Internet Research Task Force (IRTF) J. Buford
Request for Comments: 7019 Avaya Labs Research
Category: Experimental M. Kolberg, Ed.
ISSN: 2070-1721 University of Stirling
September 2013
Application-Layer Multicast Extensions to REsource LOcation And
Discovery (RELOAD)
Abstract
We define a REsource LOcation And Discovery (RELOAD) Usage for
Application-Layer Multicast (ALM) as well as a mapping to the RELOAD
experimental message type to support ALM. The ALM Usage is intended
to support a variety of ALM control algorithms in an overlay-
independent way. Two example algorithms are defined, based on Scribe
and P2PCast.
This document is a product of the Scalable Adaptive Multicast
Research Group (SAM RG).
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Research Task
Force (IRTF). The IRTF publishes the results of Internet-related
research and development activities. These results might not be
suitable for deployment. This RFC represents the consensus of the
Scalable Adaptive Multicast Research Group of the Internet Research
Task Force (IRTF). Documents approved for publication by the IRSG
are not a candidate for any level of Internet Standard; see Section 2
of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7019.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Overlay Network . . . . . . . . . . . . . . . . . . . . . 5
2.2. Overlay Multicast . . . . . . . . . . . . . . . . . . . . 5
2.3. Source-Specific Multicast (SSM) . . . . . . . . . . . . . 5
2.4. Any-Source Multicast (ASM) . . . . . . . . . . . . . . . 5
2.5. Peer . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Overlay . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Overlay Multicast . . . . . . . . . . . . . . . . . . . . 6
3.3. RELOAD . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. NAT . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.5. Tree Topology . . . . . . . . . . . . . . . . . . . . . . 7
4. Architecture Extensions to RELOAD . . . . . . . . . . . . . . 7
5. RELOAD ALM Usage . . . . . . . . . . . . . . . . . . . . . . 8
6. ALM Tree Control Signaling . . . . . . . . . . . . . . . . . 9
7. ALM Messages Mapped to RELOAD . . . . . . . . . . . . . . . . 10
7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 10
7.2. Tree Lifecycle Messages . . . . . . . . . . . . . . . . . 11
7.2.1. CreateALMTree . . . . . . . . . . . . . . . . . . . . 11
7.2.2. CreateALMTreeResponse . . . . . . . . . . . . . . . . 12
7.2.3. Join . . . . . . . . . . . . . . . . . . . . . . . . 12
7.2.4. JoinAccept (Join Response) . . . . . . . . . . . . . 14
7.2.5. JoinReject (Join Response) . . . . . . . . . . . . . 15
7.2.6. JoinConfirm . . . . . . . . . . . . . . . . . . . . . 15
7.2.7. JoinConfirmResponse . . . . . . . . . . . . . . . . . 16
7.2.8. JoinDecline . . . . . . . . . . . . . . . . . . . . . 16
7.2.9. JoinDeclineResponse . . . . . . . . . . . . . . . . . 16
7.2.10. Leave . . . . . . . . . . . . . . . . . . . . . . . . 16
7.2.11. LeaveResponse . . . . . . . . . . . . . . . . . . . . 17
7.2.12. Reform or Optimize Tree . . . . . . . . . . . . . . . 17
7.2.13. ReformResponse . . . . . . . . . . . . . . . . . . . 18
7.2.14. Heartbeat . . . . . . . . . . . . . . . . . . . . . . 18
7.2.15. Heartbeat Response . . . . . . . . . . . . . . . . . 18
7.2.16. NodeQuery . . . . . . . . . . . . . . . . . . . . . . 18
7.2.17. NodeQueryResponse . . . . . . . . . . . . . . . . . . 19
7.2.18. Push . . . . . . . . . . . . . . . . . . . . . . . . 21
7.2.19. PushResponse . . . . . . . . . . . . . . . . . . . . 22
8. Scribe Algorithm . . . . . . . . . . . . . . . . . . . . . . 22
8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 22
8.2. Create . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.3. Join . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.4. Leave . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.5. JoinConfirm . . . . . . . . . . . . . . . . . . . . . . . 24
8.6. JoinDecline . . . . . . . . . . . . . . . . . . . . . . . 24
8.7. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 24
9. P2PCast Algorithm . . . . . . . . . . . . . . . . . . . . . . 24
9.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 24
9.2. Message Mapping . . . . . . . . . . . . . . . . . . . . . 25
9.3. Create . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.4. Join . . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.5. Leave . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.6. JoinConfirm . . . . . . . . . . . . . . . . . . . . . . . 27
9.7. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 27
10. Message Format . . . . . . . . . . . . . . . . . . . . . . . 28
10.1. ALMHeader Definition . . . . . . . . . . . . . . . . . . 29
10.2. ALMMessageContents Definition . . . . . . . . . . . . . 30
10.3. Response Codes . . . . . . . . . . . . . . . . . . . . . 30
11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 31
11.1. Create Tree . . . . . . . . . . . . . . . . . . . . . . 31
11.2. Join Tree . . . . . . . . . . . . . . . . . . . . . . . 32
11.3. Leave Tree . . . . . . . . . . . . . . . . . . . . . . . 33
11.4. Push Data . . . . . . . . . . . . . . . . . . . . . . . 34
12. Kind Definitions . . . . . . . . . . . . . . . . . . . . . . 35
12.1. ALMTree Kind Definition . . . . . . . . . . . . . . . . 35
13. RELOAD Configuration File Extensions . . . . . . . . . . . . 36
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
14.1. ALM Algorithm Types . . . . . . . . . . . . . . . . . . 36
14.2. Message Code Registration . . . . . . . . . . . . . . . 36
14.3. Error Code Registration . . . . . . . . . . . . . . . . 37
15. Security Considerations . . . . . . . . . . . . . . . . . . . 38
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
17.1. Normative Reference . . . . . . . . . . . . . . . . . . 39
17.2. Informative References . . . . . . . . . . . . . . . . . 39
1. Introduction
The concept of scalable adaptive multicast includes both scaling
properties and adaptability properties. Scalability is intended to
cover:
o large group size
o large numbers of small groups
o rate of group membership change
o admission control for QoS
o use with network-layer QoS mechanisms
o varying degrees of reliability
o trees connecting nodes over the global Internet
Adaptability includes
o use of different control mechanisms for different multicast trees
depending on initial application parameters or application classes
o changing multicast tree structure depending on changes in
application requirements, network conditions, and membership
Application-Layer Multicast (ALM) has been demonstrated to be a
viable multicast technology where native multicast isn't available.
Many ALM designs have been proposed. This ALM Usage focuses on:
o ALM implemented in RELOAD-based overlays
o Support for a variety of ALM control algorithms
o Providing a basis for defining a separate hybrid ALM RELOAD Usage
RELOAD [RFC6940] [RELOAD] has an application extension mechanism in which a new
type of application defines a Usage. A RELOAD Usage defines a set of
data types and rules for their use. In addition, this document
describes additional message types and a new ALM algorithm plugin
architectural component.
This document represents the consensus of the SAM RG. It was
repeatedly discussed within the research group, as well as with other
Application-Layer Multicast experts.
1.1. Requirements Language
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 [RFC2119].
2. Definitions
We adopt the terminology defined in Section 3 of [RFC6940], [RELOAD],
specifically the distinction between "node", "peer", and "client".
