Transcript Lecture 6 - Aerobic Suspended Growth

OSI Reference Model
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ISO OSI reference model (protocol stack)
Application Layer
User interface (task-to-task)
Presentation Layer
Data representation, formatting, code conversion
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
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Dialog Control (connection establishment,
message exchange)
Packetizing, end-to-end reliability (error checking,
flow control): TCP
Routing: IP
Point-to-point error free: HDLC, LAPD
Coding, modulation: AMI, NRZ, Manchester
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OSI layer functions
Physical layer: provides electrical, functional, and procedural means to activate,
maintain, and deactivate physical links that transparently pass the bit stream for
communication; only recognizes individual bits (not characters nor frames) and provides
bit synchronization; peer-to-peer.
Data link layer: provides functional and procedural means to transfer data between
network entities and possibly correct transmission errors; provides activation,
maintenance and deactivation of data link connection; groups bits into characters and
message frames; provides frame synchronization, error control, media access control, and
flow control; peer-to-peer.
Network layer: provides routing, relaying, and switching functions to establish,
maintain, and terminate network layer connections between users.
Transport layer: provides transparent transfer of data between systems for upper layers;
provides end-to-end control and information interchange with required quality of service.
Session layer: provides mechanism for organizing dialogue between application
processes; allows full duplex or half-duplex data exchange (finite state machine message
exchange).
Presentation layer: provides different data presentation (for application layer); provides
syntax selection and conversion (encryption) by allowing user to select presentation
context.
Application layer: provides process parts necessary for communication between
processes.
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Implementation: encapsulation (5 layers)
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Protocol (statistical) de-multiplexing
based on destination address
1
1
Switch
2
arbiter
3
Based
on H2
physical
(Ethernet
link
Address)
Router
Data Link
Layer
1
Web
2
Skype
3
E-mail
Host/PC
Based
on H3 (IP)
Based
on H4
(port #)
3
3
Network
Layer
Transport
Layer
4
Sources
1
4
Application
Layer
For interactive communication we need the source address as well to know
where to respond. Hence source and destination addresses in a header.
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Handshaking between two modems in RS-232C
PC
DTE
TD
RTS
DTR
RD
CTS
DSR
RI
CD
GRND
Modem
Data Set Ready
DSR
DTR
Data Terminal Ready
RI
Ring Indicator
RTS
DCE
Request To Send
CTS
CD
Clear To Send
Carrier Detect
TD
Transmit Data
RD
Receive Data
RI
Modem
DCE
TD
RTS
DTR
RD
CTS
DSR
RI
CD
GRND
PC
RTS
RTS
DSR
DTR
RI
DTE
RTS
CTS
CD
TD
RD
DB9 bit
connector
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RS232 electrical signals
ASCII Data (binary)
0
0
1
1
1
1
0
+15 V
line
signals
Start
“0”
0
0
1
1
1
Stop
“1”
1
0
Start( “0”) +
7 data + parity +
Stop (at least 1.5 “1”)
t
parity
Stop
“1”
-15 V
Amplitude
“0” +5/+15 V
“1” -5/-15 V
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Speed
pulse/sec = baud
1200/2400/
4800/9600/
19200 baud
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Control
characters
RTS – 0011110
RI - 0000111
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Telephone switching
dialer
register
ringer
bell
Strawger step-by-step concept
signaling
marker
register
bell
dialer
voice
crossbar switch
Stage Networks: Benes (recursive approach),
Closs 3 stage networks (recursive)
Interconnection networks: Shuffle (Stone 1971),
Delta (Patel 1976), Omega (Lawrie 1975) etc.
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CCITT->ITU SS7 Network
SSP
STP
SCP
SSP
STP
SCP
All connections are duplicated for reliability
SS7 node
equivalent
Internet node
SSP - Signaling Service Point
Host
STP - Signaling Transfer Point Router
SCP - Signaling Control Point
Server
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SS7 out-of-band signaling
voice trunk
voice plane
(circuit switching network)
SSP
SCP
SSP
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signaling link
SSP
STP
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signaling plane
(data packet network)
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SS7 Call setup messaging
SSP A
SSP B
IAM
ACM
ANM
conversation
SUS/REL
IAM - Initial Address Message (A goes off hook.
