RFC 1453
A Comment on Packet Video Remote Conferencing and the Transport/Network Layers
RFC 1453: A Comment on Packet Video Remote Conferencing and the Transport/Network Layers 🎀
okay bestie, here's the tea 🫖. This one is by W. Chimiak from BGSM, dated April 1993, and it comes out of the Network Working Group 🌸. It's an informational memo, so it's giving info to the Internet community, not a standard 📚. Distribution is unlimited 🦋. The title block doesn't list anything it obsoletes or updates, so there's zero drama there 💅.
Status of This Memo 📜
this memo provides information for the Internet community. it does not specify an Internet standard. distribution of this memo is unlimited 🌈.
Abstract 🦋
okay so the new wave of multimedia apps is literally asking for new features and new mechanisms just to perform well 😭. ATM tech has gone from concept to reality, delivering super high bandwidths and new capabilities to the data link layer user 🚀. To get ready for that high bandwidth-delay data link layer, people built Delta-t [Delta-t], NETBLT [RFC 988], and VMTP [RFC 1045]. The creators of those experimental Internet protocols had iconic insights and mechanisms, and those got used to design the Xpress Transfer Protocol (XTP) [XTP92], with the goal of eventually getting ATM bandwidths all the way to a user process 💖. This RFC is basically a vehicle to tell the Internet community about XTP, since XTP builds on past Internet activity and targets general-purpose apps and multimedia apps, with the emerging ATM networks in mind ✨.
1. Introduction ✨
bestie, networking is no longer just analog telephony 📞. High-performance lower-layer networks have made exciting new apps possible: collaboratory environments, distributed client/server computing, remote conferencing, teleclassrooms, and distributed life-sciences imaging 🌈. These apps normally need a ton of bandwidth and often create operating system bottlenecks 😩. Enabling them means delivering bandwidth to the applications, not just having bandwidth available on the network 💅. This might sound obvious, but a lot of transport-layer solutions are satisfied just by having bandwidth at that layer, without enough sensitivity to higher-layer access to that bandwidth 🙈. Unavailable bandwidth at the upper layers is becoming the real issue, since the networks are turning into a high-performance virtual backplane without equally high-performance control schemes 🔥. It appears new services are needed that communicate with all layers, and the ATM architecture calls for exactly that kind of integrated control scheme 🫶.
2. Remote Conferencing 🌸
remote conferencing is the kind of app whose challenges might get met at the data link layer by the emerging broadband networks 🦋. If that happens, important medical stuff like medical imaging for diagnosis and treatment planning would be possible [CHIM92] 🩺. Remote conferencing would let imaging apps for life sciences work through national resource centers 🏥. Collaboratory conferences in molecular modeling, design efforts, and visualization of data across numerous disciplines could become possible too 🧬.
at the Second Packet Video Workshop (held December, 1992, at MCNC in the Research Triangle Park, North Carolina 🌲), a recurring theme was the use of multimedia in remote conferencing 🎥. The apps people talked about included interactive, synchronized voice and video transmission, multicast transmission, data transfer, graphics transmission, noninteractive video and audio transmission, and data base query within a virtually shared workspace 💜. A few participants doubted that current computer networks could handle these multimedia apps, and they preferred only connection-oriented, circuit-switched services 🤔. Most participants, however, were super excited about using an integrated network approach ✨.
2.1. Remote Conferencing Functions and Requirements 💅
remote conferencing, as seen at the workshop, needs a set of functions 📅. It must provide session scheduling, which covers starting a session, joining sessions that are already in progress, leaving a session without tearing it down when there are multiple participants, and ending a session 🫶.
the remote-conferencing session needs a control subsystem that is either tightly controlled for an n-to-n connection for two to 15 participants, or loosely controlled for a 1-to-n connection for any number of participants 🎀. The Multipeer-Multicast Consortium is working on defining the control requirements and the mechanisms for control 🛠️. At the Packet Video Workshop, one participant presented a conference control protocol (CCP), shown in Figure 1 [CCP92] 🍓. In this architecture, the CCP controls the Network Voice Protocol (NVP) [RFC741] and the Packet Video Protocol (PVP) [PVP81] over the experimental Internet Stream Protocol, Version 2 (ST-II) [RFC1190], rather than IP 🦋.
