Generic Stream Encapsulation, or GSE for short, is a
Data link layer
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...
protocol defined by
DVB
Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) o ...
. GSE provides means to carry packet oriented protocols such as
IP on top of uni-directional
physical layer
In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer; The layer most closely associated with the physical connection between devices. This layer may be implemented by a PHY chip.
The ...
s such as
DVB-S2
Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) is a digital television broadcast standard that has been designed as a successor for the popular DVB-S system. It was developed in 2003 by the Digital Video Broadcasting Proje ...
,
DVB-T2
DVB-T2 is an abbreviation for "Digital Video Broadcasting – Second Generation Terrestrial"; it is the extension of the television standard DVB-T, issued by the consortium DVB, devised for the broadcast transmission of digital terrestrial telev ...
and
DVB-C2
Digital Video Broadcasting - Cable (DVB-C) is the DVB European consortium standard for the broadcast transmission of digital television over cable. This system transmits an MPEG-2 or MPEG-4 family digital audio/digital video stream, using a QAM ...
.
GSE provides additional features beyond the pure carriage of IP datagrams that increase the protocol flexibility and applicability. Some key GSE functions/characteristics are:
* Support for multi-protocol encapsulation (
IPv4
Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...
,
IPv6
Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...
,
MPEG
The Moving Picture Experts Group (MPEG) is an alliance of working groups established jointly by International Organization for Standardization, ISO and International Electrotechnical Commission, IEC that sets standards for media coding, includ ...
,
ATM,
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
,
802.1pQ VLAN
A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer (OSI layer 2).IEEE 802.1Q-2011, ''1.4 VLAN aims and benefits'' In this context, virtual, refers to a physi ...
s, etc.)
* Transparency to network layer functions, including
IP encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...
and IP
header compression.
* Support of several addressing modes. In addition to the 6-byte
MAC address
A media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking techno ...
(including
multicast
In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with ...
and
unicast
Unicast is data transmission from a single sender (red) to a single receiver (green). Other devices on the network (yellow) do not participate in the communication.
In computer networking, unicast is a one-to-one transmission from one point in ...
), it supports a MAC address-less mode, and an optional 3-byte address mode.
* A mechanism for fragmenting
IP datagrams
A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication service across a packet-switched network. The deliv ...
or other
network layer
In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers.
Functions
The network layer provides the means of transfe ...
packets over
Base Band
In telecommunications and signal processing, baseband is the range of frequencies occupied by a signal that has not been modulated to higher frequencies. Baseband signals typically originate from transducers, converting some other variable into a ...
frames to support
ACM/
VCM.
* Support for hardware
filtering
Filter, filtering or filters may refer to:
Science and technology
Computing
* Filter (higher-order function), in functional programming
* Filter (software), a computer program to process a data stream
* Filter (video), a software component tha ...
.
* Extensibility: additional
link protocols can be included through specific protocol type values (e.g.
Layer 2
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer pr ...
security, IP Header Compression, etc.).
Protocol Outline
![GSE diagram](https://upload.wikimedia.org/wikipedia/commons/d/d8/GSE_diagram.png)
The
protocol
Protocol may refer to:
Sociology and politics
* Protocol (politics), a formal agreement between nation states
* Protocol (diplomacy), the etiquette of diplomacy and affairs of state
* Etiquette, a code of personal behavior
Science and technology
...
specification
A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard.
There are different types of technical or engineering specificati ...
has been published as
ETSI
The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...
TS
102 606.
[ETSI TS 102 606: "Digital Video
Broadcasting (DVB); Generic Stream Encapsulation (GSE)
Protocol"] An accompanying
implementation
Implementation is the realization of an application, or execution of a plan, idea, model, design, specification, standard, algorithm, or policy.
Industry-specific definitions
Computer science
In computer science, an implementation is a realiza ...
guidelines
A guideline is a statement by which to determine a course of action. A guideline aims to streamline particular processes according to a set routine or sound practice. Guidelines may be issued by and used by any organization (governmental or pri ...
document has been published as
ETSI
The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...
