Switching Techniques

• Some connections could be nonswitched, e.g., T1, T3, SONET

Types of Switching Protocols

1.

Circuit Switching

• Used for telephone networks, still the basis for narrowband ISDN

• It uses a synchronous Time-Division Multiplexing (TDM) technique to support multi-users and variable data rates

• -: Insufficient (monopolizing).

• -: Difficult to support high and variable (sometimes bursty) data rates

• Multirate Circuit Switching - a variant of circuit switching, e.g., ISDN/H.261 use p x 64 kbps channels

2.

Packet Switching

• X.25 protocol

• +: good if connection has high error rate

• -: High overhead (connection, error correction) -> slow

• -: The variable (unpredictable) data rate is not suitable for some multimedia data such as voice.

3.

Frame Relay

• Modern high-speed links has very low error rate. The additional bits added to each packet and the excessive error-checking become unnecessary.

• Reduction of layers: multiplexing and switching done at layer 2, layer 3 is eliminated.

• No hop-to-hop flow control and error control

• Uses variable-length (up to 1600 bytes) packets - frames

• Data rate in the range of T1 to T3

4.

Cell Relay

• Also known as Asynchronous Transfer Mode (ATM)

• Uses small and fixed-length packets - cells

• High data rate up to 100s and 1000s Mbps

    Fixed bit rate                                   Variable bit rate
	  <---------------------------------------------------->
     Simplicity                                            Complexity
-----+---------------+---------------+---------------+--------------+---
 Circuit         Multirate      Cell Relay         Frame         Packet
Switching         Circuit     (Asynchronous        Relay       Switching
		               Switching     Transfer Mode)