a. Cell DCH:

• When UE is switched ON, it assumes the CELL_DCH State by default.
• It exists when UE really requires UL/DL dedicated resource.
• UE is characterized at cell level according to its current Active set.
• Logical channels DCCH+DTCH are mapped to transport channel DCH.
• E.g. Voice call(CS), Video telephony(CS+PS)

b. Cell FACH:

• This happens when,

1. UE doesn’t require continuous circuit connection with n/w, but DL packets will work.
2. UE is forced to release the n/w resources to decrease the congestion problems (flip-flop between DCH and FACH).
3. Eventual location updates to support CELL_PCH and URA_PCH states (flip-flop between FACH and PCH).

• E.g. Call on hold(CS), File downloading(PS)
• No dedicated UL/DL is provided. However, UE will keep monitoring to DL common transport channel FACH ‘continuously’ and receives packet data meant for UE itself.
• When UL transmission is required, it uses RACH for 1-2 frames or CPCH for few more frames, depending on common access procedures; still UL transmission will be ‘discontinuous’.
• UE is known on cell level, but this time it’s based on the last cell update it made.

c. Cell PCH:

• This happens when UE doesn’t require an active connection(common/dedicated). But still needs to be connected, as it’s expecting a n/w initiated or terminated call(CS or PS) in future.
• So, no UL transmission is allowed. Selects a PCH(based on algo.) and keep monitoring (receiving) it in ‘discontinuous’ mode(DRX).
• Can commute only into CELL_FACH state.
• E.g. No outgoing call or data receive for long time
• UE is still identified on cell level, but now in the cell where UE made its last update, when it was in CELL_FACH state.
• At regular time interval, UE would have to move in CELL_FACH state to update the location area. If UE is traveling, this update will become frequent because of changing cells.
• In some cases UE can have the transition from CELL_DCH to CELL_PCH, but not vice versa; it has to GO VIA CELL_FACH.

d. URA PCH:

• This can be considered as a general case of CELL_PCH state. Because all the characteristics are same except one.
• That is, UE is known on URA(UTRAN Registration Area) level rather than cell level. It listens to PCH(and updates URA when required).
• If UE is traveling continuously from one cell to another. It would have to transit multiple time to CELL_FACH state for location update. By assigning URA_PCH state, this condition is avoided, since 1 URA CONTAINS one or more cells and vice versa.

a. Cell DCH:

b. Cell FACH:

c. Cell PCH:

d. URA PCH: