INTERNET DRAFT P Bagnall Large-scale Multicast Applications Working Group R Briscoe Expiration: 21 May 1998 A Poppitt BT 20 Nov 1998 Taxonomy of Communication Requirements for Large-scale Multicast Applications draft-ietf-lsma-requirements-02.txt Status of this Memo ------------------- This document is an Internet-Draft. 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. Internet-Drafts are draft documents valid for a maximum of six months 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.'' To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). NB: an html version of this draft may be found at http://www.labs.bt.com/people/bagnalpm/lsma/ draft-ietf-lsma-requirements-02.txt Abstract -------- The intention of this draft is to define a classification system for the communication requirements of any large-scale multicast application (LSMA). It is very unlikely one protocol can achieve a compromise between the diverse requirements of all the parties involved in any LSMA. It is therefore necessary to understand the worst-case scenarios in order to minimise the range of protocols needed. Dynamic protocol adaptation is likely to be necessary which will require logic to map particular combinations of requirements to particular mechanisms. Standardising the way that applications define their requirements is a necessary step towards this. Classification is a first step towards standardisation. 1.Introduction -------------- This taxonomy consists of a large number of parameters that are considered useful for description of communication requirements of LSMAs. To describe a particular application, each parameter would be assigned a value. Typical ranges of values are given wherever possible. Failing this, the type of any possible values is given. The parameters are collected into ten or so higher level categories, but this is purely for convenience. The parameters are pitched at a level considered meaningful to application programmers. However, they describe communications not applications - the terms "3D virtual world", or "shared TV" might imply communications requirements, but they don't accurately describe them. Assumptions about the likely mechanism to achieve each requirement are avoided where possible. The exception to this is that receiver initiated join to multicast address groups [refmcast] on an open access Internet is assumed. While the parameters describe communications, it will be noticed that few requirements concerning routing etc. are apparent. This is because applications have few direct requirements on these second order aspects of communications. Requirements in these areas will have to be inferred from application requirements (e.g. latency). The taxonomy is likely to be useful in a number of ways: 1. most simply, it can be used as a checklist to create a requirements statement for a particular LSMA. Example applications will be classified [bagnall98] using the taxonomy in order to exercise (and improve) it 2. because strictest requirement have been defined for many parameters, it will be possible to identify worst case scenarios for the design of protocols 3. because the scope of each parameter has been defined (per session, per receiver etc.), it will be possible to highlight where heterogeneity is going to be most marked 4. a step towards standardisation of the way LSMAs define their communications requirements. This could lead to standard APIs between applications and protocol adaptation middleware 5. identification of limitations in current Internet technology for LSMAs to be added to the LSMA limitations draft [limitations] 6. identification of gaps in Internet Engineering Task Force (IETF) working group coverage =20 This approach is intended to complement that used where application scenarios for Distributed Interactive Simulation (DIS) are proposed [scenarios] in order to generate network design metrics (values of communications parameters). Instead of creating the communications parameters from the applications, we try to imagine applications that might be enabled by stretching communications parameters. The above introduction assumes all the items under the "Further Work" section (near the end) have been completed. As they haven't, the reader is advised to read that section next! 2. Definitions -------------- 2.1. Definition of Sessions --------------------------- The following terms have no agreed definition, so they will be defined for this document. Session a happening or gathering consisting of flows of information related by a common description that persists for a non- trivial time (more than a few seconds) such that the participants (be they humans or applications) are involved and interested at intermediate times may be defined recursively as a super-set of other sessions Secure session a session with restricted access A session or secure session may be a sub and/or super set of a multicast group. A session can simultaneously be both a sub and a super-set of a multicast group by spanning a number of groups while time-sharing each group with other sessions. 2.2. Definitions of Roles ------------------------- Defining all possible roles is not possible. The roles in a communication are application dependant. 3. Taxonomy ----------- 3.1 Summary of Communications Parameters ---------------------------------------- Before the communications parameters are defined, typed and given worst-case values, they are simply listed for convenience. Also for convenience they are collected under classification headings. 