Network Working Group M. Tuexen, Ed. Internet-Draft Muenster Univ. of Applied Sciences Expires: April 24, 2005 Q. Xie Motorola, Inc. R. Stewart M. Shore Cisco Systems, Inc. J. Loughney Nokia Research Center October 24, 2004 Architecture for Reliable Server Pooling draft-ietf-rserpool-arch-08.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 24, 2005. Copyright Notice Copyright (C) The Internet Society (2004). Abstract This document describes an architecture and protocols for the Tuexen, et al. Expires April 24, 2005 [Page 1] Internet-Draft Architecture for Reliable Server Pooling October 2004 management and operation of server pools supporting highly reliable applications, and for client access mechanisms to a server pool. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3 2. Reliable Server Pooling Architecture . . . . . . . . . . . . . 4 2.1 RSerPool Functional Components . . . . . . . . . . . . . . 4 2.2 RSerPool Protocol Overview . . . . . . . . . . . . . . . . 5 2.2.1 Endpoint Name Resolution Protocol . . . . . . . . . . 5 2.2.2 Aggregate Server Access Protocol . . . . . . . . . . . 5 2.2.3 PU <-> NS Communication . . . . . . . . . . . . . . . 6 2.2.4 PE <-> NS Communication . . . . . . . . . . . . . . . 7 2.2.5 PU <-> PE Communication . . . . . . . . . . . . . . . 7 2.2.6 NS <-> NS Communication . . . . . . . . . . . . . . . 8 2.2.7 PE <-> PE Communication . . . . . . . . . . . . . . . 9 2.3 Failover Support . . . . . . . . . . . . . . . . . . . . . 9 2.3.1 Business Cards . . . . . . . . . . . . . . . . . . . . 9 2.3.2 Cookies . . . . . . . . . . . . . . . . . . . . . . . 10 2.4 Typical Interactions between RSerPool Components . . . . . 11 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1 Two File Transfer Examples . . . . . . . . . . . . . . . . 12 3.1.1 The RSerPool Aware Client . . . . . . . . . . . . . . 13 3.1.2 The RSerPool Unaware Client . . . . . . . . . . . . . 14 3.2 Telephony Signaling Example . . . . . . . . . . . . . . . 15 3.2.1 Decomposed GWC and GK Scenario . . . . . . . . . . . . 15 3.2.2 Collocated GWC and GK Scenario . . . . . . . . . . . . 17 4. Security Considerations . . . . . . . . . . . . . . . . . . . 18 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6.1 Normative References . . . . . . . . . . . . . . . . . . . . 19 6.2 Informative References . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . . 21 Tuexen, et al. Expires April 24, 2005 [Page 2] Internet-Draft Architecture for Reliable Server Pooling October 2004 1. Introduction 1.1 Overview This document defines an architecture, for providing a highly available reliable server function in support of a service or set of services. This is achieved by forming a pool of servers, each of which is capable of supporting the desired service(s), and providing a name service that will resolve requests from a service user to the identity of a working server in the pool. To access a server pool, the pool user consults a name server. The name service itself can be provided by a pool of name servers using a shared protocol to make the name resolution function fault-tolerant. It is assumed that the name space is kept flat and designed for a limited scale in order to keep the protocols simple, robust and fast. The server pool itself is supported by a shared protocol between servers and the name service allowing servers to enter and exit the pool. Several server selection mechanisms, called server pool policies, are supported for flexibility. 1.2 Terminology This document uses the following terms: Home Name Server: The Name Server a Pool Element has registered with. This Name Server supervises the Pool Element. Operation scope: The part of the network visible to pool users by a specific instance of the reliable server pooling protocols. Pool (or server pool): A collection of servers providing the same application functionality. Pool handle (or pool name): A logical pointer to a pool. Each server pool will be identifiable in the operation scope of the system by a unique pool handle or "name". Pool element: A server entity having registered to a pool. Pool user: A server pool user. Pool element handle (or endpoint handle): A logical pointer to a particular pool element in a pool, consisting of the name of the pool and a destination transport address of the pool element. Name space: A cohesive structure of pool names and relations that may be queried by an internal or external agent. Name server: Entity which is responsible for managing and maintaining the name space within the RSerPool operation scope. 