PPSP Rachel Huang
INTERNET-DRAFT Ning Zong
Intended Status: Standards Track Huawei
Expires: August 29, 2013 Rui S. Cruz
Mario S. Nunes
IST/INESC-ID/INOV
Joao P. Taveira
February 25, 2013
PPSP Tracker Protocol--Extended Protocol
draft-huang-ppsp-extended-tracker-protocol-02
Abstract
This document specifies an extended Peer-to-Peer Streaming Protocol -
Tracker Protocol, which is a new extension protocol complementing the
basic core messages and usages specified in the base tracker protocol
for the exchange of meta information between trackers and peers, such as
initial offer/request of participation in multimedia content streaming,
content information, peer lists and reports of activity and status. It
extends the base tracker protocol to include new optional messages
providing new usages in the communications between peer and tracker. The
extension protocol is retro-compatible with the base tracker protocol.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other groups
may also distribute working documents as Internet-Drafts.
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
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Copyright and License Notice
Copyright (c) 2013 IETF Trust and the persons identified as the document
authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions
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respect to this document. Code Components extracted from this document
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. The extended Tracker Protocol Overview . . . . . . . . . . . . 5
4.1. Extended Request Messages . . . . . . . . . . . . . . . . . 5
4.1.1. Enhanced Request Messages . . . . . . . . . . . . . . . 5
4.1.2. New Request Messages . . . . . . . . . . . . . . . . . 6
4.2. Usage of Extended Request Messages . . . . . . . . . . . . 6
4.3. Extended Tracker Transaction State Machine . . . . . . . . 8
4.3.1. Normal Operation . . . . . . . . . . . . . . . . . . . 9
4.3.2. Error Conditions . . . . . . . . . . . . . . . . . . . 10
4.4. Request/Response Syntax and Format . . . . . . . . . . . . 11
4.4.1. Extended Semantics of PPSPTrackerProtocol Elements . . 11
4.4.2. Extended Request/Response Element in Request Messages . 15
4.5. Compatibility with the Base Tracker Protocol . . . . . . . 15
5. Request/Response Processing . . . . . . . . . . . . . . . . . . 15
5.1. Extended CONNECT Request . . . . . . . . . . . . . . . . . 16
5.2. DISCONNECT Request . . . . . . . . . . . . . . . . . . . . 18
5.3. FIND Request . . . . . . . . . . . . . . . . . . . . . . . 18
5.4. Extended STAT_REPORT Request . . . . . . . . . . . . . . . 21
4.6. Error and Recovery Conditions . . . . . . . . . . . . . . . 23
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 24
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 24
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 24
8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.1 Normative References . . . . . . . . . . . . . . . . . . . 25
8.2 Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
The PPSP Tracker Protocol is one of the Peer-to-Peer Streaming
Protocol which specifies standard format/encoding of information and
messages between PPSP peers and PPSP trackers. Based on the
requirements defined in [I-D.ietf-ppsp-problem-statement], the base
tracker protocol specified in [I-D.ietf-ppsp-base-tracker-protocol]
has provided the basic core messages to be exchanged between trackers
and peers in order to carry out some fundamental operations. They're
mandatory messages covering most basic and universal use cases and
MUST be implemented in all PPSP-based streaming systems.
This document specifies some extensions to complement the basic core
messages and usages specified in [I-D.ietf-ppsp-base-tracker-
protocol]. Some new optional messages are extended to provide new
usages in some dedicated scenarios. The extension protocol is retro-
compatible with the base tracker protocol. Messages using this
specification MUST be safely rejected by trackers which don't support
this specification without affecting interoperability.
2. Terminology
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].
This draft uses terms defined in [I-D.ietf-ppsp-problem-statement]
and [I-D.ietf-ppsp-base-tracker-protocol].
3. Motivation
There are a number of possible usages and issues which may be useful
for discussion and which the base tracker protocol may not be able to
deal with.
