Network Functionality In Cellular Packet-Switched Architecture
The control functions of a wireless network can be divided into three categories: call processing, mobility management, and radio resource management
- Call processing is a function of the central switching office, while mobility management and radio resource management are functions of the metropolitan area network.
- The three operations of call set-up (initiated by the mobile), speech transmission, and handoff serve to illustrate the functionality of the system.
Transmission of speech
- Packets move between the subscriber terminal, the base station, and the central switching office in both directions over the MAN
- Packets are sent on a first-in/first-out (FIFO) basis, since speech is involved and reordering of the packets is not allowed.
- A virtual circuit is assigned at the beginning of the call for transmission of speech in packets
- Packets may be lost in the conversation, but this does not significantly affect speech quality as long as not too many packets are lost.
- The cellular packet switched handoff algorithms distributes the processing among different interface units
- The WIU determines the channel quality, and when it becomes apparent that a call can be better handled by another base station, the call handoff procedure is initiated.
- A new base station is identified on the basis of the base station identifier read from the channel quality monitor, and the call is rerouted to the new base station.
- The TIU is informed of the handoff, and the routing table in the TIU is updated to reflect this information
- The WIU keeps the TIU informed of the location of the mobile when there are gaps in speech
- As a result of the handoff, no packets are lost, and any packets sent during the duration of the handoff process can be retransmitted to the new base station from the TIU