NSA3: Tutorial 2 Solutions Guide

Source: www.dcs.gla.ac.uk
Topic: SAP Tutorial

Short Desciption:
NSA3: Tutorial 2 Solutions Guide. 1. Synchronous TDM allocates slots in fixed ... This entity is now supposed to pass each PDU on to the correct SAP ...

 

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NSA3: Tutorial 2 Solutions Guide Page 1NSA3: Tutorial 2 Solutions Guide 1. Synchronous TDM allocates slots in fixed rotation to some maximum number of sources which are currently using a given link. The receiving end of the link knows which slot belongs to each source purely by its position and it follows that a sequence of slots (a channel) must be allocated to any such source before it can use the link. This inherently means that any source wishing to use asynchronous TDM link must request and obtain a channel on the link before it can transmit alongit. Such a channel once obtained must be released before another source can use it. Both ends of the link must be made aware at setup and release time which source is using which channel. Thus synchronous TDM implies (temporary) ownership of channels on a link by individual sources. When a source has variable output it may not on the one hand have enough capacity on itschannel to cope with a sudden increase in output while on the other it may waste bandwidth whenit is quiescent for a short period but has not released its channel. Rapid acquisition and release ofchannels is typically impractical because of the overhead involved. With asynchronous TDM however chunks of link bandwidth (whether fixedsize slots or not) are allocated on an individual basis to each fragment of each message ready to be sent on the link regardless of source. As there is no fixed preallocation and fragments (packets or cells) are queued for the link as they arrive there is total flexibility when data output from any source varies. 2. In the first case the channel bandwidth is allocated equally between the channels. Each channel(and each source fortunate enough to acquire one) gets kbps25.13321000000=With asynchronous TDM we assume that a maximum of 32 active sources (equivalent to 32virtual channels) are allowed to use the line at one time. Each slot must carry an address which is 5 bits long to allow the receiver to identify which channel a pa ...

 

 

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