CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- Socket is a communication channel between 2 TCP processes. A client socket is created by
specifying the IP address and the destination port to connect to the server; whereas a server
socket binds to a specified port number and listens for incoming connections upon started a
server application.
- User Datagram Protocol (UDP) is a connectionless (does not contact the destination before
data transmission) and unreliable data delivery service, which also known as best effort service.
No sequencing. No reordering. No acknowledgment. No error recovery. No congestion control.
- Applications uses UDP are either tolerant to data lost, or perform error recovery themselves
(perform error recovery in application layer instead of transport layer).
i) Tolerant to data lost: video streaming.
ii) Handles its own reliability issues: NFS and TFTP (hence the use of TCP is unnecessary)
- Figure 2-5 shows the UDP segment structure. It does not contain SEQ, ACK and other fields as in
TCP header. Even there are many disadvantages as mentioned above, UDP advantages over TCP
are it is faster (no ACK process) and uses less network bandwidth and processing resources.
Source Port (16) Destination Port (16)
Length (16)
32 bits
Application Layer Data
Figure 2-5: UDP Segment Structure
- In network programming, a socket would fail to bind to specified port if the port is already in use
by another socket. However, a host is allowed to bind a TCP socket and a UDP socket to the
same port number at the same time, and waiting for incoming connections, as they are treated
as 2 different type of service – a host can provide TCP and UDP Echo services at the same time.
- Do not make false assumption that connection-oriented = reliable!
A connection-oriented protocol does not mean it also performs error recovery, and vice-versa.
Connection Type Reliable Example Protocol
Connection-oriented Yes TCP
Connection-oriented No TP0 and TP2
Connectionless Yes TFTP and NFS
Connectionless No UDP
Note: TPx isTransport Protocol Class x in ISO-TP (OSI Transport Layer Protocols).
- Below shows the TCP and UDP comparison chart:
Feature TCP UDP
Connection-oriented Yes No
Reliable data transfer Yes No
Ordered data transfer Yes No
Flow control Yes No
Multiplexing Yes Yes
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