1.3 Abbreviations Tuexen, et al. Expires April 24, 2005 [Page 3] Internet-Draft Architecture for Reliable Server Pooling October 2004 ASAP: Aggregate Server Access Protocol ENRP: Endpoint Name Resolution Protocol Home NS: Home Name Server NS: Name Server PE: Pool element PU: Pool user SCTP: Stream Control Transmission Protocol TCP: Transmission Control Protocol 2. Reliable Server Pooling Architecture In this section, we define a reliable server pool architecture. 2.1 RSerPool Functional Components There are three classes of entities in the RSerPool architecture: o Pool Elements (PEs). o Name Servers (NSs). o Pool Users (PUs). A server pool is defined as a set of one or more servers providing the same application functionality. These servers are called Pool Elements (PEs). PEs form the first class of entities in the RSerPool architecture. Multiple PEs in a server pool can be used to provide fault tolerance or load sharing, for example. Each server pool is identified by a unique name which is simply a byte string, called the pool handle. This allows binary names to be used. These names are not valid in the whole internet but only in smaller domains, called the operational scope. Furthermore, the namespace is assumed to be flat, so that multiple levels of query are not necessary to resolve a name request. The second class of entities in the RSerPool architecture is the class of name servers (NSs). These name servers can resolve a pool handle to a list of information which allows the PU to access a PE of the server pool identified by the handle. This information includes: o A list of IPv4 and/or IPv6 addresses. o A protocol field specifying the transport layer protocol. o A port number associated with the transport protocol, e.g. SCTP, TCP or UDP. Note that the RSerPool architecture supports both IPv4 and IPv6 addressing. In each operational scope there must be at least one name server. Tuexen, et al. Expires April 24, 2005 [Page 4] Internet-Draft Architecture for Reliable Server Pooling October 2004 All name servers within the operational scope have knowledge of all server pools within the operational scope. A third class of entities in the architecture is the Pool User (PU) class, consisting of the clients being served by the PEs of a server pool. 2.2 RSerPool Protocol Overview Based on the requirements in RFC3237 [9], two new protocols: ENRP (Endpoint Name Resolution Protocol) and ASAP (Aggregate Server Access Protocol). These are used because no existing protocols are suitable (see [3]). 2.2.1 Endpoint Name Resolution Protocol The name servers use a protocol called Endpoint Name Resolution Protocol (ENRP) for communication with each other to exchange information and updates about the server pools. ENRP is designed to provide a fully distributed fault-tolerant real-time translation service that maps a name to a set of transport addresses pointing to a specific group of networked communication endpoints registered under that name. RFC3237 [9] also requires that the name servers should not resolve a pool handle to a transport layer address of a PE which is not in operation. Therefore each PE is supervised by one specific name server, called the home NS of that PE by using ASAP. If it detects that the PE is out of service all other name servers are informed by using ENRP. 2.2.2 Aggregate Server Access Protocol The PU wanting service from the pool uses the Aggregate Server Access Protocol (ASAP) to access members of the pool. Depending on the level of support desired by the application, use of ASAP may be limited to an initial query for an active PE, or ASAP may be used to mediate all communication between the PU and PE, so that automatic failover from a failed PE to an alternate PE can be supported. ASAP uses a name-based addressing model which isolates a logical communication endpoint from its IP address(es), thus effectively eliminating the binding between the communication endpoint and its physical IP address(es) which normally constitutes a single point of failure. In addition, ASAP provides some mechanisms to support loadsharing Tuexen, et al. Expires April 24, 2005 [Page 5] Internet-Draft Architecture for Reliable Server Pooling October 2004 between PEs within the same pool and to support the upper layer in case of a