One document matched: draft-ietf-l2vpn-vpms-frmwk-requirements-00.xml
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<front>
<title abbrev="VPMS Framework and Requirements">
Framework and Requirements for Virtual Private Multicast Service (VPMS)
</title>
<author initials='Y.' surname="Kamite" fullname='Yuji Kamite'>
<organization abbrev="NTT Communications">
NTT Communications Corporation
</organization>
<address>
<postal>
<street>Granpark Tower</street>
<street>3-4-1 Shibaura, Minato-ku</street>
<region>Tokyo</region>
<code>108-8118</code>
<country>Japan</country>
</postal>
<email>y.kamite@ntt.com</email>
</address>
</author>
<author initials='F.' surname="Jounay" fullname='Frederic Jounay'>
<organization abbrev="France Telecom">
France Telecom
</organization>
<address>
<postal>
<street>2, avenue Pierre-Marzin</street>
<street>22307 Lannion Cedex</street>
<country>France</country>
</postal>
<email>frederic.jounay@orange-ftgroup.com</email>
</address>
</author>
<author initials='B.' surname="Niven-Jenkins" fullname='Ben Niven-Jenkins'>
<organization abbrev="BT">
BT
</organization>
<address>
<postal>
<street>208 Callisto House, Adastral Park</street>
<street>Ipswich, IP5 3RE</street>
<country>UK</country>
</postal>
<email>benjamin.niven-jenkins@bt.com</email>
</address>
</author>
<author initials='D.' surname="Brungard" fullname='Deborah Brungard'>
<organization abbrev="AT&T">
AT&T
</organization>
<address>
<postal>
<street>Rm. D1-3C22, 200 S. Laurel Ave.</street>
<street>Middletown, NJ, 07748</street>
<country>USA</country>
</postal>
<email>dbrungard@att.com</email>
</address>
</author>
<author initials='L.' surname="Jin" fullname='Lizhong Jin'>
<organization abbrev="Nokia Siemens Networks">
Nokia Siemens Networks
</organization>
<address>
<postal>
<street>Building 89, 1122 North QinZhou Road,</street>
<street>Shanghai, 200211</street>
<country>P.R.China</country>
</postal>
<email>lizhong.jin@nsn.com</email>
</address>
</author>
<date day="19" month="Jan" year="2009"/>
<abstract>
<t>
This document provides a framework and service level requirements for
Virtual Private Multicast Service (VPMS).
VPMS is defined as a Layer 2 VPN service that provides
point-to-multipoint
connectivity for a variety of Layer 2 link layers across an IP or
MPLS-enabled PSN.
This document outlines architectural service models of VPMS
and states generic and high level requirements.
This is intended to aid in developing protocols and
mechanisms to support VPMS.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<section title="Problem Statement">
<t>
<xref target="RFC4664"/> describes different types of
Provider Provisioned Layer 2 VPNs (L2 PPVPNs, or L2VPNs);
Some of them are widely deployed today, such as
Virtual Private Wire Service (VPWS) and
Virtual Private LAN Service (VPLS).
A VPWS is a VPN service that supplies a
Layer 2 (L2) point-to-point service.
A VPLS is an L2 service that emulates Ethernet LAN service across
a Wide Area Network (WAN).
</t>
<t>
For some use cases described hereafter, there are
P2MP (point-to-multipoint) type services for Layer 2
traffic. However, there is no straightforward way to realize them
based on the existing L2VPN specifications.
</t>
<t>
In a VPWS, a SP can set up point-to-point connectivity
per a pair of
CEs but it is not possible to replicate traffic
for point-to-multipoint
services in the SP's network side. A SP could build
multiple PWs independently and have the CEs replicate traffic over
them, but this is not only inconvenient for the customer, it’s a
waste of bandwidth resources.
</t>
<t>
In a VPLS, SPs can natively offer multipoint connectivity across
their backbone. Although it is seemingly applicable for point-to-
multipoint service as well, there remains extra complexity for SPs to
filter unnecessary traffic between irrelevant sites (i.e., from a
receiver PE to another receiver PE) because VPLS provides
multipoint-to-multipoint connectivity between CEs. Moreover, VPLS's
MAC-based learning/forwarding operation is unnecessary for
some scenarios particularly if customers only need simple
unidirectional point-to-multipoint service, or if they require non-
Ethernet Layer 2 connectivity.
</t>
<t>
Consequently, there is a real need for a solution
that natively provides point-to-multipoint service in L2VPN.
</t>
</section>
<section title="Scope of This Document">
<t>
VPMS is defined as a Layer 2 service that provides point-to-
multipoint connectivity for a variety of Layer2 link layers across an
IP or MPLS-enabled PSN. VPMS is categorized as a class of provider-
provisioned Layer 2 Virtual Private Networks (L2VPN).
</t>
<t>
This document introduces a new service framework, reference
model and functional requirements for
VPMS by extending the existing
framework <xref target="RFC4664"/> and requirements
<xref target="RFC4665"/> for L2VPNs.
