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XI. RECOMMENDATIONS We first present our basic recommendation and then provide detailed recommendations on aspects that require amplification. These are followed by additional considerations in several important areas relating to the transition plans. Many of our recommendations are closely related to each other, and care should be taken not to consider any single recommendation in isolation. BASIC RECOMMENDATION The committee unanimously recommends that DOD should adopt the ISO TP-4 (and IP) as DOD costandards with its TOP (and IP) and move toward eventual exclusive use of TP-4. Transition to use of the ISO standards, however, must be managed to maintain operational capabilities and mini- mize risks. The timing of the transition to use of these protocols is, therefore, a major concern, and the committee was divided on the best schedule to recommend. A majority of the committee favored immediate adoption of the ISO protocols as costandards with TOP, giving major procurements in 1984-85 the option of using these standards (Option l). A minority favored deferring adoption of the ISO protocols by the DOD until after a demon- stration of commercial quality implementations supporting military appli- cations (Option 2~. This difference is reflected in detailed recommenda- tions 2-4 below. The reasons for the two viewpoints are based on dif- ferences within the committee on the extent of the risk associated with adopting a protocol, TP-4, that has not been implemented on operational networks. DETAILED RECOMMENDATIONS In the following recommendations the committee provides details about actions that should be taken to implement the basic recommendations. Most of the recommendations involve actions that require the DOD to take the lead role, with occasional support from the NBS Institute for Computer Sciences and Technology. Some recommendations are directed more toward NBS. Other government agencies and parties interested in using DOD pro- tocols or in their future evolution may also find these recommendations applicable. 61

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(1). DOD should rapidly identify "open areas" of the ISO TP-4 speci- fications where various options for implementation are allowed and define a required subset for use in DOD systems (a MIL-SPEC version of the standards, for example). In doing this, the DOD should work with the NBS with the goal of developing a Federal Standard, that has relatively few options for implementation, facilitates maximum federal interoperability, and makes it clear to vendors which functions are required in their commercial products. (2~. DOD should aggressively develop and implement a plan for integra- tion of TP-4 as a costandard with TCP and for migration toward its eventual exclusive use. The plan should include provision for rapid completion of a MIL-SPEC (detailed recommendation 1), either validation or demonstration facilities (detailed recommendation 3), timing for procurement of systems with the new protocols (detailed recommendation 4), development of equipment and procedures to support a period of joint operation with both TCP and TP-4 protocols in use, and guidelines for eventual con- version of TCP systems to the new protocols. Whatever timing is chosen for the introduction of ISO protocols, an extended period must be expected when both TCP and TP-4 are in use in different systems. Hence equipment and procedures must be developed to Provide limited communication between systems using the two protocol sets. This will include dual protocol operation for some gateways, relay hosts, service hosts, and terminal concentrators. A secondary purpose of the test system described in detailed recommendation 3 should be to aid in development of this transition support equipment. Both a general transition strategy and specific transition plans for each existing system should be developed. The switchover from old to new protocols will take place at different times as appropriate for each sys- tem during an overall transition period of many years. (3~. As soon as possible, the DOD Should develop a protocol test facil- ity. If Option ~ is followed, this facility would serve primarily to validate implementations of both old and new protocol sets. If Option 2 is followed, the facility would initially focus on demonstrating the suitability of the new protocols for use in a military environment as rapidly as possible and then provide for testing of commercially supplied protocol implementations. For validation purposes, the NBS protocol-testing facility developed for ISO protocols should serve as a good basis, but extensions to deal with any DOD-specific option for the ISO protocols, performance, and DOD protocols would be necessary. DOD is now beginning such a program. -62-

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For a more complete demonstration, commercial-quality implementations of the ISO protocols must be obtained and shown to support military appli- cations in an operational subnetwork such as such as ARPANET or DODITS. In both cases the facility should also be used for development and demon- stration of the transition support equipment mentioned in detailed recom- mendation 2. (4~. Procurements of new networks and major upgrades of existing networks should favor use of ISO TP-4 as rapidly as possible. If Option ~ is followed, RFPs may specify the new protocols immediately. If Option 2 is followed, this must await successful completion of the demonstration discussed in recommendation 3. Procurements for existing networks using TOP may continue to require TCP-based equipment until an appropriate conversion point is reached (see detailed recommendation 2) . The purpose of this recommendation~is to minimize spending on new TOP implementations and their subsequent conversion to TP-4 where possible, while recognizing that some additions to TCP-based systems wi l l al so be needed. If Option 2 is followed, immediate requirements for new systems may force new implementations of TCP in these cases also because the demonstration is not completed at the time RFPs must be issued. (5~. As part of a transition plan, a transport service interface to higher-level protocols more like that of TP-4 should be developed for TCP and tested with existing higher-layer protocols. This should serve as a rapid test of whether existing DOD protocols can make effective use of the somewhat different style of service that TP-4 provides. It should also allow higher-level protocols to be modified to make use of TP-4 in parallel with the implementation of TP-4 itself, making the ultimate transition to TP-4 more rapid and certain of success. Finally, it may allow use of a single version of the higher- leve] protocols to be used on both TCP and TP-4 equipment. (6~. DOD should continue using existing DOD-specific, higher-level proto- cols for operational purposes (Teinet, FTP, and Simple Mail Transfer Protocol, for example) but minimize effort on their further development and plan to adopt suitable ISO protocols as they are developed. Research on protocols providing new services (multimedia mail, compressed video, and voice store-and-forward, for example) should continue. The committee is pleased to find that DOD is already pursuing this course of action. (7~. The NBS Institute for Computer Sciences and Technology should main- tain close liaison with DOD to ensure that DOD needs for new protocols and modifications to existing standards are effectively represented to appropriate standards bodies. This should include research areas such as multimedia mail where there is significant commercial as well as military i merest. -63-

