Instituto Tecnológico y de Estudios
Superiores de Occidente – ITESO
Materia: Redes WAN
Maestro: David Rivera
TAREA
Fecha: 20 de Agosto de 2015
Tema: Resumen Lecturas
Autor(es): Tirado Cabello David Armando
Digital Carrier Systems
The long-distance carrier system provided in the United States and throughout the world was designed to transmit voice signals over high-capacity transmission links, such as optical fiber, coaxial cable, and microwave.
SONET/SDH
SONET/SDH SONET (Synchronous Optical Network) is an optical transmission interface originally proposed by BellCore and standardized by ANSI.
Cable Modem
To support data transfer to and from a cable modem, a cable TV provider dedicates two channels, one for transmission in each direction. Each channel is shared by a number of subscribers, and so some scheme is needed for allocating capacity on each channel for transmission
An individual cable modem subscriber may experience access speeds from 500 kbps to 1.5 Mbps or more, depending on the network architecture and traffic load. The downstream direction is also used to grant time slots to subscribers. When a subscriber has data to transmit, it must first request time slots on the shared upstream channel. Each subscriber is given dedicated time slots for this request purpose.
ASYMMETRIC DIGITAL SUBSCRIBER LINE
ADSL is the most widely publicized of a family of new modem technologies designed to provide high-speed digital data transmission over ordinary telephone wire. ADSL is now being offered by a number of carriers and is defined in an ANSI standard.
ADSL Design The term asymmetric refers to the fact that ADSL provides more capacity downstream (from the carrier’s central office to the customer’s site) than upstream (from customer to carrier). ADSL was originally targeted at the expected need for video on demand and related services.
HDSL
High Data Rate Digital Subscriber Line HDSL was developed in the late 1980s by BellCore to provide a more cost-effective means of delivering a T1 data rate (1.544 Mbps). The standard T1 line uses alternate mark inversion (AMI) coding, which occupies a bandwidth of about 1.5 MHz.
HDSL uses the 2B1Q coding scheme to provide a data rate of up to 2 Mbps over two twisted-pair lines within a bandwidth that extends only up to about 196 kHz. This enables a range of about 3.7 km to be achieved.
X.25
The standard used for traditional packet-switching networks is X.25. X.25 is an ITU-T standard that specifies an interface between a host system and a packet-switching network.The functionality of X.25 is specified on three levels:
• Physical level
• Link level
• Packet level
FRAME RELAY
Frame relay is designed to provide a more efficient transmission scheme than X.25.The standards for frame relay matured earlier than those for ATM, and commercial products also arrived earlier.Accordingly, there is a large installed base of frame relay products. Interest has since shifted to ATM for high-speed data networking.
TELEWORKING
Teleworking is working away from the traditional workplace, such as working from a home office. The reasons for choosing teleworking are varied and include everything from personal convenience to allowing sick or disabled employees the opportunity to continue working.
Teleworking is a broad term referring to conducting work by connecting to a workplace from a remote location, with the assistance of telecommunications
There are three primary remote connection technologies available to organizations supporting teleworker services:
- Broadband connections - The broadband term refers to advanced communications systems capable of providing high-speed transmission of services, such as data, voice, and video, over the Internet and other networks. Transmission is provided by a wide range of technologies, including DSL, fiber-to-the-home, coaxial cable systems, wireless, and satellite. The broadband service data transmission speeds typically exceed 200 kb/s in at least one direction between the ISP and the user.
- IPsec VPNs - This is the most common option for teleworkers, combined with remote access over broadband, to establish a secure VPN over the public Internet. This type of WAN connection offers flexible and scalable connectivity. Site-to-site connections can provide a secure, fast, and reliable remote connection to teleworkers.
- Traditional private WAN Layer 2 technologies - These types of connections provide many remote connection solutions and include technologies, such as Frame Relay, ATM, and leased lines. The security of these connections is dependent upon the service provider providing them.
Comparing Broadband Solutions
A cable network is capable of transmitting signals on the cable in either direction at the same time. The following frequency scopes are used:
Downstream - The direction of an RF signal transmission, such as TV channels and data, from the source, or headend, to the destination, or subscribers. Transmission from source to destination is called the forward path. Downstream frequencies are in the range of 50 to 860 MHz.
Upstream - The direction of the RF signal transmission from subscribers to the headend. Upstream frequencies are in the range of 5 to 42 MHz.
The Data-over-Cable Service Interface Specification (DOCSIS) is an international standard developed by CableLabs
DOCSIS defines the communications and operation support interface requirements for a data-over-cable system, and permits the addition of high-speed data transfer to an existing CATV system. Cable operators employ DOCSIS to provide Internet access over their existing HFC infrastructure
Two types of equipment are required to send digital modem signals upstream and downstream on a cable system:
- Cable Modem Termination System (CMTS) at the headend of the cable operator
- Cable Modem (CM) on the subscriber end