failover between PEs becomes necessary. ASAP is also used by a PE to join or leave a server pool. It registers or deregisters itself by communicating with a name server, which will normally the home NS. ASAP allows dynamic system scalability, allowing the pool membership to change at any time. 2.2.3 PU <-> NS Communication The PU <-> NS communication is used for performing name queries and uses ASAP. The PU sends a pool handle to the NS and gets back the information necessary for accessing a server in a server pool. This communication can be based on SCTP or TCP if the PU does not support SCTP. The protocol stack for an SCTP capable PU is given in Figure 1. Tuexen, et al. Expires April 24, 2005 [Page 6] Internet-Draft Architecture for Reliable Server Pooling October 2004 ******** ******** * PU * * NS * ******** ******** +------+ +------+ | ASAP | | ASAP | +------+ +------+ | SCTP | | SCTP | +------+ +------+ | IP | | IP | +------+ +------+ Protocol stack between PU and NS Figure 1 2.2.4 PE <-> NS Communication The PE <-> NS communication is used for registration and deregistration of the PE in one or more pools and for the supervision of the PE by the home NS. This communication is based on SCTP, the protocol stack is shown in the following figure. ******** ******** * PE * * NS * ******** ******** +------+ +------+ | ASAP | | ASAP | +------+ +------+ | SCTP | | SCTP | +------+ +------+ | IP | | IP | +------+ +------+ Protocol stack between PE and NS Figure 2 2.2.5 PU <-> PE Communication The PU <-> PE communication can be divided into two parts: o control channel o data channel The data channel is used for the transmission of the upper layer data, the control channel is used to exchange RSerPool information. Tuexen, et al. Expires April 24, 2005 [Page 7] Internet-Draft Architecture for Reliable Server Pooling October 2004 There are two supported scenarios: o Multiplexed data and control channel. Both channels are transported over one transport connection. This can either be an SCTP association, with data and control channel are separated by the PPID, or an TCP connection, with data and control channel being handled by a TCP mapping layer. o Data channel and no control channel. There is no restriction on the transport protocol in this case. Note that certain enhanced failover services (e.g. business cards, state cookies, message failover) are not available when this method is used. For a given pool, all PUs and PEs should make the same choice for the style of interaction between each other: that is, for a given pool, either all PEs and PUs in that pool use a multiplexed control/data channel for PU-PE communication, or all PEs and PUs in that pool use a data channel only for PU-PE communication. When the multiplexed data and control channel is used, enhanced failover services may be provided, including: o The PE can send a business card to the PU for providing information to which other PE the PU should failover in case of a failover. o The PE can send cookies to the PU. The PE would store only the last cookie and send it to the new PE in case of a failover. See Section 2.3 for further details. 2.2.6 NS <-> NS Communication The communication between name servers is used to share the knowledge about all server pools between all name servers in an operational scope. For this communication ENRP over SCTP is used and the protocol stack is shown in Figure 3. Tuexen, et al. Expires April 24, 2005 [Page 8] Internet-Draft Architecture for Reliable Server Pooling October 2004 ******** ******** * NS * * NS * ******** ******** +------+ +------+ | ENRP | | ENRP | +------+ +------+ | SCTP | | SCTP | +------+ +------+ | IP | | IP | +------+ +------+ Protocol stack between NS and NS Figure 3 When a name initializes a UDP multicast message may be transmitted for initial detection of other name servers in the operational scope. The other name servers send a response using a unicast UDP message. 2.2.7 PE <-> PE Communication This is a special case of the PU <-> PE communication. In this case the PU is also a PE in a server pool. There is one additional point here: The PE acting as a PU can send the PE the information that it is actually a PE of a pool. This means that the pool handle is transferred via the control channel. See Section 2.3 for further details. 