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RFC 8157

Huawei's GRE Tunnel Bonding Protocol

Pages: 44
Informational
Part 1 of 2 – Pages 1 to 24
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Independent Submission                                        N. Leymann
Request for Comments: 8157                                  C. Heidemann
Category: Informational                              Deutsche Telekom AG
ISSN: 2070-1721                                                 M. Zhang
                                                             B. Sarikaya
                                                                  Huawei
                                                               M. Cullen
                                                       Painless Security
                                                                May 2017


                  Huawei's GRE Tunnel Bonding Protocol

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 bonded access to heterogeneous connections at the same time. In this document, GRE (Generic Routing Encapsulation) Tunnel Bonding is specified as an enabling approach for bonded 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 subconnection, the bonded connections promise increased access capacity and improved reliability. The solution described in this document is currently implemented by Huawei and deployed by Deutsche Telekom AG. This document will enable other developers to build interoperable implementations. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not a candidate for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc8157.
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Copyright Notice

   Copyright (c) 2017 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.

Table of Contents

1. Introduction ....................................................3 2. Acronyms and Terminology ........................................4 3. Use Case ........................................................6 4. Overview ........................................................7 4.1. Control Plane ..............................................7 4.2. Data Plane .................................................7 4.3. Traffic Classification and Distribution ....................8 4.4. Traffic Recombination ......................................8 4.5. Bypass .....................................................9 4.6. Measurement ................................................9 4.7. Policy Control Considerations ..............................9 5. Control Protocol Specification (Control Plane) .................10 5.1. GRE Tunnel Setup Request ..................................12 5.1.1. Client Identification Name .........................12 5.1.2. Session ID .........................................13 5.1.3. DSL Synchronization Rate ...........................14 5.2. GRE Tunnel Setup Accept ...................................14 5.2.1. H IPv4 Address .....................................15 5.2.2. H IPv6 Address .....................................15 5.2.3. Session ID .........................................16 5.2.4. RTT Difference Threshold ...........................16 5.2.5. Bypass Bandwidth Check Interval ....................17 5.2.6. Active Hello Interval ..............................17 5.2.7. Hello Retry Times ..................................18 5.2.8. Idle Timeout .......................................18 5.2.9. Bonding Key Value ..................................19 5.2.10. Configured DSL Upstream Bandwidth .................20 5.2.11. Configured DSL Downstream Bandwidth ...............21 5.2.12. RTT Difference Threshold Violation ................21 5.2.13. RTT Difference Threshold Compliance ...............22 5.2.14. Idle Hello Interval ...............................23 5.2.15. No Traffic Monitored Interval .....................23
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      5.3. GRE Tunnel Setup Deny .....................................24
           5.3.1. Error Code .........................................24
      5.4. GRE Tunnel Hello ..........................................25
           5.4.1. Timestamp ..........................................25
           5.4.2. IPv6 Prefix Assigned by HAAP .......................26
      5.5. GRE Tunnel Tear Down ......................................26
      5.6. GRE Tunnel Notify .........................................27
           5.6.1. Bypass Traffic Rate ................................27
           5.6.2. Filter List Package ................................28
           5.6.3. Switching to DSL Tunnel ............................31
           5.6.4. Overflowing to LTE Tunnel ..........................31
           5.6.5. DSL Link Failure ...................................32
           5.6.6. LTE Link Failure ...................................32
           5.6.7. IPv6 Prefix Assigned to Host .......................33
           5.6.8. Diagnostic Start: Bonding Tunnel ...................33
           5.6.9. Diagnostic Start: DSL Tunnel .......................34
           5.6.10. Diagnostic Start: LTE Tunnel ......................34
           5.6.11. Diagnostic End ....................................35
           5.6.12. Filter List Package ACK ...........................35
           5.6.13. Switching to Active Hello State ...................36
           5.6.14. Switching to Idle Hello State .....................37
           5.6.15. Tunnel Verification ...............................37
   6. Tunnel Protocol Operation (Data Plane) .........................38
      6.1. The GRE Header ............................................38
      6.2. Automatic Setup of GRE Tunnels ............................39
   7. Security Considerations ........................................41
   8. IANA Considerations ............................................41
   9. References .....................................................41
      9.1. Normative References ......................................41
      9.2. Informative References ....................................42
   Contributors ......................................................43
   Authors' Addresses ................................................44

