CCDA 640-864 Summary Notes – Chapter 6 – Day 13

Exam Topic 1: Wide-area networks (WAN) Overview

WAN – communication networks that are used to connect network locations that are geographically separated.

Tarrif – a fee charged by a service provider for providing WAN services to customers.

Service – WAN communications provided by service providers or telecommunication carriers

Choice of WAN Technology depends on :

• cost
• bandwidth
• reliability
• manageability
• hardware capabilities

Design requirements depend on:

• SLA – availability of the network. Example
  • bandwidth
  • allowed latency
  • permittable loss
• Cost and Usage

Key WAN design objectives:

• Design should meet company goals and policies
• Design should support current application requirements and have room for future growth
• Design should be within the allocated budget

WAN Connection Modules

Connectivity modules:

• Connection to the Internet
• Connection to the DMZ
• Connection to the WAN

Technologies can be

• Point to Point
• Point toMultipoint
  • Frame Relay
  • MPLS WAN

Exam Topic 2: WAN Transport Technologies

Integrated Services Digital Network (ISDN)

Overview:

• Standardized early 1980s
• An all digital phone line connection
• Both voice and data can be transmitted over the digital phone line
• Comes in 2 service types;
  • ISDN Basic Rate Interface (BRI)
    • Channels:2B + 1 D
      • B channels operate at 64kbps and carry user data
      • D channels
        • 16 kbps carry signaling anc control information
        • 48 kbps used for framing and synchronization
    • Total bit rate = 64 + 64 + 16 + 48 = 192 kbps
  • ISDN Primary Rate Interface (PRI)
    • North American and Japan
      • channels: 23 B + 1 D
      • All channels operate at 64 kbps
      • Total bit rate = 23 * 64 + 1* 64 = 1.536 kbps + 8 kbps (framing overhead) = 1.544 kbps
    • Rest of the World
      • Channels: 30 B + 2 D (Typically)
        • Channel 0          –           D-channel (Used mainly for clocking and synchronisation)
        • Channel 1-15    –           B-channel (Voice)
        • Channel 16        –           D-channel (Signalling)
        • Channel 17-31  –           B-channel (Voice)
      • All channels operate at 64 kbps
      • Total bit rate = 30 *64 + 2 * 64 = 2048 kbps
• Not frequently used now. Used where broadband services like DSL, Cable and wireless are unavailable

Characteristics:

• Low Bandwidth
• Medium Reliability
• Medium Latency
• Low Cost

Differences with the Old dialup connection

• Voice and data were transmitted over analog signals
• Greater bandwith than dial up
• Lower latency than dil up

Digital subscriber line (DSL)

• Uses ordinary copper telephone lines to provide high speed Internet data services
• It uses frequencies that are not used for  normal telephone conversations
• Primarily used in residential community but can be used for WAN too
• xDSL – different forms of DSL
  • ADSL (Asymmetric digital subscriber line)
    • most popular and widely available
    • Downstream bandwidth is higher than the upstream bandwidth
    • Can only be used in close proximity to the digital subscriber line access multiplexer (DSLAM) (2km max)
    • DSLAM allows the telephone lines to be connected to the Internet
    • Download speed (768 kbps to 9 Mbps )
    • Upload speed (64 kbps to 1.5 Mbps)
    • Customer Premises Equipment
      • PC
      • DSL Modem or DSL router
    • CPE connects to network access provider (NAP) DSLAMs
    • ADSL circuit has the following channels
      • Medium-speed downstream channel
      • Low-speed upstream channel
      • Basic telephone service channel
    • DSL splitters separate basic phone services from the ADSL modem/router to provide service even when ADSL signal fails
  • SDSL (Symmetric digital subscriber line)
    • Volume of data flow is equal in both directions
• Since it is a public network over the internet, it should be used with VPN or firewalls

Characteristics:

• Low /Medium Bandwidth
• Low Reliability
• Medium Latency
• Low Cost
• High speeds