2.3 Failover Support If the PU detects the failure of a PE it may fail over to a different PE. The selection to a new PE should be made such that most likely the new PE is not affected by the failed one. There are some mechanisms provided by RSerPool to support the failover to a new PE. 2.3.1 Business Cards A PE can send a business card to its peer containing its pool handle and optionally information to which other PEs the peer should failover. Presenting the pool handle is important in case of PE <-> PE communication in which one of the PEs acts as a PU for establishing the communication. The pool handle of the PE which initiated the communication may not be known by the peer. Tuexen, et al. Expires April 24, 2005 [Page 9] Internet-Draft Architecture for Reliable Server Pooling October 2004 Providing information to which PE the PU should failover can also be very important. Consider the scenario presented in the following figure. ....................... . +-------+ . . | | . . | PE 1 | . . | | . . +-------+ . . . . Server Pool . . . . . +-------+ . +-------+ . +-------+ | | . | | . | | | PU 1 |------.------| PE 2 |------.-------| PU 2 | | | . | | . | | +-------+ . +-------+ . +-------+ . . . . . . . . . +-------+ . . | | . . | PE 3 | . . | | . . +-------+ . ....................... Two PUs accessing the same PE Figure 4 PU 1 is using PE 2 of the server pool. Assume that PE 1 and PE 2 share state but not PE 2 and PE 3. Using the business card of PE 2 it is possible for PE 2 to inform PU 1 that it should fail over to PE 1 in case of a failure. A slightly more complicated situation is if two pool users, PU 1 and PU 2, use PE 2 but both, PU 1 and PU 2, need to use the same PE. Then it is important that PU 1 and PU 2 fail over to the same PE. This can be handled in a way such that PE 2 gives the same business card to PU 1 and PU 2. 2.3.2 Cookies Cookies may optionally be sent from the PE to the PU. The PU only stores the last received cookie. In case of fail over the PU sends Tuexen, et al. Expires April 24, 2005 [Page 10] Internet-Draft Architecture for Reliable Server Pooling October 2004 this last received cookie to the new PE. This method provides a simple way of state sharing between the PEs. Please note that the old PE should sign the cookie and the receiving PE should verify the signature. For the PU, the cookie has no structure and is only stored and transmitted to the new PE. 2.4 Typical Interactions between RSerPool Components The following drawing shows the typical RSerPool components and their possible interactions with each other: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ operation scope ~ ~ ......................... ......................... ~ ~ . Server Pool 1 . . Server Pool 2 . ~ ~ . +-------+ +-------+ . (d) . +-------+ +-------+ . ~ ~ . |PE(1,A)| |PE(1,C)|<-------------->|PE(2,B)| |PE(2,A)|<---+ ~ ~ . +-------+ +-------+ . . +-------+ +-------+ . | ~ ~ . ^ ^ . . ^ ^ . | ~ ~ . | (a) | . . | | . | ~ ~ . +----------+ | . . | | . | ~ ~ . +-------+ | | . . | | . | ~ ~ . |PE(1,B)|<---+ | | . . | | . | ~ ~ . +-------+ | | | . . | | . | ~ ~ . ^ | | | . . | | . | ~ ~ .......|........|.|.|.... .......|.........|....... | ~ ~ | | | | | | | ~ ~ (c)| (a)| | |(a) (a)| (a)| (c)| ~ ~ | | | | | | | ~ ~ | v v v v v | ~ ~ | +++++++++++++++ (e) +++++++++++++++ | ~ ~ | + NS +<---------->+ NS + | ~ ~ | +++++++++++++++ +++++++++++++++ | ~ ~ v ^ ^ | ~ ~ ********* | | | ~ ~ * PU(A) *<-------+ (b)| | ~ ~ ********* (b) | | ~ ~ v | ~ ~ ::::::::::::::::: (f) ***************** | ~ ~ : Other Clients :<------------->* Proxy/Gateway * <---+ ~ ~ ::::::::::::::::: ***************** ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ RSerPool components and their possible interactions. Figure 5 In this figure we can identify the following possible interactions: Tuexen, et al. Expires April 24, 2005 [Page 11] Internet-Draft Architecture for Reliable Server Pooling October 2004 (a) Server Pool Elements <-> NS: (ASAP) Each PE in a pool uses ASAP to register or de-register itself as well as to exchange other auxiliary information with the NS. The NS also uses ASAP to monitor the operational status of each PE in a pool. (b) PU <-> NS: (ASAP) A PU normally uses ASAP to request the NS for a name-to-address translation service before the PU can send user messages addressed to a server pool by the pool's name. (c) PU <-> PE: (ASAP) ASAP can be used to exchange some auxiliary information of the two parties before they engage in user data transfer. (d) Server Pool <-> Server Pool: (ASAP) A PE in a server pool can become a PU to another pool when the PE tries to initiate communication with the other pool. In such a case, the interactions described in (a) and (c) above will apply. (e) NS <-> NS: (ENRP) ENRP can be used to fulfill various Name Space operation, administration, and maintenance (OAM) functions. (f) Other Clients <-> Proxy/Gateway: standard protocols The proxy/gateway enables clients ("other clients"), which are not RSerPool aware, to access services provided by an RSerPool based server pool. It should be noted that these proxies/gateways may become a single point of failure. 