mode shown in figure 7, pool could be
   configured in classifier B and advertised by classifier B for
   creating inbound routing path.

   There is a mechanism to manage the address pools centrally.  Pools
   could be assigned to classifiers by management server which is
   handled by Operators centrally.

4.4.  NAT traversal

   TBD

4.5.  Unify home router

   TBD






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5.  IANA Considerations

   This memo includes no request to IANA.
















































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6.  Security Considerations

   TBD
















































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7.  Normative References

   [I-D.ietf-sfc-problem-statement]
              Quinn, P. and T. Nadeau, "Service Function Chaining
              Problem Statement", draft-ietf-sfc-problem-statement-13
              (work in progress), February 2015.

   [I-D.ietf-softwire-lw4over6]
              Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and
              I. Farrer, "Lightweight 4over6: An Extension to the DS-
              Lite Architecture", draft-ietf-softwire-lw4over6-13 (work
              in progress), November 2014.

   [I-D.ietf-softwire-map]
              Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, "Mapping of Address and Port
              with Encapsulation (MAP)", draft-ietf-softwire-map-13
              (work in progress), March 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson,
              "Remote Authentication Dial In User Service (RADIUS)",
              RFC 2865, June 2000.

   [RFC6052]  Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
              October 2010.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [RFC6519]  Maglione, R. and A. Durand, "RADIUS Extensions for Dual-
              Stack Lite", RFC 6519, February 2012.

   [RFC6888]  Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
              and H. Ashida, "Common Requirements for Carrier-Grade NATs
              (CGNs)", BCP 127, RFC 6888, April 2013.







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Authors' Addresses

   Xie Chongfeng
   China Telecom
   Room 502, No.118, Xizhimennei Street
   Beijing
   China

   Email: xiechf01@gmail.com,xiechf@ctbri.com.cn


   Sun Qiong
   China Telecom
   Room 708, No.118, Xizhimennei Street
   Beijing
   China

   Email: bingxuere@gmail.com,sunqiong@ctbri.com.cn


   Wei Meng
   ZTE Corporation
   No.50 Software Avenue, Yuhuatai District
   Nanjing
   China

   Email: meng.wei2@zte.com.cn,vally.meng@gmail.com


   Cui Wang
   ZTE Corporation
   No.50 Software Avenue, Yuhuatai District
   Nanjing
   China

   Email: wang.cui1@zte.com.cn


   Bhumip Khasnabish
   ZTE TX, Inc.
   55 Madison Avenue, Suite 160
   Morristown, New Jersey  07960
   USA

   Email: bhumip.khasnabish@ztetx.com






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