</t>
<t>
The technical specifications are outside the scope of this
document. There is no intent to specify
solution-specific details.
</t>
<t>
This document provides requirements from both the Service Provider's
and the Customer's point of view.
</t>
</section>
</section>
<section title="Conventions used in this document">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" in this document are to be interpreted as
described in
<xref target="RFC2119"/>
.
</t>
</section>
<section title="Terminology">
<t>
The content of this document makes use of the terminology defined in
<xref target="RFC4026"/>.
For readability purposes, we list some of the terms here
in addition to some specific terms used in this document.
</t>
<section title="Acronyms">
<t>
<list style='hanging'>
<t hangText='P2P:'>
Point-to-Point
</t>
</list>
</t>
<t>
<list style='hanging'>
<t hangText='P2MP:'>
Point-to-Multipoint
</t>
</list>
</t>
<t>
<list style='hanging'>
<t hangText='PW:'>
Pseudowire
</t>
</list>
</t>
<t>
<list style='hanging'>
<t hangText='VPMS:'>
Virtual Private Multicast Service
</t>
</list>
</t>
<t>
<list style='hanging'>
<t hangText='PE/CE:'>
Provider/Customer Edge
</t>
</list>
</t>
<t>
<list style='hanging'>
<t hangText='P:'>
Provider Router
</t>
</list>
</t>
<t>
<list style='hanging'>
<t hangText='AC:'>
Attachment Circuit
</t>
</list>
</t>
<t>
<list style='hanging'>
<t hangText='PSN:'>
Packet Switched Network
</t>
</list>
</t>
<t>
<list style='hanging'>
<t hangText='SP:'>
Service Provider
</t>
</list>
</t>
</section>
</section>
<section title="Use Cases">
<section title="Ethernet Use Case">
<t>
For multicast traffic delivery, there is a requirement to deliver a
unidirectional P2MP service in addition to the existing P2P service.
The demand is growing to provide private (P2MP native Ethernet) services, for various applications such as IP-
based delivery of TV broadcasting, content delivery networks, etc.
Moreover, many digital audio/video devices (e.g., MPEG-TS, HD-SDI)
that supports Ethernet interfaces are becoming available, which will
make Ethernet P2MP service more common. Also there are some
applications that naturally suited to static transport of VPMS. For
example, MPEG-TS/IP/ Ethernet in DVB-H is typically static broadcast
without any signaling in the upstream direction. VPMS could be a
possible solution to provide these kinds of networking connectivity
over PSNs.
</t>
<t>
Currently VPLS <xref target="RFC4761"/><xref target="RFC4762"/>
is able to give P2MP-type
replication for Ethernet traffic. Native VPLS already supports this
capability via a full mesh of PWs, and an extension to optimize
replication is also proposed [I-D.ietf-l2vpn-vpls-mcast] as an
additional feature. However, VPLS by nature requires MAC-based
learning and forwarding, which might not be needed in some cases by
particular users. Generally, video distribution applications use unidirectional P2MP traffic, but may not always require any added
complexity of MAC address management. In addition, VPLS is a service
that essentially provides any-to-any connectivity between all CEs in
a L2VPN as it emulates a LAN service. However, if only P2MP
connectivity is required, the traffic between different receivers is not always
needed, and traffic from receiver to sender is not always needed,
either. In these cases, VPMS is a service that provides much simpler
operation.
</t>
<t>
Note that VPMS provides single coverage of receiver membership; that
is, there is no distinct differentiation for multiple multicast
groups. All traffic from a particular Attachment Circuit (AC) will
be forwarded toward the same remote receivers, even if the destination MAC
address is changed. Basically in VPMS, destination MAC addresses are
not used for forwarding, which is significantly different from VPLS.
If MAC-based forwarding is preferred (i.e., multicast/unicast
differentiation of MAC address), VPLS should be chosen rather than
VPMS.
</t>
</section>
<section title="ATM-based Use Case">
<t>
A use case of ATM-based service in VPMS could be to offer the
capability for
service providers to support IP multicast wholesale services over
ATM
in case the wholesale customer relies on ATM infrastructure. The
P2MP support alleviates the constraint in terms of replication for ATM to
support IP multicast services.
</t>
<t>
Another use case of VPMS for ATM is for audio/video stream
applications. Today many digital TV broadcasting networks adopt ATM-
based distribution systems with point-to-multipoint PVPs/PVCs. The
transport network supports replicating ATM cells in transit nodes to
efficiently deliver programs to multiple terminals. For migrating
such ATM-based networks onto IP/MPLS-based networks, VPMS is considered to be
a candidate solution.
</t>
</section>
<section title="TDM-based Use Case">
<t>
Today the existing VPWS already supports TDM emulation services
(SAToP, CESoPSN or TDMoIP). It is a Layer 1 service, not Layer 2
service; however, a common architecture is being used since they are
all packet-based emulations over a SP's network. VPMS is also considered to be a solution for such TDM applications that require
point-to-multipoint topology.
</t>
<t>
In a PSN environment, the existing VPWS allows support for 2G/3G
mobile backhauling (e.g. TDM traffic for GSM's Abis interface, ATM
traffic for Release 99 UMTS's Iub interface). Currently, the
Mobile backhauling architecture is always built as a star topology
between the 2G/3G controller (e.g. BSC or RNC) and the 2G/3G Base
Stations (BTS or NodeB). Therefore VPWSes (P2P services) are used
between each Base Station and their corresponding controller and
nothing more is required.
</t>
<t>
As far as synchronization in a PSN environment is concerned,
different mechanisms can be considered to provide frequency and phase
clock required in the 2G/3G Mobile environment to guarantee mobile
handover and strict QoS. One of them consists of using Adaptive
Clock Distribution and Recovery. With this method a Master element
distributes a reference clock at protocol level by regularly sending
TDM PW packets (SAToP, CESoPSN or TDMoIP) to Slave elements. This
process is based on the fact that the volume of transmitted data
arrival is considered as an indication of the source frequency that
could be used by the Slave element to recover the source clock
frequency. Consequently, with the current methods, the PE connected
to the Master must setup and maintain as many VPWS (P2P) as their are
Slave elements, and the Master has to replicate the traffic. A
better solution to deliver the clock frequency would be to use a VPMS
which supports P2MP traffic. This may scale better than P2P
services (VPWS) with regards to the forwarding plane at the Master
since the traffic is no longer replicated to individual VPWSes (P2P)
but only to the AC associated to the VPMS (P2MP). It may ease the
provisioning process since only one source endpoint must be
configured at the Ingress PE. This alleviated provisioning process
would simplify the introduction of new Base
Stations. The main gain would be to avoid replication on the Master
and hence save bandwidth consumed by the synchronization traffic
which typically requires the highest level of QoS. This kind of
traffic will be competing with equivalent QOS traffic like VoIP, which
is why it is significant to save the slightest bandwidth.
</t>
</section>
</section>
<section title="Reference Model">
<t>
The VPMS reference model is shown in Figure 1.
</t>
<figure>
<artwork><![CDATA[
+-----+ AC1 AC2 +-----+
| CE1 |>---+ ------------------------ +--->| CE2 |
+-----+ | | | | +-----+
VPMS A | +------+ VPMS A +------+ | VPMS A
Sender +->|......>...+.......... >......|>-+ Receiver
| VPMS | . | VPMS |
| PE1 | . VPMS B | PE2 |
+-<|......<.. . ....+.....<......|<-+
| +------+ . . +------+ |
+-----+ | | . . | | +-----+
| CE4 |<---+ |Routed . . | +---| CE3 |
+-----+ AC4 |Backbone. . | AC3 +-----+
VPMS B | . . | VPMS B
Receiver | +-v-----v-+ | Sender
------| . . |-------
| . VPMS. |
| . PE3 . |
+---------+
v v
| |
AC5| |AC6
v v
+-----+ +-----+
| CE5 | | CE6 |
+-----+ +-----+
VPMS A VPMS B
Receiver Receiver
Figure 1: Reference Model for VPMS
]]></artwork>
</figure>
<t>
A VPMS instance is defined as a service entity manageable
in VPMS architecture. A single VPMS instance provides
isolated service reachability domain to each CE, so it
corresponds to a so-called "VPN" as a specific set of
sites that allows communication.
A single VPMS instance provides a unique
unidirectional point-to-multipoint L2VPN service.
In Figure 1, there are two VPMS instances shown,
VPMS A and VPMS B. In principle, there is no traffic exchange
allowed between these different instances, so they are treated
as different VPNs.
</t>
<t>
In a VPMS, a single CE-PE connection is used for transmitting frames
for delivery to multiple remote CEs, with point-to-multipoint duplication.
The SP's network (PE as well as P) has a role to duplicate frames so that
the traffic source does not need to send multiple frames to individual
receivers.
</t>
<t>
Like VPWS, an Attachment Circuit (AC) is provided to accommodate CEs
in a VPMS. In a VPMS, an AC attached to a VPMS MUST be configured as
"sender" or "receiver" not both. That is, any AC is associated with
the role of either sending side (Tx) or receiving side (Rx) from the
view of the CE. Thus every AC deals with unidirectional traffic
flows. A sender AC does not have a capability of transmitting the traffic
back to a CE at upstream side. Likewise a receiver AC does not
have a capability of receive the traffic from a CE at downstream side.
In Figure 1, AC1 and AC3 are configured as senders while AC2,
AC4, AC5 and AC6 are configured as receivers. In VPMS A, CE1 could send traffic
via AC1, but CE2 and CE5 could not send back traffic.
</t>
<t>
A CE which is locally connected to a sender AC
is called a sender CE. Also a CE which is locally
connected to a receiver AC is called a receiver CE.
