1. COMPUTER NETWORKS
CS610
Lecture-37
Hammad Khalid Khan

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

3. 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

4. TCP Segment Format

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

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

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

8. 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

9. Illustration of NAT

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

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

12. Illustration of NAT Translation

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

14. Implementation of NAT

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

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