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ICNRG                                                           G. White
Internet-Draft                                                 CableLabs
Intended status: Experimental                             S. Shannigrahi
Expires: December 27, 2018                                        C. Fan
                                               Colorado State University
                                                           June 25, 2018

    Internet Protocol Tunneling over Content Centric Mobile Networks


   This document describes a protocol that enables tunneling of Internet
   Protocol traffic over a Content Centric Network (CCN) or a Named Data
   Network (NDN).  The target use case for such a protocol is to provide
   an IP mobility plane for mobile networks that might otherwise use IP-
   over-IP tunneling, such as the GPRS Tunneling Protocol (GTP) used by
   the Evolved Packet Core in LTE networks (LTE-EPC).  By leveraging the
   elegant, built-in support for mobility provided by CCN or NDN, this
   protocol achieves performance on par with LTE-EPC, equivalent
   efficiency, and substantially lower implementation and protocol
   complexity.  Furthermore, the use of CCN/NDN for this purpose paves
   the way for the deployment of ICN native applications on the mobile

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 27, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  IPoC Overview . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Client Interest Table and Interest Deficit Report . . . . . .   5
   5.  Handling PIT Entry Lifetimes  . . . . . . . . . . . . . . . .   6
   6.  Managing the CIT, PIT lifetimes and the in-flight message
       count . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Establishing Communication  . . . . . . . . . . . . . . . . .   8
   8.  IPoC Naming Conventions . . . . . . . . . . . . . . . . . . .   8
   9.  Sequence Numbers  . . . . . . . . . . . . . . . . . . . . . .   9
   10. Packet Sequencer  . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  Packet Sequencer Example Algorithm . . . . . . . . . . .   9
   11. Client Behavior . . . . . . . . . . . . . . . . . . . . . . .  10
   12. Gateway Behavior  . . . . . . . . . . . . . . . . . . . . . .  11
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   15. Normative References  . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Content Centric Networking provides some key advantages over IP
   networking that make it attractive as a replacement for IP for
   wireless networking.  In particular, by employing stateful
   forwarding, CCN elegantly supports information retrieval by mobile
   client devices without the need for tunneling or a location
   registration protocol.  Furthermore, CCN supports a client device
   utilizing multiple network attachments (e.g. multiple radio links)
   simultaneously in order to provide greater reliability or greater
   performance.  Finally, CCN is optimized for content retrieval, where
   content can be easily retrieved from an on-path cache.

   A significant hurdle that stands in the way of deploying a CCN-only
   wireless network is that all of the applications in use today (both
   client and server) are built to use IP.

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   This hurdle could be addressed by requiring that all applications be
   rewritten to use CCN natively, however, this is a tall order in a
   world with millions of smartphone apps.  Another approach could be to
   deploy a hybrid network in which the routers support forwarding both
   IP and CCN.  However, this adds cost and complexity to the network,
   both in terms of equipment and in terms of operations.

   The protocol described in this document provides a way to eliminate
   this hurdle, by establishing an IP over CCN tunneling protocol that
   is transparent to the IP applications on either end.  In a sense,
   this protocol replaces the IP-over-GTP tunnels or IP-over-GRE tunnels
   that would exist in a traditional IP-based wireless network such as
   LTE or Community WiFi, but by using a networking plane (CCN) that
   natively supports mobility, application developers have the option to
   update their applications to run directly over CCN, gaining all of
   the advantages that come with this new protocol.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  IPoC Overview

   In the CCN (or NDN) protocol, communication is achieved by an
   application sending an Interest packet that identifies, by name, a
   piece of content that it wishes to receive.  The network routes
   Interest messages toward a producer of content corresponding to the
   name in the Interest, leaving a "breadcrumb" trail of state in the
   routers along that path.  Once the Interest arrives at a node where
   the named piece of content is present, that node returns a Content
   Object message containing the named piece of content.  The Content
   Object follows (and consumes) the breadcrumb trail back to the
   originating application.  This process is commonly referred to as
   stateful forwarding.  An application that only sends Interest
   messages is referred to as a consumer, whereas an application that
   only sends Content Object messages (in response to Interests) is
   referred to as a producer.

   Producers need to advertise the name prefixes for the content that
   they can provide, and this information needs to propagate to the
   routers of the network, much in the same way that IP prefixes need to
   propagate to routers in an IP network.  However, consumers don't need
   to advertise their presence or location at all, they can simply send
   Interest messages from wherever they are in the network, and the
   resulting Content Objects will make it back to them via the stateful
   forwarding process.  Furthermore, a consumer that is mobile can

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   redirect data in flight to the its new location by resending Interest
   messages for those in-flight content objects using its new network
   attachment point.  As a result, mobile consumer applications (which
   would be the majority of mobile applications) are handled very
   elegantly by the CCN protocol.