3.1.1 Reliability Packet loss Transactional Guaranteed Tolerated loss Semantic loss Component reliability Setup fail-over time Mean time between failures Fail over time during a stream 3.1.2 Ordering Ordering type 3.1.3 Timeliness Hard Realtime Synchronicity Burstiness Jitter expiry latency optimum bandwidth tolerable bandwidth required by time and tolerance host performance fair delay frame size content size 3.1.4 Session Control initiation start time end time duration active time session burstiness atomic join late join allowed ? temporary leave allowed ? late join with catch-up allowed ? potential streams per session active streams per sessions 3.1.5 Session Topology # of senders # of receivers 3.1.6 Directory fail-over timeout (see Reliability: fail-over time) mobility 3.1.7 Security authentication strengh tamper-proofing non-repudiation strength denial of service action restriction privacy retransmit prevention strength membership criteria membership principals collusion prevention fairness action on compromise 3.1.8 Security dynamics mean time between compromises compromise detection time limit compromise recovery time limit 3.1.9 Payment & Charging Total Cost Cost per time Cost per Mb 3.2 Definitions, types and strictest requirements ------------------------------------------------- The terms used in the above table are now defined for the context of this document. Under each definition, the type of their value is given and where possible worst-case values and example applications that would exhibit this requirement. There is no mention of whether a communication is a stream or a discrete interaction. An attempt to use this distinction as a way of characterising communications proved to be remarkably unhelpful and was dropped. 3.2.1 Types ----------- Each requirement has a type. The following is a list of all the types used in the following definintions. =B7 Application Benchmark (unknown) =B7 Bandwidth (Kb/s) =B7 Boolean =B7 Abstract Currency (1970 US$) =B7 Currency - current local =B7 Date (ms since 0/1/1970) =B7 Enumeration (int) =B7 Fraction (none) =B7 Idenfitiers =B7 Int (none) =B7 Identifiers (none) =B7 membership list/rule =B7 Duration (ms) 3.2.1 Reliability ----------------- 3.2.1.1 Packet Loss ------------------- Transactional When multiple operations must occur atomically, transactional communications guarantee that either all occur or none occur and a failure is flagged. Type: Boolean Meaning: Transactional or Not transaction Strictest Requirement: Transactional Example Application: Bank credit transfer, debit and=20 credit must be atomic. NB: Transactions are potentially much more complex, but it is believed this is an application=20 layer problem. Guaranteed Guarantees communications will succeed under certain conditions. Type: Enumerated Meaning: Deferrable =96 if communication fails it will be deferred until a time when it will be successful. Guaranteed =96 the communication will succeed so=20 long as all necessary components are working. = =20 No guarantee - failure will not be reported. Strictest Requirement: Deferrable Example Application: Stock quote feed =96 Guaranteed NB: The application will need to set parameters to more fully define Guarantees, which the middleware may translate into, for example, queue lengths. Tolerated loss This specifies the proportion of data from a communication that can be lost before the application becomes completely unusable. Type: Fraction Strictest Requirement: 0% Example Application: Video =96 20% Semantic loss The application specifies how many and which parts of the communication can be discarded if necessary. Type: Identifiers, name disposable application level frames Meaning: List of the identifiers of application frames which may be lost Strictest Requirement: No loss allowed Example Application: Video feed - P frames may be lost, I frames not =20 3.2.1.2. Component Reliability ------------------------------ Setup Fail-over time The time before a failure is detected and a replacement component is invoked. From the applications point of view this is the time it may take in exceptional circumstances for a channel to be set- up. It is not the "normal" operating delay before a channel is created. Type: Time Strictest Requirement: Application Dependent Example Application: Name lookup - 5 seconds Mean time between failures The mean time between two consecutive total failures of the channel. Type: Time Strictest Requirement: Indefinite Example Application: Telephony - 1000 hours Fail over time during a stream The time between a stream breaking and a replacement being set up. Type: Time Strictest Requirement: Equal to latency requirement Example Application: File Transfer - 10sec 3.2.2. Ordering --------------- Ordering type Specifies what ordering must be preserved for the application Type: Enumeration =20 Meaning: Timing Global Per Sender none Sequencing Global Per Sender none Causality Global Per Sender none Strictest Requirement Global timing, sequencing and Causality Example Application: Game - global causal (to make sure being hit by bullet occurs after the shot is fired!) 