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Internet Engineering Task Force                            P. Montessoro
Internet-Draft                                             R. Bernardini
Expires: December 24, 2012                                         UniUD
                                                           June 22, 2012

              REBOOK: a Network Resource Booking Algorithm


   This document describes REBOOK, a resource reservation algorithm for
   deterministic and fast dynamic resource allocation and release.
   Based on a stateful approach, it handles faults and network errors,
   and recovers from route changes and unexpected flows shutdown.  The
   distributed scheme used to store flows information have guaranteed
   constant complexity.

Status of This Memo

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   This Internet-Draft will expire on December 24, 2012.

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   document authors.  All rights reserved.

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   the Trust Legal Provisions and are provided without warranty as

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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
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   material may not have granted the IETF Trust the right to allow
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   than English.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  REBOOK Description . . . . . . . . . . . . . . . . . . . . . .  6
     2.1.  Message transport and format . . . . . . . . . . . . . . .  6
     2.2.  Node behaviour . . . . . . . . . . . . . . . . . . . . . .  7
       2.2.1.  Start-up . . . . . . . . . . . . . . . . . . . . . . .  7
       2.2.2.  Keep-Alive . . . . . . . . . . . . . . . . . . . . . .  8
       2.2.3.  Data transmission  . . . . . . . . . . . . . . . . . .  9
       2.2.4.  Reservation update . . . . . . . . . . . . . . . . . .  9
       2.2.5.  Path change  . . . . . . . . . . . . . . . . . . . . .  9
       2.2.6.  Shutdown . . . . . . . . . . . . . . . . . . . . . . . 10
     2.3.  Commands . . . . . . . . . . . . . . . . . . . . . . . . . 10
     2.4.  Router behaviour . . . . . . . . . . . . . . . . . . . . . 11
       2.4.1.  On reception of a RESV request . . . . . . . . . . . . 11
       2.4.2.  On reception of a data packet with the reference
               field  . . . . . . . . . . . . . . . . . . . . . . . . 12
       2.4.3.  On reception of a KPALV request  . . . . . . . . . . . 12
       2.4.4.  On reception of a UP_RESV request  . . . . . . . . . . 13
       2.4.5.  On reception of a RL_RESV request  . . . . . . . . . . 13
       2.4.6.  Checking packet validity . . . . . . . . . . . . . . . 13
   3.  Using the IP Router Alert field  . . . . . . . . . . . . . . . 14
   4.  Session Timeout  . . . . . . . . . . . . . . . . . . . . . . . 14
   5.  What is a resource?  . . . . . . . . . . . . . . . . . . . . . 15
   6.  Security consideration . . . . . . . . . . . . . . . . . . . . 15
   7.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 15
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     8.1.  References . . . . . . . . . . . . . . . . . . . . . . . . 15
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 16

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1.  Introduction

   A large number of applications prefer UDP as a transport protocol.
   Among others, teleconferencing, streaming applications, real-time
   communications, and networked multiplayer games; more generally,
   applications whose information value and perceived quality strictly
   relies on network delay, and also multi-cast services.  Dynamics of
   network load can impact negatively on multimedia applications;
   however, UDP doesn't offer any native congestion control mechanism
   and therefore it cannot guarantee Quality of Service (QoS).  In
   addition, congestion is often caused by these applications' high
   bandwidth requirements.

   On the other side, TCP provides a congestion control mechanism based
   on message loss only, without any explicit knowledge about the
   traffic load in intermediate network nodes along the communication
   path.  Therefore, both UDP and TCP sources need to be enhanced with a
   congestion control algorithm not only aimed at reducing loss rate and
   improving bandwidth utilization, but also at improving fairness
   towards competing connections while satisfying related QoS
   requirements.  UDP flows should become TCP-friendly whereas UDP and
   TCP flows should both become aware of network load in order to adjust
   their transmission rate before losing packets.