However, such CEs’s roles will not be
managed directly in VPMS because the configured AC’s role
(sender or receiver)
will automatically determine them.
</t>
<t>
Basically there is a one-to-one mapping between an
attachment circuit and a VPMS instance.
For example, all traffic from CE1 to
PE1 (thorough AC1) is mapped to VPMS A (to CE2 and CE5).
</t>
<t>
In a VPMS, PEs will be connected by PW technology which may
include P2MP traffic optimization (i.e., P2MP PW. See section 7.2.).
P2MP traffic optimization will
provide the benefit of traffic replication for high bandwidth efficiency.
The sender CE has only to transmit one stream towards the PE and
it does not have to replicate traffic.
Also routed backbone provides
IP or MPLS-enabled PSN tunnels for transporting the PW traffic.
</t>
<t>
Regarding end-to-end traffic topology between the PEs,
a single VPMS instance (i.e., one VPN) may correspond
to a single unidirectional P2MP PW topology.
In Figure 1, VPMS A (one instance) has a single P2MP PW
topology (from PE1 to PE2 and PE3). However, there
is also a case that a single VPMS consists of two or more P2MP PW
topology grouped which is typically used for redundancy. The
details are given in section 6.1.2.
</t>
<t>
VPMS can support various Layer 2 protocol services
such as Ethernet, ATM, etc.
</t>
</section>
<section title="Customer Requirements">
<section title="Service Topology">
<section title="Point-to-Multipoint Support">
<t>
A solution MUST support unidirectional point-to-multipoint
connectivity from a sender to multiple receivers.
A sender CE is assured to send traffic to one or more receiver CEs.
Receiver CEs include not only the CEs which are located at remote sites,
but also the local CEs which are connected to the same sender-side PE.
If there is only one receiver in the instance, it is considered equivalent to
unidirectional point-to-point traffic.
</t>
</section>
<section title="Multiple Source Support">
<t>
A solution MUST support multiple sender topologies in one VPMS
instance, where a common receiver group is reachable from two or more
senders. This means that a solution needs to support having multiple
P2MP topologies in the backbone whose roots are located apart in a
common service. In other words, each P2MP topology MUST only have a single sender, however multiple P2MP topologies can be grouped together into a single VPMS instance.
For example, in Figure 2, traffic from sender CE1
and CE2 both reach receivers CE3 and CE4 while CE1, CE2, CE3 and CE4
all are associated with a single service. This topology is useful
for increasing service reliability by redundant sources. Note that
every receiver has only to have one AC connected to each PE to
receive traffic. (in Figure 2, AC3 and AC4 respectively). Thus a
solution will also need to support protection and restoration
mechanism combining these multiple P2MP topologies. (See section 6.4
too).
</t>
<figure>
<artwork><![CDATA[
+-----+ AC1 AC2+-----+
| CE1 |>-+ ---------------------------- +-<| CE2 |
+-----+ | | | | +-----+
VPMS A | +------+ +------+ | VPMS A
Sender +->|......>.. .............+..<......|<-+ Sender
Tx | VPMS | . . . | VPMS | Tx
| PE 1 | . . . | PE 2 |
| | . . . | |
+------+ . . . +------+
| . . . |
| +.. . ...... . |
| . . . . |
| . . . . |
| +-v----v-+ +-v----v-+ |
---| . . |---| . . |---
VPMS| . . | | . . |VPMS
PE 3| . | | . |PE 4
+--------+ +--------+
v v
AC3| |AC4
v v
+-----+ +-----+
| CE3 | | CE4 |
+-----+ +-----+
VPMS A VPMS A
Receiver Receiver
Figure 2: Multiple source support
]]></artwork>
</figure>
</section>
<section title="Reverse Traffic Support">
<t>
There are cases where a reverse traffic flow is necessary. A sender CE
might sometimes want to receive traffic from a receiver CE.
There are some usage scenarios for this, such as stream monitoring through a
loopback mechanism, control channels which need feedback communication
etc. The simplest way to accomplish this is to provide different
VPMS instances for reverse traffic, i.e. a sender CE is a receiver
of another VPMS instance.
</t>
<t>
Figure 3 illustrates this kind of reverse traffic scenario,
where CE1 is configured as a sender in VPMS A and a receiver
in VPMS B. VPMS B is used for reverse traffic.
Note that a closed single
network here is composed of two VPMS instances. In operational
terms, CE1 and CE4 belong to the same closed "VPN" by
administrative policy (e.g., CE1,
CE2, CE3 and CE4 are the devices in one enterprise's intranet
network).
</t>
<t>
Such bi-directional instances can be easily created if two distinct
ACs are provisioned for sending and receiving exclusively (e.g., if
VLAN id in dot1Q tagged frame is a service delimiter, different VLAN
ids are uniquely allocated for Tx and Rx). This approach is
acceptable if a receiver CE device can change Layer 2 interface
appropriately in data transmitting and receiving.
