Working Group Name Sanjay Wadhwa
Internet Draft Juniper Networks
Expires: April 22, 2007
Jerome Moisand
Juniper Networks

Swami Subramanian
Juniper Networks

Thomas Haag
T-Systems

Norbert Voigt
Siemens

October 22, 2006

GSMP extensions for Access Node Control Mechanism

draft-wadhwa-gsmp-l2control-configuration-02.txt

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Abstract

This document describes proposed extensions to the GSMPv3 protocol to
allow its use in a broadband environment, as a control plane between
Access Nodes (e.g. DSLAM) and Broadband Network Gateways (e.g. BRAS).
These proposed extensions are required to realize a protocol for
“Access Node Control” mechanism as described in [9]. The resulting
protocol with the proposed extensions to GSMPv3 [4] is referred to as
“Access Node Control Protocol” (ANCP). This document focuses on
specific use cases of access node control mechanism for topology
discovery, line configuration, and OAM. It is intended to be
augmented by additional protocol specification for future use cases
considered in scope by the ANCP charter.

Conventions used in this document

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 RFC-2119 [1].

Table of Contents

1 Specification Requirements 4

2 Introduction4

3 Broadband Access Aggregation 4

3.1 ATM-based broadband aggregation..........................4
3.2 Ethernet-based broadband aggregation.....................6

4 Access Node Control Protocol 7

4.1 Overview.................................................7
4.2 ANCP based Access Topology Discovery.....................8
4.2.1 Goals..............................................8
4.2.2 Message Flow.......................................9
4.3 ANCP based Line Configuration...........................10
4.3.1 Goals.............................................10
4.3.2 Message Flow......................................11
4.4 ANCP based Transactional Multicast......................12
4.5 ANCP based OAM..........................................13

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4.5.1 Message Flow......................................13

5 Access Node Control Protocol (ANCP) 14

5.1 ANCP/TCP connection establishment.......................14
5.2 ANCP Connection keep-alive..............................15
5.3 Capability negotiation..................................16
5.4 GSMP Message Extensions for Access Node Control.........18
5.4.1 General Extensions................................18
5.4.2 Topology Discovery Extensions.....................21
5.4.3 Line Configuration Extensions.....................30
5.4.4 OAM Extensions....................................32
5.5 ATM-specific considerations.............................35
5.6 Ethernet-specific considerations........................36
6 IANA Considerations 36

7 Security Considerations 36

8 References 37

Author's Addresses38

Intellectual Property Statement 38

Disclaimer of Validity 39

Acknowledgment 39

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1 Specification Requirements

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 RFC 2119.

2 Introduction

DSL is a widely deployed access technology for Broadband Access for
Next Generation Networks. Several specifications like [1-3] describe
possible architectures for these access networks. In the scope of
these specifications are the delivery of voice, video and data
services.

When deploying value-added services across DSL access networks,
special attention regarding quality of service and service control is
required, which implies a tighter coordination between network
elements in the broadband access network without burdening the OSS
layer.

This draft defines extensions and modifications to GSMPv3 (specified
in [4]) and certain new mechanisms to realize a control plane between
a service-oriented layer 3 edge device (the BRAS) and a layer2 Access
Node (e.g. DSLAM) in order to perform QoS-related, service-related
and subscriber-related operations. The control protocol as a result
of these extensions and mechanisms is referred to as “Access Node
Control Protocol” (ANCP).

In addition to specifying extensions and modifications to relevant
GSMP messages applicable to access node control mechanism, this draft
also defines values that ANCP should set for relevant fields in these
GSMP messages. However, to understand the basic semantics of various
fields in GSMP messages, the reader is referred to [4].

3 Broadband Access Aggregation

3.1 ATM-based broadband aggregation

End to end DSL network consists of network and application service
provider networks (NSP and ASP networks), regional/access network,
and customer premises network. Fig 1. shows ATM broadband access
network components.

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The NSP authenticates access and provides and manages the IP address
to subscribers. It is responsible for overall service assurance and
includes internet service providers. ASP provides application
services to the application subscriber (gaming, video, content on
demand, IP telephony etc.).

The Regional/Access Network consists of the Regional Network,
Broadband Remote Access Server, and the Access Network as show in Fig
1. Its primary function is to provide end-to-end transport between
the customer premises and the NSP or ASP. The Regional/Access Network
may also provide higher layer functions such as QoS and content
distribution.

The Regional Network connects one or more BRAS and associated Access
Network to NSPs and ASPs. It supports aggregation of traffic from
multiple Access Networks and hands off larger geographic locations to
NSPs and ASPs – relieving a potential requirement for them to build
infrastructure to attach more directly to the various Access
Networks.

The Access Node terminates the DSL signal. It could consist of DSLAM
in the central office , or remote DSLAM, or a Remote Access
Multiplexer (RAM). A DSLAM hub can be used in a central office to
aggregate traffic from multiple remote physical devices, and is
considered logically to be a part of the Access Node. Access node is
the first point in the network where traffic on multiple DSL lines
will be aggregated onto a single network. In an ATM access network,
access Node is primarily an ATM concentrator, mapping PVCs from the
DSL modem to PVCs in the ATM core.

The BRAS performs multiple functions in the network. The BRAS is the
aggregation point for the subscriber traffic. It provides aggregation
capabilities (e.g. IP, PPP, ATM) between the Regional/Access Network
and the NSP or ASP. These include traditional ATM-based offerings and
newer, more native IP-based services. This includes support for
Point-to-Point Protocol over ATM (PPPoA) and PPP over Ethernet
(PPPoE), as well as direct IP services encapsulated over an
appropriate layer II transport.

Beyond aggregation, BRAS is also the injection point for policy
management and IP QoS in the Regional/Access Networks. In order to
allow IP QoS support over an existing non-IP-aware layer 2 access
network without using multiple layer 2 QoS classes, a mechanism based
on hierarchical scheduling is used. This mechanism defined in [1],
preserves IP QoS over the ATM network between the BRAS and the RGs by

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carefully controlling downstream traffic in the BRAS, so that
significant queuing and congestion does not occur further down the

ATM network. This is achieved by using a diffserv-aware hierarchical
scheduler in the BRAS that will account for downstream trunk
bandwidths and DSL synch rates.

Routing Gateway is a customer premises functional element that
provides IP routing and QOS capabilities. It may be integrated into
or be separate from the modem.