   In the last years, several methods have been introduced for QoS
   control mechanisms, mainly based on adapting the sender's
   transmission rate in accordance with the network congestion state
   (see Sect. 2), but typically with such approaches no QoS guarantees
   can be made effectively.  The proposed algorithm, that we call
   REBOOK, allows a control protocol to prevent congestion by reserving
   enough resources for supporting a dynamically changing QoS level in
   advance, therefore it would be the most straightforward approach to
   manage the problem.

   It must be outlined that REBOOK is not dependent on TCP/IP protocols,
   as it can be used in any other packet switching network.  Obviously,
   in the following the Internet and the TCP/IP protocol suite will be
   used as reference environment for its description.

   REBOOK requires a hosting protocol to carry the algorithm's messages.
   They can be handled by a dedicated signalling protocol, like RSVP
   [RFC2205] or a new ad hoc protocol, or it can be embedded in a data
   transport protocol, like TCP using the options field.

   REBOOK is designed to handle virtually every transport-layer
   connection or application-layer flows, not necessarily in real-time
   or QoS only.  In principle, except for very short flows the network
   may benefit from the preventive declaration (and the consequent

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   resource booking) of the amount of traffic that each connection is
   going to generate: if the application knows the amount of granted
   resources in advance, it can modulate the data transmission rate to
   prevent packet loss.

   REBOOK implementation will bring to a sender-oriented protocol,
   unlike RSVP which is receiver oriented.  The node initiating a
   connection is responsible for resource reservation request, based on
   the amount and type of data to be transmitted, application
   constraints and, possibly, SLA (Service Level Agreement) parameters.
   While the connection is active the amount of granted resources may be
   reduced to allow the activation of new flows in an almost-congested
   network or may be increased if switching nodes become less loaded.
   These events are acknowledged by the sender that will consequently
   adapt its transmission rate.  RSVP is receiver-oriented mainly
   because it is designed to support single-cast and multi-cast flows as

   REBOOK does not rely on any special network feature: it works even if
   only part of the network is REBOOK-aware as the resource reservation
   is effective even if part of a flow traverses unaware routers.  There
   are no special requirements to routing, which can be asymmetrical
   (transmitting and receiving flows can follow different paths),
   except, obviously, its stability: in normal conditions data packets
   and control messages must follow the same route for the duration of
   the connection.  Anyhow, if unexpected events occur, REBOOK
   identifies route changes and recovers from errors and faults in the

   REBOOK does not rely on special hardware in routers either.  Its
   status storage scheme allows direct access to table entries without
   any hardware look-up feature, simply using conventional memory
   architecture.  This makes its implementation faster and cheaper than
   today's typical solutions provided by hardware hashing.  Finally,
   REBOOK does not require any improvement in the switching fabric.  No
   additional memory for queues and buffers nor different packet
   handling.  On the contrary, the router architecture will drive the
   resource granting phase, depending on available resources left after
   previous reservations.

   It is worth observing that REBOOK is not another virtual circuit
   technique; it is an add-on to conventional routers to improve
   performance and features.  For example, it does not require any
   interaction with the routing protocols; it can work along routes
   traversing several Autonomous Systems and routers using different
   routing protocols; it does not require to be supported by all the
   routers along the path nor for the supporting routers to be
   contiguous; it does need neither hierarchy nor partitioning.  In

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   respect of existing virtual circuit techniques, the novelty consists
   in making each router autonomous in handling its REBOOK data
   structures and the effects that routing dynamics have on them,
   without any routing-aware signalling protocol.  All these features
   overcome most of the difficulties that limit a wide deployment of
   MPLS or ATM, for example.  Moreover, in case of routing instability
   or faults, REBOOK can fail in enhancing router performance, but
   packets are still forwarded in a best-effort, lookup-driven mode.

   REBOOK is scalable since its computational cost is constant,
   regardless of the number of active flows, yielding a solution to per-
   flow resource reservation and packet handling, without the need of
   aggregations.  Moreover, it is intrinsically secure since each router
   uses only the information generated in a previous phase by itself,
   allowing any form of fast and secure symmetrical cryptography without
   the need of a key exchange.

   REBOOK is based on a distributed linked data structure in the sense
   that it makes use of pointers to memory locations or indexes to table
   entries containing information stored in the routers that are very
   likely to be accessed in the future.  Unlike conventional linked data
   structures, pointers are not stored within the router they address,
   but in the end nodes, in the packets, and in adjacent routers.  When
   a packet is received by a router, the pointer to the table entry to
   be used for its processing is found in the packet itself and look-up
   procedures are avoided.  To keep the pointers consistent in a dynamic
   environment, where route changes may send packets to routers
   different than the ones the pointers refer to, a specific integrity
   check is adopted.  It makes REBOOK completely autonomous in
   identifying faults, errors and route changes.  The overhead
   introduced by this integrity check is a critical issue.  Thanks to
   careful design of the distributed linked data structure, experimental
   data demonstrate that this overhead is overcome by the speedup
   provided by the look-up-free access to table entries.

   REBOOK is a soft state algorithm.  Reservations no longer refreshed
   by keep-alive messages (due to errors, route changes or end node
   faults) are removed by a low priority table cleanup task active in
   the routers.  This is the only part of the algorithm whose cost is
   linear in the number of active flows, instead of constant.  However,
   the experimental results in [rebook] report 100 ms CPU time to handle
   a 10,000,000 flows RR table, and in current implementation this
   procedure is activated every 15 s.  Thanks to this procedure and to
   the consistency check, REBOOK messages are not required to be

   Summarizing, the main features of REBOOK are

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   Soft state:  Reservations not refreshed by keep-alive messages are
      automatically removed.

   Scalability:  The computational cost for routing and connection
      handling is constant with the number of active flows.  The only
      cost that grows linearly with the number of active flows is the
      removal of expired session, but experimental data shows that this
      is negligible.

   Consistency checks:  Routers can easily check (in constant time) if
      the received packet is actually a valid REBOOK-related packet.
      This makes it possible for routers to identify faults, errors and
      route changes.

   Safety:  Each router uses only the information generated in a
      previous phase by itself, this makes it possible to use efficient
      cryptographic protection techniques.

2.  REBOOK Description

   In a REBOOK setup there is a _source node_ that wants to reserve
   resources to send data to a _target node_ with a guaranteed quality
   of service.  Before beginning the streaming, the source node reserves
   the required resources by sending REBOOK requests to the target node.
   The intermediate REBOOK-capable routers will analyze the REBOOK
   requests and assign resources to the newly opened connection.  This
   section describes the details of the interaction between the source
   node, the target node and the intermediate routers.

2.1.  Message transport and format

   It is worth emphasizing that REBOOK is not a protocol, but an
   algorithm for resource reservations that can be "embedded" in many
   different protocol.  Because of this, we do not specify format for
   REBOOK requests or how they are transmitted over the network, leaving
   the choice of those details to the application employing REBOOK.
   This is similar to what it is done in other protocols like TFRC (TCP-
   Friendly Rate Control [RFC5348]) that requests that the source node
   will send some data (e.g., estimated RTT, timestamps, ...) to the
   receiver and that the receiver will send back some feedback data
   (e.g., loss probability), but it leaves open how those data are
   embedded in the protocol employing TFRC.

   About the way REBOOK requests are transported, we can observe that
   there are two possible approaches

   o  Via a specific protocol, "parallel" to the one used to stream the

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   o  Piggy-backed to the data stream.

   Both solutions are reasonable and the choice will be a matter of
   convenience of the specific application.

2.2.  Node behaviour

   In this section we describe an overview of the behavior of the
   different REBOOK nodes (source, target and routers).

