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Versions: 00 01 02 03 04 05 RFC 8157

Network Working Group                                         N. Leymann
Internet Draft                                              C. Heidemann
Intended Category: Informational                     Deutsche Telekom AG
                                                                M. Zhang
                                                                  Huawei
                                                            M. Wasserman
                                                       Painless Security
Expires: January 7, 2016                                    July 6, 2015

                           GRE Tunnel Bonding
                 draft-zhang-gre-tunnel-bonding-00.txt

Abstract

   It is an emerging demand to provide redundancy and load-sharing
   across wired and cellular links from a single service provider so
   that one customer is provided with "Hybrid Access" to the bonding of
   multiple heterogeneous connections.

   In this document, GRE (Generic Routing Encapsulation) Tunnel Bonding
   is specified as an enabling approach for Hybrid Access. In GRE Tunnel
   Bonding, GRE tunnels per network connections are set up and bonded
   together to form a single GRE tunnel for a subscriber. Compared with
   each composing connection, the bonding connection promises increased
   access capacity and improved reliability.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   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
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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html





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Copyright and License 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
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   publication of this document. Please review these documents
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   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. Acronyms and Terminology  . . . . . . . . . . . . . . . . . . .  4
   3. Use Case  . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4. Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1. Control Plane . . . . . . . . . . . . . . . . . . . . . . .  6
     4.2. Data Plane  . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.3. Traffic Classification and Distribution . . . . . . . . . .  7
     4.4. Traffic Recombination . . . . . . . . . . . . . . . . . . .  7
     4.5. Bypassing . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.6. Measurement . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.7. Policy Control Considerations . . . . . . . . . . . . . . .  9
   5. Control Protocol Specification (Control Plane)  . . . . . . . .  9
     5.1. GRE Tunnel Setup Request  . . . . . . . . . . . . . . . . . 11
       5.1.1. Client Identification Name  . . . . . . . . . . . . . . 11
       5.1.2. Session ID  . . . . . . . . . . . . . . . . . . . . . . 12
       5.1.3. DSL Synchronization Rate  . . . . . . . . . . . . . . . 13
     5.2. GRE Tunnel Setup Accept . . . . . . . . . . . . . . . . . . 13
       5.2.1. H IPv4 Address  . . . . . . . . . . . . . . . . . . . . 14
       5.2.1. H IPv6 Address  . . . . . . . . . . . . . . . . . . . . 14
       5.2.3. Session ID  . . . . . . . . . . . . . . . . . . . . . . 15
       5.2.4. RTT Difference Threshold  . . . . . . . . . . . . . . . 15
       5.2.5. Bypass Bandwidth Check Interval . . . . . . . . . . . . 15
       5.2.6. Active Hello Interval . . . . . . . . . . . . . . . . . 16
       5.2.7. Hello Retry Times . . . . . . . . . . . . . . . . . . . 16
       5.2.8. Idle Timeout  . . . . . . . . . . . . . . . . . . . . . 17
       5.2.9. Bonding Key Value . . . . . . . . . . . . . . . . . . . 18
       5.2.10. SOAP DSL Upstream Bandwidth  . . . . . . . . . . . . . 19
       5.2.11. SOAP DSL Downstream Bandwidth  . . . . . . . . . . . . 19
       5.2.12. RTT Difference Threshold Violation . . . . . . . . . . 20
       5.2.13. RTT Difference Threshold Compliance  . . . . . . . . . 20



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       5.2.14. Idle Hello Interval  . . . . . . . . . . . . . . . . . 21
       5.2.15. No Traffic Monitored Interval  . . . . . . . . . . . . 21
     5.3. GRE Tunnel Setup Deny . . . . . . . . . . . . . . . . . . . 22
       5.3.1. Error Code  . . . . . . . . . . . . . . . . . . . . . . 22
     5.4. GRE Tunnel Hello  . . . . . . . . . . . . . . . . . . . . . 23
       5.4.1. Timestamp . . . . . . . . . . . . . . . . . . . . . . . 23
       5.4.2. IPv6 Prefix Assigned by HAG . . . . . . . . . . . . . . 24
     5.5. GRE Tunnel Tear Down  . . . . . . . . . . . . . . . . . . . 24
     5.6. GRE Tunnel Notify . . . . . . . . . . . . . . . . . . . . . 24
       5.6.1. Bypass Traffic Rate . . . . . . . . . . . . . . . . . . 25
       5.6.2. Filter List Package . . . . . . . . . . . . . . . . . . 25
       5.6.3. Switching to DSL Tunnel . . . . . . . . . . . . . . . . 28
       5.6.4. Overflowing to LTE Tunnel . . . . . . . . . . . . . . . 28
       5.6.5. DSL Link Failure  . . . . . . . . . . . . . . . . . . . 29
       5.6.6. LTE Link Failure  . . . . . . . . . . . . . . . . . . . 29
       5.6.7. IPv6 Prefix Assigned to Host  . . . . . . . . . . . . . 29
       5.6.8. Diagnostic Start: Bonding Tunnel  . . . . . . . . . . . 30
       5.6.9. Diagnostic Start: DSL Tunnel  . . . . . . . . . . . . . 30
       5.6.10. Diagnostic Start: LTE Tunnel . . . . . . . . . . . . . 31
       5.6.11. Diagnostic End . . . . . . . . . . . . . . . . . . . . 31
       5.6.12. Filter List Package ACK  . . . . . . . . . . . . . . . 32
       5.6.13. Switching to Active Hello State  . . . . . . . . . . . 32
       5.6.14. Switching to Idle Hello State  . . . . . . . . . . . . 33
       5.6.15. Tunnel Verification  . . . . . . . . . . . . . . . . . 33
   6. Tunnel Protocol Operation (Data Plane)  . . . . . . . . . . . . 34
     6.1. The GRE Header  . . . . . . . . . . . . . . . . . . . . . . 35
     6.2. Automatic Setup of GRE Tunnels  . . . . . . . . . . . . . . 36
   7. Security Considerations . . . . . . . . . . . . . . . . . . . . 37
   8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 37
   9. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     9.1. Normative References  . . . . . . . . . . . . . . . . . . . 37
     9.2. Informative References  . . . . . . . . . . . . . . . . . . 37
   Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39

1. Introduction

   Operators used to provide subscribers with separate access to their
   fixed broadband networks and mobile networks. It becomes desirable to
   bond the fixed and wireless networks together to offer customers with
   increased access capacity and improved reliability. Solutions that
   support Hybrid Access to fixed and wireless networks are required.

   In this document, Hybrid Access focuses on the use case that DSL
   (Digital Subscriber Line) connection and LTE (Long Term Evolution)
   connection are bonded together to form a bonding connection. When the
   traffic volume exceeds the bandwidth of the DSL connection, the
   excess amount can be offloaded to the LTE connection. Hybrid Customer
   Premises Equipment (HCPE) is the equipment at the customer side



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   initiating the DSL and LTE connections. Hybrid Access Gateway (HAG)
   is the network function resides in the provider's networks to
   terminate the bonded connections. Note that if there are more than
   two connections need to be bonded, the GRE Tunnel Bonding mechanism
   can support as well. However, it's out the scope of this document.

