Subject: RE: [rohc] ROHC-TCP issue: context updating in U-mode

From: "Hongbin Liao (Intl Staffing)" <[email-masked]>
Date: Tue, 30 Apr 2002 16:06:52 +0800

Dear ROHC-TCPers
	In this mail, the second, context updating issues in U-mode.

Hongbin & Qian Zhang
04/30/2002

Context updating issues, especially in U-mode

Content updating can be considered as the mechanism which establishes a context based on another valid context already created (we will refer this context as base context.) This mechanism will reduce the overhead of context building significantly, especially for short-lived TCP connections. However, in U-mode,  the compressor knows which one of existing contexts is valid without the feedback from the decompressor. If the context being selected as the base context is invalid, the context newly being created is also invalid. This issue can be solved by giving a general principle on how to select the base context. This principle is listed as follows:
	Only context in FO/SO states should be selected as the base.

When a context is being created, the compressor will select a valid state as the base and send a CONTEXT-UPDATE packet instead of IR/IR-DYN packet. Each time the compressor send a CONTEXT-UPDATE packet, it will check the base context is still in FO/SO state. If the base is not valid, the compressor how to re-select another valid context as the base and sent CONTEXT-UPDATE. If the compressor can not find any valid context, it need send IR/IR-DYN packet.

As to handover, the compressor and decompressor MUST re-initialize the context when receiving signal CONTEXT_REINITIALIZATION.

> -----Original Message-----
> From: Qian Zhang [mailto:[email-masked]] 
> Sent: Tuesday, April 30, 2002 12:27 PM
> To: [email-masked]
> Subject: [rohc] ROHC-TCP issue: U/B mode, mode transition, and MSN
> 
> 
> Dear ROHC-TCPers,
>  
> We are working on updating the ROHC-TCP draft according to 
> what was discussed at the Minneapolis meeting. 
> We would like to discuss the following issues in separate 
> email thread. 1. U/B mode, mode transition, and MSN issues 2. 
> Context replication/updating issue, especially in U-mode
> 

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