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- Internet Engineering Task Force Raj Yavatkar, Intel
- INTERNET-DRAFT Don Hoffman, Sun Microsystems
- Yoram Bernet, Microsoft
-
- December 1996
- Expires: June 30, 1997
-
- SBM (Subnet Bandwidth Manager):
- A Proposal for Admission Control over Ethernet
-
- Status of this Memo
-
- This document is an Internet-Draft. Internet-Drafts are working
- documents of the Internet Engineering Task Force (IETF), its areas,
- and its working groups. Note that other groups may also distribute
- working documents as Internet-Drafts.
-
- Internet-Drafts are draft documents valid for a maximum of six months
- and may be updated, replaced, or obsoleted by other documents at any
- time. It is inappropriate to use Internet-Drafts as reference
- material or to cite them other than as ``work in progress.''
-
- To learn the current status of any Internet-Draft, please check the
- ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow
- Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au
- (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West
- Coast).
-
- This document is a product of the ISSLL subgroup of the Integrated Services
- working group of the Internet Engineering Task Force. Comments are
- solicited and should be addressed to the working group's mailing list
- at issll@mercury.lcs.mit.edu, and/or the author(s).
-
- Changes From Last Version
-
- This draft reflects the following changes to its previous version:
-
- 1. SBM now accepts and processes the RSVP PATH messages. A PATH mes-
- sage sent over a LAN now contains LAN_NHOP and LAN_PHOP objects.
- Section 2.2 describes changes to the RSVP operation.
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- 2. Message encapsulation rules and message formats are added.
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- 3. A section that describes the SBM operation over different LAN topo-
- logies has been added.
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- INTERNET-DRAFT SBM (Subnet Bandwidth Manager) December, 1996
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- Abstract
-
- This document outlines an architecture for RSVP-based admission
- control over IEEE 802-style LANs. The proposed architecture is
- designed to work with the current generation of IEEE 802 LANs and
- should be considered as a first step towards discovering solutions
- for implementation of IntServ capabilities over such networks.
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- 1. Introduction
-
- RSVP and Integrated-Services specifications together define an
- admission control and traffic control framework for providing
- end-to-end QoS guarantees over the Internet. However, specific
- algorithms, mechanisms, and protocols are needed to map the pro-
- posed integrated services over specific link-layer technologies
- such as the IEEE 802-style LANs. Our goal is to propose an archi-
- tecture for achieving admission control over the 802-style networks
- such as Ethernet on the basis of the framework proposed in the RSVP
- and Int-Serv working groups. Our proposal is based on the follow-
- ing architectural goals and assumptions:
-
-
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- I. We define an architecture that provides a step-by-step solution to
- the problem of managing bandwidth over shared subnetworks (such as
- an Ethernet) that works with the existing, legacy LAN infrastruc-
- ture and takes advantage of the additional functionality (such as
- an explicit support for integrated services) as it becomes avail-
- able in the new generation of switches, hubs, or bridges. As a
- result, our architecture would allow for a range of LAN bandwidth
- management solutions that vary from one that exercises purely
- administrative control (over the amount of bandwidth consumed by
- RSVP-enabled traffic flows) to one that requires cooperation (and
- enforcement) from all the end-systems attached to a shared sub-
- network.
-
-
- II. To support integrated services on a specific networking technology,
- one needs to define mechanisms for admission control, traffic flow
- separation, and traffic scheduling (the latter two are usually
- grouped together under "traffic control"). For instance, an effec-
- tive admission control mechanism for shared subnetworks requires
- managing and controlling bandwidth usage so that the aggregate
- traffic load on any shared segment does not exceed its capacity.
- This requires controlling the amount of traffic generated by both
- RSVP-enabled and non-RSVP traffic flows. Additional link level
- mechanisms for traffic flow separation and traffic control may be
- necessary to achieve the goal. Appendix A elaborates further on the
- traffic control mechanisms necessary for this purpose.
-
- In the short term, our goal is to specify only a signaling method
- and protocol for LAN-based admission control over RSVP flows and
- leave the task of specifying link layer mechanisms for traffic con-
- trol to the appropriate IEEE 802 working groups.
