SAM Research Group J. Buford
Internet-Draft Avaya Labs Research
Intended status: Experimental M. Kolberg, Ed.
Expires: December 08, 2013 University of Stirling
June 06, 2013
Application Layer Multicast Extensions to RELOAD
draft-irtf-samrg-sam-baseline-protocol-04
Abstract
We define a RELOAD Usage for Application Layer Multicast 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.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Overlay Network . . . . . . . . . . . . . . . . . . . . . 4
2.2. Overlay Multicast . . . . . . . . . . . . . . . . . . . . 5
2.3. Source Specific Multicast (SSM) . . . . . . . . . . . . . 5
2.4. Any Source Multicast (ASM) . . . . . . . . . . . . . . . 5
2.5. Peer . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Overlay . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Overlay Multicast . . . . . . . . . . . . . . . . . . . . 6
3.3. RELOAD . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. NAT . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.5. Tree Topology . . . . . . . . . . . . . . . . . . . . . . 6
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. Create Tree . . . . . . . . . . . . . . . . . . . . . 11
7.2.2. CreateTreeResponse . . . . . . . . . . . . . . . . . 12
7.2.3. Join . . . . . . . . . . . . . . . . . . . . . . . . 12
7.2.4. Join Accept (Join Response) . . . . . . . . . . . . . 14
7.2.5. Join Reject (Join Response) . . . . . . . . . . . . . 14
7.2.6. Join Confirm . . . . . . . . . . . . . . . . . . . . 14
7.2.7. Join Confirm Response . . . . . . . . . . . . . . . . 15
7.2.8. Join Decline . . . . . . . . . . . . . . . . . . . . 15
7.2.9. Join Decline Response . . . . . . . . . . . . . . . . 16
7.2.10. Leave . . . . . . . . . . . . . . . . . . . . . . . . 16
7.2.11. Leave Response . . . . . . . . . . . . . . . . . . . 17
7.2.12. Re-Form or Optimize Tree . . . . . . . . . . . . . . 17
7.2.13. Reform Response . . . . . . . . . . . . . . . . . . . 17
7.2.14. Heartbeat . . . . . . . . . . . . . . . . . . . . . . 17
7.2.15. Heartbeat Response . . . . . . . . . . . . . . . . . 18
7.2.16. NodeQuery . . . . . . . . . . . . . . . . . . . . . . 18
7.2.17. NodeQuery Response . . . . . . . . . . . . . . . . . 18
7.2.18. Push . . . . . . . . . . . . . . . . . . . . . . . . 21
7.2.19. PushResponse . . . . . . . . . . . . . . . . . . . . 21
8. Scribe Algorithm . . . . . . . . . . . . . . . . . . . . . . 22
8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 22
8.2. Create . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.3. Join . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.4. Leave . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.5. JoinConfirm . . . . . . . . . . . . . . . . . . . . . . . 23
8.6. JoinDecline . . . . . . . . . . . . . . . . . . . . . . . 23
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8.7. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 24
9. P2PCast Algorithm . . . . . . . . . . . . . . . . . . . . . . 24
9.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 24
9.2. Message Mapping . . . . . . . . . . . . . . . . . . . . . 24
9.3. Create . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.4. Join . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.5. Leave . . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.6. JoinConfirm . . . . . . . . . . . . . . . . . . . . . . . 27
9.7. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 27
10. Message Format . . . . . . . . . . . . . . . . . . . . . . . 27
10.1. ALMHeader Definition . . . . . . . . . . . . . . . . . . 29
10.2. ALMMessageContents Definition . . . . . . . . . . . . . 29
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 . . . . . . . . . . . . . . . . . . . . . . . 33
12. Kind Definitions . . . . . . . . . . . . . . . . . . . . . . 34
12.1. ALMTree Kind Definition . . . . . . . . . . . . . . . . 34
13. RELOAD Configuration File Extensions . . . . . . . . . . . . 34
14. Change History . . . . . . . . . . . . . . . . . . . . . . . 35
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
15.1. ALM Algorithm Types . . . . . . . . . . . . . . . . . . 35
15.2. Message Code Registration . . . . . . . . . . . . . . . 36
15.3. Error Code Registration . . . . . . . . . . . . . . . . 36
16. Security Considerations . . . . . . . . . . . . . . . . . . . 37
17. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 38
18. Informative References . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
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
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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 [I-D.ietf-p2psip-base] 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.