2.2.1.  Start-up

   o  Suppose that a source node needs to stream data to the target
      using a guaranteed QoS.  The node decides to reserve the required
      resources using REBOOK.  Toward such a goal, the node sends a
      REBOOK RESV request (see Section 2.3) to the target node.

   o  The packet with the RESV request travels over the network, passing
      through several routers.  If a router is REBOOK-capable, it
      reserves the requested resources (if available) and update its
      internal tables by adding an entry for the new stream(see
      Section 2.4 for details).  If not enough resources are available,
      the router can decide to reserve less than the required resource
      amount and write this information in the request.

   o  In order to be able to recover later the information about the
      registered stream, the router appends to the RESV packet a
      _reference_ to the new entry.

         Although the "reference" written by the router can be thought
         as the memory address of the entry associated with the stream,
         it is worth emphasizing that a reference is used only by the
         router that wrote it, so that, to the other nodes the reference
         appears as an opaque string of bits.  This implies that the
         reference is not constrained to be an actual address and that
         the router can give it any meaning without compromising
         interoperability.  For example, the reference could be an
         _index_ to the table, possibly extended with some CRC and
         encrypted to check for packet validity and improve security
         (see Section 2.4.6).

   o  The RESV request arrives to the target.  The RESV packet now
      contains the amount of resources reserved along the path and the
      list of table references added by the intermediate REBOOK-capable.
      The target sends back to the source the received packet with a
      RESV_ACK request (see Section 2.3).  Now the source knows the
      amount of reserved resources and the reference list.

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2.2.2.  Keep-Alive

   Periodically, starting right after receiving the RESV_ACK, the source
   sends keep-alive KPALV requests to the target node.  The KPALV
   request carries the following data

   o  The amount of reserved resources

   o  The list of table references inserted by the routers

   When a router receives a KPALV message, first it checks if it is a
   valid KPALV request relative to an already opened stream.  If the
   check is positive

   1.  It updates the amount of reserved resources.

          In order to understand why this is necessary, consider the
          following case: source S wants to send data to target T;
          suppose that the canonical required bandwidth is 3 Mbit/s, but
          that transmission can still be done with good enough quality
          as soon as the bandwidth is at least 512 kbit/s (for example,
          the source could encode the data at a lower quality).  Suppose
          also that between S and T there are two routers A and B, the
          latter with only 1 Mbit/s available.  When A processes the
          RESV request, it has enough resources and decide to reserve 3
          Mbit/s to S; however, since B has not enough bandwidth it
          reserves only 1 Mbit/s to S. Note that A is wasting 2 Mbit/s,
          since S will never be able to use more than 1 Mbit/s, but A
          reserved 3 Mbit/s to S. However, since the KPALV packet sent
          by S will contain the amount of reserved resources, A can see
          that only 1 Mbit/s will be used by S and will update
          accordingly its tables.

   2.  It stores in the table entry associated with the stream the
       reference written by the next router.  See Section 2.4 for
       details about how this value is used.

   KPALV messages are expected to be received at regular intervals.  If
   KPALV packets are not received for a time exceeding a threshold
   (possibly depending on the path RTT), the router will suppose the
   session expired and will release the reserved resources.

   Finally, observe that the target usually ignores the KPALV packets,
   unless there is a change in the reservation.  See Section 2.2.4 for

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2.2.3.  Data transmission

   In the simplest implementation of REBOOK, no special handling is
   required for data packets.  The routers will access to the routing
   tables in the usual way.

   However, in order to speed-up the access to the table, avoiding the
   look-up procedure, the source can include in every transmitted data
   packet the reference value inserted by the first router.  (See
   Section 2.4 for details about how this value is used.)  Since this
   value must be used by the routers, the router must know (i) that the
   packet belongs to a REBOOK stream and (ii) where the reference is
   stored.  A possible solution, employing the IP Router Alert field
   [RFC2113] is described in Section 3.

