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 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 (SB- ADPCM) 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 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 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 T- carrier communications (starting at T-3) Main transport method occurs at OSI Physical layer Operates at base level of 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 point- to-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