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GRE Tunnel Bonding
draft-zhang-gre-tunnel-bonding-02

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Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8157.
Authors Nicolai Leymann , Cornelius Heidemann , Mingui Zhang , Behcet Sarikaya , Margaret Cullen
Last updated 2016-05-05
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draft-zhang-gre-tunnel-bonding-02
Independent Submission                                        N. Leymann
Internet Draft                                              C. Heidemann
Intended Category: Informational                     Deutsche Telekom AG
                                                                M. Zhang
                                                             B. Sarikaya
                                                                  Huawei
                                                               M. Cullen
                                                       Painless Security
Expires: November 7, 2016                                    May 6, 2016

                           GRE Tunnel Bonding
                 draft-zhang-gre-tunnel-bonding-02.txt

Abstract

   There is an emerging demand for solutions that provide redundancy and
   load-sharing across wired and cellular links from a single service
   provider, so that a single subscriber is provided with hybrid access
   to multiple heterogeneous connections at the same time.

   In this document, GRE (Generic Routing Encapsulation) Tunnel Bonding
   is specified as an enabling approach for Hybrid Access to a wired and
   a wireless network in customer premises, e.g. homes. In GRE Tunnel
   Bonding, two GRE tunnels, one per network connection, 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. The
   solution described in this document is currently implemented by
   Huawei and deployed by Deutsche Telekom AG.

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
   material or to cite them other than as "work in progress."

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

 

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

Copyright and License Notice

   Copyright (c) 2016 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
   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. Acronyms and Terminology  . . . . . . . . . . . . . . . . . . .  4
   3. Use Case  . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4. Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1. Control Plane . . . . . . . . . . . . . . . . . . . . . . .  7
     4.2. Data Plane  . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.3. Traffic Classification and Distribution . . . . . . . . . .  7
     4.4. Traffic Recombination . . . . . . . . . . . . . . . . . . .  8
     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
       5.2.2. 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
 

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       5.2.10. Configured DSL Upstream Bandwidth  . . . . . . . . . . 19
       5.2.11. Configured DSL Downstream Bandwidth  . . . . . . . . . 19
       5.2.12. RTT Difference Threshold Violation . . . . . . . . . . 20
       5.2.13. RTT Difference Threshold Compliance  . . . . . . . . . 20
       5.2.14. Idle Hello Interval  . . . . . . . . . . . . . . . . . 21
       5.2.15. No Traffic Monitored Interval  . . . . . . . . . . . . 22
     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  . . . . . . . . . . . . . . . . . . . 25
     5.6. GRE Tunnel Notify . . . . . . . . . . . . . . . . . . . . . 25
       5.6.1. Bypass Traffic Rate . . . . . . . . . . . . . . . . . . 25
       5.6.2. Filter List Package . . . . . . . . . . . . . . . . . . 26
       5.6.3. Switching to DSL Tunnel . . . . . . . . . . . . . . . . 28
       5.6.4. Overflowing to LTE Tunnel . . . . . . . . . . . . . . . 29
       5.6.5. DSL Link Failure  . . . . . . . . . . . . . . . . . . . 29
       5.6.6. LTE Link Failure  . . . . . . . . . . . . . . . . . . . 30
       5.6.7. IPv6 Prefix Assigned to Host  . . . . . . . . . . . . . 30
       5.6.8. Diagnostic Start: Bonding Tunnel  . . . . . . . . . . . 31
       5.6.9. Diagnostic Start: DSL Tunnel  . . . . . . . . . . . . . 31
       5.6.10. Diagnostic Start: LTE Tunnel . . . . . . . . . . . . . 31
       5.6.11. Diagnostic End . . . . . . . . . . . . . . . . . . . . 32
       5.6.12. Filter List Package ACK  . . . . . . . . . . . . . . . 32
       5.6.13. Switching to Active Hello State  . . . . . . . . . . . 33
       5.6.14. Switching to Idle Hello State  . . . . . . . . . . . . 33
       5.6.15. Tunnel Verification  . . . . . . . . . . . . . . . . . 34
   6. Tunnel Protocol Operation (Data Plane)  . . . . . . . . . . . . 35
     6.1. The GRE Header  . . . . . . . . . . . . . . . . . . . . . . 35
     6.2. Automatic Setup of GRE Tunnels  . . . . . . . . . . . . . . 36
   7. Security Considerations . . . . . . . . . . . . . . . . . . . . 37
   8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 37
   9. Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . 38
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 38
     10.2. Informative References . . . . . . . . . . . . . . . . . . 38
   Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40