Latency, intramedia synchronization, and intermedia synchronization (lip-sync) are critical for the interactive voice and video streams of remote conferencing 🎧. Client/server apps, including data base operations, are equally important 💖. The ability to display noninteractive video and high-resolution graphics is necessary 🌈.
security is gonna be a thing eventually, and no cap, it's serious 😬. At the very least, there must be a mechanism to determine who can find out what about a conference, and who can join one 🔒. That determination will be part of an upper-layer protocol 👑.
+--------------+ +--------+ +-----+ +------------+
|Teleconference| | File | |Email| | Domain |
| (CCP) | |Transfer| | | |Name Service|
+----+-------+-+ +-----+--+ +-+---+ +-----+------+
| | |__ __| |
| | || |
+-----+--+ +--+-----+ +-++-+ +----+---+
|Network | | Packet | | T | | U |
| Voice | | Video | | C | | D |
|Protocol| |Protocol| | P | | P |
+---+----+ +--+-----+ +-+--+ +--+-----+
|__ __| |__ __|
| | | |
+-+---+--+ +-+-------+-+
| Stream | | I |
|Protocol| | P |
+---+----+ +---+-------+
| |
+-----+----------------------+----+
|IEEE_802.X,FDDI,DARTnet,ATOMIC...|
+---------------------------------+
Figure 1: The Connection Control Protocol Architecturethe solutions must range in geography from single machines through LAN, CAN, MAN, and WAN conferences, and in data content from PCs to high-end workstations 🗺️. Implicit in that scaling is the notion of product and application interoperability 🤝.
remote conferencing apps should take advantage of future network enhancements, as well as the functions provided by ATM, FDDI, and SMDS ⚡. Doing so should provide function versus resource trade-offs, such as cost versus error control and cost versus rate control 💸. As a result, the transport layer should be able to provide the services offered by the data link layer 🧚.
most of the presentations on remote conferencing indicated a need for some degree of multicast functionality 📣. That ranges from 1-to-n, where conference membership is completely known, to conferences where the existence of a group is known but exact membership is not 🌟.
in remote conferencing, it is preferable to use one network for all information traffic 🌐. This network should have an offered quality of service (QOS) criteria to accommodate tradeoff metrics. Those would include guaranteed throughput, connection reliability, high call-completion rate, few dropped calls, tolerable error rate, varying degrees of compression on the video and audio streams, and tolerable motion artifacts, flow control, and latency 🎬. The QOS should be an input to the transport layer from the application or transport service user 🎀.
the compression/coding function should provide time-stamping and packetizing information, as well as real-time echo cancellation ⏱️. These functions are usually at the presentation and session layer of the Open System Interconnection (OSI) model, or at the application in some Internet models, but not the transport layer 🌈.
3. Potential Solutions ✨
okay so RFC 1193 already covers real-time communications requirements, and some of them overlap with what we're doing here [RFC1193] 💅 but the requirements it lays out basically demand brand new transport/network protocols 😭 The new ones being built by the Audio Visual Transport [SCHU92] (RTC, RTCP), plus other protocols in this area (ST-II), point toward an architecture like the one in Figure 2 🦋
These approaches may work, ngl. However, they encourage a discipline where every new class of application gets its own protocol 🙈 Another approach might be to unify the protocols. The vibe is that this is one of the main goals of XTP (see Figure 3) 👑
Other design considerations of XTP include the following:
+----------------------+
| media |
| application |
+--------+----+-+------+
| |RTCP| | |
| +----+ | T |
| RTP | C |
+-----+-----+ | P |
|ST-II| UDP | | |
+ +-----+---+------|
| | IP |
+-----+-------+--------+
| Data Link Layer |
+----------------------+Figure 2: One emerging multimedia architecture 🌸
+--------------+ +--------+ +-----+ +------------++-----------+
|Teleconference| | File | |Email| | Domain || media |
| | |Transfer| | | |Name Service||application|
+------+-------+ +----+---+ +--+--+ +-----+------++-----+-----+
| | | | |
+---------------+--------+----------+-------------+
|
+-------+--------+
|Unified Protocol|
+----------------+
|Data Link Layer |
+----------------+Figure 3: Another integrated multimedia architecture 🧚
- Developing a protocol based on the work and experience of the protocol groups such as IETF, which produced NETBLT, VMTP, TCP, IP, and UDP.
- Incorporating lessons from Delta-t.
- Observing the design paradigm shift of ATM, SONET, and VMTP in the header, trailer, and information segment construction.
- Targeting the real-time requirements articulated by the Department of Defense SAFENET committee and the French Ministry of Defense military real-time specification [GAM-T-103].
