Internet Engineering Task Force Raj Yavatkar, Intel
INTERNET-DRAFT Don Hoffman, Teledesic
<draft-ietf-issll-is802-sbm-06.txt> Yoram Bernet, Microsoft
Fred Baker, Cisco
Michael Speer, Sun Microsystems
March 1998
SBM (Subnet Bandwidth Manager):
A Protocol for RSVP-based Admission Control over IEEE 802-style networks
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
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yavatkar, Ed., et. al. [Page 1]
SBM (Subnet Bandwidth Manager) March, 1998
Abstract
This document describes a signaling method and protocol for RSVP-based
admission control over IEEE 802-style LANs. The protocol is designed
to work both with the current generation of IEEE 802 LANs as well as with the
recent work completed by the IEEE 802.1 committee.
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SBM (Subnet Bandwidth Manager) March, 1998
1. Introduction
New extensions to the Internet architecture and service models have
been defined for an integrated services Inernet [RFC-1633, RFC-2205,
RFC-2210] so that applications can request specific qualities or lev-
els of service from an internetwork in addition to the current IP
best-effort service. These extensions include RSVP, a resource reser-
vation setup protocol, and definition of new service classes to be
supported by Integrated Services routers. RSVP and service class
definitions are largely independent of the underlying networking tech-
nologies and it is necessary to define the mapping of RSVP and
Integrated Services specifications onto specific subnetwork technolo-
gies. For example, a definition of service mappings and reservation
setup protocols is needed for specific link-layer technologies such as
shared and switched IEEE-802-style LAN technologies.
This document defines SBM, a signaling protocol for RSVP-based admis-
sion control over IEEE 802-style networks. SBM provides a method for
mapping an internet-level setup protocol such as RSVP onto IEEE 802-
style networks. In particular, it describes the operation of RSVP-
enabled hosts/routers and link layer devices (switches, bridges) to
support reservation of LAN resources for RSVP-enabled data flows. A
framework for providing Integrated Services over shared and switched
IEEE-802-style LAN technologies and a definition of service mappings
have been described in separate documents [Ghanwani98, Seaman97].
2. Goals and Assumptions
The SBM (Subnet Bandwidth Manager) protocol and its use for admission
control and bandwidth management in IEEE 802 level-2 networks is based
on the following architectural goals and assumptions:
I. Even though the current trend is towards increased use of
switched LAN topologies consisting of newer switches that support
the priority queuing mechanisms specified by IEEE 802.1p, we
assume that the LAN technologies will continue to be a mix of
legacy shared/ switched LAN segments and newer switched segments
based on IEEE 802.1p specification. Therefore, we specify a sig-
naling protocol for managing bandwidth over both legacy and newer
LAN topologies and that takes advantage of the additional func-
tionality (such as an explicit support for different traffic
classes or integrated service classes) as it becomes available in
the new generation of switches, hubs, or bridges. As a result,
the SBM protocol would allow for a range of LAN bandwidth
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SBM (Subnet Bandwidth Manager) March, 1998
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 or switches in a IEEE 802
LAN.
II. This document specifies only a signaling method and protocol for
LAN-based admission control over RSVP flows. We do not define
here any traffic control mechanisms for the link layer; the pro-
tocol is designed to use any such mechanisms defined by IEEE 802.
In addition, we assume that the Layer 3 end-systems (e.g., a host
or a router) will exercise traffic control by policing Integrated
Services traffic flows to ensure that each flow stays within its
traffic specifications stipulated in an earlier reservation
request submitted for admission control. This then allows a sys-
tem using SBM admission control combined with per-flow shaping at
end-systems and IEEE-defined traffic control at link layer to
realize some approximation of Controlled Load (and even
Guaranteed) services over IEEE 802-style LANs.
III. In the absence of any link-layer traffic control or priority
queuing mechanisms in the underlying LAN (such as a shared LAN
segment), the SBM-based admission control mechanism only limits
the total amount of traffic load imposed by RSVP-enabled flows on
a shared LAN. In such an environment, no traffic flow separation
mechanism exists to protect the RSVP-enabled flows from the
best-effort traffic on the same shared media and that raises the
question of the utility of such a mechanism outside a topology
consisting only of 802.1p-compliant switches. However, we assume
that the SBM-based admission control mechanism will still serve a
useful purpose in a legacy, shared LAN topology for two reasons.
First, assuming that all the nodes that generate Integrated Ser-
vices traffic flows utilize the SBM-based admission control pro-
cedure to request reservation of resources before sending any
traffic, the mechanism will restrict the total amount of traffic
generated by Integrated Services flows within the bounds desired
by a LAN administrator. Second, the best-effort traffic generated
by the TCP/IP-based traffic sources is generally rate-adaptive
(using a TCP-style "slow start" congestion avoidance mechanism or
a feedback-based rate adaptation mechanism used by audio/video
streams based on RTP/RTCP protocols) and adapts to stay within
the available network bandwidth. Thus, the combination of admis-
sion control and rate adaptation should avoid persistent traffic
congestion. This does not, however, guarantee that non-
Integrated-Services traffic will not interfere with the
Integrated Services traffic in the absence of traffic control
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SBM (Subnet Bandwidth Manager) March, 1998
support in the underlying LAN infrastructure.
3. Organization of the rest of this document
The rest of this document provides a detailed description of the SBM-
based admission control procedure(s) for IEEE 802 LAN technologies.
The document is organized as follows:
* Section 4 first defines the various terms used in the document
and then provides an overview of the admission control procedure
with an example of its application to a sample network.
* Section 5 describes the rules for processing and forwarding PATH
(and PATH_TEAR) messages at DSBMs (Designated Subnet Bandwidth
Managers), SBMs, and DSBM clients.
* Section 6 addresses the inter-operability issues when a DSBM may
operate in the absence of RSVP signaling at Layer 3 or when
another signaling protocol (such as SNMP) is used to reserve
resources on a LAN segment.
* Appendix A describes the details of the DSBM election algorithm
used for electing a designated SBM on a LAN segment when more
than one SBM is present. It also describes how DSBM clients dis-
cover the presence of a DSBM on a managed segment.
* Appendix B specifies the formats of SBM-specific messages used
and the formats of new RSVP objects needed for the SBM operation.
4. Overview
4.1. Definitions
- Link Layer or Layer 2 or L2: We refer to data-link layer techno-
logies such as IEEE 802.3/Ethernet as L2 or layer 2.
- Link Layer Domain or Layer 2 domain or L2 domain: a set of nodes
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SBM (Subnet Bandwidth Manager) March, 1998
and links interconnected without passing through a L3 forwarding
function. One or more IP subnets can be overlaid on a L2 domain.
- Layer 2 or L2 devices: We refer to devices that only implement
Layer 2 functionality as Layer 2 or L2 devices. These include
802.1D bridges or switches.
- Internetwork Layer or Layer 3 or L3: Layer 3 of the ISO 7 layer
model. This document is primarily concerned with networks that
use the Internet Protocol (IP) at this layer.
- Layer 3 Device or L3 Device or End-Station: these include hosts
and routers that use L3 and higher layer protocols or application
programs that need to make resource reservations.
- Segment: A L2 physical segment that is shared by one or more
senders. Examples of segments include (a) a shared Ethernet or
Token-Ring wire resolving contention for media access using CSMA
or token passing ("shared L2 segment"), (b) a half duplex link
between two stations or switches, (c) one direction of a switched
full-duplex link.
- Managed segment: A managed segment is a segment with a DSBM
present and responsible for exercising admission control over
requests for resource reservation. A managed segment includes
those interconnected parts of a shared LAN that are not separated
by DSBMs.
- Traffic Class: An aggregation of data flows which are given simi-
lar service within a switched network.
- User_priority: User_priority is a value associated with the
transmission and reception of all frames in the IEEE 802 service
model: it is supplied by the sender that is using the MAC ser-
vice. It is provided along with the data to a receiver using the
MAC service. It may or may not be actually carried over the net-
work: Token-Ring/802.5 carries this value (encoded in its FC
octet), basic Ethernet/802.3 does not, 802.12 may or may not
depending on the frame format in use. 802.1p defines a consistent
way to carry this value over the bridged network on Ethernet,
Token Ring, Demand-Priority, FDDI or other MAC-layer media using
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SBM (Subnet Bandwidth Manager) March, 1998
an extended frame format. The usage of user_priority is fully
described in section 2.5 of 802.1D [IEEE8021D] and 802.1p
[IEEE8021P] "Support of the Internal Layer Service by Specific
MAC Procedures".
- Subnet: used in this memo to indicate a group of L3 devices shar-
ing a common L3 network address prefix along with the set of seg-
ments making up the L2 domain in which they are located.
- Bridge/Switch: a layer 2 forwarding device as defined by IEEE
802.1D. The terms bridge and switch are used synonymously in this
document.
- DSBM: Designated SBM (DSBM) is a protocol entity that resides in
a L2 or L3 device and manages resources on a L2 segment. At most
one DSBM exists for each L2 segment.
- SBM: the SBM is a protocol entity that resides in a L2 or L3 dev-
ice and is capable of managing resources on a segment. However,
only a DSBM manages the resources for a managed segment. When
more than one SBM exists on a segment, one of the SBMs is elected
to be the DSBM.
- Extended segment: An extended segment includes those parts of a
network which are members of the same IP subnet and therefore are
not separated by any layer 3 devices. Several managed segments,
interconnected by layer 2 devices, constitute an extended seg-
ment.
- Managed L2 domain: An L2 domain consisting of managed segments is
referred to as a managed L2 domain to distinguish it from a L2
domain with no DSBMs present for exercising admission control
over resources at segments in the L2 domain.
- DSBM clients: These are entities that transmit traffic onto a
managed segment and use the services of a DSBM for the managed
segment for admission control over a LAN segment. Only the layer
3 or higher layer entities on L3 devices such as hosts and
routers are expected to send traffic that requires resource
reservations, and, therefore, DSBM clients are L3 entities.
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SBM (Subnet Bandwidth Manager) March, 1998
- SBM transparent devices: A "SBM transparent" device is unaware of
SBMs or DSBMs (though it may or may not be RSVP aware) and,
therefore, does not participate in the SBM-based admission con-
trol procedure over a managed segment. Such a device uses stan-
dard forwarding rules appropriate for the device and is tran-
sparent with respect to SBM. An example of such a L2 device is a
legacy switch that does not participate in resource reservation.
- Layer 3 and layer 2 addresses: We refer to layer 3 addresses of
L3/L2 devices as "L3 addresses" and layer2 addresses as "L2
addresses". This convention will be used in the rest of the docu-
ment to distinguish between Layer 3 and layer 2 addresses used to
refer to RSVP next hop (NHOP) and previous hop (PHOP) devices.
For example, in conventional RSVP message processing, RSVP_HOP
object in a PATH message carries the L3 address of the previous
hop device. We will refer to the address contained in the
RSVP_HOP object as the RSVP_HOP_L3 address and the corresponding
MAC address of the previous hop device will be referred to as the
RSVP_HOP_L2 address.
4.2. Overview of the SBM-based Admission Control Procedure
A protocol entity called "Designated SBM" (DSBM) exists for each
managed segment and is responsible for admission control over the
resource reservation requests originating from the DSBM clients in
that segment. Given a segment, one or more SBMs may exist on the seg-
ment. For example, many SBM-capable devices may be attached to a
shared L2 segment whereas two SBM-capable switches may share a half-
duplex switched segment. In that case, a single DSBM is elected for
the segment. The procedure for dynamically electing the DSBM is
described in Appendix A. The only other approved method for specifying
a DSBM for a managed segment is static configuration at SBM-capable
devices.
The presence of a DSBM makes the segment a "managed segment". Some-
times, two or more L2 segments may be interconnected by SBM tran-
sparent devices. In that case, a single DSBM will manage the resources
for those segments treating the collection of such segments as a sin-
gle managed segment for the purpose of admission control.
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SBM (Subnet Bandwidth Manager) March, 1998
4.2.1. Basic Algorithm
Figure 1 - An Example of a Managed Segment.
+-------+ +-----+ +------+ +-----+ +--------+
|Router | | Host| | DSBM | | Host| | Router |
| R2 | | C | +------+ | B | | R3 |
+-------+ +-----+ / +-----+ +--------+
| | / | |
| | / | |
==============================================================LAN
| |
| |
+------+ +-------+
| Host | | Router|
| A | | R1 |
+------+ +-------+
Figure 1 shows an example of a managed segment in a L2 domain that
interconnects a set of hosts and routers. For the purpose of this dis-
cussion, we ignore the actual physical topology of the L2 domain
(assume it is a shared L2 segment and a single managed segment
represents the entire L2 domain). A single SBM device is designated to
be the DSBM for the managed segment. We will provide examples of
operation of the DSBM over switched and shared segments later in the
document.