1. Introduction

   Service providers used to provide subscribers with separate access to
   their fixed broadband networks and mobile networks. It has become
   desirable to bond these heterogeneous networks together to offer
   access service to subscribers that offer increased access capacity
   and improved reliability. In this document, "Hybrid Access" is used
   to refer to such bonding access services. The Broadband Forum first
   proposes the concept of Hybrid Access and develops a set of
 

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   requirements in [WT-348].

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

   This document bases the solution on GRE (Generic Routing
   Encapsulation [RFC2890]) since GRE is widely supported in both fixed
   and mobile networks. One GRE tunnel is set up for each heterogeneous
   connection (DSL and LTE) between the HCPE and HAG. Those GRE tunnels
   are further bonded together to form a logical GRE tunnel for the
   subscriber. HCPE conceals the composing GRE tunnels from the end
   nodes, and end nodes simply treat the logical GRE tunnel as a single
   IP link. This provides an overlay: the users' IP packets (inner IP)
   are encapsulated in GRE which is in turn carried over IP (outer IP). 

2. Acronyms and Terminology

   GRE: Generic Routing Encapsulation [RFC2890]

   DSL: Digital Subscriber Line is a family of technologies that are
   used to transmit digital data over telephone lines

   LTE: Long Term Evolution.  A standard for wireless communication of
   high-speed data for mobile phones and data terminals. Commonly
   marketed as 4G LTE.

   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 subscriber access
   services.

   CIR: Committed Information Rate [RFC2698]
 

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   RTT: Round Trip Time

   AAA: Authentication, Authorization and Accounting [RFC6733] 

   SOAP: Simple Object Access Protocol. It is a protocol specification
   for exchanging structured information in the implementation of web
   services in computer networks.

   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. It routes traffic to and from
   broadband remote access devices such as Digital Subscriber Line
   Access Multiplexers (DSLAM) on an Internet service provider's (ISP)
   network.

   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. 

   PDP: Packet Data Protocol. A packet transfer protocol used in
   wireless GPRS (General Packet Radio Service)/HSDPA (High Speed
   Downlink Packet Access) networks.

   PPPoE: Point-to-Point Protocol over Ethernet is a network protocol
   for encapsulating PPP frames inside Ethernet frames.

   DNS: Domain Name System is a hierarchical distributed naming system
   for computers, services, or any resource connected to the Internet or
   a private network. 

   DHCP: Dynamic Host Configuration Protocol. A standardized network
   protocol used on Internet Protocol (IP) networks for dynamically
   distributing network configuration parameters, such as IP addresses
   for interfaces and services.

   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

 

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                 +-+                           +-+
                 | +---- Bonding Connection ---+ |
                 | |                           | |
                 | | +-+                       | |
      subscriber |C| |E+---- LTE Connection ---+H| Internet
                 | | +-+                       | |
                 | | +-+                       | |
                 | | |D+---- DSL Connection ---+ |
                 +-+ +-+                       +-+
                 \_____/
                  HCPE                         HAG

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

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

   For a Service Provider who runs heterogeneous networks, such as fixed
   and mobile, subscribers wish to use those networks simultaneously for
   increased access capacity rather than just using a single network. As
   shown by the reference model in Figure 3.1, the subscriber expects
   the whole bandwidth of the bonding connection equals the sum of the
   bandwidth of the DSL connection and the LTE connection between HCPE
   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 load balancing solutions spread load based on per-flow load-
   balancing among multiple paths. However, the solution described here
   is about per-packet offloading rather than per-flow load-balancing.
   For per-flow load-balancing, the maximum bandwidth that may be used
   by a flow is equal to the bandwidth of the connection selected.
   However, per-packet load-balancing allows a single flow to use the
   bandwidth of both connections. A GRE Tunnel Bonding mechanism could
   also support per-flow traffic classification and distribution, though
   that is out of scope for this document.

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.
   Subscribers uses this logical tunnel without knowing the composing
 

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   GRE tunnels.

