Interoperability of SCCP user messages
Sua Agreement: SCCP User Message in NO.7 Signal Network and IP Network Interoperability Wang Furong Tang Yunbo Huazhong University of Technology Electronic and Information Engineering Department Wuhan 430074 1 SUA Protocol Technical Background With Softswitch Technology Application and Promotion, Traditional Telecom Net It is moving in the direction of interoperability with IP network. Among them, the most critical problem is that the No. 7 signaling that has been widely used can be efficient and reliable in the IP network. As early as 1999, IETF began to develop IP technology-based SigTran protocol clusters, which mainly includes the adaptation protocol of the NO.7 signaling system MTP layer to provide NO.7 signaling in IP network transmission capabilities. At present, the IETF further proposes the Adapted Protocol of the SCCP layer - SIGNALLING Connection Control Part User Adaptation Layer, Signaling Connection Control Some User Messages Adapted to provide stronger address mapping and routing function, and more Simple management functions. 2 SUA protocol architecture SUA supports the IP online transmission of NO.7 signaling SCCP user messages, such as TCAP messages, RANAP messages, etc., implement TCAP over IP, Ranap over IP. SUA not only supports messaging between signaling gateways and IP signaling points (such as IP address databases), but also supports messaging between two signaling points in the same IP network. When the SUA located in the signaling gateway receives the message sent by the SCCP of the gateway, address translation and address mapping are first performed, and the IP signaling point is selected by the SCTP coupling. When SUA receives messages from the IP network, addresses and address mappings, send messages to the SCCP of the signaling gateway, and route to the No.7 signaling point. The signaling gateway can work with the IP signaling point as an endpoint or relay point, so the SCCP has no way to connect the message or connection to establish a message. When the trunker gateway is used as an endpoint, the message is selected by the PC (Dish Code) and SSN (Subsystem Number). If the subsystem is marked by the routing context and the SSN mark, the SCCP user is located in this signaling gateway from the perspective of the routing context. When the lettering gateway is used as a relay point, the GT (global code) is required to determine the message destination. The actual location of the SCCP user is independent of No.7 signaling network. GT translation generates a set of "SCCP entity set" and exports an AS (Application Server, Application Server). Depending on the SCCP called user address, the AS selection can be determined. AS (Application Server) is a logical entity that is identified by a ROUTING key. ASP (Application Server Process) is the process instance of the AS, and is identified by the routing context), which is used to process communication with it. AS and ASP are not mapping, an AS contains a set of independent ASPs, and an ASP can also serve multiple AS. Each ASP corresponds to an IP signaling point for the SCTP layer. A signaling gateway can be considered a group of AS with an No.7 signaling network interface. 3 Services provided by the SUA protocol (1) SCCP User Message Transport Support SUA Support Signal Signing Gateway and ASP (Application Server Process) Seamless Transmission.
(2) SCCP protocol category support SUA can transparently support four types of SCCP protocol type: Disorderless Non-Connection Protocol Type 0, providing sequentially controlled connection protocol type 1, facing connection protocol type 2 and providing traffic control connection protocol type 3. (3) Local management function SUA can point out errors in the SUA protocol message and can notify local management and remote signaling points as needed. (4) SCCP network management function interactive SUA Enables ASP management messages to process ASP status, thereby implementing interoperability with SCCP network management. The primitives such as N-State, N-PCState and N-Coord can be transmitted in SCCP and SUA network management functions of the signaling gateway for triggering the corresponding events in the IP network and the No.7 signaling network. (5) Signaling Gateway Process Management Management SUA provides interoperability between signaling gateways and ASP SCCP network management functions in circuit switched network and IP networks. This feature includes providing an No.7 signaling point to the ASP and, cannot be, the state indication of the congestion, and the query on the remote No.7 endpoint on the signaling gateway. (6) The relay function is to increase the spread of the network, and the SUA relay function can determine the next hop SCTP coupled to the target SUA endpoint. The judgment of the next hop can be based on the GT translation function in the NO.7 signaling network, or by the host name, IP address, or point code of the called address. SUA can configure relay functionality as needed to improve network scalability, reliability, and flexibility. 