Lecture 8 Virtual circuits ATM mPls Dejian Ye Software school Fudan University
1 Lecture 8 Virtual Circuits, ATM, MPLS Dejian Ye Software School Fudan University
Outline Exam discussion Layering review(bridges, routers, etc. 》 Exam section c Circuit switching refresher Virtual circuits- general Why virtual circuits? > How virtual circuits?- tag switching! Two modern implementations >)ATM-teleco-style virtual circuits >)MPLS-IP-style virtual circuits 2
2 Outline Exam discussion Layering review (bridges, routers, etc.) » Exam section C. Circuit switching refresher Virtual Circuits - general » Why virtual circuits? » How virtual circuits? -- tag switching! Two modern implementations » ATM - teleco-style virtual circuits » MPLS - IP-style virtual circuits
Exam stats Maxavg/min 90/63/20 B 19.6 17.9 12.8 11.0 57.6% 74.8% 58.3% 68.6% 876 321 3
3 Exam stats Max/avg/min: 90 / 63 / 20 A B C D 19.6 17.9 12.8 11.0 57.6% 74.8% 58.3% 68.6%
Common Exam Problems Routing: No one big problem; many small misunderstandings. Please check your scores Short answer: Many incorrect round-trip times vs one-way times DNS >)Always sends the full query!(e. g ra1 streaming. npr. org", not just"npr. org") Clients dont recurse: the local recursive dNs server does. Could run on clients, but usually doesnt. Routing and bridging and addressing
4 Common Exam Problems Routing: No one big problem; many small misunderstandings. Please check your scores. Short answer: Many incorrect round-trip times vs. one-way times. DNS » Always sends the full query! (e.g. “ra1.streaming.npr.org”, not just “npr.org”) » Clients don’t recurse; the local recursive DNS server does. Could run on clients, but usually doesn’t. Routing and bridging and addressing…
Packet Switching Source sends information as self-contained packets that have an address )Source may have to break up single message in multiple Each packet travels independently to the destination host >) Routers and switches use the address in the packet to determine how to forward the packets Destination recreates the message Analogy: a letter in surface mail 5
5 Packet Switching Source sends information as self-contained packets that have an address. » Source may have to break up single message in multiple Each packet travels independently to the destination host. » Routers and switches use the address in the packet to determine how to forward the packets Destination recreates the message. Analogy: a letter in surface mail