4.1. Control Plane

   A clean-slate control protocol is designed to manage the GRE tunnels
   that are setup per heterogeneous connection 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 to 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 (shown in Figure 6.1) as specified in
   [RFC2890] is being used. The GRE Protocol Type (0xB7EA) 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 human operators. 

4.2. Data Plane

   Using the control plane defined in Section 4.1, GRE tunnels can be
   automatically setup per heterogeneous connection between the HCPE and
   the HAG. For the use case described in Section 3, one GRE tunnel is
   terminated at the DSL WAN interfaces, e.g., DSL GRE tunnel, and
   another GRE tunnel is terminated at the LTE WAN interfaces, e.g., 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 subscribers.

   The GRE header [RFC2890] is used to encapsulate data packets. The
   Protocol Type is either 0x0800 [RFC2784] or 0x86DD [RFC7676], which
   indicates the inner packet is either an IPv4 packet or an IPv6
   packet. For per-packet offloading use case, the Key field is set to a
   unique value for the entire bonding. The Sequence Number field is
   used to maintain the sequence of packets transported in all GRE
   tunnels as a single flow between the HCPE and the HAG. 

4.3. Traffic Classification and Distribution

   For the offloading use case, the coloring mechanism specified in
   [RFC2698] is being used to classify subscriber's IP packets, both
   upstream and downstream, into the DSL GRE tunnel or the LTE GRE
   tunnel. Packets colored as green will be distributed into the DSL GRE
 

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   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. However, that is
   out of the scope for 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
   obtained from the management system (AAA server, SOAP server, etc.),
   or MAY be detected and reported in real-time using ANCP [RFC6320]. 

4.4. Traffic Recombination

   The recombination function at the receiver provides in-order delivery
   of subscribers' traffic. As specified in [RFC2890], the receiver
   maintains a small reordering buffer and orders 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.

4.5. Bypassing

   Service Providers provide some services that should not be delivered
   over a bonded connection. For example, Service Providers do not
   expect real-time IPTV to be carried by the LTE GRE tunnel. It is
   required that these services bypass GRE Tunnel Bonding and use the
   raw DSL bandwidth. In this way, they are not subject to the traffic
   classification and distribution specified above. There are two kinds
   of bypassing: 

   o Full bypassing: The raw DSL connection used for bypassing is not
     controlled by the 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 the HAG. 

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

4.6. Measurement

   Since control packets are routed using the same paths as the data
   packets, the real performance of the data paths (e.g., the GRE
 

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   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, the HCPE and the HAG
   need also measure the capacity of the tunnels. For example, for full
   bypassing, the HCPE is REQUIRED to measure the downstream bypassing
   bandwidth in real time, and report it to the 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 the HAG to the HCPE, and the HCPE will use the raw DSL interface
   to transmit traffic for 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, the HCPE
   and the 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 define 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 the HCPE or the HAG to send out Hello messages before
   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 the HAG. Also, the control
   plane undertakes the responsibility to bond tunnels and convey
   traffic policies.

 

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   For the purpose of measurement, control messages need to be delivered
   as GRE encapsulated packets and co-routed with data plane packets.
   The new GRE Protocol Type (0xB7EA) is allocated for this purpose and
   the standard GRE header as per [RFC2890] is used. The format of the
   GRE header 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |C| |K|S| Reserved0       | Ver |   Protocol Type 0xB7EA        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         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 0xB7EA.

   Key
      The Key field is used as a demultiplexer for the GRE tunnels at
      the HAG. This value of the Key is generated by the HAG and
      informed to the 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 0xB7EA        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         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 byte 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 that the
   HAG establish the GRE tunnels. It is sent out from HCPE's LTE and DSL
   WAN interfaces separately. Attributes that need to be included in
   this message are defined in the following subsections.

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 the HAG for authentication and
   authorization as specified in [TS23.401]. It is REQUIRED 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-byte ANSI string value set by the operator. It is
      used as the identification of the HCPE in the operator's network.

5.1.2. Session ID

   This Session ID is generated by the HAG when the LTE GRE Tunnel Setup
   Request message is received. The HAG announces the Session ID to the
   HCPE in 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-byte ANSI string value generated by the HAG. It is
      used as the identification of bonded GRE Tunnels.