3. Examples In this section the basic concepts of ENRP and ASAP will be described. First an RSerPool aware FTP server is considered. The interaction with an RSerPool aware and an non-aware client is given. Finally, a telephony example is considered. 3.1 Two File Transfer Examples In this section we present two separate file transfer examples using ENRP and ASAP. We present two separate examples demonstrating an ENRP/ASAP aware client and a client that is using a Proxy or Gateway to perform the file transfer. In this example we will use a FTP RFC959 [5] model with some modifications. The first example (the RSerPool aware one) will modify FTP concepts so that the file transfer takes place over SCTP. In the second example we will use TCP between the unaware client and the Proxy. The Proxy itself will use the modified FTP with RSerPool as illustrated in the first example. Please note that in the example we do NOT follow FTP RFC959 [5] precisely but use FTP-like concepts and attempt to adhere to the basic FTP model. These examples use FTP for illustrative purposes, FTP was chosen since many of the basic concept are well known and should be familiar to readers. Tuexen, et al. Expires April 24, 2005 [Page 12] Internet-Draft Architecture for Reliable Server Pooling October 2004 3.1.1 The RSerPool Aware Client ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ operation scope ~ ~ ......................... ~ ~ . "File Transfer Pool" . ~ ~ . +-------+ +-------+ . ~ ~ +-> |PE(1,A)| |PE(1,C)| . ~ ~ |. +-------+ +-------+ . ~ ~ |. ^ ^ . ~ ~ |. +----------+ | . ~ ~ |. +-------+ | | . ~ ~ |. |PE(1,B)|<---+ | | . ~ ~ |. +-------+ | | | . ~ ~ |. ^ | | | . ~ ~ |.......|........|.|.|.... ~ ~ | ASAP | ASAP| | |ASAP ~ ~ |(d) |(c) | | | ~ ~ | v v v v ~ ~ | ********* +++++++++++++++ ~ ~ + ->* PU(X) * + NS + ~ ~ ********* +++++++++++++++ ~ ~ ^ ASAP ^ ~ ~ | <-(b) | ~ ~ +--------------+ ~ ~ (a)-> ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Architecture for RSerPool aware client. Figure 6 To effect a file transfer the following steps would take place. 1. The application in PU(X) would send a login request. The PU(X)'s ASAP layer would send an ASAP request to its NS to request the list of pool elements (using (a)). The pool handle to identify the pool would be "File Transfer Pool". The ASAP layer queues the login request. 2. The NS would return a list of the three PEs PE(1,A), PE(1,B) and PE(1,C) to the ASAP layer in PU(X) (using (b)). 3. The ASAP layer selects one of the PEs, for example PE(1,B). It transmits the login request, the other FTP control data finally starts the transmission of the requested files (using (c)). For this the multiple stream feature of SCTP could be used. 4. If during the file transfer conversation, PE(1,B) fails, assuming the PE's were sharing state of file transfer, a fail-over to PE(1,A) could be initiated. PE(1,A) would continue the transfer until complete (see (d)). In parallel a request from PE(1,A) Tuexen, et al. Expires April 24, 2005 [Page 13] Internet-Draft Architecture for Reliable Server Pooling October 2004 would be made to the NS to request a cache update for the server pool "File Transfer Pool" and a report would also be made that PE(1,B) is non-responsive (this would cause appropriate audits that may remove PE(1,B) from the pool if the NS had not already detected the failure) (using (a)). 3.1.2 The RSerPool Unaware Client In this example we investigate the use of a Proxy server assuming the same set of scenario as illustrated above. In this example the steps will occur: 1. The FTP client and the Proxy/Gateway are using the TCP-based ftp protocol. The client sends the login request to the proxy (using (e)). 2. The proxy behaves like a client and performs the actions described under (1), (2) and (3) of the above description (using (a), (b) and (c)). 