</t>
<t>
Meanwhile it is also true that this might be considered a limitation
in some deployment scenarios. If a CE is an IP router or Ethernet
bridge, reverse traffic is normally expected to be received on the
same interface as forward traffic on the receiver CE. (i.e., the same VLAN id is to be
used for reverse traffic if the AC supports dot1Q tagged frames.)
</t>
<t>
Therefore, in a VPMS solution,
both of the two type of ACs, sending (Tx) and receiving (Rx),
SHOULD be allowed to be placed in the same physical/virtual
circuit.
In Figure 3, suppose
AC5 of VPMS A is provisioned as {VLAN id = 100, direction= Rx}.
It is expected that operators can provision AC6 of VPMS B
in the same physical port as
{VLAN id = 100, direction = Tx}.
That is, the combination between VLAN id and the flow direction
is now considered to be a service delimiter.
</t>
<t>
Note, in most implementations of VPWS today, every AC is always
considered bidirectional and a unique Layer 2 header/circuit (ATM
VPI/VCI, an Ethernet port, a VLAN etc.) is considered the service
delimiter. In contrast in VPMS, every AC is considered
unidirectional and traffic direction is an additional element to
identify a unique AC.
</t>
<figure>
<artwork><![CDATA[
+-----+ <-- Rx VPMS B
| CE1 |<----------------+
+-----+--------------+ |
VPMS A Sender --> Tx VPMS A| |
VPMS B Receiver AC1 v ^ AC2
+----------+ VPMS
| . . | PE1
| . ... |
-------| . . |--------
| +-v------^-+ |
| . . |
| + . |
+------+ . . . . +------+
+-<|......<.. . .. . ......>..... |>-+
| | VPMS | . . | VPMS | |
AC3| | PE2 | . . | PE3 | |AC4
| +------+ . . +------+ |
+-----+ | | . . | | +-----+
| CE2 |<--+ | Routed . . | +-->| CE3 |
+-----+ <-- | Backbone. . | --> +-----+
VPMS A Rx | +-v------^-+ | Rx VPMS A
Receiver -------| . . |-------- Receiver
| . ... |
| . . | VPMS
+----------+ PE4
AC5v ^AC6
| | <-- Tx VPMS B +-----+
| +----------------<| CE4 |
+------------------->+-----+
--> Rx VPMS A VPMS A Receiver
VPMS B Sender
Figure 3: Reverse traffic support
]]></artwork>
</figure>
</section>
</section>
<section title="Transparency">
<t>
A solution is intended to provide Layer 2 traffic transparency.
Transparency SHOULD be honoured per VPMS instance basis.
In other words, Layer 2 traffic can be transparently transported
from a sender CE to receiver CEs in a given instance. Note, however,
if service delimiting fields (VLAN Id in Ethernet, VPI/VCI in ATM,
DLCI in FR etc.) are assigned by SP, they are not transparent. It
depends on SP’s choice if they are assigned at each AC. Hence it
could be that some of receiver CEs are getting traffic with different
delimiting fields than the other receiver CEs.
</t>
<t>
VPMS solution SHOULD NOT require any special packet processing by the
end users (CEs).
</t>
</section>
<section title="Quality of Service (QoS)">
<t>
A customer may require that the VPMS service provide the guaranteed QoS.
In particular, for real time applications which are considered common
in point-to-multipoint delivery, delay and loss sensitive traffic
MUST be supported. The solution SHOULD provide native QoS techniques
for service class differentiation,
such as IEEE 802.1p CoS for Ethernet.
</t>
<t>
For bandwidth committed services (e.g., ATM CBR),
a solution SHOULD guarantee end-to-end bandwidth.
It MAY provide flow admission control mechanisms to achieve that.
</t>
</section>
<section title="Protection and Restoration">
<t>
A solution MUST provide protection and restoration mechanism
for end-to-end services.
</t>
<section title="Dual-homed Access Support">
<t>
A solution MUST allow dual-homed redundant access from a CE to
multiple PEs. Additionally, a solution SHOULD provide
protection mechanism between the different PEs to which a CE is attached. This is because
when an ingress PE node fails whole traffic delivery will fail unless
a backup sender PE is provided, even in case of dual-homed access.
Similarly, if an egress PE node fails, traffic toward that CE is never
received unless a backup egress PE is provided. Figure 4 is an example for this access topology.
</t>
</section>
<section title="Single/Dual Traffic Support in Dual-homed Access">
<t>
When dual-homed access to sender PEs is provided, a solution MAY allow a sender CE to
transmit just a single copy of the traffic to either one of the two sender PEs, or to
transmit a copy of the traffic to both the PEs simultaneously. The latter
scenario consumes more resource of CE-PE link than
the single traffic scenario, but it is usually applicable when a source device has only a simple
forwarding capability without any switchover functionality.