1. The peer list of a specific swarm obtained by a peer may be out
of date. It requires the peer asks the tracker for a updated one. For
example, a peer is streaming some content. After a while, it finds
out that it couldn't connect to some other peers any more because
they're stopping sharing the content. Losing most connections with
remote peers will lead to service quality decline. In this case, it
is required for the peer to have some mechanisms to update the peer
list.
2. A peer may have the requirement to inform the tracker its new
network address when the peer has changed its primary network
attachment. One example is that a peer with a LAN and a WiFi
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interface which are going through different routers. The peer is
using some PPSP-based P2P application which can keep working when the
peer switches from the LAN to the WiFi (for example, unplugging the
Ethernet cable, the P2P connection can recover automatically).
3. In the base tracker protocol, the disconnection between peer and
tracker is achieved by the timeout of STAT_REPORT messages, which
means that trackers lack the ability to free resources timely. In
some cases when the number of connected peers has reached the maximum
capability of a tracker, resources of the tracker could not be
released immediately even if some peers have already left the
connections. Some P2P applications may require to overcome the
shortage of the base tracker protocol.
4. A peer may have the requirement to stream the content from some
specific point. For example, an end user previously watched a content
and stopped watching it unfinishedly (having disconnected). But the
next day he would expect to continue watching it from where he
interrupted. So the peer may prefer the tracker could select proper
peers for specific content in a swarm.
The above use cases require the base tracker protocol to be extended.
4. The extended Tracker Protocol Overview
4.1. Extended Request Messages
4.1.1. Enhanced Request Messages
In this section, the request messages specified in the base tracker
protocol are extended to meet the needs of use cases listed in
section 3.
1. CONNECT
This message tends to solve the issue 4 raised in section 3. The
extension is that CONNECT Request message now include the information
of specific content scopes, either media content representations or
specific chunks of a media representation in a swarm. The format and
detailed processing of CONNECT Request message will be further
discussed in Section 5.1.
2. STAT_REPORT
The STAT_REPORT Request message is extended to allow the exchanges of
content data information, like chunkmaps, between an active peer and
a tracker. The information can be used by a tracker as a
qualification to select appropriate peer lists when peers request to
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the tracker for the peer lists of some specific contents. An example
of a STAT_REPORT for multiple properties is illustrated in subsection
4.5.
4.1.2. New Request Messages
Two new messages, are introduced in this section to extend those
specified in the base tracker protocol [I-D.ietf-ppsp-base-tracker-
protocol].
1. FIND
The FIND Request message allows a peer to request the tracker for the
peer list of a swarm when it has already joined the swarm. The
request can include specific content scopes, either media content
representations or specific chunks of a media representation in a
swarm, and may also include the new network address of the peer. On
receiving a FIND message, the tracker finds the peers, listed in
content status of the specified swarm that can satisfy the requesting
peer's requirements, returning the list to the requesting peer. To
create the peer list, the tracker may take peer status, capabilities
and peers priority into consideration. Peer priority may be
determined by network topology preference, operator policy
preference, etc.
2. DISCONNECT
The DISCONNECT Request message is used when the peer intends to no
longer participate in all swarms. When receiving the message from a
peer, the tracker deletes the corresponding activity records related
to the peer (including its status and all content status for the
corresponding swarms). In such a case, DISCONNECT message will have
the same effect of timer expiring (STAT_REPORT), but providing a
graceful disconnect from the system.
4.2. Usage of Extended Request Messages
An example of usage of the extended request messages is the
illustrated in Figure 1.
In that figure a peers starts by connecting to the system and joining
a specific swarm (swarm_a) in SEED mode.
While active the peer periodically updates the tracker using
STAT_REPORT messages. Later, the peer CONNECTs another swarm
(swarm_b) but in LEECH mode, i.e., the end-user intended to watch
that content while still sharing the first one. During the stream
the peer requests an updated list of peers in that swarm to the
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tracker.
When the peer wants to leave the second content unfinished, the peer
DISCONNECTs from the corresponding swarm (swarm_b) while still
sharing the first content (swarm_a).
Later the peer DISCONNECTs from the system.
Next time when the peer wants to continue watching the content it
previously streamed, the peer CONNECT the corresponding swarm in
LEECH mode with the interrupted chunk information.
