Analysis of large-scale Routing Technology in Next Generation Networks

I. Introduction

When a call is established for a traditional telephone exchange network, the signaling point code of the next exchange board is determined based on the E.164 number of the called phone number, and then the call is routed through the No. 7 signaling network according to the signaling point code, the essence of all call routes is to determine the signaling point encoding according to E.164, and then use the signaling point encoding for call routing.

Unlike the traditional PSTN (Public Switch Telephone Network) Network, in essence, the next-generation network call routing based on Softswitch determines the next hop Softswitch Based on the address of the called USER or directly locates the called terminal. The address of the called user can be in the form of E.164 number, URL (uniform Resource Locator, uniform Resource Locator) or IP address.

The convergence of networks and the diversity of addressing methods make the original PSTN network and IP network routing methods no longer meet the communication needs. In the next generation network routing technology, the problem of number translation must be taken into account. Therefore, it is necessary to study the next generation network routing technology.

This article focuses on the key routing technologies involved in large-scale next-generation Softswitch networks. These technologies are of positive significance for the development of next-generation networks based on SoftSwitch.

The control layer in the Next Generation Network is closely related to the business and needs to deal with various systems, such as routers, application servers, and database subsystems. This is part of the true embodiment of network intelligence. One of the most important problems to be solved at the control level of the Next Generation Network is the routing problem. So what is the Routing Problem of the Next Generation Network?

(1) User positioning and network addressing issues;

(2) there is a problem of Route intercommunication between different NGN (Next Generation Network) networks;

(3) questions about the mobile application of NGN users.

Ii. Next-generation network routing Solution

To address the above problems, the industry has proposed a variety of solutions for next-generation network routing.

1. Hierarchical Softswitch Routing System

For large NGN networks, we use the idea of PSTN layering to divide Softswitch into different layers for multi-level routing. However, the user plane is still carried by end-to-end grouping.

NGN network services are divided into two types: Intra-domain services and Inter-Domain services. The intra-domain service refers to the softswitch service in a certain area of NGN. The intra-domain Softswitch service only needs to know the routing information in the region. For routing information not in the local region, you only need to forward the call request to the Inter-Domain interconnection Softswitch that is connected to the intra-domain service SoftSwitch. The service Softswitch in the region focuses on providing a wide range of services for users in the region. Inter-Domain service Softswitch provides the function of routing between different domains of NGN. Once the number of softswitch routes for Inter-Domain interconnection is too large, you should consider dividing the softswitch for Inter-Domain interconnection into multi-level structures, but the softswitch for all intra-level services is still a plane structure.

This hierarchical routing Static Routing Method follows the multi-level Routing System of the PSTN network. The advantage is that the routing data of each Softswitch is relatively simple, and the network structure of the entire network is very clear.

2. Locating Server Routing System

The requirements for NGN determine that any switching device in the network can directly locate the peer device, without the need to send call signals by jump, you can set the shared location server in a centralized manner to meet such requirements.

When a certain area of softswitch expands to a certain number, the locating server can provide routing service for the softswitch in this area. Mutual routing information can be maintained between Softswitch in the domain to ensure rapid call establishment. At this time, each Softswitch only contacts the corresponding locating server. The locating server can locate the target SoftSwitch. In this case, the softswitch stores the complete routing information of the user in the control range and the routing information between the softswitch in the same domain. At the same time, you can also consider establishing a local ing library for some common addresses in the softswitch or locating server to speed up the call connection. Locate the number of servers based on the network capacity.

The locating server is not a standard network entity defined in the next generation network framework, but a functional entity proposed in the Next Generation Network to solve large-scale network routing problems, therefore, the functions and features of server locating have not been recognized by the industry. Different equipment manufacturers have different practices.

The main function of locating a server is to exchange information between locating servers through protocols, and accept Routing Query requests through protocols. The locating server supports routing information such as E.164, IP address, and URL. It supports multi-layer structure similar to PSTN and can be divided into different domains and layers. All levels of locating servers have the collection and query functions. They provide security services and can implement monitoring and other special services according to users' special needs.

From the way of obtaining route information, the locating server includes Static Routing and dynamic routing. Static Routing refers to the static configuration of routing information between servers and between the softswitch server and the locating server. Because both the softswitch server and the locating server have static IP addresses, you can save the correspondence between user numbers and IP addresses in the locating server and the softswitch server. To overcome the disadvantages of poor flexibility in Static Routing, different vendors adopt TRIP (Telephony Routing Over IP, IP telephone Routing Protocol), LDAP (Lightweight Directory Access Protocol, Lightweight Directory Access Protocol) DIAMERER, RAS (Registration Admission Status, permitted Registration Status), H.323 Annex G, and other protocols to locate the dynamic routing between the server and the locating server, and between the locating server and the softswitch server. It is precisely because different manufacturers adopt different protocols to achieve dynamic routing that communication problems exist.