1. Introduction

Service Providers used to provide subscribers with separate access to their fixed networks and mobile networks. It has become desirable to bond these heterogeneous networks together to offer access service to subscribers; this service will provide increased access capacity and improved reliability. This document focuses on the use case where a DSL (Digital Subscriber Line) connection and an LTE (Long Term Evolution) connection are bonded together. When the traffic volume exceeds the bandwidth of the DSL connection, the excess amount can be offloaded to the LTE connection. A Home Gateway (HG) is a Customer Premises Equipment (CPE) device initiating the DSL and LTE connections. A Hybrid Access Aggregation Point (HAAP) is the network function that resides in the
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   provider's networks to terminate these bonded connections.  Note that
   if there were more than two connections that need to be bonded, the
   GRE Tunnel Bonding mechanism could support that scenario as well.
   However, support for more than two connections is out of scope for
   this document.  Also, the protocol specified in this document is
   limited to the single-operator scenario only, i.e., the two peering
   boxes -- the HG and the HAAP -- are operated by a single provider.
   The adaptation of the GRE Tunnel Bonding Protocol to the
   multi-provider scenario is left for future work.

   This document bases the solution on GRE (Generic Routing
   Encapsulation [RFC2784] [RFC2890]), since GRE is widely supported in
   both fixed and mobile networks.  Approaches specified in this
   document might also be used by other tunneling technologies to
   achieve tunnel bonding.  However, such variants are out of scope for
   this document.

   For each heterogeneous connection (DSL and LTE) between the HG and
   the HAAP, one GRE tunnel is set up.  The HG and the HAAP,
   respectively, serve as the common termination point of the two
   tunnels at both ends.  Those GRE tunnels are further bonded together
   to form a logical GRE tunnel for the subscriber.  The HG conceals the
   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).

   The GRE Tunnel Bonding Protocol is developed by Huawei and has been
   deployed in networks operated by Deutsche Telekom AG.  This document
   makes this protocol available to the public, thereby enabling other
   developers to build interoperable implementations.

2. Acronyms and Terminology

GRE: Generic Routing Encapsulation [RFC2784] [RFC2890]. DSL: Digital Subscriber Line. A family of technologies 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. HG: Home Gateway. A CPE device that is enhanced to support the simultaneous use of both fixed broadband and 3GPP access connections.
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   HAAP: Hybrid Access Aggregation Point.  A logical function in an
      operator's network, terminating bonded connections while offering
      high-speed Internet.

   CIR: Committed Information Rate [RFC2697].

   RTT: Round-Trip Time.

   AAA: Authentication, Authorization, and Accounting [RFC6733].

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

   FQDN: Fully Qualified Domain Name.  Generally, a host name with at
      least one domain label under the top-level domain.  For example,
      "dhcp.example.org" is an FQDN [RFC7031].

   DSCP: The 6-bit codepoint (DSCP) of the Differentiated Services field
      (DS field) in the IPv4 and IPv6 headers [RFC2724].

   BRAS: Broadband Remote Access Server.  Routes traffic to and from
      broadband remote access devices such as Digital Subscriber Line
      Access Multiplexers (DSLAMs) on an Internet Service Provider's
      (ISP's) network.

   PGW: Packet Data Network Gateway.  In the Long Term Evolution (LTE)
      architecture for the Evolved Packet Core (EPC), 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 over Ethernet.  A network protocol for
      encapsulating PPP frames inside Ethernet frames.