3.2.3. Timeliness ----------------- Hard-real time There is a =93meta-requirement=94 on timeliness. If hard real-time is required then the interpretation of all the other requirements changes. Failures to achieve the required timeliness must be reported before the communication is made. By contrast soft real- time means that there is no guarantee that an event will occur in time. However statistical measures can be used to indicate the probability of completion in the required time, and policies such as making sure the probability is 95% or better could be used. Type: Boolean Meaning: Hard or Soft realtime Strictest Requirement: Hard Example Application: Medical monitor - Hard Synchronicity To make sure that separate elements of a session are correctly synchronised with respect to each other Type: Time Strictest Requirement: 80ms for humans Example Application: TV lip-sync value 80ms Burstiness This is a measure of the variance of bandwidth requirements over time. Type: Fraction Meaning: either: Variation in b/w as fraction of b/w for variable b/w communications or duty cycle (fraction of time at peak b/w) for intermittent b/w communications. =20 Strictest Requirement: Variation - max b/w Duty cycle ~ 0 Example Application: Sharing video clips, with chat channel sudden bursts as clips are swapped. Compressed Audio - difference between silence and talking NB: More detailed analysis of communication flow (eg max rate of b/w change or Fourier Transform of the b/w requirement) is possible but as complexity increases usefulness and computability decrease. ED: This may need to becomes two, namely B/W variance and Duty Cycle Jitter Jitter is a measure of variance in the time taken for communications to traverse from the sender (application) to the receiver, as seen from the application layer. Type: Time Strictest Requirement: <1ms Example Application: audio streaming - <1ms NB: A jitter requirement implies that the communication is a real-time stream. It makes relatively little sense for a file transfer for example. Expiry This specifies how long the information being transferred remains valid for. Type: Date Strictest Requirement: For ever Example Application: key distribution - 3600 seconds (valid for at least one hour) Latency Time between initiation and occurrence of an action from application perspective. Type: Time Strictest Requirement: Near zero for process control apps Example Application: Audio conference 20ms NB: Where an action consists of several distinct sequential parts the latency =93budget=94 must be split over those parts. For process control the requirement may take any value. Optimum Bandwidth Bandwidth required to complete communication in time Type: Bandwidth Strictest Requirement: Indefinate Example Application: Internet Phone 8kb/s Tolerable Bandwidth Minimum bandwidth that application can tolerate Type: Bandwidth Strictest Requirement: Indefinate Example Application: Internet phone 4kb/s Required by time and tolerance Time communication should complete by and time when failure to complete renders communication useless (therefore abort). Type: Date - preferred complete time Date - essential complete time Strictest Requirement: Application Dependent Example Application: Email - Preferred 5 minutes & Essential in 1 day NB: Bandwidth * Duration - Size; only two of these parameters may be specified. An API though could allow application authors to think in terms of any two. Host performance Ability of host to create/consume communication Type: Application benchmark Strictest Requirement: Full consumption Example Application: Video - consume 15 frames a second NB: Host performance is complex since load, media type, media quality, h/w assistance, and encoding scheme all affect the processing load. These are difficult to predict prior to a communication starting. To some extent these will need to be measured and modified as the communication proceeds. Fair delay Time between receipt of communication and response by the client should determine winner of race conditions, not the first response at the server. The alternative is that the transport should make sure that delivery is withheld until all reciepients have the data. The specified requirement determines what delay is acceptable between the first receiver getting the data and the last receiver getting the data (assuming no system failures, but including packet loss). Requirement: the variance in delay between users that is acceptable Type: Time Strictest Requirement: 10ms Example Application: auction room - <10ms Frame size Size of logical data packets from application perspective Type: data size Strictest Requirement: 6bytes (gaming) Example Application: video - data size of single frame update Content size The total size of the content (not relevant for continuous media) Type: data size Strictest Requirement: N/A Example Application: xxx 3.2.4. Session Control ---------------------- Initiation Which initiation mechanism will be used. Type: Enumeration Meaning: Announcement Invitation Directive Strictest Requirement: Directive Example Application: Corporate s/w update - Directive Start Time Time sender starts sending! Type: Date Strictest Requirement: Now Example Application: FTP - at 3am End Time Type: Date Strictest Requirement: Now Example Application: FTP - Now+30mins Duration (end time) - (start time) - (duration), therefore only two of three should be specified. Type: Time Strictest Requirement: - 0ms for discrete, indefinite for streams Example Application: audio feed - 60mins Active Time Total time session is active, not including breaks Type: Time Example Application: Spectator sport transmission Session Burstiness expected level of burstiness of the session Type: fixed point. variance as fraction of max bandwidth Strictest Requirement: -bandwidth Example Application: commentary & slide show: 90% of max atomic join session fails unless a certain proportion of the potential participants accept an invitation to join. Alternatively, may be specified as a specific numeric quorum. Type: fixed point (proportion