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 2 of
[I-D.ietf-p2psip-base], specifically the distinction between Node,
Peer, and Client.
2.1. Overlay Network
Overlay network - An application layer virtual or logical network in
which end points are addressable and 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
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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
which 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 which 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 remaining tree edges it is connected to.
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
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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 out-performed using
separate overlays for each multicast session. We use a single
overlay rather than separate overlays per multicast sessions.
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 which is closer
to some of the entries than the current peer which 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 re-join operations for dislocated children
nodes.
3.2. Overlay Multicast
The overlay supports concurrent multiple multicast trees. The limit
on 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 [I-D.ietf-p2psip-base] as the Peer-to-Peer 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
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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, 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 plug-in for ALM algorithms handles the ALM state and
control. The ALM Algorithm is under control of the application via
the Group API [I-D.irtf-samrg-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:
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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 tree, delay from
source to leaf nodes, bandwidth use, 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 which require ALM functionality in the overlay. Figure
2 shows the internal structure of the ALM Usage. This contains the
Group API ([I-D.irtf-samrg-common-api]) an ALM algorithm plugin (e.g.
Scribe) and the ALM messages which are then sent out to the RELOAD
network.
A RELOAD Usage is required [I-D.ietf-p2psip-base] 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 Addresses restoration of values after recovery from a network
partition
o the types of connections that can be initiated using AppConnect
an ALM GroupID is a RELOAD Node-ID. The owner of an ALM group
creates a RELOAD Node-ID as specified in [I-D.ietf-p2psip-base].
This means that a GroupID is used as a RELOAD Destination for overlay
routing purposes.
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6. ALM Tree Control Signaling
Peers use the overlay to support ALM operations such as:
o Create tree
o Join
o Leave
o Re-Form 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, and to
support 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 groupID is expected to be advertised or
distributed out of band, perhaps by publishing in the DHT.
Similarly, joining peers will discover the groupID out of band,
perhaps by a lookup in the tree.
As stated earlier, multiple algorithms will co-exist in the overlay.
1. Peer which initiates multicast group:
groupID = create(); // Allocate a unique groupId.
// The root is the nearest
// peer in the overlay.
2. Any joining peer:
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joinTree(groupID); // sends "join groupID" message
The overlay routes the join request using the overlay routing
mechanism toward the peer with the nearest id to the groupID.
This peer is the root. Peers on the path to the root join the
tree as forwarding points.
3. Leave Tree:
leaveTree(groupID) // removes this node from the tree
Propagates a leave message 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 message to its parent. A
child node receiving a leave message from a parent sends a join
message to the groupID.
4. Message forwarding:
multicastMsg(groupID, msg);
For the 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
[I-D.ietf-p2psip-base] 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 SAM
framework overlay agnostic.
As discussed in the SAM requirements document
[I-D.muramoto-irtf-sam-generic-require], 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 life-cycle (create, join, leave, re-form, heartbeat)
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o Peer region and multicast properties
The message codes are defined in Section 15.2 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
[I-D.ietf-p2psip-base]. 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 (application layer multicast)
operations defined in this section.
7.2.1. Create Tree
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 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;
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peer_id: the 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: the 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, 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 is used.
A successful Create Tree 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 Create Tree. If the StoreReq fails, the Create Tree
fails too.
After a successful Create Tree, 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. CreateTreeResponse
After receiving a CreateTree message from node S, the peer sends a
CreateTreeReponse to node S.
struct {
Dictionary options;
} CreateTreeResponse;
options: A node may provide algorithm-dependent parameters about the
created tree to the requesting node.
7.2.3. Join
Causes the distributed algorithm for peer join of a specific ALM
group to be invoked. The definition of the Join message 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.
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struct {
node_id peer_id;
node_id group_id;
Dictionary options;
} Join;
peer_id: overlay address of joining/leaving peer
group_id: the 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.
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 then 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 then 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 behaviour can be described as follows:
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if(checkAccept(msg)) {
recvJoins.add(msg.source, msg.group_id)
SEND(JOINAccept(node_id, msg.source, msg.group_id))
}
7.2.4. Join Accept (Join Response)
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 which receives neither a JoinConfirm or
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 which accepts the joining
peer
child_peer_id: overlay address of joining peer
group_id: the overlay address of the root of the tree
options: name-value list of options accepted by parent peer
7.2.5. Join Reject (Join Response)
A peer receiving a Join message responds with a JoinReject response
to indicate the request is rejected.
7.2.6. Join Confirm
A peer receiving a JoinAccept message which it wishes to accept MUST
explicitly accept it before the expiration of a timer for the
JoinAccept message using a JoinConfirm message. The joining peer
MUST include only those options from the JoinAccept which it also
accepts, completing the negotiation of options between the two peers.
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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 which is a child of
the parent peer
parent_peer_id: overlay address of the peer which is the parent of
the joining peer
group_id: the overlay address of the root of the tree
options: name-value list of options accepted by both peers
The JoinConfirm message behaviour is decribed 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. Join Confirm Response
A peer receiving a JoinConfirm message responds with a
JoinConfirmResponse message.
7.2.8. Join Decline
A peer receiving a JoinAccept message which it does not wish to
accept it MAY explicitly decline it using a JoinDecline message.
struct {
node_id peer_id;
node_id parent_peer_id;
node_id group_id;
} JoinDecline;
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peer_id: overlay address of joining peer which declines the
JoinAccept
parent_peer_id: overlay address of the peer which issued a JoinAccept
to this peer
group_id: the overlay address of the root of the tree
The behaviour 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. Join Decline Response
A peer receiving a JoinConfirm message responds with a
JoinDeclineResponse message.
7.2.10. Leave
A peer which is part of an ALM tree identified by group_id which
intends to detach from either a child or parent peer SHOULD send a
Leave message to the peer it wishes to detach from. A peer receiving
a Leave message from a peer which is neither in its parent or 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: the overlay address of the root of the tree
options: name-value list of options
The behaviour of the Leave message 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)
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7.2.11. Leave Response
A peer receiving a Leave message responds with a LeaveResponse
message.
7.2.12. Re-Form or Optimize Tree
This triggers a reorganization of either the entire tree or only a
sub-tree. It MAY include hints to specific peers of recommended
parent or child peers to reconnect to. 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: the 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 sub-tree identified by
peer_id.
options: name-value list of options
7.2.13. Reform Response
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 message from the unresponsive peer. N is configurable. RELOAD
implementations are able to read a local configuration file for
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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 Heartbeat Response 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. NodeQuery Response
The response to a NodeQuery message contains a NodeStatistics
instance for this node.
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public struct {
uint32 node_lifetime;
uint32 total_number_trees;
uint16 number_algorithms_supported;
uint8 algorithms_supported[32];
TreeData max_tree_data;
uint16 active_number_trees;
TreeData tree_data<0..2^8-1>;
ImplementationInfo imp_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.
active_number_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 the number_active_trees.
impl_info: information about the implementation of this usage
public struct {
uint32 tree_id;
uint8 algorithm;
NodeId tree_root;
uint8 number_parents;
NodeId parent<0..2^8-1>;
Uint16 number_children_nodes;
NodeId children<0..2^16-1>;
Uint32 path_length_to_root;
Uint32 path_delay_to_root;
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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 NodeId of each parent node
number_children_nodes: 0..2^16-1 indicates number of children
children: the RELOAD NodeId of each child node
path_length_to_root: number of overlay hops to the root of the
tree
path_delay_to_root: RTT in millisec. to root node
path_delay_to_child: last measured RTT in msec to child node with
largest RTT.
public struct {
uint32 join_confim_timeout;
uint32 heartbeat_interval;
uint32 heartbeat_reponse_timeout;
uint16 info_length;
uint8 info<0..2^16-1>;
} ImplementationInfo;
join_confirm_timeout: The default time for join confirm/decline,
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.