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- Thus, the proposed mechanism explicitly controls only the total
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- amount of traffic load imposed by RSVP-enabled flows on a shared
- LAN. However, the best-effort traffic generated by the TCP/IP
- sources is generally rate-adaptive (using "slow start" type conges-
- tion avoidance mechanisms or feedback-based rate adaptation used by
- sources based on RTP/RTCP protocols) and limits the amount of
- traffic generated to adapt to available capacity. A specification
- of an RSVP-based admission control mechanism for a LAN should typi-
- cally suffice to control the total amount of traffic over a shared
- LAN. This is especially true in a switched Ethernet environment if
- switches and NICs support at least two levels of priority. In such
- a multi-priority LAN, assignment of higher priority to the RSVP
- traffic (to separate it from best-effort traffic) coupled with a
- combination of admission control (over RSVP traffic to keep it
- within a fraction of any link's capacity) and per-flow policing at
- end-systems should suffice to realize an approximation to the "con-
- trolled load" service specified in the int-serv working group.
-
-
- III. For traffic control, we assume that end-systems will police indivi-
- dual RSVP-enabled data flows to ensure that each flow stays within
- its traffic specification stipulated in its reservation request for
- admission control. Additional traffic scheduling mechanisms may
- also be employed to realize a particular QoS service class.
-
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- IV. As an interim measure until 802-mediated traffic control mechanisms
- become available, we assume that all the RSVP nodes on a LAN will
- utilize the proposed admission control procedure to reserve
- bandwidth in advance of sending any RSVP-enabled data flows and
- will not send/forward such traffic if the reservation request
- fails. Thus, if all the multimedia traffic on a LAN is sent using
- RSVP for resource reservation, the proposed architecture would
- restrict the total multimedia traffic on any LAN segment within the
- bounds desired by a LAN administrator. This does not, however,
- assure that non-RSVP traffic will not interfere with the RSVP
- traffic. Appendix A.1 discusses this approach in more detail.
-
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- 2. Overview
-
- Our architecture is based on a logical entity called an SBM (Subnet
- Bandwidth Manager) responsible for handling admission control requests.
- We assume that an IP subnet corresponds to a single L2 (Layer 2) domain
- [3]. An L2 domain is defined to be a set of nodes and links intercon-
- nected without passing through a L3 (IP or Layer 3) forwarding function.
- We refer to links (point-to-point or shared segments) that interconnect
- nodes within a L2 domain simply as LAN segments. We assume that a Desig-
- nated SBM (DSBM) exists for each LAN segment (also called a Managed
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- Segment or a MS) and services reservation requests (manages bandwidth)
- for that segment. An SBM is an application-level entity that uses UDP
- for communication with its clients. The architecture makes no assump-
- tions about the number of SBMs within a LAN; a single DSBM may manage a
- shared LAN segment whereas a separate SBM may run on each switch in a
- switched LAN topology (Section 3 discusses this point in greater
- detail). In the following, we use the term "SBM client" to refer to an
- entity (host or router) that communicates with a DSBM for the purpose of
- establishing a QoS reservation.
-
- 2.1 Basic Algorithm
-
- Figure 1 - An Example of a Managed Segment.
-
- Host Host
- _______ === ------- ===
- | | | C | | SBM | | B |
- | Router| | | - /---- | |
- |_R2____| === / ===
- | | / |
- | | / |
- ==============================================================LAN
- | |
- | |
- === __|_____
- | A | | Router |
- | | | R1 |
- === |________|
- Host
-
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- Figure 1 shows an example topology consisting of hosts and routers
- interconnected across a LAN. For the purpose of this discussion, we
- ignore the actual physical topology of the LAN and a single SBM is
- assumed to be the DSBM for the entire LAN. Section 3 describes how an
- SBM operates over different LAN topologies.
-
- The basic SBM algorithm works as follows:
-
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- 1. DSBM Initialization: As part of its initial configuration, DSBM
- obtains information such as the maximum bandwidth that can be
- reserved on each LAN segment under its control. Configuration is
- likely to be static with the current Ethernet devices. Future work
- may allow for dynamic discovery of this information.
-
- 2 SBM Client Initialization: At the start, an SBM client discovers
- and binds to its DSBM using a "DSBM Discovery Protocol" (described
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- in section 2.3).
