INTERNET-DRAFT Roland Bless
Expires: January 2003 Klaus Wehrle
Internet Draft Universitaet Karlsruhe (TH)
July 2002
Document: draft-bless-diffserv-multicast-04.txt
IP Multicast in Differentiated Services Networks
<draft-bless-diffserv-multicast-04.txt>
Status of this Memo
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Abstract
This document presents some of the problems which will arise when IP
Multicast is used in DiffServ networks without taking special
precautions into account for supplying multicast services. Although
the basic DS forwarding mechanisms also work with IP Multicast, some
facts have to be considered which are related to the provisioning of
multicast resources. The presented problems mainly lead to
situations in which other service users are affected adversely in
their experienced quality. In order to retain the benefits of the
DiffServ approach, a quite simple and scalable solution for those
problems is required, not resulting in additional complexity or
costs related to forwarding mechanisms in a DiffServ domain.
Internet-Draft IP Multicast in DiffServ Networks July 2002
The proposed solution in this document is as scalable as IP
Multicast itself, and, a simple implementation requires only an
additional field for the DiffServ Codepoint in the multicast routing
table and some support by management mechanisms.
Table of Contents
1 Introduction..................................................3
1.1 Management of Differentiated Services.........................4
2 Problems of IP Multicast in DS Domains........................4
2.1 Neglected Reservation Subtree Problem (NRS Problem)...........5
2.2 Heterogeneous Multicast Groups...............................12
2.3 Dynamics of Any-Source Multicast.............................13
3 Solutions for Enabling IP-Multicast in Differentiated Services
Networks.....................................................13
3.1 Solution for the NRS Problem.................................14
3.2 Solution for Supporting Heterogeneous Multicast Groups.......18
3.3 Solution for Any-Source Multicast............................18
4 Scalability Considerations...................................19
5 Security Considerations......................................19
6 References...................................................20
7 Acknowledgements.............................................21
8 Authors' Addresses...........................................21
A Proof of the Neglected Reservation Subtree Problem...........23
A.1 Implementation of the proposed solution......................23
A.2 Test Environment and Execution...............................24
B Simulative Study of the NRS Problem and Limited Effort PHB...27
B.1 Simulation Scenario..........................................27
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B.2 Simulation Results for different router types................29
B.2.1 Interior Router............................................29
B.2.1.1 Case I:..................................................30
B.2.1.2 Case II:.................................................30
B.2.1.3 Case III:................................................31
B.2.1.4 Case IV:.................................................31
B.2.2 Boundary Router............................................32
B.2.2.1 Case I:..................................................32
B.2.2.2 Case II:.................................................32
B.2.2.3 Case III:................................................33
B.2.2.4 Case IV:.................................................34
1 Introduction
Services in the Internet offering a better quality than the current
best-effort service are increasingly required. Many advanced
applications need certain assurances from the network layer, e.g., a
maximum delay, a minimum packet loss rate or guaranteed transmission
rate. The currently used IP mechanisms are not able to offer such
guarantees, especially, if group communication is additionally
required.
The "Differentiated Services" (DiffServ or DS) approach [1, 2, 3]
defines certain building blocks and mechanisms to offer
qualitatively better services than the usual “normal” best-effort
delivery service in an IP network. In the DiffServ Architecture [2]
scalability is achieved by avoiding complexity and maintenance of
per-flow state information in core nodes and by pushing unavoidable
complexity to the network edges. Therefore, individual flows
belonging to the same service are aggregated, thereby eliminating
the need for complex classification or managing state information
per flow in interior nodes.
On the other hand, the reduced complexity in DS nodes makes it more
complex to use those "better" services together with IP Multicast
(i.e., point-to-multipoint or multipoint-to-multipoint
communication). Problems emerging from this fact are described in
section 2. Although the basic DS forwarding mechanisms also work
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with IP Multicast, some facts have to be considered which are
related to the provisioning of multicast resources. However, it is
important to integrate IP Multicast functionality right from the
beginning into the architecture, and, to provide simple solutions
for those problems not defeating the gained advantages so far.
The EF PHB [4] shows also very interesting properties within a
multicast context. The very low packet loss characteristic makes it
suitable as a basis for a highly (but not absolute) reliable
multicast service. Packet loss cannot be fully precluded, because of
aggregation effects which may nevertheless lead to packet losses.
However, in reality packet losses should occur so infrequently that
many applications can tolerate these losses, or if this is not the
case, that at least very simple retransmission schemes can be
applied.
1.1 Management of Differentiated Services
At least for Per-Domain Behaviors and services based on the EF PHB
admission control and resource reservation are required.
Furthermore, installation and updating of traffic profiles in
boundary nodes is necessary. Most network administrators will not
accomplish this task manually, even for long term service level
agreements (SLAs). Furthermore, offering services on demand requires
some kind of signaling and automatic admission control procedures.
Therefore, the concept of Bandwidth Brokers was already suggested by
Van Jacobson at a very early stage of DiffServ research [5]. In this
concept, the Bandwidth Broker (BB) is a dedicated node in each DS
domain, which keeps track of the amount of available and reserved
bandwidth for services, and, which processes admission control
requests from customers or BBs of adjacent domains. Additionally, it
installs or alters traffic profiles in boundary nodes.
Protocols for signaling a reservation request to a Differentiated
Services Domain are required. For accomplishing end-system signaling
to DS domains RSVP [6] may be used with new DS specific reservation
objects [7]. RSVP is mainly designed for use in multicast scenarios
and is already supported by many operating systems. However, when
RSVP is applied to a DiffServ network some problems will arise which
are described in the next section.
2 Problems of IP Multicast in DS Domains
Although potential problems and the complexity of providing
multicast with Differentiated Services are considered in a separate
section of [2], both aspects have to be discussed in greater detail.
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The simplicity of the DiffServ Architecture and its router models is
necessary to reach high scalability, but it causes also fundamental
problems in conjunction with the use of IP Multicast in DS domains.
The following subsections describe these problems for which a simple
solution is proposed in section 3. This solution is as scalable as
IP Multicast and needs no resource separation by using different
codepoint values for unicast and multicast traffic.
Because Differentiated Services are unidirectional by definition, we
also consider the point-to-multipoint communication being of
unidirectional nature. In traditional IP Multicast any node can send
packets spontaneously and asynchronously to a multicast group,
respectively to their multicast group address (therefore,
traditional IP Multicast offers a multipoint-to-multipoint service,
also referred to as Any-Source Multicast). This feature is discussed
in section 2.3.
For subsequent considerations we assume, unless stated otherwise, at
least a unidirectional point-to-multipoint communication scenario in
which the sender generates packets which experience a "better" Per-
Hop Behavior than the traditional default PHB, resulting in a
service of better quality compared to the default best-effort
service. In order to accomplish this, a traffic profile
corresponding to the traffic conditioning specification has to be
installed in the sender's first-hop router (the first boundary node
of the first DS domain receiving those packets). Furthermore, it
must be assured that the corresponding resources are available on
the path from the sender to all the receivers, possibly requiring
adaptation of traffic profiles at involved domain boundaries. Note
that the latter process may also be initiated on demand of a
receiver.
2.1 Neglected Reservation Subtree Problem (NRS Problem)
Typically, resources for Differentiated Services must be reserved
before actually using them. But in a multicast scenario group
membership is often highly dynamic, therefore limiting the use of a
sender-initiated resource reservation in advance. Unfortunately,
dynamic addition of new members of the multicast group using
Differentiated Services can adversely affect existing other traffic,
if resources were not explicitly reserved before use. A practical
prove of this problem is given in appendix A.3.
IP Multicast packet replication usually takes place when the packet
is handled by the "routing" core (cf. Fig. 1), i.e., when it is
forwarded according to the routing table. Thus, a DiffServ capable
node would also copy the content of the DS field [1] into the IP
packet header of every replicate. Consequently, replicated packets
get exactly the same DS codepoint (DSCP) as the original packet,
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and, therefore experience the same forwarding treatment as the
incoming packets of this multicast group (see Fig. 1, in this case
the egress interface comprises functions for (BA-) classification,
traffic conditioning and queueing).
Interface A IP Routing Interface C
+-----------+ +--------------+ +-----------+
MC-flow | | | replication | | egress |
---->| ingress |---->|------+-------|----->|(class.,TC,|---->
| | | | | | queueing) |
+-----------+ | | | +-----------+
| | |
Interface B | | | Interface D
+-----------+ | | | +-----------+
| | | | | | egress |
| ingress | | +-------|----->|(class.,TC,|---->
| | | | | queueing) |
+-----------+ +--------------+ +-----------+
Figure 1: Multicast packet replication in a DS router
Normally, the replicating node cannot test whether a corresponding
reservation exists for a particular flow of replicated packets on an
output link (resp. its corresponding interface), because a flow-
specific traffic profile is usually not available in boundary
(except in first-hop nodes) and interior nodes.
When a new receiver joins an IP Multicast group, the corresponding
multicast routing protocol (e.g., DVMRP [8, 9], PIM-DM [10] or PIM-
SM [11]) accomplishes that the multicast tree is expanded by a new
branch which connects the new receiver to the already existing
multicast tree. As a result of tree expansion and missing per-flow
classification and policing mechanisms, the new receiver will
implicitly use the service of better quality, because of the copied
"better" DSCP.
If the additional amount of resources which are consumed by the new
part of the multicast tree are not taken into account by the domain
management (cf. section 1.1), the currently provided level of
quality of service of other receivers (with correct reservations)
will be affected adversely or even violated. This negative effect on
existing traffic contracts by a neglected resource reservation -- in
the following designated as Neglected Reservation Subtree Problem
(NRS Problem) -- must be avoided under any circumstances.
One can distinguish two distinct major cases of the NRS Problem. In
order to compare their different effects a simple example of a share
of bandwidth is illustrated in Fig. 2.
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40% 40% 20%
+--------------------+---------------------+------------+
|Expedited Forwarding| Assured Forwarding | Best-Effort|
+--------------------+---------------------+------------+
---------------------------------------------------------->
output link bandwidth
Figure 2: An example bandwidth share of different
behavior aggregates
Three types of services (respectively their corresponding behavior
aggregates) share the bandwidth of the considered output link:
Expedited Forwarding, Assured Forwarding and the traditional Best-
Effort service. In this example we assume that routers perform
simple priority queueing, where EF has the highest and Best-Effort
the lowest assigned priority. When Weighted Fair Queueing (WFQ)
would be used, the described effects would essentially also occur,
only with minor differences.
The Neglected Reservation Subtree problem appears in two different
cases:
o Case 1: If the branching point of the new subtree (at first only a
branch) and the previous multicast tree is an (egress) boundary
router, as shown in Fig. 3, the additional multicast flow now
increases the amount of used resources for the corresponding
aggregate and will be greater than the originally reserved amount
on the affected output link. Consequently, the policing component
in the egress boundary router drops packets until the traffic
aggregate is in accordance to the traffic contract. But during
dropping packets, the router can not identify the responsible flow
(because of missing flow classification functionality), and, thus
randomly discards packets, whether they belong to a correctly
reserved flow or not. As a result, there will be no longer any
service guarantee for the reserved flows.
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Sender
+---+
| S | DS domains .......
+---+ ..... / \ . ..
|| . . .. / \ .. .
..||.. .... .<- ->... ..
. || . . .
. +---+ +--+ +--+ *) +--+ +--+ +--+ +------+
. |FHN|===|IN|=====|BN|###########|BN|####|IN|######|BN|####|Recv.B|
. +---+ +--+ +--+\\ +--+ +--+ +--+ +------+
. \\ \ . \\ . \ .
. +--+ +--+ . \\ . \ .
. |IN|-----|IN| . \\ .. +--+ .
. +--+ +--+ . \\ ... ....|BN|..
. || \ ... +------+ ... +--+
. || \ . |Recv.A|
.+--+ ...+--+ +------+
|BN|..... |BN|
+--+ +--+
||
FHN: First-Hop Node S: Sender
BN: Boundary Node Recv.x: Receiver x
IN: Interior Node
===: Multicast branch with reserved bandwidth
###: Multicast branch without reservation
*) Bandwidth of EF aggregated on the output link is higher than
actual reservation, EF aggregate will be limited in bandwidth
without considering the responsible flow.
Figure 3: The NRS Problem (case 1)
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+------------------+---------------------+--------------+------+
| Expedited Forw. | Expedited Forw. | Assured Forw.| BE |
| | | | |
| with reservation | excess flow | with reserv. | |
| | without reservation | | |
+------------------+---------------------+--------------+------+
| | | |
| EF with and without reservation share | 40 % | 20% |
| 40% of reserved EF aggregate. | | |
| -> EF packets with reservation and | | |
| without reservation will be | | |
| discarded! | | |
| | | |
+------------------+---------------------+--------------+------+
(a) Excess flow has EF codepoint
+------------------+---------------------+--------------+------+
| Expedited Forw. | Assured Forwarding | Assured Forw.| BE |
| | | | |
| with reservation | excess flow | with reserv. | |
| | without reservation | | |
+------------------+---------------------+--------------+------+
| | | |
| | AF with & without reservation share| 20 % |
| | 40% of reserved EF aggregate. | |
| 40% | -> EF packets with reservation and | |
| | without reservation will be | |
| | discarded! | |
| | | |
+------------------+---------------------+--------------+------+
(b) Excess flow has AF codepoint
Figure 4: Resulting share of bandwidth in a egress
boundary router with a neglected reservation
of (a) an Expedited Forwarding flow or (b) an
Assured Forwarding flow.
Fig. 4 shows the resulting share of bandwidth in cases when (a)
Expedited Forwarding and (b) Assured Forwarding is used by the
additional multicast branch causing the NRS Problem. Assuming that
the additional traffic would use another 30% of the link
bandwidth, Fig. 4 (a) illustrates that the resulting aggregate of
Expedited Forwarding (70% of the outgoing link bandwidth) is
throttled down to its originally reserved 40%. In this case, the
amount of dropped EF bandwidth is equal to the amount of excess
bandwidth. Consequently the original Expedited Forwarding
aggregate (which had 40% of the link bandwidth reserved) is
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affected by packet losses, too. The other services, e.g., Assured
Forwarding or Best-Effort, are not disadvantaged.
Fig. 4 (b) shows the same situation for Assured Forwarding. The
only difference is that now Assured Forwarding is solely affected
by discards, the other services will still get their guarantees.
In either case, packet losses are restricted to the misbehaving
service class by the traffic meter and policing mechanisms in
boundary routers. Moreover, the latter problem (case 1) occurs
only in egress boundary routers, because they are responsible,
that not more traffic is leaving the Differentiated Services
domain, than the following ingress boundary router will accept.
Therefore, those violations of SLAs will be already detected and
processed in egress boundary routers.
Sender
+---+
| S | DS domains .......
+---+ ..... / \ . ..
|| . . .. / \ .. .
..||.. .... .<- ->... ..
. || . . .
. +---+ +--+ +--+ +--+ +--+ +--+ +-------+
. |FHN|===|IN|=====|BN|===========|BN|====|IN|======|BN|===| Recv.B|
. +---+ +--+ +--+\\ +--+ +--+ +--+ +-------+
. \\ \ . \\ . # .
. +--+ +--+ . \\ . # *) .
. |IN|-----|IN| . \\ .. +--+ .
. +--+ +--+ . \\ ... ....|BN|..
