Transcript PPT - ME Kabay

DATACOMM
John Abbott College JPC
Data Transport
Networks
M. E. Kabay, PhD, CISSP
Director of Education, ICSA
President, JINBU Corp
Copyright © 1998 JINBU Corp.
All rights reserved
DC 8 - 1
Data Transport Networks
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DC 8 - 2
OSI lower-level functions
– Physical layer (1)
– Data link layer (2)
– Network layer (3)
Key technologies
– Local Area Networks (LANs)
– Wide-Area Networks / Internetworking
(WANs)
– Metropolitan Area Networks (MANs)
– Packet-Switching Networks (PSN)
Local Area Networks
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DC 8 - 3
Definition
LAN Topologies
Baseband vs Broadband Transmission
LAN Access Methods
Priority and Random Backoff
LAN Standards
Widely-Used LANs
Higher-Speed LANs
Local Area Networks
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DC 8 - 4
A local area network (LAN) is a user-owned
communications mechanism linking informationprocessing and -storage equipment within one
building or a cluster of buildings within a
circumscribed geographical area.
No absolute distinction between a LAN and a
WAN (wide-area network)
LANs evolved because of desire to
– share expensive resources
– share information
Networks linking dumb terminals to hosts are not
considered LANs
Local Area Networks
Features
 Continuous connection
 Interconnectivity
 Variety of hardware permitted
 Relatively inexpensive
 High speeds (2.5-100 Mbps)
DC 8 - 5
Local Area Networks
LAN Topologies
STAR
DC 8 - 6
RING
NET/MESH
BUS/TREE
Local Area Networks
Star topology
 Failure of CPU / Hub downs entire network
 Performance is function of node at centre
 Costs largely due to central node
DC 8 - 7
Local Area Networks
Ring topology
 Failure of any one node downs entire network
 Performance declines as # nodes increases
n
– P{network failure} = 1 - (1-p)
 Relatively low cost
DC 8 - 8
Local Area Networks
Net/Mesh topology
 Network survives node failure
 Performance declines as # nodes increases
 Higher cost
DC 8 - 9
Local Area Networks
Bus/Tree topology
 Network survives node failure
 Performance declines as nodes increase
 Medium cost
DC 8 - 10
Local Area Networks
Baseband vs Broadband Transmission
 Baseband lower installation cost
 Broadband higher bandwidth
Baseband
Broadband
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DC 8 - 11
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Local Area Networks
LAN Access Methods
 Devices may accidentally transmit at same
time: collision
 Most access methods use CSMA (Carrier
Sense Multiple Access)
– Will not begin transmitting while another
node is transmitting
 CSMA/CA (Collision Avoidance)
– If acknowledgement of message not
received, node retransmits
– But both nodes wait fairly long
DC 8 - 12
Local Area Networks
LAN Access Methods
 CSMA/CD (Collision Detection)
– Nodes can detect collision quickly
– Both nodes immediately stop transmitting
when collision occurs
 Wait a certain amount of time before starting
again
DC 8 - 13
Local Area Networks
Priority Backoff and Random Backoff
 In CSMA/CD, what determines when node
starts transmitting again?
 Priority backoff
– each node waits a fixed amount of time
before retransmitting
– short-wait nodes have priority over longwait nodes
 Random backoff
– each node waits a random time
– equalizes access to network
DC 8 - 14
Local Area Networks
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DC 8 - 15
Token Passing (1)
Local Area Networks
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DC 8 - 16
Token Passing (2)
Local Area Networks
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DC 8 - 17
Token Passing (3)
Local Area Networks
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DC 8 - 18
Token Passing (4)
Local Area Networks
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DC 8 - 19
Token Passing (5)
Local Area Networks
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DC 8 - 20
Token Passing (6)
Local Area Networks
IEEE LAN Standards
 802.1: Encapsulation standards for CSMA/CD
 802.2: Logical link protocols
 802.3: Broadband & baseband bus using
CSMA/CD
 802.4: Broadband and baseband bus using
token passing
 802.5: Token-passing rings
 802.6: Metropolitan-area networks using
cable TV facilities
 802.7: Other broadband systems
 802.8: Fibre optics
DC 8 - 21
Local Area Networks
Widely-Used LANs
 Ethernet (IEEE 802.3)
– 10 Mbps commonplace (10Base-T)
– twisted pair
– 100 m max distance between nodes
 IBM Token Ring (IEEE 802.5)
– 4 or 16 Mbps
 Banyan VINES (IEEE 802.5)
DC 8 - 22
Local Area Networks
Higher-Speed LANs
 ANSI Fiber Distributed Data Interface (FDDI)
– Fibre optics
– 100 Mbps
– Similar to IEEE 802.5
– Double rings for increased robustness
 100Base-T (IEEE 802.3)
 100VG-Any-LAN
– IEEE 802.12
– Demand priority scheme
DC 8 - 23
Wide-Area Networks (WANs):
Internetworking
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DC 8 - 24
Definition: an internet is a collection of linked
LANs
Ordinary internets are built of
– LANs
– Repeaters
– Bridges
– Routers
– Gateways
A WAN is an extension of an internet: the
connection of LANs not physically co-located
THE Internet is something else….