Access Customer
<--- Aggregation ---> <------- Premises ------->
Network Network

+-------------------+ +--------------------------+
+----------+ +-----+ | +-----+ +------+ |--|+-----+ +--+ +----------+ |
| | +-|BRAS |---| |ATM |--|Access| | ||DSL |-|RG|-|Subscriber| |
NSP---+Regional | | +-----+ | +-----+ | Node | | ||Modem| +--+ |Devices | |
|Broadband | | +-----+ | +------+ | |+-----+ +----------+ |
|Network |-+-|BRAS | +---------------|---+ +--------------------------+
ASP---+ | | +-----+ | +--------------------------+
| | | +-----+ | | +-----+ +--+ +----------+|
+----------+ +-|BRAS | +------| | DSL |-|RG|-|Subscriber||
+-----+ | |Modem| +--+ |Devices ||
| +-----+ +----------+|
+--------------------------+
RG : Routing Gateway
BRAS : Broadband Remote Access Server

Fig.1 ATM Broadband Aggregation Topology

3.2 Ethernet-based broadband aggregation

The Ethernet aggregation network architecture builds on the Ethernet
bridging/switching concepts defined in IEEE 802. The Ethernet
aggregation network provides traffic aggregation, class of service
distinction, and customer separation and traceability. VLAN tagging
defined in IEEE 802.1Q and being enhanced by IEEE 802.1ad is used as
standard virtualization mechanism in the Ethernet aggregation network.
The aggregation devices are “provider edge bridges” defined in IEEE
802.ad.
Stacked VLAN tags provide one possible way to create equivalent of
“virtual paths” and “virtual circuits” in the aggregation network. The

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“outer” vlan could be used to create a form of “virtual path” between a
given DSLAM and a given BRAS. And “inner” VLAN tags to create a form of
“virtual circuit” on a per DSL line basis. This is 1:1 VLAN allocation
model. An alternative model is to bridge sessions from multiple
subscribers behind a DSLAM into a single VLAN in the aggregation
network. This is N:1 VLAN allocation model. Architectural and
topological models of an Ethernet aggregation network in context of DSL
aggregation are defined in [8].

4 Access Node Control Protocol

4.1 Overview

There is a requirement for a control plane between service-oriented
layer 3 edge device (the BRAS) and a layer 2 Access Node (e.g. DSLAM)
in order to perform QoS-related, service-related and subscriber-
related operations. A dedicated control protocol between BRAS and
access nodes can facilitate "BRAS managed" tight QOS control in the
access network, simplified OSS infrastructure for service management,
optimized multicast replication to enable video services over DSL,
subscriber statistics retrieval on the BRAS for accounting purposes,
and fault isolation capability on the BRAS for the underlying access
technology. This dedicated control plane is referred to as “Access
Node Control Protocol” (ANCP). This document specifies relevant
extensions to GSMPv3 as defined [4] to realize ANCP.

Following sections discuss the use of ANCP for implementing:

. Dynamic discovery of access topology by the BRAS to provide
tight QOS control in the access network.

. Pushing to the access-nodes, subscriber and service data
retrieved by the BRAS from an OSS system (e.g. radius server),
to simplify OSS infrastructure for service management.

. Optimized, "BRAS controlled and managed" multicast replication
by access-nodes at L2 layer.

. BRAS controlled, on-demand access-line test capability
(rudimentary end-to-end OAM).

In addition to DSL, alternate broadband access technologies (e.g.
Metro-Ethernet, Passive Optical Networking, WiMax) will have similar
challenges to address, and could benefit from the same approach of a
control plane between a BRAS and an Access Node (e.g. OLT), providing
a unified control and management architecture for multiple access

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technologies, hence facilitating migration from one to the other
and/or parallel deployments.

GSMPv3 is an ideal fit for implementing ANCP. It is extensible and
can be run over TCP/IP, which makes it possible to run over different
access technologies.

4.2 ANCP based Access Topology Discovery

4.2.1 Goals

[1] discusses various queuing/scheduling mechanisms to avoid
congestion in the access network while dealing with multiple flows
with distinct QoS requirements. Such mechanisms require that the BRAS
gains knowledge about the topology of the access network, the various
links being used and their respective rates. Some of the information
required is somewhat dynamic in nature (e.g. DSL sync rate), hence
cannot come from a provisioning and/or inventory management OSS
system. Some of the information varies less frequently (e.g. capacity
of a DSLAM uplink), but nevertheless needs to be kept strictly in
sync between the actual capacity of the uplink and the image the BRAS
has of it.

OSS systems are rarely able to enforce in a reliable and scalable
manner the consistency of such data, notably across organizational
boundaries. Dynamic and automated discovery of the access network
topology would help to address these issues, notably when performed
by an interoperable and standardized protocol. Following section
describes ANCP messages that allow the Access Node (e.g. DSLAM) to
communicate to the BRAS, access network topology information and any
corresponding updates.

Some of the parameters that can be communicated from the DSLAM to the
BRAS include DSL line state, actual upstream and downstream data
rates of a synchronized DSL link, maximum attainable upstream and
downstream data rates, interleaving delay etc. Topology discovery is
specifically important in case the net data rate of the DSL line
changes over time. The DSL net data rate may be different every time
the DSL modem is turned on. Additionally, during the time the DSL
modem is active, data rate changes can occur due to environmental
conditions (the DSL line can get "out of sync" and can retrain to a
lower value.

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4.2.2 Message Flow

When a DSL line initially comes up or resynchronizes to a different
rate, the DSLAM generates and transmits a GSMP PORT UP EVENT message to
the BRAS. The extension field in the message carries the TLVs containing
DSL line specific parameters. On a loss of signal on the DSL line, a
GSMP PORT DOWN message is generated by the DSLAM to the BRAS. In order
to provide expected service level, BRAS needs to learn the initial
attributes of the DSL line before the subscriber can log in and access
the provisioned services for the subscriber.

<----- Port UP(EVENT Message) <----- DSL
(default line parameters) Signal

1. BRAS ----------------------- DSLAM ----------- Routing ----- Subscriber
Gateway

<----- Port UP (EVENT Message) <----- DSL
(updated line parameters) Resynch
2. BRAS ----------------------- DSLAM ----------- Routing ------ Subscriber
Gateway

<--- Port DOWN (EVENT Message) <---- DSL
Loss of Signal

3. BRAS ---------------------- DSLAM ------------- Routing ----- Subscriber
Gateway

Fig 2. Message flow (ANCP mapping) for topology discovery

The Event message with PORT UP message type (80) is used for
conveying DSL line attributes to the BRAS. This message with relevant
extensions is defined in section 5.4.2.

