Điều này dẫn đến sự gián đoạn lưu lượng truy cập gói dữ liệu từ 2-3 giây tại tất cả các thay đổi tế bào. Đối với các cuộc gọi thoại hoặc video này là không thể chấp nhận được. Với UMTS, quản lý di động cho các kết nối chuyển mạch gói có thể bây giờ cũng được kiểm soát bởi hệ thống mạng. | 206 Communication Systems for the Mobile Information Society A number of existing channels which might also be used together with an E-DCH is shown in the middle and on the right of Figure . Most of the time an E-DCH is used together with HSDPA high-speed downlink shared channels which require a separate dedicated physical control channel DPCCH to send control information for downlink HARQ processes. In order to enable applications like voice and video telephony during an E-DCH session a mobile must also support simultaneous Release 99 dedicated data and control channels in the uplink. This is necessary because these applications require a fixed and constant bandwidth of and 64 kbit s respectively. In total an E-DCH capable terminal must therefore be able to simultaneously encode the data streams of at least five uplink channels. If multi-code operation for the E-DPDCH is used up to eight code channels are used in uplink direction at once. In the downlink direction HSUPA additionally introduces two mandatory and one optional channel to the other already numerous channels that have to be monitored in downlink direction. Figure shows all channels that a mobile station has to decode while having an E-DCH assigned in the uplink direction HSDPA channels in the downlink direction and an additional dedicated channel for a simultaneous voice or video session via a circuit-switched bearer. While HSUPA only carries user data in the uplink direction a number of control channels in the downlink direction are nevertheless necessary. For the network to be able to return acknowledgments for received uplink data frames to the terminal the enhanced HARQ information channel E-HICH is introduced. The E-HICH is a dedicated channel which means that the network needs to assign a separate E-HICH to each terminal currently in E-DCH state. In order to dynamically assign and remove bandwidth to and from individual users quickly a shared channel called the enhanced access grant