The basic DSBM-based admission control procedure works as follows:
1. DSBM Initialization: As part of its initial configuration, DSBM
obtains information such as the limits on fraction of available
resources that can be reserved on each managed segment under its
control. For instance, bandwidth is one such resource. Even
though methods such as auto-negotiation of link speeds and
knowledge of link topology allow discovery of link capacity, the
configuration may be necessary to limit the fraction of link
capacity that can be reserved on a link. Configuration is likely
to be static with the current L2/L3 devices. Future work may
allow for dynamic discovery of this information. This document
does not specify the configuration mechanism.
2. DSBM Client Initialization: For each interface attached, a DSBM
client determines whether a DSBM exists on the interface. The
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SBM (Subnet Bandwidth Manager) March, 1998
procedure for discovering and verifying the existence of the DSBM
for an attached segment is described in Appendix A. If the client
itself is capable of serving as the DSBM on the segment, it may
choose to participate in the election to become the DSBM. At the
start, a DSBM client first verifies that a DSBM exists in its L2
domain so that it can communicate with the DSBM for admission
control purposes.
In the case of a full-duplex segment, an election may not be
necessary as the SBM at each end will typically act as the DSBM
for outgoing traffic in each direction.
3. DSBM-based Admission Control: To request reservation of resources
(e.g., LAN bandwidth in a L2 domain), DSBM clients (RSVP-capable
L3 devices such as hosts and routers) follow the following steps:
a) When a DSBM client sends or forwards a RSVP PATH message over
an interface attached to a managed segment, it sends the PATH
message to the segment's DSBM instead of sending it to the RSVP
session 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 des-
tination address. As part of its processing, the DSBM builds
and maintains a PATH state for the session and notes the previ-
ous L2/L3 hop that sent it the PATH message.
Let us consider the managed segment in Figure 1. Assume that a
sender to a RSVP session (session address specifies the IP
address of host A on the managed segment in Figure 1) resides
outside the L2 domain of the managed segment and sends a PATH
message that arrives at router R1 which is on the path towards
host A.
DSBM client on Router R1 forwards the PATH message from the
sender to the DSBM. The DSBM processes the PATH message and
forwards the PATH message towards the RSVP receiver (Detailed
message processing and forwarding rules are described in Sec-
tion 5). In the process, the DSBM builds the PATH state,
remembers the router R1 (its L2 and l3 addresses) as the previ-
ous hop for the session, puts its own L2 and L3 addresses in
the PHOP objects (see explanation later), and effectively
inserts itself as an intermediate node between the sender (or
R1 in Figure 1) and the receiver (host A) on the managed seg-
ment.
b) When an application on host A wishes to make a reservation for
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SBM (Subnet Bandwidth Manager) March, 1998
the RSVP session, host A follows the standard RSVP message pro-
cessing rules and sends a RSVP RESV message to the previous hop
L2/L3 address (the DSBMs address) obtained from the PHOP
object(s) in the previously received PATH message.
c) The DSBM processes the RSVP RESV message based on the bandwidth
available and returns an RESVERR message to the requester (host
A) if the request cannot be granted. If sufficient resources
are available and the reservation request is granted, the DSBM
forwards the RESV message towards the PHOP(s) based on its
local PATH state for the session. The DSBM merges reservation
requests for the same session as and when possible using the
rules similar to those used in the conventional RSVP process-
ing.
d) If the L2 domain contains more than one managed segment, the
requester (host A) and the forwarder (router R1) may be
separated by more than one managed segment. In that case, the
original PATH message would propagate through many DSBMs (one
for each managed segment on the path from R1 to A) setting up
PATH state at each DSBM. Therefore, the RESV message would pro-
pagate hop-by-hop in reverse through the intermediate DSBMs and
eventually reach the original forwarder (router R1) on the L2
domain if admission control at all DSBMs succeeds.
4.2.2. Enhancements to the conventional RSVP operation
The addition of a DSBM for admission control over managed segments
results in some additions to the RSVP message processing rules at a
DSBM client. In the following, we first motivate and summarize the
additions and a detailed description of the message processing and
forwarding rules at (D)SBMs and DSBM clients is provided in Section 5:
- Normal RSVP forwarding rules apply at a DSBM client when it is
not forwarding an outgoing PATH message over a managed segment.
However, outgoing PATH messages on a managed segment are sent to
the DSBM for the corresponding managed segment (Section 5.2
describes how the PATH messages are sent to the DSBM on a managed
segment).
- In conventional RSVP processing over point-to-point links, RSVP
nodes (hosts/routers) use RSVP_HOP object (NHOP and PHOP info) to
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SBM (Subnet Bandwidth Manager) March, 1998
keep track of the next hop (downstream node in the path of data
packets in a traffic flow) and the previous hop (upstream nodes
with respect to the data flow) nodes on the path between a sender
and a receiver. Routers along the path of a PATH message forward
the message towards the destination address based on the L3 rout-
ing (packet forwarding) tables.
For example, consider the L2 domain in Figure 1. Assume that both
the sender (some host X) and the receiver (some host Y) in a RSVP
session reside outside the L2 domain shown in the Figure, but
PATH messages from the sender to its receiver pass through the
routers in the L2 domain using it as a transit subnet. Assume
that the PATH message from the sender X arrives at the router R1.
R1 uses its local routing information to decide which next hop
router (either router R2 or router R3) to use to forward the PATH
message towards host Y. However, when the path traverses a
managed L2 domain, we require the PATH and RESV messages to go
through a DSBM for each managed segment. Such a L2 domain may
span many managed segments (and DSBMs) and, typically, SBM proto-
col entities on L2 devices (such as a switch) will serve as the
DSBMs for the managed segments in a switched topology. When R1
forwards the PATH message to the DSBM (an L2 device), the DSBM
may not have the L3 routing information necessary to select the
egress router (between R2 and R3) before forwarding the PATH mes-
sage. To ensure correct operation and routing of RSVP messages,
we must provide additional forwarding information to DSBMs.
For this purpose, we introduce new RSVP objects called LAN_NHOP
address objects that keep track of the next L3 hop as the PATH
message traverses an L2 domain between two L3 entities (RSVP PHOP
and NHOP nodes).
- When a DSBM client (a host or a router acting as the originator
of a PATH message) sends out a PATH message to the DSBM, it must
include LAN_NHOP information in the message. In the case of a
unicast destination, the LAN_NHOP address specifies the destina-
tion address (if the destination is local to its L2 domain) or
the address of the next hop router towards the destination. In
our example of an RSVP session involving the sender X and
receiver Y with L2 domain in Figure 1 acting as the transit sub-
net, R1 is the ingress node that receives the PATH message. R1
first determines that R2 is the next hop router (or the egress
node in the L2 domain for the session address) and then inserts a
LAN_NHOP object that specifies R2's IP address. When a DSBM
receives a PATH message, it can now look at the address in the
LAN_NHOP object and forward the PATH message towards the egress
node after processing the PATH message. However, we expect the
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SBM (Subnet Bandwidth Manager) March, 1998
L2 devices (such as switches) to act as DSBMs on the path within
the L2 domain and it may not be reasonable to expect these dev-
ices to have an ARP capability to determine the MAC address (we
call it L2ADDR for Layer 2 address) corresponding to the IP
address in the LAN_NHOP object.
Therefore, we require that the LAN_NHOP information (generated by
the L3 device) include both the IP address (LAN_NHOP_L3 address)
and the corresponding MAC address (LAN_NHOP_L2 address ) for the
next L3 hop over the L2 domain. The LAN_NHOP_L3 address is used
by SBM protocol entities on L3 devices to forward the PATH mes-
sage towards its destination whereas the L2 address is used by
the SBM protocol entities on L2 devices to determine how to for-
ward the PATH message towards the L3 NHOP (egress point from the
L2 domain). The exact format of the LAN_NHOP information and
relevant objects is described later in Appendix B.
- When a DSBM receives a RSVP PATH message, it processes the PATH
message according to the PATH processing rules described in the
RSVP specification. In particular, the DSBM retrieves the IP
address of the previous hop from the RSVP_HOP object in the PATH
message and stores the PHOP address in its PATH state. It then
forwards the PATH message with the PHOP (RSVP_HOP) object modi-
fied to reflect its own IP address (RSVP_HOP_L3 address). Thus,
the DSBM inserts itself as an intermediate hop in the chain of
nodes in the path between two L3 nodes across the L2 domain.
- The PATH state in a DSBM is used for forwarding subsequent RESV
messages as per the standard RSVP message processing rules. When
the DSBM receives a RESV message, it processes the message and
forwards it to appropriate PHOP(s) based on its PATH state.
- Because a DSBM inserts itself as a hop between two RSVP nodes in
the path of a RSVP flow, all RSVP related messages (such as PATH,
PATH_TEAR, RESV, RESV_CONFM, RESV_TEAR, and RESV_ERR) now flow
through the DSBM. In particular, a PATH_TEAR message is routed
exactly through the intermediate DSBM(s) as its corresponding
PATH message and the local PATH state is first cleaned up at each
intermediate hop before the PATH_TEAR message gets forwarded.
- So far, we have described how the PATH message propagates through
the L2 domain establishing PATH state at each DSBM along the
managed segments in the path. The layer 2 address (LAN_NHOP_L2
address) in the LAN_NHOP object should be used by the L2 devices
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SBM (Subnet Bandwidth Manager) March, 1998
along the path to decide how to forward the PATH message toward
the next L3 hop. Such devices will apply the standard IEEE
802.1D forwarding rules (e.g., send it on a single port based on
its filtering database, or flood it on all ports active in the
spanning tree if the L2 address does not appear in the filtering
database) to the LAN_NHOP_L2 address as are applied normally to
data packets destined to the address.
In the conventional RSVP message processing, the PATH state esta-
blished along the nodes on a path is used to route the RESV mes-
sage from a receiver to a sender in an RSVP session. As each
intermediate node builds the path state, it remembers the previ-
ous hop (stores the PHOP IP address available in the RSVP_HOP
object of an incoming message) that sent it the PATH message and,
when the RESV message arrives, the intermediate node simply uses
the stored PHOP address to forward the RESV after processing it
successfully.
In our case, we expect the SBM entities residing at L2 devices to
act as DSBMs (and, therefore, intermediate RSVP hops in an L2
domain) along the path between a sender (PHOP) and receiver
(NHOP). Thus, when a RESV message arrives at a DSBM, it must use
the stored PHOP IP address to forward the RESV message to its
previous hop. However, it may not be reasonable to expect the L2
devices to have an ARP cache or the ARP capability to map the
PHOP IP address to its corresponding L2 address before forwarding
the RESV message.
To obviate the need for such address mapping at L2 devices, we
use a RSVP_HOP_L2 object in the PATH message. The RSVP_HOP_L2
object includes the Layer 2 address (L2ADDR) of the previous hop
and complements the L3 address information included in the
RSVP_HOP object (RSVP_HOP_L3 address).
When a L3 device constructs and forwards a PATH message over a
managed segment, it includes its IP address (IP address of the
interface over which PATH is sent) in the RSVP_HOP object and add
a RSVP_HOP_L2 object that includes the corresponding L2 address
for the interface. When a device in the L2 domain receives such a
PATH message, it remembers the addresses in the RSVP_HOP and
RSVP_HOP_L2 objects in its PATH state and then overwrites the
RSVP_HOP and RSVP_HOP_L2 objects with its own addresses before
forwarding the PATH message over a managed segment.
The exact format of RSVP_HOP_L2 object is specified in APPENDIX
B.
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SBM (Subnet Bandwidth Manager) March, 1998
- When an RSVP session address is a multicast address and a SBM,
DSBM, and DSBM clients share the same L2 segment (a shared seg-
ment), it is possible for a SBM or a DSBM client to receive one
or more copies of a PATH message that it forwarded earlier when a
DSBM on the same wire forwards it (See Section 5.8 for an example
of such a case). To facilitate detection of such loops, we use a
new RSVP object called the LAN_LOOPBACK object. DSBM clients or
SBMs (but not the DSBMs reflecting a PATH message onto the inter-
face over which it arrived earlier) must overwrite (or add if the
PATH message does NOT already include a LAN_LOOPBACK object) the
LAN_LOOPBACK object in the PATH message with their own unicast IP
address.
Now, a SBM or a DSBM client can easily detect and discard the
duplicates by checking the contents of the LAN_LOOPBACK object (a
duplicate PATH message will list a device's own interface address
in the LAN_LOOPBACK object). Appendix B specifies the exact for-
mat of the LAN_LOOPBACK object.