5.1.3. DSL Synchronization Rate

   The HCPE uses the DSL Synchronization Rate to notify the 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 an unsigned integer measured in kbps.

5.2. GRE Tunnel Setup Accept

   The HAG uses the GRE Tunnel Setup Accept message as the response to
   the GRE Tunnel Setup Request message. This message indicates
   acceptance 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 below.

5.2.1. H IPv4 Address

   The HAG uses the H IPv4 Address attribute to inform the HCPE of 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 the HAG.

5.2.2. H IPv6 Address

   HAG uses the H IPv6 Address attribute to inform the HCPE of the H
   IPv6 address. The 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 IPv6 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

   The HAG uses the RTT Difference Threshold attribute to inform the
   HCPE of the acceptable threshold of RTT difference between the DSL
   link and the LTE link. If the measured RTT difference exceeds this
   threshold, the HCPE 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
      An unsigned integer measured in milliseconds. This value can be
      chosen in the range 0 through 1000.

5.2.5. Bypass Bandwidth Check Interval

   The HAG uses the Bypass Bandwidth Check Interval attribute to inform
   the HCPE of how frequently the bypass bandwidth should be checked.
   The HCPE should check the bypass bandwidth of the DSL WAN interface
   in each time period indicated 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
      An unsigned integer measured in seconds. This value can be chosen
      in the range 0 through 300.

5.2.6. Active Hello Interval

   The HAG uses the Active Hello Interval attribute to inform the HCPE
   of the pre-configured interval for sending out GRE Tunnel Hellos. The
   HCPE should send out GRE Tunnel Hellos via both the DSL and LTE WAN
   interfaces in each time period as indicated 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
      An unsigned integer measured in seconds. This value can be chosen
      in the range 0 through 100.

5.2.7. Hello Retry Times

   The HAG uses the Hello Retry Times attribute to inform the HCPE of
 

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   the retry times for sending GRE Tunnel Hellos. If the HCPE does not
   receive any acknowledgement from the HAG for the number of GRE Tunnel
   Hello attempts specified in this attribute, the HCPE will declare a
   failure of the 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
      An unsigned integer, which takes values in the range 3 through 10.

5.2.8. Idle Timeout

   The HAG uses the Idle Timeout attribute to inform the HCPE of 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, subsequent traffic will be sent over raw DSL
   rather than over a tunnel, 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
      An unsigned integer measured in seconds. It takes values 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

   The HAG uses the Bonding Key Value attribute to inform the HCPE of
   the number which is to be used as the Key of the GRE header for each
   tunneled control message. The Bonding Key Value is generated by the
   HAG and used for the purpose of demultiplexing. The HAG is REQUIRED
   to distinguish the GRE tunnels from the Bonding Key Value. Different
   tunnels MUST use different Bonding Key Values. The 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, the HAG
   can figure out the source IP address used for the LTE GRE tunnel from
   the message carrying the CIN attribute. Similarly, the HAG can figure
   out the source IP address used for the DSL GRE tunnel from the
   message carrying the DSL Synchronization Rate attribute. 

   The 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 is REQUIRED that
      different tunnels are allocated 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. Configured DSL Upstream Bandwidth

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

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

   Attribute Type
      Configured DSL Upstream Bandwidth, set to 22.

   Attribute Length
      Set to 4.

   Configured DSL Upstream Bandwidth
      An unsigned integer measured in kbps.

5.2.11. Configured DSL Downstream Bandwidth

   The HAG obtains the downstream bandwidth of the DSL link from the
   management system and uses the Configured DSL Downstream Bandwidth
   attribute to inform the HCPE. The HCPE uses the received downstream
   bandwidth as the base in calculating the bypassing bandwidth. The DSL
   GRE Tunnel Setup Accept message MUST include the Configured DSL
   Downstream Bandwidth attribute.

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

   Attribute Type
      Configured DSL Downstream Bandwidth, set to 23.

   Attribute Length
      Set to 4.
 

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   Configured DSL Downstream Bandwidth
      An unsigned integer measured in kbps.

