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dexter gerrit-no-reply at lists.osmocom.orgReview at https://gerrit.osmocom.org/2020 osmo-sgsn: Explain TCP/IP header compression The does not mention TCP/IP header compression yet. This commit adds some info about it Change-Id: I98408e72020a474d378e39263a933eb7567de146 --- M OsmoSGSN/chapters/configuration.adoc 1 file changed, 79 insertions(+), 0 deletions(-) git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals refs/changes/20/2020/1 diff --git a/OsmoSGSN/chapters/configuration.adoc b/OsmoSGSN/chapters/configuration.adoc index 9551267..dce4c78 100644 --- a/OsmoSGSN/chapters/configuration.adoc +++ b/OsmoSGSN/chapters/configuration.adoc @@ -223,3 +223,82 @@ |pdp-terminate|Forced PDP context termination during MM context release |pdp-free|Release of the PDP context memory |=== + + +=== Traffic Compression + +In order to save scarce GPRS bandwith, OsmoSGSN implements header and data +compression schemes. The compression will reduce the packet length in order +to save radio bandwith. + +===== Header Compression + +On TCP/IP connections, each packet is perpended with a fairly long TCP/IP +header. The header contains a lot of static information that never changes +throughout the connection. (source and destination address, port numbers etc.) +OsmoSGSN implements a TCP/IP header compression scheme called RFC1144, also +known as SLHC. This type of header compression removes the TCP/IP header +entirely and replaces it with a shorter version, that only contains the +information that is absolutely necessary to identify and check the packet. +The receiving part then restores the original header and forwards it to higher +layers. + +*compression rfc1144 passive*:: +TCP/IP header compression has to be actively requested by the modem. The +network will not promote compression by its-self. This is the recommended mode +of operation. + +*compression rfc1144 active slots <1-256>*:: +TCP/IP header compression is actively promoted by the network. Modems may still +actively request different compression parameters or reject the offered +compression parameters entirely. The number of slots is the the maximum number +of packet headers per subscriber that can be stored in the codebook. + +.Example: Accept compression if requested: +---- +sgsn + compression rfc1144 passive +---- + +.Example: Actively promote compression: +---- +sgsn + compression rfc1144 active slots 8 +---- + +NOTE: The usage of TCP/IP options may disturb the RFC1144 header compression +scheme. TCP/IP options may render RFC1144 ineffective if variable data is +encoded into the option section of the TCP/IP packet. + + +===== Data Compression + +Data compression works on the raw packet data, including the header part of the +packet. If enabled, header compression is applied before first data compression +is applied. OsmoSGSN implements the V.42bis data compression scheme. + +*compression rfc1144 passive*:: +V42bis data compression has to be actively requested by the modem. The network +will not promote compression by its-self. This is the recommended mode of +operation. + +*compression v42bis active direction (ms|sgsn|both) codewords <512-65535> strlen <6-250>*:: +V42bis data compression is actively promoted by the network. Modems may still +actively request different compression parameters or reject the offered +compression parameters entirely. The direction configures which of the sides is +allowed to send compressed packets. For most cases, compressing *both* +directions will be the preferred option. The following to parameters configure +the codebook size by the maxium number (*codewords*) and size (*strlen*) of +entries. + +.Example: Accept compression if requested: +---- +sgsn + compression v42bis passive +---- + +.Example: Actively promote compression: +---- +sgsn + compression v42bis active direction both codewords 512 strlen 20 +---- -- To view, visit https://gerrit.osmocom.org/2020 To unsubscribe, visit https://gerrit.osmocom.org/settings Gerrit-MessageType: newchange Gerrit-Change-Id: I98408e72020a474d378e39263a933eb7567de146 Gerrit-PatchSet: 1 Gerrit-Project: osmo-gsm-manuals Gerrit-Branch: master Gerrit-Owner: dexter <pmaier at sysmocom.de>