1. What’s the Internet: “nuts and bolts” viewPC
server
wireless
laptop
cellular
handheld
millions of connected computing devices: hosts = end systems
running network apps
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
communication links
fiber, copper, radio, satellite
transmission rate = bandwidth
wired
links
access
points
routers: forward packets (chunks of data)
router

2. What’s the Internet: “nuts and bolts” view
protocols control sending, receiving of msgs
e.g., TCP, IP, HTTP, Skype, Ethernet
Internet: “network of networks”
loosely hierarchical
public Internet versus private intranet
Internet standards
RFC: Request for comments
IETF: Internet Engineering Task Force
Home network
Institutional network
Mobile network
Global ISP
Regional ISP

3. What’s the Internet: a service view
communication infrastructure enables distributed applications:
Web, VoIP, , games, e-commerce, file sharing
communication services provided to apps:
reliable data delivery from source to destination
“best effort” (unreliable) data delivery

4. What’s a protocol? human protocols: “what’s the time?”
“I have a question”
introductions
… specific msgs sent
… specific actions taken when msgs received, or other events
network protocols:
machines rather than humans
all communication activity in Internet governed by protocols
protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

5. What’s a protocol? Hi Hi 2:00 <file> time
a human protocol and a computer network protocol: Hi
TCP connection
request Hi
TCP connection
response
Got the
time?
Get
2:00
<file>
time
Q: Other human protocols?

6. Computer networks: overview
Two most important aspects of computer networks
Hardware
And, software
Network hardware can be classified by
Transmission technology
And, scale

7. Classification of hardware by transmission technology
Communication is a primary concern in a network
=> we are dealing with both computers and
Communication (transmission) technologies
Types of transmission technology
Broadcast links
A single communication channel is shared by all machines
Restricting transmission to a set of machines => multicasting
Point-to-point links
Many connections between individual pairs of machines

8. Broadcast communication networks
Examples:
satellite networks
multi-access Ethernet.

9. General rule Smaller networks Larger networks
Broadcasting
Larger networks
Point-to-point
An alternative criterion for classifying networks
Their scale
Personal area networks, and local area networks
Metropolitan are networks, and wide are networks

10. Classification of interconnected processor by scale

11. Local area networks LANs Various topologies are possible for LANs
are privately owned networks
Within a single building or campus of few kilometers in size
Various topologies are possible for LANs
Bus
A single shared cable connect all devices
Example: IEEE Ethernet
Ring
All messages travel thru a ring in the same direction
Example: FDDI (Fiber Distributed Date Interface)

12. LANs topologies

13. Metropolitan Area Networks
A MAN
Covers a city
The best known example is
Cable television network available in many cities

14. Wide area networks WANs Within a country or even whole continent
A wide area network spans a large area, often a country or continent. The above figure presents a so-called packet switched networks. In this case, if a process on some host has a message to be sent to a process on some other host, the sending host first cuts the message into packets, each one bearing its number in the sequence. These packets are then injected into the network one at a time in quick succession. The packets are then transported over the network and deposited at the receiving host, where they are reassembled into the original message and delivered to the receiving process. A stream of packets resulting from some initial message is illustrated in the above presented figure.

15. Connectionless WAN packet-switched networks
In an IP network,
a user can send packets to a destination
without having to set up a connection first, i.e.,
without informing the network prior to transmitting them.
This simplifies the network,
as there is no need for a special signaling protocol.
The connectionless WAN IP network (packet routed network) is the one we will be concerned with in this course. That means an end user can transmit whenever he feels like it, I don’t need to ask the network to setup a connection for me. This approach is more suitable for the case where you have bursty data. Do you know what is the meaning of bursty data? This means that there is no continuous stream of data. If you establish a permanent connection, the connection would be up all the time whether using it or not, but your computer system uses part of it. Because of that they felt that the utilization of links would be less than 20% to 30% if they didn’t follow the connectionless approach. This led to the development of packet switched networks.

16. Routing in IP
User A
User B
IP network
The routing of a packet through the network is done on a hop-per-hop basis based on the destination IP address carried in the IP packet’s header.
In this case, if this is an IP network and user A wants to send stuff to user B; the way it works, is your packets will contains the destination address. So, as it goes into each IP router, the IP router extracts the destination address, scratches its head, I will look it up in a table and says for this address you have to send it out from port #5.

17. Quality of Service (QoS) in IP
Typically, an IP router does not offer QoS.
It cannot distinguish packets
belonging to different service classes
based on their destination address.
IP is almost ubiquitous.
There is a lot of interest in introducing QoS
in the IP network,
and MPLS seems to be the architecture for introducing QoS.
In the IP network you cannot easily distinguish the classes of service, because you see an IP packet that has a header but you don’t know if inside it carries voice, or just data that is why typically an IP network does not provide QoS. It cannot give higher priority to voice as opposed to file transfer for instance. In this case, the only way you can provide QoS is to underutilize the network. By doing so, the queues in the router are very small which means the delays are very small, and the packets are delivered without too much jitters where jitter is the variability of the interarrival times of packets at destination.