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The committee is pleased to find that this is already being done through contracts from DOD for ICST to represent its interests in standardization activities. Further cooperation (in demonstrating and testing protocols, for example) could occur. (8~. The NBS and DOD should collaborate from the outset in the development of new protocols for use as federal standards. This will ensure early agreement on functions, features, and services of the protocols under development. The NBS should present the developing work early to the ISO standardization activities to expedite convergence on internationally acceptable standards. Such collaboration could help ensure that future protocol standards will be developed in a single, coordinated process that results in a single standard accommodating both DOD, other federal agencies, and commercial needs. (9~. DOD and NBS should develop additions to protocol specifications to support preemption of limited resources by high-precedence users. Such capabilities are needed during high-load situations such as might develop during wartime or other crisis situations. They are not yet part of either the TOP or TP-4 specifications or existing imp] ementations. Th i s should be an example of the sort of collaboration mentioned in detailed recommendations 7 and 8. This is important to avoid possible incompatibilities between dif- ferent implementations of the same specification as discussed in Section ITI. It is likely that vendors would welcome guidance on how to deal with open areas of the specifications, and early action by DOD could result in their mandated subset becoming the de facto standard for most commercial implementations as well, with consequent benefits to DOD. This is a good area for cooperation between DOD and NBS. ADDITIONAL CONSIDERATIONS Transition Plan This section describes the major elements of a transition plan from use of TOP to use of TP-4 in DOD systems. The plan will vary depending on the option chosen. Both Option ~ and Option 2 share a number of common elements that are discussed first, including development of a MIL-SPEC, protocol-testing facilities, and transition support equipment. If Option 2 is followed, a demonstration of TP-4 must also be undertaken. MIL-SPEC. As noted in recommendation 1, several open areas and options in the ISO TP-4 must be specified in order to have complete and compatible protocol implementations. Completion of this specification by the DOD should be a top priority -64-

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Protocol-Testing Facilities. As noted in recommendation 3, test facilities for protocol implementations are essential. Under Option 1, this facility should serve primarily to validate implementations of both old and new protocol sets. If Option 2 is followed, the facility should initially focus on demonstrating the suitability of the new protocols for use in a military environment as rapidly as possible, and provide for testing of commercially supplied protocol implementations. For validation purposes, the NBS protocol-testing facility developed for ISO protocols should serve as a good basis, but extensions to deal with any DOD-specific options for the ISO protocols, performance, and DOD protocols would be necessary. The DOD has stated that such a program has been started. Transition Support Equipment. In any transition plan it must be assumed that the large body of systems with existing TOP implementations will take a substantial period of time to switch completely to the use of the ISO protocols. Some networks will include many different communities sharing a common communications backbone. Members of one community communicate primarily among themselves, but occasionally outside their community. While members of one community are likely to change over as a group, different communities will change to use the new protocols at different times. Hence an interim period must be anticipated when some systems are using the old protocols and others, the new protocols. The transition plan must provide some means of allowing interaction between old and new systems where required during this period. Toward this end, a number of relay hosts may need to be developed that support both old and new protocols. These will allow automatic-staged forwarding of electronic mail between old and new systems and manually set up file transfer or remote terminal access via the relays. Performance through these relays will not be as good as with direct connections, but the relays should provide an adequate level of service for occasional interactions among different communities of the internet system. When more frequent interaction is anticipated and better service is needed, major service hosts should support both old and new protocol sets concurrently so they can provide service directly without requiring the use of relays. Such service hosts include widely used time-sharing machines, file servers, and special servers such as Network Information Centers, Network Operations Centers, and Administrator Machines (provid- ing mailboxes of network administrators, for example). Some dual proto- co] servers may also act as relays where the load of both functions can be supported. Terminal concentrators for general use must also support both protocol sets so that connections to both old and new hosts can be made directly. -65-

