Download WAN devices

Chap 2
WANs and Routers
Andres, Wen-Yuan Liao
Department of Computer Science and Engineering
De Lin Institute of Technology
[email protected]
http://www.cse.dlit.edu.tw/~andres
Overview
 WAN
devices, technologies,
and standards
 The function of a router in a
WAN
WANs
 WANs
and devices
 WAN standards
 WAN technologies
WANs and devices
 Operates
at the physical layer
and the data link layer
 Interconnects LANs that are
usually separated by large
geographic areas
WANs and devices
 Provide
for the exchange of
data packets/frames
between routers/bridges and
the LANs they support
WAN Devices
 Routers
-- offer many services,
including internetworking and
WAN interface ports
 Switches -- connect to WAN
bandwidth for voice, data, and
video communication
WAN Devices
 Channel
service units/digital
service units (CSU/DSUs) that
interface T1/E1 services
 Terminal Adapters/Network
Termination 1 (TA/NT1s) that
interface ISDN services
WAN Devices
 Communication
servers -concentrate dial-in and dial-out
user communication
 Modems -- interface voice-grade
services
WAN Standards
WAN Standards
 WAN
physical layer protocols
describe how to provide electrical,
mechanical, operational, and
functional connections for WAN
services
WAN Standards
 WAN
data link protocols describe
how frames are carried between
systems on a single data link
WAN physical layer
 Describes
the interface between
the data terminal equipment
(DTE) and the data circuitterminating equipment (DCE)
WAN physical layer
 DCE:
service provider
– modem
 DTE:
or a CSU/DSU
the attached device
Physical layer standards
 EIA/TIA-232
 X.21
 EIA/TIA-449
 G.703
 V.24
 EIA-530
 V.35
Data link encapsulations
 HDLC
– May
-- IEEE standard
not be compatible with different
vendors
– Supports both point-to-point and
multipoint configurations with
minimal overhead
Data link encapsulations
 Frame
Relay -- uses high-quality
digital facilities
– Uses
simplified framing with no
error correction mechanisms
– Send Layer 2 information much more
rapidly than other WAN protocols
Data link encapsulations
 PPP
-- described by RFC 1661
– Contains
a protocol field to
identify the network layer protocol
Data link encapsulations
 Simple
Data Link Control Protocol (SDLC)
An IBM-designed WAN DL protocol for SNA
– Being replaced by the more versatile HDLC
–
 Serial
Line Interface Protocol (SLIP)
Popular WAN DL protocol (IP packets)
– Being replaced by the more versatile PPP
–
Data link encapsulations

Link Access Procedure Balanced (LAPB)
–
–

A data link protocol used by X.25
Has extensive error checking capabilities
Link Access Procedure D-channel (LAPD)
–
–
The WAN DL protocol used for signaling and
call setup on an ISDN D-channel
Data transmissions take place on the ISDN B
channels
Data link encapsulations
 Link
Access Procedure Frame
(LAPF)
– For
Frame-Mode Bearer Services
– A WAN DL protocol, similar to
LAPD, used with frame relay
technologies
WAN technologies
 Circuit-switched
 Cell-switched
 Dedicated
digital
 Analog services
Circuit-Switched Services
 POTS
–
(Plain Old Telephone Service)
Not a computer data service, but included
 Narrowband
ISDN
The first all-digital dial-up service
– 128 kbps (BRI)
– 3 Mbps (PRI)
–
Packet-Switched Services
 X.25
An older technology, but still widely used
– Has extensive error-checking capabilities
– Make it reliable but limits its bandwidth
– 2 Mbps (maximum)
–
Frame Relay
 A packet-switched
version of
Narrowband ISDN
 More efficient than X.25, but with
similar services
 Maximum bandwidth is 44.736 Mbps
 56kbps and 384kbps are extremely
popular
Cell-Switched Services

ATM (Asynchronous Transfer Mode)
– Closely
related to broadband ISDN
– An increasingly important WAN/LAN
– Small, fixed length (53 byte) frames
– Maximum bandwidth is 622 Mbps
Cell-Switched Services