   In addition, if a mobile device has multiple network attachment
   points, e.g. both a WiFi and a 5G/LTE connection, it can choose to
   send Interests via both of those network paths.  This capability can
   be used to enable higher capacity (by load balancing the Interests in
   an attempt to fully utilize multiple links simultaneously), higher
   reliability (by sending each Interest on multiple links), or seamless
   handover (by switching to a new link for all future Interest
   messages, while still waiting to receive Content Objects on an older

   While consumer mobility and multipath connectivity is elegantly
   handled by the CCN protocol, producer mobility (where a mobile device
   makes its resident content available to outside devices), is
   currently not.  As a result, the IPoC protocol relies solely on
   consumer behavior on the client device.

   This protocol defines two entities: an IPoC Client and an IPoC
   Gateway.  The IPoC Client (henceforth referred to as the Client)
   would exist on the mobile device, and as mentioned above, only sends
   Interest messages.  The IPoC Gateway (henceforth referred to as the
   Gateway) exists at a fixed location in the network, and publishes a
   prefix that can be routed to via the CCN network.  In general, a
   network may have many Clients, and possibly several Gateways.

   The switches and routers that exist in the path between the Client(s)
   and the Gateway(s) are assumed to provide CCN forwarding, and are not
   required to support IP forwarding.

   From the perspective of the applications running on the mobile
   device, the Client implementation functions as a tunnel endpoint,
   much in the same way that a VPN application does.  All IP traffic
   generated by applications on the mobile device are forwarded via this
   tunnel endpoint, which encapsulates them in CCN Interest messages,
   and then sends them into the CCN network.  Similarly, the Gateway
   implementation also acts as a tunnel endpoint, in this case on an IP
   routing node.  It receives Interest messages, unpacks the IP packets
   inside, and forwards them into an IP network.  IP return traffic
   arriving at the Gateway is encapsulated into CCN Content Object
   messages, and then launched into the CCN network to follow the
   stateful forwarding path left by the associated Interest message.

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4.  Client Interest Table and Interest Deficit Report

   In this communication model, the Client is able to send "upstream"
   packets at any time, by sending Interest messages.  The Gateway on
   the other hand, can only send "downstream" packets when it has a
   pending Interest (i.e. it has received an Interest message and has
   not yet responded with an associated Content Object).  As a result,
   the Client and Gateway work together to ensure that the Gateway is
   receiving Interests sufficiently to support the downstream

   For each Client, the Gateway MUST maintain a FIFO queue of names for
   which it has received Interests from the Client.  This queue is
   referred to as the Client Interest Table (CIT).  As this is a FIFO
   queue, the order in which Interest names are received is the order in
   which the associated Content Object responses will be sent.

   The typical behavior of a Client (described in more detail below) is
   to send an Interest message for every Content Object it receives,
   thus maintaining a constant number of CCN packets "in flight".  The
   Interest Deficit Report (IDR) is a message element sent in a Content
   Object from the Gateway to the Client in order to adjust the number
   of packets in flight and thus maintain an appropriate CIT size.  The
   IDR can take the value +1, to request an increase (by one) of the in-
   flight count; 0 to indicate no change to the in-flight count; or -1
   to request a decrease (by one) of the in-flight count.  The IDR can
   be included in a Content Object that carries a packet payload, or in
   a Content Object that is otherwise empty.

   The IDR is an unacknowledged message element, and as such is an
   inherently unreliable communication.  Since the IDR values are small,
   the impact of a Content Object loss is minimal.

   The Client MUST maintain an Interest Deficit Count (IDC) which it
   uses to maintain the in-flight count in response to sent Interests
   and received Content Objects.  The Client MUST decrement by one the
   IDC upon transmission of a new Interest message.  The Client MUST
   update the IDC by adding IDR+1 to its value upon receipt of a new
   Content Object.

   The Gateway SHOULD NOT discard Interest names from the CIT, and thus
   SHOULD always respond to a received Interest with a Content Object in
   order to clear the associated PIT state in the intermediate routers.
   If a new Interest arrives and the CIT is full, the gateway MUST
   consume the name at the head of the CIT by sending an empty content
   object.  In this case, the IDR value of the empty Content Object
   SHOULD be set to -1.

