Evolved Packet System (EPS): The LTE and SAE Evolution of 3G UMTS

6.5 Voice and Multimedia Telephony

This section deals with voice and general-purpose real-time conversational multimedia services in Evolved UMTS networks.

Video telephony in not new to Evolved UMTS networks, as it is already proposed as a service by 3G networks using two alternatives:

• The circuit-switched solution, based on the ITU H.324M standard (M for ‘Mobile’). H.324M is actually the low bit rate variant of H.324, using 3GPP voice-coding algorithms specially designed for wireless transmission.
• The packet-based solution, using IETF protocols for signalling and data transport like the 3GPP IMS solution.

In the scope of Evolved UMTS networks, only this latter alternative will be described in this chapter. In its most general definition, an IMS multimedia session may include any combination of the following three media types: voice, video and text.

While voice and video media flows are very constraining from real-time and requested resource perspectives, text transmission only requires a low bit rate bearer, as the transmission rate does not exceed 30 characters per second. Unlike text-messaging services, typed character flow is simply time-sampled so that no specific action is needed from the user to request transmission. In principle, the characters typed on a keyboard or drawn on a screen on the sending terminal should be rendered in real time on the display of the receiving terminal.

The media flows being set up for a multimedia session may not necessarily be arranged in ...