Download Lecture 7 - cda college

WAN Transport Methods
Chapter 7
Learning Objectives
Explain the X.25 communications protocol and
understand how to implement X.25 WAN
connections
Explain frame relay for use in WANs
Describe ISDN communications for voice, data,
and video networks; explain how to connect to
ISDN
Define SMDS networking and explain how it is
implemented
continued…
Learning Objectives
Describe DSL network communications for
high-speed networking
Explain how SONET works and how it is
implemented
Describe Ethernet-based MANs
Discuss additional WAN protocols: SLIP,
PPP, and SS7
X.25
Older, very reliable packet-switching protocol for
connecting remote networks
Offers bandwidth up to 2.048 Mbps
Defines communications between DTEs and
DCEs
Globally accepted
Can connect older LANs to WANs and older
mainframes and minicomputers to a WAN
X.25 and the OSI Model
X.25 Transmission Modes
Switched virtual circuits (SVCs)
Permanent virtual circuits (PVCs)
Datagrams
X.25 Connectivity
Communications accomplished by:
DTE
DCE
Packet assembler/disassembler (PAD)
Protocols important to maintaining X.25 network
X.3 protocol
X.20 protocol
X.28 protocol
X.29 protocol
X.25 Network
X.25 Frame Structure
Layer 3 Header and Data
X.25 Deployment
Provides worldwide connectivity between
LANs
Designed to release unused bandwidth when
nodes are not communicating
For WAN connectivity, being replaced by
faster technologies (frame relay, SMDS,
SONET, Optical Ethernet)
Frame Relay
Communications protocol that relies on packet
switching and virtual connection technology (SVC
or PVC) to transmit data packets
Uses frame relay assembler/disassembler (FRAD)
to convert packets
Achieves higher transmission rates (up to 45
Mbps) by leaving extensive error-checking
functions to intermediate nodes
Can transport IP, IPX, AppleTalk, PPP, SLIP
Frame Relay Layered
Communications
Switching and Virtual
Connections
Virtual connections are logical rather than
physical
Types of virtual connections
Permanent
Switched
Frame Relay Format
Frame Format
Data link connection identifier (DLCI)
Contained in address field
Identifies an individual virtual connection on a
frame relay network
Frame Relay
Local management interface (LMI) protocol
Used by frame relay for signaling communications
Enables frame relay to determine when to:
Create a new virtual circuit
Delete a virtual circuit that is no longer in use
Identify a virtual circuit that has failed
LMI extensions
Added to frame relay frame for additional functions
Voice over Frame Relay
(VoFR)
Transmits voice signals over the network to reduce
long-distance telephone costs between sites
Voice transmission techniques
Voice compression
Pulse code modulation (PCM)
Adaptive differential pulse code modulation (ADPCM)
Sub-band adaptive differential pulse code modulation (SBADPCM)
Silence compression
Vendor Services
Committed information rate (CIR)
Permanent virtual connection (PVC)
Port
Integrated Services Digital
Network (ISDN)
Standard for delivering data services over
telephone lines
Current practical limit of 1.536 Mbps
Theoretical limit of 622 Mbps
ISDN Applications
LAN-to-LAN connectivity
Home offices and telecommuting
Off-site backup and disaster recovery
Connecting a PBX to the RBOC
Transferring large image and data files
LAN-to-LAN video and multimedia
applications
Benefits of ISDN
Provides voice, data, and video services over one
network
Layered protocol structure compatible with OSI
reference model
Communications channels offered in multiples of
64 Kbps, 384 Kbps, and 1536 Kbps
Switched and non-switched connection services
Broadband ISDN capabilities 155 Mbps and
higher
I.200 Services for Networking
Bearer services
Circuit-mode options
Packet-mode options
Virtual call circuits and permanent virtual call circuits
Teleservices
Speech and telex
Supplementary services (voice communications)
Caller ID and conference calling
Digital Communications
Services
Basic rate interface (BRI) ISDN
Three channels
Two 64-Kbps channels for data, voice, and video
transmissions
One 16-Kbps channel used for communications
signaling
Primary rate interface (PRI) ISDN
Switched communications in multiples of 1.536
Mbps
Connecting to ISDN
Equip computer with a TA that also contains
a network terminal (NT1) network
terminator
Connect ISDN line into external TA that is
equipped with a U interface
Network Termination Unit (NTU)
Connecting via an NTU
Connecting to ISDN PRI
Broadband ISDN (B-ISDN)
Data transfer rate of 155 Mbps and higher
Currently under development; not widely
implemented
How ISDN Works
Time-compression multiplexing
Echo cancellation
ISDN and OSI
Link Access Procedure D
Channel (LAPD) Frame Format
Q.931 Connection
Control Protocol
Contains information elements
Setup
Call proceeding
Connect
Connect acknowledgement
Suspend
Resume
Disconnect
Release
Release Complete
ISDN Considerations
Available locally?