3. The ftp communication continues and will be translated by the proxy into the RSerPool aware dialect. This interworking uses (f) and (c). Note that in this example high availability is maintained between the Proxy and the server pool but a single point of failure exists between the FTP client and the Proxy, i.e. the command TCP connection and its one IP address it is using for commands. Tuexen, et al. Expires April 24, 2005 [Page 14] Internet-Draft Architecture for Reliable Server Pooling October 2004 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ operation scope ~ ~ ......................... ~ ~ . "File Transfer Pool" . ~ ~ . +-------+ +-------+ . ~ ~ . |PE(1,A)| |PE(1,C)| . ~ ~ . +-------+ +-------+ . ~ ~ . ^ ^ . ~ ~ . +----------+ | . ~ ~ . +-------+ | | . ~ ~ . |PE(1,B)|<---+ | | . ~ ~ . +-------+ | | | . ~ ~ .......^........|.|.|.... ~ ~ | | | | ~ ~ | ASAP| | |ASAP ~ ~ | | | | ~ ~ | v v v ~ ~ | +++++++++++++++ +++++++++++++++ ~ ~ | + NS +<--ENRP-->+ NS + ~ ~ | +++++++++++++++ +++++++++++++++ ~ ~ | ASAP ^ ~ ~ | ASAP (c) (b) | ^ ~ ~ +---------------------------------+ | | | ~ ~ | v | (a) ~ ~ v v ~ ~ ::::::::::::::::: (e)-> ***************** ~ ~ : FTP Client :<------------->* Proxy/Gateway * ~ ~ ::::::::::::::::: (f) ***************** ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Architecture for RserPool unaware client. Figure 7 3.2 Telephony Signaling Example This example shows the use of ASAP/RSerPool to support server pooling for high availability of a telephony application such as a Voice over IP Gateway Controller (GWC) and Gatekeeper services (GK). In this example, we show two different scenarios of deploying these services using RSerPool in order to illustrate the flexibility of the RSerPool architecture. 3.2.1 Decomposed GWC and GK Scenario In this scenario, both GWC and GK services are deployed as separate pools with some number of PEs, as shown in the following diagram. Tuexen, et al. Expires April 24, 2005 [Page 15] Internet-Draft Architecture for Reliable Server Pooling October 2004 Each of the pools will register their unique pool handle (i.e. name) with the NS. We also assume that there are a Signaling Gateway (SG) and a Media Gateway (MG) present and both are RSerPool aware. ................... . Gateway . . Controller Pool . ................. . +-------+ . . Gatekeeper . . |PE(2,A)| . . Pool . . +-------+ . . +-------+ . . +-------+ . . |PE(1,A)| . . |PE(2,B)| . . +-------+ . . +-------+ . . +-------+ . (d) . +-------+ . . |PE(1,B)|<------------>|PE(2,C)|<-------------+ . +-------+ . . +-------+ . | ................. ........^.......... | | | (c)| (e)| | v +++++++++++++++ ********* ***************** + NS + * SG(X) * * Media Gateway * +++++++++++++++ ********* ***************** ^ ^ | | | <-(a) | +-------------------+ (b)-> Deployment of Decomposed GWC and GK. Figure 8 As shown in the previous figure, the following sequence takes place: 1. the Signaling Gateway (SG) receives an incoming signaling message to be forwarded to the GWC. SG(X)'s ASAP layer would send an ASAP request to its "local" NS to request the list of pool elements (PE's) of GWC (using (a)). The key used for this query is the pool handle of the GWC. The ASAP layer queues the data to be sent to the GWC in local buffers until the NS responds. 2. the NS would return a list of the three PE's A, B and C to the ASAP layer in SG(X) together with information to be used for load-sharing traffic across the gateway controller pool (using (b)). 3. the ASAP layer in SG(X) will select one PE (e.g., PE(2,C)) and send the signaling message to it (using (c)). The selection is based on the load sharing information of the gateway controller pool. Tuexen, et al. Expires April 24, 2005 [Page 16] Internet-Draft Architecture for Reliable Server Pooling October 2004 4. to progress the call, PE(2,C) finds that it needs to talk to the Gatekeeper. Assuming it has already had gatekeeper pool's information in its local cache (e.g., obtained and stored from recent query to NS), PE(2,C) selects PE(1,B) and sends the call control message to it (using (d)). 5. We assume PE(1,B) responds back to PE(2,C) and authorizes the call to proceed. 