   This document bases the solution on GRE (Generic Routing
   Encapsulation) since GRE is widely supported in both fixed and mobile
   networks. GRE tunnels are set up per those heterogeneous connections
   (DSL+LTE) between HCPE and HAG. All these GRE tunnels are further
   bonded together to form a logical GRE tunnel for the customer. HCPE
   conceals the composing GRE tunnels from users and users simply treat
   the logical GRE tunnel as a single IP link. This provides an overlay:
   user IP packets (inner IP) is encapsulated with GRE which is in turn
   carried over IP (outer IP).

   The design of the GRE Tunnel Bonding exhibits how the function blocks
   of Hybrid Access are realized, such as traffic classification,
   distribution, recombination, measurement of the connection, etc.
   Although the industry might develop more solutions for Hybrid Access
   besides GRE Tunnel Bonding, the function blocks need to be realized
   are common and the mapping out of the function blocks here is
   referential to other potential solutions.

2. Acronyms and Terminology

   GRE: Generic Routing Encapsulation

   DSL: Digital Subscriber Line

   LTE: Long Term Evolution

   Hybrid Access: The bonding of multiple access connections based on
   heterogeneous technologies (e.g., DSL and LTE).

   HCPE: Hybrid Customer Premises Equipment (CPE). A CPE enhanced to
   support the simultaneous use of both fixed broadband and 3GPP access
   connections.

   HAG: Hybrid Access Gateway. A logical function in the operator
   network implementing a bonding mechanism for customer access
   services.

   C: The endpoint of the bonding connection at the HCPE.

   E: The endpoint of the LTE connection resides in HCPE.

   D: The endpoint of the DSL connection resides in HCPE



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   H: The endpoint of the bonding connection at HAG. Usually, this is
   also used as the endpoint for each heterogeneous connection.

   CIR: Committed Information Rate [RFC2698]

   RTT: Round Trip Time

   FQDN: A Fully Qualified Domain Name (FQDN) is a domain name that
   includes all higher level domains relevant to the entity named.
   [RFC1594]

   DSCP: The six-bit codepoint (DSCP) of the Differentiated Services
   Field (DS Field) in the IPv4 and IPv6 Headers [RFC2724].

   BRAS: Broadband Remote Access Server

   PGW: Packet Data Network Gateway. In the Long Term Evolution (LTE)
   architecture for the Evolved Packet Core (EPC), the PGW acts as an
   anchor for user plane mobility.

   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 RFC 2119 [RFC2119].

3. Use Case

               +-+                                    +-+
               | +--------- Bonding Connection -------+ |
               | |                                    | |
               | |    +-+                             | |
               |C|    |E+------ LTE Connection -------+H|
               | |    +-+                             | |
               | |    +-+                             | |
               | |    |D+------ DSL Connection -------+ |
               +-+    +-+                             +-+
               \________/
                  HCPE                                HAG


   Figure 3.1: Offloading from DSL to LTE, increased access capacity


   For a Service Provider who owns heterogeneous networks, such as fixed
   and mobile, customers wish to use its networks simultaneously with
   increased access capacity rather than just uses a single network. As
   shown by the reference model in Figure 3.1, the customer expects the
   whole bandwidth of the bonding connection equals the sum of the
   bandwidth of the DSL connection and the LTE connection between HCPE



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   and HAG. In other words, when the traffic volume exceeds the
   bandwidth of the DSL connection, the excess amount may be offloaded
   to the LTE connection.

   Most common implementation balance the load among multiple paths.
   However, the use case described here is about per-packet offloading
   rather than per-flow load-balance. For the per-flow load-balance, the
   maximum bandwidth that may be used by a flow actually equals to the
   bandwidth of the connection selected. The GRE Tunnel Bonding
   mechanism is able to support the use case that requires per-flow
   traffic classification and distribution though it's out the scope of
   this document.

   Use cases with more than two connections between HCPE and HAG is out
   the scope of this document. However, the GRE Tunnel Bonding mechanism
   can well support those use cases.

4. Overview

   In this document, the widely supported GRE is chosen as the tunneling
   technique. With the newly defined control protocol, GRE tunnels are
   setup on top of the DSL and LTE connections which are ended at D and
   H or E and H. These tunnels are bonded together to form a single
   logical bonding GRE tunnel whose endpoint IP addresses are C and H.
   Customers uses this logical tunnel without knowing the composing GRE
   tunnels.

4.1. Control Plane

   A clean-slate control protocol is designed to manage the GRE tunnels
   that are setup per heterogeneous connections between HCPE and HAG.
   The goal is to design a compact control plane for Hybrid Access only
   instead of reusing existing control planes.

   In order to measure the performance of connections, control packets
   need co-route the same path with data packets. Therefore, a GRE
   Channel is opened for the purpose of data plane forwarding of control
   plane packets. The GRE header as specified in [RFC2890] is being
   used. The GRE Protocol Type (tbd1) is used to identify this GRE
   Channel. A family of control messages are encapsulated with GRE
   header and carried over this channel. Attributes, formatted in Type-
   Length-Value style, are further defined and included in each control
   message.

   With the newly defined control plane, the GRE tunnels between HCPE
   and HAG can be established, managed and released without the
   involvement of man-power of operators.




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4.2. Data Plane

   With the new defined control plane, GRE tunnels can be automatically
   setup per heterogeneous connections between HCPE and HAG. For the use
   case depict in Section 3, there are the GRE tunnel ended at the DSL
   WAN interfaces (shorted as DSL GRE tunnel) and the GRE tunnel ended
   at the LTE WAN interfaces (shorted as LTE GRE tunnel). Each tunnel
   may carry user's IP packets as payload, which forms a typical IP-in-
   IP overlay. These tunnels are bonded together to offer a single
   access point to customers.

   The GRE header per [RFC2890] is used to encapsulate data packets. The
   Protocol Type is 0x0800, which indicates the inner header is an IP
   header. For per-packet offloading use case, the Key field is used as
   a clear-text password. The Sequence Number field is used to maintain
   the sequence of packets transported in all GRE tunnels as a single
   flow between a pair of HCPE and HAG.

   For the per-flow traffic classification and distribution, the Key
   field will be used as the demultiplexer for flows. The
   Acknowledgement field as specified in [RFC2637] will be used to
   achieve a low-level congestion and flow control.

4.3. Traffic Classification and Distribution

   For the offloading use case, the coloring mechanism specified in
   [RFC2698] is being used to classify customer's IP packets, both
   upstream and downstream, into the DSL GRE tunnel or LTE GRE tunnel.
   Packets colored as green will be distributed into the DSL GRE tunnel
   and packets colored as yellow will be distributed into the LTE GRE
   tunnel. For the scenario that requires more than two GRE tunnels,
   multiple levels of token buckets might be realized. For example, the
   packets classified as not to be distributed to DSL may be further
   colored as either to be distributed to LTE or distributed to WiFi.
   The implementation detail is out the scope of this document.

   The Committed Information Rate (CIR) of the coloring mechanism is set
   to the total DSL WAN bandwidth minus the bypassing DSL bandwidth (See
   Section 4.4.). The total DSL WAN bandwidth MAY be configured, MAY be
   got from the SOAP server and MAY be timely detected and reported by
   using ANCP [RFC6320].

   Besides the per-packet offloading use case, the GRE Tunnel Bonding
   mechanism is also applicable to per-flow classification and
   distribution.