Broadband Cable

• Uses coaxial cable to transport data over cable distribution systems
• CPE
  • Cable Modem or Universal Broadband Router (uBR)
  • Support data, voice and video TCP/IP
  • Provide services to small business, branch and teleworkers
• ISP side
  • Cable Modem Termination System (CMTS)
• Data Over Cable Service Interface Specifications (DOCSIS) protocol defines the cable procedures that the equipment needs to support.
• PC connects to TCP/IP network using PPPoE or DHCP

Characteristics:

• Low /Medium Bandwidth
• Low Reliability
• Medium Latency
• Low Cost

Wireless

• Uses electromagnetic waves to carry the signal between end points
• Wireless Implementations
  • Bridge wireless
    • Wireless bridge connects two separate wireless networks
    • High data rates provided
    • Used as a temporary solution for hard to wire sites, temporary networks, warehouses
  • Wireless LAN
    • Saves time and wiring by avoiding costly physical layer wiring solutions
  • Mobile wireless
    • Consists of cellular applications and mobile phones
    • Technologies:
      • Global System for Mobile Communications (GSM)
        • Digital mobile radio standard
        • Data transfer rate is 9600 bps
        • Can roam internationally
        • uses Time Division Multiplex Access (TDMA) in 3 frequency bands
          • 900 MHz
          • 1800 MHz
          • 1900 MHz
      • General Packet Radio Service (GPRS)
        • Increases GSM speeds from 64 kbps to 128 kbps
      • Universal Mobile Telecommunications Service (UMTS) / 3G broadband
        • Packet based transmission of digitized voice, video and data
        • Transmission rates of 2 Mbps
        • Provides location independent services to mobile users throught the world

Characteristics:

• Low / Medium Bandwidth
• Low Reliability
• Medium Latency
• Medium Cost

Frame Relay

• Deployed since 1980s
• Packet switched connection oriented Layer 2 WAN protocol
• Uses virtual circuits between connected devices
• Connection on the data link layer is established using  a DTE device (router) and DCE device (frame switch)
• Circuit types:
  • Permanent Virtual Circuit (PVC)
    • Connections are permanent
    • Used predominantly
    • Uses Data Link Connection Identifier (DLCI) to identify the local end of the PVC
    • DLCI is locally significant numeric value
  • Switched Virtual Circuit (SVC)
    • Temporary connections are created for each data transfer session
• Use is on the decline because of MPLS

Characteristics:

• Low /Medium  Bandwidth
• Medium Reliability
• Low Latency
• Medium Cost

Time-Division Multiplexing (TDM)

• Interleaves bits from multiple data, voice  and video channels over one communication medium
• Basic DS0 = 64 kbps
• North America
  • DS1 or T1
    • 24 time slots = 64 kbps + 8 kbps control
    • 1.544 Mbps of bandwidth
  • DS3 or T3
    • 44.736 Mbps of bandwidth
• Rest of the World
  • E1
    • 30 channels
    • 2.048 Mbps of bandwidth
• Service providers can gurantee or reserve bandwidth
• Customers are charged for exclusive access to the circuits
• Network is typically shared hence ISPs are more flexible in managing the newtorks and the services offered

Characteristics:

• Medium Bandwidth
• High Reliability
• Low Latency
• Medium Cost

Metro Ethernet

• Uses Ethernet to deliver low cost, high speed WAN MAN connectivity for organizations
• Deliver converged network services on the same wire
• Provides enterprise LAN type functionality out in the MAN and WAN increasing the throughput available for applications
• Bandwidth : 10 Mbps to 1 Gbps or +
• Supports higher performance
• Increased QoS  requirements
• Difference with TDM:
  • Easier to deploy
  • Easier to scale
  • Flexible bandwidth increaments
• Appealing because of the use of Ethernet

Characteristics:

• Medium / High Bandwidth
• High Reliability
• Low Latency
• Medium Cost

Synchronous optical networking (SONET) / Synchronous Digital Hierarchy (SDH)

• Has a circuit based architecture
• Delivers high speed services over optical network
• SONET
  • Defined by American National Standards Institute (ANSI )
• SDH
  • Defined by International Telecommunication Union (ITU)
• Gurantees bandwidth
• Line rates of 155 Mbps to 10 Gbps +
• Uses a ring topology to connect sites
  • The rings support ATM or Packet over SONET (POS) IP encapsulations
• Provides automatic recovery capabilities
• Has self healing mechanisms
• OC – optical carrier rates. These are digital bandwidth hierarchies
  • Supported speeds
    • OC-1 = 51.85 Mbps
    • OC-3 = 155.52 Mbps
    • OC-12 = 622.08 Mbps
    • OC-24 = 1.244 Gbps
    • OC-48 = 2.488 Gbps
    • OC-192 = 9.952 Gbps
    • OC-255 = 13.21 Gbps
  • Common circuit sizes
    • OC-3 = 155 Mbps
    • OC-12 = 622 Mbps
• Redundancy and High availability is inbuilt in the architecture

Characteristics:

• High Bandwidth
• High Reliability
• Low Latency
• High Cost

MPLS

• Uses labels (numbers) to forward packets
  • Marks packet headers that include label information
  • Specific paths in the network can be designed to correspond to the label
  • Packets that are destined to the same endpoint with the same requirements can be forwarded based on the labels, without a routing decision at every hop
• MPLS labels can be set on parameters such as
  • Source addresses
  • L3 destination address (typically)
  • Layer 2 circuit ID
  • QoS Value
• Labels can be used to implement traffic engineering
  • This overides the routing table
• Can run over:
  • Layer 2 topologies
    • ATM
    • Frame Relay
    • Packet over SONET (POS)
    • Ethernet
• Goals:
  • Maximize switching using labels
  • Minimize L3 routing
• MPLS Implementation has the following
  • Customer Edge (CE)
    • Resides at customer premises
    • Internal and external routing information is exchanged
    • Connects to the PE
  • Provider Edge (PE)
    • Ingress to MPLS service provider network
    • Resides in service provider network

Characteristics:

• High Bandwidth
• High Reliability
• Low Latency
• High Cost

Dark Fiber

• Fiber optic cables that have been installed in the ground or where right of way issues are evident
• May use signalregenerators for:
  • Jitter control over long distances
  • Maintain signal integrity
• Framing is determined by the enterprise not the provider
• Can also be used for the edge devices
• Usually owned by service providers but can be bought like leased lines for use in MAN and WAN
• Reliability of these links is not provided by the SP but designed by the enterprise
• Redundancy and High availability has to be designed with multiple links

Characteristics:

• High Bandwidth
• High Reliability
• Low Latency
• High Cost

Dense Wavelength-Division Multiplexing (DWDM)

• Uses different wavelengths of light (channels) over the same fiber strands to increase fiber optics bandwidth capabilities
• Each fiber channel is equivalent to several GE links
• Increased use of bandwidth using existing fiber base by SP
• SPs can increase services provided because of greater bandwidth
• A variety of devices can access the network

Characteristics:

• High Bandwidth
• High Reliability
• Low Latency
• High Cost

Ordering WAN Technology and Contracts

Ordering:

• Plan early
• Takes ~ 60 days for the carrier to provision circuits. If overseas (60 to 120 days)

Cost of WAN

• Access circuit charge
• Distance-based charges (at times. Most carriers have eliminated this)

Metro Ethernet

• Availability is spotty
• Lead times are long
• Construction may be necessary – more cost and time delay

Frame Relay and ATM

• Charges:
  • Access circuit charges
  • per- PVC charges
  • per-bandwidth CIR charges. CIR – rate the SP guarantess to provide

Contract periods

• Typically 1 – 5 years.
• Dark fiber (usually 20 years). Need the right of non-reversion in SLA (no matter what happens to SP, the fiber belongs to the customer for 20 years)
• Process to repair fiber cuts shouls also be defined