1. Languages for Software-Defined Networks
Speaker：Chao-Yu Wang
Advisor：Ke, Kai-Wei

2. Outline SDN introduction Frenetic project Introduction
Querying Network State
Composing Network Policies
Consistent Updates

3. SDN introduction
SDN suggests to centralize network intelligence in one network component by disassociating the forwarding process of network packets (Data Plane) from the routing process (Control plane). 

4. SDN introduction (Cont’d)

5. Frenetic project Introduction Querying Network State
Composing Network Policies
Consistent Updates

6. Introduction Programming is still difficult on controller
Modularize the network function is difficult
Frenetic decide to raise the level of abstraction for programming SDN

7. Querying Network State
Properties of Frenetic Queries
Example Frenetic Queries

8. Properties of Frenetic Queries
To tally all web server traffic excluding the host with IP source address “ ”
We need to use two rules:
A high-priority rule matching packets from with TCP source port 80
A lower-priority matching remaining traffic with TCP source port 80
Predicate like “srcip!= & srcport=80”
Frenetic query syntax: Select(), Limit(), Every(), etc.

9. Example Frenetic Queries

10. Composing Network Policies
Creating Modular Programs
Efficient Runtime System

11. Creating Modular Programs

12. Creating Modular Programs (Cont’d)
def repeater_monitor(switch):
pat1 = {in_port:1}
pat2web = {in_port:2, tp_src:80}
pat2 = {in_port:2}
install(switch, pat1, DEFAULT, None, [output(2)] )
install(switch, pat2web, HIGH, None, [output(1)] )
install(switch, pat2, DEFAULT, None, [output(2)] )
query_stats(s, pat2web)

13. Creating Modular Programs(Cont’d)

14. Efficient Runtime System

15. Efficient Runtime System (Cont’d)
Several situation it cannot proactively generate all the rules it needs to implement a policy
For example, decide to match all destination IP 90.* address
Most of OpenFlow switches don’t support arbitrary wildcards
Solved by overapproximation

16. Consistent Updates
Per-Packet Consistent Updates
Per-Flow Consistency

17. Consistent Updates
Programs often need to transition from one policy to another E.g., topology changes, application behavior, unexpected failures
To avoid anomalies, every transition must be implemented gracefully
Per-packet consistent updates, Per-flow consistency

18. Per-Packet Consistent Updates
Guarantees that every packet flowing through the network is processed with exactly one forwarding policy
Two-phase update
Stamp packets at the ingress and test for the next version number elsewhere
Install the rules for internal ports, leaving the rule for the old configuration in place (packets will be processed depending on the version number)
The controller starts updating the rules for ports at network ingress, and stamp incoming packets with the new version number

19. Per-Flow Consistency
Ensures that streams of related packets are processed with the same policy
Combining versioning with rule timeouts
Per-install the new configuration on internal switches
Leaving the old version in place
The controller sets soft timeouts on the rules for the old configuration and installs the new configuration at lower priority

20. Reference
Nate Foster, Michael J. Freedman, Arjun Guha, Rob Harrison, Naga Praveen Katta, Christopher Monsanto, Joshua Reich, Mark Reitblatt, Jennifer Rexford, Cole Schlesinger, Alec Story, and David Walker. Languages for software-defined networks. IEEE Communications Magazine, 51(2): , 2013. 
Nate Foster, Rob Harrison, Michael J. Freedman, Christopher Monsanto, Jennifer Rexford, Alec Story, and David Walker.Frenetic: A Network Programming Language. In ACM SIGPLAN International Conference on Functional Programming (ICFP), Tokyo, Japan, September 2011.