In the dual traffic case, the backup ingress PE SHOULD be able to
filter the incoming unnecessary traffic while active PE is working. Also in either case,
single traffic or dual traffic, the protection mechanism of ingress
PEs described in the previous subsection will be necessary to handle
the traffic appropriately.
</t>
<t>
In the case of dual-homed access to receiver PEs, a solution MAY allow a receiver CE to
receive a single copy of the traffic from either one of the two egress PEs, or receive
a copy of the traffic from both PEs simultaneously.
The dual
traffic approach is applicable if CE has fast switchover capability
as a receiver by selecting either one of incoming traffic,
but note that additional traffic resources are always
consumed at PE-CE link of backup side.
Specifically in the single traffic case, it might be needed to
support switchover mechanism between egress PEs in failure.
</t>
<figure>
<artwork><![CDATA[
+-----+
| CE1 |--------------+
+-----+ \
VPMS A | |
Sender | v AC1
(dual-homed)| +----+
| -----|VPMS|--------
| | | PE1| |
\ | +----+ |
\ AC2 +----+ +----+ AC4
+------>|VPMS| |VPMS|------------+
| PE2| Routed | PE3| \
+----+ Backbone +----+\ |
AC3 / | | \ AC5 v
+-----+ / | | \ +-----+
| CE2 |<-+ | | \ | CE3 |
+-----+ | +----+ | \ +-----+
VPMS A ----|VPMS|--------- \ VPMS A
Receiver | PE4| | Receiver
+----+ |
| AC6 v
\ +-----+
+--------------->| CE4 |
+-----+
VPMS A
Receiver
(dual-homed)
Figure 4: Dual homing support
]]></artwork>
</figure>
</section>
</section>
<section title="Security">
<t>
The basic security requirement raised in
Section 6.5 of <xref target="RFC4665"/>
also applies to VPMS.
</t>
<t>
In addition, a VPMS solution MAY have the mechanisms to activate the
appropriate filtering capabilities (for example, MAC/VLAN filtering
etc.), and it MAY be added with the filtering control mechanism
between particular sender/receiver sites inside a VPMS instance. For
example, in Figure 1, filtering can be added such that traffic
from CE1 to CE4 and CE5 is allowed but traffic from CE1 to CE6 is
filtered.
</t>
</section>
<section title="Reordering Prevention">
<t>
A solution SHOULD prevent Layer 2 frame reordering when
delivering customer
traffic under normal conditions.
</t>
</section>
<section title="Failure reporting">
<t>
A solution MAY provide information to the customer about
failures. For example, if there is a loss of connectivity toward
some of the receiver CEs, it is reported to the sender CE.
</t>
</section>
</section>
<section title="Service Provider Network Requirements">
<section title="Scalability">
<t>
A VPMS solution MUST be designed to scale well
with an increase in the number of any of the following metrics:
</t>
<t>
<list style='hanging'>
<t hangText='-'>the number of PEs (per VPMS instance and total in a SP network)</t>
<t hangText='-'>the number of VPMS instances (per PE and total)</t>
<t hangText='-'>the number of sender CEs (per PE, VPMS instance and total)</t>
<t hangText='-'>the number of receiver CEs (per PE, VPMS instance and total)</t>
</list>
</t>
<t>
A VPMS solution SHALL document its scalability
characteristics in quantitative terms.
A solution SHOULD quantify the amount of
state that a PE and a P device has to support.
</t>
<t>
The scalability characteristics SHOULD include:
</t>
<t>
<list style='hanging'>
<t hangText='-'>
the processing resources required by
the control plane in managing PWs
(neighborhood or session maintenance messages,
keepalives, timers, etc.)
</t>
<t hangText='-'>
the processing resources required by
the control plane in managing PSN tunnels
</t>
<t hangText='-'>
the memory resources needed for the control plane
</t>
<t hangText='-'>
other particular elements inherent to each solution that
impact scalability
</t>
</list>
</t>
</section>
<section title="Pseudo Wire Signaling and PSN Tunneling">
<t>
A VPMS solution SHOULD provide an efficient replication that can
contribute to optimizing the bandwidth usage required in a
SP's network. For supporting efficient replication, it is expected
to take advantage of PW and PSN mechanisms that are capable of
P2MP traffic.
</t>
<t>
Regarding PW mechanism,
<xref target="I-D.ietf-pwe3-p2mp-pw-requirements"/>
introduces P2MP PW concept and its requirements, showing two basic approaches of providing
replication. One is SS (Single Segment)-PW model that
provides replication by PSN tunnel such as P2MP LSP (i.e., by outer
label layer), and the other is MS (Multi Segment)-PW model
that provides replication by multiple interconnected PWs
(i.e., by inner label layer). In either case, end-to-end P2MP
topology in VPMS is common from the view of PEs and ACs.
Requirements as a provider service specified in this document
will be commonly applied regardless of P2MP PW's signaling model.
</t>
<t>
This document does not raise any specific requirements for
particular PSN tunneling schemes (point-to-point, point-to-multipoint and
multipoint-to-multipoint) that is applied only to VPMS.
