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{{IPstack}} '''Generic Stream Encapsulation''', or GSE for short, is a [[Data link layer]] protocol defined by [[Digital Video Broadcasting|DVB]]. GSE provides means to carry packet oriented protocols such as [[Internet Protocol|IP]] on top of uni-directional [[physical layer]]s such as [[DVB-S2]], [[DVB-T2]] and [[DVB-C2]].

GSE provides additional features beyond the pure carriage of IP datagrams that increase the protocol flexibility and applicability. Some key GSE functions/characteristics are:

{{IPstack}} '''Generic Stream Encapsulation''', or GSE for short, is a [[Data link layer]] protocol defined by [[DVB]]. GSE provides means to carry packet oriented protocols, like for example [[IP]], on top of uni-directional [[physical layer]]s like e.g. [[DVB-S2]], [[DVB-T2]] and [[DVB-C2]].

* Support for multi-protocol encapsulation ([[IPv4]], [[IPv6]], [[MPEG]], [[Asynchronous Transfer Mode|ATM]], [[Ethernet]], [[IEEE 802.1Q|802.1pQ]] [[VLAN]]s, etc.)

* Transparency to network layer functions, including [[Internet Protocol|IP]] [[encryption]] and [[IP header compression]].

The [[protocol]] [[specification]] has been published as [[ETSI]] TS

* Support of several addressing modes. In addition to the 6-byte [[MAC address]] (including [[multicast]] and [[unicast]]), it supports a MAC address-less mode, and an optional 3-byte address mode.

102 606 <ref name="ts102606">ETSI TS 102 606: "Digital Video

* A mechanism for fragmenting [[Internet Protocol|IP]] [[datagrams]] or other [[network layer]] [[Packet (information technology)|packets]] over [[baseband|Base Band]] frames to support [[Link adaptation|ACM]]/[[Variable Coding and Modulation|VCM]].

Broadcasting (DVB); Generic Stream Encapsulation (GSE)

* Support for hardware [[Firewall (computing)|filtering]].

Protocol"</ref>. An accompanying [[implementation]] [[guidelines]]

document has been published as [[ETSI]] TS 102 771<ref name="ts102771">ETSI TS 102 771: "Digital Video Broadcasting (DVB); Generic Stream Encapsulation (GSE) implementation guidelines"</ref>.

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]], [[IEEE 802.1Q|802.1pQ]] [[VLAN]]s, etc.)

* Transparency to network layer functions, including [[IP]] [[encryption]] and IP [[Van Jacobson TCP/IP Header Compression|header compression]].

* Support of several addressing modes. In addition to the 6-byte [[MAC]] address (including [[multicast]] and [[unicast]]), it supports a MAC address-less mode, and an optional 3-byte address mode.

* A mechanism for fragmenting [[IP]] [[datagrams]] or other [[network layer]] [[Packet (information technology)|packets]] over [[baseband|Base Band]] frames to support [[Link adaptation|ACM]]/[[Variable Coding and Modulation|VCM]].

* Support for [[hardware]] [[Firewall (computing)|filtering]].

* Extensibility: additional [[link protocol]]s can be included through specific protocol type values (e.g. [[Layer 2]] security, IP Header Compression, etc.).

== Protocol Outline ==

[[File:GSE diagram.png|right|thumb|400px|alt=Diagram of GSE encapsulation and fragmentation|How GSE carries datagrams and is carried in the physical layer]]

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 [[Communications protocol|protocol]] [[specification]] has been published as [[ETSI]] TS

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.

102 606.<ref name="ts102606">ETSI TS 102 606: "Digital Video

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]] 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 <ref>IETF RFC 3819: "Advice for Internet Subnetwork Designers"</ref> .

[[File:GSE_diagram.001.png]]

{{IPstack}} '''Generic Stream Encapsulation''', or GSE for short, is a [[Data link layer]] protocol defined by [[DVB]]. GSE provides means to carry packet oriented protocols, like for example [[IP]], on top of uni-directional [[physical layer]]s like e.g. [[DVB-S2]], [[DVB-T2]] and [[DVB-C2]].

The [[protocol]] [[specification]] has been published as [[ETSI]] TS

102 606 <ref name="ts102606">ETSI TS 102 606: "Digital Video

Broadcasting (DVB); Generic Stream Encapsulation (GSE)

Protocol"</ref>. An accompanying [[implementation]] [[guidelines]]

document has been published as [[ETSI]] TS 102 771.<ref name="ts102771">ETSI TS 102 771: "Digital Video Broadcasting (DVB); Generic Stream Encapsulation (GSE) implementation guidelines"</ref>.

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]], [[IEEE 802.1Q|802.1pQ]] [[VLAN]]s, etc.)

* Transparency to network layer functions, including [[IP]] [[encryption]] and IP [[Van Jacobson TCP/IP Header Compression|header compression]].

* Support of several addressing modes. In addition to the 6-byte [[MAC]] address (including [[multicast]] and [[unicast]]), it supports a MAC address-less mode, and an optional 3-byte address mode.

* A mechanism for fragmenting [[IP]] [[datagrams]] or other [[network layer]] [[Packet (information technology)|packets]] over [[baseband|Base Band]] frames to support [[Link adaptation|ACM]]/[[Variable Coding and Modulation|VCM]].

* Support for [[hardware]] [[Firewall (computing)|filtering]].

* Extensibility: additional [[link protocol]]s can be included through specific protocol type values (e.g. [[Layer 2]] security, IP Header Compression, etc.).

== Protocol Outline ==

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.

Line 53 ⟶ 26:

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]] 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 .<ref>IETF RFC{{IETF RFC|3819}}: "Advice for Internet Subnetwork Designers"</ref> .

[[File:GSE_diagram.png]]

=== GSE Header ===

Line 84 ⟶ 55:

| colspan="8" bgcolor="#CCFFCC"| Total Length

| colspan="16" bgcolor="#CCFFCC"| Protocol Type

| colspan="8" bgcolor="#CCFFCC"| Label (3 Bytebytes)

|-

! 64

| colspan="16" bgcolor="#CCFFCC"| Label (continuation, length 3 Bytebytes)

| colspan="16" bgcolor="#AADDBB"| Label (continuation, length 6 Bytebytes)

|-

! 96

| colspan="8" bgcolor="#AADDBB"| Label (continuation, length 6 Bytebytes)

| colspan="24" bgcolor="#FFBBBB"| [[Unidirectional Lightweight Encapsulation|ULE]] Extension Headers (Optional)

|-

! ...

Line 127 ⟶ 98:

|}

On [[DVB-S2]], [[DVB-T2]], and [[DVB-C2]] 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 payloafpayload 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.

=== CRC-32GSE Traileraddresses ===

The "Label Type" (LT) bits determine how the GSE packet address is encoded according to the following table:

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:

<math>y = x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11} + x^{10} + x^{8} + x^{7} + x^{5} + x^{4} + x^{2} + x^{1} + x^{0}</math>

If the last fragment of a paylod 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]] 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]], [[DVB-T2]] or [[DVB-C2]] modulator throuhg a second

interface.

Here is a (very likely incomplete) list of GSE en- and decapsulators:

* [http://www.newtec.eu/ Newtec]

** [http://www.newtec.eu/products/professional-equipment/elevation/modems/ip-satellite-modem-el470/ EL470 IP Satellite Modem]

** [http://www.newtec.eu/products/professional-equipment/elevation/demodulators/ip-satellite-demodulator-el970/ EL970 IP Satellite Demodulator]

* [http://www.work-microwave.de/ WORK Microwave GmbH]

** [http://www.work-microwave.de/dvb-s_s2.html#modems Challenge Series Satellite High Speed DVB-S2 IP Modem SK-IP]

* [http://www.gcs-salzburg.at/ gcs Global Communication & Services GmbH]

** [http://www.gcs-salzburg.at/odg.html.en ODG-200 Open DVB Gateway]

** [http://www.gcs-salzburg.at/bsr.html.en BSR-200 Broadband Satellite Receiver]

* [http://www.advantechwireless.com/ Advantech Wireless Inc.]

** [http://www.advantechwireless.com/catalogue/products/amt75e-dvb-ss2-high-speed-broadcast-modem-2/ AMT 75e DVB-S/S2 High Speed Broadcast Modem]

* [http://www.comtechefdata.com/ Comtech EF Data Corporation]

** [http://www.comtechefdata.com/products/Advanced-VSAT-Series/pcdm-840.asp CDM-840 Remote Router]

* [http://www.transplaneta.com/ K.S.Transplaneta Ltd.]

** [http://www.transplaneta.com/products/ip-encapsulator dpi4502 DVB2 (S2/T2/C2) compliant IPv4 / IPv6 Encapsulator]

* [http://dveo.com/ Computer Modules, Inc.]

** [http://dveo.com/broadcast-systems/ip-over-dvb-encapsulator.shtml DVB Rocket™/S2]

=== GSE-based IP Service Offerings ===

There are many IP-over-satellite service offerings, including for

instance [[ASTRA2Connect]] from [[SES Astra]] or [[Tooway]] from

[[Eutelsat]]. 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 ==

<!--- See http://en.wikipedia.org/wiki/Wikipedia:Footnotes on how to create references using <ref></ref> tags which will then appear here automatically -->

{{Reflist}}

== External links ==

* [http://www.dvb.org/technology/standards/index.xml#multiplexing Obtain GSE Standard and Guidelines from DVB free of charge]

* [http://www.dvb.org/technology/fact_sheets/DVB-GSE-Fact-Sheet.0709.pdf DVB Fact Sheet on GSE]

* [http://telecom.esa.int/telecom/www/object/index.cfm?fobjectid=30265 GSE project home page at [[ESA]]]

<!--- Categories --->

[[Category:Articles created via the Article Wizard]] [[Category:Television technology]] [[Category:Link protocols]]

]]

=== 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.

{| class="wikitable" style="text-align:center"

|+ Addressing Mode

|+ Unrolled GSE Header

|-

! width="410%" |bit offsetLT bits

! colspan="1" width="380%" | 0Addressing mode

! colspan="1" width="3%"| 1

! colspan="2" width="6%"| 2-3

! colspan="4" width="12%"| 4–7

! colspan="8" width="24%"| 8-15

! colspan="8" width="24%"| 16-23

! colspan="8" width="24%"| 24-31

|-

!| 000

| style="text-align:left" | Indicates that a 6 bytes label is present and shall be used for filtering.

| colspan="1" | Start

| colspan="1" | End

| colspan="2" | Label Type

| colspan="12"| GSE Length

| colspan="8" bgcolor="#CCFFCC"| Fragment ID

| colspan="8" bgcolor="#CCFFCC"| Total Length

|-

!| 3201

| style="text-align:left" | Indicates that a 3 bytes label is present and shall be used for filtering.

| colspan="8" bgcolor="#CCFFCC"| Total Length

| colspan="16" bgcolor="#CCFFCC"| Protocol Type

| colspan="8" bgcolor="#CCFFCC"| Label (3 Byte)

|-

!| 6410

| style="text-align:left" | No label present. All receivers shall process this packet.

| colspan="16" bgcolor="#CCFFCC"| Label (3 Byte)

| colspan="16" bgcolor="#AADDBB"| Label (6 Byte)

|-

!| 9611

| style="text-align:left" | Label re-use: no label is present; the label is the same as the previous GSE packet in the same base band frame. LT=11 is also used for intermediate and end packets (''i.e.'' Start bit 0). LT=11 shall not be used for the first GSE packet in a base band frame with Start bit 1.

| colspan="8" bgcolor="#AADDBB"| Label (6 Byte)

| colspan="24" bgcolor="#FFBBBB"| [[ULE]] Extension Headers (Optional)

|-

! ...

| colspan="24" bgcolor="#FFBBBB"| ...

| colspan="8" | Data

|-

! ...

| colspan="32"| &nbsp;<br />Data<br />&nbsp;

|}

=== 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.

{| class="wikitable" style="text-align:center"

|+ Fragmentation Principle

|-

! width="10%" | Start

! width="10%" | End

! width="80%" | GSE Packet Content

|-

| 1

| 0

| style="text-align:left" | Total payload size / Protocol type / Payload start

|-

| 0

| 0

| style="text-align:left" | Payload continuation

|-

| 0

| 1

| style="text-align:left" | Payload end / CRC-32

|-

|}

On [[DVB-S2]], [[DVB-T2]], and [[DVB-C2]] 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 payloaf 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.

=== CRC-32 Trailer ===

Each GSE Packet containing the last fragment for a payload frame, carries a [[Cyclic redundancy check|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:

Line 285 ⟶ 134:

<math>y = x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11} + x^{10} + x^{8} + x^{7} + x^{5} + x^{4} + x^{2} + x^{1} + x^{0}</math>

If the last fragment of a paylodpayload 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 ==

Line 301 ⟶ 150:

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]], [[DVB-T2]] or [[DVB-C2]] modulator throuhgthrough a second

interface.

Here is a (very likely incomplete) list of GSE en- and decapsulators:

* [https://web.archive.org/web/20120517023254/http://www.newtec.eu/ Newtec]

** [http://www.newtec.eu/products/professional-equipment/elevation/modems/ip-satellite-modem-el470/ EL470 IP Satellite Modem]

** [http://www.newtec.eu/products/professional-equipment/elevation/demodulators/ip-satellite-demodulator-el970/ EL970 IP Satellite Demodulator]

* [http://www.work-microwave.de/ WORK Microwave GmbH]

** [http://www.work-microwave.de/dvb-s_s2.html#modems Challenge Series Satellite High Speed DVB-S2 IP Modem SK-IP] {{Webarchive|url=https://web.archive.org/web/20110410220742/http://www.work-microwave.de/dvb-s_s2.html#modems |date=2011-04-10 }}

* [http://www.tebkom.at/ Tebkom GmbH]

** [https://web.archive.org/web/20150707163826/http://www.tebkom.at/product_odg.html ODG200 IP/DVB-S2 Encapsulator/Modulator with ACM support]

* [http://www.gcs-salzburg.at/ gcs Global Communication & Services GmbH]

** [http://www.gcs-salzburg.at/odg.html.en ODG-200 Open DVB Gateway]

** [http://www.gcs-salzburg.at/bsr.html.en BSR-200 Broadband Satellite Receiver]

* [http://www.advantechwireless.com/ Advantech Wireless Inc.]

** [https://web.archive.org/web/20110903085805/http://www.advantechwireless.com/catalogue/products/amt75e-dvb-ss2-high-speed-broadcast-modem-2/ AMT 75e DVB-S/S2 High Speed Broadcast Modem]

* [http://www.comtechefdata.com/ Comtech EF Data Corporation]

** [http://www.comtechefdata.com/products/Advanced-VSAT-Series/pcdm-840.asp CDM-840 Remote Router]

* [http://www.transplaneta.com/ K.S.Transplaneta Ltd.]

** [https://web.archive.org/web/20120322130601/http://www.transplaneta.com/products/ip-encapsulator dpi4502 DVB2 (S2/T2/C2) compliant IPv4 / IPv6 Encapsulator]

* [http://dveo.com/ Computer Modules, Inc.]

** [http://dveo.com/broadcast-systems/ip-over-dvb-encapsulator.shtml DVB Rocket™/S2]

* [http://www.ayecka.com/ Ayecka Communication systems LTD]

**[http://ayecka.com/products-SR1.php#SR1 SR1 - Advance DVB-S2 demodulator with hardware based, wire speed, GSE Decapsulator]

**[http://ayecka.com/products-ST1.php#ST1 ST1 - Advance DVB-S2 modulator with hardware based, wire speed, GSE encapsulator]

**[http://ayecka.com/products-SM1.php SM1 - 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]] from [[SES AstraS.A.|SES]] or [[Tooway]] from

[[Eutelsat]]. Little detail is however known about the protocols used

since the receivers are provided as part of the service by the

Line 343 ⟶ 189:

* [http://www.dvb.org/technology/standards/index.xml#multiplexing Obtain GSE Standard and Guidelines from DVB free of charge]

* [http://www.dvb.org/technology/fact_sheets/DVB-GSE-Fact-Sheet.0709.pdf DVB Fact Sheet on GSE]

* [https://web.archive.org/web/20110722013509/http://telecom.esa.int/telecom/www/object/index.cfm?fobjectid=30265 GSE project home page] at [[ESA]]]

* [https://github.com/CNES/libgse Opensource implementation of GSE]

[[Category:Television technology]]

<!--- Categories --->

[[Category:Articles created via the Article Wizard]] [[Category:Television technology]] [[Category:Link protocols]]