3. Dynamic Routing System Based on DNS (Domain Name System)

In the NGN system, the E.164 number, URI (Uniform Resource Identifier, unified Resource Identifier) address, and IP address end users both exist. A user has multiple address methods, such as Session Initiation Protocol (Session Initiation Protocol). A terminal must have an E.164 number when communicating with a POTS user, the URI address can be used directly for communication between SIP terminals. When the URI address in the NGN network is widely used, the dynamic routing of the NGN network can be achieved through a mature DNS system. In addition to the traditional Domain Name Translation DNS, which is widely used on the IP network, the NGN network also introduces a new type of DNS, this new type of DNS uses the ENUM (Telephone (E.164) Number Mapping, Telephone Number ing) Protocol to map E.164 numbers to URI addresses, called enum dns.

The enum dns system adopts a hierarchical tree structure, which is exactly the same as the current DNS system. When the NGN network grows to a certain scale, it is necessary to consider carriers and international interconnectivity like the Internet DNS system. At this time, the enum dns must be planned globally.

The first hierarchical Softswitch routing method has obvious advantages. Its implementation technology is mature, the network layer is clear, the structure is simple, and it is easy to maintain and expand. At the same time, Softswitch can provide gateway functions for external networks, therefore, there are not many interconnection points, which ensures the security of the internal structure and information of the network. However, the disadvantages of this routing system are also very obvious: signaling requires jump-by-jump transmission, and each Softswitch in the middle needs to process the call signaling, resulting in a large call latency.

The second and third solutions involve two emerging routing technologies, which are described below.

Iii. Introduction to ENUM Technology

ENUM technology is a hot topic in today's computer network resource addressing and positioning methods. It is generated with the development of network convergence, network communication technology and requirements.

Is ENUM a protocol defined by the call Number Mapping group of IETF? E.164 Number and Domain Name System (E.164 Number and DNS ). It defines how to convert E.164 to a database on the DNS server as a domain name. In other words, ENUM defines a DNS-based architecture and protocol, each domain name converted from E.164 can correspond to a series of unified resource identifiers, so that the internationally unified E.164 phone number can be used as a network address resource on the Internet. ENUM can use phone numbers to search for Registrant's email, IP phone number, unified message, IP fax, personal webpage, and other information to implement various network applications and access restrictions, query redirection and other functions. E.164 number is an important resource used in traditional telecom networks, and the DNS system is an important foundation for the Internet. The combination of ENUM and ENUM is conducive to the development of traditional telecom services towards IP packet switching, ENUM is a technology of great significance to promote the final convergence of the two networks.

Based on the DNS system, ENUM mainly draws on the basic idea of DNS. enum dns 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 is a new dns rr (DNS Resource Record) type. It 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.

1. Telephone number preprocessing

The user enters the phone number, for example, "+ 86-27-87694036" and "+", to identify the ENUM service and distinguish other digital-based network services. If the number string entered by the user contains "+ ", the ENUM service preprocessing will be executed.

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.

2. 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, DNS Resolver parses the processed string according to the DNS protocol and obtains the URI set corresponding to this ENUM from the DNS Server. Then, the application selects the corresponding URI according to 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 DNS Resolver sends this string to the DNS Server for resolution similar to the domain name, the DNS Server will correspond to the two Uris configured for this string (SIP: enumsip@cnnic.net.cn and mailto: enummail@cnnic.net.cn) return to foxmail, foxmail select mailto: enummail@cnnic.net.cn for the next communication, e-mail to the enummail@cnnic.net.Cn. the parsing process for other applications is similar.

After a period of Research and Development, The ENUM technology has been able to support Voice, E-mail, HTTP, SIP, and many other applications, the most explicit application is to find the SIP address in the SIP protocol used in the softswitch and 3G networks:

* When intercommunication between Softswitch through SIP, 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.323 URL alias in the enum dns after querying the enum dns, it does not need to send an ARQ/AFC message to the network guard;

* In the 3g ims (Internet Multimedia subsystem, Internet Multimedia subsystem), the SIP signaling routing uses SIP URLs for addressing. E.164 the user's public identity is converted to the sip url format for addressing;

* As a tool for e.ing E.164 numbers to various business addresses, ENUM can also be used for Internet FAX and Instant Message services, but specific standards are missing.

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.

Iv. 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:

* Establish and maintain the peer relationship between the route information providers;

* Exchange and synchronize the Telephone Gateway Routing information between the provider;

* Prevents stable routing loops;

* Broadcast known gateway route information in a timely and scalable manner;

* 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. Similarly, there is no restriction on the topological structure of TRIP ITADs, which can be organized into a mesh or ring-like plane topology, multi-level structure, or other topological structure. 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 Softswitch, 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 network guard and the SIP gateway are first connected to the softswitch device, and register with it. Then, all the gateway gateways in the domain (including the core devices of softswitch) are registered with LS (which has the routing functions of multiple application protocols, including H.323 and SIP. 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, 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 softswitch multi-protocol exchange.

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.

Currently, specific TRIP applications mainly include:

* Switch call routing information according to different policies;

* When the network is simple, it only supports dynamic route synchronization.

V. 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, a simple Softswitch fully interconnected plane structure is adopted. In the middle stage, you can use the server locating method to provide routing services for SoftSwitch. 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.

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