. || \ ... +------+ ... +--+
. || \ . |Recv.A| #
.+--+ ...+--+ +------+ #
|BN|..... |BN| +------+
+--+ +--+ |Recv.C|
|| +------+
FHN: First-Hop Node
S: Sender BN: Boundary Node
Recv.x: Receiver x IN: Interior Node
===: Multicast branch with reserved bandwidth
###: Multicast branch without reservation
*) Bandwidth of EF aggregated on the output link is higher than
actual reservation, EF aggregate will be limited in bandwidth
without considering the responsible flow
Figure 5: Neglected Reservation Subtree problem case 2
after join of receiver C
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o Case 2: The Neglected Reservation Subtree problem can also occur,
if the branching point between the previous multicast tree and the
new subtree is located in an interior router (as shown in Fig. 5).
Because the router is not equipped with metering or policing
functions it will not recognize any amount of excess traffic and
will forward the new multicast flow. If the latter belongs to a
higher priority service, such as Expedited Forwarding, bandwidth
of the aggregate is higher than the aggregate's reservation and
will steal bandwidth from lower priority services.
The additional amount of EF without a corresponding reservation is
forwarded together with the aggregate which has a reservation.
This results in no packets losses for Expedited Forwarding as long
as the resulting aggregate is not higher than the output link
bandwidth. Because of its higher priority, Expedited Forwarding
gets as much bandwidth as needed and as is available (strictly
speaking, it is implementation dependent whether interior routers
have something like a maximum configured service rate).
+------------------+---------------------+--------------+------+
| Expedited Forw. | Expedited Forw. | Assured Forw.| BE |
| | | | |
| with reservation | excess flow | with reserv. | |
| | without reservation | | |
+------------------+---------------------+--------------+------+
| | | | |
| 40% | 30% | 30% | 0% |
| | | | |
+------------------+---------------------+--------------+------+
EF with reservation and the excess flow use together 70%
of the link bandwidth, because EF (with or without reservation
has the highest priority.
(a) Excess flow has EF codepoint
+------------------+---------------------+--------------+------+
| Expedited Forw. | Assured Forw. | Assured Forw.| BE |
| | | | |
| with reservation | excess flow | with reserv. | |
| | without reservation | | |
+------------------+---------------------+--------------+------+
| | | |
| 40% | 60% | 0% |
| | | |
| | 10% loss | |
| | | |
+------------------+---------------------+--------------+------+
AF with reservation and the excess flow use together 60%
of the link bandwidth, because EF has the highest priority
(-> 40%). 10% of AF packets will be lost.
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(b) Excess flow has AF codepoint
Figure 6: Resulting share of bandwidth in an interior
router with a neglected reservation of (a) a
Expedited Forwarding flow or (b) an Assured
Forwarding flow
The result is, that there is no restriction for Expedited
Forwarding, but as Fig. 6 (a) shows, other services will be
extremely disadvantaged by this use of non-reserved resources.
Their bandwidth is stolen by the new additional flow. In this
case, the additional 30% Expedited Forwarding traffic preempts
resources from the Assured Forwarding traffic, which in turn
preempts resources from the best-effort traffic, resulting in 10%
packet losses for the Assured Forwarding aggregate and complete
loss of best-effort traffic. The example in Fig. 6 (b) shows that
this can also happen with lower priority services like Assured
Forwarding. When a reservation for a service flow with lower
priority is neglected, other services (with even lower priority)
can be reduced in their quality (in this case the best-effort
service). As shown in the example, the service's aggregate causing
the problem can itself be affected by packet losses (10% of the
Assured Forwarding aggregate is discarded). Besides the described
problems of case 2, case 1 will arise in the next boundary router,
that performs traffic metering and policing for flows of the
service aggregate.
Directly applying RSVP to Differentiated Services would also result
in an NRS Problem, because a receiver has to join the IP multicast
group BEFORE sending a resource reservation request (RESV message),
in order to receive the sender's PATH messages at first. Thus, the
join for receiving PATH messages will already cause an NRS Problem
if this situation is not handled in a special way (e.g., by marking
all PATH messages with codepoint 0).
2.2 Heterogeneous Multicast Groups
Heterogeneous multicast groups contain one or more receivers, which
would like to get another service or quality of service as the
sender provides or other receiver subsets currently use. A very
important characteristic which should be supported by Differentiated
Services is that participants requesting a best-effort quality only
should also be able to participate in a group communication which
otherwise utilizes a better service class. The next better support
for heterogeneity provides concurrent use of more than two different
service classes within a group. Things tend to get even more complex
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when not only different service classes are required, but also
different values for quality parameters within a certain service
class.
A further problem is to support heterogeneous groups with different
service classes in a consistent way. It is possible that some
services will not be comparable to each other so that one service
cannot be replaced by the other and both services have to be
provided over the same link within this group.
Because an arbitrary new receiver that wants to get the different
service can be grafted to any point of the current multicast
delivery tree, even interior routers may have to replicate packets
with the different service. At a first glance, this seems to be a
contradiction with respect to simplicity of the interior routers,
because they do not even have any profile available and should now
convert the service quality of individual receivers. Consequently,
in order to accomplish this, interior routers have to change the
codepoint value during packet replication.
2.3 Dynamics of Any-Source Multicast
Basically, within an IP multicast group any participant (actually,
it can be any host not even receiving packets of this multicast
group) can act as a sender. This is an important feature which
should also be available in case a specific service other than best-
effort is used within the group. Differentiated Services possess
conceptually a unidirectional character. Therefore, for every
multicast tree implied by a sender resources must be reserved
separately if simultaneous sending should be possible with a better
service. This is even true if shared multicast delivery trees are
used (e.g., with PIM-SM or Core Based Trees). If not enough
resources are reserved for a service within a multicast tree
allowing simultaneous sending of more than one participant, the NRS
problem will occur again. The same argument applies to half-duplex
traffic which would share the reserved resources by several senders,
because it cannot be ensured by the network that exactly one sender
sends packets to the group. Accordingly, the corresponding RSVP
reservation styles "Wildcard Filter" and "Shared-Explicit Filter"
[6] cannot be supported within Differentiated Services. The IntServ
approach is able to ensure the half-duplex nature of the traffic,
because every router can check each packet for conformance with the
installed reservation state.
3 Solutions for Enabling IP-Multicast in Differentiated Services
Networks
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The problems described in the previous section are mainly caused by
the simplicity of the Differentiated Services Architecture.
Solutions have to be developed which do not introduce an additional
amount of complexity which diminishes the scalability of this
approach.
In this document, a simple solution is suggested for most of the
problems. In order to keep things simple, we restrict this first
solution for supporting heterogeneous groups to the case in which
only two different services within a multicast group can be used
simultaneously.
3.1 Solution for the NRS Problem
The proposed solution consists conceptually of the following three
steps that are described in more detail later.
1. A new receiver joins a multicast group that is using a DiffServ
service. Multicast routing protocols accomplish the connection
of the new branch to the (possibly already existing) multicast
delivery tree as usual.
2. The unauthorized use of resources is avoided by re-marking at
branching nodes all additional packets leaving downwards the new
branch. At first the new receiver will get all packets of the
multicast group without QoS. The management entity of the
correspondent DiffServ domain is informed about the extension of
the multicast tree.
3. If a pre-issued reservation is available for the new branch or
somebody (receiver, sender or a third party) issues one, the
management entity instructs the branching router to set the
corresponding codepoint for the demanded service.
Usage of resources which where not reserved before must be
precluded. In the following discussed example, the case is
considered when the join of a new receiver to a DS multicast group
requires grafting of a new branch to an already existing multicast
delivering tree. The connecting node which joins both trees converts
the codepoint (and therefore the Per-Hop Behavior) to a codepoint of
a PHB which is similar to the default PHB (see (1) and (3) in Fig.