The actual type of PSN tunnel used in VPMS
will be dependent on individual deployment scenarios
(e.g., which PSN protocol is available now in the core and how much
network resources operators will want to optimize).
</t>
</section>
<section title="Discovering VPMS Related Information">
<t>
A solution SHOULD support auto-discovery methods that dynamically
allow VPMS information to be discovered by the PEs to minimize the
amount of configuration the SP must perform.
</t>
<t>
All of the requirements on discovery described in
Section 7.3 of <xref target="RFC4665"/>
SHOULD be satisfied in VPMS as well.
</t>
<t>
Auto-discovery will help operators' initial configuration of
adding a new VPN (i.e., VPMS instance),
adding/deleting new sender/receiver, and so on.
</t>
<t>
The information related to remote sites will be as follows:
</t>
<t>
<list style='hanging'>
<t hangText='-'>
Information to identify the VPMS instance
</t>
<t hangText='-'>
PE router ID / IP address as location information
</t>
<t hangText='-'>
Information to identify Attachment Circuits
and their associated group information to
compose a unique service (i.e., VPMS instance).
</t>
<t hangText='-'>
AC role in each VPMS (Sender or Receiver)
</t>
<t hangText='-'>
SP-related information (AS number, etc. for an inter-provider case)
</t>
</list>
</t>
<t>
Following is an example scenario: by default,
every PE will have the association among the information
described above. Suppose a new PE having an AC is provisioned
in the existing VPMS instance and this AC is configured as receiver.
This information will be automatically discovered by the
other existing remote PEs (i.e., ingress and egress PEs
in the same VPMS instance). Once the ingress PE discovers
this new PE/AC, it can automatically add it as the new leaf
of P2MP topology according to P2MP PW signaling mechanism.
This operation does not require any new configuration at
the existing PEs.
</t>
</section>
<section title="Activation and Deactivation">
<t>
This section raises generic requirements for handling related
information about remote sites after the initial provisioning to ease the
total operation of VPMS.
</t>
<t>
A solution SHOULD provide a way to
activate/deactivate the administrative status of each CE/AC.
After initial provisioning,
a SP might change connectivity configuration
between particular CEs inside a single VPMS instance
for operational reasons. This feature will be beneficial to
help such a scenario.
</t>
<t>
For example, in Figure 5,
CE1, CE3, CE4 and CE5 (and their ACs) are initially provisioned
for VPMS A. CE2 is not provisioned for any VPMSes. In VPMS A, CE1 is
a sender and CE3, CE4 and CE5 are receivers.
Traffic will usually flow from CE1 to all
receivers, CE3, CE4 and CE5. However, for maintenance operation,
application's request (e.g., stream program has changed) or some other reasons,
CE4 needs to
be set as administratively deactivated. Then it becomes necessary to
turn off traffic from PE4 to CE4. This operation
must be appropriately distinguished from failure cases.
</t>
<t>
When deactivating a particular site, backbone PSN/PW resources (e.g.,
admission control of PSN tunnel) MAY be released for that particular
direction in order to provide that bandwidth to other services. In
Figure 5, CE3 is now administratively activated and receiving traffic.
However, if CE3 comes to be administratively deactivated, and if
RSVP-TE (including P2P and/or P2MP) is used for backbone PSN, then TE
reserved resources from PE1 to PE3 may be released.
</t>
<t>
In addition, a solution SHOULD allow single-sided activation
operation at a sender PE. In some scenarios, operators prefer
centralized operation. This is often considered natural for one-way
digital audio/video distribution applications: SPs often want to
complete their service delivery by a single operation at one source
PE, not by multiple operations at many receiver PEs. Figure 5
illustrates this scenario, where a SP only has to do single-sided
operation at PE1 (source) to administratively activate/deactivate
various connections from AC1 to AC3, AC4 and/or AC5. It is not
needed to perform operations on PE3 and PE4 directly.
</t>
<figure>
<artwork><![CDATA[
+-----+ AC1
+ CE1 +----------------+
+-----+ |
VPMS A Sender |
(sending now) v
+----+
-----|VPMS|--------
| | PE1| |
| +----+ |
+----+ +----+
|VPMS| |VPMS|
| PE2| Routed | PE3|
+----+ Backbone +----+
AC2 / | | \ AC3
+-----+ / | | \ +-----+
+ CE2 +<-+ | | +->| CE3 |
+-----+ | +----+ | +-----+
(not provisioned) ----|VPMS|--------- VPMS A Receiver
| PE4| (receiving now)
+----+
AC5 / \ AC4
+-----+ / \ +-----+
+ CE5 +<----------+ +---------------->| CE4 |
+-----+ +-----+
VPMS A Receiver VPMS A Receiver
(receiving now) (not receiving)
CE1/AC1: Administratively activated
CE2/AC2: No VPMS provisioned
CE3/AC3: Administratively activated
CE4/AC4: Administratively deactivated
CE5/AC5: Administratively activated
Figure 5: Site activation and deactivation
]]></artwork>
</figure>
</section>
<section title="Inter-AS Support">
<t>
A solution SHOULD support inter-AS scenarios, where there is more
than one provider providing a common VPMS instance and VPN. More
specifically, it is necessary to consider the case where some of the
PEs that compose one VPMS belong to several different ASes.
