Network Working Group W A Simpson Internet Draft Daydreamer expires in six months April 1993 SIP System Discovery Status of this Memo This memo is the product of the SIP Working Group of the Internet Engineering Task Force (IETF). Comments on this memo should be submitted to the sip@caldera.usc.edu mailing list. Distribution of this memo is unlimited. 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. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' Please check the 1id-abstracts.txt listing contained in the internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the current status of any Internet Draft. Abstract This document specifies ICMP messages for the identification and location of adjacent SIP systems. This is intended to replace ARP, ICMP Router Advertisement, ICMP Redirect, and OSPF Hello in the SIP environment. [This is a rough first draft. Need assessment of needed fields, much more text describing usage. Autoconfiguration will be in a separate draft, since the issues here are already getting too big.] Simpson expires in six months [Page i] DRAFT system discovery April 1993 1. Criteria Multicast support. Nearly all of the respondents listed this as the first or second desire stated. It is noted that not all media supports multicast. Reduced net traffic. On one hand, a flood of hosts sending periodic advertisements; on the other, 2 extra packets for every address request. Two solutions were proposed: 1) Sending the first packet to the all-systems multicast, and receiving a redirect. This reduces the traffic from 3 to 2 packets. 2) Automatic router discovery. For those packets which are clearly destined off net, the packet can be sent directly to the next hop. Preference values were cited as useful. Also, carrying media addresses within the router discovery and redirect packets, so that a further query/response can be avoided. Low host overhead. A host should only retain information for those systems with with it is directly communicating. Autoconfiguration. In particular, automatic address discovery and automatic address prefix changes. Mobility support. Partly a subset of the above, as related to dynamically changing addresses while moving. In addition, the "hidden transmitter" problem (you can hear another system, it can't hear you, but there is a path through a third system which it can hear, completing the circuit). This is not well supported in any of the current protocols. Black hole detection. This was repeatedly cited as important. There is a basic Simpson expires in six months [Page 1] DRAFT system discovery April 1993 tradeoff between frequent queries and resources used. Explicit holding times were cited as useful. Media independence. There were many examples, such as point-to-point versus broadcast versus LPDN. Media level redirects between logical subnets on the same physical media. The difficulties with carrying media addresses within packets, especially in the presence of multi-media bridges. This is not well supported in any of the current protocols. Optimal route determination. This is essentially a superset of next hop router discovery, combined with resource reservation and possible policy considerations, and the ability to redirect traffic under changing conditions. The very things that have been causing so much discussion of late. This is not well supported in any of the current protocols. Simplicity. All of the above desires, and they want to keep it simple, too. Proposed Solution Space. None of the current protocols are extensible in dimensions that fix the desires above. While some have the ability to change in simple terms, such as larger addresses, none were designed to add new kinds of information to be carried in the same packet. This proposal describes two replacement packets, not much different from those already deployed. These familiar forms are re-packaged to join common functions into the same packet to reduce traffic, and are designed to be more extensible in the future. In order to foster media independence, the packets are part of ICMP, which allows the procotols to be used over broadcast, multicast, partial-mesh, and point-to-point media. This is similar to the positioning of ES-IS. All of the advertisementmessages have expiration times. Each message is composed of "optional" parts, designed to allow flexibility and extensibility. Simpson expires in six months [Page 2] DRAFT system discovery April 1993 One of the common parts is the media address, so that each message contains enough information to return a reply directly to the sender, without additional location traffic. Another common part is a list of the routers which can be heard, which allows routers to build a map of the paths between routers, and routers to hosts. This solves the "hidden transmitter" problem, when used together with the well-known link-state class of routing protocols. Examples of use: Simple case -- J to K on the same fully-connected segment. J sends the Where-Are-You (which contains its own media address) to all-systems. K sends the I-Am-Here (which contains its own media address) directly to J. At this point, they both know that they can talk directly to each other, without regard to subnet. Routed case -- J to K not on the same fully-connected segment. If no resource reservation or policy routing is desired, J simply sends its packets directly to the "best" router that it has learned from the Advertisements. If there is a better router for the first hop, that router sends the I-Am-Here to J, but never-the-less forwards the packet. In the presence of RR or PR, J sends the Where-Are-You to the "best" router that it has learned from the Advertisements. That router always returns the I-Am-Here (even if the correct hop is itself), which contains the requested RR or PR status information. J then sends its packets to the first hop router as determined from the I-Am-Here. General case -- J to K over disconnected partial mesh (radio/framerelay). J sends the Where-Are-You (which contains its own media address, and the addresses of its "heard" routers) to the all-systems address. The routers use such messages to construct a map of the current state of the topology. The routers now know who J hears, and who hears J. If the routing map doesn't contain a current whereabouts of K, the Destination Unreachable message is returned by the "best" router on J's "heard" list. If the routing map contains the current whereabouts of K, the Simpson expires in six months [Page 3] DRAFT system discovery April 1993 "best" router on K's "heard" list sends a copy of the Where-Are-You to K, with a substitute list of routers which can hear K. The list is ordered by the intersection of those routers which can also hear J, minimizing the number of hops. Of course, K may have heard J's Where-Are-You directly, in which case it adds its own address to the front of the list of routers. When K hears the J Where-Are-You, it sends the I-Am-Here to the all-systems address. The "best" router on J's "heard" list sends a copy of the I-Am-Here to J, with a substitute list of routers which can hear J. The list is ordered by the intersection of those routers which can also hear K. At this point, the routing fabric knows which routers are heard by J and K, and which routers can hear J and K. J and K know whether they can hear each other directly. If not, they know the "best" next hop router (which may not be the same in both directions). Unlike the fully-connected scenarios, this scheme requires that the I-Am-Here is sent from time to time to keep the map updated. However, only routers need store the information. Simpson expires in six months [Page 4] DRAFT system discovery April 1993 2. Additional ICMP Packets The Packet format and basic facilities are already defined for ICMP [3], as modified for SIP [1]. Up-to-date values of the ICMP Type field are specified in the most recent "Assigned Numbers" RFC [2]. This document concerns the following values: System Solicitation System Advertisement Simpson expires in six months [Page 5] DRAFT system discovery April 1993 2.1. System Solicitation A summary of the System Solicitation message format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + System Identifier + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... +-+-+-+-+-+-+-+-+-+-+-+-+ Type Code 0 Checksum The ICMP Checksum. System Identifier The System Identifier field is eight octets in length, and contains the identifier of the system which is sought. Extensions The Extensions field is variable in length and contains zero or more Extensions. These Extensions are described in a later section. Simpson expires in six months [Page 6] DRAFT system discovery April 1993 2.1.1. Description The System Solicitation (Where-Are-You) message is used to determine the presence and availability of the next hop. This message is also used for resource reservation and policy route determination. The message is sent on demand to the all-systems multicast, or to the best first hop router, as indicated by the Advertisement. The information is stored only by routers and the subject hosts. [Need more text describing use for each case, and for resource reservation and policy routing] Simpson expires in six months [Page 7] DRAFT system discovery April 1993 2.2. System Advertisement A summary of the System Advertisement message format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | LifeTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + System Identifier + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Default Metric | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Mask Size | | Area | Priority | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... +-+-+-+-+-+-+-+-+-+-+-+-+ Type Code The Code field is one octet. Up-to-date values of the System Advertisement Code field are specified in the most recent "Assigned Numbers" RFC [2]. Current values are assigned as follows: 0 RESERVED 1 Intermediate System 2 End System 3 Local Redirect 4 Remote Redirect Checksum The ICMP Checksum. Simpson expires in six months [Page 8] DRAFT system discovery April 1993 Sequence Number The Sequence Number field is two octets in length, and contains the number of System Advertisements sent. This number MUST include this advertisement. LifeTime The LifeTime field is two octets in length, and indicates the seconds remaining before the entry is considered invalid. System Identifier The System Identifier field is eight octets in length, and contains the primary identifier for this system. Other identifiers are indicated with the Other Identifiers extension. Default Metric The Default Metric field is four octets in length, and indicates the preference level for use of this system as a default router. Lower values indicate greater preference. End Systems MUST set this field to zero. Mask Size The Mask Size field is one octet in length, and indicates the number of bits in the System Identifier which indicate the subnet mask for the interface. If the System Identifier does not indicate a valid local subnet, the value is zero. End Systems SHOULD have a Mask Size of 64. Area The Area field is one octet in length, and indicates the area that the system inhabits. A value of zero indicates that no area has been assigned. End Systems must set this field to zero. Priority The Priority field is one octet in length, and indicates the priority for election to Designated Backup. A value of zero Simpson expires in six months [Page 9] DRAFT system discovery April 1993 indicates that the system is not eligible. End Systems must set this field to zero. Extensions The Extensions field is variable in length and contains zero or more Extensions. These Extensions are described in a later section. 