CCS2201 Introductions to Networks Fall 2023-2024 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: pack...

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 routers mobile network national or global ISP packet-switching: hosts break application-layer messages into packets network forwards packets local or from one router to the next, regional ISP across links on path from home network content source to destination provider network datacenter network enterprise network 3  Two key network-core functions routing Routing: algorithm  global action: Forwarding: local forwarding local forwardingtable determine aka “switching” table header value output link source- local action: 0100 0101 3 2 destination paths move arriving 0111 1001 2 1 taken by packets packets from router’s input  routing link to algorithms appropriate 1 router output 3 2 link 11 01 destination address in arriving 4 packet’s header  routing 5  forwarding forwarding 6  Packet-switching: store- and-forward L bits per packet 321 source destination R bps R bps packet transmission delay: takes L/R One-hop numerical seconds to transmit (push out) L-bit example: packet into link at R bps  L = 10 Kbits store and forward: entire packet must  R = 100 Mbps arrive at router before it can be  one-hop transmission transmitted on next link delay = 0.1 msec 7  Packet-switching: queueing R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for transmission over output link Queueing occurs when work arrives faster than it can be serviced: 8  Packet-switching: queueing R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for transmission over output link Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time: packets will queue, waiting to be transmitted on output link packets can be dropped (lost) if memory (buffer) in router fills up 9 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)  commonly used in traditional telephone networks 10  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 time band, can transmit at max rate of that narrow band frequency Time Division Multiplexing (TDM)  each time divided into slots call allocated periodic slot(s), can transmit at time maximum rate of (wider) 11 frequency band (only) during  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 Q: make human packet switching analogies of as “circuit-like” reserved as possible. resources (circuit switching) versus on-demand allocation (packet 13 switching)?  Internet structure: a “network of networks” hosts connect to Internet via mobile network access Internet Service Providers national or global ISP (ISPs) access ISPs in turn must be interconnected so that any two hosts local or regional (anywhere!) can send packets to ISP each other home network content provider resulting network of networks is network datacenter network very complex evolution driven by economics, enterprise network national policies Let’s take a stepwise approach to describe current Internet structure 14  Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access … access net access net … net access access net net access access net net … … access access net net access net access net access net access … net access net access net … access net 15  Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access … access net access net … net access access net … … net access access net net connecting each access … … ISP to each other directly … access access doesn’t scale: O(N2) … net net access connections. net access net access net access … … net access net access net … access 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 … access net access net … net access access net net access access net net … … global access net ISP access net access net access net access net access … net access net access net … access net 17  Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. access … access net access net … net access access net net access access net net ISP A … … access net ISP B access net access net ISP C access net access net access … net access net access net … access 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 … access access net net … net access access net net IXP access access net net ISP A … … access net IXP ISP B access net access net ISP C access net access net peering link access … net access net access net … access net 19  Internet structure: a “network of networks” … and regional networks may arise to connect access nets to ISPs … … access access net access net net access access net net IXP access access net net ISP A … … access net IXP ISP B access net access net ISP C access net access net regional ISP access … net access net access net … access 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 net net ISP A … … Content provider network access net IXP ISP B access net access net ISP C access net access net regional ISP access … net access net access net … access net 21