   DNS: Domain Name System.  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.
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   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 +-+ **************************** | | *+-+ +-+* | | *|E+-- LTE Connection --+ |* subscriber |C| *+-+ |H|* Internet | | *+-+ | |* | | *|D+-- DSL Connection --+ |* | | *+-+ +-+* +-+ **************************** \______/ \__/ HG HAAP C: The service endpoint of the bonding service at the HG. E: The endpoint of the LTE connection resides in the HG. D: The endpoint of the DSL connection resides in the HG. H: The endpoint for each heterogeneous connection at the HAAP. Figure 1: Offloading from DSL to LTE, Increased Access Capacity If a Service Provider runs heterogeneous networks, such as fixed and mobile, subscribers might be eager to use those networks simultaneously for increased access capacity rather than just using a single network. As shown by the reference model in Figure 1, the subscriber expects a significantly higher access bandwidth from the bonding connection than from the DSL connection. In other words, when the traffic volume exceeds the bandwidth of the DSL connection, the excess amount may be offloaded to the LTE connection. Compared to per-flow load-balancing mechanisms, which are widely used nowadays, the use case described in this document requires a per-packet offloading approach. For per-flow load balancing, the maximum bandwidth that may be used by a traffic flow is the bandwidth of an individual connection, while for per-packet offloading, a single flow may use the combined bandwidth of the two connections.
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4. Overview

In this document, the widely supported GRE is chosen as the tunneling technique. With the newly defined control protocol, GRE tunnels are set up on top of the DSL and LTE connections, which are ended at D and H or at E and H, as shown in Figure 1. These tunnels are bonded together to form a single logical bonding connection between the HG and the HAAP. Subscribers use this logical connection without knowing the GRE tunnels.

4.1. Control Plane

A clean-slate control protocol is designed to manage the GRE tunnels that are set up per heterogeneous connection between the HG and the HAAP. The goal is to design a compact control plane for bonding access 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. As shown in Figure 2 (see Section 5), the GRE header [RFC2784] with the Key extension specified by [RFC2890] is being used. The GRE Protocol Type (0xB7EA) is used to identify this GRE Channel. A family of control messages is encapsulated with a GRE header and carried over this channel. Attributes, formatted in Type-Length-Value (TLV) style, are further defined and included in each control message. With the newly defined control plane, the GRE tunnels between the HG and the HAAP can be established, managed, and released without the involvement of operators.

4.2. Data Plane

Using the control plane defined in Section 4.1, GRE tunnels can be automatically set up per heterogeneous connection between the HG and the HAAP. For the use case described in Section 3, one GRE tunnel is ended at the DSL WAN interfaces, e.g., the DSL GRE tunnel, and another GRE tunnel is ended at the LTE WAN interfaces, e.g., the LTE GRE tunnel. Each tunnel may carry a user's IP packets as payload, which forms a typical IP-over-IP overlay. These tunnels are bonded together to offer a single access point to subscribers. As shown in Figure 3 (see Section 6.1), the GRE header [RFC2784] with the Key and Sequence Number extensions specified by [RFC2890] is used to encapsulate data packets. The Protocol Type is either 0x0800 (listed as "0x800" in [RFC2784]) or 0x86DD [RFC7676], which indicates that the inner packet is either an IPv4 packet or an IPv6 packet,
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   respectively.  The GRE Key field is set to a unique value for the
   entire bonding connection.  The GRE Sequence Number field is used to
   maintain the sequence of packets transported in all GRE tunnels as a
   single flow between the HG and the HAAP.

4.3. Traffic Classification and Distribution

For the offloading use case, the coloring mechanism specified in [RFC2697] is being used to classify subscribers' IP packets, both upstream and downstream, into the DSL GRE tunnel or the LTE GRE tunnel. Packets colored as green or yellow will be distributed into the DSL GRE tunnel, and packets colored as red 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 scenario is out of scope for this document. The Committed Information Rate (CIR) of the coloring mechanism is set to the total DSL WAN bandwidth minus the bypass DSL bandwidth (see Section 4.5). The total DSL WAN bandwidth MAY be configured, MAY be obtained from the management system (AAA server, SOAP server, etc.), or MAY be detected in real time using the Access Node Control Protocol (ANCP) [RFC6320].