TS 102 771.
[ETSI TS 102 771: "Digital Video Broadcasting (DVB); Generic Stream Encapsulation (GSE) implementation guidelines"]
IP datagrams, Ethernet Frames, or other network layer packets are encapsulated in one or more GSE Packets. The encapsulation process adds control information such as the network protocol type and address label, and provides an overall integrity check when needed.
The payload frame may be encapsulated in a single GSE Packet or sliced into fragments and encapsulated in several GSE Packets. GSE Packets have in general variable length, in order to match the input IP traffic with minimum overhead.
GSE Packets may be sent in different Base Band frames, not necessarily consecutive or with the same transmission parameters (modulation format, coding rate). No constraint on the GSE Packet position within the Base Band frame is assumed. However, GSE Packets may not be reordered between the encapsulator and the de-encapsulator. In general, a Base Band frame can contain more than a single GSE Packet. Base Band frames may have fixed, or variable length.
GSE does not provide a mechanism for integrity check of single GSE Packet. A
CRC-32
A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to digital data. Blocks of data entering these systems get a short ''check value'' attached, based on t ...
is only appended to the last fragment of a fragmented payload to verify the correctness of the reassembly operation. GSE relies on the physical layer being able to ensure the required error detection and/or correction probability.
GSE Header
The GSE Packet header is highly dynamic and provides for many options. The minimum header is two bytes, comprising three flags fields, and a 12-bit payload length field. The diagram below shows all possible fields.
Fragmentation and Reassembly
The basic mechanism of GSE payload fragmentation uses the Start and End Flags, where the Start flag indicates the beginning of a payload frame, and the End flag indicates its end. This is shown in the diagram below.
On
DVB-S2
Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) is a digital television broadcast standard that has been designed as a successor for the popular DVB-S system. It was developed in 2003 by the Digital Video Broadcasting Proje ...
,
DVB-T2
DVB-T2 is an abbreviation for "Digital Video Broadcasting – Second Generation Terrestrial"; it is the extension of the television standard DVB-T, issued by the consortium DVB, devised for the broadcast transmission of digital terrestrial telev ...
, and
DVB-C2
Digital Video Broadcasting - Cable (DVB-C) is the DVB European consortium standard for the broadcast transmission of digital television over cable. This system transmits an MPEG-2 or MPEG-4 family digital audio/digital video stream, using a QAM ...
the ACM/VCM modes may cause the Base Band frames to vary in size depending on the transmission conditions. Hence there may be situations where the first fragments of a payload frame have been sent, but the encapsulator is forced to set aside the current payload frame, and start working on a new one. This may e.g. occur when large fragments have been prepared while transmission conditions were fine, but suddenly the conditions deteriorate, and only small Base Band frames are available.
This is when the Fragment ID field becomes important. It is a short-term identification of the payload frame. Whenever the encapsulator needs to move on to the next payload frame, without having finished transmitting the previous one, it uses the next available Fragment ID. That way, up to 256 payload frames can be "kept open" at any time. The decapsulator uses the Fragment ID to pick the reassembly buffer in which to store the fragment.
GSE addresses
The "Label Type" (LT) bits determine how the GSE packet address is encoded according to the following table:
CRC-32 Trailer
Each GSE Packet containing the last fragment for a payload frame, carries a
CRC-32 checksum over the payload frame. The checksum is used to detect loss of intermediate fragments.
The checksum is a 32 bit value calculated according to the generator polynomial represented by 0x104C11DB7:
If the last fragment of a payload frame is lost, the decapsulator can not directly detect that fact. It never sees the GSE frame with the End flag set and containing the CRC-32. For this situation, the decapsulator must choose a suitable time-out based on the data-rate and application.