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- 3. RSVP-based Admission Control: To reserve LAN bandwidth, RSVP nodes
- (RSVP-capable hosts and routers) follow the following steps:
-
- a) When an RSVP node sends or forwards a PATH message over a LAN
- interface, it unicasts the PATH message to its DSBM instead of
- sending it to the destination address (as is done in conventional
- RSVP processing). After processing (and possibly updating an
- ADSPEC), the DSBM will forward the PATH message toward its desti-
- nation address (See Section 3 for the case involving multiple
- Layer 2 hops between a sender and a destination). As part of its
- processing, the DSBM builds and maintains a path state for the
- session and notes the previous hop that sent it the PATH message.
-
- For example, if the sender to a session is outside the LAN and
- router R1 (see Figure 1) is on the path to the receivers, R1 will
- forward a PATH message from the sender to its DSBM (the DSBM's
- unicast address) and the DSBM will eventually send the PATH mes-
- sage to the RSVP session address. In the process, the DSBM builds
- the PATH state, remembers the sender (router R1 in Figure 1) as
- the previous hop for the session, and effectively inserts itself
- as an intermediate node between the sender (or R1 in Figure 1)
- and the receivers (or routers) on the LAN.
-
- b) When a receiver (say, host A) wishes to make a reservation
- request for the session, it follows standard RSVP rules and sends
- a RSVP RESERVE message to the previous hop address obtained from
- the PHOP object in the previously received PATH message.
-
- c) The DSBM processes the RSVP RESERVE message based on the
- bandwidth available and returns an RSVP_ERROR to the requester
- (host A) if the request cannot be granted. Admission control
- algorithm at DSBM ensures that sufficient bandwidth is available
- on managed segments (MS) between the NHOP (requester) and the
- PHOP (sender/router).
-
- In case of a successful reservation, DSBM forwards the RESERVE
- message towards the PHOP(s) based on the contents of the RESERVE
- message and its local path state for the session. The DSBM
- merges reservation requests for the same session as and when pos-
- sible using the rules similar to the conventional RSVP process-
- ing.
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- d) The RESERVE message eventually reaches the original PHOP
- (sender/router) on that MS if all reservation requests within the
- MS succeed.
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- 2.2 Changes to conventional RSVP operation
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- The addition of an SBM for admission control over Ethernet results in
- the following changes to the RSVP operation on an Ethernet:
-
- - Outgoing PATH messages on an Ethernet interface are unicast to the
- DSBM.
-
- - In conventional RSVP processing over point-to-point links, RSVP
- nodes (hosts/routers) use NHOP and PHOP objects to keep track of
- the next hop (and the previous hop) nodes on the path between a
- sender and a receiver. Over a shared LAN such as an Ethernet, we
- introduce an SBM (subnet Bandwidth Manager) as a logical entity
- that performs admission control over the LAN. Such a LAN may span
- multiple switched or shared segments between a RSVP PHOP node and a
- RSVP NHOP node. For the purpose of Layer 3 routing and RSVP seman-
- tics between two Layer 3 entities, however, the entire LAN acts a
- logical segment and the connection between RSVP PHOP and NHOP nodes
- must be maintained for the correct operation and routing of RSVP
- messages. Therefore, we introduce two new RSVP objects called
- LAN_PHOP and LAN_NHOP that keep track of the peer RSVP nodes on a
- path between a RSVP sender (or a previous hop router) and a RSVP
- receiver (or a next hop router).
-
- When an RSVP entity (a host or a router acting as the originator of
- a PATH message) sends out a PATH message over an Ethernet inter-
- face, it needs to include both LAN_NHOP and LAN_PHOP objects in the
- message as described below. When a DSBM receives a PATH message it
- passes on LAN_PHOP and LAN_NHOP objects unchanged and only modifies
- PHOP and NHOP (i.e., RSVP_HOP) objects in those messages. Thus,
- when an RSVP node finally receives the PATH message, it has the
- necessary information about RSVP peer-to-peer association (and,
- therefore, the layer 3 routing information) through the contents of
- the LAN_PHOP and LAN_NHOP objects.
