Traffic Routing in Wireless Networks
The amount of traffic capacity required in a wireless network is highly dependent upon the type of traffic carried.Some traffic may have an urgent delivery schedule while some may have no need to be sent in real-time. The type of traffic carried by a network determines the routing services, protocols, and call handling techniques which must be employed.
Two general routing services are provided by networks
- Connection oriented services (virtual circuit routing)
- Connectionless services (datagram services)
- In connection-oriented routing, the communications path between the message source and destination is fixed for the entire duration of the message, and a call set-up procedure is required to dedicate networkresources to both the called and calling parties.
- Since the path through the network is fixed, the traffic in connection-oriented routing arrives at the receiver in the exact order it was transmitted.
- Connection-oriented service relies heavily on error control coding to provide data protection in case the network connection becomes noisy.
- If coding is not sufficient to protect the traffic, the call is broken, and the entire message must be retransmitted from the beginning.
Connectionless routing, on the other hand, does not establish a firm connection for the traffic, and instead relies on packet-based transmissions
- Packets sent using connectionless routing do not necessarily arrive in the order of transmission and must to be reordered at the receiver.Several packets form a message, and each individual packet in a connectionless service is routed separately
- Because packets take different routes in a connectionless service, some packets may be lost due to network or link failure; however others may get through with sufficient redundancy to enable the entire, message to be recreated at the receiver. Thus, connectionless routing often avoids having to retransmit an entire message, but requires more overhead information for each packet
- In a connectionless service, a call set-up procedure is notrequired at the beginning of a call, and each message burst is treated independently by the network
- Circuit switching establishes a dedicated connection (a radio channel between the base and mobile, and a dedicated phone line between the MSC and the PSTN) for the entire duration of a call.
- Wireless data networks are not well supported by circuit switching, due to their short, bursty transmissions which are often followed by periods of inactivity.Circuit switching is best suited for dedicated voice-only traffic, or for instances where data is continuously sent over long periods of time
- Packet switching is also called virtual switching. Itis the most common technique used to implement connectionless services and allows a large number of data users to remain virtually connected to the same physical channel in the network.
- Packet switching breaks each message into smaller units for transmission and recovery
- When a message is broken into packets, a certain amount of control informationis added to each packet to provide source and destination identification, as wellas error recovery provisions.Packet switching (also called packet radio when used over a wireless link) provides excellent channel efficiency for bursty data transmissions of short length.
- An advantage of packet-switched data is that the channel is utilized only when sending or receiving bursts of information