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4.3 ANCP based Line Configuration

4.3.1 Goals

Following dynamic discovery of access topology (identification of DSL
line and its attributes) as assisted by the mechanism described in
the previous section (topology discovery), the BRAS could then query
a subscriber management OSS system (e.g. RADIUS server) to
retrieve subscriber authorization data (service profiles, aka user
entitlement). Most of such service mechanisms are typically enforced
by the BRAS itself, but there are a few cases where it might be
useful to push such service parameter to the DSLAM for local
enforcement of a mechanism (e.g. DSL-related) on the corresponding
subscriber line. One such example of a service parameter that can be
pushed to the DSLAM for local enforcement is DSL "interleaving
delay". Longer interleaving delay (and hence stringent error
correction) is required for a video service to ensure better video
"quality of experience", whereas for a VoIP service or for "shoot
first" gaming service, a very short interleaving delay is more
appropriate. Another relevant application is downloading per
subscriber multicast channel entitlement information in IPTV
applications where the DSLAM is performing IGMP snooping or IGMP
proxy function. Using ANCP, the BRAS could achieve the goal of
pushing line configuration to the DSLAM by an interoperable and
standardized protocol.

If a subscriber wants to choose a different service, it can require
an OPEX intensive reconfiguration of the line via a network operator,
possibly implying a business-to-business transaction between an ISP
and an access provider. Using ANCP for line configuration from the
BRAS dramatically simplifies the OSS infrastructure for service
management, allowing fully centralized subscriber-related service
data (e.g. RADIUS server back-end) and avoiding complex cross-
organization B2B interactions.

Therefore, proposed ANCP based line configuration support provides
for more flexible approach for achieving "service on demand". More
generally several service/subscriber DSL parameters (e.g. inter-
leaving delay, rate etc.) could benefit from such flexible approach
to enable a "service on demand" model.

The best way to change line parameters would be by using profiles.
These profiles (DSL profiles for different services) are pre-
configured on the DSLAMs. The BRAS can then indicate a reference to
the right DSL profile via ANCP. Alternatively, discrete DSL
parameters can also be conveyed by the BRAS in ANCP.

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4.3.2 Message Flow

Triggered by topology information reporting a new DSL line or triggered
by a subsequent user session establishment (PPP or DHCP), the BRAS may
send line configuration information (e.g. reference to a DSL profile) to
the DSLAM using GSMP Port Management messages. The BRAS may get such
line configuration data from a policy server (e.g. RADIUS). Figure 3
summarizes the interaction.

1.DSL Signal
<-----------
2. Port UP (EVENT Message)
(Access Topology Discovery)
<--------------------------
3. PPP/DHCP Session
<-----------------------------------------------------
4. Authorization
& Authentication
<-------------------
Port Management Message
(Line Configuration)
5. ---------------->
+-------------+ +-----+ +-------+ +----------+ +-----------+
|Radius/AAA |------|BRAS |---------| DSLAM |------ | Routing |------ |Subscriber |
|Policy Server| +-----+ +-------+ | Gateway | +-----------+
+-------------+ +----------+

Fig 3. Message flow - ANCP mapping for Initial Line Configuration

The BRAS may update the line configuration due to a subscriber service
change (e.g. triggered by the policy server). Figure 4 summarizes the
interaction

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1. PPP/DHCP Session
<------------------------------------------

+-------------+ 2. Service On Demand
| |<------------------------------------------------
| Web portal |
| OSS etc | 3.Change of 4.Port Management
| | Authorization Message
| Radius AAA | --------> (Updated Line
| Policy | Config - New Profile)
| | -------------.
| | +------+ +-------+ +---------+ +----------+
| |----| BRAS |-----| DSLAM |---| Routing |--|Subscriber|
| | +------+ +-------+ | Gateway | +----------+
+-------------+ +---------+

Fig 4. Message flow - ANCP mapping for Updated Line Configuration

The format of relevant extensions to port management message is
defined in section 5.4.3. The line configuration models could be
viewed as a form of delegation of authorization from the BRAS to the
DSLAM.

4.4 ANCP based Transactional Multicast

Typical IP multicast in access networks involves the BRAS terminating
user requests for receiving multicast channels via IGMP. The BRAS
authorizes the subscriber, and dynamically determines the multicast
subscription rights for the subscriber. Based on the user's
subscription, the BRAS can replicate the same multicast stream to
multiple subscribers. This leads to a waste of access bandwidth if
multiple subscribers access network services via the same access-node
(e.g. DSLAM). The amount of multicast replication is of the order of
number of subscribers rather than the number of access-nodes.

It is ideal for BRAS to send a single copy of the multicast stream to
a given access-node, and let the access-node perform multicast
replication by layer2 means (e.g. ATM point-to-multipoint cell
replication or ethernet data-link bridging) for subscribers behind
the access-node. However, operationally, BRAS is the ideal choice to
handle subscriber management functions (authentication,
authorization, accounting and address management), multicast policies

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such as per-channel authorization, and complex multicast routing
protocols. Therefore, some means is needed for the BRAS to setup
multicast replication state in the access-nodes. In ATM access
networks, ANCP can be used by the BRAS to setup P2MP cross-connects
in the DSLAMs. Protocol support for this use-case will be provided in
future.

4.5 ANCP based OAM

In case of an ATM based access aggregation network and an ATM based
local loop, end-to-end ATM OAM can be used for on-demand connectivity
testing, monitoring and fault localization. However, in case the
aggregation network between the BRAS and access-node is ethernet
based, end-to-end ATM OAM test can not be used. Ideally in Ethernet
based aggregation, end-to-end ethernet OAM as specified by ITU and
IEEE (801.ag / Y.17 ethoam) can provide access-line connectivity
testing and fault isolation. However, most DSL modems do not yet
support these standard ethernet OAM procedures. Also, various
technologies exist in the access network - ATM, EFM (ethernet in the
first mile, standardized in IEEE 802.3ah), GPON etc. These
technologies have their own link-based OAM mechanisms that have been
standardized or are under standardization in different standard
bodies. Inter-working between 802.1ag and different link-OAM
mechanisms are a work in progress and are being evaluated on a case
by case basis.

However, a simple solution based on ANCP can provide BRAS with an
access-line test capability and to some extent fault isolation.
Controlled by a local management interface the BRAS can use an ANCP
operation to trigger the access-node to perform a loopback test on
the local-loop (between the access-node and the CPE). The access-node
can respond via another ANCP operation the result of the triggered
loopback test. In case of ATM based local-loop the ANCP operation can
trigger the access-node to generate ATM (F4/F5) loopback cells on the
local loop. In case of Ethernet, the access-node can trigger an
ethernet loopback message(per EFM OAM) on the local-loop.

4.5.1 Message Flow

“Port Management” message can be used by the BRAS to request access
node to trigger a “remote loopback” test on the local loop. The
result of the loopback test can be asynchronously conveyed by the
access node to the BRAS in a “Port Management” response message. The
format of relevant extensions to port management message is defined
in section 5.4.4.