7) in order to provide a best-effort-like service for the new
branch. More specifically, this particular PHB can be different from
the default PHB providing a service which is even worse than the
best-effort service of the default PHB.
The conversion to this specific PHB could be necessary in order to
avoid unfairness being introduced otherwise within the best-effort
service aggregate, and, which results from the higher amount of
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resource usage of the incoming traffic belonging to the multicast
group. If the rate at which re-marked packets are injected into the
outgoing aggregate is not reduced, those re-marked packets will
probably cause discarding of other flow's packets in the outgoing
aggregate if resources are scarce.
Therefore, the re-marked packets from this multicast group should be
discarded more aggressively than other packets in this outgoing
aggregate. This could be accomplished by using an appropriate
configured PHB (and a related DSCP) for those packets. In order to
distinguish this kind of PHB from the default PHB, it is referred to
as Limited Effort (LE) PHB (which can be realized by an
appropriately configured AF PHB [12]). Merely dropping packets more
aggressively at the re-marking node is not sufficient, because there
may be enough resources in the outgoing BA to transmit every re-
marked packet and not requiring discarding any other packets within
the same BA. However, resources in the next node may be short for
this particular BA. Therefore, those "excess" packets must be
identifiable at this node.
[EF| ]
||
||
||
JOIN_INDICATION \/
+------+ (2) +---------------+
Management | |<----------| |
Entity | ME | | Router |
| |---------->| |
+------+ (4) +---------------+
SET_CODEPOINT // ^ \
// | \
// \ \
// \ \
|| | |
|| (1) JOIN| |
|| | |
\/ | V
[EF| ] (3) [LE| ]
(5) [EF| ]
===: Multicast branch with reserved resources for Expedited
Forwarding
---: New Multicast branch
[x| ]: IP packet with DSCP of PHB x
Figure 7: Sequence of the proposed solution
Re-marking packets is only required at branching nodes, whereas all
other nodes of the multicast tree (such with outdegree 1) replicate
packets as usual. Because a branching node may also be an interior
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router of a domain, re-marking of packets requires conceptually per-
flow classification. Though this seems to be in contradiction to the
DiffServ philosophy of a core that avoids per-flow states, IP
multicast flows are different from unicast flows: traditional IP
multicast forwarding and multicast routing require to install states
per multicast group for every outgoing link anyway. Therefore, re-
marking in interior nodes is to the same extent scalable as IP
multicast is (cf. section 4).
Re-marking with standard DiffServ mechanisms [13] for every new
branch requires activation of a default traffic profile. The latter
accomplishes re-marking by using a combination of an MF-classifier
and a marker at an outgoing link that constitutes a new branch. The
classifier will direct all replicated packets to a marker that sets
the new codepoint.
The better service will be only provided if a reservation request
was processed by the management (e.g., Bandwidth Brokers) in order
to perform a required admission control test before resources are
actually used. In case the admission test is successful, the re-
marking node will be instructed by the management entity to stop re-
marking and to use the original codepoint again (conceptually by
removing the profile).
Because reservation requests may also be initiated by the sender, an
incoming JOIN-Request of a new receiver branch should be also
signaled by a boundary node to the management node (indicated by the
JOIN_INDICATION message in step (2) in Fig. 7), so that the re-
marking node can be instructed (via the SET_CODEPOINT message in
step (4)) to immediately use the same codepoint value for replicated
packets belonging to this group as for incoming packets (EF in (5)
of Fig. 7).
A simple alternative implementation is also possible and is
described in the following. This particular implementation does not
require any additional classification of multicast groups within an
aggregate. Because every multicast packet has to be handled by the
multicast routing process (in this context, this notion signifies
the multicast forwarding part and not the multicast route
calculation and maintenance part, see Fig. 1), addition of an extra
byte in each multicast routing table entry for containing the DS
field, and, thus its DS codepoint value, per output link (resp.
virtual interface, see Fig. 8) results in nearly no additional cost.
Packets will be replicated by the multicast routing process, so this
is also the right place for setting the correct DSCP values of the
replicated packets. Their DSCP values are not copied from the
incoming original packet, but from the additional DS field in the
multicasting routing table entry for the corresponding output link
(only the DSCP value must be copied, while the two remaining bits
are ignored and are present for simplification reasons only). This
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field contains initially the codepoint of the LE PHB if incoming
packets for this specific group do not carry the codepoint of the
default PHB. When a packet arrives with the default PHB, the
outgoing replicates should also get the same codepoint in order to
retain the behavior of todays common multicast groups using the
default PHB. The SET_CODEPOINT message changes the DSCP values in
the multicast routing table and may also carry the new DSCP value
which should be set in the replicated packets. It should be noted
that although re-marking may also be performed by interior nodes,
the forwarding performance will not be decreased, because the
decision when and what to re-mark is made by the management (control
plane).
Furthermore, there must be a mechanism for DiffServ nodes to inform
a management entity about the join request of a new branch
(something like the JOIN_INDICATION message). In order to keep the
complexity of interior nodes low, this task may be preferably
handled by boundary nodes. Additionally, a mechanism must be
supplied for instructing a router to change the DSCP value for a
specific branch of a multicast group (something like the
SET_CODEPOINT message). This mechanism may be also incorporated into
an existing multicast routing protocol as an extension.
Multicast Other List
Destination Fields of
Address virtual Inter- DS
interfaces face ID Field
+--------------------------------+ +-------------------+
| X | .... | *-------------------->| C | (DSCP,CU) |
|--------------------------------| +-------------------+
| Y | .... | *-----------+ | D | (DSCP,CU) |
|--------------------------------| | +-------------------+
| ... | .... | ... | |
. . . . | +-------------------+
. ... . .... . ... . +-------->| B | (DSCP,CU) |
+--------------------------------+ +-------------------+
| ... | .... | ... | | D | (DSCP,CU) |
+--------------------------------+ +-------------------+
| ... | ... |
. . .
. . .
Figure 8: Multicast routing table with additional
fields for DSCP values
In summary, only those receivers will obtain a better service within
a DiffServ multicast group, which previously reserved the
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corresponding resources in the new branch with assistance of the
management. Otherwise they get a quality which might be even lower
than best-effort.
3.2 Solution for Supporting Heterogeneous Multicast Groups
In this document considerations are currently limited to provision
different service classes, but not different quality parameters
within a certain service class.
The proposed concept from section 3.1 provides also a limited
solution of the heterogeneity problem. Receivers are allowed to
obtain a Limited Effort service without a reservation, so that at
least two different service classes within a multicast group are
possible. Therefore, it is possible that any receiver may
participate in the multicast session without getting any quality of
service. This is useful if a receiver just wants to see whether the
content of the multicast group is of interest for it, before
requesting a better service which must be paid for (like snooping
into a group without prior reservation).
Alternatively, a receiver might not be able to receive this better
quality of service (e.g., because it is mobile and uses a wireless
link), but it may be satisfied with the reduced quality, instead of
getting no content at all.
Additionally, applying the RSVP concept of listening for PATH
messages before sending any RESV message is now possible again.
Without using the proposed solution this would have caused the NRS
Problem.
Theoretically, the proposed approach also supports more than two
different services within one multicast group, because the
additional field in the multicast routing table can store any DSCP
value. However, this would work only if PHBs can be partially
ordered, so that the "best" PHB among different required PHBs
downstream is chosen to be forwarded on a specific link. This is
mainly a management issue and out of scope for this document.
3.3 Solution for Any-Source Multicast
Every participant would have to initiate an explicit reservation if
it wants to make sure that it is possible to send with a better
service quality to the group, regardless whether other senders
within the group already use the same service class simultaneously.
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This would require a separate reservation for each sender-rooted
multicast tree.
