- Email: [email protected]
The Swiss national network for research and education (SWITCH)
75
Present Situation
The Swiss National Network for Research and Education(SWITCH) Bernhard PLATTNER Institut fOr Informatik, Eidgeni~ssische Technische Hochschule Ziirich (ETH), Ziirich, Switzerland (Tel.: + 41 1 256 5250; E-mail: [email protected], ch)
SWITCH is the n a m e of both the Swiss national network for research and education and the organization that is currently planning and implementing it. This paper describes the organizational environment of the project, the services to be offered to researchers and students at Swiss universities and the technical solutions that were selected to implement the network.
Keywords: Research Network, Services, Protocols, Gateways, L A N Interconnection, X.400, MHS, OSI Applications, File Transfer, SWITCH.
Berhard Plattner is a professor of computer science at ETH, leading a group doing research on communication systems, especially applications and higher layer protocols. At the time of writing, he was the interim director of S W I T C H and the chairman of a technical working groups which did a large part of the technical planning for SWITCH. His research interests also include real-time computing, process execution monitoring and debugging. North-Holland Computer Networks and ISDN Systems 16 (1988/89) 75-82
1. Introduction In 1986 The Swiss Federal Councils decided to support education and research in information technology and engineering with more than 200 million SFr; the funds were to be invested in advanced workstations, supercomputing, research personnel and a Swiss national network for research and education. Academic networking in Switzerland had started only about one year earlier: The Swiss part of EARN had become operational, and experimental mail services based on the U U C P network and early X.400 implementations (EAN [1]) started to be used in Swiss universities. The latter evolved to C H U N E T (Swiss University Network), a part of the European Research and Development MHS of RARE. Moreover, administrators of DECnet nodes were building a Switzerland-wide DECnet which would become known under the name of C H A D N E T (Swiss Academic DECnet) [2]. A working group under the direction of Jiirgen Harms, which since late 1984 had prepared the network proposal for the Federal Councils, started to elaborate on a project for the future network. A document describing the organizational basis and the services to be offered was first published early in 1987; a revised version appeared in September the same year. It was proposed to form a foundation (with the Swiss Federal Government and the governments of those cantons that run universities as co-founders). The proposal eventually led to the constitution of the SWITCH foundation in 1987. The organization was granted 15 million SFr for planning and implementing the SWITCH network. In addition, the founders committed their governments to contribute to the operation of the network, once official services were offered. Switzerland has eight universities and two
016%7552/88/$3.50 © 1988, Elsevier Science Publishers B.V. (North-Holland)
76
B. Plattner / S W I T C H
federal institutes of technology totalling some 85000 students and 6000 faculties. Another 23 colleges of higher education will profit from SWITCH communication services in a later phase. Obviously some form of association of CERN with SWITCH would be mutually beneficial; this issue is currently being discussed.
2. Goals and Working Hypothesis One of the driving forces in this process clearly was the arrangement EARN had made with CEPT. Since according to it the lifetime of EARN in its initial implementation is limited, a successor needs to be put into operation in 1988 or 1989. Therefore, one of the basic assumptions is that SWITCH would be required to offer similar and preferably better services in terms of functionality and quality. Specifically, SWITCH will have to provide mechanisms for the exchange of information between persons and access to the supercomputers in Zurich and Lausanne, as well as to information services (libraries and directories). Since Switzerland is a member of RARE and partner in COSINE, and Open Systems Interconnection is considered to be an important factor in inter-organization communications, the technology used by SWITCH is required to conform to international standards. However, non-standard intermediary solutions will be considered in cases where mature standards and by consequence conforming implementations are not yet available. SWITCH will be based on the bearer services offered by the Swiss PTT, as long as these services fulfill the requirements of the academic community and provided that no severe economic concerns prevent their usage. In the first place, the Swiss X.25 network, TELEPAC, will be used. As will be explained in Section 4, a combination of bridged LANs and layer 3 routers will complement TELEPAC as a transport infrastructure for specific purpose. At a later stage, the ISDN offering in Switzerland (SWISSNET) will partially replace the services just mentioned. Swiss universities, just like most universities, are very heterogeneous organizations with a large degree of autonomy. Therefore, imposing a rigid data communications scheme on them would be futile. Instead, our concept relies on a well-defined boundary between the responsibilities of SWITCH
and those of the universities: So-called SWITCH Access Systems (SAS), to be discussed in Section 4, will be physically placed where the domains of responsibilities touch. This setup will allow the universities to plan, develop and operate their internal data communication facilities partly independent of SWITCH. The latter will be responsible for offering services for communication between the participating organizations, the evaluation of products (hardware and software) and the co-ordination of their usage. SWITCH normally will not develop communications software; instead, commercially available systems will be evaluated, purchased and made available to the participant organization--if possible under site licenses.
