| Todays telecommunication arena is rapidly moving | | | | and problematic to transmit, causing delay. SigComp |
| towards next-generation networks (NGNs) that offer | | | | solves the challenges of roundtrip delays, as well as |
| ubiquitous, converged services over converged voice, | | | | mobile user equipment battery life |
| video, data and mobile networks. Until very recently, | | | | P-headers (RFCs 3455 and 3325) |
| the prevailing telecommunications paradigm was | | | | (P- Private) In addition to standard headers, the 3GPP |
| based on multiple types of networks, each serving | | | | defined additional headers targeted at solving specific |
| different types of applications. | | | | IMS network problems, such as obtaining information |
| While IP-related technology holds the most promise | | | | about the access network (cell ID) and the visited |
| for meeting the requirements of NGNs, the use of | | | | network (roamed network), and determining caller |
| the global Internet is quite limiting. The IP Multimedia | | | | identity. |
| Subsystem (IMS) is an architecture that allows | | | | Security Agreement (RFC 3329) |
| delivery of identical services to fixed and mobile | | | | This IMS SIP extension specifies how to negotiate |
| customers regardless of whether they are connected | | | | security capabilities for multiple types of endpoints. |
| through the packet-switched (PS) or circuit-switched | | | | AKA-MD5 (RFC 3310) |
| (CS) network. IMS-based services enable | | | | This IMS SIP extension determines how terminals and |
| communication in a variety of modes including voice, | | | | networks are authenticated using already defined |
| text, location, presence, messaging, pictures and | | | | mechanism (e.g. ISIM), as well as specific key |
| video, or any combination of these. | | | | exchange. |
| In addition to service creation and delivery, IMS | | | | IPSec |
| handles call control issues, and can easily be adapted | | | | IPSec is used on various IMS interfaces and between |
| to serve roaming subscribers. The IMS architecture is | | | | different IMS networks. IMS uses IPSec in the |
| inherently capable of bridging between separate | | | | transport mode, as opposed to the standard used in |
| networks, and will ultimately be used for all types of | | | | VPN services. |
| networks, such as wireline Voice-over-IP (VoIP) | | | | Media Authorization (RFC 3313) |
| networks, WiMax wireless networks and packet | | | | Ensures that only authorized media resources are |
| cable networks. | | | | used. |
| The expansion and acceptance of IMS is an indication | | | | Mobile Registration (RFCs 3327 and 3608) |
| of just how important this technology is to the | | | | On IMS networks, the terminal registration process is |
| future of unified communications. Many organizations | | | | more complicated, as it includes various security |
| which are responsible for network standardization are | | | | extensions and must deal with registration from a |
| currently adopting IMS technology. The ramifications | | | | visited network. RFC 3608 and RFC 3327 define the |
| for the industry are significant, and the entire | | | | syntax and SIP entity usage of the Service-route |
| telecommunications industry is gearing up for the | | | | and Path headers. |
| imminent widespread implementation of IMS. | | | | Reg-event Package (RFC 3680) |
| Based on a Strong Signaling Foundation: Session | | | | Used by the terminal and the P-CSCF to know the |
| Initiation Protocol (SIP) | | | | terminal registration status on the network. |
| IMS technology was originally developed for the | | | | IPv6 |
| cellular arena to define how to set up advanced | | | | IMS prefers IPv6 networks, which offers distinct |
| services for 3G cellular networks and grew out of a | | | | advantages. It permits a larger set of addresses and |
| group of standards created by the 3rd Generation | | | | contains embedded IPSec functionality that may |
| Partnership Project (3GPP). | | | | eliminate the need for entities like NATs and firewalls. |
| IMS is a Media-over-IP network and uses the Session | | | | Preconditions (RFC 4032) |
| Initiation Protocol (SIP), originally standardized by the | | | | Specifies method for negotiating QoS, security and |
| IETF, as its base signaling protocol. The 3GPP chose | | | | other required call behavior between two terminals. |
