WTCP ("Wireless
Transmission Control Protocol
The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is common ...
") is a proxy-based modification of TCP that preserves the
end-to-end semantics of TCP.
[Ratnam Karunaharan and Ibrahim Matta, ''WTCP: An Efficient Mechanism for Improving Wireless Access to TCP Services'', 200]
/ref> As its name suggests, it is used in wireless
Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The mos ...
networks to improve the performance of TCP.
Where it works
WTCP does not replace the TCP on the hosts, but is placed on a proxy in between two communicating hosts.
In wireless systems, WTCP is placed on a base station or intermediate gateway between a source host and a mobile (wireless) host. The base station is a wireless transmitter and receiver for the mobile host, and acts as a gateway to the internet for the host.
The following is a highly simplified example of what happens when the mobile host and source host have a TCP connection with each other:
When the mobile host uses its TCP to send a segment, the WTCP at the base station receives it and sends it on through the network, where it eventually reaches the awaiting host. The awaiting host might send an acknowledgment back through the network, to the base station, which transmits it to the mobile host. Despite handling some wireless-related errors, WTCP effectively does exactly what regular TCP does. The two edge hosts aren't even aware that the WTCP exists.
Performance enhancements
Instead of replacing TCP completely, WTCP works with it to enhance TCP's performance over wireless. It accomplishes this by handling the negative effects of the wireless channel, including high bit error rate
In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors.
The bit error rate (BER ...
s that are known to occur in bursts over the wireless medium.multipath
In radio communication, multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and ref ...
fading
In wireless communications, fading is variation of the attenuation of a signal with various variables. These variables include time, geographical position, and radio frequency. Fading is often modeled as a random process. A fading channel is ...
or high BER
''Ziziphus mauritiana'', also known as Indian jujube, Indian plum, Chinese date, Chinese apple, ber, and dunks is a tropical fruit tree species belonging to the family Rhamnaceae. It is often confused with the closely related Chinese jujube (' ...
) with the use of timeouts and duplicate acknowledgments. WTCP then attempts to mitigate the problem by retransmitting a lost segment only once, until it receives an acknowledgment back from the mobile host that it was received. Any other lost segments will have to wait in the WTCP's buffer until the first one is confirmed to have been received.
There are times when packets will sit in WTCP's buffer for many milliseconds. In order to avoid having either TCP end host go into its congestion avoidance mode, (due to TCP looking at a segment's timestamp and determining that it took a long time to arrive, therefore wrongly assuming it's due to congestion) WTCP uniquely hides the time spent by the packets at the WTCP proxy, so that the RTT estimation is not affected.
In one study on WTCP's performance in Wireless WANs
WANS (1280 AM) is a southern gospel radio station located in Anderson, South Carolina, United States. The station is licensed by the FCC to broadcast with 5 kW. during the daytime and 1 kW. directional at night.
Station history
WANS 12 ...
, WTCP showed an improvement of 20–200% over comparable TCP algorithms such as New Reno, Vegas
Las Vegas (; Spanish for "The Meadows"), often known simply as Vegas, is the 25th-most populous city in the United States, the most populous city in the state of Nevada, and the county seat of Clark County. The city anchors the Las Vegas ...
, and Snoop.[Sinha Prasun et al., ''WTCP: A Reliable Transport Protocol for Wireless Wide-Area Networks'', 199]
/ref>
References
{{reflist
Transport layer protocols