3. Services SWITCH will offer five services that are considered necessary to cover the academic user's needs (see also Fig. 1): -SWITCHmaiI: An interpersonal messaging service with worldwide connectivity, based on the CCITT recommendation X.400 [3]. Basic X.400 functions are complemented by gateways to other mail networks, bulletin boards and conferencing facihties. - SWITCHfile: A file transfer service based on FTAM (ISO 8571). Since commercial implementations will probably be available only in 1990, intermediary solutions based on EARN, T C P / I P (FTP) and DECnet are envisaged. - SWITCHjob: A remote job submission service to be based on the forthcoming JTM (ISO 883 x ) standard. EARN job submission functions will serve as an intermediary solution. - SWITCHterminal: Interactive access to supercomputers, special applications, library and information services. On the long term, the ISO virtual terminal service and protocol may provide a solution. However, we anticipate a rather long period with services based on X.25, T C P / I P (TELNET) and DECnet. - SWITCHinfo: A user and network information service which will use the I S O / C C I T T Directory Service standard 9594/X.500 [4]. A low profile intermediary solution using existing technology is planned; however, since the standard has advanced faster than expected
B. Plattner / S W I T C H !
Start of SWITCH services: 1.4.88
• 11
Service
1987
1988
2
3
T
T
77 5
T
-1989 ' - ' - - T ' - - -1990 --
1~1
1~2
I
1~3
1988) IPMS
x,4ooogs4) i Gateways
SWITCHmail
I
s to public MHS
S~mple
SWITCHfile
function F'rAM
FTAM (/Vl11)
ISO JTM
SWITCHjob
In~raclive ~
~ ! SWISSNET/ISDN
(as a swn'cll service)
V.2n via PSTN
SWlTCHinfo qETSERV)
l',iiiiiii!l::::i::,:ii::iiii::::i:i:L::i:iiiiiiiiiii',l
Defirdlive servi~s (conforming to international standards)
J
Fig. 1. Phased introduction of SWITCH services.
and considering the successful work in the context of RARE Working Group 3 on OSI directories, we hope that an OSI service can be operational earlier than Fig. 1 indicates. SWITCHfile and SWITCHterminal on the one hand, and SWlTCHjob on the other hand provide the necessary facilities to access supercomputers interactively and in batch mode, respectively. Figure 1 gives an approximate timetable for the introduction of SWITCH services. Note that SWITCH officially started its operation on the 1st of April, 1988. This does not imply, however, that at this date new services were introduced; it rather signifies that since this date the existing ones are run under the auspices of SWITCH. Figure 2 illustrates the protocols that will be used in SWITCH while intermediary are operated, i.e. between 1989 and approximately 1991.
