Services

• Transport entity
• This layer provides services to processes.
• Not owned by the network.
• provides interface to a network over which the user has no control

Quality of Service

Think: Making a dialup connection.

• Connection establishment delay
• Connection establishment fiaure probability
• Throughput
• Transit delay
• Residual Error rate
• Transfer failure probability
• Connection release delay
• Connection release failure probability
• Protection
• Priority
• Resilience

The OSI Transport Service primitives

T-CONNECT.request(callee, caller, exp_wanted, qos, user_data)

T-CONNECT.indication(callee, caller, exp_wanted, qos, user_data)

T-CONNECT.response(qos, responder, exp_wanted, qos, user_data)

T-CONNECT.confirm(qos, responder, exp_wanted, qos, user_data)

T-DISCONNECT.requester(user_data)

T-DISCONNECT.indication(reason, user_data)

T-DATA.request(user_data)

T-DATA.indication(user_data)

T-EXPEDITED-DATA.request(user_data)

T-EXPEDITED-DATA.indication(user_data)

T-UNIT-DATA.request(callee, caller, qos, user_data)

T-UNIT-DATA.indication(callee, caller, qos, user_data)

Transport Protocols

Network Type      Description
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A                 Flawless, no N-RESETS
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B                 Perfect packet delivery, N-RESETS
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C                 Unreliable
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Protocol      Network
class      Type      Name
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0           A      Simple Class
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1           B      Basic error recovery class
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2           A      Multiplexing class
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3           B      Error recovery and multiplexing
----------------------------------
4           C      Error detection and recovery
----------------------------------

Protocol Element                     0  1  2  3  4
-------------------------------
Connection Establishment             x  x  x  x  x
-------------------------------
Connection Refusal                   x  x  x  x  x
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Assignment to Nework Connection      x  x  x  x  x
-------------------------------
Splitting Long Messages into TPDUs   x  x  x  x  x
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Association of TPDUs with Connection x  x  x  x  x
-------------------------------
TPDU Transfer                        x  x  x  x  x
-------------------------------
Normal Release                       x  x  x  x  x
-------------------------------
Treatment of protocol Errors         x  x  x  x  x
-------------------------------
Concatenation of TPDUs to the User      x  x  x  x
-------------------------------
Error Release                        x     x
-------------------------------
TPDU Numbering                          x  o  x  x
-------------------------------
Expedited Data transfer                 o  o  x  x
-------------------------------
Transport Layer flow Control               o  x  x
-------------------------------
Resynchronization after RESET           x     x  x
-------------------------------
Retention of TPDUs until ack            x     x  x
-------------------------------
Reassignment after Network Disconnect   x     x  x
-------------------------------
Frozen references                       x     x  x
-------------------------------
Multiplexing                               x  x  x
-------------------------------
Use of Multiple etwork Connections               x
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Retransmission upon Timeout                      x
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Resequencing of TPDUs                            x
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Inactivity timer                                 x
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Transport Layer Checksum                         o
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x = present    o = optional  blank = absent