Scalability is King 1 Internet Scalability Rules Scalability

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Scalability is King 1

Scalability is King 1

Internet: Scalability Rules Scalability is : a critical factor in every decision Ease of

Internet: Scalability Rules Scalability is : a critical factor in every decision Ease of deployment and interconnection The intelligence is in the outskirts of the network 2

Internet: Design Goals The goal: to interconnect multiple existing networks and technologies • Packet

Internet: Design Goals The goal: to interconnect multiple existing networks and technologies • Packet switching over circuit switching • Reasons: - the applications were suited for this: rlogin - Packet switching was well understood - More flexible, less committal “The design philosophy of the DARPA Internet protocol”, SIGCOMM 88 3

Internet Design: Secondary Level Goals Fault-tolerance (DARPA is the army) Support multiple communication services

Internet Design: Secondary Level Goals Fault-tolerance (DARPA is the army) Support multiple communication services Accommodate various technologies & networks Allow distributed management Enable cost effective resource Ease of interconnection: adding a host Resources used in the Internet must be accountable (less attention) 4

Fault Tolerance: The Internet Premise: One Robust Connected Network Size of Largest Connected Component

Fault Tolerance: The Internet Premise: One Robust Connected Network Size of Largest Connected Component #Deleted nodes Robust to random, sensitive to focused failures The network tends to stay as one connected component 5

I. State: The Enemy of Scalability Routing state: the information that a router needs

I. State: The Enemy of Scalability Routing state: the information that a router needs to keep in order to route Large routing state is bad • Consumes memory • Makes look-up slow State = information = intelligence The trade-off: intelligent vs scalable behavior 6

I. An Interesting Antithesis Telephone network: • End devices are stupid • Core is

I. An Interesting Antithesis Telephone network: • End devices are stupid • Core is intelligent Internet: • End devices are intelligent • Core is stupid (forward packets, no guarantees) Telephone network: • Circuit switching • Ultra reliable, guarantee quality(real-time) • Centralized control • Difficult to add new users • Cumbersome to new apps Internet: • • • Packet switching Unreliable: no guarantees Decentralized Easy to add new users Easy to add new applications 7

I. Internet: Routing State What does a router know? Routing table: • IP prefix

I. Internet: Routing State What does a router know? Routing table: • IP prefix -> outgoing link What is an IP prefix? Scalability: • IP prefixes aggregate many IPs to one entry • Routers do not* keep per connection information * Some exceptions exist. 8

I. State Per Flow: pros and cons What would state per flow give us?

I. State Per Flow: pros and cons What would state per flow give us? Differentiate our behavior per flow • Provide Qo. S Be fair: share resources accordingly Monitor and measure: accountability - costing Ensure that packets follow the same path 9

II. Centralized vs Decentralized Routing Centralized • • All information exists in one place

II. Centralized vs Decentralized Routing Centralized • • All information exists in one place Decisions are taken there The decision involves the whole path OSPF: all routes have all the info: Decentralized • Each router makes a decision in isolation • Each router knows partial/aggregated information • RIP, BGP are some protocols 10

III. Dynamic vs. Static Routing is an optimization problem What are we trying to

III. Dynamic vs. Static Routing is an optimization problem What are we trying to optimize? Static metrics (non time varying) • Number of hops (hopcount) • Link capacity • Buffer space Dynamic metrics (time varying) • • End 2 end (e 2 e) Delay Link delay Link utilization Available buffer space 11

III. Dynamic or Static Routing? Static routing • Stable • Arguably: utilizes resources well

III. Dynamic or Static Routing? Static routing • Stable • Arguably: utilizes resources well in the long run Dynamic routing • Flexible - adaptable • Better performance (short term at least) 12

IV. Qo. S Aware Routing Quality of Service is tightly coupled with Reservations •

IV. Qo. S Aware Routing Quality of Service is tightly coupled with Reservations • I need 10 Mb/s with at most 100 msec e 2 e delay Problems: • Find a suitable path - Centrally easier, - Distributed: start reserving, then backtrack • Reserving resources along the path • Protecting resources from future flows 13

For next time Refresh your memory: Kurose - Ross • Textbook: chapter 1: intro

For next time Refresh your memory: Kurose - Ross • Textbook: chapter 1: intro • Textbook: chapter 4: Network Layer and routing Read: Clark’s sigcomm ‘ 88 paper Case study: How stable is Internet routing: • Run traceroute (linux) and see what happens 14