4 The internal function provided by the SUA protocol is to provide addressing and relay functions, SUA uses an address mapping function called AMF (Address Mapping Function). AMF has a variety of implementations: local GT table translation can be used in distribution mode, and DNS can be used in hierarchical mode, and the LDAP directory protocol can be used in centralized mode. When the entry message is received, the AMF is called. Depending on the context or selection keyword, AMF analyzes the address in the SCCP / SUA entry message to the SCTP coupled to the address of the corresponding IP network destination. (1) The address of the signaling gateway is mapped in an AS, and there is usually one or more ASPs in an active state. However, in some cases, when all ASPs in an AS are not activated, the signaling gateway process places the message sent to this AS into the buffer and activates the timer until ASP recovery is available. If the timer is still available in the timeout, the buffer will be emptied and triggered the corresponding return or reject. If there is no address map that matches the message, the message is usually directed to a certain or a group default ASP, or abandon the message and reported to the management function. (2) The address mapping function of the ASP's address mapping ASP can be based on other elements in the target point code or message, the NO.7 signaling network status, the signaling gateway process status and the circuit context, to the NO.7 letter The message of the network selects a specific signaling gateway process. (3) Address mapping at the relay point When using GT, hostname, SSN point code, or SSN IP address (non-relay address), you need to call relay functionality. There are several different forms based on these information translations or resolve the generated address. · Route according to the SSN: Generate the SCTP coupling ID, SSN, and optional selection context and / or IP address of the point of interest; • Select the SCTP coupling ID of the next relay point: , New GT, and optional SSN and / or circuit context; · According to the host numeral: Generate the SCTP coupling ID, new host name, and optional SSN and / or Call the context. • If the selection information indicates a local SUA user, the point is both a relay point and an endpoint.
To avoid cyclic routing, SUA continues the hop counter function in the No.7 signaling network. The hop counter is set to the maximum value at the starting endpoint (NO.7 signaling network node or IP network node), which is subsequently decremented with the call to the relay function. When the counter is reduced to 0, the corresponding return or reject process is called. (4) SCTP flow map SUA signaling gateway and AS provide mapping function to SCTP streaming by maintaining the control table of SCTP and SUA users. SUA usually takes disorder 0 class streaming SUA management information, and sequential streaming can be selected in a particular case. (5) Flow Control When the ASP needs to temporarily delete SCTP conjugate or test maintenance, the local management function can terminate communication on the corresponding SCTP coupling, and transfer communication on the current SCTP to another. Union. (6) Congestion Management In ASP, the SUA layer indicates congestion to the local SCCP user with SCCP primitives and triggered the upper layer response. If the signaling gateway discovers that the No. 7 signaling message transmission occurs, the SCCP congestion message is sent to the No.7 signaling start point. SUA in the ASP can also issue local congestion messages to the peer sua. When the lettering gateway receives this message, it is determined that the endpoint block is blocked, and the congestion process flow can be triggered in accordance with the SCCP protocol. 5 SUA protocols and SCCP protocols The mutual routing mechanism and signaling control of the interworking gateway in the signaling gateway are the key to the interoperability of the No.7 signaling network and IP network. Under SUA, you don't need to redesign the network, you can add or remove network elements. As long as the IP bandwidth is sufficient, the applications of different signaling needs can be achieved. The following is an important process when SUA and SCCP are interoperability interworking. (1) Split and reload When signaling messages are too long, when the PDU capacity is exceeded, the signaling gateway or ASP needs to perform fragmentation and reloading. If the signaling gateway or ASP cannot complete fragmentation and reload, an error report is initiated to the alignment in an appropriate message. (2) Load sharing supports multiple ASPs in the same AS to be activated simultaneously and is in a load sharing. When processing TCAP transactions or SCCP connections, the load balancing mechanism of the signaling gateway should also guarantee that subsequent messages of the same road transaction or connection are consistent with the initial message (such as Tc_Query, Tc_Begin, Cr, etc.). If you can uniquely identify the ASP based on the routing keywords (such as DPC or GT), no load balancing is required. If the ASP within the AS is uniquely identified, the signaling gateway needs to select the sequential transmission mode to ensure that the ASP arrives before and after. For connection-oriented SCCP communications, only the load balancing method is required to establish a message CR in the initial connection, which can be used along the established connection path. If the above is not satisfied, you need to enable a set of universal mechanisms in the Signaling Gateway and the ASP to support load balancing: first establish an ASP with an AS association, then ASP is activated in AS, and to all and No.7 signaling Connecting the signaling gateway sends an activation message, each of the specific fields of each message contains an independent tag allocated by the ASP. Signaling Gateway creates a list of ASPs to which a list is recorded for each routine; then the signaling gateway establishes a distribution table for each selection context, and updated when there is a new association establishment and ASP activation. (3) Selection and message distribution of the signaling gateway a. TCAP message If the TCAP message does not contain the purpose or responds to the TID (Transaction ID) tag, such as Query, Begin, Unidirectional, the load balancing is assigned ASP. If the message contains the TID tag, it is parsed by the SG and selects the corresponding ASP. Returns an error report if the corresponding ASP does not exist and the return option is activated.
