1. TCP Traffic Characteristics—Deep buffer Switch
Steve Perry, Director of Networks UNM
Piyasat Nilkaew, Director of Networks NMSU

2. Overview Network IP Protocols TCP Switch overview Deep buffer switches
precautions

3. IP Protocols 8 bit field in packet header
Identifies specific protocol to be used
Tcp identified by protocol 6

4. TCP TCP is connection oriented Considered reliable
Requires acknowledgements (ACK)
Overhead costs
Sequencing and windowing

5. TCP Throughput Transmission
Tcp relies on windowing
Receiver Window (RWND)
Congestion Window (CWND)
TCP Slow Start
increase transmission rate on receipt of ACK, until eventually Congestion or loss occurs, then decrease transmission rate
Host A
one segment
RTT
Host B
two segments
four segments
ACK

6. TCP Throughput Transmission
TCP Congestion Avoidance
Congestion & packet Loss cause sender to slow down
Windowing ramps up again
Condition known as global synchronization
TCP Slow Start
ACKs being received,
so increase rate X
loss, so decrease rate
sending rate
time
TCP’s
“sawtooth”
behavior

7. TCP Effect on Throughput
The goal is to achieve maximum capacity out of the installed Bandwidth with TCP?
Alleviate 2 factors
Latency
Packet loss

8. TCP Effect on Throughput
Latency
Time for a TCP segment (packet) to travel to ITS Destination
Round trip time (RTT)
Slow down the ACKs, hence TCp can’t transmit promptly
Restricted by the law of physics
Speed of light
Packet Loss
error along the path
Network Congestion

9. TCP Effect on Throughput
Can be alleviated by
Upgrade the bandwidth
reducing the network hops
Guarantee a clean & High Speed path
Deploy network equipment with Deep buffer

10. TCP Throughput
TCP Throughput with Increasing network distance and packet loss

11. R&E traffic characteristics
Type of R&E traffic – TCP –based, microburst traffic that can quickly consume entire available bandwidth
a. Subject to TCP Global Synchronization
TCP traffic needs deep buffer on ports when congestion occurs.
No commercially available security devices can sit in-path with line- rate process speed
100 Gbps backbone across continental US
The general rule of thumb is that you need 50ms of line-rate output queue buffer for a 10G port, so there should be around 60MB of buffer.

12. Switches Science_dmz based on 10gbps ethernet
Interface speed/forwarding fallacy
Aggregate speeds if more than one level
Typically through link aggregation

13. Switching methods Cut through switching (errors)
Fragment free (errors)
Store and forward
Used with buffering model

14. Deep buffer switches Loads the switch with additional buffer capacity
Helps to smooth spikes
Prevents drops

15. Deep buffer switches
Example

16. Shortcut Sometimes tough to get buffer size esnet has info on site:
tuning/router-switch-buffer-size-issues/

17. precautions Don’t be bound by large buffer switches
Can be pricey
Depends on traffic (local or WAN)

18. Summary Network IP Protocols TCP Switch overview Deep buffer switches
precautions

19. Questions???