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+--------+ +---------+
| Peer | | Tracker |
+--------+ +---------+
| |
|--CONNECT(swarm_a;SEED)---------->|
|<--------------------------OK-----|
: :
|--STAT_REPORT(activity)---------->|
|<--------------------------Ok-----|
: :
|--CONNECT(swarm_b;LEECH)--------->|
|<-----------------OK+PeerList-----|
: :
|--STAT_REPORT(ChunkMap_b)-------->|
|<--------------------------Ok-----|
: :
|--FIND(swarm_b)------------------>|
|<-----------------OK+PeerList-----|
: :
|--CONNECT(leave swarm_b)--------->|
|<--------------------------Ok-----|
: :
|--STAT_REPORT(activity)---------->|
|<--------------------------Ok-----|
: :
|--DISCONNECT(nil)---------------->|
|<---------------------Ok(BYE)-----|
: :
|-CONNECT(swarm_b;LEECH;ChunkMap)->|
|<-----------------OK+PeerList-----|
: :
Figure 1: Example of a session for a extended PPSP-TP.
4.3. Extended Tracker Transaction State Machine
The tracker state machine has been introduced in the base tracker
protocol [I-D.ietf-ppsp-base-tracker-protocol]. Every tracker MUST
keep a tracker state machine in which the state transitions are
triggered by peer registrations. In addition to the tracker state
machine, a transaction state machine for each registered Peer-ID is
also specified. In this specification, as some additional messages
have been introduced and some basic messages have been extended, an
updated "per-Peer-ID" transaction state machine (Figure 2) is
specified to provide more functionality and detailed control to the
tracker protocol. This extended "per-Peer-ID" transaction state
machine is compatible with the ones specified in the base tracker
protocol.
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+-----------+ +-------+ rcv CONNECT
| TERMINATE | | START | --------------- (1)
+-----------+ +-------+ strt init timer
^ |
| |
on registration error | v
on action error | +------------+
---------------- (A) +<-----| PEER | (Transient)
stop init timer | | REGISTERED |
snd error | +------------+
| |
| | process swarm actions
| | --------------------- (2)
on CONNECT Error (B) | | snd OK (PeerList)
on timeout (7) | / stop init timer
---------------- | / strt track timer
stop track timer | /
clean peer info | |
del registration | |
snd error (B) | |
| |
rcv CONNECT(@leave) | | rcv FIND
rcv DISCONNECT (nil) | | ----------------- (3)
--------------- (6) \ | ---- snd OK (PeerList)
snd OK response ---- \ | / \ rst tracker timer
/ \ \ | | |
rcv CONNECT | (5) | | | | |
----------- | v | v v | rcv STAT_REPORT
snd OK \ +--------------+ / --------------- (4)
rst track timer ----| TRACKING |---- snd OK response
+--------------+ rst track timer
Figure 2: Extended Per-Peer-ID Transaction State Machine
The state diagram in Figure 2 illustrates the complete state changes
together with the causing events and resulting actions when
implementing basic tracker protocol with extended protocol. Note that
Specific error conditions are not shown in the state diagram.
4.3.1. Normal Operation
On normal operation the extended process consists of the following
steps:
1) This step is same with step 1) in section 6.1 of the base tracker
protocol [I-D.ietf-ppsp-base-tracker-protocol].
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2) This step is same with step 2) in section 6.1 of the base tracker
protocol [I-D.ietf-ppsp-base-tracker-protocol].
3) While TRACKING, a FIND message received with valid swarm
information from the peer resets the "track timer" and is
responded with a successful condition, either for the JOIN to (an
additional) swarm or for including the appropriate list of peers
for the scope in the FIND request.
4) While TRACKING, a STAT_REPORT message received from the peer
resets the "track timer" and is responded with a successful
condition. The STAT_REPORT message MAY contain information related
with Swarm-IDs to which the peer is joined.
5) While TRACKING, a CONNECT message received with valid swarm
actions information from the peer resets the "track timer" and is
responded with a successful condition.
