Miscellaneous on VoIP technology

We now have a lot of knowledge about VoIP technology, and we are almost at risk to talk about other applications and usage knowledge. In the use of VoIP technology, we will transmit voice signals in the IP network. However, there are also many technical needs to achieve long-distance IP network spanning.

◆ Session edge controller SBC) Technology

Session edge controller SBC, or session Controller) is a VoIP call control product used in environments where the phone is completely transmitted by VoIP without gateway. It uses all three types of VoIP protocols-H.323 gatekeeper, SIP proxy, and media gateway control protocol MGCP ). It will play an important role in the future delivery of VoIP technical services, allowing you to cross multiple IP networks, even if there is a firewall to cross, it can also provide quality assurance VoIP services.

Because there is no standard solution or some solutions cannot fully meet the requirements of network administrators, many existing session edge controllers use specialized solutions. IETF-related working groups are considering whether to develop new standards for providing current and future SBC functions, and how to use existing standard mechanisms to provide these features.

SBC is generally located between two service provider networks in a peer environment, or between an access network and a backbone network that provides services to residents and enterprise users. Although some SBC only process signaling, most of them process both signaling and media. This type of SBC implements communication between the component that processes the signaling and the component that processes the media stream signaling, which is carried out within the SBC.

Some people think that Softswitch will eventually include the edge controller function. However, the functions and core technologies of SoftSwitch and SBC are obviously different, and the different positioning of the network structure eliminates the possibility of "stuffing" the functions of most SBC.

Currently, Major edge session controller vendors include Acme Packet, Jasomi Networks, Kagoor Networks, Netrake, Newport Networks Ltd, and NexTone Communications. Sonus Networks, a Softswitch vendor, also provides session control functions.

Nortel Networks and Siemens have begun to consider how to make a difference in this field. IP-IP network edge SBC, IP-PSTN network edge media gateway and SoftSwitch do not overlap, there are different roles, need to configure specialized SBC, and further improve and ensure the voice quality of VoIP technology. SBC is generally located between the softswitch and the public Internet that controls the VoIP service. It has the following features:

Assume the role of network access terminal NAT in the network of the service provider to hide the real IP addresses of connected users;

Hiding the details of the network structure of the service provider when the network is interconnected, such as the number and location of servers;

Acts as a network firewall when logging on from an interconnected network to prevent hacker attacks and denial of service attacks;

Transmission of service quality information, which is used by different service providers to complete conversion between different mechanisms;

Manage connections when a call is established, and monitor the number of sent packets and the media type that is too detailed. This prevents users from attempting to transmit video services when applying for voice services;

Provide detailed call information for billing and settlement;

Handling NAT traversal allows operators to provide services to users without having to upgrade the firewall.

Due to the above functions of session edge controller, it plays an important role in the quality control and security of VoIP technology. The security function of SBC has not been tested, because the VoIP service has not been greatly attacked. These attacks are more dangerous than previous Internet attacks, because as VoIP technology becomes a mainstream application, more people use it as a lifeline service, such as making 911 calls. If you do not have formal security measures, you will be attacked.

◆ P2P impact on VoIP technology

VoIP makes full use of the characteristics of P2P technology. Non-centralized P2P networks can be expanded without limit and will not prolong the search time and increase the cost because of expansion. The processing capability and network bandwidth of end-user machines can be used to increase each node, the processing capability and bandwidth of P2P networks are correspondingly increased. P2P technology also has advantages in penetrating firewall and Network Address Translation NAT. Traditional centralized networks can also penetrate firewalls and NAT, but they usually increase very expensive costs. The more users, the higher the cost. A typical VoIP product using P2P technology is Skype.

Skype does not use centralized server resources, but network resources of each node ), this makes the voice call access rate and voice quality largely exceed those of traditional phones.

In terms of search, Skype adopts a multi-layer network structure of the global search directory GI. This structure uses a super node to enable each node in the network to obtain all the resources of other available nodes, these resources are dynamically combined to participate in traffic distribution, path selection, and bandwidth processing to ensure minimum latency.

Skype does not specify the port to enter, but randomly selects an entry port during installation, which can enhance the translation of the penetrating Network Address to NAT ).

Intelligent Routing is used for data transmission. All node resources are used to reduce latency and ensure the quality of speech.

In addition, Skype also uses encryption technology to provide simple interfaces, including Windows, Mac OS X, Linux, and Pocket PC.