| SIP as its base protocol because previous telecom | | | | IMS Resource Reservation (RFC 3312) |
| signaling protocols failed to comply with all IMS | | | | Defines how to make resource reservations for |
| requirements. Because SIP is an Internet protocol, it | | | | phone calls or sessions. |
| can accommodate convergence, and has the | | | | Session Description Protocol (SDP) |
| potential to meet all the needs of the IMS | | | | SDP defines the basic negotiation process for the |
| architecture. For instance, SIP can signal between | | | | media streams, and includes the bit rate and codec |
| different network entities, including endpoints and | | | | to be used, as well as other media attributes. IMS |
| servers. In IMS, each network server has its own | | | | extends SDP with even more extensions, such as |
| role, in contrast to traditional networks where a | | | | grouping of media lines, QoS and preconditions |
| central office switch does it all, including call control | | | | attributes, supplemental codec support, and |
| and service control. In addition, SIP uses Internet | | | | bandwidth modifiers. |
| extensibility mechanisms. A service provider with IMS | | | | XML Usage |
| networks initially may only have a small number of | | | | IMS SIP signaling uses XML protocols extensively, |
| subscribers. As the subscriber base grows, IMS | | | | including XCAP, to implement various kinds of SIP |
| networks must be easily scalable to add more | | | | message contents, and to allow full function |
| subscribers. SIP is also very flexible, and uses | | | | interfaces between IMS entities. |
| standard extensions. SIPs flexibility enables IMS | | | | IMS Simple Extensions |
| networks to adapt and change signaling protocols to | | | | The SIMPLE group is an IETF working group that |
| meet dynamic market needs. Finally, SIP provides | | | | defines presence and instant messaging signaling |
| adequate security, with both internal and external | | | | requirements. Basic SIMPLE definitions were |
| security mechanisms. | | | | inadequate for IMS applications because they were |
| IMS SIP: A Complex Challenge | | | | not efficient enough for use on the air link. IMS SIP |
| While offering the right foundation, SIP in its IMS | | | | extended this standard with the following: |
| form has proven to be quite complex and presented | | | | . Partial Notifications / Publications |
| many technological challenges. There were many | | | | . Notifications filtering |
| gaps between the SIP initially defined by the IETF, | | | | . Resource list / SIP exploders |
| and the features required for full IMS support. To | | | | . Message Session Relay Protocol (MSRP) |
| solve this problem the 3GPP defined dozens of SIP | | | | IMS SIP Expertise: A Prerequisite for Success |
| extensions additions that are specific to IMS | | | | The use of SIP in IMS networks requires a great deal |
| networks. Collectively, these extensions comprise the | | | | of adaptation and extension of the original signaling |
| IMS SIP protocol, which is defined in the 3GPP | | | | protocol. Given the breadth, variety and complexity |
| TS.24.229 standard. These extensions, such as | | | | of IMS SIP, it is indeed an arduous task to develop |
| extended call control, presence and instant | | | | new services and applications from scratch. A more |
| messaging, extend the functionality of SIP on IMS | | | | reasonable approach is to use prepared toolkits and |
| networks. This new IMS SIP usage profile is perhaps | | | | infrastructure products that encompass all the |
| the most important in the telecommunications | | | | nuances of IMS SIP, and where much of the |
| industry, and is uniquely the most appropriate for | | | | development effort and interoperability testing (IOT) |
| NGN networks. | | | | have already been completed. |
| To illustrate the inherent complexity of IMS SIP and | | | | In order to execute IMS roadmaps and ensure |
| all its extensions, we will review the major extensions | | | | on-time deployment, developers need solutions that |
| below: | | | | are finely tuned to the unique characteristics of IMS |
| SigComp (RFC 3320) | | | | SIP and that provide the extended SIP signaling |
| The SigComp extension defines how to compress | | | | infrastructure needed for IMS applications. |
| SIP textual signaling data, which can be very large | | | | |