COMPUTER NETWORKS CS610 Lecture-37 Hammad Khalid Khan

Review Lecture 36 Achieving Reliability Packet Loss and Retransmission Adaptive Transmission Buffers, Flow Control, and Windows Three Way Handshake

Congestion Control The goal is to avoid adding retransmissions to an already congested network Reduce window size quickly in response to lost messages Assumption: loss is due to congestion Resume carefully. Otherwise the network will swing wildly between congestion and under utilization

TCP Segment Format

Network Address Translation (NAT) Chapter 26 Network Address Translation (NAT)

Network Address Translation (NAT) Extension of original addressing scheme Motivated by exhaustion of IP address space Allows multiple computers to share a single address

Network Address Translation (NAT) Requires device to perform packet translation Implementations available Stand-alone hardware device IP router with NAT functionality embedded

NAT Details Site Obtains a single valid IP address Assigns a private address to each computer Uses NAT box to connect to the internet NAT Translates address in IP datagrams

Illustration of NAT

NAT Example Site uses private network 10.0.0.0/8 internally First computer assigned 10.0.0.1 Second computer assigned 10.0.0.2 And so on . . . Site obtains a valid IP address (e.g. 128.210.24.6) Assume computer 10.0.0.1 sends to 128.211.134.4

NAT Example NAT translates the IP source address of the outgoing datagram NAT translates the destination address of incoming datagram

Illustration of NAT Translation

Illustration of NAT Translation Transparent to each end Computer at site sends and receives datagrams normally Computer in Internet receives datagrams from NAT box

Implementation of NAT

Implementation of NAT NAT device stores state information in table Value is entered in table when NAT box receives outgoing datagram for new destination

Summary Congestion Control TCP Segment Format Network Address Translation NAT Technology Implementation of NAT Basic Address Translation