However, in the specific case of best-effort service (the default
PHB), it is nevertheless possible for participants to send packets
anytime to the group without requiring any additional mechanisms.
The reason for this is that the first-hop router will mark those
packets with the DSCP of the default PHB because of a missing
traffic profile for this particular sender. First hop routers should
therefore always classify multicast packets in dependence of the
sender's address and multicast group address.
4 Scalability Considerations
The proposed solution does not the extend the DS architecture or a
DS router with additional complexity. Re-marking of packets in
interior nodes is not considered as a scalability problem or to be
in contradiction with the DiffServ approach itself, because a router
has to manage and hold information about multicast flows anyway.
Moreover, the decision when to change a re-marking policy is not
performed by the router, but by some management entity at a time
scale which is different from the time scale at the packet
forwarding level.
However, one may argue that there exists a scalability problem in
holding necessary routing information for each multicast flow. But
this problem applies to the nature of IP multicast itself. When a
router is not capable of holding and managing a multicast routing
table then IP multicast (in its current implementation) itself leads
to a scalability problem. Thus, as long as IP multicast is
considered to be scalable the herein proposed solution is also
scalable.
5 Security Considerations
Basically, the security considerations in [1] apply. The proposed
solution does not really imply new security aspects. If it is not
wanted that arbitrary end-systems can join a multicast group anytime
(thereby receiving a lower than best-effort quality) the application
has usually to preclude these participants by using authentication,
authorization or ciphering techniques at application level just as
for traditional IP multicast scenarios.
On the one hand, instructing the router to set the codepoint value
to a specific entry is naturally a powerful function which could be
an objective for theft of service attacks. On the other hand, its
security depends on the management mechanisms which are used to
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realize this functionality. This management should generally be
protected against unauthorized use, therefore preventing those
attacks.
6 References
[1] F. Baker, D. Black, S. Blake, and K. Nichols. Definition of the
Differentiated Services Field (DS Field) in the IPv4 and IPv6
Headers. RFC 2474, Dec. 1998.
[2] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, and W.
Weiss. An Architecture for Differentiated Services. RFC 2475,
Dec. 1998.
[3] K. Nichols, B. Carpenter. Definition of Differentiated Services
Per Domain Behaviors and Rules for their Specification. RFC
3086, Apr. 2001.
[4] B. Davie, A. Charny, J.C.R. Bennett, K. Benson, J.Y. Le Boudec,
W. Courtney, S. Davari, V. Firoiu, D. Stiliadis, An Expedited
Forwarding PHB. RFC 3246, March 2002.
[5] V. Jacobson, K. Nichols, and L. Zhang. A Two-bit Differentiated
Services Architecture for the Internet. RFC 2638, July 1999.
[6] R. Braden, S. Berson, S. Herzog, S. Jamin, and L. Zhang.
Resource ReSerVation Protocol (RSVP) -- Version 1. RFC 2205,
Sept. 1997.
[7] Y. Bernet, Format of the RSVP DCLASS Object, RFC 2996, November
2000.
[8] D. Waitzman, C. Partridge, and S. Deering. Distance Vector
Multicast Routing Protocol. RFC 1075, Nov. 1988.
[9] S. Deering, D. Estrin, D. Farinacci, V. Jacobson, A. Helmy, D.
Meyer, and L. Wei. Protocol independent multicast version 2
dense mode specification. Internet-Draft -- draft-ietf-pim-v2-
dm-03.txt, June 1999, work in progress.
[10] D. Estrin, D. Farinacci, A. Helmy, D. Thaler, S. Deering, M.
Handley, V. Jacobson, C. gung Liu, P. Sharma, and L. Wei.
Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol
Specification. RFC 2362, June 1998.
[11] S. Deering, D. Estrin, D. Farinacci, V. Jacobson, A. Helmy, D.
Meyer, and L. Wei. Protocol independent multicast version 2
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dense mode specification. Internet-Draft -- draft-ietf-pim-v2-
dm-03.txt, June 1999, work in progress.
[12] F. Baker, J. Heinanen, W. Weiss, and J. Wroclawski. Assured
Forwarding PHB Group. RFC 2597, June 1999.
[13] Y. Bernet, S. Blake, D. Grossman, A. Smith: An Informal
Management Model for DiffServ Routers. RFC 3290, May 2002
[14] R. Bless, K. Wehrle: "Evaluation of Differentiated Services
using an Implementation und Linux"; Proceedings of the Intern.
Workshop on Quality of Service (IWQOS'99), London, 1999
[15] R. Bless, K. Wehrle. Group Communication in Differentiated
Services Networks, Internet QoS for the Global Computing 2001
(IQ 2001), IEEE International Symposium on Cluster Computing
and the Grid), May 2001, Brisbane, Australia, IEEE Press
[16] K. Wehrle, J. Reber, V. Kahmann. A simulation suite for
Internet nodes with the ability to integrate arbitrary Quality
of Service behavior, Proceedings of Communication Networks And
Distributed Systems Modeling And Simulation Conference (CNDS
2001), Phoenix (AZ), January 2001
7 Acknowledgements
The authors wish to thank all the people from the Institute of
Telematics (University of Karlsruhe) and those from the DiffServ
community who contributed to the discussion of all the topics
related to this document.
Special thanks go to Milena Neumann for her extensive efforts in
performing the simulations. We would also like to thank the KIDS
simulation team [16].
8 Authors' Addresses
Comments and questions related to this document can be addressed to
one of the authors listed below.
Roland Bless
Institute of Telematics
Universitaet Karlsruhe (TH)
Zirkel 2
D-76128 Karlsruhe, Germany
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Phone: +49 721 608 6413
Email: bless@tm.uka.de
Klaus Wehrle
Institute of Telematics
Universitaet Karlsruhe (TH)
Zirkel 2
D-76128 Karlsruhe, Germany
Phone: +49 721 608 6414
Email: wehrle@tm.uka.de
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Appendix
A Proof of the Neglected Reservation Subtree Problem
In the following, it is shown that the NRS problem actually exists
and occurs in reality. Hence, we investigated the problem and its
solution using a standard Linux Kernel (v2.3.49) and the Linux-based
implementation KIDS, which is described in an early version detailed
in [14].
Furthermore, we implemented the proposed solution for the NRS
problem by enhancing the multicast routing table as well as the
multicast routing behavior in the Linux kernel. In the following
section, the modification is briefly described.
Additional measurements with the simulation model simulatedKIDS [16]
will be presented in appendix B. They show the effects of the NRS
problem more detailed and also the behavior of the BAs using or not
using the Limited Effort PHB for re-marking.
A.1 Implementation of the proposed solution
As described in section 3.1, the proposed solution for avoiding the
NRS Problem is just adding one byte to the routing table entries in
each Multicast router. In the Linux OS the multicast routing table
is implemented by the "Multicast Forwarding Cache (MFC)". The MFC is
a hash table consisting of an "mfc-cache"-entry for each combination
of the following three parameters: sender's IP address, multicast
group address and incoming interface.
The routing information in a "mfc-cache"-entry is kept in an array
of TTLs for each virtual interface. When the TTL is zero, a packet
matching to this "mfc-cache"-entry will not be forwarded on this
virtual interface. Otherwise, if the TTL is less than the packet's
TTL, the latter will be forwarded on the interface with a decreased
TTL.
In order to set an appropriate codepoint if bandwidth is allocated
on an outgoing link, we added a second array of bytes -- similar to
the TTL array -- for specifying the codepoint that should be used on
a particular virtual interface. The first six bits of the byte
contain the DSCP that should be used and the seventh bit indicates,
whether the original codepoint in the packet has to be changed to
the specified one (=0) or has to be left unchanged (=1). The
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default entry of the codepoint byte is zero, so initially all
packets will be re-marked to the default DSCP.