2.2.1. Description The System Advertisement (I-Am-Here) message is used to announce the presence of an intermediate or end system, to indicate changes in the topology, and to support system mobility. It contains all of the information now in the old Router Advertisement, ES Hello, IS Hello, OSPF Hello and RSPF Hello. Intermediate Systems The message is sent by each intermediate system periodically to the all-systems multicast. The information is stored by all systems. The message is also sent in response to a System Solicitation. End Systems The message is sent in response to a System Solicitation. The information is stored only by the affected systems. Local Redirect The message is sent in response to changes in the routing. The information is stored only by the affected systems. Remote Redirect The message is sent to indicate movement of a system beyond the local area. The information is stored only by the affected systems. Simpson expires in six months [Page 10] DRAFT system discovery April 1993 3. Extensions Extensions allow variable amounts of information to be carried within each Advertisement or Solicitation packet. Some extensions are common to both packet types. The end of the list of Extensions is indicated by the Payload Length of the SIP packet. A summary of the Extensions format is shown below. The fields are transmitted from left to right. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type The Type field is one octet and indicates the type of Extension. Up-to-date values of the Extension Type field are specified in the most recent "Assigned Numbers" RFC [2]. Current values are assigned as follows: 1 Media Access 2 Other Identifiers 3 System Heard 4 Routing Information 5 Service Information Length The Length field is one octet and indicates the length of the Data field which has been used. Each Extension ends on an octet boundary which is an integral multiple of four octets. Any unused portion of the Data field is padded with zeros. length actual 0 through 2 4 3 through 6 8 7 through 10 12 Simpson expires in six months [Page 11] DRAFT system discovery April 1993 Data The Data field is zero or more octets and contains the value or other information for this Extension. The format and length of the Data field is determined by the Type and Length fields. Simpson expires in six months [Page 12] DRAFT system discovery April 1993 3.1. Media Access A summary of the Media Access extension format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Media Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MAC Address ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 1 Length >= 3 Media Type The Media Type field is two octets in length. The value of this field is the same as the Hardware Type used in ARP. Up-to-date values of the Hardware Type field are specified in the most recent "Assigned Numbers" RFC [2]. [Should we use the ifType from MIB-II instead?] MAC Address The MAC Address field is variable in length, and contains the media address which is used to access this system. The MAC Address is always specified in Canonical order. The Media Access extension MUST be included in those messages sent from an interface on a multi-access media. It MUST NOT be included in a message sent from a point-to-point interface, or in messages such as the Remote Redirect which pass through intermediate systems. Simpson expires in six months [Page 13] DRAFT system discovery April 1993 3.2. Other Identifiers A summary of the Other Identifiers extension format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | | Mask Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + System Identifier + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 2 Length 14 System Identifier The System Identifier field is eight octets in length, and contains an identifier for this system. This may be another identifier for the same interface that sent the message, or may identify another interface on the same system which sent the message. Preference The Preference field is four octets in length, and indicates the preference level for use of this system to forward packets to the System Identifier. Lower values indicate greater preference. End Systems MUST set this field to zero. Mask Size The Mask Size field is one octet in length, and indicates the number of bits in the System Identifier which indicate the subnet mask for the interface. If the System Identifier does not indicate a valid local subnet, the Simpson expires in six months [Page 14] DRAFT system discovery April 1993 value is zero. End Systems SHOULD have a Mask Size of 64. Every identifier for every interface is listed in each System Advertisement message. This supports multiple identifiers per interface, as well as multi-homed systems. This enables systems to determine the best next hop without sending a Solicitation when the next hop is on another interface attached to the same system. Simpson expires in six months [Page 15] DRAFT system discovery April 1993 3.3. System Heard A summary of the System Heard extension format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Speed | Mask Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | LifeTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + System Identifier + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Quality | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | MRU | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertisement Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 4 Length 30 Sequence Number The Sequence Number field is two octets in length, and contains the last heard sequence number from the system. LifeTime The LifeTime field is two octets in length, and indicates the seconds remaining before the entry is considered invalid. System Identifier The System Identifier field is eight octets in length, and contains the primary identifier for the system. Simpson expires in six months [Page 16] DRAFT system discovery April 1993 Quality The Quality field is four octets in length, and contains an indication of the signal quality received from this system. Higher values indicate greater quality. Speed The Speed field is one octet in length, and indicates the speed of the link. Higher values indicate greater speed. The speed value is related to the log2 of the speed in bits per second. Unfortunately, there are several series which don't quite match. Is there a standard assignment out there? 