5.2.12. RTT Difference Threshold Violation

   The HAG uses the RTT Difference Threshold Violation attribute to
   inform the HCPE of the number of times in a row that the RTT
   Difference Threshold (See Section 5.2.4.) may be violated before the
   HCPE MUST stop using the LTE GRE Tunnel. If the RTT Difference
   Threshold is continuously violated for more than the indicated number
   of measurements, 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
      An unsigned integer which takes values in the range 1 through 25.
      A typical value is 3.

5.2.13. RTT Difference Threshold Compliance

   The HAG uses the RTT Difference Threshold Compliance attribute to
   inform the HCPE of the number of times in a row the RTT Difference
   Threshold (See Section 5.2.4.) must be compliant before use of the
   LTE GRE tunnel can be resumed. If the RTT Difference Threshold is
   continuously detected to be compliant across more than this number of
   measurments, the HCPE MAY resume using the LTE GRE tunnel. The LTE
   GRE Tunnel Setup Accept message MUST include the RTT Difference
   Threshold Compliance attribute.

 

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

   Attribute Type
      RTT Diff Threshold Compliance, set to 25.

   Attribute Length
      Set to 4.

   RTT Diff Threshold Compliance
      An unsigned integer which takes values in the range 1 through 25.
      A typical value is 3.

5.2.14. Idle Hello Interval

   The HAG uses the Idle Hello Interval attribute to inform the HCPE of
   the pre-configured interval for sending out GRE Tunnel Hellos when
   the subscriber is detected to be idle. The HCPE SHOULD begin to send
   out GRE Tunnel Hellos via both the DSL and LTE WAN interfaces in each
   time period as indicated 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
      An unsigned integer measured in seconds. This value can be chosen
      from the range 100 through 86,400 (24 hours) with the granularity
      of 100. The default value is 1800 (30 minutes).

 

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5.2.15. No Traffic Monitored Interval

   The HAG uses the No Traffic Monitored Interval attribute to inform
   the HCPE of 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 the Active
   Hello Interval. The LTE GRE Tunnel Setup Accept message MUST include
   the No Traffic Monitored Interval attribute.

   +-+-+-+-+-+-+-+-+
   |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
      An unsigned integer measured in seconds. This value is 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

   The HAG uses the Error Code attribute to inform the HCPE of 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.

 

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   +-+-+-+-+-+-+-+-+
   |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
      An unsigned integer. The list of the codes are listed as follows.

      1: The HAG was not reachable over LTE during the GRE tunnel setup
         request.
      2: The HAG was not reachable via DSL during the GRE tunnel setup
         request.
      3: The LTE GRE tunnel to the HAG failed.
      4: The DSL GRE tunnel to the HAG failed.
      5: The given DSL User ID is not allowed to use the GRE tunnel
         bonding service.
      6: The given User Alias (TOID)/User ID (GUID) is not allowed to
         use the GRE tunnel bonding service.
      7: The LTE and DSL User IDs do not match.
      8: The HAG denied the GRE tunnel setup request because a bonding
         session with the same User ID already exists.
      9: The HAG denied the GRE tunnel setup request because the user's
         CIN is not permitted.
      10: The HAG terminated a GRE tunnel bonding session for
         maintenance reasons.
      11: There was a communication error between the HAG and the
         management system during the LTE tunnel setup request.
      12: There was a communication error between the HAG and management
         system 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, which the HAG acknowledges by
   returning GRE Tunnel Hello messages back to the HCPE.  This continues
   until the tunnel is terminated. 

5.4.1. Timestamp

 

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   The HAG uses the Timestamp attribute to inform the HCPE of 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
      Set to 8.

   Timestamp
      The high-order 4 octets indicate an unsigned integer in units of
      one second; the low-order 4 octets indicate an unsigned integer in
      unit of one millisecond.

5.4.2. IPv6 Prefix Assigned by HAG

   The HAG uses the IPv6 Prefix Assigned by the HAG attribute to inform
   the HCPE of 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-
 

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      order one octet encodes the prefix length. These two values are
      put together to represent an IPv6 prefix.

5.5. GRE Tunnel Tear Down

   The 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

   The HCPE and the HAG use the GRE Tunnel Notify message to notify each
   other about their status, the information for the bonding tunnels,
   the actions that 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
   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 below.