- The model proposed by the Integrated Services working group
requires isolation of traffic flows from each other during their
transit across a network. The motivation for traffic flow separa-
tion is to provide Integrated Services flows protection from mis-
behaving flows and other best-effort traffic that share the same
path. The basic IEEE 802.3/Ethernet networks do not provide any
notion of traffic classes to discriminate among different flows
that request different services. However, IEEE 802.1p defines a
way for switches to differentiate among several "user_priority"
values encoded in packets representing different traffic classes
(see [IEEE802Q, IEEE8021p] for further details). The
user_priority values can be encoded either in native LAN packets
(e.g., in IEEE 802.5's FC octet) or by using an encapsulation
above the MAC layer (e.g., in the case of Ethernet, the
user_priority value assigned to each packet will be carried in
the frame header using the new, extended frame format defined by
IEEE 802.1Q [IEEE8021Q]. IEEE, however, makes no recommendations
about how a sender or network should use the user_priority
values. An accompanying document makes recommendations on the
usage of the user_priority values (see [Seaman97] for details).
Under the Integrated Services model, L3 (or higher) entities that
transmit traffic flows onto a L2 segment should perform per-flow
policing to ensure that the flows do not exceed their traffic
specification as specified during admission control. In addition,
L3 devices may label the frames in such flows with a
user_priority value to identify their service class.
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SBM (Subnet Bandwidth Manager) March, 1998
For the purpose of this discussion, we will refer to the
user_priority value carried in the extended frame header as a
"traffic class" of a packet. Under the ISSLL model, the L3 enti-
ties, that send traffic and that use the SBM protocol, may not
select the traffic class of outgoing packets. Instead, once a
sender sends a PATH message, downstream DSBMs will insert a new
traffic class object (TCLASS object) in the PATH message that
travels to the next L3 device (L3 NHOP for the PATH message). To
some extent, the TCLASS object contents are treated like the
ADSPEC object in the RSVP PATH messages. The L3 device that
receives the PATH message must remove and store the TCLASS object
as part of its PATH state for the session. Later, when the same
L3 device needs to forward a RSVP RESV message towards the origi-
nal sender, it must include the TCLASS object in the RESV mes-
sage. When the RESV message arrives at the original sender, it
must pass the user_priority value in the TCLASS object to its
local packet classifier (traffic control) so that subsequent,
outgoing data packets for this RSVP flow will have the
user_priority value included in the extended MAC header.
The format of the TCLASS object is specified in Appendix B. Note
that TCLASS and other SBM-specific objects are carried in a RSVP
message in addition to all the other, normal RSVP objects per RFC
2205.
In summary, use of TCLASS objects requires following additions to
the conventional RSVP message processing at DSBMs, SBMs, and DSBM
clients:
* When a DSBM receives a PATH message over a managed segment and
the PATH message does not include a TCLASS object, the DSBM
adds a TCLASS object to the PATH message before forwarding it.
The DSBM comes up with the appropriate user_priority value for
the TCLASS object according to some internal mapping of the
service classes. One possible set of internal mappings is pro-
posed as an example in an accompanying document [Seaman97].
* When SBM or DSBM receives a PATH or RESV message with a TCLASS
object over a managed segment in a L2 domain and needs to for-
ward it over a managed segment in the same L2 domain, it will
typically forward the message without changing the contents of
the TCLASS object. However, if the DSBM/SBM cannot support the
service class represented by the user_priority value specified
by the TCLASS object in the PATH message, it may change the
priority value in the TCLASS to a semantically "lower" service
value to reflect its capability.
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SBM (Subnet Bandwidth Manager) March, 1998
[NOTE: An accompanying document defines the int-serv mappings
over IEEE 802 networks [Seaman97] provides a precise definition
of user_priority values and describes how the user_priority
values are compared to determine "lower" of the two values or
the "lowest" among all the user_priority values.]
* When a DSBM receives a RESV message with a TCLASS object, it
may use the traffic class information (in addition to the usual
flowspec information in the RSVP message) for its own admission
control for the managed segment.
Note that this document does not specify the actual algorithm
or policy used for admission control. At one extreme, a DSBM
may use per-flow reservation request as specified by the
flowspec for a fine grain admission control. At the other
extreme, a DSBM may only consider the traffic class information
for a very coarse-grain admission control based on some static
allocation of link capacity for each traffic class. Any combi-
nation of the options represented by these two extremes may
also be used.
* When a DSBM client (residing at an L3 device such as a host or
an edge router) receives the TCLASS object in a PATH message
that it accepts over an interface, it should store the TCLASS
object as part of its PATH state for the interface. Later, when
the client forwards a RESV message for the same session on the
interface, the client must include the TCLASS object (unchanged
from what was received in the previous PATH message) in the
RESV message it forwards over the interface.
* When a DSBM client receives a TCLASS object in an incoming RESV
message over a managed segment and local admission control
succeeds for the session for the outgoing interface over the
managed segment, the client must pass the user_priority value
in the TCLASS object to its local packet classifier. This will
ensure that the data packets in the admitted RSVP flow that are
subsequently forwarded over the outgoing interface will contain
the appropriate value encoded in their frame header.
* When an L3 device receives a PATH or RESV message over a
managed segment in one L2 domain and it needs to forward the
PATH/RESV message over an interface outside that domain, the L3
device must remove the TCLASS object (along with LAN_NHOP,
RSVP_HOP_L2, and LAN_LOOPBACK objects in the case of the PATH
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SBM (Subnet Bandwidth Manager) March, 1998
message) before forwarding the PATH/RESV message. If the outgo-
ing interface is on a separate L2 domain, these objects may be
regenerated according to the processing rules applicable to
that interface.
5. Detailed Message Processing Rules
5.1. Additional Notes on Terminology
* An L2 device may have several interfaces with attached segments
that are part of the same L2 domain. A switch in a L2 domain is
an example of such a device. A device which has several inter-
faces may contain a SBM protocol entity that acts in different
capacities on each interface. For example, a SBM protocol entity
could act as a SBM on interface A, and act as a DSBM on interface
B.
* A SBM protocol entity on a layer 3 device can be a DSBM client,
and SBM, a DSBM, or none of the above (SBM transparent). Non-
transparent L3 devices can implement any combination of these
roles simultaneously. DSBM clients always reside at L3 devices.
* A SBM protocol entity residing at a layer 2 device can be a SBM,
a DSBM or none of the above (SBM transparent). A layer 2 device
will never host a DSBM client.
5.2. Use Of Reserved IP Multicast Addresses
As stated earlier, we require that the DSBM clients forward the RSVP
PATH messages to their DSBMs in a L2 domain before they reach the next
L3 hop in the path. RSVP PATH messages are addressed, according to
RFC-2205, to their destination address (which can be either an IP uni-
cast or multicast address). When a L2 device hosts a DSBM, a simple-
to-implement mechanism must be provided for the device to capture an
incoming PATH message and hand it over to the local DSBM agent without
requiring the L2 device to snoop for L3 RSVP messages.
In addition, DSBM clients need to know how to address SBM messages to
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SBM (Subnet Bandwidth Manager) March, 1998
the DSBM. For the ease of operation and to allow dynamic DSBM-client
binding, it should be possible to easily detect and address the exist-
ing DSBM on a managed segment.
To facilitate dynamic DSBM-client binding as well as to enable easy
detection and capture of PATH messages at L2 devices, we require that
a DSBM be addressed using a logical address rather than a physical
address. We make use of reserved IP multicast address(es) for the pur-
pose of communication with a DSBM. In particular, we require that
when a DSBM client or a SBM forwards a PATH message over a managed
segment, it is addressed to a reserved IP multicast address. Thus, a
DSBM on a L2 device needs to be configured in a way to make it easy to
intercept the PATH message and forward it to the local SBM protocol
entity. For example, this may involve simply adding a static entry in
the device's filtering database (FDB) for the corresponding MAC multi-
cast address to ensure the PATH messages get intercepted and are not
forwarded further without the DSBM intervention.
Similarly, a DSBM always sends the PATH messages over a managed seg-
ment using a reserved IP multicast address and, thus, the SBMs or DSBM
clients on the managed segments must simply be configured to intercept
messages addressed to the reserved multicast address on the appropri-
ate interfaces to easily receive PATH messages.
RSVP RESV messages continue to be unicast to the previous hop address
stored as part of the PATH state at each intermediate hop.
We define use of two reserved IP multicast addresses. We call these
the "AllSBM Address" and the "DSBMLogicalAddress". These are chosen
from the range of local multicast addresses, such that:
* They are not passed through layer 3 devices.
* They are passed transparently through layer 2 devices which are
SBM transparent.
* They are configured in the permanent database of layer 2 devices
which host SBMs or DSBMs, such that they are directed to the SBM
management entity in these devices. This obviates the need for
these devices to explicitly snoop for SBM related control pack-
ets.
* The two reserved addresses are 224.0.0.16 (DSBMLogicalAddress)
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SBM (Subnet Bandwidth Manager) March, 1998
and 224.0.0.17 (AllSBMAddress).
These addresses are used as described in the following table:
Type DSBMLogicaladdress AllSBMAddress
DSBM * Sends PATH messages * Monitors this address to detect
Client to this address the presence of a DSBM
* Monitors this address to
receive PATH messages
forwarded by the DSBM
SBM * Sends PATH messages * Monitors and sends on this
to this address address to participate in
election of the DSBM
* Monitors this address to
receive PATH messages
forwarded by the DSBM
DSBM * Monitors this address * Monitors and sends on this
for PATH messages to participate in election
directed to it of the DSBM
* Sends PATH messages to this
address
The L2 or MAC addresses corresponding to IP multicast addresses are
computed algorithmically using a reserved L2 address block (the high
order 24-bits are 00:00:5e). The Assigned Numbers RFC [RFC-1700] gives
additional details.
5.3. Layer 3 to Layer 2 Address Mapping
As stated earlier, DSBMs or DSBM clients residing at a L3 device must
include a LAN_NHOP_L2 address in the LAN_NHOP information so that L2
devices along the path of a PATH message do not need to separately
determine the mapping between the LAN_NHOP_L3 address in the LAN_NHOP
object and its corresponding L2 address (for example, using ARP).
For the purpose of such mapping at L3 devices, we assume a mapping
function called "map_address" that performs the necessary mapping:
L2ADDR object = map_addr(L3Addr)
We do not specify how the function is implemented; the implementation
may simply involve access to the local ARP cache entry or may require
performing an ARP function. The function returns a L2ADDR object that
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SBM (Subnet Bandwidth Manager) March, 1998
need not be interpreted by an L3 device and can be treated as an
opaque object. The format of the L2ADDR object is specified in Appen-
dix B.
5.4. Raw vs. UDP Encapsulation
We assume that the DSBMs, DSBM clients, and SBMs use only raw IP for
encapsulating RSVP messages that are forwarded onto a L2 domain.
Thus, when a SBM protocol entity on a L3 device forwards a RSVP mes-
sage onto a L2 segment, it will only use RAW IP encapsulation.
5.5. The Forwarding Rules
The message processing and forwarding rules will be described in the
context of the sample network illustrated in Figure 2.
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SBM (Subnet Bandwidth Manager) March, 1998
Figure 2 - A sample network or L2 domain consisting of switched and
shared L2 segments
..........
.
+------+ . +------+ seg A +------+ seg C +------+ seg D +------+
| H1 |_______| R1 |_________| S1 |_________| S2 |_________| H2 |
| | . | | | | | | | |
+------+ . +------+ +------+ +------+ +------+
. | /
1.0.0.0 . | /
. |___ /
. seg B | / seg E
.......... | /
2.0.0.0 | /
+-----------+
| S3 |
| |
+-----------+
|
|
|
|
seg F | .................
------------------------------ .
| | | .
+------+ +------+ +------+ . +------+
| H3 | | H4 | | R2 |____________| H5 |
| | | | | | . | |
+------+ +------+ +------+ . +------+
.
. 3.0.0.0
.................
Figure 2 illustrates a sample network topology consisting of three IP
subnets (1.0.0.0, 2.0.0.0, and 3.0.0.0) interconnected using two
routers. The subnet 2.0.0.0 is an example of a L2 domain consisting of
switches, hosts, and routers interconnected using switched segments
and a shared L2 segment. The sample network contains the following
devices:
Device Type SBM Type
H1, H5 Host (layer 3) SBM Transparent
H2-H4 Host (layer 3) DSBM Client
R1 Router (layer 3) SBM
R2 Router (layer 3) DSBM for segment F
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SBM (Subnet Bandwidth Manager) March, 1998
S1 Switch (layer 2) DSBM for segments A, B
S2 Switch (layer 2) DSBM for segments C, D, E
S3 Switch (layer 2) SBM
The following paragraphs describe the rules, which each of these dev-
ices should use to forward PATH messages (rules apply to PATH_TEAR
messages as well). They are described in the context of the general
network illustrated above. While the examples do not address every
scenario, they do address most of the interesting scenarios. Excep-
tions can be discussed separately.