4.4. Traffic Recombination




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   The recombination function at the receiver provides the in-order
   delivery of customers' traffic. As specified in [RFC2890], the
   receiver maintains a small amount of reordering buffer and order the
   data packets in this buffer by the Sequence Number field of the GRE
   header. For the offloading use case, all bonded GRE tunnels use the
   same Key value. All packets carried on these bonded GRE tunnels go
   into a single reordering buffer.

   For the per-flow classification and distribution, Sequence Numbers
   are set per Key values at the sender. Buffers per Key values are
   maintained at the receiver. In addition, the Acknowledge Number field
   can be introduced in order to achieve a low level congestion and flow
   control [RFC2637]. As stated in [RFC2637], retransmissions are not
   performed by the tunnel peers.

4.5. Bypassing

   Service Providers need some types of services not delivered by the
   bonding of GRE tunnels. For example, Service Providers do not expect
   the real-time IPTV to be carried by the LTE GRE tunnel. It's required
   that these kind of services bypass the GRE Tunnel Bonding and use
   just the raw DSL bandwidth. In this way, the do not subject to the
   traffic classification and distribution specified as above. There are
   two kinds of bypassing:

   o Fully bypassing: The raw DSL connection used for bypassing is not
     controlled by HAG. It may or may not go through HAG.

   o Partial bypassing: HAG controls the raw DSL connection used for
     bypassing. The raw DSL connection goes through HAG

   For either of the bypassing, HAG notifies the the service types that
   need to bypass the bonded GRE tunnels using the Filter List Package
   attribute as specified in Section 5.6.2. HCPE and HAG need set aside
   the DSL bandwidth for bypassing. The available DSL bandwidth for the
   GRE Tunnel Bonding  equals to the total DSL bandwidth minus the
   bypassing bandwidth.

4.6. Measurement

   Since control packets co-route the same path with data packets. The
   real performance of the data paths (e.g., the GRE tunnels) can be
   measured. The GRE Tunnel Hello messages specified in Section 5.3 are
   used to carry the timestamp information and the Round Trip Time (RTT)
   value can therefore be calculated based on the timestamp.

   Besides the end to end delay of the GRE tunnels, HCPE and HAG need
   also measure the capacity of the tunnels. For example, for the fully



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   bypassing, HCPE is REQUIRED to timely measure the downstream
   bypassing bandwidth and report it to HAG (See Section 5.6.1.).

4.7. Policy Control Considerations

   Operators and customers may input policies into the GRE Tunnel
   Bonding. These policies will be interpreted into parameters or
   actions that impact the traffic classification, distribution,
   combination, measurement and bypassing.

   Operators and customers may offer the service types that need to
   bypass the bonded GRE tunnels. These service types will be delivered
   from HAG to HCPE and HCPE will stick to raw DSL interfaces to
   transmit traffic of these service types.

   Since the GRE tunnels are setup on top of heterogeneous DSL and LTE
   connections, if the difference of the transmission delays of these
   connections exceeds a given threshold for a certain period, HCPE and
   HAG should be able to stop the offloading behavior and fallback to a
   traditional transmission mode, where the LTE GRE tunnel is disabled
   while all traffic is transmitted over the DSL GRE tunnel. Operators
   are allowed to defined this threshold and period.

   Operators may determine the maximum allowed size (See
   MAX_PERFLOW_BUFFER in [RFC2890]) of the buffer for reordering. They
   may also define the maximum time (See OUTOFORDER_TIMER in [RFC2890])
   that a packet can stay in the buffer for reordering. These parameters
   impact the traffic recombination.

   Operators may specify the interval for sending Hello messages and the
   retry times for HCPE or HAG to send out Hello messages before it
   declare the failure of a connection.

5. Control Protocol Specification (Control Plane)

   Control messages are used to establish, maintain, measure and tear
   down GRE tunnels between the HCPE and HAG. Also, the control plane
   undertakes the responsibility to bond tunnels and convey traffic
   policies.

   For the purpose of measurement, control messages need to be delivered
   as GRE encapsulated packets and delivered as co-route with data plane
   packets. The new GRE Protocol Type [tbd1] is allocated for this
   purpose and the standard GRE header as per [RFC2890] is used. The
   format of the GRE header is as follows:






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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |C| |K|S| Reserved0       | Ver |         Protocol Type         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Key (optional)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   C (Bit 0)
      Checksum Present. Set to zero (0).

   K (Bit 2)
      Key Present. Set to one (1).

   S (Bit 3)
      Sequence Number Present. Set to zero (0).

   Protocol Type (2 octets)
      Set to [tbd1].

   Key
      The Key field is used as a security feature, functioning as a 32-
      bit clear-text password. Also, the Key field is used as a
      demultiplexer for GRE tunnels at the HAG. This value of the Key is
      generated by HAG and informed to HCPE. (See Section 5.2.9.)

   The general format of the entire control message is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| |1|0|   Reserved0     | Ver |     Protocol Type = tbd1      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Key (optional)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |MsgType| Rsvd1 |                                               |
   +-+-+-+-+-+-+-+-+           Attributes                          +
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   MsgType (4 bits)
      Message Type. The control message family contains the following 6
      types of control messages:








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                   Control Message Family         Type
                  ==========================    =========
                   GRE Tunnel Setup Request       1
                   GRE Tunnel Setup Accept        2
                   GRE Tunnel Setup Deny          3
                   GRE Tunnel Hello               4
                   GRE Tunnel Tear Down           5
                   GRE Tunnel Notify              6
                   Reserved                       0,7-15

   Rsvd1 (4 bits)
      Reserved1. These bits MUST be set to zero.

   Attributes
      The Attributes field includes the attributes that need to be
      carried in the control message. Each Attribute has the following
      format.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                  (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |  (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Value              ~  (variable)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Attribute Type (1 octet)
         The Attribute Type specifies the type of the attribute.

      Attribute Length (2 octets)
         Attribute Length indicates the length of the Attribute Value.

      Attribute Value (variable)
         The Attribute Value includes the value of the attribute.

   All control messages are sent in network order (high order octets
   first). Since the Protocol Type carried in the GRE header for the
   control message is tbd1, the receiver will determine to consume it
   locally rather than further forwarding.

5.1. GRE Tunnel Setup Request

   HCPE uses the GRE Tunnel Setup Request message to request HAG to
   establish GRE tunnels. It is sent out from HCPE's LTE and DSL WAN
   interfaces separately. Attributes that need be to included in this
   message are defined in Section 5.1.1 through Section 5.1.3.

5.1.1. Client Identification Name



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   Operator uses the Client Identification Name (CIN) to identify the
   HCPE. The HCPE sends the CIN to HAG for authentication and
   authorization as specified in [TS23.401]. It's REUIRED that the GRE
   Tunnel Setup Request message sent out from the LTE WAN interface
   contains the CIN attribute while the GRE Tunnel Setup Request message
   sent out from the DSL WAN interface does not contain this attribute.

   The CIN attribute has the following format:

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Client Identification Name       (40 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      CIN, set to 3.

   Attribute Length
      Set to 40.

   Client Identification Name
      This is a 40 bytes ANSI string value set by the operator. It's
      used as the identification of HCPE in the operator's network.