6) While TRACKING, a DISCONNECT message received from the peer, or a
CONNECT message with the leave the last swarm action, the tracker
stops the "track timer", cleans the information associated with
the participation of the Peer-ID in the the swarm(s) joined,
responds with a successful condition, deletes the registration of
the Peer-ID and transitions to TERMINATED state for that Peer-ID.
7) In TRACKING state, without receiving STAT_REPORT messages from the
peer, on timeout (track timer) the tracker cleans all the
information associated with the Peer-ID in all swarms it was
joined, deletes the registration, and transitions to TERMINATE
sate for that Peer-ID.
4.3.2. Error Conditions
A) At the PEER REGISTERED state (while the "init timer" has not
expired) receiving FIND, CONNECT, STAT_REPORT messages from the
peer is considered as an error condition. The tracker responds
with error code 403 Forbidden, and resets the "init timer" one
last time. Also when a CONNECT Request only contains invalid swarm
actions, the tracker will do the same things.
B) At the TRACKING state (while the "track timer" has not expired)
receiving an CONNECT message form the peer with invalid swarm
actions (e.g., joining multiple swarms as LEECH or joining the
swarm with invalid Swarm_Id) is considered an error condition. The
tracker responds with error code 403 Forbidden, stops the "tracker
timer", deletes the registration and transitions to TERMINATE
state for that Peer-ID.
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NOTE: This situation may correspond to a malfunction at the peer
or to malicious conditions. A preventive measure would be to
reset the "track timer" one last time and if no valid message is
received proceed to TERMINATE state for the Peer-ID by de-
registering the peer and cleaning all peer information.
4.4. Request/Response Syntax and Format
The architecture specified in the base tracker protocol [I-D.ietf-
ppsp-base-tracker-protocol] doesn't have to be extended. It still
uses the same two-layer architecture of the base tracker protocol.
Besides that, the message syntax is mainly identical with that used
by the base tracker protocol except some elements are extended to
contain the new optional and updated messages:
The SwarmID element MUST be present in FIND requests, but may be
present in DISCONNECT requests.
The PeerNum element MAY be present in FIND requests and MAY contain
the attribute @abilityNAT to inform the tracker on the preferred type
of peers, in what concerns their NAT traversal situation, to be
returned in a peer list.
The PeerGroup element MUST be present in CONNECT requests and
responses, and MAY be present in FIND requests and MAY be present in
responses to FIND requests if the corresponding response returns
information about peers.
One element "ContentGroup" is added to the format of Request. It MAY
be present in requests referencing content, i.e., CONNECT and FIND,
if the request includes a content scope.
The extended semantics of the attributes and elements within a
PPSPTrackerProtocol root element is described in subsection 4.3.1.
4.4.1. Extended Semantics of PPSPTrackerProtocol Elements
Some of the semantics defined in the the base tracker protocol MUST
be extended. The extension semantics of PPSPTrackerProtocol elements
are described in bellow.
+----------------------+---------+----------------------------------+
| Element Name or | Use | Description |
| Attribute Name | | |
+----------------------+---------+----------------------------------+
| PPSPTrackerProtocol | 1 | The root element. |
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| @version | M | Provides the version of PPSP-TP. |
| Request | 0...1 | Provides the request method |
| | | and MUST be present in Request. |
| Response | 0...1 | Provides the response method |
| | | and MUST be present in Response. |
| TransactionID | M | Root transaction Identification. |
| Result | 0...N | Result of @action MUST be present|
| | | in Responses. |
| @transactionID | CM | Identifier of the @action. |
| PeerID | 0...1 | Peer Identification. |
| | | MUST be present in Request. |
| SwarmID | 0...N | Swarm Identification. |
| | | MUST be present in Requests. |
| @action | CM | Must be set to JOIN or LEAVE. |
| @peerMode | CM | Mode of Peer participation in |
| | | the swarm, "LEECH" or "SEED". |
| @transactionID | CM | Identifier for the @action. |
| PeerNUM | 0...1 | Maximum peers to be received |
| | | with capabilities indicated. |
| @abilityNAT | CM | Type of NAT traversal peers, as |
| | | "No-NAT","STUN","TURN" or "PROXY"|
| @concurrentLinks | CM | Concurrent connectivity level of |
| | | peers, "HIGH", "LOW" or "NORMAL" |
| @onlineTime | CM | Availability or online duration |
| | | of peers, "HIGH" or "NORMAL" |
| @uploadBWlevel | CM | Upload bandwidth capability of |
| | | peers, "HIGH" or "NORMAL" |
| PeerGroup | 0...1 | Information on peers (Table 3) |
| ContentGroup | 0...1 | Information on content (Table 4) |
| StatisticsGroup | 0...1 | Statistic data (Table 5) |
+----------------------+---------+----------------------------------+
| Legend: |
| Use for attributes: M=Mandatory, OP=Optional, |
| CM=Conditionally Mandatory |
| Use for elements: minOccurs...maxOccurs (N=unbounded) |
| Elements are represented by their name (case-sensitive) |
| Attribute names (case-sensitive) are preceded with an @ |
+-------------------------------------------------------------------+
Table 1: Semantics of the Extended PPSPTrackerProtocol.