4.4. Traffic Recombination

For the offloading use case, the recombination function at the receiver provides in-order delivery of subscribers' traffic. The receiver maintains a small reordering buffer and orders the data packets in this buffer via the Sequence Number field [RFC2890] of the GRE header. All packets carried on GRE tunnels that belong to the same bonding connection go into a single reordering buffer. Operators may configure the maximum allowed size (see MAX_PERFLOW_BUFFER in [RFC2890]) of the buffer for reordering. They may also configure the maximum time (see OUTOFORDER_TIMER in [RFC2890]) that a packet can stay in the buffer for reordering. The OUTOFORDER_TIMER must be configured carefully. Values larger than the difference of the normal Round-Trip Time (RTT) (e.g., 100 ms) of the two connections are not recommended. Implementation and deployment experiences have demonstrated that there is usually a large margin for the value of MAX_PERFLOW_BUFFER. Values larger than the multiplication of the sum of the line rate of the two connections and the value of OUTOFORDER_TIMER should be used.
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4.5. Bypass

Service Providers provide some services that should not be delivered over the bonding connection. For example, Service Providers may not expect real-time IPTV to be carried by the LTE GRE tunnel. It is required that IPTV traffic bypass the GRE Tunnel Bonding and use the raw DSL bandwidth. Bypass traffic is not subject to the traffic classification and distribution specified above. The raw connection used for bypass traffic is not controlled by the HAAP. It may or may not go through a device in which the HAAP resides. The HAAP may announce the service types that need to bypass the bonded GRE tunnels by using the Filter List Package attribute as specified in Section 5.6.2. The HG and the HAAP 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 bypass 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 tunnels) can be measured. The GRE Tunnel Hello messages specified in Section 5.4 are used to carry the timestamp information, and the RTT value can therefore be calculated based on the timestamp. Besides the end-to-end delay of the GRE tunnels, the HG and the HAAP need to measure the capacity of the tunnels as well. For example, the HG is REQUIRED to measure the downstream bypassing bandwidth and report it to the HAAP in real time (see Section 5.6.1).

4.7. Policy Control Considerations

Operators and users 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 bypass. Operators and users may offer the service types that need to bypass the bonded GRE tunnels. Service types defined by operators (see Section 5.6.2) will be delivered from the HAAP to the HG through the control plane (see Section 4.1), and the HG will use the raw connection to transmit traffic for these service types. Users may also define bypass service types on the HG. Bypass service types defined by users need not be delivered to the HAAP.
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   Operators may specify the interval for sending Hello messages and the
   retry times for the HG or the HAAP to send out Hello messages before
   the failure of a connection.

   Since the GRE tunnels are set up 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 HG
   and the HAAP should be able to stop the offloading behavior and
   fall back to a traditional transmission mode, where the LTE GRE
   tunnel is disused while all traffic is transmitted over the DSL GRE
   tunnel.  Operators are allowed to define this threshold and period.

5. Control Protocol Specification (Control Plane)

Control messages are used to establish, maintain, measure, and tear down GRE tunnels between the HG and the HAAP. Also, the control plane undertakes the responsibility to convey traffic policies over the GRE tunnels. 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 [RFC2784] with the Key extension specified by [RFC2890] is used. The Checksum Present bit is set to 0. The Key Present bit is set to 1. The Sequence Number Present bit is set to 0. So, the format of the GRE header for control messages of the GRE Tunnel Bonding Protocol 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Key For security purposes, the Key field is used to carry a random number. The random number is generated by the HAAP, and the HG is informed of it (see Section 5.2.9).
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   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                              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |MsgType|T-Type |                                               |
    +-+-+-+-+-+-+-+-+           Attributes                          +
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 2: Format of Control Messages of GRE Tunnel Bonding

   MsgType (4 bits)
      Message Type.  The control message family contains the following
      six types of control messages (not including "Reserved"):

                 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

   T-Type (4 bits)
      Tunnel Type.  Set to 0001 if the control message is sent via the
      primary GRE tunnel (normally the DSL GRE tunnel).  Set to 0010 if
      the control message is sent via the secondary GRE tunnel (normally
      the LTE GRE tunnel).  Values 0000 and values from 0011 through
      1111 are reserved for future use and MUST be ignored on receipt.
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   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
         The Attribute Type specifies the type of the attribute.