5.1.2. Session ID

   This Session ID is generated by HAG when the LTE GRE Tunnel Setup
   Request message is received and then notifies the Session ID to HCPE
   through the LTE GRE Tunnel Setup Accept message. For those WAN
   interfaces that need to be bonded together, the HCPE MUST use the
   same Session ID. The HCPE MUST carry the Session ID attribute in each
   DSL GRE Tunnel Setup Request message. For the first time that the LTE
   GRE Tunnel Setup Request message is sent to the HAG, the Session ID
   attribute need not be included. However, if the LTE GRE Tunnel fails
   and HCPE tries to revive it, the LTE GRE Tunnel Setup Request message
   MUST include the Session ID attribute.

   The Session ID attribute has the following format:










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   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Session ID                       (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Session ID, set to 4.

   Attribute Length
      Set to 4.

   Session ID
      This is a 4 bytes ANSI string value generated by the HAG. It's
      used as the identification of bonded GRE Tunnels.

5.1.3. DSL Synchronization Rate

   HCPE uses the DSL Synchronization Rate to notify HAG about the
   downstream bandwidth of the DSL link. The DSL GRE Tunnel Setup
   Request message MUST include the DSL Synchronization Rate attribute.
   The LTE GRE Tunnel Setup Request message SHOULD NOT include this
   attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  DSL Synchronization Rate         (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      DSL Synchronization Rate, set to 7.

   Attribute Length
      Set to 4.

   DSL Synchronization Rate
      This is a unsigned integer with the unit of kbps.

5.2. GRE Tunnel Setup Accept

   HAG uses the GRE Tunnel Setup Accept message as the response to the
   GRE Tunnel Setup Request message. This message indicates the
   permission of the tunnel establishment and carries parameters of the



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   GRE tunnels. Attributes that need be to included in this message are
   defined in Section 5.2.1 through Section 5.2.13.

5.2.1. H IPv4 Address

   HAG uses the H IPv4 Address attribute to inform HCPE the H IPv4
   address. HCPE uses the H IPv4 address as the endpoint IPv4 address of
   the GRE tunnels. The LTE GRE Tunnel Setup Accept message MUST include
   the H IPv4 Address attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  H IPv4 Address                   (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      H IPv4 Address, set to 1.

   Attribute Length
      Set to 4.

   H IPv4 Address
      Set to the pre-configured IPv4 address which is used as the
      endpoint IP address of GRE tunnels by HAG.

5.2.1. H IPv6 Address

   HAG uses the H IPv6 Address attribute to inform HCPE the H IPv6
   address. HCPE uses the H IPv6 address as the endpoint IPv6 address of
   the GRE tunnels. The LTE GRE Tunnel Setup Accept message MUST include
   the H IPv6 Address attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  H IPv4 Address                   (16 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      H IPv6 Address, set to 1.

   Attribute Length
      Set to 16.



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   H IPv6 Address
      Set to the pre-configured IPv6 address which is used as the
      endpoint IP address of GRE tunnels by HAG.

5.2.3. Session ID

   The LTE GRE Tunnel Setup Accept message MUST include Session ID
   attribute as defined in Section 5.1.2.

5.2.4. RTT Difference Threshold

   HAG uses the RTT Difference Threshold to attribute to inform HCPE the
   acceptable threshold of RTT difference between the DSL link and the
   LTE link. If the measured RTT difference exceeds this threshold
   SHOULD stop offloading traffic to the LTE GRE tunnel. The LTE GRE
   Tunnel Setup Accept message MUST include the RTT Difference Threshold
   attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  RTT Difference Threshold         (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      RTT Difference Threshold, set to 9.

   Attribute Length
      Set to 4.

   RTT Difference Threshold
      A unsigned integer with the unit of millisecond. This value can be
      chosen in the range 0 through 1000.

5.2.5. Bypass Bandwidth Check Interval

   HAG uses the Bypass Bandwidth Check Interval attribute to inform HCPE
   the interval that the bypass bandwidth should be checked. HCPE should
   check the bypass bandwidth of the DSL WAN interface in each time
   period as indicates by this interval. The LTE GRE Tunnel Setup Accept
   message MUST include the Bypass Bandwidth Check Interval attribute.








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   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Bypass Bandwidth Check Interval  (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Bypass Bandwidth Check Interval, set to 10.

   Attribute Length
      Set to 4.

   Bypass Bandwidth Check Interval
      A unsigned integer with the unit of second. This value can be
      chosen in the range 0 through 300.

5.2.6. Active Hello Interval

   HAG uses the Active Hello Interval attribute to inform HCPE the pre-
   configured interval for sending out GRE Tunnel Hellos. HCPE should
   send out GRE Tunnel Hellos via both the DSL and LTE WAN interfaces in
   each time period as indicates by this interval. The LTE GRE Tunnel
   Setup Accept message MUST include the Active Hello Interval
   attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Active Hello Interval            (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Active Hello Interval, set to 14.

   Attribute Length
      Set to 4.

   Active Hello Interval
      A unsigned integer with the unit of second. This value can be
      chosen in the range 0 through 100.

5.2.7. Hello Retry Times

   HAG uses the Hello Retry Times attribute to inform HCPE the retry



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   times for sending GRE Tunnel Hellos. If the HCPE does not receive any
   acknowledgement to the GRE Tunnel Hellos from the HAG  over a GRE
   Tunnel after it tries the times specified in this attribute, the HCPE
   will declare the failure this GRE Tunnel. The LTE GRE Tunnel Setup
   Accept message MUST include the Hello Retry Times attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Hello Retry Times                (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Hello Retry Times, set to 15.

   Attribute Length
      Set to 4.

   Hello Retry Times
      A unsigned integer number which takes value in the range 3 through
      10.

5.2.8. Idle Timeout

   HAG uses the Idle Timeout attribute to inform HCPE the pre-configured
   timeout value to terminate the DSL GRE tunnel. When an LTE GRE Tunnel
   failure is detected, all traffic will be sent over the DSL GRE
   tunnel. If the failure of the LTE GRE tunnel lasts longer than the
   Idle Timeout, the traffic will be sent over the raw DSL rather the
   tunnel over it, and the DSL GRE tunnel SHOULD be terminated. The LTE
   Tunnel Setup Accept message MUST include the Idle Timeout attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Idle Timeout                     (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Idle Timeout, set to 16.

   Attribute Length
      Set to 4.




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   Idle Timeout
      A unsigned integer number with the unit of second. It takes value
      in the range 0 through 172,800 with the granularity of 60. The
      default value is 1,440 (24 hours). The value 0 indicates the idle
      timer never expires.

5.2.9. Bonding Key Value

   HAG uses the Bonding Key Value attribute to inform HCPE the number
   which is to be used as the Key of the GRE header for each tunneled
   control messages. The Bonding Key Value is generated by HAG and used
   for the purpose of demultiplexing. HAG is REQUIRED to distinguish the
   GRE tunnels from the Bonding Key Value. Different tunnels MUST use
   different Bonding Key Values. HAG SHOULD identify the GRE tunnels by
   their source IP addresses which are carried in the outer IP header.
   Since the CIN attribute is carried in the GRE Tunnel Setup Request
   sent on the LTE GRE tunnel only, HAG can figure out the source IP
   address used for the LTE GRE tunnel from the message carrying the CIN
   attribute. Similarly, HAG can figure out the source IP address used
   for the DSL GRE tunnel from the message carrying the DSL
   Synchronization Rate attribute.