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Port Management Message
(Remote Loopback ATM loopback
Trigger Request) OR EFM Loopback
1. ----------------> 2. ---------->
<---------+
+-------------+ +-----+ +-------+ +-----------------+
|Radius/AAA |------|BRAS |---------| DSLAM |-------------| CPE |
|Policy Server| +-----+ +-------+ | (DSL Modem + |
+-------------+ | Routing Gateway)|
+-----------------+
3. <---------------
Port Management Message
(Remote Loopback Test Response)

5 Access Node Control Protocol (ANCP)

5.1 ANCP/TCP connection establishment

ANCP will use TCP for exchanging protocol messages. [5] defines the
GSMP message encapsulation for TCP. The TCP session is initiated
from the DSLAM (access node) to the BRAS (controller). This is
necessary to avoid static provisioning on the BRAS for all the DSLAMs
that are being served by the BRAS. It is easier to configure a given
DSLAM with the single IP address of the BRAS that serves the DSLAM.
This is a deviation from [5] which indicates that the controller
initiates the TCP connection to the switch.

BRAS listens for incoming connections from the access nodes. Port
6068 is used for TCP connection. Adjacency protocol messages, which
are used to synchronize the BRAS and access-nodes and maintain
handshakes, are sent after the TCP connection is established. ANCP
messages other than adjacency protocol messages may be sent only
after the adjacency protocol has achieved synchronization.

In the case of ATM access, a separate PVC (control channel) capable
of transporting IP would be configured between BRAS and the DSLAM for
ANCP messages.

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5.2 ANCP Connection keep-alive

GSMPv3 defines an adjacency protocol. The adjacency protocol is used
to synchronize states across the link, to negotiate which version of
the GSMP protocol to use, to discover the identity of the entity at
the other end of a link, and to detect when it changes. GSMP is a
hard state protocol. It is therefore important to detect loss of
contact between switch and controller, and to detect any change of
identity of switch or controller. No protocol messages other than
those of the adjacency protocol may be sent across the link until the
adjacency protocol has achieved synchronization. There are no changes
to the base GSMP adjacency protocol for implementing ANCP.

The BRAS will set the M-flag in the SYN message (signifying it is the
master). Once the adjacency is established, periodic adjacency
messages (type ACK) are exchanged. The default ACK interval as
advertised in the adjacency messages is 10 sec for ANCP. It SHOULD be
configurable and is an implementation choice. It is recommended that
both ends specify the same timer value. However, it is not necessary
for the timer values to match.

The GSMP adjacency message defined in [4] is extended for ANCP and is
shown in section 5.3 immediately following this section. The 8-bit
“version” field in the adjacency protocol messages is modified to
carry the version and sub-version of the GSMP protocol for version
negotiation. ANCP uses version 3 and sub-version 1 of GSMP protocol.
The semantics and suggested values for Code, “Sender Name”, “Receiver
Name”, “Sender Instance”, and “Receiver Instance” fields are as
defined in [4]. The “Sender Port”, and “Receiver Port” should be set
to 0 by both ends. The pType field should be set to 0. The pFlag
should be set to 1.

If the adjacency times out on either end, due to not receiving an
adjacency message for a duration of (3 * Timer value), where the
timer value is specified in the adjacency message, all the state
received from the ANCP neighbor should be cleaned up, and the TCP
connection should be closed. The BRAS would continue to listen for
new connection requests. The DSLAM will try to re-establish the TCP
connection and both sides will attempt to re-establish the adjacency.

The handling defined above will need some modifications when ANCP
graceful restart procedures are defined. These procedures will be
defined in a separate draft.

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5.3 Capability negotiation

The adjacency message as defined in [4] is extended to carry
technology specific "Capability TLVs". Both the BRAS and the access
node will advertise supported capabilities in the originated
adjacency messages. If a received adjacency message indicates absence
of support for a capability that is supported by the receiving
device, it will turn off the capability locally and will send an
updated adjacency message with the capability turned off to match the
received capability set. This process will eventually result in both
sides agreeing on the minimal set of supported capabilities. The
adjacency will not come up unless the capabilities advertised by the
controller and the controlled device match.

After initial synchronization, if at anytime a capability mismatch is
detected, the adjacency will be brought down (RSTACK will be
generated by the device detecting the mismatch), and synchronization
will be re-attempted.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver | Sub | Message Type | Timer |M| Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Name |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| Receiver Name |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiver Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PType | PFlag | Sender Instance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Partition ID | Receiver Instance |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tech Type | # of TLVs | Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Capability TLVs ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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The format of capability TLV is:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Capability Type | Capability Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Capability Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Tech Type field type indicates the technology to which the
capability extension applies. For access node control in case of DSL
networks, new type "DSL" is proposed. The value for this field is
0x05. This is the first available value in the range that is not
currently allocated. It will need to be reserved with IANA.

Capability length is the number of actual bytes contained in the
value portion of the TLV. The TLV is padded to a 4-octet alignment.
Therefore, a TLV with no data will contain a zero in the length field
(if capability data is three octets, the length field will contain a
three, but the size of the actual TLV is eight octets).

Capability data field can be empty if the capability is just a
boolean. In case the capability is a boolean, it is inferred from the
presence of the TLV (with no data). Capability data provides the
flexibility to advertise more than mere presence or absence of a
capability. Capability types can be registered with IANA. Following
capabilities are defined for ANCP as applied to DSL access:

1. Capability Type : Dynamic-Topology-Discovery = 0x01

Length (in bytes) : 0

Capability Data : NULL

2. Capability Type : Line-Configuration = 0x02

Length (in bytes) : 0

Capability Data : NULL

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3. Capability Type : Transactional-Multicast = 0x03 (controller
i.e. BRAS terminates IGMP messages from subscribers, and via l2
control protocol, signals state to the access-nodes (e.g.
DSLAMs) to enable layer2 replication of multicast streams. In
ATM access network this implies that BRAS instructs the access-
node to setup a P2MP cross-connect. The details of this will be
covered in a separate ID [6].

Length (in bytes) : 0

Capability Data : NULL

4. Capability Type : OAM = 0x04

Length (in bytes) : 0

Capability Data : NULL

5. Capability Type : Bulk Transaction = 0x05 (defined in section
5.4.1.2).

Length (in bytes) : 0

Capability Data : NULL

5.4 GSMP Message Extensions for Access Node Control

5.4.1 General Extensions

Extensions to GSMP messages for various use-cases of “Acess Node
Control” mechanism are defined in sections 5.4.2 to 5.4.4. However,
sub-sections 5.4.1.1 and 5.4.1.2 below define extensions to GSMP that
have general applicability.

5.4.1.1 Extension TLV

In order to provide flexibility and extensibility certain GSMP
messages such as “PORT MANAGEMENT” and “EVENT” messages defined in
[4] have been modified to include an extension block that follows a
TLV structure. Individual messages in the following sections describe
the usage and format of the extension block.

