Networking 101
Multimedia Streaming
{week-2}
Notes are adapted from chapter-1 in the textbook
Mohamed Abdel-Maguid
Computer Networking:
A Top Down Approach
Featuring the Internet,
3rd edition.
Jim Kurose, Keith Ross
Addison-Wesley, July
2004.
Networking 101
1-1
What’s the Internet: a service view
 communication
infrastructure enables
distributed applications:

Web, email, games, ecommerce, database., video
streaming
 communication services
provided to apps:


connectionless
connection-oriented
 cyberspace [Gibson]:
“a consensual hallucination experienced daily by
billions of operators, in every nation, ...."
Networking 101
1-2
A closer look at network structure:
 network edge:
applications and
hosts
 network core:
 routers

network of
networks
 access networks,
physical media:
communication links
Networking 101
1-3
Packet-switching: store-and-forward
L
R
 Takes L/R seconds to
R
transmit (push out)
packet of L bits on to
link or R bps
 Entire packet must
arrive at router before
it can be transmitted
on next link: store and
forward
 delay = 3L/R
R
Example:
 L = 7.5 Mbits
 R = 1.5 Mbps
 delay = 15 sec
Networking 101
1-4
Packet Switching: Message Segmenting
Now break up the message
into 5000 packets
 Each packet 1,500 bits
 1 msec to transmit
packet on one link
 pipelining: each link
works in parallel
 Delay reduced from 15
sec to 5 sec
Networking 101
1-5
Access networks and physical media
Q: How to connection end
systems to edge router?
 residential access nets
 institutional access
networks (school,
company)
 mobile access networks
Keep in mind:
 bandwidth (bits per
second) of access
network?
 shared or dedicated?
Networking 101
1-6
Residential access: point to point access
 Dialup via modem

up to 56Kbps direct access to
router
 ADSL: asymmetric digital subscriber line
up to 1 Mbps upstream (today typically < 256 kbps)
 up to 8 Mbps downstream (today typically < 1 Mbps)

Networking 101
1-7
Residential access: cable modems
 HFC: hybrid fiber coax
asymmetric: up to 10Mbps upstream, 1 Mbps
downstream
 network of cable and fiber attaches homes to
ISP router
 shared access to router among home
 issues: congestion
 deployment: available via cable companies

Networking 101
1-8
Company access: local area networks
 company/univ local area
network (LAN) connects
end system to edge router
 Ethernet:
 shared or dedicated link
connects end system
and router
 10 Mbs, 100Mbps,
Gigabit Ethernet
 deployment: institutions,
home LANs happening now
 LANs
Networking 101
1-9
Wireless access networks
 shared wireless access
network connects end system
to router

via base station aka “access
point”
 wireless LANs:
 802.11b (WiFi): 11 Mbps
 wider-area wireless access
 provided by BT, Vodafone
 3G ~ 384 kbps
 WAP/GPRS < 56Kbps
router
base
station
mobile
hosts
Networking 101
1-10
Home networks
Typical home network components:
 ADSL or cable modem
 router/firewall/NAT
 Ethernet
 wireless access
point
to/from
cable
headend
cable
modem
router/
firewall
Ethernet
(switched)
wireless
laptops
wireless
access
point
Networking 101
1-11
Internet structure: network of networks
 a packet passes through many networks!
local
ISP
BT
ISP
BT-2 ISP
local
ISP
local
ISP
BT-ISP
BT 1 ISP
BT 1 ISP
BT-2 ISP
local
local
ISP
ISP
local
ISP
NAP
BT 1 ISP
BT-2 ISP
local
ISP
BT ISP
local
ISP
Networking 101
1-12
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
B
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
Networking 101
1-13
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
transmission
A
propagation
B
nodal
processing
queueing
Networking 101
1-14
Delay in packet-switched networks
3. Transmission delay:
 R=link bandwidth (bps)
 L=packet length (bits)
 time to send bits into
link = L/R
transmission
A
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!
propagation
B
nodal
processing
queueing
Networking 101
1-15
Nodal delay
d nodal  d proc  d queue  d trans  d prop
 dproc = processing 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
Networking 101
1-16
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!
Networking 101
1-17
“Real” Internet delays and routes
 What do “real” Internet delay & loss look like?
 Tracert 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
Networking 101
1-18
“Real” Internet delays and routes
C:\>tracert 194.66.25.89
Three delay measements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
1
1 ms
22 ms
1 ms (none) [192.168.11.1]
2
21 ms
9 ms
12
17 ms
16 ms
19 ms 212.250.14.34
13
19 ms
16 ms
16 ms po3-3.lond-scr4.ja.net [146.97.35.237]
14
15
*
*
* Request timed out
21 ms 22 ms 22 ms po3-0.warr-scr.ja.net [146.97.33.54]
16
*
*
*
Request timed out
17
*
*
*
Request timed out
18
19
24 ms
10 ms 10.129.87.254
49 ms
44 ms gw-staffs.core.netnw.net.uk [194.66.25.89]
Networking 101
1-19
Packet loss
 queue (aka buffer) preceding link in buffer
has finite capacity
 when packet arrives to full queue, packet is
dropped (aka lost)
 lost packet may be retransmitted by
previous node, by source end system, or
not retransmitted at all
Networking 101
1-20
Protocol layering and data
Each layer takes data from above
 adds header information to create new data unit
 passes new data unit to layer below
source
M
Ht M
Hn Ht M
Hl Hn Ht M
application
transport
network
link
physical
destination
application
Ht
transport
Hn Ht
network
Hl Hn Ht
link
physical
M
message
M
segment
M
M
datagram
frame
Networking 101
1-21
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
Networking 101
1-22
What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
req
Hi
TCP connection
response
Got the
time?
Get http://www.awl.com/kurose-ross
2:00
<file>
time
Networking 101
1-23
Protocols ?!
 Http ‘Hyper text transfer protocol’
 TCP
‘ Transmission control protocol’
 UDP ‘User datagram protocol’
 ICMP ‘Internet control messaging protocol’
 MMS ‘Multimedia streaming protocol’
 RTSP ‘ Real time streaming protocol’
 ARP ‘Address resolution protocol’
Networking 101
1-24
Sample Ethernet traffic
Host 192.168.11.1 sends a Ping to host 192.168.11.1
Source
192.168.11.2
192.168.11.1
192.168.11.2
192.168.11.1
192.168.11.2
192.168.11.1
192.168.11.2
192.168.11.1
192.168.11.2
192.168.11.1
192.168.11.1
192.168.11.2
Destination
Broadcast
192.168.11.2
192.168.11.1
192.168.11.2
192.168.11.1
192.168.11.2
192.168.11.1
192.168.11.2
192.168.11.1
192.168.11.2
192.168.11.2
192.168.11.1
Protocol Info
ARP Who has 192.168.11.1? Tell 192.168.11.2
ARP 192.168.11.1 is at 00:90:4c:49:00:2a
ICMP Echo (ping) request
ICMP Echo (ping) reply
ICMP Echo (ping) request
ICMP Echo (ping) reply
ICMP Echo (ping) request
ICMP Echo (ping) reply
ICMP Echo (ping) request
ICMP Echo (ping) reply
ARP Who has 192.168.11.2? Tell 192.168.11.1
ARP 192.168.11.2 is at 00:07:40:4e:08:84
Networking 101
1-25
Lab 1
 Open any packet capture tool
 Open windows performance monitor
 Setup a counter to record your computer bandwidth
 Start packet capturing
 Ping any other computer
 Open winmedia player and request any video using
mms protocol
 request another video file using Http protocol
 Stop capture and examine the captured packets
Networking 101
1-26