Review

• IP
• TCP
• presentation layer

IP

• addresses:
  • class A, B, C
  • subnets and subnet masks
  • CIDR, Classless InterDomain Routing
• domain names
• TTL
• fragmentation:
  • ID
  • offset
  • "last" bit
• header checksum
• demultiplexing

Routing

• distance vector:
  • exchange "I can get to X with metric M" information
  • use route to whoever can reach X with least metric M[min]
• link-state:
  • exchange "I am connected to X with metric M" information
  • build map of entire network
  • use map to determine next hop (or entire route) to X
• RIP: distance vector
• OSPF: link state
• BGP: path state

IP

• IPv6:
  • 128-bit addresses
  • no header checksum
  • "extension headers" instead of options
  • flows
• Mobile IP
• ICMP, Internet Control Message Protocol
• DHCP, Dynamic Host Configuration Protocol
• Multicast routing:
  • leaf-initiated join

Transport Protocols

• TCP: reliable, connection-oriented, expensive
• UDP: unreliable, packet-oriented, cheap
• source port number, destination port number
• IP pseudo-header checksum

TCP

• 32-bit sequence numbers, ack numbers
• cumulative acks
• connection setup: three way handshake of SYN, SYN+ACK, ACK
• connection close: FIN, ACK, FIN, ACK (4 packets)
• reset connection when hopelessly out of synch
• powerful timeout computation: T = t + 4D

TCP Windows

• flow control:
  • don't send faster than receiver can receive
  • 16-bit window in ack packet tells how many bytes can send beyond ack number
• congestion control:
  • additive (linear) increase, multiplicative decrease
  • bandwidth-delay product is amount of data buffered by network
  • Reno:
    • slow start up to limit l
    • linear increase
    • when packet is lost, go back to slow start, set l= l /2
  • Vegas: keep 1-3 "extra" packets in the network, X = W - RD

Retransmission

• Stop and Wait
• Alternating Bit Protocol
• Go Back N
• Selective Retransmission

Data Encodings

• Integer, structure, array encodings
• XDR, ASN.1
• lossless data compression:
  • Huffman Coding
  • Lempel-Ziv (dictionary)
• lossy data compression:
  • GIF
  • JPEG
  • MPEG

Cryptography

• threats
• one-time pad
• RSA (Rivest-Shamir-Adleman)
• DES (Digital Encryption Standard)
• digital signatures