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All Extension TLV's will be designated as follow:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x|x|x|x|x|x|x|x| Message Type | Tech Type | Block Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Extension Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

x: Reserved Flags

These are generally used by specific messages and will be
defined in those messages.

Message Type

An 8-bit field corresponding to the message type where the
extension block is used.

Tech Type

An 8-bit field indicating the applicable technology type value.
The Message Type plus the Tech Value uniquely define a single
Extension Type and can be treated as a single 16 bit extension
type. “Tech Type” value of 0x05 SHOULD be used by ANCP for DSL
technology.

0x00 Extension block not it use.

0x01 – 0x04 Already in use by various technologies

0x05 DSL

0x06 - 0xFE Reserved

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0xFF Base Specification Use

Block Length

A 8-bit field indicating the length of the Extension Value
field in bytes. When the Tech Type = 0x00, the length value
MUST be set to 0.

Extension Value

A variable length field that is an integer number of 32 bit
words long. The Extension Value field is interpreted according
to the specific definitions provided by the messages in the
following sections.

5.4.1.2 Bulk Transaction Message

ANCP elements MAY support a bulk transaction capability. This
capability is negotiated during adjacency synchronization and follows
general ANCP capability negotiation rules.

In a bulk transaction, several messages can be bundled together in a
single transaction. Bulk transaction uses message type 13. Reception
of “Bulk Transaction Message” by a node that has not advertised bulk
transaction capability MUST silently discard the received message.

The Bulk Transaction message has the following format:

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In a Bulk Transaction Message, each of the message in the payload is
framed with a complete header and is acted on individually. The
response to the Bulk Transaction message contains the response
message that would have been generated by each of the messages had it
been sent individually. Each response message will have the
appropriate result and code field filled. Any message can be included
in the bulk Transaction message except for adjacency message and
another bulk transaction message. If a prohibited message is included
in a bulk Transaction message, it MUST be included in the Bulk
response with a failure response. The response code for that failure
is 0x81 (“Message type prohibited in bulk Transaction”). While the
individual message would fail, this would not constitute a failure
for the Bulk Transaction message

5.4.2 Topology Discovery Extensions

The GSMP Event message with PORT UP message type (80) is used for
conveying DSL line attributes to the BRAS. The version field should be
set to 3, and the sub field should be set to 1. The I and subMessage
fields SHOULD be set to 1 to signify no fragmentation. The Port and
Label fields should be set to 0. The “Port Session Number” should be set
to 0, and the “Event Sequence Number” should be 0. The Tech Type field
is extended with new type "DSL". The value for this field is 0x05. The
message SHOULD be generated when a line first comes UP, or any of the
attributes of the line change e.g. the line re-trains to a different
rate or one or more of the configured line attributes are
administratively modified. Also, when the ANCP session first comes up,
the DSLSM SHOULD transmit a PORT UP message to the BRAS for each line
that is up. A DSLAM MAY use a Bulk Transaction message as defined in [4]
to aggregate the transmission of PORT UP messages.

When a DSL line goes down (idle or silent), the DSLAM SHOULD transmit an
Event message with PORT DOWN message type (81) to the BRAS. It is
recommended that the DSLAMs use a dampening mechanism per DSL line to
control the rate of state changes per DSL line, communicated to the
BRAS.

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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Sub | Message Type | Result| Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Partition ID | Transaction Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I| SubMessage Number | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port Session Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Event Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x|S|x|x| |
+-+-+-+-+ Label |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x|x|x|x|x|x|x|x| Message Type | Tech Type | Block Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Extension Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The format of the "Extension Value" field for Tech Type “DSL” is
as follows :

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # of TLVs | Extension block length (bytes)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ TLVs ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The “Extension Value” contains one or more TLVs to identify a DSL line
and define it’s characteristics. A TLV can consist of multiple sub-TLVs.
First 2 byte of the “Extension Value” contains the number of TLVs that
follow. The next 2 bytes contain the total length of the TLVs carried in
the extension block in bytes (existing “Block Length” field in the GSMP
message is limited to 255 bytes and is not sufficient).

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General format of a TLV is :

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The value field in each TLV is padded to a 4-octet alignment. The Length
field in each TLV contains the actual number of bytes in the TLV (not
including the padding if present). If a TLV is not understood by the
BRAS, it is silently ignored. Currently defined types start from 0x01.

Following TLVs are currently defined:

1. Type (Access-Loop-Circuit-ID = 0x01): This is a mandatory TLV and
contains an identifier of the subscriber’s connection to the access
node (i.e. “local loop”). The “local loop” can be ATM based or
Ethernet based. The “Access Loop Circuit ID” has local significance
at the access node. The exact usage on the BRAS is beyond the scope
of this document. The format used for “local loop” identification
in ANCP messages MUST be identical to what is used by the access
nodes in subscriber signaling messages when the access nodes act as
“signaling relay agents” as outlined in [7] and [8].

Length : (upto 63 bytes)

Value : ASCII string.

For an ATM based local loop the string consists of slot/port and
VPI/VCI information corresponding to the subscriber’s DSL
connection. Default syntax for the string inserted by the access
node as per [8] is:

“Access-Node-Identifier atm slot/port:vpi.vci”

The Access-Node-Identifier uniquely identifies the access node in
the access network. The slot/port and VPI/VCI uniquely identifies
the DSL line on the access node. Also, there is one to one

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correspondence between DSL line and the VC between the access node
and the BRAS.

For local loop which is Ethernet based (and tagged), the string
consists of slot/port and VLAN tag corresponding to the
subscriber. Default syntax for the string inserted by the access
node as per [8] is:

"Access-Node-Identifier eth slot/port[:vlan-id]"

2. Type (Access-Loop-Remote-Id = 0x02): This is an optional TLV and
contains an identifier to uniquely identify a user on a local loop
on the access node. The exact usage on the BRAS is out of scope of
this document. It is desirable that the format used for the field
is similar to what is used by the access nodes in subscriber
signaling messages when the access nodes act as “signaling relay
agents” as outlined in [7] and [8].

Length : (upto 63 bytes)

Value : ASCII string

3. Type (Access-Aggregation-Circuit-ID-Binary = 0x06)

Length : (8 bytes)

Value : two 32 bit integers.

For ethernet access aggregation, where a per-subscriber (stacked)
VLAN can be applied (1:1 model defined in [8]), the VLAN stack
provides a convenient way to uniquely identify the DSL line. The
outer VLAN is equivalent to virtual path between a DSLAM and the
BRAS and inner VLAN is equivalent to a virtual circuit on a per DSL
line basis. In this scenario, any subscriber data received by the
access node and transmitted out the uplink to the aggregation
network will be tagged with the VLAN stack assigned by the access
node

This TLV can carry the VLAN tags assigned by the access node in the
ANCP messages. The VLAN tags can uniquely identify the DSL line
being referred to in the ANCP messages, assuming the VLAN tags are
not in any way translated in the aggregation network and are unique
across physical ports. Each 32 bit integer (least significant bits)

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contains a 12 bit VLAN identifier (which is part of the VLAN tag
defined by IEEE 802.1Q).

