40. IMSI(International Mobile Subscriber Identity), for GSM
IMSI: 310150123456789
MCC 310 USA
MNC 150 Cingular (AT&T)
MSIN 123456789
41. TUP(Telephone User Part), ISUP(ISDN User Part),SCCP (Skinny Call Control Protocol)
ISUP的简单流程
A subscriber telco switch A telco switch B B subscriber
Off hook
Dial digits --->
-- IAM -->
-Ringing ->
<-- ACM --
Off hook
<-- ANM --
----------------------- Conversation -----------------------
On hook
-- REL --> On hook
<-- RLC --
At the time ATM was designed, 155 Mbit/s SDH (135 Mbit/s payload) was considered a fast optical network link, and many PDH links in the digital network were considerably slower, ranging from 1.544 to 45 Mbit/s in the USA (2 to 34 Mbit/s in Europe).
At this rate, a typical full-length 1500 byte (12000-bit) data packet would take 77.42 µs to transmit. In a lower-speed link, such as a 1.544 Mbit/s T1 link, a 1500 byte packet would take up to 7.8 milliseconds.
A queuing delay induced by several such data packets might be several times the figure of 7.8 ms, in addition to any packet generation delay in the shorter speech packet. This was clearly unacceptable for speech traffic.
ATM was designed to implement a low-jitter network interface. However, to be able to provide short queueing delays, but also be able to carry large datagrams, it had to have cells. ATM broke up all packets, data, and voice streams into 48-byte chunks, adding a 5-byte routing header to each one so that they could be reassembled later. The choice of 48 bytes was, as is all too often the case, political instead of technical.[2] When the CCITT was standardizing ATM, parties from the United States wanted a 64-byte payload because having the size be a power of 2 made working with the data easier and this size was felt to be a good compromise between larger payloads optimized for data transmission and shorter payloads optimized for real-time applications like voice; parties from Europe wanted 32-byte payloads because the small size (and therefore short transmission times) simplify voice applications with respect to echo cancellation. Most of the interested European parties eventually came around to the arguments made by the Americans, but France and a few allies held out until the bitter end. With 32 bytes, France would have been able to implement an ATM-based voice network with calls from one end of France to the other requiring no echo cancellation. 48 bytes (plus 5 header bytes = 53) was chosen as a compromise between the two sides, but it was ideal for neither and everybody has had to live with it ever since. 5-byte headers were chosen because it was thought that 10% of the payload was the maximum price to pay for routing information. ATM multiplexed these 53-byte cells instead of packets. Doing so reduced the worst-case queuing jitter by a factor of almost 30, removing the need for echo cancellers.
47. FDDI(Fiber distributed data interface )
千兆以太网出现前,其主备双环令牌网结构有一定优势
48. WiMAX(Worldwide Interoperability for Microwave Access)
The WiMAX forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL", 34.56Mbps
49. 叙述TCP的三次握手过程
the three-way (or 3-step) handshake occurs:
The active open is performed by the client sending a SYN to the server.
In response, the server replies with a SYN-ACK.
Finally the client sends an ACK back to the server.
At this point, both the client and server have received an acknowledgment of the connection.