IT Life: Chapter 2: Connecting to the WAN Part 4

Private WAN Infrastructures

An overview of private WAN infrastructures: Leased Lines, Dial-up, ISDN, Frame Relay, ATM, MPLS, Ethernet WANs, and VSAT.

Leased Lines

Dedicated permanent connections
Point-to-Point link
Pre-established WAN path
Usually leased from service providers
Also known as: Leased Circuits, Serial line, Point-to-Point link, and T1/E1 or T3/E3 links.
Available at different speeds
Price based on bandwidth and distance between points
Usually uses layer two protocols HDLC or PPP
America uses the T-Carrier system an Europe uses the E-Carrier system to define the digital capacity of a serial copper link.
Optical Carrier (OC) is used to define the digital capacity of a Fiber-Optic link.

These are charts of the T/E-Carrier speeds and OC speeds

The Good

Simple point-to-point lines require minimal expertise to install and maintain
High quality links (with adequate bandwidth) removes latency/jitter
Always on dedicated connection good for applications that require high availability.

The Bad

Generally the most expensive. Not only the price of the connection, but each line needs it’s own interface on the end devices;p increasing hardware costs.
Fixed capacity requires the ISP to send people to adjust. (Limited flexibility)

Dial-up

Used when there is no other option
Provides low-capacity dedicated switched connections
Uses copper cable on the local loop
Can be used for voice/data
Needs Modem for data transfers
Speed limited to <56kbps
Charges more during peak hours
Good for intermittent, low-volume data transfers
Most enterprises do not support dial-up

ISDN

Circuit-Switching technology that allows PSTN to carry digital signals.
Higher-capacity than PSTN
Uses Time Division Multiplexing (TDM)
Uses 64kbps bearer channels (B) for data/voice
Uses 16kbps signaling channels (D) for call setup
Two types of interfaces Basic Rate Interface (BRI) and Primary Rate Interface (PRI)
Can be used to add capacity to a Leased Line
Can be used as a back up should a leased line fail.
Costs are per B channel
Known for being expensive

ISDN is becoming less popular because of DSL and cable internet is cheaper and faster

TDM

Allows two or more signals on a single channel
Signals appear simultaneous but are actually taking turns on the channel

BRI

For use in homes/ small enterprise
Provides two B channels and one D channel
May only use one B channel and later activate the second
Top speed of 144kbps. 128kbps for data 16kbps for overhead
Has a connection set up time of <1second
May require a terminal adapter (TA) to connect to a router
Can not handle video but can handle multiple simultaneous voice/data transfers

PRI

For use in larger organizations
North American PRI has twenty-three B channels and one D channel giving it a top speed of 1.544mbps including the 16kbps for overhead.
Europe, Australia, and other countries PRI has thirty B channels and one D channel giving it a top speed of 2.048mbps including the 16kbps overhead.
Allows video conferencing and high-bandwidth data with no latency

Frame Relay

Layer 2 non broadcast multi-access (NBMA) WAN technology.
Single router interface can connect to multiple sites using Private Virtual Circuits (PVCs)
PVCs carry voice/data traffic
Can support 4mbps or more
only leasing line to service provider edge, making it cheaper.
PVCs are Identified by DLCIs this enables bidirectional communications

Asynchronous Transfer Mode (ATM)

Capable of transferring voice/video/data through private or public networks
Uses Cell-Based instead of Frame-Based architecture
Calls have a fixed length of 53bytes
Cells have a 5byte header leaving 48bytes of payload
The smaller data cells removes the delay and allows video/voice to travel without delay.
Higher overhead from reassembling data packets
Typical ATM links require 20% more bandwidth to carry the same volume of traffic as Frame Relay
Designed to be scalable T1/E1-OC12 and up
Offers both PVC and SVC, PVC being more common.
Allows multiple VCs on a signal leased line connection to the network edge.

Ethernet WAN

Ethernet was designed for LANs and was unusable for WANs because of maximum length restrictions (1km). Newer Ethernet WANs use Fiber. The IEEE 1000Base-LX supports fiber lengths of 5km and IEE 1000Base-GX supports length of 70km.

Known as: Metropolitan Ethernet (MetroE), Ethernet over MPLS (EoMPLS) and Virtual Private LAN Service (VPLS)
Provides a switched, high-bandwidth, layer 2 network
Capable of handling data/voice/video on a converged network
No additional hardware/data conversion needed
Inexpensively connect to multiple sites and the internet, in a metropolitan area
Cheaper, than other technologies, to connect to an existing Ethernet LAN
Easier, than TDM/Frame Relay, to host/use VOIP/stream/broadcast video

Multiprotocol Label Switching (MPLS)

A multiprotocol high-performance WAN technology
Ability to handle any payload (IPv4/IPv6/Ethernet/ATM/DSL/Frame Relay) *protocols*
Supports a range of WAN links (T/E-Carrier/Ethernet/ATM/Frame Relay/DSL) *physical links*
Uses short-Path labels instead of IP addresses
Labels identify paths between routers not endpoints
Routes IPv4/IPv6 and switches the others
MPLS is primarily a service provider WAN technology

This is why Ethernet WANs work. The Ethernet connection is encapsulated with the MPLS label than is transferred, over fiber, to the other side. The encapsulation is removed and leaves the Ethernet signal.

Very Small Aperture Terminal (VSAT)

Uses satellite communications
Can be used where there is no service provider locations
Creates a private WAN while providing connectivity to remote locations
A router connects to a satellite dish that communicates with a satellite in geosynchronous orbit (22,236 Miles). The satellite then sent the signal back town to the end location.

*The book doesn't say, but this is expensive and slow*

This chapter will be continued in Part 5.

IT Life

Monday, January 19, 2015

Chapter 2: Connecting to the WAN Part 4