Switched Multi Megabit Data Service (SMDS)
SMDS or Switched Multi Megabit Data Service is used to communicate on the Public Data Networks using the WAN networking technology. The SMDS technology uses fiber or copper wires for networking. There are many components in the SMDS networking environment that make data transfer possible like the DQDB or the distributed queue dual bus.
The functionality of SMDS is delivered through telecommunication services and it is capable of providing high speed connections, high level performances and data transport through packet switching. SMDS cannot be considered as a whole new technology or a protocol. In fact it is a tool that functions using the current technology and supports the protocols.
When the clients functionalities extend over a wide geographical area using SMDS capabilities different geographical locations can be easily networked using the telecommunications platform for support. It provides a transparent level of service.
Using the existing customer premises equipment the SMDS technology can be easily deployed and requires only a minimum level of investment like a dedicated lease line for data transfer. The dedicated lease line is also beneficial because it reduces the number of terminations in data transfer.
The SMDS is now being considered equal to the asynchronous transfer mode or the ATM technology because even the SMDS uses the 53 octet cells like the ATM and also support up to 9188 packet lengths.
SMDS Network Functionality
The SMDS lets the customers create networks using the customer premises equipment and the Local Area Networks even if the network is nation wide. The SMDS network can be divided into three parts
- The customer premises
- The dedicated connection
- The public network based on SMDS
The customer premises includes the Local Area Network, the equipments, routers, servers, the service channels and all the components that have been included in the network.
Usually the dedicated line is a DSL line which could operate at a minimum of 1.5 Mbps. The network also includes the exchange links, carriers and connections.
To be able to communicate between the CPE or the customer premises equipment and the SMDS carrier the device needs a communication protocol and the protocol used here is the SMDS Interface protocol or more commonly known as the SIP. The entire network communication takes place in a connectionless environment using the subscriber network interface or the SNI.
The SIP is again based on the DQDB because it supports the SMDS features and is an open based protocol. Even emerging technologies like the broadband ISDN can be supported by a combination of the SMDS features. It can support video and voice transfers on the ISDN lines.
SIP or the SMDS interface protocol is a three level protocol that comprises of SIP level 1, SIP level 2and SIP level 3. These three layers jointly control the network at the clients end. Each level has its own individual functionality and does not depend or mix with the other level like for example the SIP level 3 takes care of the frames by receiving them and sending them, the SIP level 2 takes care of the physical medium and the SIP level 1 takes care of the transmission environment.
SIP Level 1
The PDU’s that are being generated at the ISP level 2 will be transmitted using SIP level 1. There are two layers within the SIP level 1 that are used for transmission.
SIP Level 2
After the SIP level 3 completes the processing of PDU it passes them over to the SIP level 2 and the SIP level 2 converts them into 53 octets.
SIP Level 3
The SIP level contains all information I the 9188 octet’s format and send all this information to level 2 to be transmitted in the right format.