Browse Prior Art Database

GTP-U sequence number resynchronisation

IP.com Disclosure Number: IPCOM000198226D
Original Publication Date: 2010-Jul-31
Included in the Prior Art Database: 2010-Jul-31
Document File: 2 page(s) / 174K

Publishing Venue

Motorola

Related People

Newman, Gary: INVENTOR

Abstract

When a DL packet is deemed as invalid (exceeds expected + receive window), the packet should be placed onto a buffer. If the following N packets received are in sequence (each being placed onto the buffer in turn) then they should be sent to Layer 2 & the expected sequence number be updated to be the next in this sequence. If however one of the following packets received before N is reached is not in sequence, all packets on the buffer should be discarded.

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GTP-U Sequence Number Re-Synchronization

By Gary Newman

Motorola, Inc.

Home & Networks Mobility

 

ABSTRACT

When a DL packet is deemed as invalid, the packet should be placed onto a secondary buffer. If the following N packets received are in sequence then they should be processed and the expected sequence number be updated to be the next in this sequence. If however one of the following packets received before N is reached is not in sequence, all packets on the buffer should be discarded.

PROBLEM

When GTP-U packets are received that contain a sequence number that is larger than the expected sequence number + receive window size, these packets are discarded.
In the case of SRNS Relocation the proposal is to sync the DL sequence number to the first DL packet received.
If this packet is corrupted the sequence number could be incorrect. If the actual DL sequence number is greater than the initial sequence number + receive window size, the DL packets will be discarded.  GTP-U uses a receive timer to determine if a packet is lost. This timer is by design larger than the time it will take to receive the next packet.  When the timer expires the expected sequence number is incremented.  Therefore although the expected sequence number will increment, the received sequence number will increment faster. To re-sync the received sequence number will have to catch up with the expected sequence number which could result in up to 65536 DL packets being discarded.
A similar scenario could occur if a prolonged jitter is experienced which would cause the received sequence numbers to drift beyond the receive window.

 

SOLUTION

When a DL packet is deemed as invalid (exceeds expected + receive window), the packet should be placed onto a secondary buffer.
If the followi...