Traffic Engineering

Question 1

Traffic Engineering definition

Answer 1

• a fancy way of describing how network operators deal with large amounts of data flowing through their networks
• the process of reconfiguring the network in response to changing traffic loads in order to achieve some operational goal.

Question 2

Example operational goal accomplished by traffic engineering

Answer 2

relieve congestion on certain links
balance load more evenly
maintain traffic ratios with peers

Question 3

Steps to traffic engineering

Answer 3

1. Measurement
   - figure out the current traffic loads
   - measure the topology: connectivity, capacity of each link and router
   - measure the traffic or offered load
2. Modeling
   form a model of how configurations affect the underlying paths in the network
3. Control
   decide which changes to make and
   - adjust link weighs accordingly
   - use SDN to directly control the routes

Question 4

Key questions traffic engineering tries to address

Answer 4

• avoid congested links and satisfy certain requirements such as delay
• TCP senders send less traffic during congestion and routing protocols will adapt to topology changes

Question 5

Link utilization function

Answer 5

cost of congestion increases as the loads on the links continue to increase

Question 6

Data Center Networking 3 characteristics

Answer 6

1. Multi-tenancy

- - a data center provider provides service to multiple independent users

Question 7

Data center topologies - pods

Answer 7

Before:
In a “flat” layer 2 topology, every server has a MAC address. Each switch stores a forwarding table entry for every MAC address.

With pod:
Each server in a pod is assigned a pseudo MAC address in addition to their real MAC address. Switch at the top of each pod has entries for all of the servers inside the pod as well as entries for reaching other pods in the topology.

Question 8

pods - fabric manager

Answer 8

A map between real MAC address and pseudo MAC address is established. When a host issues an ARP query, the query is intercepted by the switch at the top of the pod and forwards it to the fabric manager. The fabric manager responds with the pseudo MAC address corresponding to the IP address in question. The querying host then sends the frame with the destination pseudo MAC address. And the switch can forward to the pod corresponding to the pseduo MAC adderess. Once frame reaches the destination pod, the switch can map the pseudo MAC address back to the real MAC address.

Question 9

Data Center (intradomain) traffic engineering

Answer 9

existing data center topologies:

• • provide limited server-to-server capacity
• • resources are fragmented, which lower utilization and cost efficiency

Question 10

VL2

Answer 10

provide the abstraction of one big layer 2 switch in order to reduce the fragmentation

Question 11

Goals of Valiant Load Balancing

Answer 11

• • spread traffic evenly across the servers

- - ensure traffic load is balanced independently of the destinations of flows

Question 12

Goals of jellyfish

Answer 12

higher throughput

incremental expandability