Topic 8: WAN - Chapter 11 & 12: Wide Area Networks. Business Data Communications, 4e. LANs, WANs, and MANs. Ownership WANs can be either public or private LANs are usually privately owned Capacity LANs are usually higher capacity, to carry greater internal communications load Coverage
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Business Data Communications, 4e
Connects subscriber to local telco exchange
Telco switching centers
Also known as end office
>19,000 in US
Connections between exchanges
Carry multiple voice circuits using FDM or synchronous TDM
Managed by IXCs (inter-exchange carriers)Public Switched Telephone Network (PSTN)
1. Dial-up line
2. Dedicated line
The oldest packet switched service is X.25, a standard developed by ITU-T. X.25 offers datagram, switched virtual circuit, and permanent virtual circuit services (Data link layer protocol: LAPB (Link Access Procedure-Balanced), network layer protocol PLP).
Although widely used in Europe, X.25 is not widespread in North America. The primary reason is transmission speed, now 2.048 Mbps (up from 64 Kbps).
1. Frame relay only operates at the data link layer.
2. Frame relay networks do not perform error control.
3. Frame relay defines two connection data rate that are negotiated per connection and for each virtual circuit as it is established: Committed information rate (CIR) and Maximum allowable rate (MAR).
ATM has four important differences from frame relay:
T Carrier circuits are dedicated digital circuits and are the most commonly used form of dedicated circuit services in North America today.
Instead of a modem, a channel service unit (CSU) or data service unit (DSU) are used to connect the circuit into the network.
T-1 circuit (a.k.a. a DS-1 circuit) provides a data rate of 1.544 Mbps. T-1’s allow 24 simultaneous 64 Kbps channels (with TDM) which transport data, or voice messages using pulse code modulation. (64Kbps x 24 = 1.536Mbps)
T-2 circuit (6.312 Mbps) is basically a multiplexed bundle of four T-1 circuits.
T-3 circuit (44.376 Mbps) is equal to the capacity of 28 T-1 circuits (672 64Kbps channels).
T-4 circuit (274.176 Mbps) is equal to the capacity of 178 T-1s.
Fractional T-1, (FT-1) offers portions of a 1.544 Mbps T-1 for a fraction of its full costs.
T-Carrier Designation DS Designation Speed
DS-1 (24 DS-0)
DS-2 (96 DS-0)
DS-3 (672 DS-0)
DS-4 (178 T-1)
A term for the series of standard digital transmission rates or levels based on DS0, a transmission rate of 64 Kbps, the bandwidth normally used for one telephone voice channel.
Both the North American T-carrier system and the European E-carrier systems of transmission operate using the DS series as a base multiple. The digital signal is what is carried inside the carrier system.
SONET Designation SDH Designation Speed
Characteristics of SMDS:
SNI: Subscriber network interface
CPE: Customer premises equipment
SIP is used for communications between CPE and SMDS carrier equipment
In January 1999, AT&T announced the first VPN services to be based on MPLS --- its IP-Enabled Frame Relay service.
Cable & Wireless and Cisco Systems conducted a trial of IP-VPN service based on MPLS with Hongkong Telecom in March, 1999.
MCI/Worldcom Started to offer MPLS-based IP-VPN service in March, 1999.
AT&T Network Services (http://www.ipservices.att.com/backbone/)
BBN Planet (GTE)
Cable & Wireless USA
UUNET, a part of MCI WorldCom
vBNS (very high speed Backbone Network Services )
Figure 9-11 Gigapops and high speed backbones of Internet 2/Abilene, vBNS, and CA*Net 3
ISP Point-of Presence
Figure 9-2 Inside an ISP Point of Presence
Wireless Access Office
Figure 9-9 Fixed wireless architecture
(plus WML, etc.)
(plus WML, etc.)
(plus WML, etc.)
(plus HTML, jpeg, etc.)
Figure 9-10 Mobile wireless architecture for WAP applications
Montana State U
Figure 9-12 Inside the Pacific/Northwest Gigapop