IAM contains dialed digits of B)
ACM - Address Confirmation Message (ringing)
ANM - ANswer Message (B goes off-hook)
SUS/REL - Suspend/Release (B hangs up first)
REL - RELease (A hangs up first)
RLC - ReLease Confirmation
REL
RLC
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SS7 Protocol Stack vs. OSI
CCITT #7
Layers
OSI Layers
User
Processes
7
OSI
Application
6
Presentation
STP function
Ne tw o rk
App lic a tion
P ro cess
TCAP
- NS P - Network Service Part
ISDN
User
Part
ASP
4
TCAP - Transaction Capability Application Part
ASP - Application Service Part
5
Session
SCCP - Signaling Connection Control Part
4
Transport
3
Ne two rk
Signalling Network Functions
3
2
Da ta Link
Link
2
Physical
Physical
1
1
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SCCP
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MTP - Message Transfer Part
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Telephone Network - hierarchical
satellites
*
*
*
* delay points
*
Undersea cable (fiber)
*
Regional
*
Regional
*
Toll SW
*
Local
Toll SW
Local
Local
*
Toll SW
Toll SW
Local
Local
Local
Local
*
Local
Voice network overall delay 1 sec => 100 msec per delay point
(with speed of sound 1000 km/h) equivalent to 300 m.
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The ARPANET
56 kbps link
IMP – Interface Message Processor (minicomputer) connected to at least two other IMPs.
1960 DoD contracted RAND co. to figure distributed network. Paul Baran of
RAND wrote paper and DoD gave it to AT & T for review. They rejected it
upfront. However, after Soviets launched Sputnik in 1957 President Eisenhower
initiated ARPA (Advanced Research Project Agency). ARPA director, Larry
Roberts, got idea from employee Wesley Clark to build packet network. Roberts
published paper on ACM SIGOPS 1967 and saw British paper by Donald Davies
that describes such network implemented at National Physical Laboratory in
England which referenced Baran. Roberts started building ARPANET.
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DoD reference model architecture
1. DoD network connects wide variety of heterogeneous host computers and terminals.
2. Fundamental concept is computer communications - interprocess communications.
3. There is no hierarchical network structure.
4. Internetwork connectivity.
T
T
T
TIP
H
Network A
H
IMP
T - terminal
H - Host computer
G - Gateway (Router)
IMP - Interface Message
Processor
TIP - Terminal IMP
T
T
T
TIP
H
Network B
G
G
H
IMP
backbone
network
H
H
TIP
T
H
TIP
G
H
Network C
H
H
T
H
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The ARPANET evolution
Growth of the ARPANET (a) December 1969. (b) July 1970.
(c) March 1971. (d) April 1972. (e) September 1972.
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NSFNET backbone (subnet) in 1988.
NSF connected its supercomputers in: San Diego, Boulder, Champaign, Pittsburgh,
Ithaca, and Princeton, using LSI-11 as IMPs which used TCP/IP over 56 kbps lines.
NSF also funded about 20 regional networks to connect them to the backbone. 1995
NSF backbone was sold to AOL. At this time operators: PcBell, Ameritech (Chicago),
MFS (Wash DC), and Sprint were also offering backbones. For that NAPs were created
to offer a backbone to the NSF regional networks.
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PSTN vs. Internet topology
(a) Structure of the telephone system.
(b) Baran’s from RAND 1960 proposed distributed
switching system. AT&T dismissed it.
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Internet multiplexing
Process Layer
Port Numbers
T
e
l
n
e
t
23
F
T
P
H
T
T
P
D
N
S
B
O
O
T
P
20/21
80
53
67/68
Host to Host
Layer
IGRP
Internet Layer
88
ARP
0806
Network
Interface
Layer
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D
H
C
P
T
F
T
P
69
TCP
UDP
6
17
ICMP
S
N
M
P
151/162 520
OSPF
01
IP
0800
R
I
P
89
Protocol
Codes
RARP
0806
Ethernet, Token Ring, FDDI, PPP, etc.
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Internet protocols
TELNET - remote terminal connection service. Allows user terminal to mimic the terminal
at the remote side.
FTP - File Transfer Protocol (put/get file to/from remote machine).
HTTP - Hypertext Transport Protocol.
DNS - Domain Name Server On-line distributed database for translating IP machine names
into IP addresses.
BOOTP - Bootstrap Protocol defines each device autoconfiguration on the server (improvement
to the RARP).
DHCP - Dynamic Host Configuration Protocol (improvement to BOOTP) allows network
administrator to configure workstation by providing dynamic address assignment.
TFTP - Trivial File Transfer Protocol (same as FTP with minimal capability).
SNMP - Simple Network Monitoring Protocol used to monitor IP gateways and networks they
are attached to.
RIP - Routing Information Protocol used to exchange the routing information among small
set of computers (every 30 sec hosts exchange information).
TCP - reliable Transmission Control Protocol (connection oriented).
UDP - unreliable Universal Transport Protocol (connectionless).
IGRP - Interior Gateway Routing Protocol (proprietary routing protocol developed by Cisco).
ICMP - Internet Control Message Protocol part of IP that handles error and control messages.
OSPF - Open Shortest Path First routing protocol.
ARP - Address Resolution Protocol used to dynamically bind IP addresses to physical addresses.
RARP - Reverse ARP used by newly installed machine to find its IP address.
IP - Internet Protocol.
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OSI vs. TCP/IP stack
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A Critique of the OSI reference model
• Very complicated documentation difficult to understand and implement.
• Loose set of prescription leading to
incompatible implementations.
• Layers are of different complexities.
The OSI does not allow layer bypassing.
• Development influenced by telephony
personnel: focus is on connection oriented
service rather on connectionless service
dominating in data communication.
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A Critique of the TCP/IP Reference Model
• Service, interface, and protocol not
distinguished
• Not a general model
• Host-to-network “layer” not really a layer
• No mention of physical and data link layers
• Minor protocols deeply entrenched, hard to
replace
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Present day Internet
POP – Point Of Presence are ISP (e.g. AOL) modems connected to Regional ISP network.
Regional ISP network is connected to the backbone. Backbones are connected by NAP
(Network Access Point) or by their own routers. Finally Server Farm (multiplicity of
identical servers) are connected to the router.
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PSTN vs. Internet
Telephone people like connection oriented service for
two reason:
• Quality of Service (QoS): by setting up a connection
the subnet reserves resources (link, buffer, CPU
routing) for this connection. If insufficient the
connection is rejected upfront and caller is notified by
busy tone.
• Billing: accustomed to charge connection time (per
minute). Maintaining the billing records is very
expensive (if they established flat rate they will save a
lot of money, like for instance cable TV).
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PSTN vs. Internet (more)
• Internet grew up with fault tolerance in mind: if a node
down the route fails there will be automatically another
route. This leads to connectionless networks.
• Billing was not on their agenda. It came much later and is
still under discussion. Some charge by the GB of
download.
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Connectionless switching - Datagrams
Host D
Host E
2
0 Switch 1
3
Routing Table for Switch 2
Switch 2
3
1
Host C
1
2
0
Switch 3
0
Host A
Host F
1
3
Host G
PLUS-es
•Host just sends any PDU anywhere.
•Each PDU is independent of previous.
•Switch or link failure has no impact
on PDU delivery.
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Host H
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Host B
Dest.
addr
Port
A
3
B
0
C
3
D
3
E
2
F
1
G
0
H
0
MINUS-es
•Unreliable:
source does not know about delivery.
•Mis-sequencing: earlier sent PDU
may come before the current PDU.