Which protocol used by provider?
Twisted-pair copper wire or fiber-optic
cabling?
Connecting to ISDN
Through a T-carrier
Circuit mode services
Packet mode services
Switched Multimegabit Data
Service (SMDS)
High-speed WAN technology, often
implemented over T-1 carrier lines
High-speed bus with bandwidth of up to
155 Mbps
Compatible with wide range of LAN-based
protocols
SMDS Applications
High-speed links for regional networks
Transmission of large image files (medical
X-rays)
Transmission of CAD graphics
Fast access to library holdings and
electronic catalogs
SMDS Architecture
SMDS and OSI
SMDS Cell
SMDS Considerations
Advantages
High-speed network communications
Compatible with B-ISDN, T-carrier, SONET, and ATM
Strong security options for users
Disadvantages
Not as universally available as X.25, frame relay, and
ISDN
Designed to transport data only
Digital Subscriber Line (DSL)
Uses advanced modulation technologies on
existing telecommunications networks for
high-speed networking between subscriber
and telco
Can turn existing twisted-pair telephone
wire into a high-speed WAN for
communications up to 55 Mbps
(downstream)
DSL Applications
Residential lines for telecommuting
Internet access
Accessing multimedia over a network
Quick transmission of a large image file
Taking an interactive class or seminar
Implementing a distributed client/server
application among geographically dispersed
users
DSL Basics
Synchronous Optical Network
(SONET)
Fiber-optic communication technology capable of
high-speed data transmissions (over one gigabit
per second)
Advantages
Nonproprietary
Can connect to interfaces for ATM, ISDN, routers, and
other equipment
High-speed communications possible over long
distances
Enables delivery of voice, data, and video
communications
SONET Communications
Media and Characteristics
Uses single-mode fiber-optic cable and Tcarrier communications (starting at T-3)
Main transport method occurs at OSI
Physical layer
Operates at base level of 51.84 Mbps or
optical carrier level 1 (OC-1)
SONET Transmission Rates
SDH Levels
Compared to SONET
SONET Network Topology
and Failure Recovery
Ring topology
Methods of failure recovery
Unidirectional path switching
Automatic protection switching
Bidirectional line switching
SONET and OSI
SONET Frame
Point-to-Point Protocol (PPP)
over SONET
Work is underway to implement RFC 2615,
which outlines how to enable Point-to-Point
(PPP) protocol to be directly transported
over SONET and SDH
Ethernet-based MANs
(Optical Ethernet)
High-speed Ethernet carried on fiber-optic
cable and used for MANs
Consists of:
Gigabit or 10 Gigabit Ethernet backbone
Multimode fiber-optic cable connections of up
to 6 miles
Single-mode fiber-optic cable connections of
up to 43.4 miles
Additional WAN Protocols
Serial Line Internet Protocol (SLIP)
Point-to-Point Protocol (PPP)
Signaling System 7 (SS7)
SLIP
Designed for UNIX environments for pointto-point communications between
computers, serves, and hosts using TCP/IP
Compressed Serial Line Internet Protocol
(CSLIP)
Compresses header information in each packet
sent across a remote link
Reduces overhead of SLIP by decreasing
header size
SLIP
SLIP and CSLIP
Do Not Support…
Network connection authentication; no security
Automatic setup of network connection at multiple
OSI layers at same time for faster communications
Synchronous connections
Remote set up of new account using remote
administration tools in Windows NT Server or
Windows 2000 Server over the Internet
PPP
Remote communications protocol that
enables connections to networks, intranets,
extranets, and VPNs through the Internet
Supplemented by Point-to-Point Tunneling
Protocol (PPTP)
Recommended on network where users
connect using multiple protocols
Advantages of PPP
over SLIP or CSLIP
Lower overhead
Greater capabilities
Stronger security
Supports more network protocols
PPP and SLIP Compared
SS7
WAN protocol for telecommunications
networks
Determines most efficient routes through
telecommunication network
Performs functions using:
Service control points (SCPs)
Service switching points (SSPs)
Signal transfer points
How SS7 Enables Fast
Communications
Keeps databases of routing information at
different strategic points throughout a WAN
Quickly directs central site’s query about
fastest route
Tracks every telecommunications call to
determine fastest route
Chapter Summary
Older WAN technologies
X.25
Frame relay
ISDN
Newer WAN technologies
SMDS
DSL
SONET
Ethernet-based MANs
continued…
Chapter Summary
WAN protocols
SLIP
PPP
SS7