Fate Sharing Connection State No State State Lose state information for an entity if (and only if? the entity itself is lost Examples: >)OK to lose TCP state if one endpoint crashes NoT okay to lose if an intermediate router reboots >)Is this still true in today's network? NATs and firewalls Survivability compromise: Heterogenous network - less information available to end hosts and Internet level recovery mechanisms
6 Fate Sharing Lose state information for an entity if (and only if?) the entity itself is lost. Examples: » OK to lose TCP state if one endpoint crashes – NOT okay to lose if an intermediate router reboots » Is this still true in today’s network? – NATs and firewalls Survivability compromise: Heterogenous network -> less information available to end hosts and Internet level recovery mechanisms Connection State No State State
Types of Service Recall from last time tcP ys UDP >) Elastic apps that need reliability: remote login or emai >)Inelastic, loss-tolerant apps: real-time voice or video >)Others in between, or with stronger requirements Biggest cause of delay variation: re liable delivery Today's net: 100ms rtt Reliable delivery can add seconds Original Internet model: TCP/P one layer >) First app was remote login. >)But then came debugging, voice, etc. >)These differences caused the layer split, added UDP No Qos support assumed from below >)In fact, some underlying nets only supported reliable delivery Made Internet datagram service less useful! >)Hard to implement without network support >Qos is an ongoing debate
7 Types of Service Recall from last time TCP vs. UDP » Elastic apps that need reliability: remote login or email » Inelastic, loss-tolerant apps: real-time voice or video » Others in between, or with stronger requirements » Biggest cause of delay variation: reliable delivery – Today’s net: ~100ms RTT – Reliable delivery can add seconds. Original Internet model: “TCP/IP” one layer » First app was remote login… » But then came debugging, voice, etc. » These differences caused the layer split, added UDP No QoS support assumed from below » In fact, some underlying nets only supported reliable delivery – Made Internet datagram service less useful! » Hard to implement without network support » QoS is an ongoing debate…
Varieties of Networks Discussed a lot of this last time o Interconnect the arpanet. x25 networks, LANs, satellite networks, packet networks, serial links. Mininum set of assumptions for underlying net 》 Minimum packet size > Reasonable delivery odds, but not 100% > Some form of addressing unless point to point Important non-assumptions 》 Perfect reliability 》 Broadcast, multicast >) Priority handling of traffic >) Internal knowledge of delays, speeds, failures, etc Much engineering then only has to be done once 8
8 Varieties of Networks Discussed a lot of this last time - » Interconnect the ARPANET, X.25 networks, LANs, satellite networks, packet networks, serial links… Mininum set of assumptions for underlying net » Minimum packet size » Reasonable delivery odds, but not 100% » Some form of addressing unless point to point Important non-assumptions: » Perfect reliability » Broadcast, multicast » Priority handling of traffic » Internal knowledge of delays, speeds, failures, etc. Much engineering then only has to be done once
TheOther" goals Management > Today's Internet is decentralized-BGP >Very coarse tools. Still in the"assembly language"stage Cost effectiveness Economies of scale won out >)Internet cheaper than most dedicated networks >) Packet overhead less important by the year Attaching a host >)Not awful; DHCP and related autoconfiguration technologies helping. A ways to go, but the path is there
9 The “Other” goals Management » Today’s Internet is decentralized - BGP » Very coarse tools. Still in the “assembly language” stage Cost effectiveness » Economies of scale won out » Internet cheaper than most dedicated networks » Packet overhead less important by the year Attaching a host » Not awful; DHCP and related autoconfiguration technologies helping. A ways to go, but the path is there But…
Accountability Huge problem Accounting o Billing? (mostly flat-rate. But phones are moving that way too people like it!) >)Inter-prov ider payments Hornet,'s nest. Complicated. olitical. Hard Accountability and security 》 Huge problem 》 Worms, vIruses,etc Partly a host problem. But hosts very trusted 》 Authentication Purely optional. Many philosophical issues of privacy Vs security. 10
10 Accountability Huge problem. Accounting » Billing? (mostly flat-rate. But phones are moving that way too - people like it!) » Inter-provider payments – Hornet’s nest. Complicated. Political. Hard. Accountability and security » Huge problem. » Worms, viruses, etc. – Partly a host problem. But hosts very trusted. » Authentication – Purely optional. Many philosophical issues of privacy vs. security