The semantics of PeerGroup element is almost identical with that in
the base tracker protocol. It is listed below for convenience of
reading.
+----------------------+---------+----------------------------------+
| Element Name or | Use | Description |
| Attribute Name | | |
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+----------------------+---------+----------------------------------+
| PeerGroup | 0...1 | Contains description of peers. |
| PeerInfo | 1...N | Provides information on a peer. |
| @swarmID | 0...1 | Swarm Identification. |
| PeerID | 0...1 | Peer Identification. |
| | | MAY be present in responses. |
| PeerAddress | 0...N | IP Address information. |
| @addrType | M | Type of IP address, which can be |
| | | "ipv4" or "ipv6" |
| @priority | CM | The priority of this interface. |
| | | Used for NAT traversal. |
| @type | CM | Describes the address for NAT |
| | | traversal, which can be "HOST" |
| | | "REFLEXIVE" or "PROXY". |
| @connection | OP | Access type ("3G", "ADSL", etc.) |
| @asn | OP | Autonomous System number. |
| @ip | M | IP address value. |
| @port | M | IP service port value. |
| @peerProtocol | OP | PPSP Peer Protocol supported. |
+----------------------+---------+----------------------------------+
| Legend: |
| Use for attributes: M=Mandatory, OP=Optional, |
| CM=Conditionally Mandatory |
| Use for elements: minOccurs...maxOccurs (N=unbounded) |
| Elements are represented by their name (case-sensitive) |
| Attribute names (case-sensitive) are preceded with an @ |
+-------------------------------------------------------------------+
Table 2: Semantics of PeerGroup.
Table 3 describes the semantics of StatisticsGroup element.
StatisticsGroup element has been extended to contain content
information which indicate by "Representation" attribute.
+----------------------+---------+----------------------------------+
| Element Name or | Use | Description |
| Attribute Name | | |
+----------------------+---------+----------------------------------+
| StatisticsGroup | 0...1 | Provides statistic data on peer |
| | | and content. |
| Stat | 1...N | Groups statistics property data. |
| @property | M | The property to be reported |
| | | property values and elements |
| | | in Table 5 of [I-D.ietf-ppsp-base|
| | | -tracker-protocol] |
| Representation | 0...N | Describes a component of
content.| | @id | CM | Unique identifier for
this | | | | Representation.
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| | SegmentInfo | 1...N | Provides segment
information by | | | | segment range.
The chunkmap can | | | | be encoded in
Base64 [RFC4648]. | | @startIndex | CM | The index of
the first media | | | | segment in
the chunkmap report | | | | for this
Representation. | | @endIndex | CM | The
index of the last media | | | |
segment in the chunkmap report | | | |
for this Representation. | | @chunkmapSize| CM |
Size of chunkmap reported. | +----------------------+---------
+----------------------------------+ | Legend:
| | Use for attributes:
M=Mandatory, OP=Optional, | |
CM=Conditionally Mandatory | | Use for elements:
minOccurs...maxOccurs (N=unbounded) | | Elements are
represented by their name (case-sensitive) | | Attribute
names (case-sensitive) are preceded with an @ | +----------
---------------------------------------------------------+
Table 3: Semantics of StatisticsGroup.