2.2.4.  Reservation update

   In some cases it could be necessary to update the resource reserved.
   For example, in a video streaming application the user could decide
   to receive a better quality (but more expensive) version of the
   video, so the source needs to reserve more resources.  Another case
   where it is necessary to update the reservation is when some routers
   in the path are not REBOOK capable, so that their service is of best-
   effort type.  If congestion at the non-REBOOK router happens, the
   source detects it by using known congestion control procedures
   (e.g.,TFRC [RFC5348]) and it can decide to update the reserved
   bandwidth.  Finally, a third case is when a router receives a request
   that cannot satisfy and it can decide to reduce the amount of
   resources assigned to another node in order to satisfy the new

   In all those cases, the reservation can be changed by using a KPALV
   request with the new reservation.  If the source wants to reduce the
   allocated resources, it just generates the request with the new
   allocation value; if an intermediate router wants to reduce the
   reserved bandwidth, it will wait for the first KPALV packet to arrive
   and it will update the reservation value in it.

   When the target receives a KPALV packet with different resource
   values, it sends to the source a PRL_ACK (see Section 2.3) with the
   new values.

   Finally, if the source desires to increase the reserved resources, it
   can use the request UP_RESV (see Section 2.3).

2.2.5.  Path change

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2.2.6.  Shutdown

   When the transmission is concluded, the source can release the
   reserved resources by sending a RL_RESV request.  This will cause the
   intermediate routers to release the allocated resources.

2.3.  Commands

   RESV  Sent at the beginning of a session.  When it leaves the source
      it contains the amount of required resources (R_req) and the
      minimum admissible amount of resources (R_min) and the current
      amount of reserved resources (R_curr), initialized to R_req.  The
      request is modified by intermediate routers as follows

      *  If the router cannot allocate R_curr resources, it writes in
         R_curr the reserved amount of resources.

      *  The router creates a new entry in its tables for the new stream
         and append to the RESV request a "reference" to the new entry.

   RESV_ACK  Sent by the target to the source when the target receives
      the RESV requests.  Its payload stores the value of R_curr in the
      received RESV request and the list of router references.

   KPALV  Keep-alive request sent by the source to the target.  They
      carry the values of R_min, R_req and R_curr, together with the
      router references.  They are used, beside for keeping the
      connection "hot" to that the routers release the resources, for
      updating the resource reservation.  They are ignored by the target
      node, unless the resource reservation has been changed.

   PRL_ACK  Sent by the target to the source when a KPALV with changed
      reservation is received.  Its payload stores the value of R_curr
      in the received RESV request and the list of router references.

   UP_RESV  Sent by the source to increase the amount of reserved
      resources.  It is handled like a RESV request, with the difference
      that the stream entry in the router tables must by already

   RL_RESV  Sent by the source at the end of the session.  The routers
      will release the allocated resources and will remove the stream
      entry from their tables.

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2.4.  Router behaviour

   In this section we describe the expected behavior of a REBOOK-capable
   router, with reference to a specific implementation.  It is clear
   that the implementation details are mostly a private matter of the
   router and that they can be changed as long as the router behavior
   "seen" by the rest of the network does not change.

   In the reference implementation chosen here the router uses two

   o  The usual _routing table_ mapping destinations to router ports

   o  A _stream table_ addressed via the reference that the router
      writes in the RESV packet.  Each entry of the table contains
      information relative to the specific stream and it is expected to
      contain at least

      *  The current values of R_min, R_req and R_curr

      *  The reference of the next router

      *  The session expiration time T_exp.  If no KPALV packets are
         received before T_exp, the session is considered expired and
         the allocated resources released

      *  A reference to the routing table pointing to the entry
         associated with the target address.

