DVB-GSE (Generic Stream Encapsulation) - Protocol
Generic Stream Encapsulation (GSE); Part 1: Protocol
The present document includes the definition of the Generic Stream Encapsulation (GSE) protocol, which allows for efficient encapsulation of IP and other network layer packets over a “generic” physical layer. Such a “generic” physical layer is intended as a transport mode that carries a sequence of data bits or data packets, possibly organized in frames, but with no specific timing constraints.
The first generation of DVB standards only supported data transport using the MPEG format (see ISO/IEC 13818-1 ), with a Transport Stream packet multiplex (MPEG-TS). Multi Protocol Encapsulation (EN 301 192 ) is the DVB standard for encapsulation of audio/video and other content on MPEG-TS packets. The second generation of DVB standards features backwards compatibility modes for carrying MPEG-TS as well as generic modes for carrying arbitrary packets of variable length. These are referred to as Generic Streams (GS).
The GSE protocol has been devised as an adaptation layer to provide network layer packet encapsulation and fragmentation functions over Generic Stream. GSE provides efficient encapsulation of IP datagrams over variable length Layer 2 packets, which are then directly scheduled on the physical layer into Base Band frames.
GSE maximizes efficiency of IP datagrams transport reducing overhead by a factor 2 to 3 with respect to MPE over MPEG-TS. This is achieved without any compromise of the functionalities provided by the protocol, due to the variable length Layer 2 packet size, suited to IP traffic characteristics. For example in an interactive DVB-S2 system, the overhead is reduced on average from about 10 % for MPE/MPEG-TS to 2 % to 3 % for GSE. Hence yielding an overall throughput gain of about 5 % to 15 %, the actual benefit is of course dependent on the concrete system and traffic characteristics.
In addition to the overhead reduction, GSE provides a more efficient system operation for interactive systems that utilize advanced physical layer techniques such as for instance Adaptive Coding and Modulation (ACM). The inherent channel rate variability experienced in ACM systems makes the Generic Stream format more suited than the Transport Stream. GSE provides a flexible fragmentation and encapsulation method, which permits use of a smart scheduler to optimize system performance, either by increasing the total throughput and/or by improving the average packet end-to-end delay. In addition, GSE flexibility leads to a reduction in packet loss under fading variations, allowing the scheduler at the transmitter to dynamically change transmission parameters (for example modulation format, coding rate) for a particular network layer packet.
GSE also provides additional features that increase the protocol flexibility and applicability. Some key GSE functions/characteristics are:
- Support for multi-protocol encapsulation (IPv4, IPv6, MPEG, ATM, Ethernet, 802.1pQ VLANs, etc.).
- Transparency to network layer functions, including IP encryption and IP header compression.
- Support of several addressing modes: In addition to the 6-byte MAC address (including multicast and unicast), it supports a MAC addressless mode, and an optional 3-byte address mode.
- A mechanism for fragmenting IP datagrams or other network layer packets over Base Band frames to support ACM/VCM.
- Support for hardware filtering.
- Extensibility: additional link protocols can be included through specific protocol type values (e.g. Layer 2 security, IP Header Compression, etc.).
- Low complexity.
The present document specifies the Generic Stream Encapsulation (GSE) protocol.