SMDS (Switched Multimegabit Data Service)
– Closely
related to ATM
– Typically used in MANs
– Maximum bandwidth is 44.736 Mbps
– Usage not very widespread; cost is
relatively high
Dedicated Digital Services
T series of services in the U.S
 E series of services in Europe
 T1 -- 1.544 Mbps
 T3 -- 44.736 Mbps
 E1 -- 2.048 Mbps
 E3 -- 34.368 Mbps

Dedicated Digital Services
 xDSL
– DSL:
Digital Subscriber Line
– x: a family of technologies
– A new and developing WAN
technology (home use)
Dedicated Digital Services
 xDSL
Bandwidth decreases with increasing
distance from the phone companies
equipment
– Top speeds of 51.84 Mbps (near a
phone company office)
– From 100s of kbps to several Mbps)
–
Dedicated Digital Services
 HDSL
-- high-bit-rate DSL
 SDSL -- single-line DSL
 ADSL -- asymmetric DSL
 VDSL -- very-high-bit-rate DSL
 RADSL -- rate adaptive DSL
Dedicated Digital Services
 SONET (Synchronous Optical
Network)
 A family of very high-speed physical
layer technologies
 For optical fiber, also for copper
cables
Dedicated Digital Services
 SONET
 OC (optical carrier) levels: 51.84 Mbps
(OC-1) to 9,952 Mbps (OC-192)
 Wavelength division multiplexing (WDM)
 Usage is widespread among Internet
backbone entities
Other WAN Services
 Dial-up
modems (switched analog)
– Maximum
 Cable
– Put
bandwidth approx. 56 kbps
modems (shared analog)
data signals on the same cable as
television signals
Other WAN Services
– Increase
in popularity in regions
that have large amounts of existing
cable TV coaxial cable (90% of
homes in U.S.)
– Maximum bandwidth can be 10
Mbps
– Degrades as more users
Other WAN Services
 Wireless
–
The signals are electromagnetic waves
 Terrestrial
Bandwidths typically in the 11 Mbps range
(e.g. microwave)
– Cost is relatively low; line-of-sight is
usually required
–
Other WAN Services
 Satellite
– Serve
mobile users and remote
users
– Usage is widespread; cost is high
WANs and Routers
 Router
basics
 The function of a router in a
WAN
Router basics
 Routers
need the Internetworking
Operating Software (IOS) to run
configuration files
 Selects the best paths and
manages the switching of packets
 Network layer
Internal configuration
components
 RAM/DRAM
– Stores
routing tables, ARP cache,
fast-switching cache, packet buffering
(shared RAM), and packet hold
queues
– Provides temporary and/or running
memory
– Be lost when you power down or
restart
Internal configuration
components
 NVRAM
– Stores
-- nonvolatile RAM
a router’s
backup/startup configuration
file
– Content remains when you
power down or restart
Internal configuration
components
 Flash -- Erasable, reprogrammable ROM
 Hold the operating system image and
microcode
 Update software without removing and
replacing chips on the processor
 Content remains when you power down
 Store multiple versions of IOS software
Internal configuration
components
 ROM
– Contains
power-on diagnostics, a
bootstrap program, and operating
system software
– Software upgrades: replacing
pluggable chips
Internal configuration
components
 Interface
– Network
connection through which
packets enter and exit a router
– It can be on the motherboard or on
a separate interface module
The function of a router in a WAN
 While
routers can be used to
segment LAN devices, their major
use is as WAN devices
 Routers have both LAN and WAN
interfaces
The function of a router in a WAN
 WAN
technologies are frequently
used to connect routers
Communicate with each other by WAN
connections
– Make up autonomous systems and the
backbone of the Internet
–
The function of a router in a WAN
 Two
main functions of routers
– The
selection of best paths
(Logical Address)
– The
switching of packets to the
proper outgoing interface
The function of a router in a WAN
 Any
internetwork includes:
Consistent end-to-end addressing
– Addresses that represent network
topologies
– Best path selection
– Dynamic routing
– Switching
–