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Connection-oriented switching:
PVC (Permanent VC) and SVC (Switched VC)
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SVC (Host A to Host B)
VC Tables
Switch 1
In Port In VCI
2
5
Switch 2
In Port In VCI
3
11
Host E
Host D
Out Port
Out VCI
1
11
Switch 1 0
3
11
2
Switch 2
3
1
1
Out Port
Out VCI
0
7
2
Host C
0
Host F
7
5
0
4
1
Switch 3
In Port In VCI
0
7
Out Port
Out VCI
3
4
Host A
VC is identified with (port #, VCI #) pair.
No two pairs are ever the same.
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Host G
2 Switch 3 Host B
Host H
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SVC Setup
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Host A sends setup message (that contains destination address of Host B) into
the network i.e. Switch 1.
Switch 1 (receiving the setup message toward Host B) creates new Incoming
VCI (# 5) in its VC table and forwards setup message (datagram) to Port 1
(which he chooses by routing algorithm towards host B) to Switch 2.
Switch 2 does the same (In VCI # 11) and forwards connection request to Port 0
to Switch 3.
Switch 3 does the same (In VCI # 7) and forwards connection request to Port 3
to Host B.
When host B gets a setup message it chooses #4 for this VCI and sends it with
the acknowledgment (towards the host A) to switch 3.
Switch 3 fills-in that #4 as the outgoing VCI, takes the incoming VCI #7 and
forwards ack to the incoming (now outgoing) port #0 (from the table) to switch
2.
Switch 2 fills-in #7 as an outgoing VCI, takes its incoming VCI #11 and
forwards ack to port #3 towards switch 1.
Switch 1 fills-in #11 as and outgoing VCI, takes its incoming VCI #5 and
forwards it to the host A.
Now Host A gets #5 as its VCI toward host B.
Host B will receive messages from the Host A with VCI #4 (as set by the last
switch #3 as its output VCI).
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VC disconnect
1.
2.
Either Host A or Host B, can clear VC. For that it sends
disconnect message with VC #.
Disconnect message propagates along the VC path and
destroys its entry in the VC table at each router.
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Connectionless vs. Connection oriented Switching
• SVC has overhead: it takes time and link capacity
to establish (before sending payload) and tear
down afterwards.
• During VC setup nodes allocate buffers for
message store.
• If some node(s) along the path fails the new VC
have to be established and old VC entries in the
VC tables erased.
• Since messages using VC go the same path they
preserve sequencing.
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Frame Relay (subset of HDLC) as an
example of PVC
Bits
8
16
8
Variable
16
8
Field
flag
addr/VCI
control
payload
CRC
flag
Very popular in creation of VPNs (Virtual Private Networks).
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ATM Virtual Circuits
Bytes
5
48
Header
bits
User Data (payload)
4
8
GFC
VPI
16
VCI
3
1
8
Type CLP CRC
UNI - Generic VPI – Virtual Path Id
Flow Control VCI – Virtual Circuit Id
NNI – VPI extension
Header Error Check
Cell Loss Priority
1- management content
0- user data
third bit 1 – user signalling
• Data Packet is split into fixed length ATM cells.
• Each cell is switched independently hence cell header.
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The ATM Reference Model
ATM switch is fast 155 Mbps and used to connect Ethernet networks.
Since ATM is not shared-media (like Ethernet) the broadcast and multicast
are complicated to implement.
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ATM layers vs. OSI protocol stack
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Architecture of the original Ethernet
•
•
•
•
The first idea of sharing common channel with many active users was ALOHA
network 1970 by Norman Abramson. Any host simply sends at will. If
acknowledgement doesn’t come back within round trip time it resends it again
after some random time.
Bob Metcalfe and David Boggs 1976 used the same concept in Xerox PARC
(Palo Alto Research Center) to build first Ethernet over coax cable: 2.5 km long,
repeaters every 500 m, capacity 256 machines, speed 2.94 Mbps. Improvement:
source listen whether anybody is transmitting before it transmits: CSMA.