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heartbeat timeout interval: 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 behaviour 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 PushReponse to node S.
struct {
Dictionary options;
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} 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 which 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 |
+---------+-------------------+-----------------+
| 7.2.2 | Join | Join |
+---------+-------------------+-----------------+
| 7.2.3 | JoinAccept | |
+---------+-------------------+-----------------+
| 7.2.4 | JoinConfirm | |
+---------+-------------------+-----------------+
| 7.2.5 | JoinDecline | |
+---------+-------------------+-----------------+
| 7.2.6 | Leave | Leave |
+---------+-------------------+-----------------+
| 7.2.7 | Reform | |
+---------+-------------------+-----------------+
| 7.2.8 | Heartbeat | |
+---------+-------------------+-----------------+
| 7.2.9 | NodeQuery | |
+---------+-------------------+-----------------+
| 7.2.10 | Push | Multicast |
+---------+-------------------+-----------------+
| | Note 1 | deliver |
+---------+-------------------+-----------------+
| | Note 1 | forward |
+---------+-------------------+-----------------+
| | Note 1 | route |
+---------+-------------------+-----------------+
| | Note 1 | send |
+---------+-------------------+-----------------+
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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 SHALL 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 SHALL add the joining node as a child.
Otherwise the node SHALL create a child table for the group and add
the joining node. It SHALL then send the JOIN request towards the
rendevous point terminating the JOIN message from the child.
To adapt the Scribe algorithm into 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 SHALL 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 SHALL
travel up the multicast tree and stop at a node which has still
children remaining after removing the leaving node.
8.5. JoinConfirm
This message is not part of the Scribe protocol, but 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.
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8.7. Multicast
A message to be multicast to a group MUST be sent to the rendevous
node from where it is forwarded down the tree. If a node is a member
of the tree rather than just a forwarder it SHALL 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). The remainder of this section will assume f=2 for the
discussion. This is to keep the complexity for the description down.
However, the algorithm scales for any number f.
P2PCast distinguishes the following types of nodes:
o Incomplete Nodes: A node with less than f children in its proper
stripe;
o Only-Child Nodes: A node whose parent (in any multicast tree) is
an incomplete node;
o Complete Nodes: A node with exactly f children in its proper
stripe
o Special Node: A single node which 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 |
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+---------+-------------------+-----------------+
| 7.2.1 | CreateALMTree | Create |
+---------+-------------------+-----------------+
| 7.2.2 | Join | Join |
+---------+-------------------+-----------------+
| 7.2.3 | JoinAccept | |
+---------+-------------------+-----------------+
| 7.2.4 | JoinConfirm | |
+---------+-------------------+-----------------+
| 7.2.5 | JoinDecline | |
+---------+-------------------+-----------------+
| 7.2.6 | Leave | Leave |
+---------+-------------------+-----------------+
| 7.2.7 | Reform | Takeon |
| | | Substitute |
| | | Search |
| | | Replace |
| | | Direct |
| | | Update |
+---------+-------------------+-----------------+
| 7.2.8 | Heartbeat | |
+---------+-------------------+-----------------+
| 7.2.9 | NodeQuery | |
+---------+-------------------+-----------------+
| 7.2.10 | 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 of the type of A
the joining algorithm continues as follows:
o Incomplete Nodes: 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
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A's place in the tree) thus becoming an internal node in the
stripe that node A didn't choose.
o Only-Child Nodes: As this node has a parent which is an incomplete
node, the joining node will be redirected to the parent node and
will handle the request as detailed above.
o Complete Nodes: 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, 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
reorganisation. 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 reorganisation 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 node which makes us
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 into 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
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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 which 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 reorganisation 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 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 SHALL
pass the multicast data up to the application.
10. Message Format
All messages are mapped to the RELOAD experimental message type. The
mapping is given in the following table. The message codes are given
in Section 15.2. The format of the body of a message is given in
Figure 5.
+-------------------------+------------------+
| Message |RELOAD Code Point |
+-------------------------+------------------+
| CreateALMTree | exp_a_req |
+-------------------------+------------------+
| CreateALMTreeResponse | exp_a_ans |
+-------------------------+------------------+
| Join | exp_a_req |
+-------------------------+------------------+
| JoinAccept | exp_a_ans |
+-------------------------+------------------+
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| 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 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,
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
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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 Algorith ID of the ALM algorithm being
used. Each multicast tree uses only one algorithm. Trees with
different ALM algorithms can co-exist, and can share the same
nodes. ALM Algorithm ID codes are defined in Section 15.1
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 15.2.
