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

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)

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

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

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

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)

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

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

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

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

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.)

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

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?

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

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