4. The S W I T C H Architecture
4.1. S W I T C H Access Systems As mentioned in Section 2, we strive at a clear separation between the responsibilities of the participating organizations and SWITCH. The separation will be supported physically by S W I T C H Access Systems (SAS) at the boundary between SWITCH and the universities (Fig. 3). Besides marking the border between SWITCH and the universities, the SAS will carry all traffic that enters or leaves a university. While this implies a potential b o t t l e n e c k - - a problem which may be attacked by selecting products allowing performance scaling-- it also offers considerable advantages:
78
B. Plattner / S W I T C H SWlTCHmail
SWITCHfile SWlTCHterminal SWlTCHjob
CCITT X.400 (MRS)
FTP DECNET
TELNET DECNET a < o_ Central directory service, accessible via SWlTCHmail and SWlTCHterminal
X
ISO/CCITT standard protocols
(xl
TCP/IP DECNET
z rr < ILl
X ¢q
>
TELEPAC SWlTCHlan
TELEPAC
SWlTCHinfo
EARN
0 < n 1.1.1 .J !l.U
TELEPAC SWlTCHlan
i Fig. 2. Protocolstacks used during an intermediaryphase. - The SAS hides from SWITCH the usually complex topology of the intra-university network; It creates a single point where statistics may be gathered about inter-university traffic. SWITCH accounting mechanisms will also be placed in the SAS; It creates a narrow interface between the university and the providers of wide-area communication, such as the PTT and SWITCH; It will ease the management of routing tables. Obviously, the concept of an SAS is not applicable in the context of end-to-end protocols, which are normally used in layers 4 and higher. Therefore, the functions of an SAS are limited to - layer 2 bridges (MAC level bridges for LAN interconnection), - layer 3 routers and relays, -
-
-
4
Univ. A
layer 7 routers and relays; prominent instances of systems utilizing layer 7 store-and-forward techniques are X.400 message handling systems, layer 7 gateways. The SAS also appears to be useful for achieving full transport layer connectivity, an issue which the European network community has been discussing for some time. Since European wide-area communication services are connection-oriented (public X.25 services), and the intra-university infrastructure, based on LAN technology, tends to be operated in a connection-less mode, the two variants of transport protocols that would be used according to ISO (class 0 and class 4) clash. Three solutions are discussed: - Using a transport relay, i.e. a transport level gateway between TP0 and TP4; -
-
Univ. B
"~
(X.25fFELEPAC, leased lines,
_ _
Responsibility of SWITCH
-Responsibility -I of Universitiy F
Fig. 3. SWITCHarchitecturalmodel.
~,
79
B. Plattner / S W I T C H OSI (X.400) networks (RARE)
Central SWITCH
non-OSl networks
. \ \ Central
Telex Teletex Postal Mail
\
~ ~
Transport Networks )" (TELEPAC, SWITOHlan)
~ /
\
Fig. 4. Topology of SWITCHmail.
- Consistent usage of X.25 for wide and local area communication, i.e. using the X.25 packet level protocol on top of LLC2 in the LAN environment; Using the ISO connection-less Internet Protocol on top of wide-area X.25. Specific functions required with all three solutions would naturally be implemented in the SAS. 4.2. SWITCHmail The SAS approach is best demonstrated by the operational model and topology of SWITCHmail,
illustrated by Fig. 4. SWITCHmail currently uses, and will use, X.400 protocols between universities and with other X.400-based mail networks in Europe, such as the RARE R & D message handling system and--in the future--COSINE. A S W I T C H Central System (SCS) therefore acts as a single entry and exit point to/from the Swiss academic environment. The SAS will perform a similar task for each university. In terms of X.400, both SCS and SAS are message transfer agents (MTA) which route and relay messages, gather statistics and support accounting mechanisms. The architecture is not strictly hierarchical since direct associations between SAS will normally be established for traffic within Switzerland. The SAS will also connect to the public X.400 service planned by the Swiss PTT (arCom4°°) which, besides establishing additional X.400 connectivity, will provide SWITCH with gateways to TELEX, TELETEX and postal mail services. The SCS also provides connectivity to nonX.400 mail networks like CSnet, ARPANET, BITNET/EARN, etc., at least as long as no common European gateway assumes these functions. Similar gateway functions will also to be built into the SAS, since it may not be possible to achieve a complete X.400 penetration of the universities from the start. Several obstacles hamper the spread of X.400 in this environment, e.g. unavailability of products for certain models of computes and the quality and price of available products. Moreover, most X.400 implementations integrally support lower layer OSI protocols and
B
CER
'-='=-- 2Mbit/s leased lines
64kbit/s or 2Mbit/s
=="=~
leased lines
Fig. 5. The topology of SWITCHlan.
80
B. Plattner / S W I T C H
C)
ETHERNETMAC level bridge O IP router Fig. 6. SWITCHIanusage of bridges and routers.
