Week2_CCS2201_Introduction to Networks(1).pdf

CCS2201 Introductions to Networks Fall 2023-2024 Lecture 2 Network Core Assoc. Prof. Hisham Dahshan 1  Introduction Overview. What is the Internet? What is a protocol? Network edge Network core: packet/ci...

CCS2201 Introductions to Networks Fall 2023-2024 Lecture 2 Network Core Assoc. Prof. Hisham Dahshan 1  Introduction Overview. What is the Internet? What is a protocol? Network edge Network core: packet/circuit switching, internet structure Performance: loss, delay, throughput Protocol layers, service models Security History 2 The network core mesh of interconnected mobile network routers national or global ISP packet-switching: hosts break application-layer messages into packets local or network forwards packets regional ISP from one router to the next, home network content across links on path from provider network datacenter source to destination network enterprise network  Two key network-core functions routing algorithm Routing: Forwarding: local local forwarding forwarding table table  global action: aka “switching” header value output link determine source- local action: 0100 0101 3 2 destination paths move arriving packets from 0111 1001 2 1 taken by packets router’s input link to  routing algorithms appropriate 1 router output link 3 2 11 01 destination address in arriving 4 packet’s header  routing 5  forwarding forwarding 6  Packet-switching: store-and-forward source noitanitsed R bps spb R packet transmission delay: :elpmaxetakes laciremun poh-enO L/R seconds to transmit (push out) stibK 01 = L  L-bit packet into link at R bps spbM 001 = R  store and forward: entire yaled npacket oissimsnart poh-eno  must arrive at router before it can cesm 1.0 = be transmitted on next link Packet-switching: queueing C D s/bM 5. E nac ti naht retsaf sevir ra k ro Packet-switching: queueing C D s/bM 5. E knil ot )spb ni( etar lavir ra fi : fo doirep emos rof knil fo )sp knil tuptuo no dettimsnart eb ot retuor ni )reffub( y romem fi )ts Alternative to packet switching: circuit switching end-end resources allocated to, reserved for “call” between source and destination in diagram, each link has four circuits. call gets 2nd circuit in top link and 1st circuit in right link. dedicated resources: no sharing circuit-like (guaranteed) performance circuit segment idle if not used by call (no sharing) lanoitidart ni sk ro  Circuit switching: FDM and TDM Frequency Division Multiplexing (FDM) 4 users frequency optical, electromagnetic frequencies divided into (narrow) frequency bands  each call allocated its own band, can transmit at max time rate of that narrow band Time Division Multiplexing (TDM) frequency  time divided into slots  each call allocated periodic slot(s), can transmit at maximum rate of (wider) time frequency band (only) during its time 11 slot(s)  Packet switching versus circuit switching example:  1 Gb/s link N …..  each user: users 1 Gbps link 100 Mb/s when “active” active 10% of time Q: how many users can use this network under circuit-switching and packet switching?  circuit-switching: 10 users  packet switching: with 35 users, probability > 10 active at same time is less than.0004 * 12  Packet switching versus circuit switching Is packet switching a “slam dunk winner”?  great for “bursty” data – sometimes has data to send, but at other times not resource sharing simpler, no call setup  excessive congestion possible: packet delay and loss due to buffer overflow protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior with packet-switching? “It’s complicated.” We’ll study various techniques that try to make packet switching as “circuit-like” as possible. Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)? 13  Internet structure: a “network of networks” hosts connect to Internet via mobile network access Internet Service national or global ISP Providers (ISPs) access ISPs in turn must be interconnected so that any two hosts local or (anywhere!) can send regional ISP packets to each other home network content resulting network of provider network networks is very complex datacenter network evolution driven by enterprise economics, national policies network Let’s take a stepwise approach to describe current Internet structure  Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? … access net access net … access net access access net net access access net net … … access access net net access net access net access net access net … access access … net access net net 15  Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? … access net access net … access net access access net … … net access access net net connecting each access ISP to … … each other directly doesn’t scale: O … access (N2) connections. access … net net access net access net access net access … access … … net access net access net net 16  Internet structure: a “network of networks” Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement. … access net access net … access net access access net net access access net net … … global access net ISP access net access net access net access net access net … access access … net access net net 17  Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. … access net access net … access net access access net net access access ISP A net net … … access net ISP B access net access ISP C net access net access net access net … access access … net access net net 18  Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. who will want to be connected Internet exchange point … access net access net … access net access access net net IXP access access ISP A net net … … access net IXP ISP B access net access ISP C net access net access net peering link access net … access access … net access net net 19  Internet structure: a “network of networks” … and regional networks may arise to connect access nets to ISPs … access net access net … access net access access net net IXP access access ISP A net net … … access net IXP ISP B access net access ISP C net access net access net regional ISP access net … access access … net access net net 20  Internet structure: a “network of networks” … and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users … … access net access net access net access access net net IXP access access ISP A net net … … Content provider network access net IXP ISP B access net access ISP C net access net access net regional ISP access net … access access … net access net net 21