2.1. Overlay Network
Overlay network: An application-layer virtual or logical network with
addressable end points that provides connectivity, routing, and
messaging between end points. Overlay networks are frequently used
as a substrate for deploying new network services or for providing a
routing topology not available from the underlying physical network.
Many peer-to-peer systems are overlay networks that run on top of the
Internet. In Figure 1, "P" indicates overlay peers, and peers are
connected in a logical address space. The links shown in the figure
represent predecessor/successor links. Depending on the overlay
routing model, additional or different links may be present.
P P P P P
..+....+....+...+.....+...
. +P
P+ .
. +P
..+....+....+...+.....+...
P P P P P
Figure 1: Overlay Network Example
2.2. Overlay Multicast
Overlay Multicast (OM): Hosts participating in a multicast session
form an overlay network and utilize unicast connections among pairs
of hosts for data dissemination [BUFORD2009] [KOLBERG2010]
[BUFORD2008]. The hosts in overlay multicast exclusively handle
group management, routing, and tree construction, without any support
from Internet routers. This is also commonly known as Application-
Layer Multicast (ALM) or End-System Multicast (ESM). We call systems
that use proxies connected in an overlay multicast backbone "proxied
overlay multicast" or POM.
2.3. Source-Specific Multicast (SSM)
SSM tree: The creator of the tree is the source. It sends data
messages to the tree root that are forwarded down the tree.
2.4. Any-Source Multicast (ASM)
ASM tree: A node sending a data message sends the message to its
parent and its children. Each node receiving a data message from one
edge forwards it to the remaining tree edges to which it is
connected.
2.5. Peer
Peer: An autonomous end system that is connected to the physical
network and participates in and contributes resources to overlay
construction, routing, and maintenance. Some peers may also perform
additional roles such as connection relays, super nodes, NAT
traversal assistance, and data storage.
3. Assumptions
3.1. Overlay
Peers connect in a large-scale overlay, which may be used for a
variety of peer-to-peer applications in addition to multicast
sessions. Peers may assume additional roles in the overlay beyond
participation in the overlay and in multicast trees. We assume a
single-structured overlay routing algorithm is used. Any of a
variety of multi-hop, one-hop, or variable-hop overlay algorithms
could be used.
Castro, et al. [CASTRO2003] compared multi-hop overlays and found
that tree-based construction in a single overlay outperformed using
separate overlays for each multicast session. We use a single
overlay rather than separate overlays per multicast session.
An overlay multicast algorithm may leverage the overlay's mechanism
for maintaining overlay state in the face of churn. For example, a
peer may store a number of DHT (Distributed Hash Table) entries.
When the peer gracefully leaves the overlay, it transfers those
entries to the nearest peer. When another peer joins that is closer
to some of the entries than the current peer that holds those
entries, than those entries are migrated. Overlay churn affects
multicast trees as well; remedies include automatic migration of the
tree state and automatic rejoin operations for dislocated child
nodes.
3.2. Overlay Multicast
The overlay supports concurrent multiple multicast trees. The limit
on the number of concurrent trees depends on peer and network
resources and is not an intrinsic property of the overlay.
3.3. RELOAD
We use RELOAD [RFC6940] [RELOAD] as the peer-to-peer (P2P) overlay for data
storage and the mechanism by which the peers interconnect and route
messages. RELOAD is a generic P2P overlay, and application support
is defined by profiles called Usages.
3.4. NAT
Some nodes in the overlay may be in a private address space and
behind firewalls. We use the RELOAD mechanisms for NAT traversal.
We permit clients to be leaf nodes in an ALM tree.
3.5. Tree Topology
All tree control messages are routed in the overlay. Two types of
data or media topologies are envisioned: 1) tree edges are paths in
the overlay, and 2) tree edges are direct connections between a
parent and child peer in the tree, formed using the RELOAD AppAttach
method.
4. Architecture Extensions to RELOAD
There are two changes as depicted in Figure 2. New ALM messages are
mapped to RELOAD Message Transport using the RELOAD experimental
message type. A plugin for ALM algorithms handles the ALM state and
control. The ALM algorithm is under control of the application via
the Group API [COMMON-API].
+---------+
|Group API|
+---------+
|
------------------- Application ------------------------
+-------+ |
| ALM | |
| Usage | |
+-------+ |
-------------- Messaging Service Boundary --------------
|
+--------+ +-----------+---------+ +---------+
| Storage|<---> | RELOAD | ALM |<-->| ALM Alg |
+--------+ | Message | Messages| +---------+
^ | Transport | |
| +-----------+---------+
v | |
+-------------+ |
| Topology | |
| Plugin | |
+-------------+ |
^ |
v v
+-------------------+
| Forwarding & |
| Link Management |
+-------------------+
---------- Overlay Link Service Boundary --------------
Figure 2: RELOAD Architecture Extensions
The ALM components interact with RELOAD as follows:
o ALM uses the RELOAD data storage functionality to store an ALMTree
instance when a new ALM tree is created in the overlay and to
retrieve ALMTree instance(s) for existing ALM trees.
o ALM applications and management tools may use the RELOAD data
storage functionality to store diagnostic information about the
operation of trees, including average number of trees, delay from
source to leaf nodes, bandwidth use, and packet loss rate. In
addition, diagnostic information may include statistics specific
to the tree root or to any node in the tree.
5. RELOAD ALM Usage
Applications of RELOAD are restricted in the data types that can be
stored in the DHT. The profile of accepted data types for an
application is referred to as a Usage. RELOAD is designed so that
new applications can easily define new Usages. New RELOAD Usages are
needed for multicast applications since the data types in base RELOAD
and existing Usages are not sufficient.
We define an ALM Usage in RELOAD. This ALM Usage is sufficient for
applications that require ALM functionality in the overlay. Figure 2
shows the internal structure of the ALM Usage. This contains the
Group API ([COMMON-API]), an ALM algorithm plugin (e.g., Scribe), and
the ALM messages that are then sent out to the RELOAD network.
A RELOAD Usage is required [RFC6940] [RELOAD] to define the following:
o Kind-ID and code points
o data structures for each Kind
o access control rules for each Kind
o the Resource Name used to hash to the Resource ID that determines
where the Kind is stored
o address restoration after recovery from a network partition (to
form a single coherent network)
o the types of connections that can be initiated using AppConnect
An ALM group_id is a RELOAD node_id. The owner of an ALM group
creates a RELOAD node_id as specified in [RFC6940]. [RELOAD]. This means that a
group_id is used as a RELOAD Destination for overlay routing
purposes.
6. ALM Tree Control Signaling
Peers use the overlay to support ALM operations such as:
o CreateALMTree
o Join
o Leave
o Reform or optimize tree
There are a variety of algorithms for peers to form multicast trees
in the overlay. The approach presented here permits multiple such
algorithms to be supported in the overlay since different algorithms
may be more suitable for certain application requirements; the
approach also supports experimentation. Therefore, overlay messaging
corresponding to the set of overlay multicast operations MUST carry
algorithm identification information.
For example, for small groups, the join point might be directly
assigned by the rendezvous point, while for large trees the Join
request might be propagated down the tree with candidate parents
forwarding their position directly to the new node.
Here is a simplistic notation for forming a multicast tree in the
overlay. Its main advantage is the use of the overlay for routing
both control and data messages. The group creator does not have to
be the root of the tree or even in the tree. It does not consider
per-node load, admission control, or alternative paths. After the
creation of a tree, the group_id is expected to be advertised or
distributed out of band, perhaps by publishing in the DHT.
