DVB-GSE (Generic Stream Encapsulation) - Logic Link Control

Introduction

As introduced in part 1, the Generic Stream Encapsulation (GSE) protocol is a link layer which provides multiplexing mechanisms that make it possible for several network protocols (for example IP, IPX, Decnet, and Appletalk) to coexist within a multipoint network and to be transported over the same network media. GSE is designed to be deployed across all DVB broadcast bearers which provide a Generic Stream mode.

This abstraction from the MAC layer allows to provision services on top of network protocols independently of the underlying physical layer.

The DVB-GSE link layer hides any MAC layer specifics from the upper layers. It thus enables receivers to present DVB-GSE streams as regular, LAN-type network interfaces to upper layers. The logical link control protocol defined in the present document provides the necessary information to receivers to accomplish this.

On a Point-to-Point Protocol (PPP) link according to [i.3], two hosts establish a connection on any point-to-point serial interface (e.g. RS-232), and exchange IP datagrams. The PPP implementation encapsulates this link as a normal network interface, so that applications can use it as if it were a regular LAN interface. To achieve this, a Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection, and a family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols is defined. When the connection establishment begins, the two hosts first use the LCP to negotiate the configuration parameters (e.g. link speed) of the serial data link. After this is completed, the two hosts use the appropriate NCPs to negotiate the configuration of the network interface (e.g. use of IPv4 or IPv6, IP addresses to use), and thus conclude the connection establishment phase. After this, the hosts present new LAN-type network interfaces to applications running on them.

The LLC protocol for DVB-GSE adopts the same partitioning of information. One set of information is needed to enable the DVB-GSE layer to configure the underlying MAC and physical layer devices. This first set of information is referred to as Link Control Data (LCD) in the present document. A second set of information is needed to configure the network interfaces which represent the DVB-GSE streams and make them available for the upper layers. This second set of information is referred to as Network Control Data (NCD) in the present document.

Once these network interfaces have been made available to the upper layers, the properties of the MAC and physical layers are no longer exposed to upper layers, and applications can act on these interfaces like on any other network interface. Use of the tunnelling mechanism defined in [11] in combination with a return channel allows for the interfaces to be used for reading and writing.

Scope

The present document specifies a Logical Link Control (LLC) method to be used on DVB streams where the Generic Stream Encapsulation (GSE) protocol is used as the link layer.