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5.  Handling PIT Entry Lifetimes

   Intermediate routers between the Client and the gateway, as well as
   CCN forwarder implementations within the two IPoC endpoints will
   store PIT entries for the Client's Interests for a finite lifetime,
   and will age-out (purge) Interests that exceed that lifetime.  Since
   the CIT at the gateway stores Interest names for a time in
   anticipation of downstream packets, it would be possible, when there
   is a gap in the flow of downstream packets, that the name at the head
   of the CIT queue is associated with entries that have been aged-out
   of the PIT in one or more of the intermediate forwarders.  If the
   gateway were to use this aged-out name in an attempt to deliver a
   downstream packet, the packet transmission would fail when the
   Content Object arrived at the PIT that no longer held an entry for
   this name.

   To avoid this situation, the Gateway MUST record the arrival time of
   each CIT entry, and compare it against a CIT lifetime value.  When
   the CIT entry at the head of the CIT "expires", the gateway MUST send
   a Content Object using that CIT entry, thereby cleaning up the PIT
   state in the intervening forwarders, and potentially triggering a new
   Interest to be sent by the Client (as discussed further below).

6.  Managing the CIT, PIT lifetimes and the in-flight message count

   At any instant in time, a certain number of Interest names can be
   considered "in-flight" from the Client's perspective (these in-flight
   Interests correspond to the entries in the Client's PIT).  Some
   fraction of the in-flight Interest names will correspond to Interest
   messages (possibly containing IP packets) that are in transit to the
   gateway, some fraction will correspond to Content Object messages
   (also possibly containing IP packets) that are in transit to the
   Client, and the remainder correspond to the entries in the gateway's
   CIT or to messages that were lost in transit.  The gateway controls
   the number of these in-flight messages via the IDR, which can either
   trigger or suppress the Client sending Interests.

   Since the gateway cannot send a downstream packet to the Client
   unless it has a CIT entry, it would ideally like to ensure that it
   always has at least one CIT entry every time a downstream packet
   arrives.  However, due to the round trip time between the gateway and
   the Client, and the fluctuation of downstream and upstream packet
   arrival rates, the number of in-transit messages (Interests or
   Content Objects) will fluctuate.  If the only goal was that the CIT
   never becomes empty, the gateway could simply use the IDR to build a
   very high in-flight message count.  This would ensure that the CIT
   never drains completely, even in the case where the upstream path and
   the downstream path are both saturated with in-transit messages.  The

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   problem with this approach is that when the connection becomes idle,
   ALL of the in-flight messages would then exist in the CIT, which
   could be a large memory burden on the gateway and on the PIT in each
   intervening router.  Furthermore, since each of these CIT entries has
   a certain lifetime, driven by the PIT lifetime, they will shortly
   expire, triggering the gateway to transmit Content Objects that
   heavily utilize the downstream and upstream links for approximately
   one RTT.  This pattern of unnecessary network traffic would then
   periodically repeat at a period equal to the CIT lifetime.

   So, it is important that the gateway adjust the in-flight message
   count continuously, to minimize the times that the CIT is starved or

   The gateway MUST establish a target minimum value for the number of
   CIT entries.  This value "n" provides a bound on the number of
   downstream packets that can be sent in the first IPoC RTT (between
   gateway and client) after an idle period, and also establishes the
   quiescent IPoC message refresh rate during idle periods (this rate r
   = n/L, where L is the CIT lifetime).  Selecting a low value of n
   minimizes the quiescent load on the network, but has the downside of
   reducing the size of packet burst that the IPoC connection can handle
   with low latency.

   Whenever the gateway sends a Content Object and there are fewer than
   n CIT entries, it MUST include an IDR in the CO, with the value 1,
   triggering the Client to send two Interest messages in response to
   the CO.

   The gateway also MUST establish a maximum CIT size "N".  Whenever the
   gateway receives a new Interest while the CIT contains N entries, it
   MUST make room for the new CIT entry by using the head of line CIT
   entry to send an empty Content Object containing an IDR with the
   value -1, triggering the Client to suppress sending an Interest in

   Further, whenever the CIT entry at the head of line expires (reaches
   its CIT lifetime), the Gateway MUST consume that CIT entry by sending
   an empty Content Object.  The expiration of a CIT entry is a good
   indication that the CIT contains more entries than are needed to
   support the current data rate.  In this situation, the Gateway SHOULD
   use the IDR to reduce the in-flight count.  One mechanism for doing
   this is described here:

   If the number of CIT entries is less than n, the empty Content Object
   sent to consume the expiring CIT entry will contain an IDR with the
   value 1.  If the number of CIT entries is greater than n, the CO will
   contain an IDR with value -1, and if it is equal to n, the value 0.

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   The result of this process is that during idle periods, the CIT will
   drain down to the point of having n entries, and will refresh those
   entries as they expire.