will first be available with X.25 and transport class 0, thereby conflicting with the LAN environment used in the universities. Hence, SAS will provide local gateway facilities, i.e. connects X.400 with SMTP, UUCP, RSCS and other commonly used mail protocols. More detailed information about SWITCHmail, especially about naming and addressing, is given in a companion paper in this issue [5]. 4.3. S W I T C H l a n
As outlined in Section 3, the intermediary solutions envisaged for SWITCHfile and SWITCHterminal depend on T C P / I P and DECnet. Since both protocol suites run well on Ethernets, one way of supporting a multi-protocol, wide-area transport infrastructure is to link Ethernet seg-
ments located in the universities with MAC-level bridges, i.e. devices that store and forward Ethernet packets. SWITCH thus plans to establish a wide-area network using LAN bridges as depicted in Fig. 5. The main goal of this infrastructure we call SWITCHlan is to provide confortable access to Swiss supercomputers or their frontends. Two star h u b s - - a t ETH Ziirich (ETHZ) and Lausanne (EPFL), future supercomputer sites--have already been interconnected with a 2 M b i t / s link leased from the public services; an additional link going through the University of Bern is under consideration. The universities in the neighborhood of the two hubs will be connected to them by 64 k b i t / s or preferably 2 M b i t / s leased lines. Obviously, not all existing nodes (including many personal workstations like SUNs and hundreds of Apple Macintosh II) can be in-
Fig. 7. SAS functions: Layer 7.
B. Plattner / S W I T C H
81
X.25 Switch PAD
DECNET Router
~!iiiiDECNET
IP Router Fi ;. 8. SAS functions: Layer 3.
tegrated into a Switzerland-wide Ethernet. SWlTCHlan should rather be seen as a multi-protocol backbone, linking the T C P / I P or DECnet based networks of the Swiss universities. Thus, the intra-university Ethernets will not be bridged with SWITCHlan; instead, T C P / I P or DECnet routers will be used to connect into the universities (see also Fig. 6).
4.4. S W I T C H Access Systems Reoisited T h e subsections on S W l T C H m a i l and SWITCHlan served to concretize our notion of a SAS. The SAS will consist of possibly several physical systems that collectively offer layer 7 routing for SWlTCHmail, and D O D IP routing, DECnet routing and MAC level bridging for SWlTCHlan. X.25 switching and PAD functions will also be placed into a SAS where required. Figures 7 - 9 illustrate the various SAS components in different layers.
X.21
Telepac connection G.7xx 2Mbit/s 64kBit/s
X.25 Switch / ~ PAD - IEEE 802.3 MAC level
bridge
X.21 X.28 t
SAS IEEE 802.3 segment
Fig. 9. SAS functions: Layer 2 and 1.
5. Summary and Outlook The services SWITCH will offer are ubiquitous --almost all national academic networks being built plan to, or do offer their users the same or similar capabilities. Switzerland's speciality is its smallness: Interconnecting 10 organizations seems to be a manageable task. We therefore take a rather centralized approach as long as interconnection of the organizations is the concern, and allow as much freedom as possible for the deployment of intra-university communications. Still implementing SWITCH is an ambitious undertaking. Since the rather small personnel basis of SWITCH does not allow to pursue the detailed specification and implementation of all services at once, SWITCHmail and SWITCHlan have been given priority. The X.400 MHS in Switzerland, which has been operational for two and a half years now, has provided us with many experiences both in establishing a working system and performing day-to-day management. Much of the previous work, however, was done by idealistic and committed persons belonging to research groups in some of the Swiss universities. One important task to be finished is to hand the achievements over to a staff that will professionally operate and develop the future network. SWITCH is currently evaluating the results of a request for information, which yielded numerous answers to specific questions asked about the ca-
82
B. Plattner / SWITCH
pabilities of potential equipment for SWITCHlan and of X.400 implementations. The next step will be to come up with a specific selection of products for SAS components in all relevant layers and recommendations for the software to be run in the end-systems, i.e. in the computers currently installed at the universities. A performance analysis and simulation of SWITCHlan was contracted, the results of which will be available in the third quarter of 1988. It will provide numerical data about expected queue lengths given the SWITCHlan interconnection scheme and estimated traffic figures.
Acknowledgment Many people contributed to the work described in this paper. The author wishes to acknowledge
the work done in the SWITCH working group directed by Jiirgen Harms, and its technical subgroup, which the author had the pleasure to chair.
References [1] G. Neufeld, EAN: A Distributed Message System, Proc. Canadian Information Processing Society National Meeting, Ottawa (1983) 144-149. [2] R. Kessi, CHADNET, A Short Description, Swiss Institute for Nuclear Research, Villigen, Switzerland, 1987. [3] Recommendation X.400 ft., ITU, Geneva, 1984. [4] ISO DP9594/ CCITT Draft Recommendation X.500, Geneva, 1988. [5] H. Lubich and B. Plattner, Naming and Addressing in SWITCHmail, Computer Networks and ISDN Systems 16 (1988) 48-54, this issue.