-
- When sending out a PATH message over an Ethernet interface, first
- RSVP node (sender or an edge router forwarding the PATH message)
- must include two new objects, namely, a LAN_NHOP object and a
- LAN_PHOP object. The LAN_NHOP object specifies the destination IP
- address of the PATH message. In case of a unicast destination, the
- LAN_NHOP address specifies the destination address or the address
- of the next hop router towards the destination. The LAN_PHOP object
- in the PATH message specifies the IP address of the RSVP node
- (sender or forwarding router) that originated the PATH message on
- the LAN.
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- - When an SBM receives a RSVP PATH message, it processes it according
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- to the PATH processing rules described in the RSVP specification.
- In particular, it remembers the PHOP address from which it received
- the messages and forwards the path message with the PHOP object
- modified to reflect its IP address. LAN_PHOP and LAN_NHOP objects
- in the PATH message are passed along unchanged.
-
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- - The path state in SBM is used for forwarding subsequent RESV mes-
- sages for the same session. When an SBM receives a RESV message, it
- processes the message and forwards it to appropriate PHOP(s) based
- on its path state.
-
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- - Because a DSBM inserts itself as a hop between a source of traffic
- on the LAN (sender or router) and the receiver, all RSVP related
- messages (such as PATH, PATH_TEAR, RESV, RESV_CONFM, RESV_TEAR, and
- RESV_ERR) now flow through the DSBM.
-
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- - When RSVP session address is a multicast address, it is possible
- for a router that originated a PATH message to receive one or more
- copies of the PATH message when a DSBM on the path to the destina-
- tion forwards it (i.e., multicasts it). However, the router can
- detect and discard the duplicates either based on the contents of
- the LAN_PHOP object (lists one of its interface addresses) or based
- on who forwarded it (any PATH message coming from a SBM other than
- its own DSBM).
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- 2.3 Discovering and Binding to a DSBM
-
- DSBM listens to a well-known SBM multicast address (SBM_GRP - an UDP
- multicast address with a local scope -- of the form, <224.0.0.x, port
- XXXX>, TBD) and an SBM client locates its DSBM by multicasting a
- LOCATE_SBM request to the SBM_GRP address with a restricted multicast
- scope (multicast TTL=1). DSBM replies to the client's query and provides
- its unicast address for further communication. After the initial
- handshake between the DSBM and an SBM client, the SBM client is con-
- sidered bound to its DSBM and SBM client uses DSBM's unicast address for
- subsequent communication.
-
- To allow recovery from DSBM failures and binding to a newly elected
- DSBM, the SBM client must listen to the subsequent, periodic I_AM_DSBM
- refresh messages from its DSBM to detect the DSBM failure. These refresh
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- messages (or "DSBM advertisements") are sent to the SBM_GRP address
- every refresh interval (e.g., every 30 seconds; the refresh interval is
- a configuration parameter). The client must repeat the binding pro-
- cedure if original DSBM fails (or is replaced by another one).
-
- 2.4 More than one active SBM on a LAN segment
-
- For the sake of redundancy and fault tolerance, it is possible to have
- more than one active SBM on any LAN segment that can act as a backup
- DSBM if necessary. In such a case, exactly one SBM acts as the DSBM for
- the segment at any time and is elected using an DSBM election algorithm.
- Once a DSBM is elected, other SBMs stay around and step in to elect a
- new DSBM if the previously elected DSBM terminates or crashes for some
- reason.
-
- The election algorithm works as follows: When a SBM comes up on an IP
- subnet, it must first discover whether a DSBM already exists on the sub-
- net. It does so by listening for incoming I_AM_DSBM messages for a ran-
- dom amount of time. If no other DSBM is present, it announces its wil-
- lingness to be a DSBM by periodically multicasting a DSBM WILLING mes-
- sage to the SBM_GRP address with the restricted multicast scope (TTL=1).
- If another SBM exists on the same subnet and considers itself a current
- or a better choice, it replies to the new SBM via a multicast I AM DSBM
- message to the same group. Ties between candidate DSBMs may be broken
- based on a priority field in the I_AM_DSBM message (priority specified
- by the network administrator) or simply based on IP address ordering.
- (e.g. candidate with the lower IP address wins). If the new SBM does not
- hear a response from a better choice within K (K >= 3) periodic
- announcements, it declares itself to be the SBM by multicasting a
- I_AM_DSBM message.
