Transcript Voice over Mobile IP

Ch 1. Computer Networks and
the Internet
Myungchul Kim
[email protected]
What is the Internet?

One sentence definition?
–
–

A nuts-and-bolts description
A service description
A nuts-and-bolts description
–
–
–
–
–
–
–
–
–
–
Hosts or end systems
A network of communication links and packet switches
Transmission rate
Packets
Packet switches: routers and link-layer switches
Route or path
Internet Service Providers (ISPs)
Protocols: TCP and IP
Internet Standards: Request for comments (RFCs) by IETF
Intranet
2

A service description
–
–

An infrastructure for providing services to distributed applications: remote login,
electronic mail, Web surfing, instant messaging, VoIP, audio and video streaming,
Internet telephony, distributed games, peer-to-peer (P2P) file sharing, IPTV…
Application Programming Interface (API)
Protocols
–
Figure 1.2.
3

Definition of a Protocol
–
Defines the format and the order of messages exchanged
between two or more communicating entities, as well as the
actions taken on the transmission and/or receipt of a message or
other event
–
Similar to a human analogy: there are specific messages we
send, and specific actions we take in response to the received
reply messages or other events
4
The Network Edge



Host = end system: clients and servers
Peer-to-peer: acts as both a client and a server
Access networks: connect an end system to its edge
router
–
–
–

Residential access
Company access
Wireless access
Residential access
–
–
–
Digital subscriber line (DSL): point-to-point
Hybrid fiber-coaxial cable (HFC): cable modems, shared
Very-high speed DSL (VDSL)
5

Company access
–

Wireless access
–
–
–
–
–

Ethernet : shared
Wireless LAN
IEEE 802.11 WiFi
3G Wireless: HSDPA (High-Speed Downlink Packet Access)
IEEE 802.16 WiMax
WiBro
Physical media
–
–
–
–
–
Twisted-pair copper wire
Coaxial cable
Fiber optics
Terretrial radio channels: wireless LAN, the cellular access
Satellite Radio channels
6
The Network Core

Circuit switching
–
–
–

Packet switching
–
–
–

Reserved for the communication session
A circuit: at the guaranteed constant rate
Telephone network
The network resources on demand
Internet
Best effort
Multiplexing in Circuit-switched networks
–
–
The dedicated circuits are idle during silent periods
Frequency-division multiplexing (FDM) or Time-division
multiplexing (TDM)
7

Fig 1.6.
8

Packet switching
–
Message -> packets
Routers = packet switches
Store-and-forward transmission: the switch must receive the entire
packet before it can begin to transmit the first bit of the packet onto the
outbound link -> store-and-forward delay
Output queue -> queueing delay
Packet loss
–
Fig 1.7
–
–
–
–
9

Packet switching vs Circuit switching
–
Packet switching is not suitable for real-time services?
–
Sharing of network resources -> statistical multiplexing of
resources
10
–
Figure 1.11
11
ISPs and Internet Backbones




Tier-1 ISPs: Internet Backbone
Tier-2 ISPs: regional or national coverage
Access ISPs
Points of Presence (POPs): the points at which the ISP
connects to other ISPs
12
Delay and loss in Packet-switched networks

Fig 1.18

Processing delay
–
–
–

Examine the packet’s header and determine where to direct the packet
Check for bit-level errors
Microseconds or less
Queuing delay
–
–
–
–
A packet waits to be transmitted onto the link
Depends on the number of earlier-arriving packets that are queued and
waiting for transmission across the link.
congestion
Microseconds to milliseconds.
13

Transmission delay
–
–
–
–

Propagation delay
–
–
–

Store-and-forward delay
Transmit all of the packet’s bits into the link
L/R where L bits = length of the packet, R = 10 Mbps for a 10 Mbps
Ethernet link
Microseconds to milliseconds
Propagation speed of the link
d/s where d = distance and s = the propagation speed of the link
Milliseconds
Comparing transmission and propagation delay
–
–
–
–
d nodal = d proc + d queue + d trans + d prop
d prop : hundreds of milliseconds for two routers by a satellite link
d trans : hundreds of milliseconds for low-speed dial-up modem links
d proc : at the max rate of a router
14

Queuing delay
–
–
–
–
Traffic intensity La/R where a = the average rate of packets arrival at
the queue (packets/sec), L bits of a packet, R = the transmission rate
(bits/sec), and the infinite queue.
If La/R > 1, the queue will tend to increase without bound and the
queuing delay will approach infinity.
If La/R ≤ 1, the nature of the arriving traffic impacts the queuing delay.
Periodically or in bursts or random
Fig 1.19
15

Packet loss
–
–

A queue has finite capacity.
Performance of a node = delay + packet loss
End-to-end delay
–
d end-end = N (d proc + d trans + d prop) for N-1 routers
where the network is uncongested.
16

Traceroute
–
–
–

Repeats experiment three times to get the round-trip delays between
souce and destination
The queuing delay is varying with time. -> the round-trip delays are
varying.
(Next slide)
Other delays
–
–
Media accessing delays in WiFi, Ethernet, …
Packetization delays in VoIP
17
“Real” Internet delays and routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
Three delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
link
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms
16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
* means no response (probe lost, router not replying)
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
18
Throughput

throughput: rate (bits/time unit) at which bits
transferred between sender/receiver
–
–
instantaneous: rate at given point in time
average: rate over long(er) period of time
link
capacity
that
can carry
server,
with
server
sends
bits pipe
Rs bits/sec
fluid
at rate
file of
F bits
(fluid)
into
pipe
Rs bits/sec)
to send to client
link that
capacity
pipe
can carry
Rfluid
c bits/sec
at rate
Rc bits/sec)
19
Throughput (more)

Rs < Rc What is average end-end throughput?
Rs bits/sec

Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec
Rc bits/sec
bottleneck link
link on end-end path that constrains end-end throughput
20
Protocol layers and their service models



A layered architecture allows us to discuss a well-defined,
specific part of a large and complex system.
Protocol stack
Service model
– Layer (n-1) is said to offer services to layer (n)
21

Layer functions
–
–
–
–
–
–
Error control
Flow control
Segmentation and reassembly
Multiplexing
Connection setup
Drawbacks of layering
 Duplicated lower-layer functionality
 Accessing an information in another layer
22
–
–
–
–
–
Application layer: HTTP, SMTP, FTP, DNS
Transport layer: TCP, UDP
Network layer: IP, routing
Link layer: Ethernet, PPP, WiFi
Physical layer
23

The internet protocol stack
24
source
message
segment
M
Ht
M
datagram Hn Ht
M
frame Hl Hn Ht
M
Encapsulation
application
transport
network
link
physical
link
physical
switch
destination
M
Ht
M
Hn Ht
Hl Hn Ht
M
M
application
transport
network
link
physical
Hn Ht
Hl Hn Ht
M
M
network
link
physical
Hn Ht
M
router
25
Networks under attack


Network security
The bad guys can put malware into your host via the Internet
–

The bad guys can attack servers and network infrastructure
–

A packet sniffer: Ethereal
The bad guys can masquerade as someone you trust
–
–

Denial-of-service (DoS) attacks, Distributed DoS attacks
The bad guys can sniff packets
–

Botnet, Self-replicating, Viruses, Worms, Trojan hoars
IP spoofing: with a false source address
Authentication
The bad guys can modify or delete messages
–
–
Man-in-the-middle attacks
Integrity of the data
26