ContentGroup is a new element extended in this specification. The
semantics of this element is described in Table 4.
+----------------------+---------+----------------------------------+
| Element Name or | Use | Description |
| Attribute Name | | |
+----------------------+---------+----------------------------------+
| ContentGroup | 0...1 | Provides information on content. |
| Representation | 1...N | Describes a component of content.|
| @id | M | Unique identifier for this |
| | | Representation. |
| SegmentInfo | 1 | Provides segment information. |
| @startIndex | M | The index of the first media |
| | | segment in the request scope for |
| | | this Representation. |
| @endIndex | OP | The index of the last media |
| | | segment in the request scope for |
| | | this Representation. |
+----------------------+---------+----------------------------------+
| Legend: |
| Use for attributes: M=Mandatory, OP=Optional, |
| CM=Conditionally Mandatory |
| Use for elements: minOccurs...maxOccurs (N=unbounded) |
| Elements are represented by their name (case-sensitive) |
| Attribute names (case-sensitive) are preceded with an @ |
+-------------------------------------------------------------------+
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Table 4: Semantics of ContentGroup
The Representation element describes a component of a content
identified by its attribute @id in the MPD. This element MAY be
present for each component desired in the scope of the JOIN or FIND
request. The scope of each Representation is indicated in the
SegmentInfo element by the attribute @startIndex and, optionally,
@endIndex.
The peer may use this information in CONNECT or FIND requests, for
example, to join a swarm starting from a specific point and to find
adequate peers in the swarm for that content scope.
4.4.2. Extended Request/Response Element in Request Messages
Table 5 specifies the valid string representations for the requests
extended in this specification to complement those define in the base
tracker protocol. These values MUST be treated as case-sensitive.
+----------------------+
| Extended XML Request |
| Methods String Values|
+----------------------+
| DISCONNECT |
| FIND |
+----------------------+
Table 5: Extended Valid Strings for Request Element of Requests.
The response elements in response messages are identical with those
specified in the base tracker protocol, which can be found in
subsection 7.2.3 of [I-D.ietf-ppsp-base-tracker-protocol].
4.5. Compatibility with the Base Tracker Protocol
Trackers are RECOMMNEDED to implement extended tracker protocol to be
compatible with either peers using base tracker protocol or peers
using extended tracker protocol. But it is not mandatory. Peers
implementing the extended tracker protocol sending extended request
messages to legacy tracks will get respond with 400 (Bad request,
with reason-phrase "Unknown Messages"), which indicate the messages
couldn't be recognized by the tracker. In this case, the peers MUST
stop interacting with the track in extended request messages while
using base tracker protocol to do communications.
5. Request/Response Processing
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5.1. Extended CONNECT Request
This method is used when a peer wants to join one or multiple swarms.
The tracker records the Peer-ID, connect-time, IP addresses and link
status.
The peer MUST properly form the XML message-body, set the Request
method to CONNECT, generate and set the TransactionID, and set the
PeerID with the identifier of the peer. The peer SHOULD also include
the IP addresses of its network interfaces in the CONNECT message.
Extended CONNECT request is retro-compatible with the CONNECT request
message defined in the base tracker protocol specification.
An example of the message-body of the extended CONNECT Request is the
following.
CONNECT
656164657220
12345.0
1111
5
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In this example, the peer wants to participate in swarm 1111 to
watch the program as LEECH, and it also wishes to start from a
specific point of the content. So the CONNECT request message
contains a ContentGroup element to include the information which
could be used by the tracker to restrict the searching for peer
list. The extended CONNECT request MAY include a PeerNum element
to indicate to the tracker the number of peers to be returned in
a list corresponding to the indicated properties, being
@abilityNAT for NAT traversal (considering that PPSP-ICE NAT
traversal techniques may be used), and optionally
@concurrentLinks, @onlineTime and @uploadBWlevel for the
preferred capabilities. For the case that PeerMode is LEECH, the
tracker will search and select a proper list of peers satisfying
the conditions requested. The peer list MUST contain the Peer-IDs
and the corresponding IP addresses. To create the peer list, the
tracker may take peer status and network location information
into consideration, to express network topology preference or
operators' policy preferences, with regard to the possibility of
connecting with other IETF effors such as ALTO [I.D.ietf-alto-
protocol]. Thus a PeerGroup MAY also be needed in an extended
CONNECT request messages.