Also, in case of an ATM aggregation network, where the DSLAM is
directly connected to the BRAS (without an intermediate ATM
switch), the two values can contain VPI and VCI on the DSLAM uplink
(and can uniquely identify the DSL line on the DSLAM).

This TLV is optional.

4. Type (Access-Aggregation-Circuit-ID-ASCII = 0x03)

Length : (upto 63 bytes)

Value : ASCII string.

This field contains information pertaining to an uplink on the
access node. For Ethernet access aggregation, assuming the access
node assigns VLAN tags (1:1 model), typical format for the string
is:

“Access-Node-Identifier eth slot/port [:inner-vlan-id][:outer-vlan-id]”

The slot/port corresponds to the ethernet uplink on the access node
towards the BRAS.

For an ATM aggregation network, typical format for the string is:

“Access-Node-Identifier atm slot/port:vpi.vci”

This TLV allows the BRAS to associate the information contained in
the ANCP messages to the DSL line on the access node.

If the access node inserts this string in the ANCP messages, when
referring to local loop characteristics (e.g. DSL line in case of a
DSLAM), then it should be able to map the information contained in
the string uniquely to the local loop (e.g. DSL line).

On the BRAS, the information contained in this string can be used
to derive an “aggregation network” facing construct (e.g. an IP
interface) corresponding to the local loop (e.g. DSL line). The
association could be based on “local configuration” on the BRAS.

The access node can also convey to the BRAS, the characteristics
(e.g. bandwidth) of the uplink on the access node. This TLV then

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serves the purpose of uniquely identifying the uplink whose
characteristics are being defined. A separate set of sub-TLVs will
be defined for the uplink characteristics (TBD).

This TLV is optional.

5. Type (DSL Line Attributes = 0x04):

Length : variable (up to 1024 bytes)

Value : This consists of one or more Sub-TLVs corresponding to DSL
line attributes. No sub-TLVs other than the “DSL type” and “DSL
line state” SHOULD be included in a PORT DOWN message.

The general format of the sub-TLVs is identical to the general TLV
format. The value field in each sub-TLV is padded to a 4-octet
alignment. The Length field in each sub-TLV contains the actual
number of bytes in the TLV (not including the padding if present).
Current defined sub-TLV types are start from 0x81.

Following sub-TLVs are currently defined :

. Type (DSL-Type = 0x91) : Defines the type of transmission system
in use. This is a mandatory TLV.

Length : (4 bytes)

Value : (Transmission system : ADSL1 = 0x01, ADSL2 = 0x02,
ADSL2+ = 0x03, VDSL1 = 0x04, VDSL2 = 0x05, SDSL = 0x06, UNKNOWN
= 0x07).

. Type (Actual-Data-Rate-Upstream = 0x81) : Actual data rate
upstream of a synchronized DSL line. This is a mandatory TLV.
This rate value and all the subsequent ones account for the DSL
overhead (i.e. signify the net rate).

Length : (4 bytes)

Value : (Rate in Kb/sec)

. Type (Actual-Data-Rate-Downstream = 0x82) : Actual data rate
downstream of a synchronized DSL line. This is a mandatory TLV.

Length : (4 bytes)

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Value : (Rate in Kb/sec)

. Type (Minimum-Data-Rate-Upstream = 0x83) : Minimum data rate
desired by the operator. This is optional.

Length : (4 bytes)

Value : (Rate in Kb/sec)

. Type (Minimum-Data-Rate-Downstream = 0x84) : Minimum data rate
desired by the operator. This is optional.

Length : (4 bytes)

Value : (Rate in Kb/sec)

. Type (Attainable-Data-Rate-Upstream = 0x85) : Maximum upstream
rate that can be attained on the DSL line. This is an optional
TLV.

Length : (4 bytes)

Value : (Rate in Kb/sec)

. Type (Attainable-Data-Rate-Downstream = 0x86) : Maximum
downstream rate that can be attained on the DSL line. This is
an optional TLV.

Length : (4 bytes)

Value : (Rate in Kb/sec)

. Type (Maximum-Data-Rate-Upstream = 0x87) : Maximum data rate
desired by the operator. This is optional.

Length : (4 bytes)

Value : (Rate in Kb/sec)

. Type (Maximum-Data-Rate-Downstream = 0x88) : Maximum data rate
desired by the operator. This is optional.

Length : (4 bytes)

Value : (Rate in Kb/sec)

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. Type (Minimum-Low-Power-Data-Rate-Upstream = 0x89) : Minimum
data rate desired by the operator in low power state. This is
optional.

Length : (4 bytes)

Value : (Rate in Kb/sec)

. Type (Minimum-Low-Power-Data-Rate-Downstream = 0x8A) : Minimum
data rate desired by the operator in low power state. This is
optional.

Length : (4 bytes)

Value : (Rate in Kb/sec)

. Type (Maximum-Interleaving-Delay-Upstream = 0x8B) : maximum one
way interleaving delay. This is optional.

Length : (4 bytes)

Value : (Time in msec)

. Type (Actual-Interleaving-Delay-Upstream = 0x8C) : Value
corresponding to the interleaver setting. This is optional.

Length : (4 bytes)

Value : (Time in msec)

. Type (Maximum-Interleaving-Delay-Downstream = 0x8D) : maximum
one way interleaving delay. This is optional.

Length : (4 bytes)

Value : (Time in msec)

. Type (Actual-Interleaving-Delay-Downstream = 0x8E) : Value
corresponding to the interleaver setting. This is optional.

Length : (4 bytes)

Value : (Time in msec)

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. Type (DSL line state = 0x8F) : The state of the DSL line. For
PORT UP message, at this time, the TLV is optional (since the
message type implicitly conveys the state of the line). For PORT
DOWN, the TLV is mandatory, since it further communicates the
state of the line as IDLE or SILENT.

Length : (4 bytes)

Value : { SHOWTIME = 0x01, IDLE = 0x02, SILENT = 0x03 }

. Type (Access Loop Encapsulation = 0x90) : The data link protocol
and, optionally the encapsulation overhead on the access loop.
This is an optional TLV. However, when this TLV is present, the
data link protocol MUST minimally be indicated. The
encapsulation overhead can be optionally indicated.

Length : (3 bytes)

Value : The three bytes (most to least significant) and valid
set of values for each byte are defined below.