   The specific method used to generate this number is up to
   implementations. The Pseudo Random Number Generator defined in ANSI
   X9.31 Appendix A.2.4 is RECOMMENDED. Both the LTE GRE Tunnel Setup
   Accept message and the DSL GRE Tunnel Setup Accept message MUST
   include the Bonding Key Value attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Bonding Key Value                (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Bonding Key Value, set to 20.

   Attribute Length
      Set to 4.

   Bonding Key Value
      A 32-bit number generated by the HAG. It's REQUIRED that different
      tunnels are allocated with different Key values. The HAG MAY set
      aside a few bits (e.g., the highest 4 bits) in the Key field as
      the demultiplexer for the tunnels while other bits are filled in
      with a value generated by a random number generator.



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5.2.10. SOAP DSL Upstream Bandwidth

   HAG obtains the upstream bandwidth of the DSL link from the SOAP
   server and uses the SOAP DSL Upstream Bandwidth attribute to inform
   HCPE. The HCPE uses this informed upstream bandwidth as the Committed
   Information Rate for the DSL link [RFC2698]. The DSL GRE Tunnel Setup
   Accept message MUST include the SOAP DSL Upstream Bandwidth
   attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  SOAP DSL Upstream Bandwidth      (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      SOAP DSL Upstream Bandwidth, set to 22.

   Attribute Length
      Set to 4.

   SOAP DSL Upstream Bandwidth
      A unsigned integer with the unit of kbps.

5.2.11. SOAP DSL Downstream Bandwidth

   HAG obtains the downstream bandwidth of the DSL link from the SOAP
   server and uses the SOAP DSL Downstream Bandwidth attribute to inform
   HCPE. The HCPE uses this informed downstream bandwidth as the base in
   calculating of the bypassing bandwidth. The DSL GRE Tunnel Setup
   Accept message MUST include the SOAP DSL Downstream Bandwidth
   attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  SOAP DSL Downstream Bandwidth    (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      SOAP DSL Downstream Bandwidth, set to 23.

   Attribute Length
      Set to 4.



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   SOAP DSL Downstream Bandwidth
      A unsigned integer with the unit of kbps.

5.2.12. RTT Difference Threshold Violation

   HAG uses the RTT Difference Threshold Violation attribute to inform
   HCPE the times of the measurements that the RTT Difference Threshold
   (See Section 5.2.4.) is continuously detected to be violated. If RTT
   Difference Threshold is continuously detected to be violated more
   than this informed times, the HCPE MUST stop using the LTE GRE
   tunnel. The LTE GRE Tunnel Setup Accept message MUST include the RTT
   Difference Threshold Violation attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  RTT Diff Threshold Violation     (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      RTT Difference Threshold Violation, set to 24.

   Attribute Length
      Set to 4.

   RTT Difference Threshold Violation
      A unsigned integer which takes from the range 1 through 25.

5.2.13. RTT Difference Threshold Compliance

   HAG uses the RTT Difference Threshold Compliance attribute to inform
   HCPE the times of the measurements that the RTT Difference Threshold
   (See Section 5.2.4.) is continuously detected to be compliant. If the
   RTT Difference Threshold is continuously detected to be compliant
   more than this informed times, the HCPE MAY resume the LTE GRE
   tunnel. The LTE GRE Tunnel Setup Accept message MUST include the RTT
   Difference Threshold Compliance attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  RTT Diff Threshold Compliance    (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+




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   Attribute Type
      RTT Diff Threshold Compliance, set to 25.

   Attribute Length
      Set to 4.

   RTT Diff Threshold Compliance
      A unsigned integer which takes from the range 1 through 25.

5.2.14. Idle Hello Interval

   HAG uses the Idle Hello Interval attribute to inform HCPE the pre-
   configured interval for sending out GRE Tunnel Hellos when the
   customer is detected to be idle. HCPE SHOULD begin to send out GRE
   Tunnel Hellos via both the DSL and LTE WAN interfaces in each time
   period as indicates by this interval, if the bonding tunnels have
   seen no traffic longer than the "No Traffic Monitored Interval" (See
   Section 5.2.15.). The LTE GRE Tunnel Setup Accept message MUST
   include the Idle Hello Interval attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Idle Hello Interval               (4 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Idle Hello Interval, set to 31.

   Attribute Length
      Set to 4.

   Idle Hello Interval
      A unsigned integer with the unit of second. This value can be
      chosen in the range 100 through 86,400 (24 hours) with the
      granularity of 100. The default value is 1800 (30 minutes).

5.2.15. No Traffic Monitored Interval

   HAG uses the No Traffic Monitored Interval attribute to inform HCPE
   the pre-configured interval for switching the GRE Tunnel Hello mode.
   If traffic is detected on the bonding GRE tunnels before this
   informed interval expires, the HCPE SHOULD switch to Active Hello
   Interval. The LTE GRE Tunnel Setup Accept message MUST include the No
   Traffic Monitored Interval attribute.




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   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  No Traffic Monitored Interval      (4 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      No Traffic Monitored Interval, set to 32.

   Attribute Length
      Set to 4.

   No Traffic Monitored Interval
      A unsigned integer with the unit of second. This value can be
      chosen in the range 30 through 86,400 (24 hours). The default
      value is 60.

5.3. GRE Tunnel Setup Deny

   HAG MUST sends the GRE Tunnel Setup Deny message to HCPE if the GRE
   tunnel setup request from this HCPE is denied. The HCPE MUST
   terminate the GRE tunnel setup process as soon as it receives the GRE
   Tunnel Setup Deny message.

5.3.1. Error Code

   HAG uses the Error Code attribute to inform HCPE the error code. The
   error code depicts the reason why the GRE tunnel setup request is
   denied. Both the LTE GRE Tunnel Setup Deny message and the DSL GRE
   Tunnel Setup Deny message MUST include the Error Code attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Error Code                        (4 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Error Code, set to 17.

   Attribute Length
      Set to 4.

   Error Code



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      A unsigned integer. The list of the codes are listed as follows.

      1: HAG is not reachable via LTE during GRE tunnel setup request.
      2: HAG is not reachable via DSL during GRE tunnel setup request.
      3: LTE GRE tunnel to the HAG fails.
      4: DSL GRE tunnel to the HAG fails.
      5: The given DSL User ID is not allowed to use GRE tunnel bonding
         service.
      6: The given User Alias (TOID)/User ID (GUID) is not allowed to
         use GRE tunnel bonding service.
      7: LTE and DSL User IDs mismatching.
      8: HAG denies the GRE tunnel setup request since a bonding session
         with the same User ID already exists.
      9: HAG denies the GRE tunnel setup request since the user's CIN is
         not permitted.
      10: HAG terminates a GRE tunnel bonding session for maintenance
         reasons.
      11: There is a communication error between the HAG and SOAP server
         during the LTE tunnel setup request.
      12: There is a communication error between the HAG and SOAP server
         during the DSL tunnel setup request.

5.4. GRE Tunnel Hello

   After the GRE tunnel is established, the HCPE begins to periodically
   send out GRE Tunnel Hello messages while the HAG acknowledges by
   returning the GRE Tunnel Hello messages back to HCPE, until the
   tunnel is terminated.