required) or int (quorum) Strictest Requirement: 1.0 (proportion) Example Application: price list update, committee meeting Note: whether certain participants are essential is application dependent. late join allowed ? does joining a session after it starts make sense Type: Boolean & indirection Strictest Requirement: allowed Example Application: game - not allowed, indirect to spectator channel temporary leave allowed ? does leaving and then coming back make sense for session Type: Boolean Strictest Requirement: allowed Example Application: FTP - not allowed late join with catch-up allowed ? is there a mechanism for a late joiner to see what they've missed Type: Boolean & indirection Strictest Requirement: allowed Example Application: sports event broadcast, allowed, indirect to highlights channel potential streams per session total number of streams that are part of session, whether being consumed or not Type: Int Strictest Requirement: indefinite example app: football match mcast - multiple camera's, commentary, 15 streams active streams per sessions (ie max app can handle) maximum number of streams that an application can consume simeultaneously Type: int Strictest Requirements: indefinite example app: football match mcast - 6, one main video, four user selected, one audio commentary =20 3.2.5. Session Topology ----------------------- Note: topology may be dynamic. One of the challenges in designing adaptive protocol frameworks is to predict the topology before the first join. # of senders the number of senders is a result the middleware may pass up to the application Type: int Strictest Requirement: indefinite example app: network MUD - 100 # of receivers the number of receivers is a results the middleware may pass up to the application Type: int Strictest Requirement: indefinite example app: video mcast - 100,000 3.2.6. Directory ---------------- fail-over timeout (see Reliability: fail-over time) mobility defines restrictions on when directory entries may be changed Type: Enumeration Meaning: while entry is in use while entry in unused never Strictest Requirement: while entry is in use example app: voice over mobile phone, while entry is in use (as phone gets new address when changing cell). =20 3.2.7. Security --------------- The strength of any security arrangement can be stated as the expected cost of mounting a successful attack. This allows mechanisms such as physical isolation to be considered alongside encryption mechanisms. An example type would be 1970 UD$ (to inflation proof). Security is an othogonal requirement. Many requirements can have a security requirement on them which mandates that the cost of causing the system to fail to meet that requirement is more than the specified ammount. In terms of impact on other requirements though, security does potentially have a large impact so when a system is trying to determine which mechanisms to use and whether the requirements can be met security will clearly be a major influence. Authentication Strength Authentication aims to ensure that a principal is who they claim to be. For each role in a communication (see 2.1) there is a strength for the authentication of the principle who has taken on that role. The principal could be a person, organisation or other legal entity. It could not be a process since a process has no legal representation. Requirement: That the cost of hijacking a role is in excess of the specified amount. Each role is a different requirement. Type: Abstract Currency Strictest Requirement: budget of largest attacker Example Application: inter-governmental conference Tamper-proofing This allows the application to specify how much security will be applied to ensuring that a communication is not tampered with. This is specified as the minimum cost of successfully tampering with the communication. Each non-security requirement has a tamper-proofing requirement attached to it. Requirement: The cost of tampering with the communication is in excess of the specified amount. Type: Abstract Currency: data is unchanged and complete? Abstract Currency: no replay of transmission is= possible? Abstract Currency: data timeliness is assured (no= malicious packet delay)? Strictest Requirement: Each budget of largest attacker Example Application: stock price feed Non-repudiation strength The non-repdiation strength defines how much care is taken to make sure there is a reliable audit trail on all interactions. It is measured as the cost of faking an audit trail, and therefore being able to "prove" an untrue event. There are a number of possible parameters of the event that need to be proved. The following list is not exclusive but shows the typical set of requirements. 1. Time 2. Ordering (when relative to other events) 3. Whom 4. What (the event itself) There are a number of events that need to be provable. 