6. PE(2,C) issues media control commands to the Media Gateway (using (e)). RSerPool will provide service robustness to the system if some failure would occur in the system. For instance, if PE(1, B) in the Gatekeeper Pool crashed after receiving the call control message from PE(2, C) in step (d) above, what most likely will happen is that, due to the absence of a reply from the Gatekeeper, a timer expiration event will trigger the call state machine within PE(2, C) to resend the control message. The ASAP layer at PE(2, C) will then notice the failure of PE(1, B) through (likely) the endpoint unreachability detection by the transport protocol beneath ASAP and automatically deliver the re-sent call control message to the alternate GK pool member PE(1, A). With appropriate intra-pool call state sharing support, PE(1, A) will be able to correctly handle the call and reply to PE(2, C) and hence progress the call. 3.2.2 Collocated GWC and GK Scenario In this scenario, the GWC and GK services are collocated (e.g., they are implemented as a single process). In such a case, one can form a pool that provides both GWC and GK services as shown in the figure below. The same sequence as described in 5.2.1 takes place, except that step (4) now becomes internal to the PE(3,C) (again, we assume Server C is selected by SG). Tuexen, et al. Expires April 24, 2005 [Page 17] Internet-Draft Architecture for Reliable Server Pooling October 2004 ........................................ . Gateway Controller/Gatekeeper Pool . . +-------+ . . |PE(3,A)| . . +-------+ . . +-------+ . . |PE(3,C)|<---------------------------+ . +-------+ . | . +-------+ ^ . | . |PE(3,B)| | . | . +-------+ | . | ................|....................... | | | +-------------+ | | | (c)| (e)| v v +++++++++++++++ ********* ***************** + NS + * SG(X) * * Media Gateway * +++++++++++++++ ********* ***************** ^ ^ | | | <-(a) | +-------------------+ (b)-> Deployment of Collocated GWC and GK. Figure 9 4. Security Considerations The RSerPool protocol must allow us to secure the RSerPool infrastructure. There are security and privacy issues that relate to the namespace, pool element registration and user queries of the namespace. In [2] a complete threat analysis of RSerPool components is presented. 5. Acknowledgements The authors would like to thank Bernard Aboba, Phillip Conrad, Harrie Hazewinkel, Matt Holdrege, Lyndon Ong, Christopher Ross, Maureen Stillman, Werner Vogels and many others for their invaluable comments and suggestions. Tuexen, et al. Expires April 24, 2005 [Page 18] Internet-Draft Architecture for Reliable Server Pooling October 2004 6. References 6.1 Normative References [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] Stillman, M., "Threats Introduced by Rserpool and Requirements for Security in response to Threats", draft-ietf-rserpool-threats-03 (work in progress), July 2004. [3] Loughney, J., "Comparison of Protocols for Reliable Server Pooling", draft-ietf-rserpool-comp-08 (work in progress), July 2004. 6.2 Informative References [4] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [5] Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9, RFC 959, October 1985. [6] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service Location Protocol, Version 2", RFC 2608, June 1999. [7] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene, L., Lin, H., Juhasz, I., Holdrege, M. and C. Sharp, "Framework Architecture for Signaling Transport", RFC 2719, October 1999. [8] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson, "Stream Control Transmission Protocol", RFC 2960, October 2000. [9] Tuexen, M., Xie, Q., Stewart, R., Shore, M., Ong, L., Loughney, J. and M. Stillman, "Requirements for Reliable Server Pooling", RFC 3237, January 2002. Authors' Addresses Michael Tuexen (editor) Muenster Univ. of Applied Sciences Stegerwaldstr. 39 48565 Steinfurt Germany EMail: tuexen@fh-muenster.de Tuexen, et al. Expires April 24, 2005 [Page 19] Internet-Draft Architecture for Reliable Server Pooling October 2004 Qiaobing Xie Motorola, Inc. 1501 W. Shure Drive, #2309 Arlington Heights, IL 60004 USA Phone: +1-847-632-3028 EMail: qxie1@email.mot.com Randall R. Stewart Cisco Systems, Inc. 8725 West Higgins Road Suite 300 Chicago, IL 60631 USA Phone: +1-815-477-2127 EMail: rrs@cisco.com Melinda Shore Cisco Systems, Inc. 809 Hayts Rd Ithaca, NY 14850 USA Phone: +1 607 272 7512 EMail: mshore@cisco.com John Loughney Nokia Research Center PO Box 407 FIN-00045 Nokia Group FIN-00045 Finland EMail: john.loughney@nokia.com Tuexen, et al. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Tuexen, et al. Expires April 24, 2005 [Page 21]