5.4.1. Timestamp

   HAG uses the Timestamp attribute to inform HCPE the timestamp value
   that is used for RTT calculation. Both the LTE GRE Tunnel Hello
   message and DSL GRE Tunnel Hello message MUST include the Timestamp
   attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Timestamp                         (8 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Timestamp, set to 5.

   Attribute Length



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      Set to 8.

   Timestamp
      The high-order 4 octets indicate a unsigned integer with the unit
      of second; the low-order 4 octets indicate a unsigned integer with
      the unit of millisecond.

5.4.2. IPv6 Prefix Assigned by HAG

   HAG uses the IPv6 Prefix Assigned by HAG attribute to inform HCPE the
   assigned IPv6 prefix. This IPv6 prefix is to be captured by the
   Lawful Interception. Both the LTE GRE Tunnel Hello message and the
   DSL GRE Tunnel Hello message MUST include the IPv6 Prefix Assigned by
   HAG attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  IPv6 Prefix Assigned by HAG       (16 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      IPv6 Prefix Assigned by HAG, set to 13.

   Attribute Length
      Set to 17.

   IPv6 Prefix Assigned by HAG
      The highest-order 16 octets encode an IPv6 address. The lowest-
      order one octet encodes the length of a network mask. These two
      values are put together to represent an IPv6 prefix.

5.5. GRE Tunnel Tear Down

   HAG can terminate a GRE tunnel by sending the GRE Tunnel Tear Down
   message to the HCPE. The Error Code attribute as defined in Section
   5.3.1 MUST be included in this message.

5.6. GRE Tunnel Notify

   HCPE and HAG uses the GRE Tunnel Notify message to notify each other
   about their status, the information for the bonding tunnels, the
   actions need to be taken, etc.

   Usually, the receiver just sends the received attributes back as the
   acknowledgement for each GRE Tunnel Notify message. There is an



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   exception for the Filter List Package. Since the size of the Filter
   List Package attribute can be very large, a special attribute is
   specified in Section 5.6.12 as the acknowledgement.

   Attributes that need be to included in the GRE Tunnel Notify message
   are defined in Section 5.6.1 through Section 5.6.15.

5.6.1. Bypass Traffic Rate

   There are a few types of traffic that need to transmitted over the
   raw DSL WAN interface rather than the bonding GRE tunnels. The HCPE
   has to set aside a bypass bandwidth on the DSL WAN interface for
   these kind of traffic types. Therefore, the available bandwidth of
   the DSL GRE tunnel is the entire DSL WAN interface bandwidth minus
   the occupied bypass bandwidth.

   HCPE uses the Bypass Traffic Rate attribute to inform HAG the
   downstream bypass bandwidth for the DSL WAN interface. The Bypass
   Traffic Rate attribute will be included in the DSL GRE Tunnel Notify
   message. HAG calculates the available downstream bandwidth for the
   DSL GRE tunnel as the SOAP DSL Downstream Bandwidth minus this
   informed bypass bandwidth. This available DSL bandwidth will be used
   as the Committed Information Rate (CIR) of the coloring system
   [RFC2698].

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Bypass Traffic Rate               (4 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Bypass Traffic Rate, set to 6.

   Attribute Length
      Set to 4.

   Bypass Traffic Rate
      A unsigned integer with the unit of kbps.

5.6.2. Filter List Package

   HAG uses the Filter List Package attribute to inform HCPE the service
   types that need to bypass the bonding GRE tunnels. Each Filter List
   Package carries a collection of Filter List TLVs and each such Filter
   List TLV specifies a filter item. At the HCPE, a list of filter items



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   is maintained. Also, HCPE need maintain an exception list of filter
   items. For example, the packets carrying the control messages defined
   in this document should be excluded from the filter list.

   Incoming packets that match an filter item in the filter list while
   not match any item in the exception list MUST be transmitted over the
   raw DSL rather than the bonding GRE tunnels. Both the LTE GRE Tunnel
   Notify message and GRE Tunnel Notify message MAY include the Filter
   List Package attribute. The DSL GRE Tunnel Notify message is
   preferred.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Filter List TLVs                  (variable) ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Filter List Package, set to 8.

   Attribute Length
      The total length of the Filter List TLVs. The maximum length is
      969 bytes.

   Filter List TLVs
      Each Filter List TLV has the following format.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Commit_Count                                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Packet_Sum               |         Packet_ID             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Type                  |          Length               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Enable                |     Description Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                 Description Value (0~4 bytes)                 ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                        Value (0~32 bytes)                     ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Commit_Count
         A unsigned integer which identifies the version of the Filter
         List Package. HCPE will refresh its filter list, when a new



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         Commit_Count is received.

      Packet_Sum
         If the Filter List Package attribute might make the control
         message larger than the MTU, fragmentation is used. The
         Packet_Sum indicates the total number of Filter List Packages.

      Packet_ID
         The fragmentation index of one of those multiple Filter List
         Packages.

      Type
         The Type of the Filter List TLV. Currently used types are
         described as follows.

                     Filter List TLVs           Type
                 =========================   ============
                 FQDN [RFC1594]                  1
                 DSCP [RFC2724]                  2
                 Destination Port                3
                 Destination IP                  4
                 Destination IP&Port             5
                 Source Port                     6
                 Source IP                       7
                 Source IP&Port                  8
                 Source Mac                      9
                 Protocol                        10
                 Source IP Range                 11
                 Destination IP Range            12
                 Source IP Range&Port            13
                 Destination IP Range&Port       14
                 Reserved

      Length
         The length of the Filter List TLV. Commit_Count, Packet Sum,
         Packet ID, Type and Length are excluded.

      Enable
         Whether the filter item defined in this Filter List TLV is
         enabled. One means enabled and zero means disabled. Other
         possible values are reserved.

      Description Length
         The length of the Description Value.

      Description Value
         A variable ASCII string that describes the Filter List TLV
         (e.g., "FQDN").



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      Value
         A variable ASCII string that specify the value of the Filter
         List TLV (e.g. "www.yahoo.com"). As an example, Type = 1 and
         Value = "www.yahoo.com" means that packets whose FQDN field
         equal "www.yahoo.com" match the filter item.

5.6.3. Switching to DSL Tunnel

   If the RTT difference is continuously detected to violate the RTT
   Difference Threshold (See Section 5.2.4.) more than the times
   described by the RTT Difference Threshold Violation (See Section
   5.2.12.), HCPE uses the Switching to DSL Tunnel attribute to inform
   HAG to use the DSL GRE tunnel only. When HAG receives this attribute,
   it MUST begin to transmit downstream traffic to this HCPE solely over
   the DSL GRE tunnel. The DSL GRE Tunnel Notify message MAY include the
   Switching to DSL Tunnel attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Switching to DSL Tunnel, set to 11.

   Attribute Length
      Set to 0.

5.6.4. Overflowing to LTE Tunnel

   If the RTT difference is continuously detected to not violated the
   RFF Difference Threshold (See Section 5.2.4.) more than the times
   described by the RTT Difference Compliance (See Section 5.2.13), HCPE
   uses the Overflowing to LTE Tunnel attribute to inform HAG that LTE
   GRE tunnel can be used again. The DSL GRE Tunnel Notify message MAY
   include the Overflowing to LTE Tunnel attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Overflowing to LTE Tunnel, set to 12.

   Attribute Length



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      Set to 0.