Data Link (1 byte): {ATM AAL5 = 0,

ETHERNET = 1}

Encaps 1 (1 byte): {NA = 0,

Untagged Ethernet = 1,

Single-tagged Ethernet = 2}

Encaps 2 (1 byte):{ NA = 0,

PPPoA LLC = 1,

PPPoA NULL = 2,

IPoA LLC = 3,

IPoA NuLL = 4,

Ethernet over AAL5 LLC with FCS = 5,

Ethernet over AAL5 LLC without FCS = 6,

Ethernet over AAL5 NULL with FCS = 7,

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Ethernet over AAL5 NULL without FCS = 8}

If this TLV is present, the Data Link protocol MUST be indicated as
defined above. However, the Access Node can choose to not convey the
encapsulation on the access loop by specifying a value of 0 (NA) for the
two encapsulation fields.

5.4.3 Line Configuration Extensions

The BRAS uses extension block in the Port Management messages to convey
service attributes of the DSL lines to the DSLAM. TLVs are defined for
DSL line identification and service data for the DSL lines. Port number
is set to 0 in the message. A new action type "Configure Connection
Service Data" (value 0x8) is defined. The "Function" field is set to the
action type. This action type indicates to the device being controlled
(access-node i.e. DSLAM) to apply service configuration data contained
in the extension value (TLVs), to the DSL line (identified by one of the
TLVs in the extension value). The Tech Type field is extended with new
type "DSL". The value for this field is 0x05.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Sub | Message Type | Result| Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Partition ID | Transaction Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|I| SubMessage Number | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Port Session Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Event Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|x|x|x|x|x|x|x| Duration | Function | X-Function |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Event Flags | Flow Control Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|x|x|x|x|x|x|x|x| Message Type | Tech Type | Block Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Extension Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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The format of the "Extension Value" field is as follows:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # of TLVs | Extension Block length (bytes)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ TLVs ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The “Extension Value” field contains one or more TLVs containing DSL
line identifier and desired service attributes of the the DSL line.
First 2 byte of the “Extension Value” contains the number of TLVs
that follow. The next 2 bytes contain the total length of the
extension block in bytes (existing “Block Length” field in the GSMP
message is limited to 255 bytes and is not sufficient).

General format of a TLV is:

The value field is padded to a 4-octet alignment. The Length field in
each TLV contains the actual number of bytes in the TLV (not
including the padding if present). If a TLV is not understood by the
access-node, it is silently ignored. Depending upon the deployment
scenario, the BRAS may specify “Access Loop Circuit-ID” or the
“Access Aggregation Circuit-ID) as defined in section 5.4.1.
Following TLVs can appear in this message:

o Type (Access-Loop-Circuit-ID = 0x01) : defined in section 5.4.1

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o Type (Access-Aggregation-Circuit-ID-Binary = 0x06): defined in
section 5.4.1.

o Type (Access-Aggregation-Circuit-ID-ASCII = 0x03): defined in
section 5.4.1.

o Type (Service-Profile-Name = 0x05): Reference to a pre-configured
profile on the DSLAM that contains service specific data for the
subscriber.

Length : (upto 64 bytes)

Value : ASCII string containing the profile name (BRAS learns
from a policy server after a subscriber is authorized).

In future, more TLVs MAY be defined for individual service attributes
of a DSL line (e.g. rates, interleaving delay, multicast channel
entitlement access-list etc).

5.4.4 OAM Extensions

GSMP “Port Management” message (type 32) SHOULD be used by the BRAS
to trigger access node to run a loopback test on the local loop. The
message format is defined in section 5.4.2. The version field SHOULD
be set to 3 and sub-version field SHOULD be set to 1. The remaining
fields in the GSMP header have standard semantics. The function type
used in the request message SHOULD be set to “remote loopback” (type
= 0x09). The port, “port session number”, “event sequence number”,
duration, “event flags”, “flow control flags” and code fields SHOULD
all be set to 0. The result field SHOULD be set to “AckAll” to
indicate requirement for the access node to send a success for
failure response. The transaction ID SHOULD contain a sequence number
inserted by the BRAS in each request that it generates. The extension
field format is also defined above in section 5.4.2. The extension
value field can contain one or more TLVs including the access-line
identifier on the DSLAM and OAM test characteristics desired by the
BRAS.

The TLV format is defined above in section 5.4.2. The value field is
padded to a 4-octet alignment. The Length field in each TLV contains
the actual number of bytes in the TLV (not including the padding if
present). If a TLV is not understood by the BRAS, it is silently
ignored. Depending upon the deployment scenario, the BRAS may specify
“Access Loop Circuit-ID” or the “Access Aggregation Circuit-ID) as
defined in section 5.4.1. Following TLVs can appear in this message:

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o Type (Access-Loop-Circuit-ID = 0x01) : defined in section 5.4.1

o Type (Access-Aggregation-Circuit-ID-Binary = 0x06): defined in
section 5.4.1.

o Type (Access-Aggregation-Circuit-ID-ASCII = 0x03): defined in
section 5.4.1.

o Type (OAM-Loopback-Test-Parameters = 0x07): Parameters related to
loopback test. This is an optional TLV. If this TLV is not present
in the request message, the DSLAM SHOULD use locally determined
default values for the test parameters.

Length: 4 bytes

Value : two 1 byte numbers (listed in order of most to least
significant)

o Count (1 byte) : Number of loopback cells/messages that should
be generated on the local loop as part of the loopback test.
The BRAS SHOULD restrict the “count” to be greater than 0 and
less than or equal to 32. The DSLAM SHOULD discard the request
for a loopback test, if the received test parameters contain
an out of range value for the “count” field. The DSLAM MAY
optionally send a failure response to the BRAS with the code
“invalid test parameter”.

o Timeout (1 byte) : Upper bound on the time in seconds that the
BRAS would wait for a response from the DSLAM. If the total
time taken by the DSLAM to complete a test with requested
parameters, exceeds the specified “timeout” value, it can
choose to omit the generation of a response to the BRAS. DSLAM
SHOULD use a locally determined value for the “timeout”, if
the received value of the “timeout” parameter is 0.

o Type (Opaque-Data = 0x08) : This is an optional TLV. If present in
the request message, the DSLAM SHOULD reflect it back in the
response unmodified.

Length : 8 bytes

Value : Two 32 bit integers inserted by the BRAS (not to be
interpreted by the DSLAM, but just reflected back in the
response).

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The access node generates a success or failure response when it deems
the loopback test to be complete. “Port Management” message (type 32)
is used. The result field SHOULD be set to success or failure. The
function type SHOULD be set to 0x09. The transaction ID SHOULD be
copied from the sequence number contained in the corresponding
request. The other parameters not explicitly defined here SHOULD be
set as specified in the request message above. The code field SHOULD
be set to a value in the range 0x500 to 0x5ff (to be reserved with
IANA) to indicate the status of the executed test. The valid values
defined are (can be extended in future):

0x500 : Specified access line does not exist.