7.  Establishing Communication

   Communication is established by the Client sending an Interest to a
   Gateway, where the name in the Interest message includes a Gateway
   prefix followed by /init/<random_string>.  For example, if the
   established Gateway prefix is ccnx:/ipoc, the name might be
   ccnx:/ipoc/init/2Fhwte2452g5shH4.  The Gateway has a process that
   will respond to the ccnx:/ipoc/init prefix by sending IP
   configuration information, similar to the information contained in a
   DHCP Offer, including an assigned IP address.

   Upon configuring itself using the information in the init response,
   the Client can begin IP communication.  The naming convention for
   subsequent Interest messages is described in the next section.

8.  IPoC Naming Conventions

   The Client and Gateway can use one of the following data naming
   conventions, the appropriate naming convention is chosen by the
   Gateway via configuration, and is communicated to the Client during
   the Establishing Communication protocol.



   The various components of an IPoC name are described in more detail

   o  ccnx:/ipoc - The name prefix used in all IPoC messages

   o  zone_id - An optional zone identifier to allow for zone-based IP
      address re-use.

   o  hex_ipaddr - For IPv4 addresses, this field comprises 4 separate
      name segments, each representing a single octet of an IPv4 address
      encoded as a hexadecimal string.  For example, a message from a
      Client with IPv4 address would use: "c0/00/02/64" for
      this name component.  For IPv6 addresses, the textual convention
      defined in Section 2.2 paragraph 1 of [RFC4291] is used, with each
      colon replaced by a CCN name segment delimiter.  For example a
      Client with the IPv6 address: 2001:DB8::fe21:67cf would use
      "2001/DB8/0/0/0/0/fe21/67cf" for this name component.

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   o  b64_seq - This a base64-encoded value representing the Upstream
      Sequence Number for this upstream Interest message

   An example Interest name is: ccnx:/ipoc/c0/00/02/64/AAAAGw==

9.  Sequence Numbers

   Upstream Sequence Numbers (USN) are monotonically increasing unsigned
   32-bit integer values embedded in the Interest names to indicate the
   proper ordering for upstream data packets.  Since Interest messages
   may arrive out-of-order due to the use of multiple network paths, the
   Gateway uses the USN to ensure that upstream IP packets are delivered
   in the proper order.

   Content Objects that carry IP packet payloads include Downstream
   Sequence Numbers (DSN), which are monotonically increasing unsigned
   32-bit integer values that indicate the proper ordering of downstream
   data packets.  DSN are used by the Client to ensure that downstream
   IP packets are delivered in the proper order.

   The USN and DSN are independent sequence numbers and thus have no
   relationship to one another.

10.  Packet Sequencer

   The Packet Sequencer (PS or Sequencer) is a FIFO queue that exists
   both at the Client and Gateway to ensure in-order delivery of IP
   packets contained in upstream Interests and downstream Content
   Objects.  The order in which the packets are delivered is decided by
   the Packet Sequence Number (PSN) embedded in the Interest or Content
   Object names.

   The client MUST implement a Packet Sequencer to ensure in-order
   delivery of IP packets.  The gateway MUST implement a Packet
   Sequencer to ensure in-order delivery of IP packets.

10.1.  Packet Sequencer Example Algorithm

   The first PSN (FPSN) delivered to the Sequencer establishes a
   baseline to which all subsequent PSNs are evaluated based on an
   expected ascending incremental order.  The Sequencer also notes the
   last PSN (LPSN) it forwarded, and for the first packet, FPSN is equal
   to LPSN.  If an arriving packet has the expected sequence number
   (LPSN + 1), the sequencer does not queue the packet and simply
   forwards it.  The Sequencer also tracks the highest sequence number
   that has arrived (MAXPSN).

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   Discontinuities in the sequence order result in a "gap" in the
   sequence.  If the arriving packet has a sequence number LPSN + n,
   where n > 1, we declare this as a gap.  For example, if the last
   forwarded PSN had a sequence number 6 (LPSN), and a new packet
   arrives with sequence number 10 (MAXPSN), a new gap is created which
   represents the sequence numbers 7, 8, and 9.  A timer with a validity
   window is started providing a limited amount of time for the sequence
   numbers in the gap to arrive.

   Each time a packet with a sequence number in the gap arrives, the
   Sequencer tries to do a partial release of the queue; this releases
   any consecutive packets between LPSN and MAXPSN.  In our example, if
   sequence 8 arrives first, the Sequencer sees there are no consecutive
   packets to send and does nothing.  If sequence 7 arrives after that,
   the Sequencer releases both 7 and 8 but waits for sequence 9.  When
   sequence 9 arrives, it releases 9 and 10.  If a packet does not
   arrive and the validity window expires, the Sequencer releases all
   packets up to MAXPSN and reset the LPSN.