-
- The designated SBM of the MS periodically multicasts the I_AM_DSBM mes-
- sage. Other SBMs in the MS listen to the periodic announcements and
- assume that the SBM has terminated functioning if they do not hear K (K
- >= 3) successive periodic announcements. In that case, all the SBMs ini-
- tiate the election algorithm to elect a new DSBM.
-
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- 3. Various LAN Topologies
-
- Our goal is to offer an admission control solution that works with the
- existing, shared segments LANs as well as newer, switched LAN topolo-
- gies. In the following, we consider three different LAN topologies and
- describe how our solution works in each case.
-
- 3.1 Shared LAN segments
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- Figure 1 shows a sample topology where entire IP subnet spans a single
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- shared segment. Actual physical topology in this case may consist of
- multiple physical segments interconnected by hubs. However, for practi-
- cal purposes, such a LAN acts as if all hosts are attached to a single
- shared segment. In this case, a single DSBM manages shared bandwidth for
- the entire subnet.
-
- 3.2 Switched LAN segments
-
- Figure 2 shows a sample topology where an IP subnet spans a switched
- Ethernet consisting of one or more switches interconnecting all the
- end-systems within the subnet. In this case, we assume that one SBM
- resides at each switch, the DSBM is responsible for managing outgoing
- interfaces at the switch, and that the DSBM accesses its switch's local
- MAC address table to discern forwarding information.
-
- In this case, PATH and RESV messages between two end-systems on the sub-
- net will propagate hop-by-hop from one DSBM to another DSBM as they
- travel across the switches along the path.
-
- For example, let us assume a unicast RSVP session addressed to host D in
- Figure 2. Let us also assume that the sender in the session resides out-
- side the LAN shown in Figure 2 and the router R1 forwards a PATH message
- towards its receiver on the LAN.
-
- When a PATH message for the session arrives at R1, the following
- sequence of events will happen:
-
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- 1. R1 forwards the PATH message to its DSBM (B1 in Figure 2).
-
-
- 2. B1 processes the PATH message, builds the path state, and then for-
- wards the PATH message to the next DSBM on the path towards the
- LAN_NHOP address (forwarding information discerned from the MAC
- address table).
-
- In the case of a LAN with multiple hops (segments) between an RSVP
- sender (LAN_PHOP) and a destination (LAN_NHOP), the DSBMs forward
- the PATH message hop-by-hop until it reaches a managed segment
- where the destination resides. At that point, the DSBM for the
- managed segment will send the PATH message directly to the destina-
- tion.
-
- In the case of a multicast destination where many receivers are
- scattered across a LAN, the DSBM at each intermediate hop must for-
- ward the PATH message to the session destination address for all
- outgoing interfaces where group members reside. We assume that the
- DSBM has access to a switch's local MAC address table to discern
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- such forwarding information.
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- 3. B2 will then process the PATH message and forward it to the
- LAN_NHOP address.
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- 4. When the host D decides to make a reservation for the session, it
- looks up its path state to determine the previous hop(s) for the
- session and sends the RSVP RESV message to its PHOP (B2). If the
- admission control at B2 succeeds, it will forward the RESV message
- to the PHOP (B1) according to its path state, and finally, the RSVP
- RESV message will arrive at R1 if admission control at intermediate
- switches succeeds.
-
-
- 5. Any admission control failure results in a RESV_ERROR being sent to
- the requester and the RESV state at intermediate nodes is removed.