0x501 : Loopback test timed out.

0x502 : Reserved

0x503 : DSL line status showtime.

0x504 : DSL line status idle.

0x505 : DSL line status silent.

0x506 : DSL line status training.

0x507 : DSL line integrity error.

0x508 : DSLAM resource not available.

0x509 : Invalid test parameter.

The Extension value can contain one or more TLVs including the TLV to
identify the access line on which the test was performed, and details
from executing the test. The access line identifier SHOULD be identical
to what was contained in the request. The relevant TLVs are:

o Type (Access-Loop-Circuit-ID = 0x01) : defined in section 5.4.1

o Type (Access-Aggregation-Circuit-ID-Binary = 0x06): defined in
section 5.4.1.

o Type (Access-Aggregation-Circuit-ID-ASCII = 0x03): defined in
section 5.4.1.

o Type (Opaque-Data = 0x08) : Data inserted by the BRAS in the
request reflected back by the DSLAM.

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Length : 8 bytes

Value : Two 32 bit integers as received in the request (opaque to
the DSLAM).

o Type (OAM-Loopback-Test-Response-String = 0x09)

Length (upto 128 bytes)

Value : Suitably formatted ASCII string containing useful details
about the test that the BRAS will display for the operator,
exactly as received from the DSLAM (no manipulation/interpretation
by the BRAS). This is an optional TLV, but it is strongly
recommended, that in case of ATM based local loop, the DSLAM at
the very least indicates via this TLV, the total loopback cells
generated and the total loopback cells successfully received as
part of executing the requested loopback test.

5.5 ATM-specific considerations

The topology discovery and line configuration involve the DSL line
attributes. For ATM based access networks, the DSL line on the DSLAM
is identified by the port and PVP/PVC corresponding to the
subscriber. The DSLAMs are connected to the BRAS via an ATM access
aggregation network. Since, the DSLAM (access-node) is not directly
connected to the BRAS, the BRAS needs a mechanism to learn the DSL
line identifier (more generally referred to as "Access Loop Circuit-
ID") corresponding to a subscriber. The "Access loop circuit-ID" has
no local significance on the BRAS. The ANCP messages for topology
discovery and line configuration carry opaque "Access loop Circuit-
ID" which has only local significance on the DSLAMs.

The access loop circuit identifier can be carried as an ASCII string
in the ANCP messages. This allows ANCP to be decoupled from the
specifics of the underlying access technology being controlled. On
the other hand, this requires a BRAS mechanism by which such
identifier can be correlated to the context of an “aggregation
network” facing IP interface (corresponding to the subscriber) on the
BRAS. This would typically require local configuration of such IP
interfaces, or of the underlying ATM interfaces.

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5.6 Ethernet-specific considerations

One possible way of approaching the use of Ethernet technology in the
access aggregation network is to recreate the equivalent of Virtual
Paths (VPs) and Virtual Circuits (VCs) by using stacked Virtual LAN
tags. As an example, one could use an “outer” VLAN to create a form of
“virtual path” between a given DSLAM and a given BRAS. And then use
“inner” VLAN tags to create a form of “virtual circuit” on a per DSL
line basis. In this case, VLAN tags conveyed in topology discovery and
line configuration messages will allow to uniquely identify the DSL line
in a straightforward manner, assuming the VLAN tags are not translated
in some way by the aggregation network, and are unique across physical
ports.

However, some carriers do not wish to use this “connection oriented”
approach. Therefore, an alternative model is to bridge sessions from
multiple subscribers behind a DSLAM to a single VLAN in the aggregation
network. This is the N:1 model. In this model, or in the case where user
traffic is sent untagged, the access node needs to insert the exact
identity of the DSL line in the topology discovery and line
configuration messages, and then have a mechanism by which this can be
correlated to the context of an “aggregation network” facing IP
interface (for the subscriber) on the BRAS. This can either be based on
local configuration on the BRAS, or on the fact that such DSLAM (access
node) typically inserts the “Access Loop Circuit ID” in subscriber
signaling messages relayed to the BRAS (i.e. DHCP or PPPoE discovery
messages).

Section 5.4.1 defines “Access Loop Circuit ID”.

6 IANA Considerations

New Tech-Type, capability types, sub-TLV types related to topology
discovery and line configuration will need to be reserved.

7 Security Considerations

The BRAS and DSLAMs are implicitly in a trusted domain, so security
for ANCP is not a strong requirement. However, if needed security can
be provided using IP security as indicated in [RFC3293].

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8 References

[1] DSLForum TR-059, DSL Evolution - Architecture Requirements for
the Support of QoS-Enabled IP Services, Tom Anschutz (BellSouth
Telecommunications), 09/2003.

[2] DSLForum TR-058, Multi-Service Architecture & Framework
Requirements, Mark Elias (SBC) and Sven Ooghe (Alcatel),
09/2003.

[3] DSLForum TR-092, Broadband Remote access server requirements
document.

[4] Doria, A. et al, "General Switch Management Protocol- V3" (GSMP
v3), RFC 3292, June 2002.

[5] Worster, T., Doria, A. and J. Buerkle, "General Switch
Management Protocol (GSMP) Packet Encapsulations for
Asynchronous Transfer Mode (ATM), Ethernet and Transmission
Control Protocol (TCP)", RFC 3293, June 2002.

[6] GSMP extensions for ANCP - Transactional Multicast, draft-
moisand-gsmp-ancp-multicast-00 (work in progress).

[7] “DHCP Relay Agent Information Option”, RFC 3046, January 2001.

[8] Architecture & Transport: Migration to Ethernet Based DSL
Aggregation, DSL Forum WT-101, Cohen et al.

[9] Framework for Access Node Control Mechanism in Broadband
Networks, draft-ietf-ancp-framework-00.txt.

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Author's Addresses

Sanjay Wadhwa
Juniper Networks
10 Technology Park Drive
Westford, MA 01886

Email: swadhwa@juniper.net

Jerome Moisand
Juniper Networks
10 Technology Park Drive
Westford, MA 01886

Email: jmoisand@juniper.net

Swami Subramanian
Juniper Networks
10 Technology Park Drive
Westford, MA 01886

Email: ssubramanian@juniper.net

Thomas Haag
T-systems

Email: thomas.haag@t-systems.com

Norber Voigt
Siemens

Email: norbert.voigt@siemens.com

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Acknowledgment

Thanks to Peter Arberg, Josef Froehler, Derek Harkness, Kim
Hyldgaard, Sandy Ng, Robert Peschi, and Michel Platnic for their
input to this document.

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