Virtual circuits source-to-dest path behaves much like te| ephone circuit” performance-WISe network actions along source-to-dest path 今c叫 all setup, teardown for each call before data can flow s each packet carries Vc identifier(not destination host address) g every router on source -dest path maintains “ state” for each passing connection link, router resources(bandwidth, buffers )may be allocated to vc (dedicated resources predictable service) Network Layer 4-12
Network Layer 4-12 Virtual circuits ❖ call setup, teardown for each call before data can flow ❖ each packet carries VC identifier (not destination host address) ❖ every router on source-dest path maintains “state” for each passing connection ❖ link, router resources (bandwidth, buffers) may be allocated to VC (dedicated resources = predictable service) “ source-to-dest path behaves much like telephone circuit” ▪ performance-wise ▪ network actions along source-to-dest path
VC implementation a Vc consists of 1. path from source to destination 2. VC numbers, one number for each link along path 3. entries in forwarding tables in routers along path packet belonging to VC carries VC number (rather than dest address) Vc number can be changed on each link new vc number comes from forwarding table Network Layer 4-13
Network Layer 4-13 VC implementation a VC consists of: 1. path from source to destination 2. VC numbers, one number for each link along path 3. entries in forwarding tables in routers along path ❖ packet belonging to VC carries VC number (rather than dest address) ❖ VC number can be changed on each link. ▪ new VC number comes from forwarding table
VC forwarding table VC number. forwarding table in nea∈ number northwest router: Incoming interface Incoming VC Outgoing interface Outgoing VC# 12 22 2 63 18 7 3123 97 87 VC routers maintain connection state information Network Layer 4-14
Network Layer 4-14 VC forwarding table 12 22 32 1 2 3 VC number interface number Incoming interface Incoming VC # Outgoing interface Outgoing VC # 1 12 3 22 2 63 1 18 3 7 2 17 1 97 3 87 … … … … forwarding table in northwest router: VC routers maintain connection state information!
Virtual circuits: signaling protocols , used to setup, maintain teardown VC wo used in atM frame-relay x 25 s not used in today s Internet application transport 5, data flow begins 6. receive data application transport network 4 call connected 3. accept ce network data link initiate call 2. incoming chlt data link physical H physical Network Layer 4-15
Network Layer 4-15 application transport network data link physical Virtual circuits: signaling protocols ❖ used to setup, maintain teardown VC ❖ used in ATM, frame-relay, X.25 ❖ not used in today’s Internet 1. initiate call 2. incoming call 4. call connected 3. accept call 5. data flow begins 6. receive data application transport network data link physical
Datagram networks no call setup at network layer routers: no state about end-to-end connections no network-level concept of connection packets forwarded using destination host address application application transport transport network 1. send datagrams data link 2. receive datagrams network I data link physical d physical Network Layer 4-16
Network Layer 4-16 Datagram networks ❖ no call setup at network layer ❖ routers: no state about end-to-end connections ▪ no network-level concept of “connection” ❖ packets forwarded using destination host address 1. send datagrams application transport network data link physical application transport network data link physical 2. receive datagrams