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Frame Relay Call Control

Frame Relay Call Control. Subscriber must first be connected to a frame handler This is called an access connection When access connection is made, multiple logical channels can be multiplexed on the connection These are called frame relay connections They can be on-demand or semi-permanent.

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Frame Relay Call Control

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  1. Frame Relay Call Control • Subscriber must first be connected to a frame handler • This is called an access connection • When access connection is made, multiple logical channels can be multiplexed on the connection • These are called frame relay connections • They can be on-demand or semi-permanent

  2. Frame Relay Call Control • Two types of access connection • Switched Access • User on switched network where exchange does not have frame handling capability • Exchange provides switched access (demand or semi-permanent) to remote frame handler • Integrated Access • User connected to pure frame relay network or switched network with integrated frame handling in local exchange • User has direct logical access to frame handler

  3. Frame Relay Connections • Analogous to virtual circuit in X.25 • Can be established when access connection established to frame handler • Multiple connections supported over single link • Called data link connections • Each connection has a unique Data link connection identifier (DLCI)

  4. Frame Relay Connections • Data transfer sequence • Establish logical connection between two endpoints and assign unique DLCI • Exchange information in data frames - each frame has a DLCI • Release logical connection

  5. Frame Relay Connections • Establishment and release of Logical connection is made by messages over dedicated call control logical connection with DLCI =0

  6. The establishment and release of a frame relay connection is accomplished by the exchange of Q.931/Q.933 messages over a logical connection dedicated to call control (DLCI = 0). • A frame with DLCI=0 has a call control message in the information field

  7. Either side may request the establishment of a logical connection by sending a SETUP message • The other side must reply either with a CONNECT message to accept the connection or with a RELEASE COMPLETE message to refuse the connection.

  8. Frame Relay Call Control • The side sending the SETUP message may choose the DLCI for the connection by choosing an unused value; otherwise, the accepting side assigns the DLCI within the CONNECT message.

  9. Frame Relay Call Control • After the connection is established, data transfer can proceed • Clearing a connection is accomplished by the exchange of DISCONNECT, RELEASE, and RELEASE COMPLETE messages.

  10. Frame Relay Control Signalling Frame Relay Network NT ISDN NT Setup Setup D-channel Q.931 exchange to establish B-channel circuit- switched connection Connect Connect ack Connect Connect ack Setup B-channel Q.933 exchange to establish B-channel frame - mode connection Setup Connect Connect ack Connect ack Connect Frame relay Q.922 exchange of user data on B-Channel Message exchange for switched access to frame handler over ISDN

  11. Frame Relay Control Signalling Frame Relay Network NT ISDN NT Disconnect Disconnect B-channel Q.933 exchange to release B-channel frame- mode connection Release Release Release complete Release complete D-channel Q.931 exchange to release B-channel circuit - switched connection Disconnect Disconnect Release Release Release complete Release complete Message exchange for terminating switched access to frame handler

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