2.4.1.  On reception of a RESV request

   When the router receives a RESV request

   o  It creates a new entry in the stream table for the new stream.
      Let REF be the reference to the new entry.  It look-ups the
      routing information required for the stream and set the routing
      table reference in the stream table entry accordingly.

   o  It checks the amount of resources that it can allocate to the
      stream and update the stream table accordingly.  If the allocated
      resources are less the R_curr value in the RESV request, update
      the RESV value to the actual amount of allocated resources.

   o  It appends to the RESV request the value of REF and forward the
      updated request to the next hop.

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2.4.2.  On reception of a data packet with the reference field

   As explained in Section 2.2.3, the source can optionally include in
   the data packet the reference belonging to the first router.  In this
   case, when the router receives a packet that is marked as a REBOOK

   o  It checks for the packet validity.  This is done both for security
      and for detecting events like route changes and faults.  The check
      can be done in constant time by checking the REBOOK reference in
      the packet, see Section 2.4.6 for details.  If the check is
      positive, continue, otherwise the REBOOK reference is invalidated
      and the packet is handled as a normal one.

   o  By using the router reference field embedded in the packet, it
      accesses the entry in the stream table.

   o  It copies the router reference stored in the table in the
      corresponding data packet field.  Note that in this way the next
      REBOOK-capable router will find in the RRef field the reference
      value that it wrote in the RESV packet during the setup phase.

   o  It finds the corresponding entry in the routing table and forward
      the packet toward the right output port.

   o  Finally, note that the access to the table at constant cost allows
      to implement new features, e.g., accounting and security controls.

   Note that the operations above require a constant time, independent
   on the number of entries in the stream table.

2.4.3.  On reception of a KPALV request

   When the router receives a KPALV

   o  It checks for the packet validity.  This is done both for security
      and for detecting events like route changes and faults.  The check
      can be done in constant time by checking the REBOOK reference in
      the packet, see Section 2.4.6 for details.  If the check is
      positive, continue, otherwise discard the packet (GIUSTO?)

   o  It finds the corresponding entries in the stream table.

   o  It updates the expiring time T_exp of the session

   o  If the value of R_curr in the KPALV request is lower than the
      corresponding value stored in the table, it updates the table (and
      release the corresponding resources too)

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   o  If the router lowered the resources assigned to the stream because
      of some resource re-assignation, it update the R_curr value in the
      KPALV request

   o  The (possibly updated) KPALV request is forwarded to the next hop

2.4.4.  On reception of a UP_RESV request

   The behavior is similar to the case of reception of a RESV request,
   with the difference that the stream must already have an entry in the
   stream table

2.4.5.  On reception of a RL_RESV request

   When the router receives a RL_RESV

   o  It checks its validity (see Section 2.4.6).  If the check is
      positive, continue, otherwise discard the packet (GIUSTO?)

   o  It deletes the entry associated to the stream from the stream
      table and releases the associated resources.

2.4.6.  Checking packet validity

   For safety reasons, a router must check if the received REBOOK packet
   is a valid one.  The check can be done by exploiting some
   redundancies in the REBOOK structure

   o  When a router receives for the first time a RESV request, it opens
      a new entry in the stream table and initialize it with the data
      stored in the request, including the FlowID, that is, the (source
      address, target address) pair, where each address is, of course, a
      (host address, port) pair.  When a data packet or a REBOOK request
      is received, the router can check that the FlowID of the received
      request matches the FlowID stored in the stream table.

   o  If the router use only B <32 bits of the 32 bits of the reference,
      it can use the remaining 32-B bits for the validity check.  A
      possible approach is to fill the unused 32-B bits with parity bits
      and encrypting the result.  The check for reference validity is
      immediate and it is very difficult to forge a valid reference.
      Note that since the reference value is an opaque 32-bit string for
      the other nodes, this type of checks can be implemented privately
      by the router without problems of interoperability.

   o  Another low-cost validity check supposes that the free entries in
      the stream table are organized in a linked list.  In this case the
      router initializes the empty stream table by joining its entries

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      in random order, making unpredictable the order the entries will
      be used by the router.  Moreover, in order to avoid a fast reuse
      of the same entry, released entries can be inserted at the end of
      the free list, while allocated entries can be extracted from the
      In order to check the validity of the REBOOK packet, the router
      can verify that the referenced entry is really used.