WANs
Repeaters
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LANs on each floor
Repeaters on each floor
Fibre optic link under roadway
ThickLAN backbone risers
DC 8 - 25
7-Applications
6-Presentation
5-Session
4-Transport
3-Network
2-Link
1-Physical
7-Applications
6-Presentation
5-Session
4-Transport
3-Network
2-Link
1-Physical
WANs
Bridges
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10Base-T
Local bridge
100Base-T
Remote bridge
Digital Leased Line
Remote bridge
DC 8 - 26
WANs
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Bridges
 Protocol insensitive
 Learning
– modify routing table automatically as
devices are added
 Filtering
– discard packets staying on local bus
 Forwarding
– send packets to right network
DC 8 - 27
7-Applications
6-Presentation
5-Session
4-Transport
3-Network
2-Link
1-Physical
WANs
Routers &
Brouters
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Intelligence: can be addressed
Requires protocol agreement
Montreal
Can select alternate routes
Bridges becoming smarter
– now called brouters
7-Applications
6-Presentation
5-Session
4-Transport
3-Network
2-Link
1-Physical
Québec
Halifax
DC 8 - 28
WANs
Gateways
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DC 8 - 29
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7-Applications
6-Presentation
5-Session
4-Transport
3-Network
2-Link
1-Physical
Sometimes called protocol converters
Can link LANs with different protocols
Especially important in multi-vendor
internetworks; e.g., linking OSI system with
SNA network
Multiprotocol switches are hardware
Software protocol conversion also common
WANs
Internetworking Transmission Options
 Commercial services make internetworking
possible at low cost
 Switched Multi-Megabit Data Service (SMDS)
– offered by many carriers in Canada / US
– connectionless: simply routes packets or
frames
 Connectionless Broadband Data Service
(CBDS)
– popular in Europe
DC 8 - 30
WANs
Internetworking Transmission Options:
T-carriers (leased lines)
 T1:
1.544 Mbps 24 voice
 T1C:
3.152 Mbps 48 voice
 T2:
6.312 Mbps 96 voice
4 T1
 T3:
44 Mbps
672 voice 28 T1
 T4:
274 Mbps 4032 voice 168 T1
DC 8 - 31
WANs
The Internet
 TCP/IP based internetworking
 Store-and-forward technology
 Began as DARPA project in late 1960s
 Steady expansion during 1970s-80s
 Explosive growth late 1980s and in 90s
 Now thought to have several million hosts
 NOT the “Information Superhighway”
 More details in Hot Topics course
DC 8 - 32
WANs
Wireless Data Transport
 Wireless LANs
– radio
– infrared
 Broadcast
– beepers
– stock quotes
 Two-way
– cellular modems
– Cellular Digital Packet Data (CDPD)
DC 8 - 33
Packet-Switching Networks
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DC 8 - 34
Public Packet-Switching Networks
X.25
PSN Services
Routing Data in PSNs
Frame Relay Networks
Packet-Switching Networks
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DC 8 - 35
Cost of leased lines can be prohibitive for
sporadic use
Virtual circuits established for sessions at
low cost
Packet Assembler-Disassembler (PAD)
– Links devices to PSN cloud
– Data disassembled into packets
– Packets routed through PSN cloud
– Packets reassembled into data stream
Packet-Switching Networks
DATACOMM
OVERHEAD
Destination
DATA I/O
Sequence ID
DATA
CRC
PAD
Route ID
PACKET
DC 8 - 36
Packet-Switching Networks
Montreal
Node
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DC 8 - 37
Circuits
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Vancouver
Node
Processor
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Buffers
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Halifax
Node
Packets
Packet-Switching Networks
Montreal
Node
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DC 8 - 38
Circuits
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Vancouver
Node
Processor
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Buffers
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Halifax
Node
Packets
Packet-Switching Networks
Public PSNs
 Widely-available public nodes
 Charge by kilopacket
 Datapac (Stentor / Bell Canada)
 Telenet (SPRINT)
 Tymnet (MCI)
 ARPANET (US govt)
DC 8 - 39
Packet-Switching Networks
CCITT X.25 (“X-and-a-quarter”)
 Most common standard for PSN
 Functions divided into 3 levels that
correspond to OSI stack’s lower layers
– Physical level: CCITT V.24/V.28 like RS232-C
– Frame level: LAP-B data link like SDLC
– Packet level: network addressing and
routing
 PAD used to convert asynch to X.25 flow
DC 8 - 40
Packet-Switching Networks
PSN Services
 Closed user group
 Incoming calls only
 Outgoing calls only
 Flow-control negotiation
– define packet size, other parms
 Throughput class negotiation
– define allowable use of bandwidth
 Reverse charging = collect calls
– like 800 number for datacomm
DC 8 - 41
Packet-Switching Networks
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DC 8 - 42
Routing Data in PSNs
Virtual circuit unlike telephone call circuit
– Applies to one packet at a time
– No user control over how individual
packets reach destination
Packets often arrive at destination nodes out
of sequence
Destination nodes therefore buffer and
resequence the packets to reconstitute
original data stream
Packet-Switching Networks
Frame Relay Networks
 X.25 and other PSN have heavy overhead
– designed for analog phone circuits
– extensive error correction
 Digital circuits much higher reliability, lower
noise
 Frame Relay drops node-based error checking
 Functions at OSI layers 1 & 2 (application &
presentation)
 User systems do their own error-checking and
recovery
DC 8 - 43
Homework
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DC 8 - 44
Read Chapter 8 of your textbook in detail,
adding to your workbook notes as appropriate.
Review and be prepared to define or expand all
the terms listed at the end of Chapter 8 of your
textbook (no hand-in required)
Answer all the exercises on page 187 of the
textbook using a computer word-processing
program or absolutely legible handwriting (hand
in after quiz Monday morning)
Scan Chapters 9 and 10 of your textbook before
coming to class on Day 4.