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 Section 8 and Section 9
describing the various ALM methods for the definitions of the
payload contents.
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10.3. Response Codes
Response codes are defined in section 6.3.3.1 in 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 Section 15.3.
Error_Unknown_Algorithm: The multicast algorithm is not known or
not supported.
Error_Child_Limit_Reached: The maximum number of children 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 hopcount 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
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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. "GroupID" refers to a peer
responsible for storing the ALMTree instance with GroupID.
11.1. Create Tree
A node with "NODE-MATCH" rights sends a request CreateTree 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 CreateTree succeeds, the
ALMTree instance can be retrieved using Fetch. An example message
flow for ceating a tree is depicted in Figure 6.
P1 P2 P3 P4 GroupID
| | | | |
| | | | |
| | | | |
| CreateTree | | |
|------------------------------->|
| | | | |
| | | | | StoreReq
| | | | |--+
| | | | | |
| | | | | |
| | | | |<-+
| | | | | StoreResponse
| | | | |--+
| | | | | |
| | | | | |
| | | | |<-+
| | | | |
| | | | |
| | CreateTreeResponse |
|<-------------------------------|
| | | | |
| | | | |
| Fetch | | |
|------------------------------->|
| | | | |
| | | | |
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| | FetchResponse |
|<-------------------------------|
| | | | |
Figure 6: Message flow example for CreateTree.
11.2. Join Tree
P1 joins node GroupID 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 GroupID
| | | | |
| | | | |
| Join |
|------------------------------->|
| | | | |
| JoinAccept |
|<-------------------------------|
| | | | |
| | | | |
| |Join |
| |----------------------->|
| | | | |
| Join|
|<-------------------------------|
| | | | |
|JoinAccept | | |
|------>| | | |
| | | | |
|JoinConfirm | | |
|<------| | | |
| | | | |
| | | |Join |
| | | |------>|
| | | | Join |
|<-------------------------------|
| | | | |
| Join | | | |
|------>| | | |
| | | | |
| JoinAccept | | |
|----------------------->| |
| | | | |
| | JoinAccept | |
| |--------------->| |
| | | | |
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| | | | |
| | Join Confirm | |
|<-----------------------| |
| | | | |
| | Join Decline | |
| |<---------------| |
| | | | |
| | | | |
Figure 7: Message flow example for tree Join.
11.3. Leave Tree
P1 P2 P3 P4 GroupID
| | | | |
| | | | |
| | | Leave | |
|<-----------------------| |
| | | | |
| LeaveResponse | | |
|----------------------->| |
| | | | |
| | | | |
Figure 8: Message flow example for Leave tree.
11.4. Push Data
The multicast data is pushed recursively P1 => GroupID => 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 GroupID
| | | | |
| Push | | | |
|------------------------------->|
| | | | |
| | | PushResponse|
|<-------------------------------|
| | | | |
| | | | Push|
|<-------------------------------|
| | | | |
| PushResponse | | |
|------------------------------->|
| | | | |
|Push | | | |
|------>| | | |
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| | | | |
|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 in 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.) 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.
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14. Change History
o Version 02: Remove Hybrid ALM material. Define ALMTree kind.
Define new RELOAD messages. Define RELOAD architecture
extensions. Add Scribe as base algorithm for ALM usage. Define
code points. Define preliminary ALM-specific security issues.
o Version 03: Add P2Pcast Algorithm.
o Version 04: Add mapping to RELOAD experimental message. Modified
IANA considerations section. Changed category of id from
Informational to Experimental. New algorithm identification
coding. New message coding. Added push message. Create Tree
access policy changed to use NODE-MATCH. Create Tree StoreReq
clarified. Updated the diagrams in the Examples section. Added a
Push data example. Defined the ALMTree kind.