The response MUST have the same TransactionID value as the
request. This specification doesn't do any extension to the
response of CONNECT messages. An example of a Response message
for the extended CONNECT Request from a leecher is:
SUCCESSFUL
12345
656164657220
956264622298
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3332001256741
5.2. DISCONNECT Request
This method is used when the peer intends to leave the system and
no longer participate.
The tracker SHOULD delete the corresponding activity records
related with the peer in the corresponding swarms (including its
status and all content status).
The peer MUST properly form the XML message-body, set the Request
method to DISCONNECT, set the PeerID with the identifier of the
peer, randomly generate and set the TransactionID.
An example of the message-body of a DISCONNECT Request for the
peer leaving all joined swarms is the following:
DISCONNECT
656164657221
12345
An example of a Response message for the DISCONNECT Request is the
following:
SUCCESSFUL
12345
5.3. FIND Request
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This method allows peers to request to the tracker, whenever needed,
a new peer list for the swarm or for specific scope of chunks of a
media content representation of that swarm.
The peer MUST properly form the XML message-body, set the request
method to FIND, set the PeerID with the identifier of the peer, set
the SwarmID with the identifier of the swarm the peer is interested
in. And optionally, in order to find peer having the specific chunks,
the peer also may include information about the content in the JOIN
request message.
This message is mainly used for leechers to update the peer list. It
is unnecessary to set the PeerMode element in FIND request messages.
The peer MUST generate and set the TransactionID for the request.
An example of the message-body of a FIND Request is the following:
FIND
656164657221
1111
12345
5
The FIND request MAY include a PeerNum element to indicate to the
tracker the number of peers to be returned in a list corresponding to
the indicated properties, being @abilityNAT for NAT traversal
(considering that PPSP-ICE NAT traversal techniques may be used), and
optionally @concurrentLinks, @onlineTime and @uploadBWlevel for the
preferred capabilities.
In the case of a FIND with a specific scope of a stream content the
request SHOULD include a ContentGroup to specify the content
Representations segment range of interest.
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When receiving a well-formed FIND Request the tracker processes the
information to check if it is valid. In case of success a response
message with a Response value of SUCCESSFUL will be generated and the
tracker will include the appropriate list of peers satisfying the
conditions requested. The peer list returned MUST contain the Peer-
IDs and the corresponding IP Addresses.
The tracker may take peer status and network location information
into consideration when selecting the peer list to return, to express
network topology preferences or Operators' policy preferences, with
regard to the possibility of connecting with other IETF efforts such
as ALTO [I.D.ietf-alto-protocol].
An example of a Response message for the FIND Request is the
following:
SUCCESSFUL
12345
956264622298
3332001256741
The Response MUST include a PeerGroup with PeerInfo data that
includes the public IP address of the selected active peers in the
swarm.
The tracker MAY also include the attribute @asn with network location
information of the transport addresses of the peers, corresponding to
the Autonomous System Numbers of the access network provider of each
peer in the list.
The response MAY also include a PeerGroup with PeerInfo data that
includes the requesting peer public IP address. If STUN-like function
is enabled in the tracker, the PeerAddress includes the attribute
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@type with a value of REFLEXIVE, corresponding to the transport
address "candidate" of the peer.
An example of a Response message for the FIND Request including the
requesting peer public IP address is the following:
SUCCESSFUL
12345
656164657221
956264622298
3332001256741
5.4. Extended STAT_REPORT Request
This message still uses the specifications of the base tracker
protocol [I-D.ietf-ppsp-base-tracker-protocol]. The Stat element
has been extended with one property, "ContentMap", to allow peers
reporting map of chunks they have. The tracker would not have the
ability to treat the FIND and JOIN requests for specific content
chunks, unless peers report this kind of information. Examples
are provided below.