Similarly, joining peers will discover the group_id out of band,
perhaps by a lookup in the tree.
As stated earlier, multiple algorithms will coexist in the overlay.
1. Peer that initiates multicast group:
group_id = create(); // Allocate a unique group_id.
// The root is the nearest
// peer in the overlay.
2. Any joining peer:
joinTree(group_id); // sends "join group_id" message
The overlay routes the Join request using the overlay routing
mechanism toward the peer with the nearest ID to the group_id.
This peer is the root. Peers on the path to the root join the
tree as forwarding points.
3. Leave Tree:
leaveTree(group_id); // removes this node from the tree
Propagates a Leave request to each child node and to the parent
node. If the parent node is a forwarding node and this is its
last child, then it propagates a Leave request to its parent. A
child node receiving a Leave request from a parent sends a Join
request to the group_id.
4. Message forwarding:
multicastMsg(group_id, msg);
For message forwarding, both Any-Source Multicast (ASM) and
Source-Specific Multicast (SSM) approaches may be used.
7. ALM Messages Mapped to RELOAD
7.1. Introduction
In this document, we define messages for overlay multicast tree
creation, using an existing protocol (RELOAD) in the P2P-SIP WG
[RFC6940]
[RELOAD] for a universal structured peer-to-peer overlay protocol.
RELOAD provides the mechanism to support a number of overlay
topologies. Hence, the overlay multicast framework defined in this
document can be used with P2P-SIP and makes the Scalable Adaptive
Multicast (SAM) framework overlay agnostic.
As discussed in the SAM requirements document [SAM-GENERIC], there
are a variety of ALM tree formation and tree maintenance algorithms.
The intent of this specification is to be algorithm agnostic, similar
to how RELOAD is overlay algorithm agnostic. We assume that all
control messages are propagated using overlay routed messages.
The message types needed for ALM behavior are divided into the
following categories:
o Tree lifecycle (Create, Join, Leave, Reform, Heartbeat)
o Peer region and multicast properties
The message codes are defined in Section 14.2 of this document.
Messages are mapped to the RELOAD experimental message type.
In the following sections, the protocol messages as mapped to RELOAD
are discussed. Detailed example message flows are provided in
Section 11.
In the following descriptions, we use the datatype Dictionary, which
is a set of opaque values indexed by an opaque key with one value for
each key. A single dictionary entry is represented by a
DictionaryEntry as defined in Section 7.2.3 of the RELOAD document
[RFC6940].
[RELOAD]. The Dictionary datatype is defined as follows:
struct {
DictionaryEntry elements<0..2^16-1>;
} Dictionary;
7.2. Tree Lifecycle Messages
Peers use the overlay to transmit ALM operations defined in this
section.
7.2.1. CreateALMTree
A new ALM tree is created in the overlay with the identity specified
by group_id. The common interpretation in a DHT-based overlay of
group_id is that the peer with a peer_id closest to and less than the
group_id is the root of the tree. However, other overlay types are
supported. The tree has no children at the time it is created.
The group_id is generated from a well-known session key to be used by
other peers to address the multicast tree in the overlay. The
generation of the group_id from the session_key MUST be done using
the overlay's ID-generation mechanism.
struct {
node_id peer_id;
opaque session_key<0..2^32-1>;
node_id group_id;
Dictionary options;
} ALMTree;
peer_id: overlay address of the peer that creates the multicast tree.
session_key: a well-known string that when hashed using the overlay's
ID-generation algorithm produces the group_id.
group_id: overlay address of the root of the tree.
options: name-value list of properties to be associated with the
tree, such as the maximum size of the tree, restrictions on peers
joining the tree, latency constraints, preference for distributed or
centralized tree formation and maintenance, and Heartbeat interval.
Tree creation is subject to access control since it involves a Store
operation. The NODE-MATCH access policy defined in Section 7.3.2 of
RELOAD [RFC6940]
[RELOAD] is used.
A successful CreateALMTree causes an ALMTree structure to be stored
in the overlay at the node G responsible for the group_id. This node
G performs the RELOAD-defined StoreReq operation as a side effect of
performing the CreateALMTree. If the StoreReq fails, the
CreateALMTree fails too.
After a successful CreateALMTree, peers can use the RELOAD Fetch
method to retrieve the ALMTree struct at address group_id. The
ALMTree Kind is defined in Section 12.1.
7.2.2. CreateALMTreeResponse
After receiving a CreateALMTree message from node S, the peer sends a
CreateALMTreeResponse to node S.
struct {
Dictionary options;
} CreateALMTreeResponse;
options: A node may provide algorithm-dependent parameters about the
created tree to the requesting node.
7.2.3. Join
Join causes the distributed algorithm for peer join of a specific ALM
group to be invoked. The definition of the Join request is shown
below. If successful, the joining peer is notified of one or more
candidate parent peers in one or more JoinAccept messages. The
particular ALM join algorithm is not specified in this protocol.
struct {
node_id peer_id;
node_id group_id;
Dictionary options;
} Join;
peer_id: overlay address of joining/leaving peer
group_id: overlay address of the root of the tree
options: name-value list of options proposed by joining peer
RELOAD is a request-response protocol. Consequently, the messages
JoinAccept and JoinReject (defined below) are matching responses for
Join. If JoinReject is received, then no further action on this
request is carried out. If JoinAccept is received, then either a
JoinConfirm or a JoinDecline message (see below) is sent. The
matching response for JoinConfirm is JoinConfirmResponse. The
matching response for JoinDecline is JoinDeclineResponse.
The following list shows the matching request-responses according to
the request-response mechanism defined in RELOAD [RFC6940]. [RELOAD].
Join -- JoinAccept: Node C sends a Join request to node P. If
node P accepts, it responds with JoinAccept.
Join -- JoinReject: Node C sends a Join request to node P. If
node P does not accept the Join request, it responds with
JoinReject.
JoinConfirm -- JoinConfirmResponse: If node P sent node C a
JoinAccept and node C confirms with a JoinConfirm request, then
node P responds with a JoinConfirmResponse.
JoinDecline -- JoinDeclineResponse: If node P sent node C a
JoinAccept and node C declines with a JoinDecline request, then
node P responds with a JoinDeclineResponse.
Thus, Join, JoinConfirm, and JoinDecline are treated as requests as
defined in RELOAD, are mapped to the RELOAD exp_a_req message, and
are therefore retransmitted until either a retry limit is reached or
a matching response received. JoinAccept, JoinReject,
JoinConfirmResponse, and JoinDeclineResponse are treated as message
responses as defined above and are mapped to the RELOAD exp_a_ans
message.
The Join behavior can be described as follows:
if(checkAccept(msg)) {
recvJoins.add(msg.source, msg.group_id)
SEND(JoinAccept(node_id, msg.source, msg.group_id))
}
7.2.4. JoinAccept (Join Response)
JoinAccept tells the requesting joining peer that the indicated peer
is available to act as its parent in the ALM tree specified by
group_id, with the corresponding options specified. A peer MAY
receive more than one JoinAccept from different candidate parent
peers in the group_id tree. The peer accepts a peer as parent using
a JoinConfirm message. A JoinAccept that receives neither a
JoinConfirm nor JoinDecline message MUST expire. RELOAD
implementations are able to read a local configuration file for
settings. It is assumed that this file contains the timeout value to
be used.
struct {
node_id parent_peer_id;
node_id child_peer_id;
node_id group_id;
Dictionary options;
} JoinAccept;
parent_peer_id: overlay address of a peer that accepts the joining
peer
child_peer_id: overlay address of joining peer
group_id: overlay address of the root of the tree
options: name-value list of options accepted by parent peer
7.2.5. JoinReject (Join Response)
A peer receiving a Join request responds with a JoinReject response
to indicate the request is rejected.
7.2.6. JoinConfirm
A peer receiving a JoinAccept message that it wishes to accept MUST
explicitly accept it using a JoinConfirm message before the
expiration of a timer for the JoinAccept message. The joining peer
MUST include only those options from the JoinAccept that it also
accepts, completing the negotiation of options between the two peers.
struct {
node_id child_peer_id;
node_id parent_peer_id;
node_id group_id;
Dictionary options;
} JoinConfirm;
child_peer_id: overlay address of joining peer that is a child of the
parent peer
parent_peer_id: overlay address of the peer that is the parent of the
joining peer
group_id: overlay address of the root of the tree
options: name-value list of options accepted by both peers
The JoinConfirm message behavior is described below:
if(recvJoins.contains(msg.source,msg.group_id)){
if !(groups.contains(msg.group_id)) {
groups.add(msg.group_id)
SEND(msg,msg.group_id)
}
groups[msg.group_id].children.add(msg.source)
recvJoins.del(msg.source, msg.group_id)
}
7.2.7. JoinConfirmResponse
A peer receiving a JoinConfirm message responds with a
JoinConfirmResponse message.
7.2.8. JoinDecline
A peer receiving a JoinAccept message that it does not wish to accept
MAY explicitly decline it using a JoinDecline message.
struct {
node_id peer_id;
node_id parent_peer_id;
node_id group_id;
} JoinDecline;
peer_id: overlay address of joining peer that declines the JoinAccept
parent_peer_id: overlay address of the peer that issued a JoinAccept
to this peer
group_id: overlay address of the root of the tree
The behavior of the JoinDecline message is described as follows:
if(recvJoins.contains(msg.source,msg.group_id))
recvJoins.del(msg.source, msg.group_id)
7.2.9. JoinDeclineResponse
A peer receiving a JoinConfirm message responds with a
JoinDeclineResponse message.
7.2.10. Leave
A peer that is part of an ALM tree identified by group_id that
intends to detach from either a child or parent peer SHOULD send a
Leave request to the peer from which it wishes to detach. A peer
receiving a Leave request from a peer that is neither in its parent
nor child lists SHOULD ignore the message.
struct {
node_id peer_id;
node_id group_id;
Dictionary options;
} Leave;
peer_id: overlay address of leaving peer
group_id: overlay address of the root of the tree
options: name-value list of options
The behavior of the Leave request can be described as:
groups[msg.group_id].children.remove(msg.source)
if (groups[msg.group].children = 0)
SEND(msg,groups[msg.group_id].parent)
7.2.11. LeaveResponse
A peer receiving a Leave request responds with a LeaveResponse
message.
7.2.12. Reform or Optimize Tree
This triggers a reorganization of either the entire tree or only a
subtree. It MAY include hints to specific peers of recommended
parent or child peers to which to reconnect. A peer receiving this
message MAY ignore it, MAY propagate it to other peers in its
subtree, and MAY invoke local algorithms for selecting preferred
parent and/or child peers.
struct {
node_id group_id;
node_id peer_id;
Dictionary options;
} Reform;
group_id: overlay address of the root of the tree
peer_id: if omitted, then the tree is reorganized starting from the
root; otherwise, it is reorganized only at the subtree identified by
peer_id.
options: name-value list of options
7.2.13. ReformResponse
A peer receiving a Reform message responds with a ReformResponse.
struct {
Dictionary options;
} ReformResponse;
options: algorithm-dependent information about the results of the
Reform operation
7.2.14. Heartbeat
A child node signals to its adjacent parent nodes in the tree that it
is alive. If a parent node does not receive a Heartbeat message
within N Heartbeat time intervals, it MUST treat this as an explicit
Leave request from the unresponsive peer. N is configurable. RELOAD
implementations are able to read a local configuration file for
settings. It is assumed that this file contains the value for N to
be used.
struct {
node_id peer_id_src;
node_id peer_id_dst;
node_id group_id;
Dictionary options;
} Heartbeat;
peer_id_src: source of Heartbeat
peer_id_dst: destination of Heartbeat
group_id: overlay address of the root of the tree
options: an algorithm may use the Heartbeat message to provide state
information to adjacent nodes in the tree
7.2.15. Heartbeat Response
A parent node responds with a HeartbeatResponse to a Heartbeat from a
child node indicating that it has received the Heartbeat message.
7.2.16. NodeQuery
The NodeQuery message is used to obtain information about the state
and performance of the tree on a per-node basis. A set of nodes
could be queried to construct a centralized view of the multicast
trees, similar to a web crawler.
struct {
node_id peer_id_src;
node_id peer_id_dst;
} NodeQuery;
peer_id_src: source of query
peer_id_dst: destination of query
7.2.17. NodeQueryResponse
The response to a NodeQuery message contains a NodeStatistics
instance for this node.
public struct {
uint32 node_lifetime;
uint32 total_number_trees;
uint16 number_algorithms_supported;
uint8 algorithms_supported[32];
TreeData max_tree_data;
uint16 number_active_trees;
TreeData tree_data<0..2^8-1>;
ImplementationInfo impl_info;
} NodeStatistics;
node_lifetime: time the node has been alive in seconds since last
restart
total_number_trees: total number of trees this node has been part
of during the node lifetime
number_algorithms_supported: value between 0..2^16-1 corresponding
to the number of algorithms supported
algorithms_supported: list of algorithms, each byte encoded using
the corresponding algorithm code
max_tree_data: data about tree with largest number of nodes that
this node was part of. NodeQuery can be used to crawl all the
nodes in an ALM tree to fill this field. This is intended to
support monitoring, algorithm design, and general experimentation
with ALM in RELOAD.
number_active_trees: current number of trees that the node is part
of
tree_data: details of each active tree; the number of such is
specified by number_active_trees
impl_info: information about the implementation of this Usage
public struct {
uint32 tree_id;
uint8 algorithm;
node_id tree_root;
uint8 number_parents;
node_id parent<0..2^8-1>;
uint16 number_child_nodes;
node_id children<0..2^16-1>;
uint32 path_length_to_root;
uint32 path_delay_to_root;
uint32 path_delay_to_child;
} TreeData;
tree_id: the ID of the tree
algorithm: code identifying the multicast algorithm used by this
tree
tree_root: node_id of tree root, or 0 if unknown
number_parents: 0 .. 2^8-1 indicates number of parent nodes for
this node
parent: the RELOAD node_id of each parent node
number_child_nodes: 0..2^16-1 indicates number of children
children: the RELOAD node_id of each child node
path_length_to_root: number of overlay hops to the root of the
tree
path_delay_to_root: RTT in milliseconds to root node
path_delay_to_child: last measured RTT in milliseconds to child
node with largest RTT
public struct {
uint32 join_confirm_timeout;
uint32 heartbeat_interval;
uint32 heartbeat_response_timeout;
uint16 info_length;
uint8 info<0..2^16-1>;
} ImplementationInfo;
join_confirm_timeout: The default time for JoinConfirm/
JoinDecline, intended to provide sufficient time for a Join
request to receive all responses and confirm the best choice.
Default value is 5000 msec. An implementation can change this
value.
heartbeat_interval: The default Heartbeat interval is 2000 msec.
Different interoperating implementations could use different
intervals.
heartbeat_response_timeout: The default Heartbeat timeout is 5000
msec and is the max time between Heartbeat reports from an
adjacent node in the tree at which point the Heartbeat is missed.
info_length: length of the info field
info: implementation-specific information, such as name of
implementation, build version, and implementation-specific
features
7.2.18. Push
A peer sends arbitrary multicast data to other peers in the tree.
Nodes in the tree forward this message to adjacent nodes in the tree
in an algorithm-dependent way.
struct {
node_id group_id;
uint8 priority;
uint32 length;
uint8 data<0..2^32-1>;
} Push;
group_id: overlay address of root of the ALM tree
priority: the relative priority of the message; highest priority is
255. A node may ignore this field.
length: length of the data field in bytes
data: the data
In pseudocode, the behavior of Push can be described as:
foreach(groups[msg.group_id].children as node_id)
SEND(msg,node_id)
if memberOf(msg.group_id)
invokeMessageHandler(msg.group_id, msg)
7.2.19. PushResponse
After receiving a Push message from node S, the receiving peer sends
a PushResponse to node S.
struct {
Dictionary options;
} PushResponse;
options: A node may provide feedback to the sender about previous
Push messages in some window, for example, the last N Push messages.
The feedback could include, for each Push message received, the
number of adjacent nodes that were forwarded the Push message and the
number of adjacent nodes from which a PushResponse was received.
8. Scribe Algorithm
8.1. Overview
Figure 3 shows a mapping between RELOAD ALM messages (as defined in
Section 5 of this document) and Scribe messages as defined in
[CASTRO2002].
+---------+-------------------+-----------------+
| Section |RELOAD ALM Message | Scribe Message |
+---------+-------------------+-----------------+
| 7.2.1 | CreateALMTree | Create |
+---------+-------------------+-----------------+
| 7.2.3 | Join | Join |
+---------+-------------------+-----------------+
| 7.2.4 | JoinAccept | |
+---------+-------------------+-----------------+
| 7.2.6 | JoinConfirm | |
+---------+-------------------+-----------------+
| 7.2.8 | JoinDecline | |
+---------+-------------------+-----------------+
| 7.2.10 | Leave | Leave |
+---------+-------------------+-----------------+
| 7.2.12 | Reform | |
+---------+-------------------+-----------------+
| 7.2.14 | Heartbeat | |
+---------+-------------------+-----------------+
| 7.2.16 | NodeQuery | |
+---------+-------------------+-----------------+
| 7.2.18 | Push | Multicast |
+---------+-------------------+-----------------+
| | Note 1 | deliver |
+---------+-------------------+-----------------+
| | Note 1 | forward |
+---------+-------------------+-----------------+
| | Note 1 | route |
+---------+-------------------+-----------------+
| | Note 1 | send |
+---------+-------------------+-----------------+
Figure 3: Mapping to Scribe Messages
Note 1: These Scribe messages are handled by RELOAD messages.
The following sections describe the Scribe algorithm in more detail.
8.2. Create
This message will create a group with group_id. This message MUST be
delivered to the node whose node_id is closest to the group_id. This
node becomes the rendezvous point and root for the new multicast
tree. Groups MAY have multiple sources of multicast messages.
8.3. Join
To join a multicast tree, a node SHOULD send a Join request with the
group_id as the key. This message gets routed by the overlay to the
rendezvous point of the tree. If an intermediate node is already a
forwarder for this tree, it SHOULD add the joining node as a child.
Otherwise, the node SHOULD create a child table for the group and add
the joining node. It SHOULD then send the Join request towards the
rendezvous point terminating the Join request from the child.
To adapt the Scribe algorithm to the ALM Usage proposed here, after a
Join request is accepted, a JoinAccept message MUST be returned to
the joining node.
8.4. Leave
When leaving a multicast group, a node SHOULD change its local state
to indicate that it left the group. If the node has no children in
its table, it MUST send a Leave request to its parent, from where it
SHOULD travel up the multicast tree and stop at a node that still has
children remaining after removing the leaving node.
8.5. JoinConfirm
This message is not part of the Scribe protocol but is required by
the basic protocol proposed in this document. Thus, the Usage MUST
send this message to confirm a joining node accepting its parent
node.
8.6. JoinDecline
Like JoinConfirm, this message is not part of the Scribe protocol.
Thus, the Usage MUST send this message if a peer receiving a
JoinAccept message wishes to decline it.
8.7. Multicast
A message to be multicast to a group MUST be sent to the rendezvous
node from where it is forwarded down the tree. If a node is a member
of the tree rather than just a forwarder, it SHOULD pass the
multicast data up to the application.
9. P2PCast Algorithm
9.1. Overview
P2PCast [P2PCAST] creates a forest of related trees to increase load
balancing. P2PCast is independent of the underlying P2P substrate.
Its goals and approach are similar to SplitStream [SPLITSTREAM]
(which assumes Pastry as the P2P overlay). In P2PCast, the content
provider splits the stream of data into f stripes. Each tree in the
forest of multicast trees is an (almost) full tree of arity f. These
trees are conceptually separate: every node of the system appears
once in each tree, with the content provider being the source in all
of them. To ensure that each peer contributes as much bandwidth as
it receives, every node is a leaf in all the trees except for one, in
which the node will serve as an internal node (proper tree of this
node). To reduce the complexity of the discussion that follows, the
remainder of this section will assume that f = 2. However, the
algorithm scales for any number f.
P2PCast distinguishes the following types of nodes:
o Incomplete Node: A node with less than f children in its proper
stripe
o Only-Child Node: A node whose parent (in any multicast tree) is an
incomplete node
o Complete Node: A node with exactly f children in its proper stripe
o Special Node: A single node that is a leaf in all multicast trees
of the forest
9.2. Message Mapping
Figure 4 shows a mapping between RELOAD ALM messages (as defined in
Section 5 of this document) and P2PCast messages as defined in
[P2PCAST].
+---------+-------------------+-----------------+
| Section |RELOAD ALM Message | P2PCast Message |
+---------+-------------------+-----------------+
| 7.2.1 | CreateALMTree | Create |
+---------+-------------------+-----------------+
| 7.2.3 | Join | Join |
+---------+-------------------+-----------------+
| 7.2.4 | JoinAccept | |
+---------+-------------------+-----------------+
| 7.2.6 | JoinConfirm | |
+---------+-------------------+-----------------+
| 7.2.8 | JoinDecline | |
+---------+-------------------+-----------------+
| 7.2.10 | Leave | Leave |
+---------+-------------------+-----------------+
| 7.2.12 | Reform | Takeon |
| | | Substitute |
| | | Search |
| | | Replace |
| | | Direct |
| | | Update |
+---------+-------------------+-----------------+
| 7.2.14 | Heartbeat | |
+---------+-------------------+-----------------+
| 7.2.16 | NodeQuery | |
+---------+-------------------+-----------------+
| 7.2.18 | Push | Multicast |
+---------+-------------------+-----------------+
Figure 4: Mapping to P2PCast Messages
The following sections describe the mapping of the P2PCast messages
in more detail.
9.3. Create
This message will create a group with group_id. This message MUST be
delivered to the node whose node_id is closest to the group_id. This
node becomes the rendezvous point and root for the new multicast
tree. The rendezvous point will maintain f subtrees.
9.4. Join
To join a multicast tree, a joining node N MUST send a Join request
to a random node A already part of the tree. Depending on the type
of A, the joining algorithm continues as follows:
o Incomplete Node: Node A will arbitrarily select for which tree it
wants to serve as an internal node and adopt N in that tree. In
the other tree, node N will adopt node A as a child (taking node
A's place in the tree), thus becoming an internal node in the
stripe that node A didn't choose.
o Only-Child Node: As this node has a parent that is an incomplete
node, the joining node will be redirected to the parent node and
will handle the request as detailed above.
o Complete Node: The contacted node A must be a leaf in the other
tree. If node A is a leaf node in Stripe 1, node N will become an
internal node in Stripe 1, taking the place of node A and adopting
it at the same time. To find a place for itself in the other
stripe, node N starts a random walk down the subtree rooted at the
sibling of node A (if node A is the root and thus does not have
siblings, node N is sent directly to a leaf in that tree), which
ends as soon as node N finds an incomplete node or a leaf. In
this case, node N is adopted by the incomplete node.
o Special Node: as this node is a leaf in all subtrees, the joining
node MAY adopt the node in one tree and become a child in the
other.
P2PCast uses defined messages for communication between nodes during
reorganization. To use P2PCast in this context, these messages are
encapsulated by the message type Reform. In doing so, the P2PCast
message is to be included in the options parameter of Reform. The
following reorganization messages are defined by P2PCast:
Takeon: To take another peer as a child
Substitute: To take the place of a child of some peer
Search: To obtain the child of a node in a particular stripe
Replace: Different from Substitute in that the calling node that
makes a node its child sheds off a random child
Direct: To direct a node to its would-be parent
Update: A node sends its updated state to its children
To adapt the P2PCast algorithm to the ALM Usage proposed here, after
a Join request is accepted, a JoinAccept message MUST be returned to
the joining node (one for every subtree).
9.5. Leave
When leaving a multicast group, a node will change its local state to
indicate that it left the group. Disregarding the case where the
leaving node is the root of the tree, the leaving node must be
complete or incomplete in its proper tree. In the other trees, the
node is a leaf and can just disappear by notifying its parent. For
the proper tree, if the node is incomplete, it is replaced by its
child. However, if the node is complete, a gap is created that is
filled by a random child. If this child is incomplete, it can simply
fill the gap. However, if it is complete, it needs to shed a random
child. This child is directed to its sibling, which sheds a random
child. This process ripples down the tree until the next-to-last
level is reached. The shed node is then taken as a child by the
parent of the deleted node in the other stripe.
Again, for the reorganization of the tree, the Reform message type is
used as defined in the previous section.
9.6. JoinConfirm
This message is not part of the P2PCast protocol but is required by
the basic protocol defined in this document. Thus, the Usage MUST
send this message to confirm a joining node accepting its parent
node. As with Join and JoinAccept, this MUST be carried out for
every subtree.
9.7. Multicast
A message to be multicast to a group MUST be sent to the rendezvous
node from where it is forwarded down the tree by being split into k
stripes. Each stripe is then sent via a subtree. If a receiving
node is a member of the tree rather than just a forwarder, it MAY
pass the multicast data up to the application.
10. Message Format
All messages are mapped to the RELOAD experimental message type. The
mapping is shown in Figure 5. The message codes are listed in
Section 14.2. The format of the body of a message is provided in
[RFC6940].
[RELOAD].
+-------------------------+------------------+
| Message |RELOAD Code Point |
+-------------------------+------------------+
| CreateALMTree | exp_a_req |
+-------------------------+------------------+
| CreateALMTreeResponse | exp_a_ans |
+-------------------------+------------------+
| Join | exp_a_req |
+-------------------------+------------------+
| JoinAccept | exp_a_ans |
+-------------------------+------------------+
| JoinReject | exp_a_ans |
+-------------------------+------------------+
| JoinConfirm | exp_a_req |
+-------------------------+------------------+
| JoinConfirmResponse | exp_a_ans |
+-------------------------+------------------+
| JoinDecline | exp_a_req |
+-------------------------+------------------+
| JoinDeclineResponse | exp_a_ans |
+-------------------------+------------------+
| Leave | exp_a_req |
+-------------------------+------------------+
| LeaveResponse | exp_a_ans |
+-------------------------+------------------+
| Reform | exp_a_req |
+-------------------------+------------------+
| ReformResponse | exp_a_ans |
+-------------------------+------------------+
| Heartbeat | exp_a_req |
+-------------------------+------------------+
| HeartbeatResponse | exp_a_ans |
+-------------------------+------------------+
| NodeQuery | exp_a_req |
+-------------------------+------------------+
| NodeQueryResponse | exp_a_ans |
+-------------------------+------------------+
| Push | exp_a_req |
+-------------------------+------------------+
| PushResponse | exp_a_ans |
+-------------------------+------------------+
Figure 5: RELOAD Message Code Mapping
For Data Kind-IDs, the RELOAD specification [RFC6940] [RELOAD] states: "Code
points in the range 0xF0000001 to 0xFFFFFFFE are reserved for private
use". ALM Usage Kind-IDs are defined in the private use range.
All ALM Usage messages map to the RELOAD Message Extension mechanism.
Code points for the Kinds defined in this document MUST NOT conflict
with any defined code points for RELOAD. RELOAD defines exp_a_req
and exp_a_ans for experimental purposes. This specification uses
only these message types for all ALM messages. RELOAD defines the
MessageContents data structure. The ALM mapping uses the fields as
follows:
o message_code: exp_a_req for requests and exp_a_ans for responses
o message_body: contains one instance of ALMHeader followed by one
instance of ALMMessageContents
o extensions: unused
10.1. ALMHeader Definition
struct {
uint32 sam_token;
uint16 alm_algorithm_id;
uint8 version;
} ALMHeader;
The fields in ALMHeader are used as follows:
sam_token: The first four bytes identify this message as an ALM
message. This field MUST contain the value 0xD3414D42 (the string
"SAMB" with the high bit of the first byte set).
alm_algorithm_id: The ALM Algorithm ID of the ALM algorithm being
used. Each multicast tree uses only one algorithm. Trees with
different ALM algorithms can coexist and can share the same nodes.
ALM Algorithm ID codes are defined in Section 14.1.
version: The version of the ALM protocol being used. This is a
fixed-point integer between 0.1 and 25.4. This document describes
version 1.0 with a value of 0xA.
10.2. ALMMessageContents Definition
struct {
uint16 alm_message_code;
opaque alm_message_body;
} ALMMessageContents;
The fields in ALMMessageContents are used as follows:
alm_message_code: This indicates the message being sent. The
message codes are listed in Section 14.2.
alm_message_body: The message body itself, represented as a
variable-length string of bytes. The bytes themselves are
dependent on the code value. See Sections 8 and 9, which describe
the various ALM methods for the definitions of the payload
contents.
10.3. Response Codes
Response codes are defined in Section 6.3.3.1 of RELOAD [RFC6940]. [RELOAD]. This
specification maps to RELOAD ErrorResponse as follows:
ErrorResponse.error_code = Error_Exp_A;
Error_info contains an ALMErrorResponse instance.
public struct {
uint16 alm_error_code;
opaque alm_error_info<0..2^16-1>;
} ALMErrorResponse;
alm_error_code: The following error code values are defined. Numeric
values for these are defined in Section 14.3.
Error_Unknown_Algorithm: The multicast algorithm is not known or
not supported.
Error_Child_Limit_Reached: The maximum number of child nodes has
been reached for this node.
Error_Node_Bandwidth_Reached: The overall data bandwidth limit
through this node has been reached.
Error_Node_Conn_Limit_Reached: The total number of connections to
this node has been reached.
Error_Link_Cap_Limit_Reached: The capacity of a link has been
reached.
Error_Node_Mem_Limit_Reached: An internal memory capacity of the
node has been reached.
Error_Node_CPU_Cap_Limit_Reached: An internal processing capacity
of the node has been reached.
Error_Path_Limit_Reached: The maximum path length in hop count
over the multicast tree has been reached.
Error_Path_Delay_Limit_Reached: The maximum path length in message
delay over the multicast tree has been reached.
Error_Tree_Fanout_Limit_Reached: The maximum fanout of a multicast
tree has been reached.
Error_Tree_Depth_Limit_Reached: The maximum height of a multicast
tree has been reached.
Error_Other: A human-readable description is placed in the
alm_error_info field.
11. Examples
All peers in the examples are assumed to have completed
bootstrapping. "Pn" refers to peer N. "group_id" refers to a peer
responsible for storing the ALMTree instance with group_id.
11.1. Create Tree
A node with "NODE-MATCH" rights sends a CreateALMTree request to the
group_id node, which also has NODE-MATCH rights for its own address.
The group_id node determines whether to create the new tree and, if
so, performs a local StoreReq. If the CreateALMTree succeeds, the
ALMTree instance can be retrieved using Fetch. An example message
flow for creating a tree is depicted in Figure 6.
P1 P2 P3 P4 group_id
| | | | |
| | | | |
| | | | |
| CreateALMTree | | |
|------------------------------->|
| | | | |
| | | | | StoreReq
| | | | |--+
| | | | | |
| | | | | |
| | | | |<-+
| | | | | StoreResponse
| | | | |--+
| | | | | |
| | | | | |
| | | | |<-+
| | | | |
| | | | |
| | CreateALMTreeResponse |
|<-------------------------------|
| | | | |
| | | | |
| Fetch | | |
|------------------------------->|
| | | | |
| | | | |
| | FetchResponse |
|<-------------------------------|
| | | | |
Figure 6: Message Flow Example for CreateALMTree
11.2. Join Tree
P1 joins node group_id as child node. P2 joins the tree as a child
of P1. P4 joins the tree as a child of P1. The corresponding
message flow is shown in Figure 7.
P1 P2 P3 P4 group_id
| | | | |
| | | | |
| Join |
|------------------------------->|
| | | | |
| JoinAccept |
|<-------------------------------|
| | | | |
| | | | |
| |Join |
| |----------------------->|
| | | | |
| Join|
|<-------------------------------|
| | | | |
|JoinAccept | | |
|------>| | | |
| | | | |
|JoinConfirm | | |
|<------| | | |
| | | | |
| | | |Join |
| | | |------>|
| | | | Join |
|<-------------------------------|
| | | | |
| Join | | | |
|------>| | | |
| | | | |
| JoinAccept | | |
|----------------------->| |
| | | | |
| | JoinAccept | |
| |--------------->| |
| | | | |
| | | | |
| | JoinConfirm | |
|<-----------------------| |
| | | | |
| | JoinDecline | |
| |<---------------| |
| | | | |
| | | | |
Figure 7: Message Flow Example for Tree Join
11.3. Leave Tree
P1 P2 P3 P4 group_id
| | | | |
| | | | |
| | | Leave | |
|<-----------------------| |
| | | | |
| LeaveResponse | | |
|----------------------->| |
| | | | |
| | | | |
Figure 8: Message Flow Example for Leave Tree
11.4. Push Data
The multicast data is pushed recursively P1 => group_id => P1 => P2,
P4 following the tree topology created in the Join example above. An
example message flow is shown in Figure 9.
P1 P2 P3 P4 group_id
| | | | |
| Push | | | |
|------------------------------->|
| | | | |
| | | PushResponse|
|<-------------------------------|
| | | | |
| | | | Push|
|<-------------------------------|
| | | | |
| PushResponse | | |
|------------------------------->|
| | | | |
|Push | | | |
|------>| | | |
| | | | |
|PushResponse | | |
|<------| | | |
| | | | |
| Push | | | |
|----------------------->| |
| | | | |
| | PushResponse | |
|<-----------------------| |
| | | | |
| | | | |
| | | | |
Figure 9: Message Flow Example for Pushing Data
12. Kind Definitions
12.1. ALMTree Kind Definition
This section defines the ALMTree Kind per Section 7.4.5 of RELOAD
[RFC6940]. [RELOAD].
An instance of the ALMTree Kind is stored in the overlay for each ALM
tree instance. It is stored at the address group_id.
Kind-ID: 0xF0000001. (This is a private-use code point per
Section 14.6 of RELOAD [RFC6940].) [RELOAD].) The Resource Name for the ALMTree Kind-ID
is the session_key used to identify the ALM tree.
Data Model: The data model is the ALMTree structure.
Access Control: NODE-MATCH. The node performing the store operation
is required to have NODE-MATCH access.
Meaning: The meaning of the fields is given in Section 7.2.1.
struct {
node_id peer_id;
opaque session_key<0..2^32-1>;
node_id group_id;
Dictionary options;
} ALMTree;
13. RELOAD Configuration File Extensions
There are no ALM parameters defined for the RELOAD configuration
file.
14. IANA Considerations
This section contains the new code points registered by this
document.
14.1. ALM Algorithm Types
IANA has created the "SAM ALM Algorithm IDs" registry. Entries in
this registry are 16-bit integers denoting Application-Layer
Multicast algorithms as described in Section 10.1 of this document.
Code points in the range 0x0003 to 0x7FFF SHALL be registered via
RFC 5226 [RFC5226] Expert Review. Code points in the range 0x8000 to
0xFFFF are reserved for private use. The initial contents of this
registry are:
+----------------+-------------------+-----------+
| Algorithm Name | ALM Algorithm ID | RFC |
+----------------+-------------------+-----------+
| INVALID-ALG | 0x0000 | RFC 7019 |
| SCRIBE-SAM | 0x0001 | RFC 7019 |
| P2PCAST-SAM | 0x0002 | RFC 7019 |
| Reserved | 0x8000-0xFFFF | RFC 7019 |
+----------------+-------------------+-----------+
Figure 10: "SAM ALM Algorithm IDs" Registry Allocations
These values have been made available for the purposes of
experimentation. These values are not meant for vendor-specific use
of any sort and MUST NOT be used for operational deployments.
14.2. Message Code Registration
IANA has created the "SAM ALM Message Codes" registry. Entries in
this registry are 16-bit integers denoting message codes as described
in Section 10.2 of this document. Code points in the range 0x0014 to
0x7FFF SHALL be registered via RFC 5226 [RFC5226] Expert Review.