-
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- Figure 2 - An example of a switched topology
- ---------
- | Router |
- | R1 |
- |_________|
- /
- /
- /
- ++++++
- Switch + B1 +
- S1 + +
- ++++++
- / |__
- / |
- / |
- ++++++ ++++++
- switch + B2 + + B3 + switch
- S2 + + + + S3
- ++++++ ++++++
- / |__ |_____
- / | |
- / | |
- Host Host Host
- === ==== ===
- | D | | E | | F |
- | | | | | |
- === === ===
-
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- 3.3 Combination of Shared and Switched segments (heterogeneous case)
-
- Previous two cases represent two popular topologies (shared segment
- topology is popular among legacy LANs and switched topology is popular
- with the newer installations). However, we must also consider a more
- general case when an IP subnet spans a combination of shared and
- switched segments. In this case, we still assume that a DSBM exists at
- each switch. However, the DSBM at a switch is not only responsible for
- managing bandwidth across its incident point-to-point links to its
- peers, but also manages shared segments that are incident to it. When
- more than one switch is attached to a shared segment, the DSBM will
- determine the directly attached segments that it manages >From the con-
- figuration information supplied at the startup time. Shared segments
- (and any non-SBM switches attached to them) are treated as a single log-
- ical segment for the purpose of admission control. When a RESV request
- arrives at the DSBM, it will perform admission control over all the
- managed segments under its domain that are affected by the RESV message
- before forwarding the RESV towards the previous hop address.
-
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- 4. Layer 2 Support Issues
-
- When an SBM resides on a switch, we assume that it has access to the
- local MAC address table so that it can discern the information necessary
- for forwarding PATH and RESV messages to their respective LAN_NHOP and
- LAN_PHOP addresses. An accompanying document [3] describes the require-
- ments for mapping IP Integrated Services over IEEE 802 traffic control
- mechanisms.
-
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- 5. Message Encapsulation and Formats
-
- To minimize changes to existing RSVP implementations and to ensure quick
- deployment of an SBM in conjunction with RSVP, all communication to and
- from a DSBM will be performed using messages constructed using the
- current rules for RSVP message formats. For more details on the RSVP
- message formats, refer to the RSVP specification (draft-ietf-rsvp-spec-
- 14.ps). No changes to the RSVP message formats are proposed, but new
- message types and new LAN_NHOP and LAN_PHOP objects are added to the
- RSVP message formats to accommodate DSBM-related messages. These addi-
- tions are described below.
-
- All messages to a DSBM (except messages related to DSBM discovery and
- advertizements) are addressed to the DSBM's unicast address. In partic-
- ular, all RSVP-related messages (PATH, RESV, and other TEAR and ERROR
- messages) directed to a DSBM are sent to the DSBM's unicast address. An
- RSVP node discovers its DSBM (and DSBM's unicast address) using a
- discovery method described in Section 2.3 earlier.
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- Each message must occupy exactly one IP datagram. If it exceeds the MTU,
- such a datagram will be fragmented by IP and reassembled at the reci-
- pient node. This has a consequence that a single message may not exceed
- the maximum IP datagram size, approximately 64K bytes.
-
- 5.1. RSVP-related Message Formats
-
- All RSVP messages directed to and from a DSBM may contain various RSVP
- objects defined in the RSVP specification and messages continue to fol-
- low the formatting rules specified in the RSVP specification. In addi-
- tion, an RSVP implementation must also recognize two new object classes,
- LAN_NHOP and LAN_PHOP, that are described below.
-
-
- 5.2 LAN_NHOP and LAN_PHOP Objects
-
- Both LAN_NHOP and LAN_PHOP objects have the same structure as the
- RSVP_HOP object, but are identified as separate object classes to dis-
- tinguish them from each other and from the RSVP_HOP objects.
-
- LAN_NHOP objects use object class = 40; IPv4 LAN_NHOP object uses
- <Class=40, C-Type=1> and IPv6 LAN_NHOP object uses <Class=40,
- C-Type=2>.
-
- IPv4 LAN_NHOP object: class = 40, C-Type =1
-
- +---------------+---------------+---------------+---------------+
- | IPv4 Next Hop Address |
- +---------------+---------------+---------------+---------------+
- | Logical Interface Handle |
- +---------------+---------------+---------------+---------------+
-
- IPv6 LAN_NHOP object: Class = 40, C-Type = 2
- +---------------+---------------+---------------+---------------+
- | |
- + +
- | |
- + IPv6 next Hop Address +
- | |
- + +
- | |
- +---------------+---------------+---------------+---------------+
- | Logical Interface Handle |
- +---------------+---------------+---------------+---------------+
-
- LAN_PHOP objects use class=41; IPv4 LAN_PHOP and IPv6 LAN_PHOP objects
- use C-Types 1 and 2 respectively. These objects are structured same as
- those shown above.