</t>
</section>
<section title="Co-existence with Existing L2VPNs">
<t>
A solution MUST co-exist with the existing L2VPNs
(e.g., VPWS, VPLS)
across the same SP's network. A solution MUST NOT impede
the operation
of auto-discovery and signalling mechanism that
are already supported by the PEs for those existing L2VPNs.
</t>
</section>
<section title="Operation, Administration and Maintenance">
<section title="Fault Management">
<section title="Fault Detection">
<t>
A solution MUST provide tools that detect reachability failure and traffic looping of P2MP transport in a VPMS instance. If multiple sources are supported (i.e., multiple P2MP topologies are grouped together into a single VPMS instance), such tools MUST be able to perform distinguishing each P2MP topology.
</t>
</section>
<section title="Fault Notification">
<t>
A solution MUST provide fault notification and trouble tracking mechanisms. (e.g. SNMP-trap and syslog that notify fault to remote NMS.)
</t>
<t>
In VPMS one point of failure at upstream often affects a number of downstream PEs and ACs that might raise a notification message. Hence notification messages MAY be summarized or compressed for operators' ease of management.
</t>
<t>
In case of receiver-side failure (receiver PE or its AC), this fault status SHOULD be able to be monitored at sender PE. This will help an operator to monitor each receiver PEs/AC in a centralized manner; that is, a sender PE can collect receiver-side information. How this status is transferred depends on a solution.
</t>
<t>
In contrast, in case of sender-side failure (sender PE or its AC), this fault status SHOULD also be able to be monitored at receiver PEs. This will help an operator to troubleshoot at receiver PEs (i.e., distinguish local AC’s failure from remote upstream AC’s failure easily).
</t>
<t>
In any case of failure at SP’s network, fault information MAY be notified to the customer. Specifically, such fault MAY trigger generating customer OAM message toward CEs (e.g., AIS) and/or shutting down receiver ACs.
</t>
</section>
<section title="Fault Isolation">
<t>
A solution MUST provide diagnostic/troubleshooting tools
for P2MP transport in a VPMS instance.
</t>
</section>
</section>
<section title="Testing">
<t>
A solution MUST provide a mechanism for testing each P2MP connectivity and verifying the associated information in a VPMS instance. The connectivity is between sender and all receiver ACs.
</t>
<t>
Operators will run testing before and after service activation. Testing mechanism SHOULD support end-to-end testing of the data path used by customer's data. End-to-end testing will have CE-to-CE path test and PE-to-PE path test. A solution MUST support PE-to-PE path test and MAY support CE-to-CE path test. In either case the data path provided for each VPMS is unidirectional, hence if loopback testing is supported, additional consideration about reverse-path might also be needed (see section 6.1.3).
</t>
</section>
<section title="Performance Management">
<t>
A solution MUST offer mechanisms to monitor traffic performance parameters and statistics in each P2MP traffic.
</t>
<t>
A solution MUST provide access to:
</t>
<t>
<list style='hanging'>
<t hangText='-'>
Traffic statistics (total traffic forwarded, incoming, outgoing, dropped, etc., by period of time)
</t>
</list>
</t>
<t>
A solution SHOULD provide access to:
</t>
<t>
<list style='hanging'>
<t hangText='-'>
Performance information related to traffic usage, e.g., one-way delay, one-way jitter, one-way loss, delay variations (the difference of various one-way delay from a particular sender PE to multiple receiver PEs) etc.
</t>
</list>
</t>
<t>
All or part of this information SHOULD be made available through standardized SNMP MIB Modules (Management Information Base).
</t>
<t>
It is expected that such information can be used for SLA monitoring between sender and receiver, to give the SP a clear picture of current service providing to the customer.
</t>
</section>
</section>
<section title="Security">
<t>
TBD (for further study for next revision)
</t>
</section>
</section>
<section title="Security Considerations">
<t>
Security consideration will be covered by section 6.5. and section 7.8.
(This is for further study for next revision.)
</t>
</section>
<section title="IANA Considerations">
<t>
This document has no actions for IANA.
</t>
</section>
<section title="Acknowledgments">
<t>
Many thanks to Ichiro Fukuda, Kazuhiro Fujihara, Ukyo Yamaguchi and Kensuke Shindome for their valuable review and feedback.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119;
&rfc4026;
</references>
<references title="Informative References">
&rfc4664;
&rfc4665;
&rfc4761;
&rfc4762;
&I-D.ietf-pwe3-p2mp-pw-requirements;
&I-D.ietf-l2vpn-vpls-mcast;
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-21 21:15:42 |