3.  Using the IP Router Alert field

   A possible solution to embed REBOOK information inside data packet is
   to exploit the IP Router Alert field.  This will require the
   allocation of a suitable code-point in the IANA maintained registry.
   A REBOOK value in the IP Router Alert field will signal to the router
   that the 32-bit reference value has been stored between the next
   level protocol header and the data payload.

4.  Session Timeout

   As already explained, because of the soft state nature of REBOOK,
   sessions that are not refreshed by keep-alive messages are considered
   expired and their resources released.  An important issue is the
   choice of the timeout interval: if it is too short, the source will
   send many keep-alive packets, increasing the overhead; if it is too
   long, the resources associated with a crashed session (i.e., a
   session where the source crashed) can remain unavailable for a long
   time (until the session expires), reducing the efficiency of the
   router.  Note that it is important that the source knows the session
   timeout, in order to choose the keep-alive frequency.

   Some possible solutions about the choice of the session timeout are
   the following

   Fixed  The timeout value could be fixed by the protocol.  This is
      maybe the simplest solution and it has the advantage of a low
      overhead, but maybe is too rigid.

   RTT based  The timeout could be fixed to a multiple of the round trip
      time (RTT) between the source and the target.  The source would
      send keep-alive packet with a frequency that depends on the RTT
      and the expiration time should be long enough to keep in account
      the probability that a keep-alive packet gets lost.  This overhead
      of this solution is low.  It is important that the difference
      between the RTT estimated by the router and the RTT estimated by
      the source is small.

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   Timeout as a resource  With this approach the timeout is considered a
      resource that can be negotiated by using the REBOOK mechanism (see
      Section 5).  Therefore, the source will send its timeout request
      in the RESV packet and the routers will change the timeout value
      in the RESV request according to their needs.  Moreover, timeout
      can be changed dynamically during the session by the usual REBOOK
      procedure.  The drawback of this approach is that it introduces
      overhead in the RESV and KPALV packets.  Note that with this
      approach, the session timeout is the smallest among the timeouts
      chosen by the routers.

5.  What is a resource?

   In this document we talked generically about "resources" to be
   reserved, without describing in details what a resource is.
   Typically one can expect bandwidth to be a negotiable resource, but
   other types of resources are possible.  For example, the source could
   want to improve the latency by assigning to the stream a higher
   priority, so that the router will store the packets in a high-
   priority queue.  Another example of possible resource is the session
   timeout (see Section 4).  Depending on the application using REBOOK,
   it could prove useful to keep the set of resources extensible, maybe
   by using a Type-Length-Value format, so that routers that do not
   recognize some resources can skip them.

6.  Security consideration

   To be written

7.  IANA considerations

   To be written

8.  References

8.1.  References

   [RFC2113]  Katz, D., "IP Router Alert Option", RFC 2113,
              February 1997.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC5348]  Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
              Friendly Rate Control (TFRC): Protocol Specification",
              RFC 5348, September 2008.

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8.2.  Informative References

   [rebook]   Montessoro, P. and D. Daniele, "REBOOK: A Deterministic,
              Robust and Scalable Resource Booking Algorithm", J Netw
              Syst Manage DOI 10.1007/s10922-010-9167-8, may 2010.

Authors' Addresses

   Pierluca Montessoro
   University of Udine
   Via delle Scienze 208
   Udine  33100

   Phone: +39-0432-55-8286
   EMail: montessoro@uniud.it

   Riccardo Bernardini
   University of Udine
   Via delle Scienze 208
   Udine  33100

   Phone: +39-0432-55-8271
   EMail: riccardo.bernardini@uniud.it

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