Application point of view: Software Exchange Device Application Instances in networking

The Softswitch device has become one of the important devices in the networking device. Here we mainly introduce the detailed analysis of key routing technologies of the softswitch device. Based on the DNS system, ENUM mainly draws on the basic idea of DNS. ENUMDNS adopts a tree structure and hierarchical authorization mechanism, which completes the route from E.164 number to URI to IP address step by step, the distribution of E.164 numbers, domain names, and data is effectively realized, and the query and management efficiency is improved.

I also borrowed a very important concept in DNS in ENUM? NAPTR, NAPTR is a new DNSRR (DNSResource Record) type, which is actually a regular expression based on rewrite rules. It completes the resolution and translation of a specific string to the new domain name identifier or URI. It allows DNS to complete a wider range of query services, such as ing and parsing from E.164 to URI. Therefore, ENUM serves as a bridge between PSTN and IP network services. The core of ENUM technology includes E.164 number preprocessing, ENUM resolution, and DNS configuration.

First, remove the characters except "+" to get "+ 862787694036", then remove "+", and then add ". "to get" 8.6.2.7.8.7.6.9.4.0.3.6 "(the reason why we simply add a value between each digit is not to distinguish the country code specified by ITU from the country code, so as to simplify the processing, because DNS supports 127 levels, the E.164 Standard 16-bit phone number is enough); finally, reverse it and add the suffix ". e164.tld, "Get the symbol string" 6.3.O.4.9.6.7.8.7.2.6.8.e164.tld ", where tld is a top-level domain.

ENUM resolution process and DNS Configuration

When a user uses a specific device or program that supports the ENUM technology to enter a phone number, the client application processes the entered phone number according to the preprocessing process, DNSResolver parses the processed string according to the DNS protocol and obtains the URI set corresponding to this ENUM from DNSServer. Then, the application selects the corresponding URI based on its own application requirements, continue to execute the relevant protocols to complete the expected operations. For example, if a user wants to send E-mail to an E.164 user who owns "+ 86-10-62553604", when he enters the phone number in the foxmail address bar that supports the ENUM technology, foxmail pre-processes the phone number as "4. o.6.3.5.5.2.6.O. 1.6.8.e164.tld. Then, the user's local DNSResolver sends this string to DNSServer for resolution of similar domain names.

After a period of Research and Development, The ENUM technology has been able to support Voice, E-mail, HTTP, SIP, and many other applications, among them, the most explicit application is to find the SIP address in the SIP protocol used in the softswitch device and 3G network: When the softswitch is interconnected through the SIP, The ENUM can be used to determine the user's Softswitch; when a Softswitch device is interconnected through H.323, if the softswitch device initiates a call through the H.323URL alias in the ENUMDNS after querying, the ARQ/AFC message is not required to be sent to the network guard; in 3 GIMS (InternetMultimediasubsystem, Internet Multimedia Subsystem), SIP signaling routing uses SIP URLs for addressing. E.164 the user's public identity is converted to the sip url format for addressing. ENUM, as a tool for e.ing E.164 numbers to various business addresses, can also be used for InternetFAX and InstantMessage services, but there is no specific standard.

The Development and Research of these applications greatly enriches the content of traditional telecom services and Internet services, and makes the relationship between traditional telecom and Internet more closely. Further strengthening the study of ENUM technical features and operation services will effectively promote the development of the network, so as to effectively use existing network resources, especially broadband network resources. With its unique features, the ENUM technology expands the application space of E.164 numbers, bringing infinite vitality to the transformation of traditional telecom services.

TRIP Technology Introduction

A trip is an Inter-Domain gateway location and routing protocol. It integrates the advantages of SIP, BGP-4 and other routing protocols, and provides seamless interfaces for other application protocols such as H.323 and SIP, so that gateway with the same protocol can share the TRIP protocol, finally, Global Telephone routing for homogeneous networks across different domains is realized. A device that represents the TRIP function is called a locating server. Its main function is to exchange information with other locating servers, this information includes the accessibility of the telephone destination, the route to the destination, and the information about the telephone destination gateway that exists in the PSTN. The TRIP protocol allows managers of each gateway resource to establish their own local available gateway database based on different policies, and then aggregate, broadcast, exchange and share the information of different gateways between databases according to different policies. First, make the information available to you locally, and then spread the information to other suppliers according to certain policies, the gateway information in these databases can be directly queried and used by signaling servers, Softswitch devices, and other users. The TRIP protocol is a dedicated protocol for IP Telephone Gateway Routing information exchange between different management domains. It is a protocol independent of any signaling protocol. Its main functions are as follows:

Establishes and maintains the peer relationship between route information providers;

Exchange and synchronize the route information of the telephone gateway between the provider;

Prevents loops of stable routes;

And time-based and scalable way to broadcast known gateway route information;

Defines and describes the syntax, semantics, and routing information transmission rules of the circuit gateway route data.

As a routing mechanism unrelated to the specific call protocol, TRIP can solve the problem of Route intercommunication caused by different domains and different network structures. By sending and receiving TRIP messages, a TRIP can transmit the routing information between the domain and the domain, and store the optimal routing information in the telephone routing information database (TRIB) according to certain policies. In this way, the Softswitch itself does not need to maintain a large amount of routing information, but directly locates remote devices by requesting a TRIP to host a certain number of servers, so as to avoid the hop-by-hop processing and forwarding of call signals in the IP network.

A trip is a common tool for exchanging route information. Its Route UPDATE contains two meanings: 1. Location server (LS) located in different IP address telephone management domains (ITAD) route Interaction: Second, route synchronization is performed between LS located in the same ITAD. The first layer means to complete the essentially routing function, while the second layer means to maintain the consistency of the routing. TRIP does not specify the connection structure and form between LS. The LS in an ITAD can be configured as a mesh, star, or any other connection topology. Likewise, there is no limit on the topology of TRIPITADs, and it can be organized into a mesh or annular plane topology, multi-level structure, or other topology. In H.323 and SIP networks, to complete gateway routing and gateway locating, LS must have the Server registration function (equivalent to the network guard function in H.323 ), so that local LS can perceive all gateway devices in local ITAD.

When a TRIP is applied to a Softswitch device, its routing mechanism has not changed, but the ITAD Domain Based on the softswitch device is processed as a two-level hybrid network, the H.323 and SIP gateways are first connected to and registered with the softswitch device, and then all the gateway gateways in the domain (including the core Softswitch device) are forwarded to the LS (with the routing function of multiple application protocols, including H.323, SIP) registration. In this way, when a call is initiated from the IP domain to the PSTN domain, LS can discover the egress of the gateway through the softswitch device, or use the H.323 of the softswitch device, the SIP intercommunication function is addressing the corresponding protocol gateway or network guard, and then forwarded to the LS of other domains through LS. The above description is mainly about the seamless integration of the network based on the softswitch device with the existing SIP network and the H.323 network, so as to give full play to the characteristics of the multi-protocol exchange of the softswitch device. Through the timely update of the TRIP route, the call initiated by the IP domain can quickly find the best gateway route, and the corresponding route statistics can be carried out to prepare for the optimization of the gateway location in the future.

The main problem solved by the TRIP protocol is the gateway routing problem of the IP Phone. From a high point of view, it is to solve the ing problem. A given phone number maps the IP address of a telephone gateway. It can also be called "the conversion from a telephone number to an IP address ". Generally, we encounter many conversions between phone numbers and IP addresses, only when "a user's phone number is given a circuit switching network, determining the IP address of the gateway that can complete the call "is a problem to be solved by the TRIP protocol, only when it really involves the signaling information between one call device and another response device, layer-by-layer selection of IP gateway routing is required when uploading and transmitting IP networks, therefore, the TRIP protocol solves the problem of telephone number and IP address conversion, but not all IP address and address conversion problems can be solved.

Conclusion

Network Development is not achieved overnight. Different operators can choose different routing schemes based on their own network conditions and gradually evolve. For example, in the initial stage of network construction, simple Softswitch devices are deployed in a flat structure. In the medium term, you can use the server locating method to provide routing services for Softswitch devices. In the later stage, the server can be located hierarchically to provide large-scale routing services for the whole network. In future routing services, both ENUM and TRIP technologies can well complete the global telephone routing function, which may become an indispensable part of future Softswitch applications.