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Gateways must support both old and new IPs so hosts using either one may send internet traffic. This requirement could be relaxed in the case of entire networks that will switch over simultaneously and hence will only need one type of IP traffic. Gateways should not have to translate between old and new IPs--it will be assumed that both source and destination hosts are using the same protocols or going through an explicit relay intermediate host. This latter point requires some elaboration. If one type of IP packet arrives at a destination host or gateway that only handles the other type, it must be discarded. It would be good if, in addition, a suitable ICMP error packet could be returned in the unsupported protocol so it would be meaningful to the source. To avoid this situation the internet-host name table maintained by the Network Information Center - should indicate which protocolts) each host supports. Then when a source host looks up the address of a destination, it will also determine which type protocol to use or if a relay is required. Demonstration Plan - If Option 2 is followed, a major demonstration of the ISO protocols in a military environment must be undertaken. Any such demonstration should proceed by stages beginning with the implementation of TP-4 in one network.~5 Then the demonstration would be extended to include inter- netting (still with DOD IP) to validate the suitability of TP-4 as a replacement for TOP. The demonstration would then be further extended to employ the ISO IP in place of DOD IP. Stand-Alone TP-4 Network-Demonstration. The first stage of any transition plan must be to establish a demonstration network or subnet- work using TP-4 in place of TOP under existing higher-level protocols. This step will require selection of a suitable network (or subnetwork), procurement of TP-4 implementations for hosts and terminal access con- trollers on that network, and modification of higher-level protocols to use TP-4. The demonstration should include sufficient use of real applications to test the protocols in an operational environment. To limit the amount of change attempted at one time, the DOD IP may be retained and used under TP-4. Alternatively, if ISO IP development status seems to warrant it, ISO IP may be installed along with TP-4. ]5For the remainder of this chapter, the use of TOP and TP-4 to include their respective IPs will no longer hold. The four entities--Transmission Control Protocol (TCP) and its Internet Protocol (DOD IP) and the Transport Protocol (TP-4) and its Internetwork Protocol (ISO IP)--will be treated individually. -66 -

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In the latter case, all TP-4 hosts would be on the same network anyway, so that IP will only be used between hosts and no gateways will be involved and no gateway modifications will be needed. The hosts involved could be dedicated to the demonstration and hence only support TP-4 and only be able to interact with other demonstration network hosts or be concurrently supporting TOP and DOD IP for operational traffic to other "normal" hosts. In the latter case, no forwarding or relaying of traffic by hosts between normal and ISO logical networks would be allowed or performed (the demonstration network would be logically closed). Stand-Alone TP-4 Internet Demonstration. The next step would be to expand the demonstration to include more than one network (at least logically) and hence involve gateways. If only TP-4 is involved, this is a simple extension to test TP-4 over longer internet paths with more variable performance. If ISO IP is also being tested at the same time, modification of the gateways involved will also be required as indicated in the next section. Stand-Alone ISO IP Demonstration. Once TP-4 has been tested, . introduction of the ISO IP to replace DOD IP may commence. In addition to simply replacing one IP with the other in hosts and gateways, this will require modification of the gateways to perform ICMP and GGP on top of the ISO IP. These gateways could either be dedicated to the demonstration and hence have only ISO IP, or could be concurrently supportin g normal o pera- tional traffic via DOD IP. In the latter case, once again, no forwarding of traffic between ISO demonstration internet and normal systems would be allowed. At the conclusion of these three steps, the ISO TP-4 and IP could be deemed to have demonstrated their basic functional suitability in a military environment. The transition support equipment described above should have been developed in parallel, providing the capability to smoothly and successfully switch operational systems using the old protocols to use of the new protocols. Switchover of User Systems Once the above preparations have been made and the demonstration completed, if Option 2 is being followed, the switchover of user systems can commence. Each network or commun i ty wi thi n a network should be able to switch at its convenience and maintain the ability to interact with other systems. The user systems will not be required to support opera- tional use of both protocol sets simultaneously at any time unless they wish to do so for their own reliability purposes. -67-

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Switchover of user systems also requires a personnel-training effort. While earlier steps involved a relatively small number of specialists and support staff at major sites, this step wild affect all user sites, and their network support staff must be trained in the new procedures. Once switchover of all systems to the new protocol set is complete, support for the old protocols by TACS, service hosts, and gateways can be removed. Lessons Learned from-the ARPANET NCP-to-TCP Transition The following points summarize some important lessons learned during the ARPANET transition from NCP to TCP.~6 Conversion of TACs and service hosts to support both protocols before the transition of user hosts starts is essential. Relay capabilities were heavily used for mail, but used little for other purposes. The Network Information Center was not ready to support the new protocols and this caused problems in distributing the host name table. There were significant performance probe ems that required care- ful analysis and parameter tuning after the transition. These were unavoidable because no service host had been stressed prior to the switchover, with a full user load over a long time period using the new protocols. i6For additional information, see ARPANET Request for Comments: NCP/TCP Transition Plan, d. Postel, (Menlo Park, California: SR] International Telecommunications Sciences Center, November 1981~. -68-