The forwarding rules are applied to received PATH messages (routers
and switches) or originating PATH messages (hosts), as follows:
1. Determine the interface(s) on which to forward the PATH message
using standard forwarding rules:
* If there is a LAN_LOOPBACK object in the PATH message, and it
carries the address of this device, silently discard the message.
(See the section below on "Additional notes on forwarding the
PATH message onto a managed segment).
* Layer 3 devices use the RSVP session address and perform a rout-
ing lookup to determine the forwarding interface(s).
* Layer 2 devices use the LAN_NHOP_L2 address in the LAN_NHOP
information and MAC forwarding tables to determine the forwarding
interface(s). (See the section below on "Additional notes on for-
warding the PATH message onto a managed segment")
2. For each forwarding interface:
* If the device is a layer 3 device, determine whether the inter-
face is on a managed segment managed by a DSBM, based on the
presence or absence of I_AM_DSBM messages. If the interface is
not on a managed segment, strip out RSVP_HOP_L2, LAN_NHOP,
LAN_LOOPBACK, and TCLASS objects (if present), and forward to
the unicast or multicast destination.
(Note that the RSVP Class Numbers for these new objects are
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SBM (Subnet Bandwidth Manager) March, 1998
chosen so that if an RSVP message includes these objects, the
nodes that are RSVP-aware, but do not participate in the SBM
protocol, will ignore and silently discard such objects.)
* If the device is a layer 2 device or it is a layer 3 device
*and* the interface is on a managed segment, proceed to rule
#3.
3. Forward the PATH message onto the managed segment:
* If the device is a layer 3 device, insert LAN_NHOP address
objects, a LAN_LOOPBACK, and a RSVP_HOP_L2 object into the PATH
message. The LAN_NHOP objects carry the LAN_NHOP_L3 and
LAN_NHOP_L2 addresses of the next layer 3 hop. The RSVP_HOP_L2
object carries the device's own L2 address, and the
LAN_LOOPBACK object contains the IP address of the outgoing
interface.
An L3 device should use the map_addr() function described ear-
lier to obtain an L2 address corresponding to an IP address.
* If the device hosts the DSBM for the segment to which the for-
warding interface is attached, do the following:
- Retrieve the PHOP information from the standard RSVP HOP
object in the PATH message, and store it. This will be used
to route RESV messages back through the L2 network. If the
PATH message arrived over a managed segment, it will also
contain the RSVP_HOP_L2 object; then retrieve and store also
the previous hop's L2 address in the PATH state.
- Copy the IP address of the forwarding interface (layer 2 dev-
ices must also have IP addresses) into the standard RSVP HOP
object and the L2 address of the forwarding interface into
the RSVP_HOP_L2 object.
- If the PATH message received does not contain the TCLASS
object, insert a TCLASS object. The user_priority value
inserted in the TCLASS object is based on service mappings
internal to the device that are configured according to the
guidelines listed in [Seaman97]. If the message already
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SBM (Subnet Bandwidth Manager) March, 1998
contains the TCLASS object, the user_priority value may be
changed based again on the service mappings internal to the
device.
* If the device is a layer 3 device and hosts a SBM for the seg-
ment to which the forwarding interface is attached, it *is
required* to retrieve and store the PHOP info.
If the device is a layer 2 device and hosts a SBM for the seg-
ment to which the forwarding interface is attached, it is *not*
required to retrieve and store the PHOP info. If it does not do
so, the SBM must leave the standard RSVP HOP object and the
RSVP_HOP_L2 objects in the PATH message intact and it will not
receive RESV messages.
If the SBM on a L2 device chooses to overwrite the RSVP HOP and
RSVP_HOP_L2 objects with the IP and L2 addresses of its for-
warding interface, it will receive RESV messages. In this case,
it must store the PHOP address info received in the standard
RSVP_HOP field and RSVP_HOP_L2 objects of the incident PATH
message.
In both the cases mentioned above (L2 or L3 devices), the SBM
must forward the TCLASS object in the received PATH message
unchanged.
* Copy the IP address of the forwarding interface into the
LAN_LOOPBACK object, unless the SBM protocol entity is a DSBM
reflecting a PATH message back onto the incident interface.
(See the section below on "Additional notes on forwarding a
PATH message onto a managed segment").
* If the SBM protocol entity is the DSBM for the segment to which
the forwarding interface is attached, it must send the PATH
message to the AllSBMAddress.
* If the SBM protocol entity is a SBM or a DSBM Client on the
segment to which the forwarding interface is attached, it must
send the PATH message to the DSBMLogicalAddress.
5.6.1. Additional notes on forwarding a PATH message onto a
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SBM (Subnet Bandwidth Manager) March, 1998
managed segment
Rule #1 states that normal IEEE 802.1D forwarding rules should be
used to determine the interfaces on which the PATH message should
be forwarded. In the case of data packets, standard forwarding
rules at a L2 device dictate that the packet should not be for-
warded on the interface from which it was received. However, in
the case of a DSBM that receives a PATH message over a managed
segment, the following exception applies:
E1. If the address in the LAN_NHOP object is a unicast address,
consult the filtering database (FDB) to determine whether
the destination address is listed on the same interface
over which the message was received. If yes, follow the
rule below on "reflecting a PATH message back onto an
interface" described below; otherwise, proceed with the
rest of the message processing as usual.
E2. If there are members of the multicast group address (speci-
fied by the addresses in the LAN_NHOP object), on the seg-
ment from which the message was received, the message
should be forwarded back onto the interface from which it
was received and follow the rule on "reflecting a PATH mes-
sage back onto an interface" described below.
*** Reflecting a PATH message back onto an interface ***
Under the circumstances described above, when a DSBM reflects
the PATH message back onto an interface over which it was
received, it must address it using the AllSBMAddress.
Since it is possible for a DSBM to reflect a PATH message back
onto the interface from which it was received, precautions must
be taken to avoid looping these messages indefinitely. The
LAN_LOOPBACK object addresses this issue. All SBM protocol enti-
ties (except DSBMs reflecting a PATH message) overwrite the
LAN_LOOPBACK object in the PATH message with the IP address of
the outgoing interface. DSBMs which are reflecting a PATH mes-
sage, leave the LAN_LOOPBACK object unchanged. Thus, SBM proto-
col entities will always be able to recognize a reflected multi-
cast message by the presence of their own address in the
LAN_LOOPBACK object. These messages should be silently dis-
carded.
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SBM (Subnet Bandwidth Manager) March, 1998
5.7. Applying the Rules -- Unicast Session
Let's see how the rules are applied in the general network illus-
trated previously (see Figure 2).
Assume that H1 is sending a PATH for a unicast session for which
H5 is the receiver. The following PATH message is composed by H1:
RSVP Contents
RSVP session IP address IP address of H5 (3.0.0.35)
Sender Template IP address of H1 (1.0.0.11)
PHOP IP address of H1 (1.0.0.11)
RSVP_HOP_L2 n/a (H1 is not sending onto a managed
segment)
LAN_NHOP n/a (H1 is not sending onto a managed
segment)
LAN_LOOPBACK n/a (H1 is not sending onto a managed
segment)
IP Header
Source address IP address of H1 (1.0.0.11)
Destn address IP addr of H5 (3.0.0.35, assuming raw mode &
router alert)
MAC Header
Destn address The L2 addr corresponding to R1 (determined
by map_addr() and routing tables at H1)
Since H1 is not sending onto a managed segment, the PATH message
is composed and forwarded according to standard RSVP processing
rules.
Upon receipt of the PATH message, R1 composes and forwards a PATH
message as follows:
RSVP Contents
RSVP session IP address IP address of H5
Sender Template IP address of H1
PHOP IP address of R1 (2.0.0.1)
(seed the return path for RESV messages)
RSVP_HOP_L2 L2 address of R1
LAN_NHOP LAN_NHOP_L3 (2.0.0.2) and
LAN_NHOP_L2 address of R2 (L2ADDR)
(this is the next layer 3 hop)
LAN_LOOPBACK IP address of R1 (2.0.0.1)
IP Header
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SBM (Subnet Bandwidth Manager) March, 1998
Source address IP address of H1
Destn address DSBMLogical IP address (224.0.0.16)
MAC Header
Destn address DSBMLogical MAC address
* R1 does a routing lookup on the RSVP session address, to
determine the IP address of the next layer 3 hop, R2.
* It determines that R2 is accessible via seg A and that seg A
is managed by a DSBM, S1.
* Therefore, it concludes that it is sending onto a managed
segment, and composes LAN_NHOP objects to carry the layer 3
and layer 2 next hop addresses. To compose the LAN_NHOP
L2ADDR object, it invokes the L3L2 address mapping function
("map_address") to find out the MAC address for the next hop
L3 device, and then inserts a LAN_NHOP_L2ADDR object (that
carries the MAC address) in the message.
* Since R1 is not the DSBM for seg A, it sends the PATH message
to the DSBMLogicalAddress.
Upon receipt of the PATH message, S1 composes and forwards a PATH
message as follows:
RSVP Contents
RSVP session IP address IP address of H5
Sender Template IP address of H1
PHOP IP addr of S1 (seed the return path for RESV
messages)
RSVP_HOP_L2 L2 address of S1
LAN_NHOP LAN_NHOP_L3 (IP) and LAN_NHOP_L2
address of R2
(layer 2 devices do not modify the LAN_NHOP)
LAN_LOOPBACK IP addr of S1
IP Header
Source address IP address of H1
Destn address AllSBMIPaddr (224.0.0.17, since S1 is the
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SBM (Subnet Bandwidth Manager) March, 1998
DSBM for seg B).
MAC Header
Destn address All SBM MAC address (since S1 is the DSBM for
seg B).
* S1 looks at the LAN_NHOP address information to determine the
L2 address towards which it should forward the PATH message.
* From the bridge forwarding tables, it determines that the L2
address is reachable via seg B.
* S1 inserts the RSVP_HOP_L2 object and overwrites the RSVP HOP
object (PHOP) with its own addresses.
* Since S1 is the DSBM for seg B, it addresses the PATH message
to the AllSBMAddress.
Upon receipt of the PATH message, S3 composes and forwards a
PATH message as follows:
RSVP Contents
RSVP session IP addr IP address of H5
Sender Template IP address of H1
PHOP IP addr of S3 (seed the return
path for RESV messages)
RSVP_HOP_L2 L2 address of S3
LAN_NHOP LAN_NHOP_L3 (IP) and
LAN_NHOP_L2 (MAC) address of R2
(L2 devices don't modify LAN_NHOP)
LAN_LOOPBACK IP address of S3
IP Header
Source address IP address of H1
Destn address DSBMLogical IP addr (since S3 is
not the DSBM for seg F)
MAC Header
Destn address DSBMLogical MAC address
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SBM (Subnet Bandwidth Manager) March, 1998
* S3 looks at the LAN_NHOP address information to determine the
L2 address towards which it should forward the PATH message.
* From the bridge forwarding tables, it determines that the L2
address is reachable via segment F.
* It has discovered that R2 is the DSBM for segment F. It
therefore sends the PATH message to the DSBMLogicalAddress.
* Note that S3 may or may not choose to overwrite the PHOP
objects with its own IP and L2 addresses. If it does so, it
will receive RESV messages. In this case, it must also store
the PHOP info received in the incident PATH message so that
it is able to forward the RESV messages on the correct path.
Upon receipt of the PATH message, R2 composes and forwards a PATH
message as follows:
RSVP Contents
RSVP session IP addr IP address of H5
Sender Template IP address of H1
PHOP IP addr of R2 (seed the return path for RESV
messages)
RSVP_HOP_L2 Removed by R2 (R2 is not sending onto a
managed segment)
LAN_NHOP Removed by R2 (R2 is not sending onto a
managed segment)
IP Header
Source address IP address of H1
Destn address IP address of H5, the RSVP session address
MAC Header
Destn address L2 addr corresponding to H5, the next
layer 3 hop
* R2 does a routing lookup on the RSVP session address, to
determine the IP address of the next layer 3 hop, H5.
* It determines that H5 is accessible via a segment for which
there is no DSBM (not a managed segment).
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SBM (Subnet Bandwidth Manager) March, 1998
* Therefore, it removes the LAN_NHOP and RSVP_HOP_L2 objects
and places the RSVP session address in the destination
address of the IP header. It places the L2 address of the
next layer 3 hop, into the destination address of the MAC
header and forwards the PATH message to H5.
5.8. Applying the Rules - Multicast Session
The rules described above also apply to multicast (m/c) sessions.
For the purpose of this discussion, it is assumed that layer 2
devices track multicast group membership on each port individu-
ally. Layer 2 devices which do not do so, will merely generate
extra multicast traffic. This is the case for L2 devices which do
not implement multicast filtering or GARP/GMRP capability.
Assume that H1 is sending a PATH for an m/c session for which H3
and H5 are the receivers. The rules are applied as they are in the
unicast case described previously, until the PATH message reaches
R2, with the following exception. The RSVP session address and the
LAN_NHOP carry the destination m/c addresses rather than the uni-
cast addresses carried in the unicast example.
Now let's look at the processing applied by R2 upon receipt of the
PATH message. Recall that R2 is the DSBM for segment F. Therefore,
S3 will have forwarded its PATH message to the DSBMLogicalAddress,
to be picked up by R2. The PATH message will not have been seen by
H3 (one of the m/c receivers), since it monitors only the
AllSBMAddress, not the DSBMLogicalAddress for incoming PATH mes-
sages. We rely on R2 to reflect the PATH message back onto seg f,
and to forward it to H5. R2 forwards the following PATH message
onto seg f:
RSVP Contents
RSVP session addr m/c session address
Sender Template IP address of H1
PHOP IP addr of R2 (seed the return path for
RESV messages)
RSVP_HOP_L2 L2 addr of R2
LAN_NHOP m/c session address and corresponding L2 address
LAN_LOOPBACK IP addr of S3 (DSBMs reflecting a PATH
message don't modify this object)
IP Header
Source address IP address of H1
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SBM (Subnet Bandwidth Manager) March, 1998
Destn address AllSBMIP address (since R2 is the DSBM for seg F)
MAC Header
Destn address AllSBMMAC address (since R2 is the
DSBM for seg F)
Since H3 is monitoring the All SBM Address, it will receive the
PATH message reflected by R2. Note that R2 violated the standard
forwarding rules here by sending an incoming message back onto the
interface from which it was received. It protected against loops
by leaving S3's address in the LAN_LOOPBACK object unchanged.
R2 forwards the following PATH message on to H5:
RSVP Contents
RSVP session addr m/c session address
Sender Template IP address of H1
PHOP IP addr of R2 (seed the return path for RESV
messages)
RSVP_HOP_L2 Removed by R2 (R2 is not sending onto a
managed segment)
LAN_NHOP Removed by R2 (R2 is not sending onto a
managed segment)
LAN_LOOPBACK Removed by R2 (R2 is not sending onto a
managed segment)
IP Header
Source address IP address of H1
Destn address m/c session address
MAC Header
Destn address MAC addr corresponding to the m/c
session address
* R2 determines that there is an m/c receiver accessible via a
segment for which there is no DSBM. Therefore, it removes the
LAN_NHOP and RSVP_HOP_L2 objects and places the RSVP session
address in the destination address of the IP header. It
places the corresponding L2 address into the destination
address of the MAC header and multicasts the message towards
H5.
5.9. Merging Traffic Class objects
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SBM (Subnet Bandwidth Manager) March, 1998
When a DSBM client receives TCLASS objects from different senders
(different PATH messages) in the same RSVP session and needs to
combine them for sending back a single RESV message (as in a
wild-card style reservation), the DSBM client should use the
semantically "lowest" user_priority value among the values
received in TCLASS objects of the PATH messages.
Similarly, when a SBM or DSBM needs to merge RESVs from different
next hops at a merge point, it should merge the TCLASS values in
the incoming RESVs to the semantically "lowest" user_priority
value among those received.
[NOTE: As stated earlier, an accompanying document defines the
int-serv mappings over IEEE 802 networks [Seaman97] provides a
precise definition of user_priority values and describes how the
priority values are compared to determine semantically "lower" of
the two values or the semantically "lowest" among all the
user_priority values.]
5.10. Operation of SBM Transparent Devices
We previously defined SBM Transparent devices. Since no SBM tran-
sparent devices were illustrated in the example provided, we will
describe the operation of these in the following paragraph.
SBM transparent devices are unaware of the entire SBM/DSBM proto-
col. They do not intercept messages addressed to either of the SBM
related local group addresses (the DSBMLogicalAddrss and the
ALLSBMAddress), but instead, pass them through. As a result, they
do not divide the DSBM election scope, they do not explicitly par-
ticipate in routing of PATH or RESV messages, and they do not par-
ticipate in admission control. They are entirely transparent with
respect to SBM operation.
According to the definitions provided, physical segments intercon-
nected by SBM transparent devices are considered a single managed
segment. Therefore, DSBMs must perform admission control on such
managed segments, with limited knowledge of the segment's topol-
ogy. In this case, the network administrator should configure the
DSBM for each managed segment, with some reasonable approximation
of the segment's capacity. A conservative policy would configure
the DSBM for the lowest capacity route through the managed seg-
ment. A liberal policy would configure the DSBM for the highest
capacity route through the managed segment. A network administra-
tor will likely choose some value between the two, based on the
level of guarantee required and some knowledge of likely traffic
patterns.
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SBM (Subnet Bandwidth Manager) March, 1998
This document does not specify the configuration mechanism or the
choice of a policy.
5.11. Operation of SBMs Which are NOT DSBMs
In the example illustrated, S3 hosts a SBM, but the SBM on S3 did
not win the election to act as DSBM on any segment. One might ask
what purpose such a SBM protocol entity serves. Such SBMs actually
provide two useful functions. First, the additional SBMs remain
passive in the background for fault tolerance. They listen to the
periodic announcements from the current DSBM for the managed seg-
ment (Appendix A describes this in more detail) and step in to
elect a new DSBM when the current DSBM fails or ceases to be
operational for some reason. Second, such SBMs also provide the
important service of dividing the election scope and reducing the
size and complexity of managed segments. For example, consider the
sample topology in Figure 3 again. the device S3 contains an SBM
that is not a DSBM for any f the segments, B, E, or F, attached to
it. However, if the SBM protocol entity on S3 was not present,
ssegments B and F would not be separate segments from the point of
view of the SBM protocol. Instead, they would constitute a single
managed segment, managed by a single DSBM. Because the SBM entity
on S3 divides the election scope, seg B and seg F are each
managed by separate DSBMs. Each of these segments have a trivial
topology and a well defined capacity. As a result, the DSBMs for
these segments do not need to perform admission control based on
approximations (as would be the case if S3 were SBM transparent).
Note that, SBM protocol entities which are not DSBMs, are not
required to overwrite the PHOP in incident PATH messages with
their own address. This is because it is not necessary for RESV
messages to be routed through these devices. RESV messages are
only required to be routed through the correct sequence of DSBMs.
SBMs may not process RESV messages that do pass through them,
other than to forward them towards their destination address,
using standard forwarding rules.
SBM protocol entities which are not DSBMs are required to
overwrite the address in the LAN_LOOPBACK object with their own
address, in order to avoid looping multicast messages. However, no
state need be stored.
6. Inter-Operability Considerations
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SBM (Subnet Bandwidth Manager) March, 1998
There are a few interesting inter-operability issues related to
the deployment of a DSBM-based admission control method in an
environment consisting of network nodes with and without RSVP
capability. In the following, we list some of these scenarios and
explain how SBM-aware clients and nodes can operate in those
scenarios:
6.1. An L2 domain with no RSVP capability.
It is possible to envisage L2 domains that do not use RSVP signal-
ing for requesting resource reservations, but, instead, use some
other (e.g., SNMP or static configuration) mechanism to reserve
bandwidth at a particular network device such as a router. In that
case, the question is how does a DSBM-based admission control
method work and interoperate with the non-RSVP mechanism. The
SBM-based method does not attempt to provide an admission control
solution for such an environment. The SBM-based approach is part
of an end2end signaling approach to establish resource reserva-
tions and does not attempt to provide a solution for SNMP-based
configuration scenario.
As stated earlier, the SBM-based approach can, however, co-exist
with any other, non-RSVP bandwidth allocation mechanism as long as
resources being reserved are either partitioned statically between
the different mechanisms or are resolved dynamically through a
common bandwidth allocator so that there is no over-commitment of
the same resource.
6.2. An L2 domain with SBM-transparent L2 Devices.
This scenario has been addressed earlier in the document. The
SBM-based method is designed to operate in such an environment.
When SBM-transparent L2 devices interconnect SBM-aware devices,
the resulting managed segment is a combination of one or more phy-
sical segments and the DSBM for the managed segment may not be as
efficient in allocating resources as it would if all L2 devices
were SBM-aware.
6.3. An L2 domain on which some RSVP-based senders are not DSBM
clients.
All senders that are sourcing RSVP-based traffic flows onto a
managed segment MUST be SBM-aware and participate in the SBM
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SBM (Subnet Bandwidth Manager) March, 1998
protocol. Use of the standard, non-SBM version of RSVP may result
in over-allocation of resources, as such use bypasses the resource
management function of the DSBM. All other senders (i.e., senders
that are not sending streams subject to RSVP admission control)
should be elastic applications that send traffic of lower priority
than the RSVP traffic, and use TCP-like congestion avoidance
mechanisms.
All DSBMs, SBMs, or DSBM clients on a managed segment (a segment
with a currently active DSBM) must not accept PATH messages from
senders that are not SBM-aware. PATH messages from such devices
can be easily detected by SBMs and DSBM clients as they would not
be multicast to the ALLSBMAddress (in case of SBMs and DSBM
clients) or the DSBMLogicalAddress (in case of DSBMs).
6.4. A non-SBM router that interconnects two DSBM-managed L2
domains.
Multicast SBM messages (e.g., election and PATH messages) have
local scope and are not intended to pass between the two domains.
A correctly configured non-SBM router will not pass such messages
between the domains. A broken router implementation that does so
may cause incorrect operation of the SBM protocol and consequent
over- or under-allocation of resources.
6.5. Interoperability with RSVP clients that use UDP encapsulation
and are not capable of receiving/sending RSVP messages using
RAW_IP
This document stipulates that DSBMs, DSBM clients, and SBMs use
only raw IP for encapsulating RSVP messages that are forwarded
onto a L2 domain. RFC-2205 (the RSVP Proposed Standard) includes
support for both raw IP and UDP encapsulation. Thus, a RSVP node
using only the UDP encapsulation will not be able to interoperate
with the DSBM unless DSBM accepts and supports UDP encapsulated
RSVP messages.
7. Guidelines for Implementors
In the following, we provide guidelines for implementors on dif-
ferent aspects of the implementation of the SBM-based admission
control procedure including suggestions for DSBM initialization,
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SBM (Subnet Bandwidth Manager) March, 1998
etc.
7.1. DSBM Initialization
As stated earlier, DSBM initialization includes configuration of
maximum bandwidth that can be reserved on a managed segment under
its control. We suggest the following guideline.
In the case of a managed segment consisting of L2 devices inter-
connected by a single shared segment, DSBM entities on such dev-
ices should assume the bandwidth of the interface as the total
link bandwidth. In the case of a DSBM located in a L2 switch, it
might additionally need to be configured with an estimate of the
device's switching capacity if that is less than the link
bandwidth, and possibly with some estimate of the buffering
resources of the switch (see [Ghanwani98] for the architectural
model assumed for L2 switches). Given the total link bandwidth,
the DSBM may be further configured to limit the maximum amount of
bandwidth for RSVP-enabled flows to ensure spare capacity for
best-effort traffic.
7.2. Operation of DSBMs in Different L2 Topologies
Depending on a L2 topology, a DSBM may be called upon to manage
resources for one or more segments and the implementors must bear
in mind efficiency implications of the use of DSBM in different L2
topologies. Trivial L2 topologies consist of a single "physical
segment". In this case, the 'managed segment' is equivalent to a
single segment. Complex L2 topologies may consist of a number of
'physical segments', separated by SBM-transparent L2 switches.
Admission control on such an L2 extended segment can be performed
from a single pool of resources, similar to a single shared seg-
ment, from the point of view of a single DSBM.
This configuration compromises the efficiency with which the DSBM
can allocate resources. This is because the single DSBM is
required to make admission control decisions for all reservation
requests within the L2 topology, with no knowledge of the actual
physical segments affected by the reservation.
We can realize improvements in the efficiency of resource alloca-
tion by subdividing the complex segment into a number of managed
segments, each managed by their own DSBM. In this case, each DSBM
manages a managed segment having a relatively simple topology.
Since managed segments are simpler, the DSBM can be configured
with a more accurate estimate of the resources available for all
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SBM (Subnet Bandwidth Manager) March, 1998
reservations in the managed segment. In the ultimate configura-
tion, each physical segment is a managed segment and is managed by
its own DSBM. We make no assumption about the number of managed
segments but state, simply, that in complex L2 topologies, the
efficiency of resource allocation improves as the granularity of
managed segments increases.
8. Security Considerations
The message formatting and usage rules described in this note
raise some security issues, but they are no different than the
ones raised by the use of RSVP and Integrated Services; the need
to control and authenticate access to enhanced qualities of ser-
vice. This requirement is discussed further in [RFC-2205], [RFC-
2211], and [RFC-2212]. [Baker97] describes the mechanism used to
protect the integrity of RSVP messages carrying the information
described here. A SBM implementation should satisfy these require-
ments and provide the suggested mechanisms just as though it were
a conventional RSVP implementation and also protect the addi-
tional, SBM-specific objects in a message.
In addition, it is also necessary to authenticate DSBM candidates
during the election process, and a mechanism based on a shared
secret among the DSBM candidates may be used. The mechanism
defined in [Baker97] should be used.
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SBM (Subnet Bandwidth Manager) March, 1998
9. References
[RFC-2205] R. Braden, L. Zhang, S. Berson, S. Herzog, S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
Specification ", RFC-2205, September 1997.
[Baker97] F. Baker., "RSVP Cryptographic Authentication", draft-
ietf-rsvp-md5-05.txt, August 1997.
[RFC-2206] F. Baker, J. Krawczyk, "RSVP Management Information
Base", RFC 2206, September 1997.
[RFC-2211] J. Wroclawski, "Specification of the Controlled-Load
Network Element Service", RFC-2211, September 1997.
[RFC-2212] S. Shenker, C. Partridge, R. Guerin, "Specification of
Guaranteed Quality of Service", RFC-2212, September 1997.
[RFC-2215] S. Shenker, J. Wroclawski, "General Characterization
Parameters for Integrated Service Network Elements", RFC-2215,
September 1997.
[RFC-2210] J. Wroclawski, "The Use of RSVP with IETF Integrated
Services", RFC 2210, September 1997.
[RFC-2213] F. Baker, J. Krawczyk, "Integrated Services Management
Information Base", RFC 2213, September 1997.
[Ghanwani98] A. Ghanwani, W. Pace, V. Srinivasan, A.Smith,
M.Seaman "A Framework for Providing Integrated Services Over
Shared and Switched LAN Technologies", Internet Draft <draft-
ietf-issll-is802-framework-04.txt>, March 1998.
[Seaman97] M. Seaman, A. Smith, E. Crawley, "Integrated Service
Mappings on IEEE 802 Networks", Internet Draft <draft-ietf-issll-
is802-svc-mapping-03.txt>, November 1997.
[IEEE802Q] "IEEE Standards for Local and Metropolitan Area Net-
works: Virtual Bridged Local Area Networks", Draft Standard
P802.1Q/D9, February 20, 1998.
[IEEEP8021p] "Information technology - Telecommunications and
information exchange between systems - Local and metropolitan area
networks - Common specifications - Part 3: Media Access Control
(MAC) Bridges: Revision (Incorporating IEEE P802.1p: Traffic Class
Expediting and Dynamic Multicast Filtering)", ISO/IEC Final CD
15802-3 IEEE P802.1D/D15, November 24, 1997.
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SBM (Subnet Bandwidth Manager) March, 1998
[IEEE8021D] "MAC Bridges", ISO/IEC 10038, ANSI/IEEE Std 802.1D-
1993.
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SBM (Subnet Bandwidth Manager) March, 1998
APPENDIX A
DSBM Election Algorithm
A.1. Introduction
To simplify the rest of this discussion, we will assume that there
is a single DSBM for the entire L2 domain (i.e., assume a shared
L2 segment for the entire L2 domain). Later, we will discuss how a
DSBM is elected for a half-duplex or full-duplex switched segment.
To allow for quick recovery from the failure of a DSBM, we assume
that additional SBMs may be active in a L2 domain for fault toler-
ance. When more than one SBM is active in a L2 domain, the SBMs
use an election algorithm to elect a DSBM for the L2 domain. After
the DSBM is elected and is operational, other SBMs remain passive
in the background to step in to elect a new DSBM when necessary.
The protocol for electing and discovering DSBM is called the "DSBM
election protocol" and is described in the rest of this Appendix.
A.1.1. How a DSBM Client Detects a Managed Segment
Once elected, a DSBM periodically multicasts an I_AM_DSBM message
on the AllSBMAddress to indicate its presence. The message is sent
every period (e.g., every 5 seconds) according to the
DSBMRefreshInterval timer value (a configuration parameter).
Absence of such a message over a certain time interval (called
"DSBMDeadInterval"; another configuration parameter typically set
to a multiple of RefreshInterval) indicates that the DSBM has
failed or terminated and triggers another round of the DSBM elec-
tion. The DSBM clients always listen for periodic DSBM advertise-
ments. The advertisement includes the unicast IP address of the
DSBM (DSBMAddress) and DSBM clients send their PATH/RESV (or
other) messages to the DSBM. When a DSBM client detects the
failure of a DSBM, it waits for a subsequent I_AM_DSBM advertise-
ment before resuming any communication with the DSBM. During the
period when a DSBM is not present, a DSBM client may forward out-
going PATH messages using the standard RSVP forwarding rules.
The exact message formats and addresses used for communication
with (and among) SBM(s) are described in Appendix B.
A.2. Overview of the DSBM Election Procedure
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When a SBM first starts up, it listens for incoming DSBM adver-
tisements for some period to check whether a DSBM already exists
in its L2 domain. If one already exists (and no new election is in
progress), the new SBM stays quiet in the background until an
election of DSBM is necessary. All messages related to the DSBM
election and DSBM advertisements are always sent to the AllSBMAd-
dress.
If no DSBM exists, the SBM initiates the election of a DSBM by
sending out a DSBM_WILLING message that lists its IP address as a
candidate DSBM and its "SBM priority". Each SBM is assigned a
priority to determine its relative precedence. When more than one
SBM candidate exists, the SBM priority determines who gets to be
the DSBM based on the relative priority of candidates. If there is
a tie based on the priority value, the tie is broken using the IP
addresses of tied candidates (one with the higher IP address in
the lexicographic order wins). The details of the election proto-
col start in Section A.4.
A.2.1 Summary of the Election Algorithm
For the purpose of the algorithm, a SBM is in one of the four
states (Idle, DetectDSBM, ElectDSBM, I_AM_DSBM).
A SBM (call it X) starts up in the DetectDSBM state and waits for
a ListenInterval for incoming I_AM_DSBM (DSBM advertisement) or
DSBM_WILLING messages. If an I_AM_DSBM advertisement is received
during this state, the SBM notes the current DSBM (its IP address
and priority) and enters the Idle state. If a DSBM_WILLING message
is received from another SBM (call it Y) during this state, then X
enters the ElectDSBM state. Before entering the new state, X first
checks to see whether it itself is a better candidate than Y and,
if so, sends out a DSBM_WILLING message and then enters the
ElectDSBM state.
When a SBM (call it X) enters the ElectDSBM state, it sets a timer
(called ElectionIntervalTimer that is typically set to a value at
least equal to the DeadIntervalTimer value) to wait for the elec-
tion to finish and to discover who is the best candidate. In this
state, X keeps track of the best (or better) candidate seen so far
(including itself). Whenever it receives another DSBM_WILLING mes-
sage, it updates its notion of the best (or better) candidate
based on the priority (and tie-breaking) criterion. During the
ElectionInterval, X sends out a DSBM_WILLING message every
RefreshInterval to (re)assert its candidacy.
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SBM (Subnet Bandwidth Manager) March, 1998
At the end of the ElectionInterval, X checks whether it is the
best candidate so far. If so, it declares itself to be the DSBM
(by sending out the I_AM_DSBM advertisement) and enters the
I_AM_DSBM state; otherwise, it decides to wait for the best candi-
date to declare itself the winner. To wait, X re-initializes its
ElectDSBM state and continues to wait for another round of elec-
tion (each round lasts for an ElectionTimerInterval duration).
A SBM is in Idle state when no election is in progress and the
DSBM is already elected (and happens to be someone else). In this
state, it listens for incoming I_AM_DSBM advertisements and uses
a DSBMDeadInterval timer to detect the failure of DSBM. Every time
the advertisement is received, the timer is restarted. If the
timer fires, the SBM goes into the DetectDSBM state to prepare to
elect the new DSBM. If a SBM receives a DSBM_WILLING message from
the current DSBM in this state, the SBM enters the ElectDSBM state
after sending out a DSBM_WILLING message (to announce its own
candidacy).
In the I_AM_DSBM state, the DSBM sends out I_AM_DSBM advertise-
ments every refresh interval. If the DSBM wishes to shut down
(gracefully terminate), it sends out a DSBM_WILLING message (with
SBM priority value set to zero) to initiate the election pro-
cedure. The priority value zero effectively removes the outgoing
DSBM from the election procedure and makes way for the election of
a different DSBM.
A.3. Recovering from DSBM Failure
When a DSBM fails (DSBMDeadInterval timer fires), all the SBMs
enter the ElectDSBM state and start the election process.
At the end of the ElectionInterval, the elected DSBM sends out an
I_AM_DSBM advertisement and the DSBM is then operational.
A.4. DSBM Advertisements
The I_AM_DSBM advertisement contains the following information:
1. DSBM address information -- contains the IP and L2 addresses
of the DSBM and its SBM priority (a configuration parameter
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SBM (Subnet Bandwidth Manager) March, 1998
-- priority specified by a network administrator). The prior-
ity value is used to choose among candidate SBMs during the
election algorithm. Higher integer values indicate higher
priority and the value is in the range 0..255. The value zero
indicates that the SBM is not eligible to be the DSBM. The
IP address is required and used for breaking ties. The L2
address is for the interface of the managed segment.
2. refresh interval -- contains the value of the refresh inter-
val in seconds. Value zero indicates the parameter has been
omitted in the message. Receivers may substitute their own
default value in this case.
3. SBMDeadInterval -- contains the value of the SBMDeadInterval
in seconds. If the value is omitted (or value zero is speci-
fied), a default value (from initial configuration) should be
used.
A.5. DSBM_WILLING Messages
When a SBM wishes to declare its candidacy to be the DSBM during
an election phase, it sends out a DSBM_WILLING message. The
DSBM_WILLING message contains the following information:
1. DSBM address information -- Contains the SBM's own addresses
(IP and L2 address), if it wishes to be the DSBM. The IP
address is required and used for breaking ties. The L2
address is the address of the interface for the managed seg-
ment in question. Also, the DSBM address information
includes the corresponding priority of the SBM whose address
is given above.
A.6. SBM State Variables
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SBM (Subnet Bandwidth Manager) March, 1998
For each network interface, a SBM maintains the following state
variables related to the election of the DSBM for the L2 domain on
that interface:
a) LocalDSBMAddrInfo -- current DSBM's IP address (initially,
0.0.0.0) and priority. All IP addresses are assumed to be in
network byte order. In addition, current DSBM's L2 address is
also stored as part of this state information.
b) OwnAddrInfo -- SBM's own IP address and L2 address for the
interface and its own priority (a configuration parameter).
c) DSBM RefreshInterval in seconds. When the DSBM is not yet
elected, it is set to a default value specified as a confi-
guration parameter.
d) DSBMDeadInterval in seconds. When the DSBM is not yet
elected, it is initially set to a default value specified as
a configuration parameter.
f) ListenInterval in seconds -- a configuration parameter
that decides how long a SBM spends in the DetectDSBM state
(see below).
g) ElectionInterval in seconds -- a configuration parameter
that decides how long a SBM spends in the ElectDSBM state
when it has declared its candidacy.
Figure 3 shows the state transition diagram for the election pro-
tocol and the various states are described below. A complete
description of the state machine is provided in Section A.10.
A.7. DSBM Election States
DOWN -- SBM is not operational.
DetectDSBM -- typically, the initial state of a SBM when it
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SBM (Subnet Bandwidth Manager) March, 1998
starts up. In this state, it checks to see whether a DSBM
already exists in its domain.
Idle -- SBM is in this state when no election is in progress
and it is not the DSBM. In this state, SBM passively monitors
the state of the DSBM.
