Transport Level Protocols

Question 1

Transmission Control Protocol - TCP

Answer 1

• connection oriented (setup required between client and server)
• reliable transport: data delivered without loss, duplication or transmission errors
• point-to-point
• reliable connection establishment: 3-way handshake used; each TCP connection is established between pair of ports; one port can connect to multiple destinations
• graceful connection termination: TCP guarantees delivery of all data after endpoint shutdown by application (connection is open until both parties have closed their sides of the connection)
• stream interface
• flow control (receiver will not be overwhelmed with data; tells the sender the maximum speed at which the data can be sent to the receiver device)
• congestion control (does not insert a new packet until an old one leaves; timeouts associated with retransmission are due to congestion rate; limits the flow of packets at each node of the network)
• does NOT provide: timing, min. bandwidth guarantees

Question 2

User Datagram Protocol - UDP

Answer 2

• connectionless
• delivers independent messages called datagrams between applications or processes on host computers
• messages must fit in one UDP datagram
• ‘best-effort delivery’: datagrams may be lost, delivered out of order, etc.
• does NOT provided: connection setup, reliability, flow control, congestion control, timing, bandwidth guarantee
• UDP header: port numbers, message length, checksum (integrity of data)

Question 3

Datagram Lifetime - TTL (time-to-live)

Answer 3

Datagrams could loop indefinitely which leads to the consumption of resources. Transport protocol may need upper bound on datagram life.

Datagram is marked with lifetime by the time to live field in IP. Once lifetime expires, the datagram is discarded, not forwarded.

The time to live is decremented at each passing through a router (hop count).

Question 4

TCP/IP Reference Model (general characteristics of a reference model)

Answer 4

• not all functions or layers need to be used in an application
• physical info moves down-across-up
• each layer converses logically with peer
• each layer relies on the lower layer to perform more primitive functions
• each layer provides services to the next higher layer
• changes in one layer should not require changes in other layers

Question 5

TCP/IP Protocol Architecture

Answer 5

Application Layer - communication between processes or applications
- remote access RLOGIN
- file transfer FTP, TFTP
- electronic mail SMTP
- info retrieval NIR
- network management SNMP

Transport Layer (TCP/UDP/..) - end to end transfer of data
- may include reliability (TCP)

Internet Layer (IP) - routing of data, address resolution, routing protocols

Subnet Level:
Net Access - logical interface between end system and network
Physical Access - transmission medium, signal rate and encoding