CS4550: Computer Networks II network layer basics 1 circuit switches, control signals

1. CS4550:Computer Networks IInetwork layer basics 1circuit switches, control signals

2. network layer basics • circuit switching basics(1) • switching techniques • control signaling • spanning tree & shortest path algorithms(2) • basic routing techniques (3) • congestion control techniques (3)

3. basic switch design switching matrix control unit ... network interface ... ... ... trunks digital/analog devices

4. basic switch design • control unit contains program (OS) which receives & services requests • signaling - passing of messages between CU, other parts of switch, network, & customer • trunks - high capacity media connections to other switches • blocking/nonblocking switches

5. telephone calls • 4 formal phases: 1. call request 2. call confirm 3. info transfer 4. call clear • see procedure for tel call in text • exercise : describe the basic procedure of a control unit in handling a call

6. basic switching techniques • space division switching : data follows distinct physical paths through switch • crossbar switch • multi-stage switch • time division switching : data routed through switch using TDM • TDM bus switching • TSI : time slot interchange • TMS (another technique, not covered here)

7. crossbar switch inputs outputs at each crosspoint is a gate, enabled in 1 of 2 directions. CU enables/disables the gate settings # of switching elements = #in X #out

8. multi-stage switch example • combine small crossbars in stages for increased utilization, redundancy N=Inputs k crossbars N= outputs 1 1 }n n{ N·N n n n·k n·k n·k N·N n n n·k n·k n·k 9 9 #of switching elements = 2kN + k(N/n)2

9. TDM bus switching inputs outputs each I/O line connected via a gate; the bus receives bits from inputs, transmits to outputs whenever the gate is opened by CU

10. TSI : time slot interchange . . . . . . ... ... ... In out buffer counter Mapping table

11. control signaling : purpose • messages passed between parts of NW, & between user & NW, to maintain NW, for billing info, to create/terminate connections, etc. • functions -communicate with user (dial tone, busy signal) -send DA (number dialed) to proper switches -send call info (channel seized, released, busy) -billing info -equipment status (down, busy, up, etc.)

12. control signaling • in channel : same channel as user • in band • out of band • common channel : separate control channel from user • associated mode • nonassociated mode

13. control signals : in channel • used throughout early telco networks; still in wide use • use same communication channel as the customer • with 4K Hz analog channel, used the unused portions of the spectrum • advantages? • disadvantages?

14. control signals : in channel guard bands 4KHz 3KHz in band : more bandwidth, less time for use out of band : more time, less bandwidth, more difficult electronics and protocols

15. control signals : common channel • use different channels than user • associated mode - control channels on same physical transmission links • nonassociated mode - control channels on their own separate physical link/network analogy: highway patrol cars versus helicopter traffic control