      Attribute Length
         Attribute Length indicates the length of the Attribute Value
         in bytes.

      Attribute Value
         The Attribute Value includes the value of the attribute.

   All control messages are sent in network byte order (high-order bytes
   first).  The Protocol Type carried in the GRE header for the control
   message is 0xB7EA.  Based on this number, the receiver will decide to
   consume the GRE packet locally rather than forward it further.

5.1. GRE Tunnel Setup Request

The HG uses the GRE Tunnel Setup Request message to request that the HAAP establish the GRE tunnels. It is sent out from the HG'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

An operator uses the Client Identification Name (CIN) to identify the HG. The HG sends the CIN to the HAAP 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 contain the CIN attribute while the GRE Tunnel Setup Request message sent out from the DSL WAN interface does not contain this attribute.
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   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 string value encoded in UTF-8 and set by the
      operator.  It is used as the identification of the HG in the
      operator's network.

5.1.2. Session ID

This Session ID is generated by the HAAP when the LTE GRE Tunnel Setup Request message is received. The HAAP announces the Session ID to the HG in the LTE GRE Tunnel Setup Accept message. For those WAN interfaces that need to be bonded together, the HG MUST use the same Session ID. The HG 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 HAAP, the Session ID attribute need not be included. However, if the LTE GRE tunnel fails and the HG 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: +-+-+-+-+-+-+-+-+ |Attribute Type | (1 byte) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attribute Length | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+ | Session ID (4 bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
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   Attribute Type
      Session ID, set to 4.

   Attribute Length
      Set to 4.

   Session ID
      An unsigned integer generated by the HAAP.  It is used as the
      identification of bonded GRE tunnels.

5.1.3. DSL Synchronization Rate

The HG uses the DSL Synchronization Rate to notify the HAAP 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 An unsigned integer measured in kbps.

5.2. GRE Tunnel Setup Accept

The HAAP 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 GRE tunnels. Attributes that need to be included in this message are defined below.
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5.2.1. H IPv4 Address

The HAAP uses the H IPv4 Address attribute to inform the HG of the H IPv4 address. The HG uses the H IPv4 address as the destination endpoint IPv4 address of the GRE tunnels (the source endpoint IPv4 addresses of the GRE tunnels are the DSL WAN interface IP address (D) and the LTE WAN interface IP address (E), respectively, as shown in Figure 1). 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 (e.g., an IP address of a Line Card in the HAAP), which is used as the endpoint IP address of GRE tunnels by the HAAP.

5.2.2. H IPv6 Address

The HAAP uses the H IPv6 Address attribute to inform the HG of the H IPv6 address. The HG uses the H IPv6 address as the destination endpoint IPv6 address of the GRE tunnels (the source endpoint IPv6 addresses of the GRE tunnels are the DSL WAN interface IP address (D) and the LTE WAN interface IP address (E), respectively, as shown in Figure 1). 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) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
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   Attribute Type
      H IPv6 Address, set to 2.

   Attribute Length
      Set to 16.

   H IPv6 Address
      Set to the pre-configured IPv6 address (e.g., an IP address of a
      Line Card in the HAAP), which is used as the endpoint IP address
      of GRE tunnels by the HAAP.

5.2.3. Session ID

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

5.2.4. RTT Difference Threshold

The HAAP uses the RTT Difference Threshold attribute to inform the HG of the acceptable threshold of the RTT difference between the DSL link and the LTE link. If the measured RTT difference exceeds this threshold, the HG 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.
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5.2.5. Bypass Bandwidth Check Interval

The HAAP uses the Bypass Bandwidth Check Interval attribute to inform the HG of how frequently the bypass bandwidth should be checked. The HG 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. +-+-+-+-+-+-+-+-+ |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 10 through 300.

5.2.6. Active Hello Interval

The HAAP uses the Active Hello Interval attribute to inform the HG of the pre-configured interval for sending out GRE Tunnel Hellos. The HG 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) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
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   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 1 through 100.