An example of the message-body of an enhanced STAT_REPORT request
is the following:
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STAT_REPORT
656164657221
12345
1111
512
768
1024000
2222
1024
2048
512000
1111
A/8D/wP/A/8D/wP/A/8D/wP/A/8D/wP/....
A/8D/wP/A/8D/wP/A/8D/wP/A/8D/wP/....
A/8D/wP/A/8D/wP/A/8D/wP/A/8D/wP/....
2222
A/8D/wP/A/8D/wP/A/8D/wP/A/8D/wP/....
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A/8D/wP/A/8D/wP/A/8D/wP/A/8D/wP/....
If the request is valid the tracker process the received
information for future use, and generates a response message with
a Response value of SUCCESSFUL.
The response MUST have the same TransactionID value as the
request.
An example of a Response message for the START_REPORT Request is
the following:
SUCCESSFUL
12345
4.6. Error and Recovery Conditions
This document does not introduce any new error and recovery
conditions. The implementation of error treatment MUST refer to
the base tracker protocol specification [I-D.ietf-ppsp-base-
tracker-protocol], subsection 8.6.
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5. Security Considerations
The extended tracker protocol proposed in this document
introduces no new security considerations beyond those described
in the base tracker protocol specification [I-D.ietf-ppsp-base-
tracker-protocol].
6. IANA Considerations
There are presently no IANA considerations with this document.
7. Acknowledgments
The authors would like to thank many people for their help and
comments, particularly: Zhang Yunfei, Martin Stiemerling, Johan
Pouwelse and Arno Bakker.
The authors would also like to thank the people participating in
the EU FP7 project SARACEN (contract no. ICT-248474)
[refs.saracenwebpage] for contributions and feedback to this
document.
The views and conclusions contained herein are those of the
authors and should not be interpreted as necessarily representing
the official policies or endorsements, either expressed or
implied, of the SARACEN project or the European Commission.
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8 References
8.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[ISO.8601.2004] International Organization for Standardization, "Data
elements and interchange formats - Information interchange
- Representation of dates and times", ISO Standard 8601,
December 2004.
8.2 Informative References
[I-D.ietf-ppsp-problem-statement] Zhang, Y., Zong, N., Camarillo, G.,
Seng, J., and Y. Yang, "Problem Statement of P2P Streaming
Protocol (PPSP)", draft-ietf-ppsp-problem-statement-13
(work in progress), February 2013.
[I-D.ietf-ppsp-base-tracker-protocol] Cruz, R., Nunes, M., Gu, Y.,
Xia, J., and J. Taveira, "PPSP Tracker Protocol-Base
Protocol (PPSP-TP/1.0)", draft-ietf-ppsp-base-tracker-
protocol-00 (work in progress), February 2013.
[I.D.ietf-alto-protocol] Alimi, R., Penno, R., Yang, Y., "ALTO
Protocol", draft-ietf-alto-protocol-11, (work in
progress), March 2012.
[ISO.IEC.23009-1] ISO/IEC, "Information technology -- Dynamic
adaptive streaming over HTTP (DASH) -- Part 1: Media
presentation description and segment formats", ISO/IEC DIS
23009-1, Aug. 2011.
[refs.saracenwebpage] "SARACEN Project Website",
http://www.saracen-p2p.eu/.
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Authors' Addresses
Rachel Huang
Huawei
Phone: +86-25-56623633
EMail: rachel.huang@huawei.com
Ning Zong
Huawei
Phone: +86-25-56624760
EMail: zongning@huawei.com
Rui Santos Cruz
IST/INESC-ID/INOV
Phone: +351.939060939
Email: rui.cruz@ieee.org
Mario Serafim Nunes
IST/INESC-ID/INOV
Rua Alves Redol, n.9
1000-029 LISBOA, Portugal
Phone: +351.213100256
Email: mario.nunes@inov.pt
Joao P. Taveira
IST/INOV
Email: joao.silva@inov.pt
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