ElectDSBM -- SBM is in this state when a DSBM election is in
progress.
IAMDSBM -- SBM is in this state when it is the DSBM for the
L2 domain.
A.8. Events that cause state changes
StartUp -- SBM starts operation.
ListenInterval Timeout -- The ListenInterval timer has fired.
This means that the SBM has monitored its domain to check for
an existing DSBM or to check whether there are candidates
(other than itself) willing to be the DSBM.
DSBM_WILLING message received -- This means that the SBM
received a DSBM_WILLING message from some other SBM. Such a
message is sent when a SBM wishes to declare its candidacy to
be the DSBM.
I_AM_DSBM message received -- SBM received a DSBM advertise-
ment from the DSBM in its L2 domain.
SBMDeadInterval Timeout -- The SBMDeadInterval timer has
fired. This means that the SBM did not receive even one DSBM
advertisement during this period and indicates possible
failure of the DSBM.
RefreshInterval Timeout -- The RefreshInterval timer has
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SBM (Subnet Bandwidth Manager) March, 1998
fired. In the I_AM_DSBM state, this means it is the time for
sending out the next DSBM advertisement. In the ElectDSBM
state, the event means that it is the time to send out
another DSBM_WILLING message.
ElectionInterval Timeout -- The ElectionInterval timer has
fired. This means that the SBM has waited long enough after
declaring its candidacy to determine whether or not it suc-
ceeded.
CONTINUED ON NEXT PAGE
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A.9. State Transition Diagram (Figure 3)
+-----------+
+--<--------------<-|DetectDSBM |---->------+
| +-----------+ |
| |
| |
| |
| +-------------+ +---------+ |
+->---| Idle |--<>---|ElectDSBM|--<--+
+-------------+ +---------+
| |
| |
| |
| +-----------+ |
+<<- +---| IAMDSBM |-<-+
| +-----------+
|
| +-----------+
+>>-| SHUTDOWN |
+-----------+
A.10. Election State Machine
Based on the events and states described above, the state changes
at a SBM are described below. Each state change is triggered by an
event and is typically accompanied by a sequence of actions. The
state machine is described assuming a single threaded implementa-
tion (to avoid race conditions between state changes and timer
events) with no timer events occurring during the execution of the
state machine.
The following routines will be frequently used in the description
of the state machine:
ComparePrio(FirstAddrInfo, SecondAddrInfo)
-- determines whether the entity represented by the first parameter
is better than the second entity using the priority information
and the IP address information in the two parameters.
If any address is zero, that entity
automatically loses; then first priorities are compared; higher
priority candidate wins. If there is a tie based on
the priority value, the tie is broken using the IP
addresses of tied candidates (one with the higher IP address in the
lexicographic order wins). Returns TRUE if first entity is a better
yavatkar, Ed., et. al. [Page 48]
SBM (Subnet Bandwidth Manager) March, 1998
choice. FALSE otherwise.
SendDSBMWilling Message()
Begin
Send out DSBM_WILLING message listing myself as a candidate for
DSBM (copy OwnAddr and priority into appropriate fields)
start RefreshIntervalTimer
goto ElectDSBM state
End
AmIBetterDSBM(OtherAddrInfo)
Begin
if (ComparePrio(OwnAddrInfo, OtherAddrInfo))
return TRUE
change LocalDSBMInfo = OtherDSBMAddrInfo
return FALSE
End
UpdateDSBMInfo()
/* invoked in an assignment such as LocalDSBMInfo = OtherAddrInfo */
Begin
update LocalDSBMInfo such as IP addr, DSBM L2 address,
DSBM priority, RefreshIntervalTimer, DSBMDeadIntervalTimer
End
A.10.1 State Changes
In the following, the action "continue" or "continue in current
state" means an "exit" from the current action sequence without a
state transition.
State: DOWN
Event: StartUp
New State: DetectDSBM
Action: Initialize the local state variables (LocalDSBMADDR and
LocalDSBMAddrInfo set to 0). Start the ListenIntervalTimer.
State: DetectDSBM
New State: Idle
Event: I_AM_DSBM message received
Action: set LocalDSBMAddrInfo = IncomingDSBMAddrInfo
start DeadDSBMInterval timer
goto Idle State
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SBM (Subnet Bandwidth Manager) March, 1998
State: DetectDSBM
Event: ListenIntervalTimer fired
New State: ElectDSBM
Action: Start ElectionIntervalTimer
SendDSBMWillingMessage();
State: DetectDSBM
Event: DSBM_WILLING message received
New State: ElectDSBM
Action: Cancel any active timers
Start ElectionIntervalTimer
/* am I a better choice than this dude? */
If (ComparePrio(OwnAddrInfo, IncomingDSBMInfo)) {
/* I am better */
SendDSBMWillingMessage()
} else {
Change LocalDSBMAddrInfo = IncomingDSBMAddrInfo
goto ElectDSBM state
}
State: Idle
Event: SBMDeadInterval timer fired.
New State: ElectDSBM
Action: start ElectionIntervalTimer
set LocalDSBMAddrInfo = OwnAddrInfo
SendDSBMWiliingMessage()
State: Idle
Event: I_AM_DSBM message received.
New State: Idle
Action: /* first check whether anything has changed */
if (!ComparePrio(LocalDSBMAddrInfo, IncomingDSBMAddrInfo))
change LocalDSBMAddrInfo to reflect new info
endif
restart DSBMDeadIntervalTimer;
continue in current state;
State: Idle
Event: DSBM_WILLING Message is received
New State: Depends on action (ElectDSBM or Idle)
Action: /* check whether it is from the DSBM itself (shutdown) */
if (IncomingDSBMAddr == LocalDSBMAddr) {
cancel active timers
Set LocalDSBMAddrInfo = OwnAddrInfo
Start ElectionIntervalTimer
SendDSBMWillingMessage() /* goto ElectDSBM state */
}
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SBM (Subnet Bandwidth Manager) March, 1998
/* else, ignore it */
continue in current state
State: ElectDSBM
Event: ElectionIntervalTimer Fired
New State: depends on action (I_AM_DSBM or Current State)
Action: If (LocalDSBMAddrInfo == OwnAddrInfo) {
/* I won */
send I_AM_DSBM message
start RefreshIntervalTimer
goto I_AM_DSBM state
} else { /* someone else won, so wait for it to declare
itself to be the DSBM */
set LocalDSBMAddressInfo = OwnAddrInfo
start ElectionIntervalTimer
SendDSBMWillingMessage()
continue in current state
}
State: ElectDSBM
Event: I_AM_DSBM message received
New State: Idle
Action: set LocalDSBMAddrInfo = IncomingDSBMAddrInfo
Cancel any active timers
start DeadDSBMInterval timer
goto Idle State
State: ElectDSBM
Event: DSBM_WILLING message received
New State: ElectDSBM
Action: Check whether it's a loopback and if so, discard, continue;
if (!AmIBetterDSBM(IncomingDSBMAddrInfo)) {
Change LocalDSBMAddrInfo = IncomingDSBMAddrInfo
Cancel RefreshIntervalTimer
} else if (LocalDSBMAddrInfo == OwnAddrInfo) {
SendDSBMWillingMessage()
}
continue in current state
State: ElectDSBM
Event: RefreshIntervalTimer fired
New State: ElectDSBM
Action: /* continue to send DSBMWilling messages until
election interval ends */
SendDSBMWillingMessage()
State: I_AM_DSBM
Event: DSBM_WILLING message received
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SBM (Subnet Bandwidth Manager) March, 1998
New State: I_AM_DSBM
Action: send I_AM_DSBM message /* reassert myself */
restart RefreshIntervalTimer
State: I_AM_DSBM
Event: RefreshIntervalTimer fired
New State: I_AM_DSBM
Action: send I_AM_DSBM message
restart RefreshIntervalTimer
State: I_AM_DSBM
Event: I_AM_DSBM message received
New State: depends on action (I_AM_DSBM or Idle)
Action: /* check whether other guy is better */
If (ComparePrio(OwnAddrInfo, IncomingAddrInfo)) {
/* I am better */
send I_AM_DSBM message
restart RefreshIntervalTimer
continue in current state
} else {
Set LocalDSBMAddrInfo = IncomingAddrInfo
cancel active timers
start DSBMDeadInterval timer
goto Idle State
}
State: I_AM_DSBM
Event: Want to shut myself down
New State: DOWN
Action: send DSBM_WILLING message with My address filled in, but
priority set to zero
goto Down State
A.10.2 Suggested Values of Interval Timers
To avoid DSBM outages for long period, to ensure quick recovery
from DSBM failures, and to avoid timeout of PATH and RESV state at
the edge devices, we suggest the following values for various
timers.
Assuming that the RSVP implementations use a 30 second timeout for
PATH and RESV refreshes, we suggest that the RefreshIntervalTimer
should be set to about 5 seconds with DSBMDeadIntervalTimer set to
15 seconds (K=3, K*RefreshInterval). The DetectDSBMTimer should be
set to a random value between (DeadIntervalTimer, 2*DeadInterval-
Timer). The ElectionIntervalTimer should be set at least to the
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SBM (Subnet Bandwidth Manager) March, 1998
value of DeadIntervalTimer to ensure that each SBM has a chance to
have its DSBM_WILLING message (sent every RefreshInterval in
ElectDSBM state) delivered to others.
A.10.3. Guidelines for Choice of Values for SBM_PRIORITY
Network administrators should configure SBM protocol entity at
each SBM-capable device with the device's "SBM priority" for each
of the interfaces attached to a managed segment. SBM_PRIORITY is
an 8-bit, unsigned integer value (in the range 0-255) with higher
integer values denoting higher priority. The value zero for an
interface indicates that the SBM protocol entity on the device is
not eligible to be a DSBM for the segment attached to the inter-
face.
A separate range of values is reserved for each type of SBM-
capable device to reflect the relative priority among different
classes of L2/L3 devices. L2 devices get higher priority followed
by routers followed by hosts. The priority values in the range of
128..255 are reserved for L2 devices, the values in the range of
64..127 are reserved for routers, and values in the range of 1..63
are reserved for hosts.
A.11. DSBM Election over switched links
The election algorithm works as described before in this case
except each SBM-capable L2 device restricts the scope of the elec-
tion to its local segment. As described in Section B.1 below, all
messages related to the DSBM election are sent to a special multi-
cast address (AllSBMAddress). AllSBMAddress (its corresponding MAC
multicast address) is configured in the permanent database of
SBM-capable, layer 2 devices so that all frames with AllSBMAddress
as the destination address are not forwarded and instead directed
to the SBM management entity in those devices. Thus, a DSBM can be
elected separately on each point-to-point segment in a switched
topology. For example, in Figure 2, DSBM for "segment A" will be
elected using the election algorithm between R1 and S1 and none of
the election-related messages on this segment will be forwarded by
S1 beyond "segment A". Similarly, a separate election will take
place on each segment in this topology.
When a switched segment is a half-duplex segment, two senders (one
sender at each end of the link) share the link. In this case, one
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SBM (Subnet Bandwidth Manager) March, 1998
of the two senders will win the DSBM election and will be respon-
sible for managing the segment.
If a switched segment is full-duplex, exactly one sender sends on
the link in each direction. In this case, either one or two DSBMs
can exist on such a managed segment. If a sender at each end
wishes to serve as a DSBM for that end, it can declare itself to
be the DSBM by sending out an I_AM_DSBM advertisement and start
managing the resources for the outgoing traffic over the segment.
If one of the two senders does not wish itself to be the DSBM,
then the other DSBM will not receive any DSBM advertisement from
its peer and assume itself to be the DSBM for traffic traversing
in both directions over the managed segment.
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APPENDIX B
Message Encapsulation and Formats
To minimize changes to the existing RSVP implementations and to
ensure quick deployment of a 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 and
raw IP encapsulation. For more details on the RSVP message for-
mats, refer to the RSVP specification (RFC 2205). No changes to
the RSVP message formats are proposed, but new message types and
new L2-specific objects are added to the RSVP message formats to
accommodate DSBM-related messages. These additions are described
below.
B.1 Message Addressing
For the purpose of DSBM election and detection, AllSBMAddress is
used as the destination address while sending out both
DSBM_WILLING and I_AM_DSBM messages. A DSBM client first detects a
managed segment by listening to I_AM_DSBM advertisements and
records the DSBMAddress (unicast IP address of the DSBM).
B.2. Message Sizes
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 recipient node. This has a consequence that a single mes-
sage may not exceed the maximum IP datagram size, approximately
64K bytes.
B.3. 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 con-
tinue to follow the formatting rules specified in the RSVP specif-
ication. In addition, an RSVP implementation must also recognize
new object classes that are described below.
