[ppsp] 答复: Requirements comments: draft-ietf-ppsp-reqs-03
Ning Zong <zongning@huawei.com> Wed, 03 August 2011 23:59 UTC
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Date: Thu, 04 Aug 2011 07:59:05 +0800
From: Ning Zong <zongning@huawei.com>
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To: 'Johan Pouwelse' <peer2peer@gmail.com>, ppsp@ietf.org
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Subject: [ppsp] 答复: Requirements comments: draft-ietf-ppsp-reqs-03
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Hi, Johan, Thank you for your comments. I will do a new revision shortly. BR, Ning Zong -----邮件原件----- 发件人: ppsp-bounces@ietf.org [mailto:ppsp-bounces@ietf.org] 代表 Johan Pouwelse 发送时间: 2011年7月29日 11:23 收件人: ppsp@ietf.org 主题: [ppsp] Requirements comments: draft-ietf-ppsp-reqs-03 Dear PPSP people, The V03 requirements document reads as a mature piece of text and seems nearly ready to be finalized. Solid piece of work. Listed below are some proposed minor textual changes. As small as they are textual, in terms of technical impact they are larger. All issues below where also raised and discussed publicly at PPSP IETF meeting 81 in Canada. Disclosure: in my capacity as scientific director of P2P-next I'm responsible for one of the three submitted peer protocols in PPSP. My comments are derived from our years of experience both measuring and deploying P2P streaming systems. Key comments are specifically targeted at enabling PPSP on low-power devices such as smartphones, TV settop boxes and tablets. The text currently contains some requirements which will add both needless complexity and battery drain, according to our experience. We very much welcome discussions regarding the remarks below. Please respond, even if you agree. . . In section 3 "Overview of PPSP", page 5. The definition of "report" lists many examples, but omits a commonly used item which is important for load balancing and fairness. Please consider adding "total amount of bytes uploaded/downloaded to neighbour peers". Still in Section 3 on page 6 regarding the very first sentence. Please make only minimal required functionality mandatory (see low-power remark above). For instance, by replacing existing text with: " 1) Standard format/encoding of information between PPSP peers and PPSP tracker. Some of this exchanged information may be explicitly marked as optional. Exchanged information may include peer list, swarm ID, chunk information, content availability, streaming status including online time, link status, node capability and other streaming parameters." PPSP.REQ-7 on page 7. Please replace with the following outcome of IETF meeting discussion. "The tracker protocol is recommended to be carried over TCP. The peer protocol is recommended to be carried over UDP in order to: facilitate NAT traversal techniques such as STUN/ICE, minimize network socket usage and facilitate congestion control algorithm for less-than-best-effort 'background' transmissions such as IETF LEDBAT." PPSP.REQ-8 on page 7. This requirement is very restrictive for our design space. Do we really desire explicit QoS communication or do we simply require that the whole architecture support the QoS needed for streaming? Please consider replacing this text with: "The tracker and peer protocols MUST support acceptable QoS (e.g. video quality, delay requirements) for both on-demand and live streaming. In other words, the two protocols together must be fit-for-purpose. For instance, the protocols must be able to provision sport events with less than 1 minute of total end-to-end delay." The second paragraph of PPSP.REQ-8 on page 7, beginning with: "The quality for P2P live streaming system could be very bad. Dependent from the".. The purpose and meaning of this whole section could be clarified, sharpened and made more demanding. My hope is that this paragraph can be replaced with clear requirements or that the entire paragraph is deleted {not fully happy with text below, please help out if you're inspired}: "PPSP.REQ-9: For both the live and on-demand streaming case the tracker and peer protocols MUST facilitate low startup delay (e.g. must not include non-functional Round Trip Time (RTT) delays). PPSP.REQ-10: The tracker and peer protocol together MUST facilitate low startup delay, low channel/content switching time and minimal end-to-end delay for both on-demand and live streaming, even for very popular content. The tracker and peer protocol do NOT include the algorithm required for scalable streaming. However, the tracker and peer protocol SHALL NOT restrict or place limits on any such algorithm. The first paragraph on page 8 ends with "The tracker protocol must provide the possibility for the request of alternative peer addresses, if the quality is not sufficient for the user". Why do we specify a solution or mechanism in the requirements, instead of the survey? Can we delete this entire paragraph or move it to the survey? Section 4.3 "PPSP Peer Protocol Requirements" on page 9. To prevent DoS problems it is vital that hearsay amongst peers is not allowed. Please revise PPSP.PP.REQ-1 with: "The streaming content available request message MUST allow a peer to obtain information about chunk availability of another peer. The chunk information MUST at least contain the chunk ID. This chunk availability information MUST NOT be passed on to other peer, unless validated (e.g. prevent hearsay and DoS)." Again on page 9 a similar issue exists with the peer list. Please revise PPSP.PP.REQ-3 by adding: "This additional list of peers MUST only contain peers which have been checked to be valid and online recently (e.g. prevent hearsay and DoS)." Concerning PPSP.PP.REQ-5 on page 10. Why is this required? This restricts the protocol design space. Please make this explicit information-based approach optional, as a feedback based approach utilising simple "failure detection" could perhaps yield similar or superior results. Greetings, johan. _______________________________________________ ppsp mailing list ppsp@ietf.org https://www.ietf.org/mailman/listinfo/ppsp