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 bypass bandwidth on the DSL WAN interface for these
   traffic types. Therefore, the available bandwidth of the DSL GRE
   tunnel is the entire DSL WAN interface bandwidth minus the occupied
   bypass bandwidth. 

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

 

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   +-+-+-+-+-+-+-+-+
   |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
      An unsigned integer measured in kbps.

5.6.2. Filter List Package

   The HAG uses the Filter List Package attribute to inform the HCPE of
   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 is maintained. Also, the HCPE needs to 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 a filter item in the filter list while
   not matching 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
 

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

      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
 

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                 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").

      Value
         A variable ASCII string that specifies 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
         equals "www.yahoo.com" match the filter item.

   The lengths of the auxiliary Description Value and Value fields are
   restricted to a maximum of 4 bytes and 32 bytes respectively, which
   aims to limit the size of the Filter List TLV sent on the GRE tunnel.

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
   specified in the RTT Difference Threshold Violation (See Section
   5.2.12.), the HCPE uses the Switching to DSL Tunnel attribute to
   inform the HAG to use the DSL GRE tunnel only. When the 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.

 

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   +-+-+-+-+-+-+-+-+
   |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
   RTT Difference Threshold attribute (See Section 5.2.4.) more than the
   number of times specified in the RTT Difference Compliance attribute
   (See Section 5.2.13), the 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
      Set to 0.

5.6.5. DSL Link Failure

   When the 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. The 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)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
 

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   Attribute Type
      DSL Link Failure, set to 18.

   Attribute Length
      Set to 0.

5.6.6. LTE Link Failure

   When the HCPE detects the LTE WAN interface status is down, it MUST
   tear down the LTE GRE tunnel. It informs the 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 the HCPE changes the IPv6 prefix assigned to the host, it uses the
   IPv6 Prefix Assigned to Host attribute to inform the HAG. Both the
   LTE GRE Tunnel Notify message and the DSL GRE Tunnel Notify message
   MAY include the IPv6 Prefix Assigned to Host attribute.

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

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

   Attribute Length
      Set to 17.

 

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

5.6.8. Diagnostic Start: Bonding Tunnel

   The HCPE uses the Diagnostic Start: Bonding Tunnel attribute to
   inform the 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

   The HCPE uses the Diagnostic Start: DSL Tunnel attribute to inform
   the 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.

   +-+-+-+-+-+-+-+-+
   |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

   The HCPE uses the Diagnostic Start: LTE Tunnel attribute to inform
   the HAG to switch to diagnostic mode to test the performance of the
   entire bonding tunnel. The Diagnostic Start: LTE Tunnel attribute
 

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   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

   The HCPE uses the Diagnostic End attribute to inform th HAG to stop
   operating in 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.

5.6.12. Filter List Package ACK

   The HCPE uses the Filter List Package ACK attribute to acknowledge
   the Filter List Package sent by the 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
 

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

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

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

 

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   The 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. The HCPE sends the HAG a GRE Tunnel
   Notify message containing the Switching to Idle Hello State
   attribute.

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

   When the 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

   The HAG uses the Tunnel Verification attribute to inform the 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 means to detect the tunnel faster than
   the GRE 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 the 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 sends GRE Tunnel Notify
   messages carrying the Tunnel Verification attribute until the
   verification ends. The HCPE MUST respond to the HAG with the 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
 

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   HCPE, the 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. The HCPE SHOULD terminate the GRE tunnel setup request
   process immediately.

   If the HAG does not receive a Tunnel Verification ACK message after 3
   attempts (1 initial attempt and 2 retries), 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 the HCPE and the 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. 

                     +--------------------------------+
                     |          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.

 

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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 0x0800/86DD    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Checksum (optional)      |       Reserved1 (Optional)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Key (optional)                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Sequence Number (optional)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 6.1 The GRE header

   The Checksum is not used in the GRE Tunnel Bonding, therefore the C
   bit is set to zero. The Protocol Type field in the GRE header MUST be
   set to 0x0800 for IPv4 or 0x86DD for IPv6.

   The Key bit is set to one so that the Key field is present. 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 field used in control packets, each bonding of GRE
   tunnels gets a single Key value. HCPE MUST carry this number in each
   GRE header. 

   The S bit is set to one, and the Sequence Number field is present and
   used for in-order delivery as per [RFC2890]. 