Present Situation
The Swiss National Network for Research and Education(SWITCH) Bernhard PLATTNER Institut fOr Informatik, Eidgeni~ssische Technische Hochschule Ziirich (ETH), Ziirich, Switzerland (Tel.: + 41 1 256 5250; E-mail: [email protected], ch)
SWITCH is the n a m e of both the Swiss national network for research and education and the organization that is currently planning and implementing it. This paper describes the organizational environment of the project, the services to be offered to researchers and students at Swiss universities and the technical solutions that were selected to implement the network.
Keywords: Research Network, Services, Protocols, Gateways, L A N Interconnection, X.400, MHS, OSI Applications, File Transfer, SWITCH.
Berhard Plattner is a professor of computer science at ETH, leading a group doing research on communication systems, especially applications and higher layer protocols. At the time of writing, he was the interim director of S W I T C H and the chairman of a technical working groups which did a large part of the technical planning for SWITCH. His research interests also include real-time computing, process execution monitoring and debugging. North-Holland Computer Networks and ISDN Systems 16 (1988/89) 75-82
1. Introduction In 1986 The Swiss Federal Councils decided to support education and research in information technology and engineering with more than 200 million SFr; the funds were to be invested in advanced workstations, supercomputing, research personnel and a Swiss national network for research and education. Academic networking in Switzerland had started only about one year earlier: The Swiss part of EARN had become operational, and experimental mail services based on the U U C P network and early X.400 implementations (EAN [1]) started to be used in Swiss universities. The latter evolved to C H U N E T (Swiss University Network), a part of the European Research and Development MHS of RARE. Moreover, administrators of DECnet nodes were building a Switzerland-wide DECnet which would become known under the name of C H A D N E T (Swiss Academic DECnet) [2]. A working group under the direction of Jiirgen Harms, which since late 1984 had prepared the network proposal for the Federal Councils, started to elaborate on a project for the future network. A document describing the organizational basis and the services to be offered was first published early in 1987; a revised version appeared in September the same year. It was proposed to form a foundation (with the Swiss Federal Government and the governments of those cantons that run universities as co-founders). The proposal eventually led to the constitution of the SWITCH foundation in 1987. The organization was granted 15 million SFr for planning and implementing the SWITCH network. In addition, the founders committed their governments to contribute to the operation of the network, once official services were offered. Switzerland has eight universities and two
016%7552/88/$3.50 © 1988, Elsevier Science Publishers B.V. (North-Holland)
76
B. Plattner / S W I T C H
federal institutes of technology totalling some 85000 students and 6000 faculties. Another 23 colleges of higher education will profit from SWITCH communication services in a later phase. Obviously some form of association of CERN with SWITCH would be mutually beneficial; this issue is currently being discussed.
2. Goals and Working Hypothesis One of the driving forces in this process clearly was the arrangement EARN had made with CEPT. Since according to it the lifetime of EARN in its initial implementation is limited, a successor needs to be put into operation in 1988 or 1989. Therefore, one of the basic assumptions is that SWITCH would be required to offer similar and preferably better services in terms of functionality and quality. Specifically, SWITCH will have to provide mechanisms for the exchange of information between persons and access to the supercomputers in Zurich and Lausanne, as well as to information services (libraries and directories). Since Switzerland is a member of RARE and partner in COSINE, and Open Systems Interconnection is considered to be an important factor in inter-organization communications, the technology used by SWITCH is required to conform to international standards. However, non-standard intermediary solutions will be considered in cases where mature standards and by consequence conforming implementations are not yet available. SWITCH will be based on the bearer services offered by the Swiss PTT, as long as these services fulfill the requirements of the academic community and provided that no severe economic concerns prevent their usage. In the first place, the Swiss X.25 network, TELEPAC, will be used. As will be explained in Section 4, a combination of bridged LANs and layer 3 routers will complement TELEPAC as a transport infrastructure for specific purpose. At a later stage, the ISDN offering in Switzerland (SWISSNET) will partially replace the services just mentioned. Swiss universities, just like most universities, are very heterogeneous organizations with a large degree of autonomy. Therefore, imposing a rigid data communications scheme on them would be futile. Instead, our concept relies on a well-defined boundary between the responsibilities of SWITCH
and those of the universities: So-called SWITCH Access Systems (SAS), to be discussed in Section 4, will be physically placed where the domains of responsibilities touch. This setup will allow the universities to plan, develop and operate their internal data communication facilities partly independent of SWITCH. The latter will be responsible for offering services for communication between the participating organizations, the evaluation of products (hardware and software) and the co-ordination of their usage. SWITCH normally will not develop communications software; instead, commercially available systems will be evaluated, purchased and made available to the participant organization--if possible under site licenses.
3. Services SWITCH will offer five services that are considered necessary to cover the academic user's needs (see also Fig. 1): -SWITCHmaiI: An interpersonal messaging service with worldwide connectivity, based on the CCITT recommendation X.400 [3]. Basic X.400 functions are complemented by gateways to other mail networks, bulletin boards and conferencing facihties. - SWITCHfile: A file transfer service based on FTAM (ISO 8571). Since commercial implementations will probably be available only in 1990, intermediary solutions based on EARN, T C P / I P (FTP) and DECnet are envisaged. - SWITCHjob: A remote job submission service to be based on the forthcoming JTM (ISO 883 x ) standard. EARN job submission functions will serve as an intermediary solution. - SWITCHterminal: Interactive access to supercomputers, special applications, library and information services. On the long term, the ISO virtual terminal service and protocol may provide a solution. However, we anticipate a rather long period with services based on X.25, T C P / I P (TELNET) and DECnet. - SWITCHinfo: A user and network information service which will use the I S O / C C I T T Directory Service standard 9594/X.500 [4]. A low profile intermediary solution using existing technology is planned; however, since the standard has advanced faster than expected
B. Plattner / S W I T C H !
Start of SWITCH services: 1.4.88
• 11
Service
1987
1988
2
3
T
T
77 5
T
-1989 ' - ' - - T ' - - -1990 --
1~1
1~2
I
1~3
1988) IPMS
x,4ooogs4) i Gateways
SWITCHmail
I
s to public MHS
S~mple
SWITCHfile
function F'rAM
FTAM (/Vl11)
ISO JTM
SWITCHjob
In~raclive ~
~ ! SWISSNET/ISDN
(as a swn'cll service)
V.2n via PSTN
SWlTCHinfo qETSERV)
l',iiiiiii!l::::i::,:ii::iiii::::i:i:L::i:iiiiiiiiiii',l
Defirdlive servi~s (conforming to international standards)
J
Fig. 1. Phased introduction of SWITCH services.
and considering the successful work in the context of RARE Working Group 3 on OSI directories, we hope that an OSI service can be operational earlier than Fig. 1 indicates. SWITCHfile and SWITCHterminal on the one hand, and SWlTCHjob on the other hand provide the necessary facilities to access supercomputers interactively and in batch mode, respectively. Figure 1 gives an approximate timetable for the introduction of SWITCH services. Note that SWITCH officially started its operation on the 1st of April, 1988. This does not imply, however, that at this date new services were introduced; it rather signifies that since this date the existing ones are run under the auspices of SWITCH. Figure 2 illustrates the protocols that will be used in SWITCH while intermediary are operated, i.e. between 1989 and approximately 1991.
4. The S W I T C H Architecture
4.1. S W I T C H Access Systems As mentioned in Section 2, we strive at a clear separation between the responsibilities of the participating organizations and SWITCH. The separation will be supported physically by S W I T C H Access Systems (SAS) at the boundary between SWITCH and the universities (Fig. 3). Besides marking the border between SWITCH and the universities, the SAS will carry all traffic that enters or leaves a university. While this implies a potential b o t t l e n e c k - - a problem which may be attacked by selecting products allowing performance scaling-- it also offers considerable advantages:
78
B. Plattner / S W I T C H SWlTCHmail
SWITCHfile SWlTCHterminal SWlTCHjob
CCITT X.400 (MRS)
FTP DECNET
TELNET DECNET a < o_ Central directory service, accessible via SWlTCHmail and SWlTCHterminal
X
ISO/CCITT standard protocols
(xl
TCP/IP DECNET
z rr < ILl
X ¢q
>
TELEPAC SWlTCHlan
TELEPAC
SWlTCHinfo
EARN
0 < n 1.1.1 .J !l.U
TELEPAC SWlTCHlan
i Fig. 2. Protocolstacks used during an intermediaryphase. - The SAS hides from SWITCH the usually complex topology of the intra-university network; It creates a single point where statistics may be gathered about inter-university traffic. SWITCH accounting mechanisms will also be placed in the SAS; It creates a narrow interface between the university and the providers of wide-area communication, such as the PTT and SWITCH; It will ease the management of routing tables. Obviously, the concept of an SAS is not applicable in the context of end-to-end protocols, which are normally used in layers 4 and higher. Therefore, the functions of an SAS are limited to - layer 2 bridges (MAC level bridges for LAN interconnection), - layer 3 routers and relays, -
-
-
4
Univ. A
layer 7 routers and relays; prominent instances of systems utilizing layer 7 store-and-forward techniques are X.400 message handling systems, layer 7 gateways. The SAS also appears to be useful for achieving full transport layer connectivity, an issue which the European network community has been discussing for some time. Since European wide-area communication services are connection-oriented (public X.25 services), and the intra-university infrastructure, based on LAN technology, tends to be operated in a connection-less mode, the two variants of transport protocols that would be used according to ISO (class 0 and class 4) clash. Three solutions are discussed: - Using a transport relay, i.e. a transport level gateway between TP0 and TP4; -
-
Univ. B
"~
(X.25fFELEPAC, leased lines,
_ _
Responsibility of SWITCH
-Responsibility -I of Universitiy F
Fig. 3. SWITCHarchitecturalmodel.
~,
79
B. Plattner / S W I T C H OSI (X.400) networks (RARE)
Central SWITCH
non-OSl networks
. \ \ Central
Telex Teletex Postal Mail
\
~ ~
Transport Networks )" (TELEPAC, SWITOHlan)
~ /
\
Fig. 4. Topology of SWITCHmail.
- Consistent usage of X.25 for wide and local area communication, i.e. using the X.25 packet level protocol on top of LLC2 in the LAN environment; Using the ISO connection-less Internet Protocol on top of wide-area X.25. Specific functions required with all three solutions would naturally be implemented in the SAS. 4.2. SWITCHmail The SAS approach is best demonstrated by the operational model and topology of SWITCHmail,
illustrated by Fig. 4. SWITCHmail currently uses, and will use, X.400 protocols between universities and with other X.400-based mail networks in Europe, such as the RARE R & D message handling system and--in the future--COSINE. A S W I T C H Central System (SCS) therefore acts as a single entry and exit point to/from the Swiss academic environment. The SAS will perform a similar task for each university. In terms of X.400, both SCS and SAS are message transfer agents (MTA) which route and relay messages, gather statistics and support accounting mechanisms. The architecture is not strictly hierarchical since direct associations between SAS will normally be established for traffic within Switzerland. The SAS will also connect to the public X.400 service planned by the Swiss PTT (arCom4°°) which, besides establishing additional X.400 connectivity, will provide SWITCH with gateways to TELEX, TELETEX and postal mail services. The SCS also provides connectivity to nonX.400 mail networks like CSnet, ARPANET, BITNET/EARN, etc., at least as long as no common European gateway assumes these functions. Similar gateway functions will also to be built into the SAS, since it may not be possible to achieve a complete X.400 penetration of the universities from the start. Several obstacles hamper the spread of X.400 in this environment, e.g. unavailability of products for certain models of computes and the quality and price of available products. Moreover, most X.400 implementations integrally support lower layer OSI protocols and
B
CER
'-='=-- 2Mbit/s leased lines
64kbit/s or 2Mbit/s
=="=~
leased lines
Fig. 5. The topology of SWITCHlan.
80
B. Plattner / S W I T C H
C)
ETHERNETMAC level bridge O IP router Fig. 6. SWITCHIanusage of bridges and routers.
will first be available with X.25 and transport class 0, thereby conflicting with the LAN environment used in the universities. Hence, SAS will provide local gateway facilities, i.e. connects X.400 with SMTP, UUCP, RSCS and other commonly used mail protocols. More detailed information about SWITCHmail, especially about naming and addressing, is given in a companion paper in this issue [5]. 4.3. S W I T C H l a n
As outlined in Section 3, the intermediary solutions envisaged for SWITCHfile and SWITCHterminal depend on T C P / I P and DECnet. Since both protocol suites run well on Ethernets, one way of supporting a multi-protocol, wide-area transport infrastructure is to link Ethernet seg-
ments located in the universities with MAC-level bridges, i.e. devices that store and forward Ethernet packets. SWITCH thus plans to establish a wide-area network using LAN bridges as depicted in Fig. 5. The main goal of this infrastructure we call SWITCHlan is to provide confortable access to Swiss supercomputers or their frontends. Two star h u b s - - a t ETH Ziirich (ETHZ) and Lausanne (EPFL), future supercomputer sites--have already been interconnected with a 2 M b i t / s link leased from the public services; an additional link going through the University of Bern is under consideration. The universities in the neighborhood of the two hubs will be connected to them by 64 k b i t / s or preferably 2 M b i t / s leased lines. Obviously, not all existing nodes (including many personal workstations like SUNs and hundreds of Apple Macintosh II) can be in-
Fig. 7. SAS functions: Layer 7.
B. Plattner / S W I T C H
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X.25 Switch PAD
DECNET Router
~!iiiiDECNET
IP Router Fi ;. 8. SAS functions: Layer 3.
tegrated into a Switzerland-wide Ethernet. SWlTCHlan should rather be seen as a multi-protocol backbone, linking the T C P / I P or DECnet based networks of the Swiss universities. Thus, the intra-university Ethernets will not be bridged with SWITCHlan; instead, T C P / I P or DECnet routers will be used to connect into the universities (see also Fig. 6).
4.4. S W I T C H Access Systems Reoisited T h e subsections on S W l T C H m a i l and SWITCHlan served to concretize our notion of a SAS. The SAS will consist of possibly several physical systems that collectively offer layer 7 routing for SWlTCHmail, and D O D IP routing, DECnet routing and MAC level bridging for SWlTCHlan. X.25 switching and PAD functions will also be placed into a SAS where required. Figures 7 - 9 illustrate the various SAS components in different layers.
X.21
Telepac connection G.7xx 2Mbit/s 64kBit/s
X.25 Switch / ~ PAD - IEEE 802.3 MAC level
bridge
X.21 X.28 t
SAS IEEE 802.3 segment
Fig. 9. SAS functions: Layer 2 and 1.
5. Summary and Outlook The services SWITCH will offer are ubiquitous --almost all national academic networks being built plan to, or do offer their users the same or similar capabilities. Switzerland's speciality is its smallness: Interconnecting 10 organizations seems to be a manageable task. We therefore take a rather centralized approach as long as interconnection of the organizations is the concern, and allow as much freedom as possible for the deployment of intra-university communications. Still implementing SWITCH is an ambitious undertaking. Since the rather small personnel basis of SWITCH does not allow to pursue the detailed specification and implementation of all services at once, SWITCHmail and SWITCHlan have been given priority. The X.400 MHS in Switzerland, which has been operational for two and a half years now, has provided us with many experiences both in establishing a working system and performing day-to-day management. Much of the previous work, however, was done by idealistic and committed persons belonging to research groups in some of the Swiss universities. One important task to be finished is to hand the achievements over to a staff that will professionally operate and develop the future network. SWITCH is currently evaluating the results of a request for information, which yielded numerous answers to specific questions asked about the ca-
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pabilities of potential equipment for SWITCHlan and of X.400 implementations. The next step will be to come up with a specific selection of products for SAS components in all relevant layers and recommendations for the software to be run in the end-systems, i.e. in the computers currently installed at the universities. A performance analysis and simulation of SWITCHlan was contracted, the results of which will be available in the third quarter of 1988. It will provide numerical data about expected queue lengths given the SWITCHlan interconnection scheme and estimated traffic figures.
Acknowledgment Many people contributed to the work described in this paper. The author wishes to acknowledge
the work done in the SWITCH working group directed by Jiirgen Harms, and its technical subgroup, which the author had the pleasure to chair.
References [1] G. Neufeld, EAN: A Distributed Message System, Proc. Canadian Information Processing Society National Meeting, Ottawa (1983) 144-149. [2] R. Kessi, CHADNET, A Short Description, Swiss Institute for Nuclear Research, Villigen, Switzerland, 1987. [3] Recommendation X.400 ft., ITU, Geneva, 1984. [4] ISO DP9594/ CCITT Draft Recommendation X.500, Geneva, 1988. [5] H. Lubich and B. Plattner, Naming and Addressing in SWITCHmail, Computer Networks and ISDN Systems 16 (1988) 48-54, this issue.