5.2.7. Hello Retry Times

The HAAP uses the Hello Retry Times attribute to inform the HG of the retry times for sending GRE Tunnel Hellos. If the HG does not receive any acknowledgement from the HAAP for the number of GRE Tunnel Hello attempts specified in this attribute, the HG 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 that takes values in the range 3 through 10.

5.2.8. Idle Timeout

The HAAP uses the Idle Timeout attribute to inform the HG 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 GRE Tunnel Setup Accept message MUST include the Idle Timeout attribute.
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   +-+-+-+-+-+-+-+-+
   |Attribute Type |                   (1 byte)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Attribute Length             |   (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+
   |  Idle Timeout                     (4 bytes)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   Attribute Type
      Idle Timeout, set to 16.

   Attribute Length
      Set to 4.

   Idle Timeout
      An unsigned integer measured in seconds.  It takes values in the
      range 0 through 172,800 with a granularity of 60.  The default
      value is 86,400 (24 hours).  The value 0 indicates that the idle
      timer never expires.

5.2.9. Bonding Key Value

The HAAP uses the Bonding Key Value attribute to inform the HG of the number that is to be carried as the Key of the GRE header for subsequent control messages. The Bonding Key Value is generated by the HAAP and used for security purposes. The method used to generate this number is left up to implementations. The pseudorandom number generator defined in ANSI X9.31, Appendix A.2.4 [ANSI-X9.31-1998] is RECOMMENDED. Note that random number generation "collisions" are allowed in the GRE Tunnel Bonding Protocol. +-+-+-+-+-+-+-+-+ |Attribute Type | (1 byte) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attribute Length | (2 bytes) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...-+ | Bonding Key Value (4 bytes) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
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   Attribute Type
      Bonding Key Value, set to 20.

   Attribute Length
      Set to 4.

   Bonding Key Value
      A 32-bit random number generated by the HAAP.

5.2.10. Configured DSL Upstream Bandwidth

The HAAP obtains the upstream bandwidth of the DSL link from the management system and uses the Configured DSL Upstream Bandwidth attribute to inform the HG. The HG uses the received upstream bandwidth as the CIR [RFC2697] for the DSL link. 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.
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5.2.11. Configured DSL Downstream Bandwidth

The HAAP obtains the downstream bandwidth of the DSL link from the management system and uses the Configured DSL Downstream Bandwidth attribute to inform the HG. The HG 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. Configured DSL Downstream Bandwidth An unsigned integer measured in kbps.

5.2.12. RTT Difference Threshold Violation

The HAAP uses the RTT Difference Threshold Violation attribute to inform the HG of the number of times in a row that the RTT Difference Threshold (see Section 5.2.4) may be violated before the HG MUST stop using the LTE GRE tunnel. If the RTT Difference Threshold is continuously violated for more than the indicated number of measurements, the HG 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) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
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   Attribute Type
      RTT Difference Threshold Violation, set to 24.

   Attribute Length
      Set to 4.

   RTT Difference Threshold Violation
      An unsigned integer that takes values in the range 1 through 25.
      A typical value is 3.

5.2.13. RTT Difference Threshold Compliance

The HAAP uses the RTT Difference Threshold Compliance attribute to inform the HG of the number of times in a row that 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 measurements, the HG MAY resume using 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) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+ Attribute Type RTT Difference Threshold Compliance, set to 25. Attribute Length Set to 4. RTT Difference Threshold Compliance An unsigned integer that takes values in the range 1 through 25. A typical value is 3.
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5.2.14. Idle Hello Interval

The HAAP uses the Idle Hello Interval attribute to inform the HG of the pre-configured interval for sending out GRE Tunnel Hellos when the subscriber is detected to be idle. The HG 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 bonded tunnels have seen no traffic for a period 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 in the range 100 through 86,400 (24 hours) with a granularity of 100. The default value is 1800 (30 minutes).

5.2.15. No Traffic Monitored Interval

The HAAP uses the No Traffic Monitored Interval attribute to inform the HG of the pre-configured interval for switching the GRE Tunnel Hello mode. If traffic is detected on the bonded GRE tunnels before this interval expires, the HG 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) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
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   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.



(page 24 continued on part 2)

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