quartz/content/notes/25-advanced-topics.md

title	aliases	tags
25-advanced-topics		cosc203 lecture

Datacenter networks

• 10's to 100's of thousands of hosts, often closely coupled, in close proximity
  • e-business :(e.g., amazon)
  • content servers: youtube etc
  • search engines, data mining (e.g., google)
• challenges
  • multiple applications, each server many clients
  • reliability
  • managing/balancing load
  • procesing, networking, data bottlenecks

network elements

• server racks, 20-40 server blades: host

• Top of Rack (TOR) switch

• Tier 2 switches: connect to ~16 TORS below

• tier 1 switches connect to ~16 T-2s below

• border routers: connections outside

• 

• multipath communcation

  • rich interconnecitions so many routes
  • increased throughput
  • increased reliability through redundancy

application-layer routing

• load balancer: app-layer routing
• recieves external client requests
• directs workload within data center
• returns results to client (data center internals are hidden)
• 

protocols

• similar to TCP/IP protocols
• link layer
  • RoCE: remote DMA (RDMA) over converged internet
    • direct memory access
    • communcation between memory of different computers
• transport layer
  • ECN (explicit congestion notification) used in transport layer congestion control
  • experimentation with hop-by-hop (backpressure) congestion
• routing management
  • SDN widely used
  • place related servers, as close as possible together

Software Defined networks

• separate control plane and data plane
  • monollithic router contains switching hardware, runs proprietary implementation of internet standard protocols in proprietary router
  • different "middleboxes" for different network layer functions:
    • firewalls, load balancers, NAT boxes

logically centralized control plane

• easier network management: avoid router misconfigs, greater flexibility of traggic flows
• table based forwarding allows "programming" routers
  • compute tables centrally and distribute
• open implementation of control plane