Furthermore, we modified the multicast forwarding code for
considering this information while replicating multicast packets. To
change an "mfc-cache"-entry we implemented a daemon for exchanging
the control information (e.g. JOIN-INDICATION - and SET-CODEPOINT-
messages) with a management entity (e.g., a bandwidth broker).
Currently, the daemon uses a proprietary protocol, but it is planned
to migrate to the COPS protocol (RFC 2748).
A.2 Test Environment and Execution
Sender
+---+ FHN: First Hop Node
| S | BN: Boundary Node
+---+
+#
+#
+#
+---+ +--+ +------+
|FHN|++++++++++++|BN|+++++++++++| host |
| |############| |***********| B |
+---+ +--+## +------+
+# #
+# #
+# #
+------+ +------+
|host A| |host C|
+------+ +------+
+++ EF flow (group1) with reservation
### EF flow (group2) with reservation
*** EF flow (group2) without reservation
Figure A.1: Evaluation of NRS-Problem described in
Figure 3
In order to prove NRS problem case 1, as described in section 2.1, a
testbed shown in Figure A.1 was built. It is a reduced version of
the network shown in Figure 5 and consists of two DS-capable
routers, a first-hop router and an egress boundary router. The
absence of interior routers does not have any effects on to the
proof of the described problem.
The testbed comprises of two Personal Computers (Pentium III at 450
Mhz, 128 MB Ram, 3 network cards Intel eepro100) used as DiffServ
routers, as well as one sender and three receiver systems (also
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PCs). On the routers KIDS has been installed and a mrouted
(Multicast Routing Daemon) was used to perform multicast routing.
The network was completely built of separate 10BaseT Ethernet
segments in full-duplex mode. In [14] we evaluated the performance
of the software routers and found out that even a PC at 200Mhz had
no problem to handle up to 10Mbps DS traffic on each link.
Therefore, the presented measurements are not a result of
performance bottlenecks caused by these software routers.
The sender generated two shaped UDP traffic flows of 500kbps
(packets of 1.000 byte constant size) each and sends them to
multicast group 1 (233.1.1.1) and 2 (233.2.2.2). In both
measurements receiver A had a reservation along the path to the
sender for each flow, receiver B has reserved for flow 1 and C for
flow 2. Therefore, two static profiles are installed in the first-
hop router with 500kbps EF bandwidth and a token bucket size of
10.000byte for each flow.
In the egress boundary router one profile has been installed for the
output link to host B and one related for the output link to host C.
Each of them permits up to 500kbps Expedited Forwarding, but only
the aggregate of Expedited Forwarding traffic carried on the
outgoing link is considered.
In measurement 1 the hosts A and B joined to group 1 and A, B and C
joined to group 2. Those joins are using a reservation for the group
towards the sender. Only the join of host B to group 2 has no
admitted reservation. As described in section 2.1 this will cause
the NRS problem (case 1). Metering and policing mechanisms in the
egress boundary router throttle down the EF aggregate to the
reserved 500kbps, no depending on whether individual flows have
reserved or not.
+--------+--------+--------+
| Host A | Host B | Host C |
+---------+--------+--------+--------+
| Group 1 | 500kbps| 250kbps| 500kbps|
+---------+--------+--------+--------+
| Group 2 | 500kbps| 250kbps| |
+---------+--------+--------+--------+
Figure A.2: Results of measurement 1 (without the
proposed solution): Average bandwidth of
each flow.
--> Flows of group 1 and 2 on the link to
host B share the reserved aggregate of
group 1.
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Figure A.2 shows the obtained results. Host A and C received their
flows without any interference. But host B received data from group
1 only with half of the reserved bandwidth, so one half of the
packets have been discarded. Figure A.2 also shows that receiver B
got the total amount of bandwidth for group 1 and 2, that is exactly
the reserved 500kbps. Flow 2 got Expedited Forwarding without
actually having reserved any bandwidth and additionally violated the
guarantee of group 1 on that link.
For measurement 2 the previously presented solution (cf. section
3.1) has been installed in the boundary router. Now it checks during
duplicating the packets, whether the codepoint has to be changed to
Best-Effort (or Limited Effort) or whether it can be just
duplicated. In this measurement it changed the codepoint for group 2
on the link to Host B to Best-Effort.
+--------+--------+--------+
| Host A | Host B | Host C |
+---------+--------+--------+--------+
| Group 1 | 500kbps| 500kbps| 500kbps|
+---------+--------+--------+--------+
| Group 2 | 500kbps| 500kbps| |
+---------+--------+--------+--------+
Figure A.3: Results of measurement 1 (with the
proposed solution): Average bandwidth of
each flow.
--> Flow of group 1 on the link to host B
gets the reserved bandwidth of group 1.
The flow of group 2 has been re-marked to
Best-Effort.
Results of this measurement are presented in Figure A.3. Each host
received its flows with the reserved bandwidth and without any
packet loss. Packets from group 2 are re-marked in the boundary
router so that they have been treated as best-effort traffic. In
this case, they got the same bandwidth as the Expedited Forwarding
flow, because there was not enough other traffic on the link
present, and thus no need to discard packets.
The above measurements confirm that the Neglected Reservation
Subtree problem is to be taken seriously and that the presented
solution will solve it.
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B Simulative Study of the NRS Problem and Limited Effort PHB
This section shows some results from a simulative study which shows
the correctness of the proposed solution and the effect of re-
marking the responsible flow to Limited Effort. A proof of the NRS
problem has also been given in appendix A and in [15]. This section
shows the benefit for the default Best Effort traffic when Limited
Effort is used for re-marking instead of Best Effort. The results
strongly motivate the use of Limited Effort.
B.1 Simulation Scenario
In the following scenario Boundary Routers had a link speed of 10
Mpbs and Interior Routers had a link speed of 12 Mbps. In Boundary
Routers a 5 Mbps aggregate for EF has been reserved.
When Limited Effort was used, LE got 10% capacity (0.5Mpbs) from the
original BE aggregate and BE 90% (4.5Mbps) of the original BE
aggregate capacity. The bandwidth between LE and BE is shared by
using WFQ scheduling.
The following topology was used, where Sx is a sender, BRx a
Boundary Router, IRx an Interior Router and Dx a
destination/receiver.
+--+ +--+ +---+ +--+
|S1| |S0| /=|BR5|=====|D0|
+--+ +--+ // +---+ +--+
\\ || //
\\ || //
+--+ \+---+ +---+ +---+ +---+ +--+
|S2|===|BR1|=====|IR1|=====|IR2|======|BR3|=====|D1|
+--+ +---+ /+---+ +---+ +---+ +--+
// \\ +--+
// \\ /=|D2|
+--+ +---+ // \\ // +--+
|S3|===|BR2|=/ +---+/
+--+ +---+ /=|BR4|=\
|| +--+ // +---+ \\ +--+
+--+ |D4|=/ \=|D3|
|S4| +--+ +--+
+--+
Figure B.1: Simulation Topology
The following table shows the flows in the simulation runs, e.g.,
EF0 is sent from Sender S0 to Destination D0 with a rate of 4 Mbps
using an EF reservation.
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In the presented cases (I to IV) different amounts of BE traffic
were used to show the effects of Limited Effort in different cases.
The intention of these four cases is described after the table.
In all simulation models EF sources generated constant rate traffic
with constant packet sizes using UDP.
The BE sources also generated constant rate traffic, where BE0 used
UDP and BE1 used TCP as transport protocol.