1. sender proved sent 2. receiver proves received 3. sender proves received. Type: Abstract Currency Strictest Requirement: Budget of largest attacker Example Application: Full audit trail: billing based on usage logs. Random partial records: to deter users from fraud with the threat of the possibility of being able to detect it. Denial of service There may be a requirement for some systems (999,911,112 emergency sevices access for example) that denial of service attacks cannot be launched. While this is difficult (maybe impossible) in many systems at the moment it is still a requirement, just one that can't be met. Type: Abstract Currency Meaning: Cost of launching a denial of service attack is greater than specified amount. Strictest Requirement: budget of largest attacker Example Application: web hosting, to prevent individual hackers stalling system. Action restriction For any given comunication there are a two actions, send and receive. Operations like adding to members to a group are done as a send to the membership list. Examining the list is a request to and receive from the list. Other actions can be generalised to send and receive on some communication, or are application level not comms level issues. Type: Membership list/rule for each action. Strictest Requirement: Send and receive have different policies. Example Application: TV broadcast, sender policy defines transmitter, receiver policy is null. NB: Several actions may share the same membership policy. Privacy Privacy defines how well obscured a principals identity is. This could be for any interaction. A list of participants may be obscured, a sender may obscure their identity when they send. For each possible action there is a need to define the privacy required. There are also different types of privacy. For example knowing two messages were sent by the same person breaks the strongest type of privacy even if the identity of that sender is still unknown. For each "level" of privacy there is a cost associated with violating it. The requirement is that this cost is excessive for the attacker. Type: Abstract Currency Meaning: Level of privacy, expected cost to violate privacy level for:- =B7 openly identified =B7 anonymously identified (messages from the same sender can be linked) =B7 unadvertised (but tracable) [ed:what does this mean?] =B7 undetectable Strictest Requirement: All levels budget of attacker Example Application: Secret ballot voting system - anonymously identified Retransmit prevention strength This is extremely hard at the moment. This is not to say it's not a requirement. Type: Abstract Currency Meaning: The cost of retransmitting a secure piece of information should exceed the specified amount. Strictest Requirement: Cost of retransmitting value of information Membership Criteria If a principal attempts to participate in a communication then a check will be made to see if it is allowed to do so. The requirement is that certain principals will be allowed, and others excluded. Given the application is being protected from network details there are only two types of specification available, per user, and per organisation (where an organisation may contain other organisations, and each user may be a member of multiple organisations). Rules could however be built on properties of a user, for example does the user own a key? Host properties could also be used, so users on slow hosts or hosts running the wrong OS could be excluded. Type: Macros Meaning: Include or exclude =B7 users (list) =B7 organisations (list) =B7 hosts (list) =B7 user properties (rule) =B7 org properties (rule) =B7 hosts properties (rule) Strictest Requirement: List of individual users Example Application: Corporate video-conference - organisation membership Membership Principals Entities that may join a rule-based secure session atomically. That is, a group of individuals is a principal if they can only all join or leave together. Principals can be considered as the SUBJECT field of an access control list, but this is not intended to imply ACL is a good method to use. Type: Enumeration Meaning: values: certified individuals certified group ids (corporations, organisations) lists (i.e. lists of lists, such as multicast groups, secure sessions) hosts [ed:get Bob to explain] Strictest Requirement: mixture of all types. Example Application: N/A Collusion prevention Which aspects of collusion it is required to prevent. Collusion is defined as malicious co-operation between members of a secure session. Superficially, it would appear that collusion is not a relevant threat in a multicast, because everyone has the same information, however, wherever there is differentiation, it can be exploited. Type: Abstract Currency Meaning: time race collusion - cost of colluding key encryption key (KEK) sharing - cost of colluding sharing of differential QoS (not strictly collusion as across sessions not within one) - cost of colluding =20 Strictest Requirement: For all threats cost attackers combined resources Example Application: A race where delay of the start signal may be allowed for, but one participant may fake packet delay while receiving the start signal from another participant. NB: Time race collusion is the most difficult one to prevent. Also note that while these may be requirements for some systems this does not mean there are neccessarily solutions. Setting tough requirements may result in the middleware being unable to create a valid channel. Fairness Fairness is orthogonal to many other requirements. Of particular interest are Reliability and Timeliness requirements. When a communication is first created the creator may wish to specify a set of requirements for these parameters. Principals which join later may wish to set tigher limits. Fairness enforces a policy that any improvement is requirement by one principal must be matched by all others, in effect requirements can only be set for the whole group. This increases the likelyhood that requirements of this kind will fail to be met. If fairness if not an issue then some parts of the network can use more friendly methods to achieve those simpler requirements. Type: delta of the requirement that needs to be fair. Meaning: The variance of performance with respect to any other requirement is less than the specified