0 link is down 8 1,200 or less 9 2,400 4,800 9,600 10 14,400 19,200 12 28,800 38,400 14 57,600 64,000 17 128,000 18 153,600 19 256,000 22 1,544,000 T1 23 2,048,000 E1 24 4,000,000 Token Ring 6,312,000 T2 25 10,000,000 Ethernet 26 16,000,000 Token Ring 28 44,736,000 T3 30 155,520,000 STS-3/STM-1 32 622,080,000 STS-12/STM-4 34 2,488,320,000 STS-48/STM-16 Mask Size The Mask Size field is one octet in length, and indicates the number of bits in the System Identifier which indicate the subnet mask for the interface. If the System Identifier does not indicate a valid local subnet, the Simpson expires in six months [Page 17] DRAFT system discovery April 1993 value is zero. End Systems SHOULD have a Mask Size of 64. Advertisement Count The Advertisement Count field is four octets in length, and indicates the number of advertisements that have been heard from the identified system. Error Count The Error Count field is four octets in length, and indicates the number of errors which have been detected on the link with the identified system. The System Heard extension MUST be included in every System Advertisement. Simpson expires in six months [Page 18] DRAFT system discovery April 1993 3.4. Routing Information A summary of the Routing Information extension format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Designated Backup + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 5 Length 14 Designated Backup The Designated Backup field is eight octets in length, and contains the identifier of the designated backup for this area. This extension is included in the Intermediate System Advertisement of the Designated Router, to assert its status as the Designated Router, and indicate the Designated Backup. Simpson expires in six months [Page 19] DRAFT system discovery April 1993 3.5. Service Information A summary of the Service Information extension format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | QoS | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Preference | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 6 Length 6 QoS The Quality of Service field is two octets in length, and indicates a service for which transit will be accepted. Preference The Preference field is four octets in length, and indicates the preference level for use of this network to forward packets of the indicated service. Lower values indicate greater preference. This extension is included in the Intermediate System Advertisement to indicate that it will accept transit traffic. If this extension is not included, the system will treat the link as a stub network. Simpson expires in six months [Page 20] DRAFT system discovery April 1993 4. Abstraction Algorithm An Area is defined to be a collection of subnets which are aggregated as the same next hop. The areas are learned from the Advertisements, which contain the necessary subnet information. The subnets are assigned by hand. When the subnet mask shortens by at least one bit, a new level of area is created. The area is defined by an area index (assigned by the designated router of the affected area), and the count of bits common to the subnet. This can be expressed as a pair of 8-bit numbers. Discovery of stub areas (probably the most common type) is easy and automatic. Discovery of aggregate areas is made by routers one hop out from the area. This is communicated through its Advertisements, which are heard by the routers bordering the area. This algorithm results in a few, fairly large areas. There can never be more than 64 levels of area, and it is more likely to be 5 to 10 because of natural assignment boundaries. The numbering space also places a limit on the number of routers bordering an area to 255, but that is highly unlikely. Fragmentation of areas simply results in automatic generation of internal areas, and has no effect on area levels farther out. Simpson expires in six months [Page 21] DRAFT system discovery April 1993 Security Considerations Security issues are not discussed in this memo. References [1] [2] Acknowledgments Chair's Address The working group can be contacted via the current chairs: Author's Address Questions about this memo can also be directed to: William Allen Simpson Daydreamer Computer Systems Consulting Services P O Box 6205 East Lansing, MI 48826-6205 EMail: Bill.Simpson@um.cc.umich.edu Simpson expires in six months [Page 22] DRAFT system discovery April 1993 Table of Contents 1. Criteria .............................................. 1 2. Additional ICMP Packets ............................... 5 2.1 System Solicitation ............................. 6 2.1.1 Description ..................................... 6 2.2 System Advertisement ............................ 8 2.2.1 Description ..................................... 10 3. Extensions ............................................ 11 3.1 Media Access .................................... 13 3.2 Other Identifiers ............................... 14 3.3 System Heard .................................... 16 3.4 Routing Information ............................. 19 3.5 Service Information ............................. 20 4. Abstraction Algorithm ................................. 21 SECURITY CONSIDERATIONS ...................................... 22 REFERENCES ................................................... 22 ACKNOWLEDGEMENTS ............................................. 22 CHAIR'S ADDRESS .............................................. 22 AUTHOR'S ADDRESS ............................................. 22