5.6.5. DSL Link Failure

   When HCPE detects the DSL WAN interface status is down, it MUST tear
   down the DSL GRE tunnel. It informs HAG about the failure using the
   DSL Link Failure attribute. HAG MUST tear down the DSL GRE tunnel
   upon the DSL Link Failure attribute is received. The DSL Link Failure
   attribute SHOULD be carried in the LTE GRE Tunnel Notify message.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

   Attribute Type
      DSL Link Failure, set to 18.

   Attribute Length
      Set to 0.

5.6.6. LTE Link Failure

   When HCPE detects the LTE WAN interface status is down, it MUST tear
   down the LTE GRE tunnel. It informs HAG about the failure using the
   LTE Link Failure attribute. HAG MUST tear down the LTE GRE tunnel
   upon the LTE Link Failure attribute is received. The LTE Link Failure
   attribute SHOULD be carried in the DSL GRE Tunnel Notify message.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      LTE Link Failure, set to 19.

   Attribute Length
      Set to 0.

5.6.7. IPv6 Prefix Assigned to Host

   If HCPE changes the IPv6 prefix assigned to the host, it uses the
   IPv6 Prefix Assigned to Host attribute to inform HAG. Both the LTE
   GRE Tunnel Notify message and the DSL GRE Tunnel Notify message MAY
   include the IPv6 Prefix Assigned to Host attribute.



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   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  IPv6 Prefix Assigned to Host      (4 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      IPv6 Prefix Assigned to Host, set to 21.

   Attribute Length
      Set to 17.

   IPv6 Prefix Assigned to Host
      The highest-order 16 octets encode an IPv6 address. The lowest-
      order one octet encodes the length of a network mask. These two
      values are put together to represent an IPv6 prefix.

5.6.8. Diagnostic Start: Bonding Tunnel

   HCPE uses the Diagnostic Start: Bonding Tunnel attribute to inform
   HAG to switch to diagnostic mode to test the performance of the
   entire bonding tunnel. The Diagnostic Start: Bonding Tunnel attribute
   SHOULD be carried in the DSL GRE Tunnel Notify message.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Diagnostic Start: Bonding Tunnel, set to 26.

   Attribute Length
      Set to 0.

5.6.9. Diagnostic Start: DSL Tunnel

   HCPE uses the Diagnostic Start: DSL Tunnel attribute to inform HAG to
   switch to diagnostic mode to test the performance of the DSL GRE
   tunnel. The Diagnostic Start: DSL Tunnel attribute SHOULD be carried
   in the DSL GRE Tunnel Notify message.







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   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Diagnostic Start: DSL Tunnel, set to 27.

   Attribute Length
      Set to 0.

5.6.10. Diagnostic Start: LTE Tunnel

   HCPE uses the Diagnostic Start: LTE Tunnel attribute to inform HAG to
   switch to diagnostic mode to test the performance of the entire
   bonding tunnel. The Diagnostic Start: LTE Tunnel attribute SHOULD be
   carried in the DSL GRE Tunnel Notify message.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Diagnostic Start: LTE Tunnel, set to 18.

   Attribute Length
      Set to 0.

5.6.11. Diagnostic End

   HCPE uses the Diagnostic End attribute to inform HAG to stop the
   diagnostic mode. The Diagnostic End attribute SHOULD be carried in
   the DSL GRE Tunnel Notify message.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Diagnostic End, set to 29.

   Attribute Length
      Set to 0.



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5.6.12. Filter List Package ACK

   HCPE uses the Filter List Package ACK attribute to acknowledge the
   Filter List Package sent by HAG. Both the LTE GRE Tunnel Notify
   message and the DSL GRE Tunnel Notify message MAY include the Filter
   List Package ACK attribute.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Filter List Package ACK           (5 bytes)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Filter List Package ACK, set to 30.

   Attribute Length
      Set to 5.

   Filter List Package ACK
      The highest-order 4 octets are the Commit_Count as defined in
      Section 5.6.2. The lowest-order 1 octet encodes the following
      error codes:

      0: The Filter List Package is acknowledged.
      1: The Filter List Package is not acknowledged. The HCPE is a new
         subscriber and has not ever received a Filter List Package. In
         this case, HAG SHOULD tear down the bonding tunnels and force
         the HCPE to re-establish the GRE Tunnels.
      2: The Filter List Package is not acknowledged. The HCPE has
         already got a valid Filter List Package. The filter list on the
         HCPE will continue to be used while HAG need do nothing.

5.6.13. Switching to Active Hello State

   If traffic is being sent/receive over the bonding GRE tunnels before
   the "No Traffic Monitored Interval" expires (See Section 5.2.15.),
   HCPE sends to HAG a GRE Tunnel Notify message containing the
   Switching to Active Hello State attribute.

   HAG will switch to active hello state and send HCPE a GRE Tunnel
   Notify message carrying the Switching to Active Hello State attribute
   as the ACK.

   When HCPE receives the ACK, it will switch to active hello state,
   start RTT detection and start sending GRE Tunnel Hello messages with



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   the Active Hello Interval (See Section 5.2.6.).

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Switching to Active Hello State, set to 33.

   Attribute Length
      Set to 0.

5.6.14. Switching to Idle Hello State

   HCPE initiates switching to idle hello state when the bonding of GRE
   Tunnels is successfully established and the LTE GRE Tunnel Setup
   Accept message carrying the Idle Hello Interval attribute (See
   Section 5.2.14.) is received. HCPE sends to HAG a GRE Tunnel Notify
   message containing the Switching to Idle Hello State attribute.

   HAG will switch to idle hello state, clear RTT state and send HCPE a
   GRE Tunnel Notify message carrying the Switching to Idle Hello State
   attribute as the ACK.

   When HCPE receives the ACK, it will switch to idle hello state, stop
   RTT detection, clear RTT state as well and start sending GRE Tunnel
   Hello messages with the Idle Hello Interval (See Section 5.2.14).

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Switching to Idle Hello State, set to 34.

   Attribute Length
      Set to 0.

5.6.15. Tunnel Verification

   HAG uses the Tunnel Verification attribute to inform HCPE to verify
   whether an existing LTE GRE tunnel is still functioning. The Tunnel
   Verification attribute SHOULD be carried in the LTE GRE Tunnel Notify
   message. It provides a mean to detect the tunnel faster than the GRE



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   Tunnel Hello, especially when the LTE GRE tunnel is in the Idle Hello
   state and it takes much longer time to detect this tunnel.

   When HAG receives an LTE GRE Tunnel Setup Request and finds the
   requested tunnel is conflicting with an existing tunnel, the HAG
   initiates the Tunnel Verification. The HAG drops all conflicting LTE
   GRE Tunnel Setup Request messages and send GRE Tunnel Notify messages
   carrying the Tunnel Verification attribute until the verification
   ends. HCPE MUST response to HAG same Tunnel Verification attribute as
   the ACK if the tunnel is still functioning.

   If the ACK of the Tunnel Verification attribute is received from the
   HCPE, HAG judges that the existing tunnel is still functioning. An
   LTE GRE Tunnel Deny message (with Error Code = 8) will be sent to the
   HCPE. HCPE SHOULD terminate the GRE tunnel setup request process
   immediately.

   If HAG does not receive a Tunnel Verification ACK message until up to
   3 times (1 sending + 2 resending), it will regard the existing tunnel
   as failed and the LTE GRE Tunnel Setup Request will be accepted.

