TCP Review - Stanford University

TCP Review - Stanford University

Midterm Review CS144 Review Session 5 May 2, 2008 Derrick Isaacson Maria Kazandjieva Ben Nham Announcements Upcoming dates Sat, 5/3: Lab 3 due with extension Mon, 5/5: In-class midterm Wed, 5/14: Lab 4 due

Lab 4 is out and is more complex than labs 1, 2, and 3 Midterm Review 1. 2. 3. 4. 5. 6. 7.

8. 9. Applications & app programming IP and forwarding Routing Transport & reliability TCP & congestion control DNS DCCP & NAT Queuing, caching, & content distribution Questions

Applications & app programming Telnet Web/HTTP BitTorrent Skype

Definitions End-to-End principle - dumb network, smart terminals Throughput bits/time Latency time for message to cross network Goodput application level throughput Jitter variation in latency P2P BitTorrent Tracker Tit-for-Tat - choked, top, and probing peers

BitTyrant Skype Distributed index located at super-peers Ch. 2 R.25 Skype uses P2P techniques for two important functions. What are they? 1. ? 2. ? P2P BitTorrent Tracker

Tit-for-Tat - choked, top, and probing peers BitTyrant Skype Distributed index located at super-peers Ch. 2 R.25 Skype uses P2P techniques for two important functions. What are they? 1. Query index (find someone) 2. Relays get around NATs Network layer: IP, forwarding, routing

IP Skinny waist of internet Connectionless

Best-effort delivery (unreliable) TTL Framentation Classful networks class A, B, C Classless Inter-Domain Routing (CIDR) Network layer supporting protocols

ARP map IP to link layer ethernet address ICMP ping, TTL exceeded, etc. DHCP dynamic IP address assignment DNS (later) Switching

Optical switch Bridge connect multiple LANs VLAN broadcast to portion of LAN Banyan networks one path from input to output Bisection bandwidth worst-case aggregate bandwidth between two equal-sized sets Routing Forwarding moving packets from input port to output port Routing populating forwarding table

Goal find lowest cost path between two nodes Distance Vector (Bellman-Ford) algorithm local, issues dealing with failures, RIP Link State (Dijkstras) algorithm global, broadcasts LSP, OSPF Path Vector next slide Autonomous Systems Each AS corresponds to an administrative domain Want own intra-domain routing protocol Want to set inter-domain routing based on policies (financial, legal, )

Issues transit/peering relationships, local/transit traffic, multihomed, Path Vector BGP, ASPATH announces, allows policy choices based on ASes in path, Multi-Exit Discriminators Datagram Congestion Control Protocol Make UDP play well with TCP Connection oriented Acks for congestion control NOT for reliable transport Acks are for last packet received rather than cumulative Uses sequence number windows to protect against

attacks need to resynchronize when a large burst of losses cause packets to fall past window Congestion Conrol IDs (CCIDs) what type of congestion control you use CCID 2: TCP CC (AIMD) CCID 3: TCP-friendly CC uses sending rate rather than congestion window receiver reports loss rate once per RTT NAT Expand 32 bit address space Translates local IP addresses to globally

routable IP addresses, and vice versa NAT types & problem Full cone, restricted cone, port restricted, symmetric Problems Incoming connections Port mapping constraints Solutions Rendezvous servers (Skype) STUN

NAT Hole-Punchingb Queuing Routers handle burstiness of traffic by queuing incoming packets Routers try to provide fairness, high throughput, and low delay Fair Queuing provide each flow an equal portion Packets placed in per flow FIFO Calculate Fi for each packet, or time it would complete being transmitted if we served just that flow Next packet to transmit is one with lowest Fi timestamp

Packets will be sent out within one maximum packet transmission time of perfect fairness Congestion avoidance Random Early Detection (RED) Dropped packets imply congestion in the internet Drop random packets early to fairly signal to all flows that congestion is increasing Use average queue length Make drop probability a function

of time since last drop to avoid over penalizing one flow. Caching & content distribution Web proxies, DNS servers, network file systems use to decrease latency and save bandwidth TTL, polling, callbacks, leases to deal with consistency Internet Cache Protocol allow proxies to query each other Reverse proxies content distribution networks like Akamai

Use some kind of hashing to locate cached data

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