-
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- 5.3 RSVP PATH Message Format
-
- As specified in the RSVP specification, an RSVP_PATH message contains
- the RSVP Common Header and the relevant RSVP objects. For the RSVP Com-
- mon Header, refer to the RSVP specification (draft-ietf-rsvp-spec-
- 14.ps). Changes to an RSVP_PATH message include addition of the LAN_NHOP
- and the LAN_PHOP objects as specified below.
-
- <RSVP_PATH> ::= <RSVP Common Header> [INTEGRITY>]
- <LAN_PHOP> <LAN_NHOP> <SESSION><RSVP_HOP><TIME_VALUES>
- [<POLICY DATA>] <sender descriptor>
-
- If the INTEGRITY object is present, it must immediately follow the RSVP
- common header. LAN_NHOP object must always precede the SESSION object.
-
- 5.4 RSVP RESV Message Format
-
- As specified in the RSVP specification, an RSVP_RESV message contains
- the RSVP Common Header and relevant RSVP objects. No Changes to the RESV
- message format are needed with the SBM protocol.
-
- 5.5. Additional RSVP message types to handle SBM interactions
-
- New RSVP message types are introduced to allow interactions between a
- DSBM and an RSVP node (host/router) for the purpose of discovering and
- binding to a DSBM. New RSVP message types needed are as follows:
-
- RSVP Msg Type (8 bits) Value
-
- SBM_QUERY 64
- SBM_REPLY 65
- DSBM_WILLING 66
- I_AM_DSBM 67
-
-
-
- All SBM-specific messages are formatted as RSVP messages with an RSVP
- common header followed by SBM-specific objects.
-
- <SBMP_MESSAGE> ::= <SBMP common header> <SBM-specific objects>
-
- where <SBMP common header> ::= <RSVP common Header> [<INTEGRITY>]
-
-
- For each SBM message type, there is a set of rules for the permissible
- choice of object types. These rules are specified using Backus-Naur Form
- (BNF) augmented with square brackets surrounding optional sub-sequences.
- The BNF implies an order for the objects in a message. However, in many
-
-
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- (but not all) cases, object order makes no logical difference. An imple-
- mentation should create messages with the objects in the order shown
- here, but accept the objects in any permissible order. Any exceptions to
- this rule will be pointed out in the specific message formats.
-
- 5.5.1 SBM_QUERY Message
-
- SBM_QUERY message contains a single address object in the format that is
- same as the RSVP SESSION object and gives the IP address of the request-
- ing node. The SBM_QUERY message is multicast to the well known
- DSBM_GROUP address as described earlier.
-
- <SBM_QUERY message> ::= <SBMP common header> <IP address>
-
- where <IP address> object is same as the <SESSION> object.
-
- 5.5.2 SBM_REPLY Message
-
- SBM_REPLY message provides the IP address of the node sending out the
- reply.
-
- <SBM_REPLY Message> ::= <SBM Common Header> <IP ADDRESS>
-
- The SBM_REPLY message is unicast to the sender of the SBM_QUERY message
- .
-
- 5.5.3 DSBM_WILLING Message
-
- <DSBM_WILLING message> ::= <SBM Common Header> <IP ADDRESS>
-
- IP ADDRESS is the address of the DSBM sending out this message. All
- DSBM_WILLING messages are multicast to the well known DSBM_GROUP
- address.
-
- 5.5.4 I_AM_DSBM Message
-
- <I_AM_DSBM> ::= <SBM Common Header> <IP ADDRESS> [<PRIORITY>]
-
- IP ADDRESS is the address of the DSBM sending out this message. All
- I_AM_DSBM messages are multicast to the well known DSBM_GROUP address.
- The optional PRIORITY object specifies the relative priority of the
- requesting SBM. When multiple, redundant SBMs are present on a LAN, a
- priority level is assigned to each one of them by a network administra-
- tor and is used to break ties when multiple candidate DSBMs participate
- in the DSBM election algorithm. The default priority of an SBM is 1 and
- higher priority values represent higher precedence.