b. SCCP Connection Messages If the SCCP is not included in the connection message, the SCCP does not include a DRN (destination reference number) tag, such as the connection establishment message, the load balancing is assigned an ASP. If the message contains the DRN tag, it is parsed by the SG and selects the corresponding ASP. If the corresponding ASP does not exist, the message is discarded. (4) Multi-signal gateway SUA relay each ASP will send its independent markers to the signaling gateway process. For the considering of system fault tolerance and robustness, multiple signaling gateways can run together to provide optional routes for ASP. 6 SUA protocols and other protocols (1) Comparison of SUA and SCCP M3UA Although SUA and SCCP M3UA are located above SCTP IP, from SUA's perspective, it has the architecture of the underlying SCTP and IP networks. More intuitive understanding. From a horizontal, SUA simplifies the cumbersome configuration process of each element of NO.7 signaling network, which reduces management and maintenance costs. From the longitudinal comparison, SUA has only one layer, and its management functions are also simple, only the SUA ASP management is required; and SCCP M3UA needs to take into account SCCP management and M3UA ASP management. SUA expands the addressing capabilities of signaling, which can use IP addresses, hostnames, and DNS, such as routing addressing, providing a more efficient and flexible mechanism for routing and adjustment. In addition, SUA does not require use of No.7 signaling point code to save a large number of points resources. (2) Comparison of SUA and TI-SCCP, the end of 2002, ITU-T develops a set of protocols called Ti-SCCP (Transport Independent Signalling Connection Control Part, Transmission Independent Signalling Connection Control Part, " The SCCP defined in the Q.711 ~ Q.716 specification makes it possible to run in a variety of transport networks. Like SUA, TI-SCCP can be run directly on SCTP directly using the SCTP signaling transmitting converter (STC) defined in the Q.2150.3 specification. However, its addressing capacity is limited, and it does not support extension addressing methods such as IP address, hostname and DNS. In addition, TI-SCCP needs to introduce the MAP protocol work together when transmitting long messages. It can't be done like SUA, all of the slice / reloading work is completed by the sub-SCTP. Moreover, the introduction of the MAP protocol will cause a series of adaptation problems. (3) Comparison of SUA and No.7 Signaling Systems Optimize the transmission of transaction messages. Sua as the carrier of TCAP, while maintaining all the functionality of NO.7 signaling, the network is robust to the operators level. SUA uses a common packet transmission bearer signal, which can enhance the bandwidth and connectivity of the network by simple operation, without having to restructuring the network like the No.7 signaling network E1 / T1 channel. SUA simplifies the cumbersome configuration process of NO.7 signaling network, which is more fully utilized by IP routing mechanisms. It takes a distributed application, which can be reconfigured according to demand. Sua also promotes equipment manufacturers to deduce the previously vertically integrated value-added business as a horizontal distribution. At this level, traditional techniques (such as roaming, number transplant databases), value-added services (such as short message services) and next-generation network technologies (such as SIP, ENUM, LDAP, etc.) can be integrated. 7 Conclusion SUA takes full advantage of the performance of the group transmission signaling, which greatly saves operational costs.
