CSE561 10/9/2002 Notes

Project
1. get as much of the design out of the way as possible, as soon as possible
2. make sure that you stay on track and don't move off onto a tangent
3. for October 22, have 3 pages including
   • background reading (probably a few papers)
   • identify hypothesis (identify the question precisely)
   • method and explanation of experiments (how you intend to answer the hypothesis; sketch details and be specific, though later refinements are okay)
   • 1-2 pages of introduction (synopsis)
     • What's the question?
     • alternative technologies and approaches
     • What's wrong with these alternatives? (be fair to other/current systems/ideas)
     • What do you plan to do? (your contribution and approach)
     • evaluation of your results (what you expect to show)

Transport/Addressing
1. API?
   • sockets: read/write byte interface (pipe)
     • handshaking
     • two-way
2. TCP: two-way byte stream
   • connection halts if outgoing buffer fills up (needs to receive acknowledgements in order to empty)
   • data must be broken into packets (might ask IP for suggested packet size)
   • (denial of service attacks try to fill up a host's limited resources)
   • Why is the byte # used for the (32-bit) sequence number?
     • fragmentation in IP
     • it could be possible to retransmit multiple small packets as one larger packet
     • Nagle's Algorithm: 1 partial packet is sent at a time, bulk up typing based on round trip time
3. Other kinds of connections are UDP and RPC
4. How do you prevent a fast sender from overwhelming a slow receiver?
   • drop packets (cheap way)
   • receiver specifies a sliding window size and the sender must stop when the window is full
   • every acknowledgement carries the remaining window size
   • to prevent "silly window syndrome" (where the sender sends small amounts of data just because there is a small amount of room available in the receiver's window), the receiver will sometimes wait until its window is half empty before telling the sender

Connection Setup / Tear Down
1. connection setup
   • buffer allocated
   • pick random sequence number (if you always choose 1, then it is vulnerable to attacks, masquerading; randomization also helps eliminate confusion with old packets)
   • window size
2. asymmetric open
   • sender sends SYN with initial sequence number, x
   • receiver acknowledges a SYN requesting x+1 and sending it's own sequence number, y
   • sender acknowledges with a request for y+1
   • they begin sending eachother data based on their numbers
3. symmetric close (send FIN, but sometimes the host doesn't wait for acknowledgement)
4. SYN cookies help to prevent flooding attacks

Addressing
1. IP has:
   • destination address
   • source address
2. TCP has:
   • to: port
   • from: port
   • sequence number
   • acknowledgement number
   • flags
   • checksum
3. unique identity, globally unique - Internet style
   • depending on the route, a host may have different numbers because of interfaces
   • virtual hosts may have a unique address
4. Domain Name System
   • takes a name, looks up an address
   • multiple servers serve names, so there can be temporary inconsistancies as changes propegate
   • some names may map to a list of hosts (eg. a server farm somewhere, may send back a round robin element instead)
   • if the host representing the name goes down, then the location would look unavailable to some while the DNS updates
5. load balancers
   • forward requests to multiple hosts (server farm)
   • if one host fails, then another can take over
6. NATs
   • similar to load balancers, but meant to function the other way around
   • distinguish different connections through selecting the port number
7. Is global addressability necessary?
   • IPv6 - 128 bit address
   • IPv4 - 32 bit address
   • all IPv4 addresses haven't been used up yet (probably because of increased use of systems like NATs)
   • perceived limit on addresses makes them cost
   • names as addresses have the following considerations: routability, aggregation, length