xDSL

When referring to xDSL, it doesn’t necessarily point out to one single type of technology. Rather, xDSL is a line-up of different types of DSL. The ‘x’ stands for the many variations of the DSL. Each variation has its own capabilities. Also, they differ in their speeds, throughput, and facilities used.

Asymmetrical Digital Subscriber Line (ADSL)

ADSL is the most popular of these variations under today’s technology. It is a new modem technology that converge the twisted pair telephone lines with the high speed communication access capability for various services.

ISDN(like) Digital Subscriber Line (IDSL)

The IDSL technique is all digital, operating at two channels of 64 Kbps for voice or nonvoice operation and a 16Kbps data channel for signaling, control, and data packets. ISDN, was very slow to catch on, but the movement to the internet created a whole new set of demands for the carriers to deal with.

          High bit-rate Digital Subscriber Line (HDSL)

HDSL was developed as a more efficient way of transmitting T1 and E1 over the existing copper wires. It does not require the repeaters on a local loop of 12K. Also, its modulation rate is more advanced.

Consumer Digital Subscriber Line (CDSL)

The Speeds of the ADSL are impractical for regular consumers. Thus, a lower-speed communications capability was developed. This was done by using the CDSL model. Unlike ADSL, CDSL does not use, nor need, a splitter on the line. It also has a 1Mbps Download rate and a 160 Kbps Upload Rate.

Single High Speed Digital Subscriber Line (SHDSL)

SHDSL has an increased reach of at least 30 percent greater than any earlier symmetric DSL technology. It also supports repeaters which further increase its reach capability. It also has an increase in symmetric bandwidth.

Rate-Adaptive Digital Subscriber Line (RADSL)

RADSL was developed to achieve variations in the throughput and be sensitive to the line conditions. This gives the flexibility to adapt to the changing conditions and adjust the speeds in each direction to potentially maximize the throughput on each line.

Very High-bit rate Digital Subscriber Line (VDSL)

VDSL was developed to fulfill the demand of faster and more reliable communications capabilities. It is develop to achieve higher speeds.

Single or Symmetric Digital Subscriber Line (SDSL)

SDSL was developed to provide high-speed communications on a single cable pair at distances of more than 10K. It was designed to deliver 1.544 Mbps on the single pair, however, the providers offer it at 768 Kbps.

Asynchronous Transfer Mode (ATM)

ATM is a member of the fast packet-switching family called cell relay. An evolution from many other set of protocols that was develop in 1992.It is designed to carry any form of traffic an enables the traffic to be delivered asynchronously to the network.

ATM techniques is more like a combination of TDM with cells using preassigned slots, an statistical TDM with cells using whatever slots are available.

Comparing ATM to other technologies, ATM can be used in LAN, CAN, MAN, and WAN. Comparing it to Frame Relay, which was discussed in my previous topic, frame relay can only be used in Wide Area Networks. Dial-up network as well as leased lines are also limited MAN and WAN.

One of the many Features and Functions of the ATM is that it is a single technology which is capable of handling voice, data, video, and multimedia. Also, Its Bandwidth is always available as needed. It is also scalable and its quality of service is well defined. it also has its management systems and services prebuilt into ATM and it is a Hardware-based switching instead of complicated routing and software schemes.

When dealing with traffic management, Some of the goals of the ATM is that, it has to be flexible. It must meet the diverse needs of the end-user population. It must be cost efficient. Robustness in the event of failure or in the event of excess demand is a requirement of the traffic management goals.

Frame Relay

Frame Relay is a fast packet-switching technology introduce in 1992. Since this technology falls into the category of packet-switching family, we should know the definition of packet switching.

Packet Switching is a store and forward switching technology for queuing networks where user messages are broken down into small pieces called packets. Each packet has its own associated overhead containing the destination address and control information. Packets are sent from source to destination over shared facilities and use a statistical time-division multiplexing concept to share the resources.

Fast Packet Switching is a combination of packet switching and faster networking using high-speed communications and low-delay networking. Fast packet is a “hold an forward” technology designed to reduce delay, reduce overhead and processing, improve speed, and reduce costs. It is designed to run on a high-speed circuits with low (or no) error rates.

Comparing the X.25 network with the Frame Relay Services, both use statistical TDM. The OSI layer used by the X.25 is the layer 3(Network). While the Frame Relay uses the Layer 2(Data Link). X.25 uses ACK and NAK, and requests retransmissions. The Frame Relay on the other hand, only requests retransmissions by higher-level protocols. The Packet/Frame Size of the X.25 is up to 128 bytes on average network and up to 512 bytes in some implementations. It also has a transmission speed of up to 64 Kbps. The Packet/Frame Size of the Frame Relay however, is up to 1610 bytes in networks and up to 4096 bytes in some vendor products. It has a transmission speed that starts at 56 Kbps up to 50 Mbps, Depending on the vendor.

Now, comparing Frame Relay and IP, Frame Relay is multiprotocol support and has a predictable and reliable performance. It also has a Robust Network management Capabilities. But it is only in WAN. IP on the other hand is an Any-to-any connectivity. But it does have a limited quality of service an security concerns. It is in LAN or WAN.

Frame Relay Selected for Wireless Data on GPRS, this is because it is widely deployed as a networking architecture. It is also base on the PVC from the PCU to the network device called a  Serving GPRS Support Node which operates at speeds up to 2.048 Mbps. The standards allow for the sharing of the circuitry from many devices by interleaving the data frames on the same physical channel. Also, it does minimize the overhead on the channel.