Introduction
Summary
keywords packet switching, delay, structure of internet, CDN,
TODO
HW
- Find the cable TV service providers(CATV) left in Korea
- Find the internet service providers in GIST : KISTI
- Content Service Providers owned by their own.
- which city has the highest IXPs?
Exercise link of problem examples on slide 1-37. packet switching vs. circuit switching Caravan analogy on slide 1-54.
Next time
Recap
Access Networks : Digital Subscriber line(DSL)
- replaced by fiber optics connections
Packet switches
- files are divided into chunks
- chunks are padded with headers, where it has info on destination & source
- the core route & forward the packets.
- Routing algorithm tells us which packet from which subnet should be routed to which another core.
Store-and Forward
not forwarded until the whole ENTIRE packet is ALL received. receive AND THEN start forwarding.
Alternative to Packet Switching: circuit switching
- call setup time.
- guarantees performance.
- circuit still reserved event if not used by call. idle state. not shared circuit.
Multiplexing techniques
FDM
allocated own band
TDM
allocated own time slot
Packet Switching vs. Circuit Switching
| Packet switch | Circuit Switch | |
|---|---|---|
| users max | can do more than 10 | max. 10 |
| probability of being 10 active | < 0.004 | - |
#todo 1: write about packet switching advantages
Structure of internet
![[../images/20230905134236.png]]
- not contected one-by-one. It does not scale efficiently.
- ISPs connected to end access net.
- ISP - IXP - ISP (exchanging through IXP)
- ISP - ISP (peering link)
IXP Internet exchange points, ususally under governement control
regional ISP useful in efficiency in remote areas,
Tier-1 ISP national & international coverage
Content service providers private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs
![[../images/20230905134252.png]]
Delay, Packet loss, throughput
Delay
transmission delay:
- caused by bandwidth
- about bandwidth, per one hop
- *$L/R$ seconds to transmit $L$ bit packet into link at $R$ bps.
propagation delay:
- caused by length of link
- $d/s$ , where $d$ is length of physical link, $s$ is propagation speed(ex. light speed)
queueing delay:
- caused by conjestions
- packet loss happens.
- when arrival rate exceeds transmission rate
- because of memory
- because of traffic.
processing delay:
- time required to modify each packet
- check errors, and do some other neccessary computations
Packet queueing delay
it is not easy to compute queueing delay.
-
$R$: link bandwidth (bps)
-
$L$: packet length (bits)
-
$a$: average packet arrival rate
-
*$La/R$ ~ 0: avg. queueing delay small
-
$La/R$ -> 1: avg. queueing delay large
-
$La/R$> 1: more “work” arriving is more than can be serviced - average delay infinite!
![[../images/20230905135524.png]]
#todo: needs more analogies on traffics
Traceroute : command to trace route
![[../images/20230905140558.png]]
- separate pings are sent for each hop device
- 3 delay measures
Packet loss
#todo : fill out packet loss
Throughput
rate at which bits are being sent from sender to reciever (end-to-end).
- determined by minimum bandwidth.
- usually happens near the end user. bottleneck link : link with minimum bandwidth.
skip security.