amount. Example Application: Networked game, latency to receive positions of players must be within 5ms for all players. Action on compromise The action to take on detection of compromise (until security reassured). Not sure this has anything to do with communications, really. Type: Boolean Meaning: warn but continue pause Scope: Per communication Strictest Requirement: pause Example Application: Secure video conference - if intruder alert, everyone is warned, but they can continue while knowing not to discuss sensitive matters (cf. catering staff during a meeting). =20 3.2.7.1. Security Dynamics -------------------------- Security dynamics are the temporal properties of the security mechanisms that are deployed. They may affect other requirements such as latency or simply be a reflection of the security limitations of the system. The requirements are often concerned with abnormal circumstances (eg. system violation). Mean time between compromises This is not the same as the strength of a system. A fairly weak system may have a very long time between compromises because it is not worth breaking in to, or it is only worth it for very few people. Mean time between compromises is a combination of strength, incentive and scale. Type: Time Scope: Per communication Strictest Requirement: indefinate Example Application: Secure Shell - 1500hrs Compromise detection time limit The average time it must take to detect a compromise (one predicted in the design of the detection system, that is). Type: Time Scope: Per communication Strictest Requirement: Round trip time Example Application: Secure Shell - 2secs Compromise recovery time limit The maximum time it must take to re-seal the security after a breach. This combined with the compromise detection time limit defines how long the system must remain inactive to avoid more security breaches. For example if a compromise is detected in one minute, and recovery takes five, then one minute of traffic is now insecure and the members of the communication must remain silent for four minutes after detection while security is re- established. Type: Time Scope: Per communication Strictest Requirement: 1 second Example Application: Audio conference - 10 seconds 3.2.8. Payment & Charging ------------------------- Total Cost The total cost of communication must be limited to this amount. This would be useful for tranfer as opposed to stream type applications. Type: Currency Meaning: Maximum charge allowed Scope: Per user per communication Strictest Requirement: Free Example Application: File Transfer: comms cost must be < 1p/Mb Cost per Time This is the cost per unit time. Some applications may not be able to predict the duration of a communication. It may be more meaningful for those to be able to specifiy price per time instead. Type: Currency Scope: Per user per communication Strictest&Requirement: Free Example Application Video Conference - 15p / minute Cost per Mb This is the cost per unit of data. Some communications may be charged by the amount of data transfered. Some applications may prefer to specify requirements in this way. Type: Currency Scope: Per user per communication Strictest&Requirement: Free Example Application Email advertising - 15p / Mb 4. Mapping of Requirements to IETF Working Groups -------------------------= ------------------------ TBA 5. Further Work --------------- Attempt to simplify! Refine definitions and types. In particular clarify where enumerations aren't intended to be "one of" types. Complete specifying worst case values & example apps. Identification of scope of each parameter (per communication, per receiver, per sender etc.) to highlight potential heterogeneity problems Mapping between requirements and IETF Working Groups Exercising the taxonomy with some scenarios Exercising the taxonomy with some media-types which represent large sub- sets of application capabilities so can potentially be "macros" or shorthand to set values (or ranges) for a large number of parameters at once. 6. Security Considerations -------------------------= - See comprehensive security section of taxonomy. 7. References ------------- [Bagnall97] Bagnall Peter, Poppitt Alan, Example LSMA classifications [TBA] [refmcast] IP multicast ref [limitations] Pullen M, Myjak M, Bouwens C, Limitations of Internet Protocol Suite for Distributed Simulation in the Large Multicast Environment, Internet Draft, 26 Mar 1997, draft-ietf-lsma-limitations- 01.txt [scenarios] Seidensticker S, Smith W, Myjak W, Scenarios and Appropriate Protocols for Distributed Interactive Simulation, Internet Draft, 21 Jul 1997, draft-ietf-lsma-scenarios-01.txt [rmodp] Open Distributed Processing Reference Model (RM-ODP), ISO/IEC 10746-1 to 10746-4 or ITU-T (formerly CCITT) X.901 to X.904. Jan 1995. Catalogue entries: [blaze95] Blaze, Diffie, Rivest, Schneier, Shimomura, Thompson and Wiener, Paper on minimal key lengths for security in secret key ciphers? late 1995 8. Authors' Addresses --------------------- Bob Briscoe B54/74 BT Labs Martlesham Heath Ipswich, IP5 3RE England Phone: +44 1473 645196 Fax: +44 1473 640929 EMail: briscorj@boat.bt.com Home page: http://www.labs.bt.com/people/briscorj/ Peter Bagnall B54/74 BT Labs Martlesham Heath Ipswich, IP5 3RE England Phone: +44 1473 647372 Fax: +44 1473 640929 EMail: pbagnall@jungle.bt.co.uk Home page: http://www.labs.bt.com/people/bagnalpm/ Alan Poppitt B54/74 BT Labs Martlesham Heath Ipswich, IP5 3RE England Phone: +44 1473 640889 Fax: +44 1473 640929 EMail: apoppitt@jungle.bt.co.uk Home page: http://www.labs.bt.com/people/poppitag/