15. IANA Considerations
This section contains the new code points registered by this
document. [NOTE TO IANA/RFC-EDITOR: Please replace RFC-to-be with
the RFC number for this specification in the following list. ]
15.1. ALM Algorithm Types
IANA SHALL create a "SAM ALM Algorithm ID" Registry. Entries in this
registry are 16-bit integers denoting Application Layer Multicast
algorithms as described in section Section 10.1 of [RFC-to-be]. Code
points in the range 0x3 to 0x7fff SHALL be registered vi RFC 5226
Expert Review. Code points in the range 0x7fff to 0xfffe are
reserved for private use. The initial contents of this registry are:
+----------------+-------------------+-----------+
| Algorithm Name | ALM Algorith ID | RFC |
+----------------+-------------------+-----------+
| INVALID-ALG | 0 | RFC-to-be |
| SCRIBE-SAM | 1 | RFC-to-be |
| P2PCAST-SAM | 2 | RFC-to-be |
| Reserved | 0x3..0xffff | RFC-to-be |
+----------------+-------------------+-----------+
Figure 10
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.
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15.2. Message Code Registration
IANA SHALL create a "SAM ALM Message Code" Registry. Entries in this
registry are 16-bit integers denoting message codes as described in
section Section 10.2 of [RFC-to-be]. Code points in the range 0x14
to 0x7fff SHALL be registered vi RFC 5226 Expert Review. Code points
in the range 0x7fff to 0xfffe are reserved for private use. The
initial contents of this registry are:
+-------------------------+----------------------+-----------+
| Message Code Name | Message Code Value | RFC |
+-------------------------+----------------------+-----------+
| InvalidMessageCode | 0 | RFC-to-be |
| CreateALMTRee | 1 | RFC-to-be |
| CreateALMTreeResponse | 2 | RFC-to-be |
| Join | 3 | RFC-to-be |
| JoinAccept | 4 | RFC-to-be |
| JoinReject | 5 | RFC-to-be |
| JoinConfirm | 6 | RFC-to-be |
| JoinConfirmResponse | 7 | RFC-to-be |
| JoinDecline | 8 | RFC-to-be |
| JoinDeclineResponse | 9 | RFC-to-be |
| Leave | 10 | RFC-to-be |
| LeaveResponse | 11 | RFC-to-be |
| Reform | 12 | RFC-to-be |
| ReformResponse | 13 | RFC-to-be |
| Heartbeat | 14 | RFC-to-be |
| HeartbeatResponse | 15 | RFC-to-be |
| NodeQuery | 16 | RFC-to-be |
| NodeQueryResponse | 17 | RFC-to-be |
| Push | 18 | RFC-to-be |
| PushResponse | 19 | RFC-to-be |
| Reserved | 0x14..0xffff | RFC-to-be |
+-------------------------+----------------------+-----------+
Figure 11
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.
15.3. Error Code Registration
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IANA SHALL create a "SAM ALM Error Code" Registry. Entries in this
registry are 16-bit integers denoting error codes as described in
section Section 10.3 of [RFC-to-be]. Code points in the range 0x14
to 0x7fff SHALL be registered vi RFC 5226 Expert Review. Code points
in the range 0x7fff to 0xfffe are reserved for private use. The
initial contents of this registry are:
+----------------------------------+--------------+-----------+
| Error Code Name | Code Value | RFC |
+----------------------------------+--------------+-----------+
| InvalidErrorCode | 0 | RFC-to-be |
| Error_Unknown_Algorithm | 1 | RFC-to-be |
| Error_Child_Limit_Reached | 2 | RFC-to-be |
| Error_Node_Bandwidth_Reached | 3 | RFC-to-be |
| Error_Node_Conn_Limit_Reached | 4 | RFC-to-be |
| Error_Link_Cap_Limit_Reached | 5 | RFC-to-be |
| Error_Node_Mem_Limit_Reached | 6 | RFC-to-be |
| Error_Node_CPU_Cap_Limit_Reached | 7 | RFC-to-be |
| Error_Path_Limit_Reached | 8 | RFC-to-be |
| Error_Path_Delay_Limit_Reached | 9 | RFC-to-be |
| Error_Tree_Fanout_Limit_Reached | 10 | RFC-to-be |
| Error_Tree_Depth_Limit_Reached | 11 | RFC-to-be |
| Error_Other | 12 | RFC-to-be |
| Reserved | 0x14..0xffff | RFC-to-be |
+----------------------------------+--------------+-----------+
Figure 12
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.
16. Security Considerations
Overlays are vulnerable to DOS and collusion attacks. We are not
solving overlay security issues. We assume the node authentication
model as defined in [I-D.ietf-p2psip-base].
