Wide Area Networks

Download Report

Transcript Wide Area Networks

Wide Area Networks
Computer Networks
Autumn 2000
John Kristoff
1
Motivation
Ñ Connect multiple sites
Ñ Span geographic distances
Ñ Cross public right-of-way
Ñstreets
Ñbuildings
Ñrailroads
Autumn 2000
John Kristoff
2
Building blocks
Ñ Point-to-point long distance connections
Ñleased circuits
Ñprovided by telecommunications companies
Ñ Packet switches
ÑIP routers
ÑATM switches
Ñmany types...
Autumn 2000
John Kristoff
3
Long-Distance
Transmission Technology
Ñ Lease transmission facilities from
telecommunications companies
ÑGenerally point-to-point
ÑNOT part of the conventional telephone
system
ÑCopper, fiber, microwave or satellite
ÑAnalog or digital
Autumn 2000
John Kristoff
4
WAN Transmission
Equipment
Ñ Analog
ÑMODEM required at each end
Ñ Digital
ÑCSU/DSU required at each end
Autumn 2000
John Kristoff
5
CSU/DSUs
Ñ
Ñ
Ñ
Performs two functions, usually in a single box
Needed because telecommunications digital
encoding differs from computer industry digital
encoding
DSU
Ñ translates between the two encodings
Ñ
CSU
Ñ terminates line
Ñ allows for maintenance
Autumn 2000
John Kristoff
6
CSU/DSU Illustrated
Autumn 2000
John Kristoff
7
Standards for WAN
Circuits
Ñ
Ñ
Ñ
Specified by telephony industry in each region
Can differ around the world
North America and Japan examples
Ñ DS0, DS1, DS3, T1, T3, Fractional T1
Ñ OC1, OC3, OC12, OC48, SONET
Ñ
Rest of the world examples
Ñ E1, E2, E3
Ñ SDH
Autumn 2000
John Kristoff
8
Inverse Multiplexing
Ñ Recall multiplexing
Ñ Instead of intertwining, you combine
Ñ Combines two or more circuits
Ñ Produces intermediate capacity circuit
Ñ Special hardware required
Autumn 2000
John Kristoff
9
Inverse Multiplexing
Illustrated
Autumn 2000
John Kristoff
10
Early WAN Technologies
Ñ ARPANET
Ñ historically important in packet switching
Ñ fast when invented, slow by current standards
Ñ precursor to today’s Internet
Ñ X.25 protocol suite
Ñ
Ñ
Ñ
Ñ
early commercial service
still used
more popular in Europe
service by telecommunications companies
Autumn 2000
John Kristoff
11
Recent WAN Technologies
Ñ SMDS
Ñ offered by telecommunications companies
Ñ not as popular as frame relay
Ñ Frame relay
Ñ widely used commercial service
Ñ offered by telecommunications companies
Ñ ATM
Ñ offered by telecommunications companies
Ñ designed for both WAN and LAN
Autumn 2000
John Kristoff
12
Future WAN Technologies
Ñ Packet over SONET
Ñprovided by telecommunications companies
Ñremoves intermediate complexity
Ñ Packet over DWDM
Ñprovided by telecommunications companies
and long haul fiber optic providers
Ñ Ethernet?
Autumn 2000
John Kristoff
13
Asynchronous Transfer
Mode (ATM)
Ñ Connection oriented using virtual circuits
Ñ Use of fixed sized packets called cells
Ñ Defines service categories for QoS
networking
Ñ Operates on LANs using LAN Emulation
(LANE)
Ñ Usually used for high-speed WAN
connectivity
Autumn 2000
John Kristoff
14
Virtual Circuits
Ñ Circuit ID instead of full host address pairs
Ñ Switches swap IDs using translation tables
Ñ Switch stores connection state for hosts
Autumn 2000
John Kristoff
15
Cell Format
Autumn 2000
John Kristoff
16
Service Types
Ñ CBR
constant bit rate
Ñ VBR-NRT variable bit rate - non real time
Ñ VBR-RT
variable bit rate - real time
Ñ ABR
available bit rate
Ñ UBR
unspecified bit rate
Autumn 2000
John Kristoff
17
LANE and MPOA
Ñ Overview
Ñ Backwards compatibility of ATM nodes with LANs such as Token Ring and
Ethernet. Must support the broadcast nature of LANs with the virtual circuit
nature of ATM.
Ñ LAN Emulation Client (LEC)
Ñ Provides abstraction for LAN protocols to ATM network
Ñ LAN Emulation Server (LES)
Ñ Manages and supports LECs
Ñ LAN Emulation Configuration Server (LECS)
Ñ Maintains emulated LANs (ELANs) and supports LECs
Ñ Broadcast and Unknown Server (BUS)
Ñ Distributes broadcasts/multicasts
Autumn 2000
John Kristoff
18
How ATM is Used in a LAN
Ñ 1. LEC - Implemented at each client (bridge listens to all)
Ñ 2. LEC contacts LECS to going a ELAN via a pre-configured SVC or
discovered dynamically via integrated local management interface
(ILMI)
Ñ 3. LECS assign LEC to a ELAN and direct them to a LES
Ñ 4. LEC setups up connection to LES and registers addresses
Ñ 5. LES assigns a BUS to the LEC
Ñ 6. LEC queries LES for a MAC address to ATM address translation
Ñ 7. LECS responds directly or forwards query to another LEC
Ñ 8. MAC broadcasts are sent to BUS so that an associated ATM
broadcast can be sent to all stations in the ELAN.
Autumn 2000
John Kristoff
19
ATM Summary
The aim was to combine the flexibility of
packet data networks (e.g. Internet) with
the per-user quality of service guarantees
of a circuit switched network (e.g.
telephone network). A monumental task!
Although an important technology, it may
follow the path of similar technologies
(e.g. Token Ring). Stay tuned.
Autumn 2000
John Kristoff
20
Final Thoughts
Ñ Local loop
Ñ ISDN
Ñ Digital Subscriber Line (DSL)
Ñ Cable modems
Ñ Cellular
Ñ CIR/CAR
Ñ Everything over IP
Autumn 2000
John Kristoff
21