GSE Implementations
Products Supporting GSE
Since GSE packets are directly inserted into base-band frames of the
modulation scheme, GSE products come in the form of "GSE Routers" or
"GSE Modems", which - from the outside - act very much like a DSL
Router or DSL Modem used by consumers. More generically these devices
are also referred to as "GSE Encapsulators". These products have a standard
IP network interface (most often
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
or a similar
LAN
interface) to collect IP traffic which is to be forwarded over the
uni-directional link on the other end. To optimise the packaging into
base-band frames, these devices typically generate complete base-band
frames with the GSE packets as payload, which are then transferred to
the
DVB-S2
Digital Video Broadcasting - Satellite - Second Generation (DVB-S2) is a digital television broadcast standard that has been designed as a successor for the popular DVB-S system. It was developed in 2003 by the Digital Video Broadcasting Proje ...
,
DVB-T2
DVB-T2 is an abbreviation for "Digital Video Broadcasting – Second Generation Terrestrial"; it is the extension of the television standard DVB-T, issued by the consortium DVB, devised for the broadcast transmission of digital terrestrial telev ...
or
DVB-C2
Digital Video Broadcasting - Cable (DVB-C) is the DVB European consortium standard for the broadcast transmission of digital television over cable. This system transmits an MPEG-2 or MPEG-4 family digital audio/digital video stream, using a QAM ...
modulator through a second
interface.
Here is a (very likely incomplete) list of GSE en- and decapsulators:
Newtec*
EL470 IP Satellite Modem*
EL970 IP Satellite DemodulatorWORK Microwave GmbH*
*
ttp://www.tebkom.at/ Tebkom GmbH*
ODG200 IP/DVB-S2 Encapsulator/Modulator with ACM supportAdvantech Wireless Inc.*
AMT 75e DVB-S/S2 High Speed Broadcast ModemComtech EF Data Corporation*
CDM-840 Remote RouterK.S.Transplaneta Ltd.*
dpi4502 DVB2 (S2/T2/C2) compliant IPv4 / IPv6 EncapsulatorComputer Modules, Inc.*
DVB Rocket™/S2Ayecka Communication systems LTDSR1 - Advance DVB-S2 demodulator with hardware based, wire speed, GSE DecapsulatorST1 - Advance DVB-S2 modulator with hardware based, wire speed, GSE encapsulatorSM1 - Advance DVB-S2 Modem with hardware based, wire speed, GSE EnCapsulator / DeCapsulator
GSE-based IP Service Offerings
There are many IP-over-satellite service offerings, including for
instance
ASTRA2Connect
SES Broadband (previously ASTRA2Connect) is a two-way satellite broadband Internet service available across Europe, which launched in March 2007, and uses the Astra series of geostationary satellites.
SES Broadband is owned and operated by SES ...
from
SES
SES, S.E.S., Ses and similar variants can refere to:
Business and economics
* Socioeconomic status
* Scottish Economic Society, a learned society in Scotland
* SES, callsign of the TV station SES/RTS (Mount Gambier, South Australia)
* SES S.A., ...
or
Tooway
Tooway satellite broadband Internet service available across Europe. The first version of the service was launched in 2007 via two Eutelsat geostationary satellites, Hot Bird 6 and Eurobird 3, respectively at the 13° and 33° East orbital po ...
from
Eutelsat
Eutelsat S.A. is a French satellite operator. Providing coverage over the entire European continent, the Middle East, Africa, Asia and the Americas, it is the world's third-largest satellite operator in terms of revenues.
Eutelsat's satellit ...
. Little detail is however known about the protocols used
since the receivers are provided as part of the service by the
operators and very little technical detail is disclosed.
References
{{Reflist
External links
Obtain GSE Standard and Guidelines from DVB free of chargeDVB Fact Sheet on GSEGSE project home pageat
ESA
, owners =
, headquarters = Paris, Île-de-France, France
, coordinates =
, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (1205 ...
Opensource implementation of GSE
Television technology
Link protocols