ALM Usage specific security issues:
o Right to create GroupID at some node_id
o Right to store Tree info at some Location in the DHT
o Limit on # messages / sec and bandwidth use
o Right to join an ALM tree
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17. Acknowledgement
Marc Petit-Huguenin, Michael Welzl, Joerg Ott, and Lars Eggert
provided important comments on earlier versions of this document.
18. Informative References
[AGU1984] Aguilar, L., "Datagram Routing for Internet Multicasting",
ACM Sigcomm 84 1984, March 1984,
<http://dl.acm.org/citation.cfm?id=802060>.
[BUFORD2008]
Buford, J. and H. Yu, "Peer-to-Peer Overlay Multicast",
Encyclopedia of Wireless and Mobile Communications 2008,
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, 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://
research.microsoft.com/en-us/um/people/antr/past/
jsac.pdf>.
[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://research.microsoft.com/en-us/um/people/
mcastro/publications/infocom-compare.pdf>.
[HE2005] He, Q. and M. Ammar, "Dynamic Host-Group/Multi-Destination
Routing for Multicast Sessions", J. Telecommunication
Systems vol. 28, pp. 409-433, 2005, <http://
ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1284204&a
bstractAccess=no&userType=inst>.
[I-D.ietf-mboned-auto-multicast]
Bumgardner, G., "Automatic Multicast Tunneling", draft-
ietf-mboned-auto-multicast-14 (work in progress), June
2012.
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[I-D.ietf-p2psip-base]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", draft-ietf-p2psip-base-26 (work in
progress), February 2013.
[I-D.ietf-p2psip-sip]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S.,
Schulzrinne, H., and T. Schmidt, "A SIP Usage for RELOAD",
draft-ietf-p2psip-sip-09 (work in progress), February
2013.
[I-D.irtf-p2prg-rtc-security]
Schulzrinne, H., Marocco, E., and E. Ivov, "Security
Issues and Solutions in Peer-to-peer Systems for Realtime
Communications", draft-irtf-p2prg-rtc-security-05 (work in
progress), September 2009.
[I-D.irtf-sam-hybrid-overlay-framework]
Buford, J., "Hybrid Overlay Multicast Framework", draft-
irtf-sam-hybrid-overlay-framework-02 (work in progress),
February 2008.
[I-D.irtf-samrg-common-api]
Waehlisch, M., Schmidt, T., and S. Venaas, "A Common API
for Transparent Hybrid Multicast", draft-irtf-samrg-
common-api-06 (work in progress), August 2012.
[I-D.matuszewski-p2psip-security-overview]
Yongchao, S., Matuszewski, M., and D. York, "P2PSIP
Security Overview and Risk Analysis", draft-matuszewski-
p2psip-security-overview-01 (work in progress), October
2009.
[I-D.muramoto-irtf-sam-generic-require]
Muramoto, E., "Requirements for Scalable Adaptive
Multicast Framework in Non-GIG Networks", draft-muramoto-
irtf-sam-generic-require-01 (work in progress), November
2006.
[KOLBERG2010]
Kolberg, M., "Employing Multicast in P2P Networks",
Handbook of Peer-to-Peer Networking (Ed. X.Shen, H. Yu, J.
Buford, M. Akon) 2010, 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
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Computer Systems Group Report 2003, May 2003, <http://
www.scs.stanford.edu/~reddy/research/p2pcast/report.pdf>.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.
[RFC1930] Hawkinson, J. and T. Bates, "Guidelines for creation,
selection, and registration of an Autonomous System (AS)",
BCP 6, RFC 1930, March 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, July
2003.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC4286] Haberman, B. and J. Martin, "Multicast Router Discovery",
RFC 4286, December 2005.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP
/MLD Proxying")", RFC 4605, August 2006.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
[RFC5058] Boivie, R., Feldman, N., Imai, Y., Livens, W., and D.
Ooms, "Explicit Multicast (Xcast) Concepts and Options",
RFC 5058, November 2007.
[SPLITSTREAM]
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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 2003, October 2003, <http://
research.microsoft.com/en-us/um/people/antr/PAST/
SplitStream-sosp.pdf>.
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. 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
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