Understanding TCP/IP

Understanding TCP/IP

Alena Kabelova, Libor Dostalek

Language: English

Pages: 478


Format: PDF / Kindle (mobi) / ePub

This book is suitable for the novice and experienced system administrators, programmers, and anyone who would like to learn how to work with the TCP/IP protocol suite. It can be read even by those who have little background in networking

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direction. Figure 4.8: I-frame When sending data in the opposite direction is not necessary, an S-frame is used for received data confirmation (using the RR command). If the received frame is found to be incorrect after checking the checksum, an S-frame is used to ask for a repeat of the transfer (using the REJ command)—a negative confirmation. This S-frame will repeat the number of the last correctly received frame within its N(R) field. It's possible to confirm frames one by one. But that

doesn't take care of keeping the correct frame order. Moreover, certain protocols might not like changes in the frame order. Numbers in the MP header serve to preserve the order of the fragments (the numbers are strictly incremental). The B (begin) and E flags (end) signal that the fragment carries the beginning (or the end) of the packet. If a fragment has the B and E bytes set up, it is a fragment carrying the whole (uncut) packet. The MP header is 4 bytes long, and the fragment number is 24

Frame Category: Unnumbered Frame LLC: Command = UI LLC: LLC Data: Number of data bytes remaining = 43 (0x002B) SNAP: ETYPE = 0x01A2 SNAP: Snap Organization code = 00 00 81 SNAP: Snap etype : 0x01A2 SNAP: Snap Data: Number of data bytes remaining = 38 (0x0026) The chosen frame does not carry an IP-datagram as you might have expected. As for the Internet, each station must support the Ethernet II protocol. Only the stations that somehow agree on using Ethernet ISO 8800-3 can actually use it. That

point is stationary and forms a base radio station and data bridge. The access point is usually connected to the network via, for example, an Ethernet. Security features such as encryption or filtration of link or IP addresses can also be set in the access point. The number of end stations that can be connected to one access point is 15-38. Figure 4.43: WLAN Access Point 123 Link Layer Roaming (Several Access Points) If roaming is enabled, the end stations can move freely with

considered as wasteful; so virtual web servers are used instead. In that case, many web servers share one IP address and server specification is accomplished on the application level in the HTTP protocol (via the host header). As most computers use one network interface, it is common for the IP address of a network interface to be called the computer IP address. An IP address has four bytes. It is written in a dotted notation—adjacent bytes of the 4-byte address are separated by a dot. The

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