B.3.1. Object Formats
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SBM (Subnet Bandwidth Manager) March, 1998
All objects are defined using the format specified in the RSVP
specification. Each object has a 32-bit header that contains
length (of the object in bytes including the object header), the
object class number, and a C-Type. All unused fields should be set
to zero and ignored on receipt.
B.3.2. LAN_NHOP, RSVP_HOP_L2, and LAN_LOOPBACK Objects
LAN_NHOP, LAN_LOOPBACK, and RSVP_HOP_L2 objects are identified as
separate object classes and the value of Class_Num for the objects
is chosen so that non-SBM aware RSVP nodes will ignore the objects
without forwarding them or generating an error message.
B.3.3. IEEE 802 Canonical Address Format
The 48-bit MAC Addresses used by IEEE 802 were originally defined
in terms of wire order transmission of bits in the source and des-
tination MAC address fields. The same wire order applied to both
Ethernet and Token Ring. Since the bit transmission order of Eth-
ernet and Token Ring data differ - Ethernet octets are transmitted
least significant bit first, Token Ring most significant first -
the numeric values naturally associated with the same address on
different 802 media differ. To facilitate the communication of
address values in higher layer protocols which might span both
token ring and Ethernet attached systems connected by bridges, it
was necessary to define one reference format - the so called
canonical format for these addresses. Formally the canonical for-
mat defines the value of the address, separate from the encoding
rules used for transmission. It comprises a sequence of octets
derived from the original wire order transmission bit order as
follows. The least significant bit of the first octet is the first
bit transmitted, the next least significant bit the second bit,
and so on to the most significant bit of the first octet being the
8th bit transmitted; the least significant bit of the second octet
is the 9th bit transmitted, and so on to the most significant bit
of the sixth octet of the canonical format being the last bit of
the address transmitted.
This canonical format corresponds to the natural value of the
address octets for Ethernet. The actual transmission order or for-
mal encoding rules for addresses on media which do not transmit
bit serially are derived from the canonical format octet values.
This document requires that all L2 addresses used in conjunction
with the SBM protocol be encoded in the canonical format as a
sequence of 6 octets. In the following, we define the object
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SBM (Subnet Bandwidth Manager) March, 1998
formats for objects that contain L2 addresses that are based on
the canonical representation.
B.3.4. RSVP_HOP_L2 object
RSVP_HOP_L2 object uses object class = 161; it contains the L2
address of the previous hop L3 device in the IEEE Canonical
address format discussed above.
RSVP_HOP_L2 object: class = 161, C-Type represents the addressing format
used. In our case, C-Type=1 represents the IEEE Canonical Address
format.
0 1 2 3
+---------------+---------------+---------------+----------------+
| Length | 161 |C-Type(addrtype)|
+---------------+---------------+---------------+----------------+
| Variable length Opaque data |
+---------------+---------------+---------------+----------------+
C-Type = 1 (IEEE Canonical Address format)
When C-Type=1, the object format is:
0 1 2 3
+---------------+---------------+---------------+---------------+
| 12 | 161 | 1 |
+---------------+---------------+---------------+---------------+
| Octets 0-3 of the MAC address |
+---------------+---------------+---------------+---------------+
| Octets 4-5 of the MAC addr. | ///// | //// |
+---------------+---------------+---------------+---------------+
//// -- unused (set to zero)
B.3.5. LAN_NHOP object
LAN_NHOP object represents two objects, namely, LAN_NHOP_L3
address object and LAN_NHOP_L2 address object.
<LAN_NHOP object> ::= <LAN_NHOP_L2 object> <LAN_NHOP_L3 object>
LAN_NHOP_L2 address object uses object class = 162 and uses the
same format (but different class number) as the RSVP_HOP_L2
object. It provides the L2 or MAC address of the next hop L3
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SBM (Subnet Bandwidth Manager) March, 1998
device.
0 1 2 3
+---------------+---------------+---------------+----------------+
| Length | 162 |C-Type(addrtype)|
+---------------+---------------+---------------+----------------+
| Variable length Opaque data |
+---------------+---------------+---------------+----------------+
C-Type = 1 (IEEE 802 Canonical Address Format as defined below)
See the RSVP_HOP_L2 address object for more details.
LAN_NHOP_L3 object uses object class = 163 and gives the L3 or IP
address of the next hop L3 device.
LAN_NHOP_L3 object: class = 163, C-Type specifies IPv4 or IPv6 address
family used.
IPv4 LAN_NHOP_L3 object: class =163, C-Type = 1
+---------------+---------------+---------------+---------------+
| Length = 8 | 163 | 1 |
+---------------+---------------+---------------+---------------+
| IPv4 NHOP address |
+---------------------------------------------------------------+
IPv6 LAN_NHOP_L3 object: class =163, C-Type = 2
+---------------+---------------+---------------+---------------+
| Length = 20 | 163 | 2 |
+---------------+---------------+---------------+---------------+
// IPv6 NHOP address (16 bytes) |
+---------------------------------------------------------------+
B.3.6. LAN_LOOPBACK Object
The LAN_LOOPBACK object gives the IP address of the outgoing
interface for a PATH message and uses object class=164; both IPv4
and IPv6 formats are specified.
IPv4 LAN_LOOPBACK object: class = 164, C-Type = 1
0 1 2 3
+---------------+---------------+---------------+---------------+
| Length | 164 | 1 |
+---------------+---------------+---------------+---------------+
| IPV4 address of an interface |
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SBM (Subnet Bandwidth Manager) March, 1998
+---------------+---------------+---------------+---------------+
IPv6 LAN_LOOPBACK object: class = 164, C-Type = 2
+---------------+---------------+---------------+---------------+
| Length | 164 | 2 |
+---------------+---------------+---------------+---------------+
| |
+ +
| |
+ IPV6 address of an interface +
| |
+ +
| |
+---------------+---------------+---------------+---------------+
B.3.7. TCLASS Object
TCLASS object (traffic class based on IEEE 802.1p) uses object
class = 165.
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | 165 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /// | /// | //// | //// | PV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Only 3 bits in data contain the user_priority value (PV).
B.4. RSVP PATH and PATH_TEAR Message Formats
As specified in the RSVP specification, a PATH and PATH_TEAR mes-
sages contain the RSVP Common Header and the relevant RSVP
objects. For the RSVP Common Header, refer to the RSVP specifica-
tion (RFC 2205). Enhancements to an RSVP_PATH message include
additional objects as specified below.
<PATH Message> ::= <RSVP Common Header> [<INTEGRITY>]
<RSVP_HOP_L2> <LAN_NHOP>
<LAN_LOOPBACK> [<TCLASS>] <SESSION><RSVP_HOP>
<TIME_VALUES> [<POLICY DATA>] <sender descriptor>
<PATH_TEAR Message> ::= <RSVP Common Header> [<INTEGRITY>]
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SBM (Subnet Bandwidth Manager) March, 1998
<LAN_LOOPBACK> <LAN_NHOP> <SESSION> <RSVP_HOP>
[<sender descriptor>]
If the INTEGRITY object is present, it must immediately follow the
RSVP common header. L2-specific objects must always precede the
SESSION object.
B.5. RSVP RESV Message Format
As specified in the RSVP specification, an RSVP_RESV message con-
tains the RSVP Common Header and relevant RSVP objects. In addi-
tion, it may contain an optional TCLASS object as described ear-
lier.
B.6. 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
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 permis-
sible 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 (but not all) cases, object order
makes no logical difference. An implementation should create mes-
sages 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.
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DSBM_WILLING Message
<DSBM_WILLING message> ::= <SBM Common Header> <DSBM IP ADDRESS>
<DSBM L2 address> <SBM PRIORITY>
I_AM_DSBM Message
<I_AM_DSBM> ::= <SBM Common Header> <DSBM IP ADDRESS> <DSBM L2 address>
<SBM PRIORITY> <DSBM Timer Intervals>
<SBM_INFO>
All I_AM_DSBM messages are multicast to the well known AllSBMAd-
dress. The default priority of a SBM is 1 and higher priority
values represent higher precedence. The priority value zero indi-
cates that the SBM is not eligible to be the DSBM.
Relevant Objects
DSBM IP ADDRESS objects use object class = 42; IPv4 DSBM IP
ADDRESS object uses <Class=42, C-Type=1> and IPv6 DSBM IP ADDRESS
object uses <Class=42, C-Type=2>.
IPv4 DSBM IP ADDRESS object: class = 42, C-Type =1
0 1 2 3
+---------------+---------------+---------------+---------------+
| IPv4 DSBM IP Address |
+---------------+---------------+---------------+---------------+
IPv6 DSBM IP ADDRESS object: Class = 42, C-Type = 2
+---------------+---------------+---------------+---------------+
| |
+ +
| |
+ IPv6 DSBM IP Address +
| |
+ +
| |
+---------------+---------------+---------------+---------------+
<DSBM L2 address> Object is the same as <RSVP_HOP_L2> object with C-Type
=1 for IEEE Canonical Address format.
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SBM (Subnet Bandwidth Manager) March, 1998
<DSBM L2 address> ::= <RSVP_HOP_L2>
a SBM may omit this object by including a NULL L2 address object. For
C-Type=1 (IEEE Canonical address format), such a version of the L2
address object contains value zero in the six octet s corresponding to the
MAC address (see section B.3.4 for the exact format).
SBM_PRIORITY Object: class = 43, C-Type =1
0 1 2 3
+---------------+---------------+---------------+---------------+
| //// | //// | //// | SBM priority |
+---------------+---------------+---------------+---------------+
TIMER INTERVAL VALUES.
The two timer intervals, namely, DSBM Dead Interval and DSBM
Refresh Interval, are specified as integer values each in the
range of 0..255 seconds. Both values are included in a single
"DSBM Timer Intervals" object described below.
DSBM Timer Intervals Object: class = 44, C-Type =1
+---------------+---------------+---------------+----------------+
| //// | //// | DeadInterval |Refresh Interval|
+---------------+---------------+---------------+----------------+
SBM_INFO Object.
The SBM_INFO object is designed to provide additional information
about the managed segment. This object uses <Class=45, C-Type=1>
and includes information such as media type (shared or switched,
half duplex vs full duplex, etc.) and whether (and how much)
traffic a sender can send before receiving a RESV message from a
receiver.
SBM_INFO Object: class = 45, C-Type = 1
0 1 2 3
+---------------+---------------+---------------+----------------+
| //// | //// | //// | Media Type |
+---------------+---------------+---------------+----------------+
| OptFlowSpec (limit on traffic allowed to send without RESV) |
| |
+---------------+---------------+---------------+----------------+
Media Type values: 0 (Shared segment); a default
1 (switched, half duplex)
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SBM (Subnet Bandwidth Manager) March, 1998
2 (switched, full duplex)
OptFlowSpec:
This parameter specifies whether or not a sender can send traffic
when its RESV request fails. The parameter is an Intserv SENDER_TSPEC
object (see RFC 2210 for contents and encoding rules).
If the token bucket rate (r) specified in
this parameter is zero, it indicates that the sender(s) must not send
traffic if their RESV request fails; otherwise, the parameter specifies
per-session limit on the amount of traffic that can be sent when RESV
attempt for the session fails.
<OptFlowSpec> ::= <Intserv Sender_TSPEC object> (class=12, C-Type =2)
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SBM (Subnet Bandwidth Manager) March, 1998
ACKNOWLEDGEMENTS
Authors are grateful to Eric Crawley (Argon), Russ Fenger (Intel),
David Melman (Siemens), Ramesh Pabbati (Microsoft), Mick Seaman
(3COM), Andrew Smith (Extreme Networks) for their constructive
comments on the SBM design and the earlier versions of this docu-
ment.
6. Authors` Addresses
Raj Yavatkar
Intel Corporation
2111 N.E. 25th Avenue,
Hillsboro, OR 97124
USA
phone: +1 503-264-9077
email: yavatkar@ibeam.intel.com
Don Hoffman
Teledesic Corporation
2300 Carillon Point
Kirkland, WA 98033
USA
phone: +1 425-602-0000
Yoram Bernet
Microsoft
1 Microsoft Way
Redmond, WA 98052
USA
phone: +1 206 936 9568
email: yoramb@microsoft.com
Fred Baker
Cisco Systems
519 Lado Drive
Santa Barbara, California 93111
USA
phone: +1 408 526 4257
email: fred@cisco.com
Michael Speer
Sun Microsystems, Inc
901 San Antonio Road UMPK15-215
Palo Alto, CA 94303
phone: +1 650-786-6368
email: speer@Eng.Sun.COM
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