18. Internetworks Internetwork or internet
A collection of interconnected networks
Deals with how to connect different kinds of networks
It is formed when distinct networks are interconnected
Resulting in the Internet
That really covers the whole Planet

19. Network Core: Circuit Switching
End-end resources reserved for “call”
link bandwidth, switch capacity
dedicated resources: no sharing
circuit-like (guaranteed) performance
call setup required

20. Network Core: Circuit Switching
network resources (e.g., bandwidth) divided into “pieces”
pieces allocated to calls
resource piece idle if not used by owning call (no sharing)
dividing link bandwidth into “pieces”
frequency division
time division

21. Circuit Switching: FDM and TDM
4 users
Example:
FDM
frequency
time
TDM
frequency
time
Two simple multiple access control techniques.
Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling.

22. Numerical example
How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?
All links are Mbps
Each link uses TDM with 24 slots/sec
500 msec to establish end-to-end circuit
Let’s work it out!

23. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
end systems, access networks, links
1.3 Network core
circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History

24. How do loss and delay occur?
packets queue in router buffers
packet arrival rate to link exceeds output link capacity
packets queue, wait for turn
packet being transmitted (delay) A
free (available) buffers: arriving packets
dropped (loss) if no free buffers
packets queueing (delay) B

25. Four sources of packet delay
1. nodal processing:
check bit errors
determine output link
2. queueing
time waiting at output link for transmission
depends on congestion level of router A B
propagation
transmission
nodal
processing
queueing

26. Delay in packet-switched networks
3. Transmission delay:
R=link bandwidth (bps)
L=packet length (bits)
time to send bits into link = L/R
4. Propagation delay:
d = length of physical link
s = propagation speed in medium (~2x108 m/sec)
propagation delay = d/s
Note: s and R are very different quantities! A B
propagation
transmission
nodal
processing
queueing

27. Transmission vs. propagation applet
An applet
Illustrating the difference between
Transmission delay and propagation delay
An interactive animation
Speaks a thousand words

28. Nodal delay dproc = processing delay dqueue = queuing delay
typically a few microsecs or less
dqueue = queuing delay
depends on congestion
dtrans = transmission delay
= L/R, significant for low-speed links
dprop = propagation delay
a few microsecs to hundreds of msecs

29. Queueing delay (revisited)
R=link bandwidth (bps)
L=packet length (bits)
a=average packet arrival rate
traffic intensity = La/R
La/R ~ 0: average queueing delay small
La/R -> 1: delays become large
La/R > 1: more “work” arriving than can be serviced, average delay infinite!

30. Queuing delay vs. packet loss
Applet can be found at:

31. “Real” Internet delays and routes
What do “real” Internet delay & loss look like?
Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i:
sends three packets that will reach router i on path towards destination
router i will return packets to sender
sender times interval between transmission and reply.
3 probes
3 probes
3 probes

32. “Real” Internet delays and routes
traceroute: gaia.cs.umass.edu to
Three delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
1 cs-gw ( ) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu ( ) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu ( ) 6 ms 5 ms 5 ms
4 jn1-at wor.vbns.net ( ) 16 ms 11 ms 13 ms
5 jn1-so wae.vbns.net ( ) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu ( ) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu ( ) 22 ms 22 ms 22 ms
( ) 104 ms 109 ms 106 ms
9 de2-1.de1.de.geant.net ( ) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net ( ) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net ( ) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr ( ) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr ( ) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr ( ) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net ( ) 135 ms 128 ms 133 ms
( ) 126 ms 128 ms 126 ms
17 * * *
18 * * *
19 fantasia.eurecom.fr ( ) 132 ms 128 ms 136 ms
trans-oceanic
link
* means no response (probe lost, router not replying)

34. Tracing LAU’s webserver

35. Tracing webserver (cont’d)

36. Packet loss
queue (aka buffer) preceding link in buffer has finite capacity
packet arriving to full queue dropped (aka lost)
lost packet may be retransmitted by previous node, by source end system, or not at all
buffer
(waiting area)
packet being transmitted A B
packet arriving to
full buffer is lost

37. Throughput
throughput: rate (bits/time unit) at which bits transferred between sender/receiver
instantaneous: rate at given point in time
average: rate over longer period of time
pipe that can carry
fluid at rate
Rc bits/sec)
pipe that can carry
fluid at rate
Rs bits/sec)
link capacity
Rs bits/sec
link capacity
Rc bits/sec
server sends bits
(fluid) into pipe
server, with
file of F bits
to send to client

38. Throughput (more) Rs < Rc What is average end-end throughput?
Rc bits/sec
Rs bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
link on end-end path that constrains end-end throughput
bottleneck link

39. Throughput: Internet scenarioRs
per-connection end-end throughput: min(Rc,Rs,R/10)
in practice: Rc or Rs is often bottleneck Rs Rs R Rc Rc Rc
10 connections (fairly) share backbone bottleneck link R bits/sec