Code points in the range 0x8000 to 0xFFFF are reserved for private
use. The initial contents of this registry are:
+-------------------------+----------------------+-----------+
| Message Code Name | Message Code Value | RFC |
+-------------------------+----------------------+-----------+
| InvalidMessageCode | 0x0000 | RFC 7019 |
| CreateALMTree | 0x0001 | RFC 7019 |
| CreateALMTreeResponse | 0x0002 | RFC 7019 |
| Join | 0x0003 | RFC 7019 |
| JoinAccept | 0x0004 | RFC 7019 |
| JoinReject | 0x0005 | RFC 7019 |
| JoinConfirm | 0x0006 | RFC 7019 |
| JoinConfirmResponse | 0x0007 | RFC 7019 |
| JoinDecline | 0x0008 | RFC 7019 |
| JoinDeclineResponse | 0x0009 | RFC 7019 |
| Leave | 0x000A | RFC 7019 |
| LeaveResponse | 0x000B | RFC 7019 |
| Reform | 0x000C | RFC 7019 |
| ReformResponse | 0x000D | RFC 7019 |
| Heartbeat | 0x000E | RFC 7019 |
| HeartbeatResponse | 0x000F | RFC 7019 |
| NodeQuery | 0x0010 | RFC 7019 |
| NodeQueryResponse | 0x0011 | RFC 7019 |
| Push | 0x0012 | RFC 7019 |
| PushResponse | 0x0013 | RFC 7019 |
| Reserved | 0x8000-0xFFFF | RFC 7019 |
+-------------------------+----------------------+-----------+
Figure 11: "SAM ALM Message Codes" Registry Allocations
These values have been made available for the purposes of
experimentation. These values are not meant for vendor-specific use
of any sort and MUST NOT be used for operational deployments.
14.3. Error Code Registration
IANA has created the "SAM ALM Error Codes" registry. Entries in this
registry are 16-bit integers denoting error codes as described in
Section 10.3 of this document. Code points in the range 0x000D to
0x7FFF SHALL be registered via RFC 5226 [RFC5226] Expert Review.
Code points in the range 0x8000 to 0xFFFF are reserved for private
use. The initial contents of this registry are:
+----------------------------------+---------------+-----------+
| Error Code Name | Code Value | RFC |
+----------------------------------+---------------+-----------+
| InvalidErrorCode | 0x0000 | RFC 7019 |
| Error_Unknown_Algorithm | 0x0001 | RFC 7019 |
| Error_Child_Limit_Reached | 0x0002 | RFC 7019 |
| Error_Node_Bandwidth_Reached | 0x0003 | RFC 7019 |
| Error_Node_Conn_Limit_Reached | 0x0004 | RFC 7019 |
| Error_Link_Cap_Limit_Reached | 0x0005 | RFC 7019 |
| Error_Node_Mem_Limit_Reached | 0x0006 | RFC 7019 |
| Error_Node_CPU_Cap_Limit_Reached | 0x0007 | RFC 7019 |
| Error_Path_Limit_Reached | 0x0008 | RFC 7019 |
| Error_Path_Delay_Limit_Reached | 0x0009 | RFC 7019 |
| Error_Tree_Fanout_Limit_Reached | 0x000A | RFC 7019 |
| Error_Tree_Depth_Limit_Reached | 0x000B | RFC 7019 |
| Error_Other | 0x000C | RFC 7019 |
| Reserved | 0x8000-0xFFFF | RFC 7019 |
+----------------------------------+---------------+-----------+
Figure 12: "SAM ALM Error Codes" Registry Allocations
These values have been made available for the purposes of
experimentation. These values are not meant for vendor-specific use
of any sort and MUST NOT be used for operational deployments.
15. Security Considerations
Overlays are vulnerable to DoS and collusion attacks. We are not
solving overlay security issues. We assume that the node
authentication model as defined in [RFC6940] [RELOAD] will be used.
Security issues specific to ALM Usage include the following:
o The right to create group_id at some node_id
o The right to store Tree info at some location in the DHT
o A limit on number of messages per second and bandwidth use
o The right to join an ALM tree
16. Acknowledgements
Marc Petit-Huguenin, Michael Welzl, Joerg Ott, and Lars Eggert
provided important comments on earlier versions of this document.
17. References
17.1. Normative Reference
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
17.2. Informative References
[BUFORD2008]
Buford, J. and H. Yu, "P2P: Overlay Multicast",
Encyclopedia of Wireless and Mobile Communications, 2008,
<http://www.tandfonline.com/doi/abs/10.1081/
E-EWMC-120043583>.
[BUFORD2009]
Buford, J., Yu, H., and E. Lua, "P2P Networking and
Applications (Chapter 9)", Morgan Kaufman, 2009,
<http://www.sciencedirect.com/science/book/9780123742148>.
[CASTRO2002]
Castro, M., Druschel, P., Kermarrec, A., and A. Rowstron,
"SCRIBE: A large-scale and decentralized application-level
multicast infrastructure", IEEE Journal on Selected Areas
in Communications, Vol. 20, No. 8, October 2002, <http://
ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1038579>.
[CASTRO2003]
Castro, M., Jones, M., Kermarrec, A., Rowstron, A.,
Theimer, M., Wang, H., and A. Wolman, "An Evaluation of
Scalable Application-level Multicast Built Using Peer-to-
peer Overlays", Proceedings of IEEE INFOCOM 2003, April
2003, <http://ieeexplore.ieee.org/xpl/
login.jsp?tp=&arnumber=1208986>.
[COMMON-API]
Waehlisch, M., Schmidt, T., and S. Venaas, "A Common API
for Transparent Hybrid Multicast", Work in Progress, April
2013.
[KOLBERG2010]
Kolberg, M., "Employing Multicast in P2P Overlay
Networks", Handbook of Peer-to-Peer Networking, 2010,
<http://link.springer.com/content/pdf/
10.1007%2F978-0-387-09751-0_30.pdf>.
[P2PCAST] Nicolosi, A. and S. Annapureddy, "P2PCast: A Peer-to-Peer
Multicast Scheme for Streaming Data", Stanford Secure
Computer Systems Group Report, May 2003, <http://
www.scs.stanford.edu/~reddy/research/p2pcast/report.pdf>.
[RELOAD] Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S.,
and H. Schulzrinne, "REsource LOcation And Discovery
(RELOAD) Base Protocol", Work in Progress, February 2013.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6940] Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S.,
and H. Schulzrinne, "REsource LOcation And Discovery
(RELOAD) Base Protocol", RFC 6940, September 2013.
[SAM-GENERIC]
Muramoto, E., Imai, Y., and N. Kawaguchi, "Requirements
for Scalable Adaptive Multicast Framework in Non-GIG
Networks", Work in Progress, November 2006.
[SPLITSTREAM]
Castro, M., Druschel, P., Nandi, A., Kermarrec, A.,
Rowstron, A., and A. Singh, "SplitStream: High-Bandwidth
Multicast in a Cooperative Environment", SOSP '03, Lake
Bolton, New York, October 2003,
<http://dl.acm.org/citation.cfm?id=945474>.
Authors' Addresses
John Buford
Avaya Labs Research
211 Mt. Airy Rd.
Basking Ridge, New Jersey 07920
USA
Phone: +1 908 848 5675
EMail: buford@avaya.com
Mario Kolberg (editor)
University of Stirling
Dept. of Computing Science and Mathematics
Stirling FK9 4LA
UK
Phone: +44 1786 46 7440
EMail: mkolberg@ieee.org
URI: http://www.cs.stir.ac.uk/~mko