-
- PRIORITY Object: class = 42, C-Type =1
-
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- +---------------+---------------+---------------+---------------+
- | //// | //// | //// | priority |
- +---------------+---------------+---------------+---------------+
-
-
- 6. References
-
- [1] R Braden, L Zhang, S Berson, S Herzog, J Wroclaswki, "Resource
- Reservation Protocol", Internet Draft draft-ietf-rsvp-spec12.txt,May
- 1996.
-
- [2] S.Shenker, "Specification of General Characterization Parameters",
- draft-ietf-intserv-charac-00.txt,Nov 1995
-
- [3] D.Hoffman, "Integrated Services/RSVP Requirements for Layer 2
- Traffic Control", draft-hoffman-issll-l2tcreq-00.txt, December 1996.
-
- [4] Y.Bernet, "Admission Control for Best-Effort Traffic", in prepara-
- tion.
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- APPENDIX A
- Traffic Control Issues on a LAN
-
- A.1 Application Behavior
-
- Because of its goal to support existing 802 infrastructures, this propo-
- sal makes no assumptions about any traffic separation or policing
- mechanisms on the MS. Consequently, there are no network enforced
- mechanisms to keep non-adaptive traffic from interfering with the
- traffic over reserved flows. In these sorts of environments we propose
- that applications are expected to be well behaved and follow the follow-
- ing set of rules:
-
-
- - For both unicast and multicast flows, an RSVP-based sender is not
- to transmit any traffic on a RSVP flow until at least one RESERVE
- has been received for that flow. The outgoing flow should be pol-
- iced at the sender host to be less than or equal to the maximum
- flow reserved. RESERVE TEARS are indications that the sender should
- no longer send a flow.
-
- - For multicast flows, the receiver is to leave the session multicast
- group if a reservation error (RESV_ERROR) or a Path Tear is
- received. This rule may create some difficulty in environments
- where source-specific multicast pruning is not implemented (the
- default case in the current MBONE). A reservation error from a path
- toward any one specific sender would result in the receiver drop-
- ping all senders, even those with the fully reserved paths. Appli-
- cations running in such environments should restrict sessions to a
- single sender if at all possible.
-
-
- A.2 Traffic Control Mechanisms in Layer 2
-
- An effective admission control mechanism for shared subnetworks requires
- managing and controlling bandwidth usage so that the aggregate traffic
- load on any shared segment does not exceed its capacity. This requires
- controlling the amount of traffic generated by both RSVP-enabled and
- best-effort traffic flows.
-
- We do not assume any particular explicit support for integrated ser-
- vices is assumed from the LAN infrastructure (NICs, switches, hubs, or
- bridges) and assume that an appropriate IEEE 802 working group will
- specify the traffic control solutions for the link-level devices (an
- accompanying document [3] provides recommendations to the IEEE 802.1
- committee on the Layer 2 facilities needed to facilitate mapping of
- int-serv services over Ethernet).
-
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- In the absence of any layer 2 support, some topologies such as a shared
- Ethernet segment may pose a problem when unrestricted best-effort
- traffic can interfere with the traffic from RSVP-enabled traffic.
- Therefore, an explicit end-system based control over the amount of
- best-effort traffic that can be sent over Ethernet may be necessary to
- implement a particular service class. Further investigation and experi-
- mentation is necessary in this area [4].
-
-
-
-
- ACKNOWLEDGEMENTS
-
- Many thanks to Ema Patki for her active participation with the earlier
- versions of this draft. Authors are also thankful to Fred Baker of Cisco
- Systems and John ("JJ") Krawczyk of Bay Networks for their constructive
- comments on the SBM design and the earlier versions of this draft.
-
-
-
- 6. Authors` Addresses
- Raj Yavatkar
- Intel Corporation
- MS: JF3-206
- 2111 N.E. 25th Avenue,
- Hillsboro, OR 97124
- USA
- phone: +1 503-264-9077
- email: yavatkar@ibeam.intel.com
-
- Don Hoffman
- Sun Microsystems, Inc.
- MS: UMPK14-305
- 2550 Garcia Avenue
- Mountain View, California 94043-1100
- USA
- phone: +1 503-297-1580
- email: don.hoffman@eng.sun.com
-
- Yoram Bernet
- Microsoft
- 1 Microsoft Way
- Redmond, WA 98052
- USA
- phone: +1 206 936 9568
- email: yoramb@microsoft.com
-
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