Mechanisms in XTP let an application approach the performance it wants 🔥 There's a session-scheduling mechanism for joining and leaving a multicast conference. The XTP mechanism for multicast satisfies the loosely controlled session requirements. The tightly controlled session would need multiple XTP associations.
The priority mechanism that uses the 32-bit SORT field lets an application prioritize data. Because XTP is a transport layer, this priority mechanism follows through every node traversed. There's also an out-of-band delivery mechanism. However, XTP does not offer latency control by itself; it just provides a priority mechanism 🙈
The selective acknowledgement, fast negative acknowledgement, and selective retransmission let an application choose an appropriate level of error control 💖 Put the priority mechanism and these error-control mechanisms together and you're likely to approach the latency and synchronization requirements of remote conferencing ✨
Noninteractive audio and video, as well as graphics presentation, can be accommodated in many ways by the application. It's important that the transport layer provides adequate mechanisms to deliver the appropriate data streams in a manner compatible with the applications. These applications can probably be accomplished with extant protocols, as well as XTP 🫶
The scalability of the solution will be a function of the standards used. At the Packet Video Workshop, some applications sacrificed computer network standards in favor of desired performance. This approach usually impedes scalability 😭 From the explanation of the applications taking this approach, it seemed like using XTP would have provided an adequate transport service for them.
XTP was designed to provide mechanisms that accommodate application requirements, that is, the ability to respond to QOS requests. For example, guaranteed throughput may be accomplished by using XTP's rate and burst control together with flow control or no flow control. Tolerable error rate can be accomplished with partially error controlled connections (PECC), a service that can be placed in the application or just above the transport layer [PECC92]. Motion artifacts and varying degrees of compression should be handled above the transport layer, in coordination with the transport layer or possibly in a network management function 💜
3.1. Synthesize the Hardware Fabrication Process into the Design 🛠️
To produce an affordable solution, the hardware fabrication process should be a design consideration. Technologies are evolving too fast to assume that a generic protocol design will anticipate all fabrication advances, but that shouldn't stop anyone from using the features of advanced hardware fabrication processes 💅
System interface problems and VLSI techniques should be considered in the specification of the protocol. The ATM and SONET standards seem to support this philosophy. NETBLT and VMTP design efforts seem to support this approach too. XTP does use it ✨
It's very helpful to break the protocol down into parallel-state machines for execution on more inexpensive hardware. This reduces the context switching and interrupt handling requirements of the hardware, which lowers production costs while producing a scalable protocol machine 🧚
4. Multimedia Applications over XTP 🎀
Alongside the IETF efforts to enable multimedia applications such as remote conferencing, the XTP forum members have been experimenting with major elements of these applications 🌈
- At the University of Virginia, more than 100 simulated voice channels were run on an FDDI network [UVAVOICE92]. The purpose of this experiment was to test the limits of FDDI and a software version of XTP in a simulated interactive voice environment. Multicasted, noninteractive video has been supported there for several years 🎥
UVa also has a video-mail demo over XTP/FDDI that uses Fluent multimedia interface and standard JPEG compression. This PC-based demo delivers full frame, full color, 30 frames/sec video from any network disk to a remote VGA screen. It's important that users could not discern any difference in playback between a local disk and a remote disk 😭 An Xpress File System (XFS) is used on server and client systems.
- The Technical University of Berlin, Germany, reports that the coordination, implementation, and operation of multimedia services (CIO) of the R&D in Advanced Communications Technologies in Europe (RACE) is using XTP as a starting point for design [XTPRACE] 🇪🇺
- At the Naval Command, Control, and Ocean Surveillance Center Research, Development, Test and Evaluation Division NRaD (formerly the Naval Ocean Systems Command (NOSC)), voice is multicasted over XTP/FDDI. A simple multicast is distributed to a group with a latency of around 25 ms, where the latency represents the delay from the voice signal at the microphone to the audio signal at the speaker. This group is currently doing research on an n-party multicast of voice (telephone conference-call paradigm [n x n multicast]) 📞
- Commercially, Starlight Networks Inc. migrated a subset of XTP into the transport layer of its video application server. By using XTP rate control, full-motion, full-screen compressed video is delivered at a constant 1.2 Mbps over switched-hub Ethernet to viewstations. This network delivers at least 10 simultaneous video streams 💖
Therefore, XTP has been used in applications that were previously placed over IP or even a data link layer 👑
5. Policy versus Mechanism 🦋
Separating protocol policies and mechanisms [XTPbk] lets you adopt new policies without altering offered mechanisms. An excellent example is UVa's Partially Error Controlled Connections (PECC). This control system maximizes error control in such a way that receiving FIFOs are never starved, i.e., the application, driver, or operating system buffer control, and not the transport layer, becomes the bottleneck 🙌
Because XTP is mechanism-rich and policy-tolerant, this very dynamic error control policy mechanism is possible 🧠 Separating policy and mechanism lets an error-control or flow-control policy adapt to the data link layer conditions without shutting down a connection and rebuilding (or multiplexing) a new one on a different protocol stack. This may also provide an easier way for a network management subsystem to maintain a desired QOS ✨
6. Summary 💜
Remote conferencing presents new opportunities for research, business, and administration 🌟 Although some people are proposing that only classical circuit-switched mechanisms be used, most network engineers are searching for ways to use the new features of FDDI, SMDS, and ATM in multimedia applications such as remote conferencing. Some new applications have been placed directly on a data link layer. New Transport/Network layer combinations have been proposed and are being tested.