+----+--------+-------+----------+-----------+-----------+---------+
|Flow| Source | Dest. | Case I | Case II | Case III | Case IV |
+----+--------+-------+----------+-----------+-----------+---------+
| EF0| S0 | D0 | 4 Mbps | 4 Mbps | 4 Mbps | 4 Mbps |
+----+--------+-------+----------+-----------+-----------+---------+
| EF1| S1 | D1 | 2 Mbps | 2 Mbps | 2 Mbps | 2 Mbps |
+----+--------+-------+----------+-----------+-----------+---------+
| EF2| S2 | D2 | 5 Mbps | 5 Mbps | 5 Mbps | 5 Mbps |
+----+--------+-------+----------+-----------+-----------+---------+
| BE0| S3 | D3 | 1 Mbps | 2.25 Mbps | 0.75 Mbps |3.75 Mbps|
+----+--------+-------+----------+-----------+-----------+---------+
| BE1| S4 | D4 | 4 Mbps | 2.25 Mbps | 0.75 Mbps |3.75 Mbps|
+----+--------+-------+----------+-----------+-----------+---------+
Table B.1: Direction, amount and Codepoint of flows in the four
simulation cases (case I to IV)
The four cases (I to IV) used in the simulation runs had the
following characteristics:
Case I: In this scenario the BE sources sent together exactly 5 Mbps
so there is no congestion in the BE queue.
Case II: BE is sending less than 5 Mbps, so there is space available
in the BE queue for re-marked traffic. BE0 and BE1 are sending
together 4.5 Mbps, which is exactly the share of BE, when LE is
used. So when multicast packets are re-marked to LE because of the
NRS problem, then LE should get 0.5 Mbps and BE 4.5 Mbps, which is
still enough for BE0 and BE1. LE should not show a greedy behavior
and should not use resources from BE.
Case III: In this case BE is very low. BE0 and BE1 use together only
1.5 Mbps. So when LE is used, it should be able to use the unused
bandwidth resources from BE.
Case IV: BE0 and BE1 send together 7.5 Mbps so there is congestion
in the BE queue. In this case LE should get 0.5 Mbps (not more and
not less).
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In each scenario loss rate and throughput of the considered flows
and aggregates have been metered.
B.2 Simulation Results for different router types
B.2.1 Interior Router
When the branching point of a newly added multicast subtree is
located in an Interior Router the NRS problem can occur as described
in section 2.1 (Case 2).
In the simulation runs presented in the following four subsections
D3 joins to the multicast group of sender S0 without making any
reservation or resource allocation. Consequently a new branch is
added to the existing multicast tree. The branching point issued by
the join of D3 is located in IR2. On the link to BR3 no bandwidth
was allocated for the new flow (EF0).
The metered throughput of flows on the link between IR2 and BR3 in
the four different cases is shown in the following four subsections.
The situation before the new receiver joins is shown in the second
column. The situation after the join without the proposed solution
is shown in column three. The fourth column presents the results
when the proposed solution of section 3.1 is used and the
responsible flow is re-marked to LE.
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B.2.1.1 Case I:
+--------+-----------------+-----------------+------------------+
| | before join | after join |after join, |
| | | (no re-marking) |(re-marking to LE)|
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: 4.007 Mbps | LE0: 0.504 Mbps |
|achieved| EF1: 2.001 Mbps | EF1: 2.003 Mbps | EF1: 2.000 Mbps |
|through-| EF2: 5.002 Mbps | EF2: 5.009 Mbps | EF2: 5.000 Mbps |
|put | BE0: 1.000 Mbps | BE0: 0.601 Mbps | BE0: 1.000 Mbps |
| | BE1: 4.000 Mbps | BE1: 0.399 Mbps | BE1: 3.499 Mbps |
+--------+-----------------+-----------------+------------------+
|BA | EF: 7.003 Mbps | EF: 11.019 Mbps | EF: 7.000 Mbps |
|through-| BE: 5.000 Mbps | BE: 1.000 Mbps | BE: 4.499 Mbps |
|put | LE: --- | LE: --- | LE: 0.504 Mbps |
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: 0 % | LE0: 87.4 % |
|packet | EF1: 0 % | EF1: 0 % | EF1: 0 % |
|loss | EF2: 0 % | EF2: 0 % | EF2: 0 % |
|rate | BE0: 0 % | BE0: 34.8 % | BE0: 0 % |
| | BE1: 0 % | BE1: 59.1 % | BE1: 0 % |
+--------+-----------------+-----------------+------------------+
(*) EF0 is re-marked to LE and signed as LE0
B.2.1.2 Case II:
+--------+-----------------+-----------------+------------------+
| | before join | after join |after join, |
| | | (no re-marking) |(re-marking to LE)|
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: 4.003 Mbps | LE0: 0.500 Mbps |
|achieved| EF1: 2.000 Mbps | EF1: 2.001 Mbps | EF1: 2.001 Mbps |
|through-| EF2: 5.002 Mbps | EF2: 5.005 Mbps | EF2: 5.002 Mbps |
|put | BE0: 2.248 Mbps | BE0: 0.941 Mbps | BE0: 2.253 Mbps |
| | BE1: 2.252 Mbps | BE1: 0.069 Mbps | BE1: 2.247 Mbps |
+--------+-----------------+-----------------+------------------+
|BA | EF: 7.002 Mbps | EF: 11.009 Mbps | EF: 7.003 Mbps. |
|through-| BE: 4.500 Mbps | BE: 1.010 Mbps | BE: 4.500 Mbps |
|put | LE: --- | LE: --- | LE: 0.500 Mbps |
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: 0 % | LE0: 87.4 % |
|packet | EF1: 0 % | EF1: 0 % | EF1: 0 % |
|loss | EF2: 0 % | EF2: 0 % | EF2: 0 % |
|rate | BE0: 0 % | BE0: 58.0 % | BE0: 0 % |
| | BE1: 0 % | BE1: 57.1 % | BE1: 0 % |
+--------+-----------------+-----------------+------------------+
(*) EF0 is re-marked to LE and signed as LE0
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B.2.1.3 Case III:
+--------+-----------------+-----------------+------------------+
| | before join | after join |after join, |
| | | (no re-marking) |(re-marking to LE)|
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: 3.998 Mbps | LE0: 3.502 Mbps |
|achieved| EF1: 2.000 Mbps | EF1: 2.001 Mbps | EF1: 2.001 Mbps |
|through-| EF2: 5.000 Mbps | EF2: 5.002 Mbps | EF2: 5.003 Mbps |
|put | BE0: 0.749 Mbps | BE0: 0.572 Mbps | BE0: 0.748 Mbps |
| | BE1: 0.749 Mbps | BE1: 0.429 Mbps | BE1: 0.748 Mbps |
+--------+-----------------+-----------------+------------------+
|BA | EF: 7.000 Mbps | EF: 11.001 Mbps | EF: 7.004 Mbps |
|through-| BE: 1.498 Mbps | BE: 1.001 Mbps | BE: 1.496 Mbps |
|put | LE: --- | LE: --- | LE: 3.502 Mbps |
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: 0 % | LE0: 12.5 % |
|packet | EF1: 0 % | EF1: 0 % | EF1: 0 % |
|loss | EF2: 0 % | EF2: 0 % | EF2: 0 % |
|rate | BE0: 0 % | BE0: 19.7 % | BE0: 0 % |
| | BE1: 0 % | BE1: 32.6 % | BE1: 0 % |
+--------+-----------------+-----------------+------------------+
(*) EF0 is re-marked to LE and signed as LE0
B.2.1.4 Case IV:
+--------+-----------------+-----------------+------------------+
| | before join | after join |after join, |
| | | (no re-marking) |(re-marking to LE)|
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: 4.001 Mbps | LE0: 0.500 Mbps |
|achieved| EF1: 2.018 Mbps | EF1: 2.000 Mbps | EF1: 2.003 Mbps |
|through-| EF2: 5.005 Mbps | EF2: 5.001 Mbps | EF2: 5.007 Mbps |
|put | BE0: 2.825 Mbps | BE0: 1.000 Mbps | BE0: 3.425 Mbps |
| | BE1: 2.232 Mbps | BE1: --- | BE1: 1.074 Mbps |
+--------+-----------------+-----------------+------------------+
|BA | EF: 7.023 Mbps | EF: 11.002 Mbps | EF: 7.010 Mbps |
|through-| BE: 5.057 Mbps | BE: 1.000 Mbps | BE: 4.499 Mbps |
|put | LE: --- | LE: --- | LE: 0.500 Mbps |
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: 0 % | LE0: 75.0 % |
|packet | EF1: 0 % | EF1: 0 % | EF1: 0 % |
|loss | EF2: 0 % | EF2: 0 % | EF2: 0 % |
|rate | BE0: 23.9 % | BE0: 73.3 % | BE0: 0 % |
| | BE1: 41.5 % | BE1: --- | BE1: 0 % |
+--------+-----------------+-----------------+------------------+
(*) EF0 is re-marked to LE and signed as LE0
NOTE: BE1 has undefined throughput and loss in situation "after join
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(no re-marking)", because TCP is going into retransmission back-off
timer phase and closes the connection after 512 seconds.
B.2.2 Boundary Router
When the branching point of a newly added multicast subtree is
located in a Boundary Router the NRS problem can occur as described
in section 2.1 (Case 1).
In the simulation runs presented in the following four subsections
D3 joins to the multicast group of sender S1 without making any
reservation or resource allocation. Consequently, a new branch is
added to the existing multicast tree. The branching point issued by
the join of D3 is located in BR3. On the link to BR4 no bandwidth
was allocated for the new flow (EF1).
The metered throughput of the flows on the link between BR3 and BR4
in the four different cases is shown in the following four
subsections. The situation before the new receiver joins is shown in
the second column. The situation after the join but without the
proposed solution is shown in column three. The fourth column
presents results when the proposed solution of section 3.1 is used
and the responsible flow is re-marked to LE.
B.2.2.1 Case I:
+--------+-----------------+-----------------+------------------+
| | before join | after join |after join, |
| | | (no re-marking) |(re-marking to LE)|
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: --- | EF0: --- |
|achieved| EF1: --- | EF1: 1.489 Mbps | LE1: 0.504 Mbps |
|through-| EF2: 5.002 Mbps | EF2: 3.512 Mbps | EF2: 5.002 Mbps |
|put | BE0: 1.000 Mbps | BE0: 1.000 Mbps | BE0: 1.004 Mbps |
| | BE1: 4.000 Mbps | BE1: 4.002 Mbps | BE1: 3.493 Mbps |
+--------+-----------------+-----------------+------------------+
|BA | EF: 5.002 Mbps | EF: 5.001 Mbps | EF: 5.002 Mbps |
|through-| BE: 5.000 Mbps | BE: 5.002 Mbps | BE: 4.497 Mbps |
|put | LE: --- | LE: --- | LE: 0.504 Mbps |
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: --- | EF0: --- |
|packet | EF1: --- | EF1: 25.6 % | LE1: 73.4 % |
|loss | EF2: 0 % | EF2: 29.7 % | EF2: 0 % |
|rate | BE0: 0 % | BE0: 0 % | BE0: 0 % |
| | BE1: 0 % | BE1: 0 % | BE1: 0 % |
+--------+-----------------+-----------------+------------------+
(*) EF1 is re-marked to LE and signed as LE1
B.2.2.2 Case II:
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+--------+-----------------+-----------------+------------------+
| | before join | after join |after join, |
| | | (no re-marking) |(re-marking to LE)|
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: --- | EF0: --- |
|achieved| EF1: --- | EF1: 1.520 Mbps | LE1: 0.504 Mbps |
|through-| EF2: 5.003 Mbps | EF2: 3.482 Mbps | EF2: 5.002 Mbps |
|put | BE0: 2.249 Mbps | BE0: 2.249 Mbps | BE0: 2.245 Mbps |
| | BE1: 2.252 Mbps | BE1: 2.252 Mbps | BE1: 2.252 Mbps |
+--------+-----------------+-----------------+------------------+
|BA | EF: 5.003 Mbps | EF: 5.002 Mbps | EF: 5.002 Mbps |
|through-| BE: 4.501 Mbps | BE: 4.501 Mbps | BE: 4.497 Mbps |
|put | LE: --- | LE: --- | LE: 0.504 Mbps |
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: --- | EF0: --- |
|packet | EF1: --- | EF1: 24.0 % | LE1: 74.8 % |
|loss | EF2: 0 % | EF2: 30.4 % | EF2: 0 % |
|rate | BE0: 0 % | BE0: 0 % | BE0: 0 % |
| | BE1: 0 % | BE1: 0 % | BE1: 0 % |
+--------+-----------------+-----------------+------------------+
(*) EF1 is re-marked to LE and signed as LE1
B.2.2.3 Case III:
+--------+-----------------+-----------------+------------------+
| | before join | after join |after join, |
| | | (no re-marking) |(re-marking to LE)|
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: --- | EF0: --- |
|achieved| EF1: --- | EF1: 1.084 Mbps | LE1: 2.000 Mbps |
|through-| EF2: 5.001 Mbps | EF2: 3.919 Mbps | EF2: 5.000 Mbps |
|put | BE0: 0.749 Mbps | BE0: 0.752 Mbps | BE0: 0.750 Mbps |
| | BE1: 0.749 Mbps | BE1: 0.748 Mbps | BE1: 0.750 Mbps |
+--------+-----------------+-----------------+------------------+
|BA | EF: 5.001 Mbps | EF: 5.003 Mbps | EF: 5.000 Mbps |
|through-| BE: 1.498 Mbps | BE: 1.500 Mbps | BE: 1.500 Mbps |
|put | LE: --- | LE: --- | LE: 2.000 Mbps |
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: --- | EF0: --- |
|packet | EF1: --- | EF1: 45.7 % | LE1: 0 % |
|loss | EF2: 0 % | EF2: 21.7 % | EF2: 0 % |
|rate | BE0: 0 % | BE0: 0 % | BE0: 0 % |
| | BE1: 0 % | BE1: 0 % | BE1: 0 % |
+--------+-----------------+-----------------+------------------+
(*) EF1 is re-marked to LE and signed as LE1
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B.2.2.4 Case IV:
+--------+-----------------+-----------------+------------------+
| | before join | after join |after join, |
| | | (no re-marking) |(re-marking to LE)|
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: --- | EF0: --- |
|achieved| EF1: --- | EF1: 1.201 Mbps | LE1: 0.500 Mbps |
|through-| EF2: 5.048 Mbps | EF2: 3.803 Mbps | EF2: 5.004 Mbps |
|put | BE0: 2.638 Mbps | BE0: 2.535 Mbps | BE0: 3.473 Mbps |
| | BE1: 2.379 Mbps | BE1: 2.536 Mbps | BE1: 1.031 Mbps |
+--------+-----------------+-----------------+------------------+
|BA | EF: 5.048 Mbps | EF: 5.004 Mbps | EF: 5.004 Mbps |
|through-| BE: 5.017 Mbps | BE: 5.071 Mbps | BE: 4.504 Mbps |
|put | LE: --- | LE: --- | LE: 0.500 Mbps |
+--------+-----------------+-----------------+------------------+
| | EF0: --- | EF0: --- | EF0: --- |
|packet | EF1: --- | EF1: 40.0 % | LE1: 68.6 % |
|loss | EF2: 0 % | EF2: 23.0 % | EF2: 0 % |
|rate | BE0: 30.3 % | BE0: 32.1 % | BE0: 0 % |
| | BE1: 33.3 % | BE1: 32.7 % | BE1: 0 % |
+--------+-----------------+-----------------+------------------+
(*) EF1 is re-marked to LE and signed as LE1
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