If two or more hosts listen for Ether to free they will transmit at the same time
and cause a jam that is detectable: CD. Hence CSMA/CD. Then each backs off
random time before retransmit.
1983 10 Mbps Ethernet became IEEE 802.3 standard.
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Wireless LANs
a)
Wireless networking with a base station.
b)
Ad hoc networking.
Driving forces: people wanted to have their Laptop connected to Internet.
Lack of standard until 802.11 – WiFi (group):
•
Laptop can talk to base station (access point)
•
Ad hoc networking – Laptops can talk to each other.
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Wireless LAN
802.11 is made after Ethernet. However, the range of a single radio
may not cover the entire system, hence CSMA doesn’t work.
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A connection between 802.11 and outside
world is called Portal
1999 WiFi standard was finalized with three:
802.11a
54 Mbps
802.11b
11 Mbps (good error immunity)
802.11g
54 Mbps (modulation scheme of 802.11)
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Network Standardization
Who’s Who in the Telecommunications World
–
–
Service Providers: Bells (local), AT&T, Sprint, MCI (long distance),
Verizon (wireless), TV cable services, ISPs (AOL, Netzero).
Vendors (manufacturers): Lucent, Nokia, Ericsson,
Nortel etc.
Who’s Who in the International Standards World
–
CCITT -> ITU (under UN 1947 - predecessor 1865), ISO (1946),
IEEE (society like ACM and Internet Society), ETSI (European
Telecommunication Standard Institute)
Who’s Who in the Internet Standards World
–
IAB (Architecture) Board in 1989 split into: IRTF (Research)
IETF (Engineering). IETF is in charge of RFCs.
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ITU (International Telecommunications Union)
1865 inception, UN 1947 CCITT, 1993 ITU
Main sectors
• Radio communications (ITU-R)
• Telecommunications Standardization (ITU-T)
• Development (ITU-D)
Members
• National governments (all Nations + US State Department)
• Sector members:
service providers: AT&T, Vodaphone, etc.
telecom equipm. Manufact. : Cisco, Nokia, etc.
computer manufact.: HP, Toshiba, etc.
chip manufact.: Intel, Motorola, etc.
media company: Time Warnet, AOL, etc.
non-profit scientific org.: IFIP, IATA, etc.
• Associate members: smaller org. interested in particular study groups.
• Regulatory agencies: like FCC.
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ITU operations
14 Study Groups:
from telephone billing
to multimedia services
ITU-T task: technical
recommendations
about: telephone,
telegraph, data
communication
interfaces)
Working Groups
Expert Teams
They publish recommendations every 4 years.
3000 (60,000 pages) since inception
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ISO (International Standard Organization)
non-treaty organization founded 1946
Members:
National Standard Organizations (US: ANSI, GB: BSI, France: AFNOR,
Germany: DIN + 85 other countries)
Activity:
Very broad: from telephone pole coating to ISO 9000.
Operations
Working Groups. 100,000 volunteers assigned by their employers,
government officials, academic experts.
Process
•
•
•
•
•
National Standard Org. suggest international standard
Working Group is formed to come with CD (Committee Draft)
CD is circulated to all members bodies for 6 months.
If approved DIS (Draft Intern`l Std.) circulated for comments.
If acquired enough votes it become IS (Intern`l Standard).
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IEEE 802 Standards
The 802 working groups. The important ones are marked with *. The ones
marked with  are hibernating.
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Internet Standards
DoD
NSF
1983
IAB (Internet Activity/Architecture Board)
To streamline researchers involved in ARPANET
and Internet activities. 10 members each heading
a task force on some issue.
1989
IRTF (Int. Research
Task Force)
Subsidiary of IAB for
long term research.
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IETF (Int. Engineering
Task Force)
for short term research.
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Adopter formal
ISO Standard
Procedures:
RFC > Proposed
Standard > Draft
> Internet Standard
Working
Groups
RFC
46
The principal metric prefixes
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