   +-+-+-+-+-+-+-+-+
   |Attribute Type |                    (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |    (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Attribute Type
      Tunnel Verification, set to 35.

   Attribute Length
      Set to 0.


6. Tunnel Protocol Operation (Data Plane)

   GRE tunnels are set up over heterogeneous connections, such as LTE
   and DSL, between HCPE and HAG. Users' IP (inner) packets are
   encapsulated in GRE packets which in turn are carried over IP
   (outer). The general structure of the packets is shown as below.











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                     +--------------------------------+
                     |          Media Header          |
                     +--------------------------------+
                     |         Outer IP Header        |
                     +--------------------------------+
                     |           GRE Header           |
                     +--------------------------------+
                     |         Inner IP Packet        |
                     +--------------------------------+

6.1. The GRE Header

   The GRE header is first standardized in [RFC2874]. [RFC2890] adds the
   optional key and sequence number fields which makes the whole GRE
   header have the following format.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |C| |K|S| Reserved0       | Ver |         Protocol Type         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Checksum (optional)      |       Reserved1 (Optional)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Key (optional)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Sequence Number (optional)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Checksum is not used in the GRE Tunnel Bonding, therefore the C
   bit is set to zero.

   The Key bit is set to one. For per-packet traffic distribution, the
   Key field is used as a 32-bit random number. It is generated by the
   HAG and notified to HCPE. Different from the Key filed used in
   control packets, each bonding of GRE tunnels gets a single Key value.
   HCPE MUST carry this number in each GRE header. For the per-flow
   traffic classification and distribution, the Key field will be used
   to identify the traffic flows.

   The S bit is set to one and the sequence number is present for in-
   order delivery as per [RFC2890].

   For the per-flow traffic, the GRE header need also enable the
   Acknowledgement Number field as used in PPTP [RFC2637]. The A bit
   (Bit 8) is set to one to indicate this field is present in the GRE
   header. This acknowledgement number and the sequence number field are
   used to achieve a low-level congestion and flow control. Unless
   explicitly pointed out, the acknowledgement number field is used as



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   per [RFC2637]. The enhanced GRE header has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| |1|1| Rsvd0 |1| Rsvd1 | Ver |         Protocol Type         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Key (optional)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Sequence Number (optional)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Acknowledgement Number (optional)                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6.2. Automatic Setup of GRE Tunnels

   The HCPE gets the DSL WAN interface IP address (D) from BRAS via
   PPPoE, and gets the LTE WAN interface IP address (E) through PDP from
   PGW. The DNS resolution of HAG's domain name is requested via DSL/LTE
   WAN interface. The DNS server will reply with the corresponding HAG
   IP address (H) which MAY be pre-configured by operators.

   After the interface IP addresses have been acquired, the HCPE starts
   the following GRE Tunnel Bonding procedure. It's REQUIRED that the
   HCPE first sets up the LTE GRE tunnel and then sets up the DSL GRE
   tunnel.

   The HCPE sends the GRE Tunnel Setup Request message to HAG via the
   LTE WAN interface. The HAG, which receives the GRE Tunnel Setup
   Request message, will initiate the Authentication and Authorization
   procedure, as specified in [TS23.401], to check whether HCPE is being
   trusted by the PGW.

   If the Authentication and Authorization succeed, HAG will reply to
   HCPE's LTE WAN interface with the GRE Tunnel Setup Accept message in
   which a Session ID randomly generated by the HAG is carried.
   Otherwise, the HAG MUST send to the HCPE's LTE WAN interface the GRE
   Tunnel Setup Deny message and the HCPE MUST terminate the tunnel set
   up process upon it receives the GRE Tunnel Setup Deny message.

   After the LTE GRE tunnel is successfully set up, the HCPE will obtain
   the C address over the tunnel from HAG through DHCP. After that, the
   HCPE starts to set up the DSL GRE tunnel. It sends GRE Tunnel Setup
   Request message with HAG's address as the destination IP of GRE via
   the DSL WAN interface, carrying the aforementioned session ID
   received from the HAG. The HAG, which receives the GRE Tunnel Setup
   Request message, will initiate the Authentication and Authorization
   procedure in order to check whether HCPE is trusted by the BRAS.



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   If the Authentication and Authorization succeed, the HAG will reply
   to the HCPE's DSL WAN interface with the GRE Tunnel Setup Accept
   message. In this way, the two tunnels with the same Session ID can be
   used to carry traffic from the same user. That is to say, the two
   tunnels are "bonded" together. Otherwise, if the Authentication and
   Authorization fail, the HAG MUST send to the HCPE's DSL WAN interface
   the GRE Tunnel Setup Deny message. Meanwhile, it MUST send to the
   HCPE's LTE WAN interface the GRE Tunnel Tear Down message. The HCPE
   MUST terminate the tunnel set up process upon it receives the GRE
   Tunnel Setup Deny message and MUST tear down the LTE GRE tunnel that
   has been set up upon it receives the GRE Tunnel Tear Down Message.

7. Security Considerations

   As a security feature, the Key field of the GRE header of the control
   messages and the data packets for the per-packet traffic distribution
   could be generated as a 32-bit clear-text password.

8. IANA Considerations

   No IANA action is required in this document. RFC Editor: please
   remove this section before publication.

9. References

9.1. Normative References

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

   [RFC2698] Heinanen, J. and R. Guerin, "A Two Rate Three Color
             Marker", RFC 2698, September 1999.

   [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
             RFC 2890, September 2000.

   [TS23.401] "3GPP TS23.401, General Packet Radio Service (GPRS)
             enhancements for Evolved Universal Terrestrial Radio Access
             Network (E-UTRAN) access", September 2013.

9.2. Informative References

   [RFC1594] Marine, A., Reynolds, J., and G. Malkin, "FYI on Questions
             and Answers - Answers to Commonly asked "New Internet User"
             Questions", RFC 1594, March 1994.

   [RFC2724] Handelman, S., Stibler, S., Brownlee, N., and G. Ruth,
             "RTFM: New Attributes for Traffic Flow Measurement", RFC



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             2724, October 1999.

   [RFC2637] Hamzeh, K., Pall, G., Verthein, W., Taarud, J., Little, W.,
             and G. Zorn, "Point-to-Point Tunneling Protocol (PPTP)",
             RFC 2637, July 1999.

   [RFC6320] Wadhwa, S., Moisand, J., Haag, T., Voigt, N., and T.
             Taylor, Ed., "Protocol for Access Node Control Mechanism in
             Broadband Networks", RFC 6320, October 2011.










































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Author's Addresses


   Nicolai Leymann
   Deutsche Telekom AG
   Winterfeldtstrasse 21-27
   Berlin  10781
   Germany

   Phone: +49-170-2275345
   Email: n.leymann@telekom.de


   Cornelius Heidemann
   Deutsche Telekom AG
   Heinrich-Hertz-Strasse 3-7
   Darmstadt  64295
   Germany

   Phone: +4961515812721
   Email: heidemannc@telekom.de


   Mingui Zhang
   Huawei Technologies
   No.156 Beiqing Rd. Haidian District,
   Beijing 100095 P.R. China

   EMail: zhangmingui@huawei.com


   Margaret Wasserman
   Painless Security

   EMail: mrw@painless-security.com
















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