IMS SIP The Right Solution for Widespread Next Generation Networks

Today's telecommunication arena is rapidly moving towards next generation networks (NGNs) that offer ubiquitous, converged services over converged voice, video, data and mobile networks. Until very recently, was the prevailing telecommunications paradigm based on several different types of networks, each serving different types of applications.

While IP technology provides the most promising to meet the requirements of NGN is the use of the global Internet rather limiting. IP Multimedia Subsystem (IMS) is an architecture that allows delivery of identical services to fixed and mobile customers - whether they are connected via packet switched (PS) or circuit switched (CS) networks. IMS-based services enable communication in a variety of ways - including voice, text, location, presence, messaging, photos and video, or a combination thereof.

In addition to service development and delivery, IMS handles call control issues and can be easily adapted to serve roaming subscribers. IMS architecture itself is able to build bridges between different networks, and ultimately will be used for all types of networks such as wireline Voice over IP (VoIP) networks, WiMax wireless networks and packet cable networks.

Expansion and acceptance of IMS is an indication of how important this technology is the future of unified communications. Many organizations responsible for network standardization is currently adopting IMS technology. Implications for industry are considerable, and the entire telecommunications industry is ready for the imminent widespread implementation of IMS.

Based on a strong Signaling Foundation: Session Initiation Protocol (SIP)

IMS technology was originally developed for cellular arena to define how to configure advanced services for 3G wireless networks and grew out of a group of standards created by the 3rd Generation Partnership Project (3GPP).

IMS is a Media-over-IP network and uses Session Initiation Protocol (SIP), which was originally standardized by the IETF, as its base signaling protocol. 3GPP chose SIP as its base protocol, because the former telecommunications signaling protocols failed to abide by all IMS requirements. Because SIP is an Internet protocol that can accommodate convergence and has the potential to meet all requirements of the IMS architecture. For example, the SIP signal between different network entities, including endpoints and servers. In IMS, each network server has its own role, in contrast to traditional networks where a central office switch does it all, including call management and service control. In addition, SIP uses the Internet extensibility mechanisms. A provider of IMS network in the first instance can have only a small number of subscribers. As the subscriber base grows, IMS network must be easily scalable to add more subscribers. SIP is also very flexible and uses standard extensions. SIP's flexibility enables IMS networks to adapt and modify the signaling protocols to meet dynamic market needs. Finally, SIP provides adequate security, both internal and external security mechanisms.

IMS SIP: a complex challenge

At the same time gives the right foundation, SIP in its IMS form has proven to be very complex and presents many technological challenges. There were many gaps between SIP originally defined by the IETF, and the functions required for full IMS support. To solve this problem 3GPP defined dozens of SIP extensions - add-ons that are specific to the IMS network. Collectively, these extensions include IMS SIP protocol, as defined in 3GPP TS.24.229 standard. These extensions, such as enhanced call control, presence and instant messaging, extend the functionality of SIP for IMS networks. This new IMS SIP user profile is perhaps the most important in the telecommunications industry and is uniquely the most appropriate for NGN networks.

To illustrate the inherent complexity of IMS SIP and all extensions, we will review the major extensions below:

SigComp (RFC 3320)

The SigComp extension defines how to compress SIP textual signaling data, which can be very large and problematic to transmit, causing delay. SigComp solves the challenges roundtrip delay, as well as mobile user equipment battery

P-headers (RFC 3455 and 3325)

(P-private) in addition to standard headers, the 3GPP defined additional headers targeted at solving specific IMS network problems, such as information about access to the network (cell ID) and the visited network (roamed network) and determine Caller ID .

Security Agreement (RFC 3329)

This IMS SIP extension specifies how to negotiate security for several types of endpoints.

AKA-MD5 (RFC 3310)

This IMS SIP extension determines how terminals and networks that pass through already defined mechanism (eg ISIM), and specific key exchange.

IPSec

IPSec is used in various IMS interfaces and between different IMS networks. IMS uses IPSec in transport mode, as opposed to the standard used in VPN services.

Media Authorization (RFC 3313)

Ensures that only authorized media resources are used.

Mobile Registration (RFC 3327 and 3608)

About IMS network, the terminal registration process is more complicated since it contains various security extensions and dealing with registration of a visited network. RFC 3608 and RFC 3327 defines the syntax and SIP entity using the Service route and Path headers.

Reg-event package (RFC 3680)

Used by the terminal and the P-CSCF to know the terminal registration status on the network.

IPv6

IMS prefers IPv6 networks, which offer different benefits. It gives a larger set of addresses and contains built-in IPsec features that can eliminate the need for devices that NAT and firewalls.

Preconditions (RFC 4032)

Specifies method for negotiating QoS, security and other required call behavior between two terminals.

IMS Resource Reservation (RFC 3312)

Defines how to make resource reservations for telephone calls or meetings.

Session Description Protocol (SDP)

SDP defines the basic negotiation of media streams, and includes the bit rate and codec to be used, as well as other media attributes. IMS extends SDP with even more enhancements, such as grouping of media lines, QoS and preconditions attributes, additional codecs and bandwidth modifiers.

XML Usage

IMS SIP signaling uses XML protocols, extensive, including XCAP, to implement various forms of SIP message content, and to provide full function interfaces between IMS entities.

IMS Simple Extensions

The SIMPLE group is an IETF working group that defines the presence and instant messaging signaling requirements. Basic simple definitions were inadequate for IMS applications, because they were not effective enough for use in flight. IMS SIP extended this standard with the following:

. Partial Releases / Publications

. Announcements filtering

. Resource List / SIP exploder

. Message Session Relay Protocol (MSRP)

IMS SIP Expertise: A prerequisite for success

The use of SIP in IMS networks require much adaptation and extension of the initial signaling protocol. Given the breadth, variety and complexity of IMS SIP, it is indeed a difficult task to develop new services and applications from scratch. A more reasonable approach is to use prepared tools and infrastructure products, which include all the nuances of IMS SIP and how much of the development effort and interoperability testing (IOT) has already been completed.

To perform IMS roadmaps and ensure on-time deployment, developers need solutions that are tailored to the unique characteristics of IMS SIP and that provide the extended SIP signaling infrastructure necessary for IMS applications.