   The sequencer removes data packets from the queue in sequence-order
   (lowest PSN first).  If the queue exceeds capacity, the Sequencer
   discards the packet with the lowest PSN.  Any IP packets in those
   Interests or content objects are discarded.

   Ideally, the gap validity window should be set to the RTT between the
   Client and the Gateway.  However, since packets can take multiple
   paths and the Sequencer may not know the RTT for each of these paths,
   it should dynamically adjust the validity window based on the inter-
   arrival time between consecutive packets.

11.  Client Behavior

   The three main functions of the Client are:

   1.  Send Interest messages containing upstream IP packets whenever
       they arrive

   2.  Send Interest messages to the gateway in order to keep the
       appropriate in-flight count

   3.  Receive downstream IP packet data in Content Object messages

   Content Object messages containing downstream IP packet data are
   added to the Packet Sequencer and then forwarded to the IP stack on
   the device.

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   Once an IP address is acquired using the initialization process
   described above, the startup sequence for a particular Client looks
   like this:

   o  Initialize IDC to a startup value: INIT_IDC.

   o  Send Interest messages to the Gateway containing the initial
      upstream IP packets (e.g.  TCP SYN packets or DNS queries),
      decrementing IDC for each Interest sent.

   The client MUST decrement the IDC upon transmission of any Interest
   message, whether or not it contains an upstream packet.

   Whenever the client receives a Content Object, it MUST increment the
   IDC by IDR+1 to ensure that the appropriate in-flight count is

   The Client MUST maintain two internal timer intervals.  A short timer
   (T0) is used to pace Interest messages when there are outstanding
   interests to be sent as per the Interest Deficit Counter.  The long
   timer (T1) is used as a keep-alive when the Client has no outstanding
   Interests to be sent.  Whenever the client sends an Interest message,
   it restarts the T0 and T1 timers.  When the T0 timer expires, if the
   IDC is greater than zero, the Client MUST send an empty Interest
   message.  When the T1 timer expires, the Client MUST send an empty
   Interest message (regardless of the IDC value).

12.  Gateway Behavior

   IPoC gateway behavior is slightly more complex since it must manage
   connections with multiple Clients simultaneously.  The standard
   process for on-boarding a new Client looks something like this:

   o  An Interest is received with the /init/<random_string> name.

   o  The gateway establishes new CIT (and other Client-specific)
      structures for this Client and responds with a Content Object
      containing the IP parameters (yiaddr, giaddr, etc.) to configure
      the Client's IP stack.

   o  The gateway enters a normal processing loop in which it receives
      Interests from the Client and responds with Content Objects.

   Interests received from the Client may contain IP packets that the
   gateway will add to its upstream Packet Sequencer using the PSN found
   in the Interest name.  The Interest name will then be added the
   Client-specific CIT for later use in creating Content Objects.  If
   the CIT is full, the gateway will immediately send an empty Content

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   Object back to the Client, removing the first name from the CIT, and
   therefore making room for the new name to be added.

   When downstream IP packets become available, the gateway will remove
   the first name from the CIT queue and use it to create a Content
   Object containing the IP packets.  If the CIT is empty, IP packets
   are buffered by the gateway.

   If IP packets are waiting in buffer when a new Interest (CIT entry)
   arrives, the gateway will immediately dequeue the waiting packets (up
   to a maximum CO size limit), form and transmit a Content Object using
   the newly arrived CIT name.

13.  Security Considerations


14.  IANA Considerations

   This document has no actions for IANA.

15.  Normative References

              Mosko, M., Solis, I., and C. Wood, "CCNx Messages in TLV
              Format", draft-irtf-icnrg-ccnxmessages-06 (work in
              progress), October 2017.

              Mosko, M., Solis, I., and C. Wood, "CCNx Semantics",
              draft-irtf-icnrg-ccnxsemantics-06 (work in progress),
              October 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

Authors' Addresses

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   Greg White
   858 Coal Creek Circle
   Louisville, CO  80027

   Email: g.white@cablelabs.com

   Susmit Shannigrahi
   Colorado State University
   Computer Sc. Dept.
   1100 Center Ave Mall
   Ft. Collins, CO  80523

   Email: susmit@colostate.edu

   Chengyu Fan
   Colorado State University
   Computer Sc. Dept.
   1100 Center Ave Mall
   Ft. Collins, CO  80523

   Email: chengyu.fan@colostate.edu

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