It is believed that XTP should be considered as a possible solution, because its forum membership includes commercial, government, and research institutions, some of which have implemented various applications that contribute to an overall remote-conferencing application 🫶
7. References 📚
okay bestie, the receipts 🧾✨ every single source the RFC is built on, dumped here so you can go find them yourself 🫶
[CCP92]Schooler, E., "An Architecture for Multimedia Connection Management", in Proceedings of the 4th IEEE ComSoc International Workshop on Multimedia Communications, Monterey, CA, April 1992.[CHIM92]Chimiak, W., "The Digital Radiology Environment", IEEE JSAC, Vol. 10, No. 7, pp. 1133-1144, September 1992.[Delta-t]Watson, R. W., "Delta-t Protocols Specification", Lawrence Livermore Laboratory, April 15, 1983.[GAM-T-103]French Ministry of Defense, "GAM-T-103 Military Real-Time Local Area Network Reference Model (Transfer Layer)", February 7, 1987.[PECC92]Dempsey, B., Strayer, T. and Weaver A., "Adaptive Error Control for Multimedia Data Transfer", in Proceedings of the IWACA 92, Munich, Germany, pp. 279-288, March 1992.[PVP81]Cole, R., "PVP - A Packet Video Protocol", W-Note 28, Information Sciences institute, University of California, Los Angeles, CA, August 1981.[RFC1045]Cheriton, D., "VMTP: Versatile Message Transaction Protocol Specification", RFC 1045, Stanford University, February 1988.[RFC998]Clark, D., Lambert, M., and L. Zhang, "NETBLT: A Bulk Data Transfer Protocol", RFC 998, MIT, March 1987.[RFC1193]Ferrari, D., "Client Requirements For Real-Time Communication Services", RFC 1193, UC Berkeley, November 1990.[RFC1190]Topolcic, C., Editor, "Experimental Internet Stream Protocol: Version 2 (ST-II)", RFC 1190, CIP Working Group, October 1990.[SCHU92]Schulzrinne, H., "A Transport Protocol for Audio and Video Conferences and other Multiparticipant Real-Time Applications", Internet Engineering Task Force, Internet-Draft, October 1992.[UVAVOICE92]Weaver, A. C. and McNabb, J.F., "Digitized Voice Distribution Using XTP and FDDI", Transfer, Vol. 5, No. 6, pp. 2-7 (November/December 1992).[XTP92]Xpress Transfer Protocol, version 3.6, XTP Forum, 1900 State Street, Suite D, Santa Barbara, California 93101 USA, January 11, 1992.[XTPbk]Strayer, W.T., Dempsey, B.J., and Weaver, A.C., "XTP: The Xpress Transfer Protocol", Addison-Wesley Publishing Company, Inc., 1992.[XTPRACE]Rebensburg, K. and Miloucheva, I., "The Use of XTP in a Large European Communication Project", XTP Forum Research Affiliate Annual Report, Document 92-183, pp. 105-112, 1992.
Security Considerations 🔐
Security issues are discussed in section 2.1. Bestie, this one is serious, so please don't skip it 🥺🔐
Author's Address 💌
William J. Chimiak
Department of Radiology
Bowman Gray School of Medicine
Medical Center Boulevard
Winston-Salem, NC 27157-1022
Phone: 919-716-2815
EMail: chim@relito.medeng.wfu.edu📦 where this page comes from
- ietf: rfc1453 1993-04
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms