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daniel gerrit-no-reply at lists.osmocom.orgdaniel has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-gsm-manuals/+/16769 ) Change subject: OS#2722: Add information about RACH tuning parameters ...................................................................... OS#2722: Add information about RACH tuning parameters Change-Id: I9a6b84cb988be2143672b954e7c6827f691f4a01 --- M common/chapters/bibliography.adoc M common/chapters/bts.adoc 2 files changed, 60 insertions(+), 0 deletions(-) git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals refs/changes/69/16769/1 diff --git a/common/chapters/bibliography.adoc b/common/chapters/bibliography.adoc index 96a8555..623f648 100644 --- a/common/chapters/bibliography.adoc +++ b/common/chapters/bibliography.adoc @@ -69,6 +69,9 @@ - [[[3gpp-ts-44-006]]] 3GPP TS 44.006: Mobile Station - Base Station System (MS - BSS) interface; Data Link (DL) layer specification http://www.3gpp.org/DynaReport/44006.htm +- [[[3gpp-ts-44-018]]] 3GPP TS 44.018: Mobile radio interface layer 3 + specification; Radio Resource Control (RRC) protocol + http://www.3gpp.org/DynaReport/44018.htm - [[[3gpp-ts-44-064]]] 3GPP TS 44.064: Mobile Station - Serving GPRS Support Node (MS-SGSN); Logical Link Control (LLC) Layer Specification http://www.3gpp.org/DynaReport/44064.htm diff --git a/common/chapters/bts.adoc b/common/chapters/bts.adoc index 2a8c83a..223cec1 100644 --- a/common/chapters/bts.adoc +++ b/common/chapters/bts.adoc @@ -408,6 +408,15 @@ letting in more and more subscribers. This is especially useful for isolated cells with a huge number of subscribers. +Other options control the behaviour of the MS when it needs to access the +random access channel before a dedicated channel is established. + +If the BTS is connected to the BSC via a high-latency connection the MS should +wait longer for an answer to a RACH request. If it does not the network will +have to deal with an increased load due to duplicate RACH requests. However, +in order to minimize the delay when a RACH request or response gets lost the +MS should not wait too long before retransmitting. + ==== Load Management Every SIM card is member of one of the ten regular ACCs (0-9). Access to the @@ -446,3 +455,51 @@ <1> Turn on access-control-class ramping <2> Enable more ACCs every 30 seconds <3> At each step enable one more ACC + + +==== RACH Parameter Configuration + +The following parameters allow control over how the MS can access the random +access channel (RACH). It is possible to set a minimum receive level under +which the MS will not even attempt to access the network. + +The RACH is a shared channel which means multiple MS can choose to send a +request at the same time. To minimize the risk of a collision each MS will +choose a random number of RACH slots to wait before trying to send a RACH +request. + +On very busy networks the range this number is chosen from should be +high to avoid collisions, but a lower range reduces the overall delay when +trying to establish a channel. + +The option `rach tx integer N` controls the range from which this number X +is chosen. It is `0 <= X < max(8,N)`. + +After sending a RACH request the MS will wait a random amount of slots before +retransmitting its RACH request. The range it will wait is also determined by +the option `rach tx integer N`, but calculating it is not so straightforward. +It is defined as `S <= X < S+N` where `S` is determined from a table. + +In particular `S` is lowest when `N` is one of 3, 8, 14 or 50 and highest when +`N` is 7, 12 or 32. + +For more information see _3GPP TA 44.018_ <<3gpp-ts-44-018>> Ch. 3.3.1.1.2 and +Table 3.3.1.1.2.1 in particular. + +The amount of times the MS attempts to retransmit RACH requests can also be +changed. A higher number means more load on the RACH while a lower number can +cause channel establishment to fail due to collisions or bad reception. + +.Example: Configure RACH Access Parameters +---- +network + bts 0 + rxlev access min 20 <1> + rach tx integer 50<2> + rach max transmission <3> +---- +<1> Allow access to the network if the MS receives the BCCH of the cell at +-90dBm or better (20dB above -110dBm). +<2> This number affects how long the MS waits before (re-)transmitting RACH +requests. +<3> How often to retransmit the RACH request. -- To view, visit https://gerrit.osmocom.org/c/osmo-gsm-manuals/+/16769 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-gsm-manuals Gerrit-Branch: master Gerrit-Change-Id: I9a6b84cb988be2143672b954e7c6827f691f4a01 Gerrit-Change-Number: 16769 Gerrit-PatchSet: 1 Gerrit-Owner: daniel <dwillmann at sysmocom.de> Gerrit-MessageType: newchange -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/gerrit-log/attachments/20200108/6b7f3ae1/attachment.htm>