6.2. Automatic Setup of GRE Tunnels

   The HCPE gets the DSL WAN interface IP address (D) from the Broadband
   Remote Access Server (BRAS) via Point-to-Point Protocol over Ethernet
   (PPPoE), and gets the LTE WAN interface IP address (E) through Packet
   Data Protocol (PDP) from the Packet Data Network Gateway (PGW). The
   Domain Name System (DNS) resolution of the HAG's domain name is
   requested via the DSL/LTE WAN interface. The DNS server will reply
   with the corresponding HAG IP address (H) which MAY be pre-configured
   by the operator.

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

   The HCPE sends the GRE Tunnel Setup Request message to the 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 the HCPE is
 

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   trusted by the PGW.

   If the Authentication and Authorization succeed, the HAG will reply
   to the 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 once 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 the HAG through Dynamic Host
   Configuration Protocol (DHCP). After that, the HCPE starts to set up
   the DSL GRE tunnel. It sends a GRE Tunnel Setup Request message with
   the HAG's address as the destination IP of GRE Tunnel 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 the HCPE is trusted by the BRAS.

   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 once it receives the GRE
   Tunnel Setup Deny message and MUST tear down the LTE GRE tunnel that
   has been set up once it receives the GRE Tunnel Tear Down Message.

7. Security Considerations

   Malicious devices controlled by attackers may intercept the control
   messages sent on the GRE tunnels. Later on, the rogue devices may
   fake control messages to disrupt the GRE tunnels or attract traffic
   of the target HCPE.

   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. 

   Moreover, GRE over IP Security (IPSec) could be used to enhance the
   security.

8. IANA Considerations

 

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   The GRE Protocol Type for the GRE Channel is set to 0xB7EA which is
   under the control of IEEE Registration Authority. Please update the
   "IEEE 802 Numbers" IANA web page [802Type] which is of primarily
   historic interest.

9. Contributors

   Li Xue Individual

   Email: xueli_jas@163.com

10. References 

10.1. Normative References

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

   [RFC2698] Heinanen, J. and R. Guerin, "A Two Rate Three Color
             Marker", RFC 2698, DOI 10.17487/RFC2698, September 1999,
             <http://www.rfc-editor.org/info/rfc2698>.
   [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
             RFC 2890, DOI 10.17487/RFC2890, September 2000,
             <http://www.rfc-editor.org/info/rfc2890>.

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

10.2. Informative References

   [WT-348]  Broadband Forum Work on "Hybrid Access for Broadband
             Networks" (WT-348), October 21, 2014,
             <http://datatracker.ietf.org/liaison/1355/>.

   [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
             2724, DOI 10.17487/RFC2724, October 1999, <http://www.rfc-
             editor.org/info/rfc2724>.

   [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
 

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             "Generic Routing Encapsulation (GRE)", RFC 2784, DOI
             10.17487/RFC2784, March 2000, <http://www.rfc-
             editor.org/info/rfc2784>.

   [RFC6320] Wadhwa, S., Moisand, J., Haag, T., Voigt, N., and T.
             Taylor, Ed., "Protocol for Access Node Control Mechanism in
             Broadband Networks", RFC 6320, DOI 10.17487/RFC6320,
             October 2011, <http://www.rfc-editor.org/info/rfc6320>.

   [RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
             Ed., "Diameter Base Protocol", RFC 6733, DOI
             10.17487/RFC6733, October 2012, <http://www.rfc-
             editor.org/info/rfc6733>.

   [RFC7676] Pignataro, C., Bonica, R., and S. Krishnan, "IPv6 Support
             for Generic Routing Encapsulation (GRE)", RFC 7676, DOI
             10.17487/RFC7676, October 2015, <http://www.rfc-
             editor.org/info/rfc7676>.

   [802Type] IANA, "IEEE 802 Numbers",
             <http://www.iana.org/assignments/ieee-802-numbers>.

 

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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

   Behcet Sarikaya
   Huawei USA
   5340 Legacy Dr. Building 3
   Plano, TX  75024

   EMail: sarikaya@ieee.org

   Margaret Cullen
   Painless Security
   14 Summer St. Suite 202
   Malden, MA 02148  USA

   EMail: margaret@painless-security.com

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