Understanding the network.pdf - Back to Home

end-to-end, sequenced data delivery. Because the data loss might occur because of
LLP delivery problems, a variety of services are needed to address such a condition.
A connection-oriented transport must be able to perform the following data handling
functions:
• Multiplexing—A connection-oriented transport service must be able to move
the data in and out of the Layer 3 carrier.
• Segmenting—Data, in most cases, needs to be transmitted in several units.
Segmenting is the process of breaking the data into segments and
reassembling it at the remote end.
• Blocking—Some data segments are small enough to be moved in one data
unit. Blocking is the process of putting multiple data segments into a single
data unit and extracting them at the remote end.
• Concatenating—This is the process of putting multiple data units into a single
Layer 3 carrier and extracting them at the remote end.
• Error detection and error recovery—The transport service must have a way
of detecting if the data has become damaged during the Layer 3 carrying
process and have the means to resend it.
• Flow control—The transport must be able to regulate itself as to the number
of data units it passes to the adjacent layers.
• Expedite data transfer—The transport needs to be able to provide for special
delivery service for certain data units and override normal flow control
conditions.
Some connection-oriented transport protocols are the following:
• ISO—Transport Protocol class 4 (TP4)
• TCP/IP—Transmission Control Protocol (TCP)
A connectionless transport is also known as a datagram transport. Connectionless
transport has no requirement for data sequencing, data integrity checking, or loss
due to LLP delivery problems. Connectionless transport is used when fast delivery of
unimportant data is required, for things like domain name service lookups or voice
and video transport. The main requirement for this transport mechanism is
consistent data delivery speed, but a slow, consistent stream is preferred over a fast,
intermittent one.
Common connectionless transport protocols are the following:
• ISO—Transport Protocol class 0 (TP0)
• TCP/IP—User Datagram Protocol (UDP)
• AppleTalk—AppleTalk Transaction Protocol (ATP)
Routing Table Maintenance Protocol (RTMP)